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                 Detrital zircon geochronology and provenance of
                 Devono-Mississippian strata in the northern
                 Canadian Cordilleran miogeocline1,2
                 Yvon Lemieux, Thomas Hadlari, and Antonio Simonetti



                 Abstract: U–Pb ages have been determined on detrital zircons from the Upper Devonian Imperial Formation and Upper
                 Devonian – Lower Carboniferous Tuttle Formation of the northern Canadian Cordilleran miogeocline using laser ablation –
                 multicollector – inductively coupled plasma – mass spectrometry. The results provide insights into mid-Paleozoic sediment
                 dispersal in, and paleogeography of, the northern Canadian Cordillera. The Imperial Formation yielded a wide range of de-
                 trital zircon dates; one sample yielded dominant peaks at 1130, 1660, and 1860 Ma, with smaller mid-Paleozoic
                 (*430 Ma), Neoproterozoic, and Archean populations. The easternmost Imperial Formation sample yielded predominantly
                 late Neoproterozoic – Cambrian zircons between 500 and 700 Ma, with lesser Mesoproterozoic and older populations. The
                 age spectra suggest that the samples were largely derived from an extensive region of northwestern Laurentia, including the
                 Canadian Shield, igneous and sedimentary provinces of Canada’s Arctic Islands, and possibly the northern Yukon. The pres-
                 ence of late Neoproterozoic – Cambrian zircon, absent from the Laurentian magmatic record, indicate that a number of
                 grains were likely derived from an exotic source region, possibly including Baltica, Siberia, or Arctic Alaska – Chukotka. In
                 contrast, zircon grains from the Tuttle Formation show a well-defined middle Paleoproterozoic population with dominant
                 relative probability peaks between 1850 and 1950 Ma. Additional populations in the Tuttle Formation are mid-Paleozoic
                 (*430 Ma), Mesoproterozoic (1000–1600 Ma), and earlier Paleoproterozoic and Archean ages (>2000 Ma). These data lend
                 support to the hypothesis that the influx of sediments of northerly derivation that supplied the northern miogeocline in Late
                 Devonian time underwent an abrupt shift to a source of predominantly Laurentian affinity by the Mississippian.
                    ´      ´         ˆ             ´´ ´       ´                ´            `
                 Resume : Des ages U–Pb ont ete determines par spectrometrie de masse a plasma inductif avec multicollecteur apres abla-`
                                                 ´                                                 ´           ´
                 tion au laser sur des zircons detritiques provenant de la Formation Imperial (Devonien superieur) et de la Formation Tuttle
                      ´                    `   ´                ´                   `                                   ´
                 (Devonien – Carbonifere inferieur) du miogeoclinal de la Cordillere canadienne septentrionale. Les resultats fournissent des
                                                 ´                ´ ¨                       ´ ´                        `
                 apercus de la dispersion des sediments au Paleozoıque moyen et de la paleogeographie de la Cordillere canadienne septen-
                        ¸
                                                           ´                                             ´           ´
                 trionale. La Formation Imperial a donne une grande plage de dates sur des zircons detritiques; un echantillon a donne des´
                                     `                                                                        ´ ¨
                 pics dominants a 1130, 1660 et 1860 Ma ainsi que des populations moindres datant du Paleozoıque moyen (*430 Ma), du
                    ´        ´     ¨               ´     ´                  `                                      ´
                 Neoproterozoıque et de l’Archeen. L’echantillon le plus a l’est de la Formation Imperial a donne des zircons datant surtout
                         ´       ´     ¨                                                                                          ´
                 du Neoproterozoıque tardif – Cambrien, soit entre 500 et 700 Ma, avec des populations moindres datant du Mesoprotero-      ´
                    ¨                                      ˆ        `            ´                                        ´
                 zoıque et plus anciennes. Les plages d’ages suggerent que les echantillons proviennent surtout d’une region extensive dans
                 le nord-ouest de la Laurentie, incluant le Bouclier canadien, les provinces ignees et sedimentaires des ˆles de l’Arctique ca-
                                                                                                 ´        ´               ı
                                                                    ´                              ´      ´   ¨
                 nadien et possiblement du nord du Yukon. La presence de zircons datant du Neoproterozoıque tardif – Cambrien, lesquels
                                           ´
                 sont absents des donnees magmatiques laurentiennes, indique qu’un certain nombre de grains proviennent sans doute d’une
                  ´                                                           ´
                 region source exotique, possiblement de Baltica, de la Siberie ou du terrane Arctic Alaska – Chukotka. Cependant, les zir-
                                                                                         ´             ´    ´    ¨
                 cons provenant de la Formation Tuttle montrent une population bien definie du Paleoproterozoıque moyen avec des pics de
                               ´                                                                                            ´ ¨
                 probabilite relative entre 1850 et 1950 Ma. D’autres populations dans la Formation Tuttle datent du Paleozoıque moyen
                                         ´   ´      ¨                                   ´      ´     ¨      ´                  ´
                 (*430 Ma), du Mesoproterozoıque (1000–1600 Ma) ainsi que du Paleoproterozoıque inferieur et de l’Archeen (>2000 Ma).
                               ´                      `                 ´                                                 ´
                 Ces donnees supportent l’hypothese que l’influx de sediments provenant du Nord qui a fourni le miogeoclinal septentrional
                         ´                                                                  ´
                 au Devonien tardif a subi un changement abrupt vers une source d’affinite surtout laurentienne vers le Mississippien.
                                  ´
                 [Traduit par la Redaction]


  Received 23 November 2009. Accepted 26 May 2010. Published on the NRC Research Press Web site at cjes.nrc.ca on 9 February 2011.
  Paper handled by Associate Editor W.J. Davis.
  Y. Lemieux and T. Hadlari.3,4 Northwest Territories Geoscience Office, Box 1500, 4601-B, 52 Avenue, Yellowknife, NT X1A 2R3,
  Canada.
  A. Simonetti.5 Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G
  2E3, Canada.
  1This article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.
  2Northwest   Territories Geoscience Office Contribution 0047. Geological Survey of Canada Contribution 20100432.
  3Corresponding author (e-mail: thomas.hadlari@nrcan-rncan.gc.ca).
  4Present address: Geological Survey of Canada, 3303, 33rd St. NW, Calgary, AB T2L 2A7, Canada.
  5Present address: 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556.


Can. J. Earth Sci. 48: 515–541 (2011)                        doi:10.1139/E10-056                                Published by NRC Research Press
516                                                                                              Can. J. Earth Sci. Vol. 48, 2011


Introduction                                                      folded miogeoclinal strata are exposed at the mountain front.
                                                                  The area preserves a relatively complete Cambrian to Dev-
   Despite an increasing number of U–Pb geochronology and         onian, rift to post-rift passive-margin succession that lies
Nd isotopic studies that provided new perspectives on re-         with a pronounced unconformity on a thick succession of
gional patterns of sediment dispersal in northwestern Canada      Proterozoic sedimentary rock (Fig. 3; Aitken et al. 1982). A
and adjacent Arctic region in Paleozoic time (e.g., McNicoll      wedge of Cretaceous siliciclastic strata, interpreted to have
et al. 1995; Garzione et al. 1997; Gehrels et al. 1999; Patch-    been deposited in a foreland basin setting, overlies the Pale-
ett et al. 1999; Miller et al. 2006), the tectonic setting and    ozoic succession.
paleogeography during deposition of the Devono-Mississip-
                                                                     In Cambrian to Middle Devonian time, the northern Cana-
pian succession in the northern Canadian Cordilleran mio-
                                                                  dian Cordilleran miogeocline was a continental margin
geocline is not well understood.
                                                                  marked by deposition of extensive carbonate platform and
   Prior to the late Devonian, the northern Cordilleran mar-      minor associated siliciclastic rocks (Mackenzie Platform;
gin was dominated by an extensive shallow-water carbonate         Fritz et al. 1991), and, to the west, deeper water siliciclastic
platform thickening markedly westward toward a fine-              and minor carbonate succession (Fig. 3; Pugh 1983). Detrital
grained basinal succession (e.g., Fritz et al. 1991). The plat-
                                                                  zircon ages from Cambrian sandstone in east-central Alaska
form was flanked to the east by the Laurentian Precambrian
                                                                  suggest provenance largely from regions of the Canadian
Shield, which provided most of the sediment for the clastic
                                                                  Shield (Gehrels et al. 1999).
deposits (Gordey et al. 1991). By the late Devonian, an in-
                                                                     In the late Devonian, passive-margin sedimentation was
flux of fine siliciclastic sediment blanketed the northern
                                                                  interrupted by a major change in tectono-sedimentological
shelf and platform, marking a profound change in depositio-
                                                                  elements with uplift of clastic sourcelands north and west of
nal regime and tectonic setting along the Cordilleran margin
                                                                  the platform and influx of thick wedges of coarse and fine
(Morrow and Geldsetzer 1988). In northern Yukon and
                                                                  clastic sediments (Pugh 1983; Gordey et al. 1991). The
Northwest Territories, the Middle Devonian to Early Car-
                                                                  Upper Devonian Imperial Formation (Bassett 1961), mark-
boniferous Imperial Assemblage, including the Hare Indian,
                                                                  ing the transition from carbonate to sand-grade siliciclastic
Canol, Imperial, Tuttle, and Ford Lake formations, was in-
                                                                  deposition in the northern miogeocline (e.g., Gordey et al.
terpreted by Gordey et al. (1991) to have been derived from
                                                                  1991), includes a thick sequence of marine shale, siltstone,
an uplifted region in northern Yukon. On the basis of Nd
                                                                  and very fine- to fine-grained sandstone that overlies black
isotopic constraints, Garzione et al. (1997) and Patchett et
                                                                  siliceous shale of the Canol Formation. Within the study
al. (1999) argued that the Imperial Assemblage was likely
derived from Ordovician to Early Carboniferous orogenic           area, the Imperial Formation has been interpreted as Fras-
systems in Greenland and the Canadian Arctic, as proposed         nian–Famennian shelf sandstones and basinal turbidites with
by Embry and Klovan (1976). More recently, detailed sedi-         an eastward or northeastward sediment source inferred from
mentology of the Upper Devonian Imperial Formation and            outcrop studies (Braman and Hills 1992), and as a west- to
Tuttle Formation (Hadlari et al. 2009) indicated derivation       southwestward-prograding submarine slope and fan complex
from a northeastern and eastern source region.                    (Hadlari et al. 2009). To the north and west, the Imperial
                                                                  Formation is composed of turbidites interpreted to have
   Paleozoic sediment dispersal in the northern Cordillera
                                                                  been derived largely from northern source regions (Gordey
can be better constrained with detrital zircon geochronology
                                                                  et al. 1991; Braman and Hills 1992). Seventeen single zircon
data. Few U–Pb detrital zircon studies have been carried out
                                                                  dates from the Imperial Formation in northwestern Yukon
in strata of the miogeocline in the northern Canadian Cordil-
                                                                  (C. Garzione, G. Ross, J. Patchett, and G. Gehrels unpub-
lera (e.g., Beranek et al. 2010). In this paper, we present
                                                                  lished data, discussed in Gehrels et al. 1999) indicated a
new U–Pb detrital zircon dates obtained using laser ablation
                                                                  dominance of >1.8 Ga detritus, consistent with derivation
– multicollector – inductively coupled plasma – mass spec-
                                                                  from Canadian Shield sources, with a subordinate population
trometry (LA–MC–ICP–MS) from the Upper Devonian Im-
                                                                  of mid-Paleozoic (400–450 Ma) grains. Single zircon grains
perial Formation and Upper Devonian – Lower
Carboniferous Tuttle Formation exposed in the northern            from a Late Devonian sandstone-bearing unit in east-central
Mackenzie Mountains (Figs. 1, 2). The purpose of the study        Alaska yielded chiefly 430 Ma, Paleoproterozoic (>1.8 Ga),
is to constrain the provenance of sandstones within these         and Archean grains, consistent with an influx of detritus, in
two units to better understand regional patterns of mid-Pale-     part, from Laurentian source regions (Gehrels et al. 1999).
ozoic sediment dispersal in the northern Cordillera and to        Similar results have been reported from Devonian to Car-
draw conclusions regarding paleogeography of northern             boniferous sandstones of northeastern Yukon Territory (Be-
Laurentia. As our data indicate, the zircons from the Impe-       ranek et al. 2010).
rial and Tuttle formations were likely derived from an ex-           East of Arctic Red River (see Fig. 2 for location), Impe-
tensive region of northern Laurentia, including the               rial Formation is unconformably overlain by wedge of Cre-
northwestern Canadian Shield, provinces of Canada’s Arctic        taceous clastic sediments deposited in a foreland basin
Islands, and Greenland.                                           setting (Aitken et al. 1982); west of Arctic Red River, how-
                                                                  ever, the Imperial Formation is conformably overlain by the
                                                                  Upper Devonian – Lower Carboniferous Tuttle Formation, a
Geological setting                                                thick succession of alternating conglomerate, coarse- to fine-
  The study area lies along the northern margin of the            grained sandstone, siltstone, and shale. The contact with the
Mackenzie Mountains and encompasses the southern Peel             Imperial Formation is interpreted as a facies boundary and,
Plateau and Plain (Peel Region) of the northern Interior          therefore, is diachronous (Pugh 1983). Hills and Braman
Plains (Figs. 2); it occupies a region where imbricated and       (1978) and Braman and Hills (1992) interpreted the Tuttle

                                                                                                     Published by NRC Research Press
Lemieux et al.                                                                                                                     517


Fig. 1. Tectonic assemblage map of Yukon Territory, Northwest Territories and Nunavut showing location of study area and Fig. 2. Geol-
ogy after Wheeler et al. (1996), paleocurrent data from Embry and Klovan (1976) and Hadlari et al. (2009).




Formation as a southward-advancing turbidite succession. In             The sub-Cretaceous unconformity marks a hiatus in the
contrast, Pugh (1983) viewed the unit as a deltaic depositio-        sedimentary record as Late Carboniferous to Jurassic strata
nal system and interpreted the shale-out to the west as indi-        are absent from the northern Interior Plains. The end of con-
cating southwest-prograding deposition despite a progressive         tinental margin sedimentation and beginning of widespread
southward decrease in grain size and trend to better sorting.        compressional deformation in the northern Cordillera in
By the mid-Mississippian, marine clastic and carbonate dep-          Mesozoic time (e.g., Berman et al. 2007) influenced the de-
osition with sediment derivation from the craton to the east         velopment of foreland basins adjacent to the mountain front
was re-established (Gordey et al. 1991).                             (Dixon 1999). Clastic sedimentation in the northern Interior

                                                                                                         Published by NRC Research Press
Fig. 2. Simplified geological map (modified after Hadlari et al. 2009) of southern Peel Plateau and Peel Plain, and the northern Mackenzie Mountains showing seismic line traces and
                                                                                                                                                                                                                         518

                                  clinoform progradation directions, turbidite paleocurrents, and locations of the detrital zircon samples. Geology after Wheeler et al. (1996).




Published by NRC Research Press
                                                                                                                                                                                                                         Can. J. Earth Sci. Vol. 48, 2011
Lemieux et al.                                                                                                                          519


Fig. 3. Schematic stratigraphic section for the southern Peel Plateau and Peel Plain and northern Mackenzie Mountains. Modified after
Morrow et al. (2006).




                                                                                                           Published by NRC Research Press
520                                                                                            Can. J. Earth Sci. Vol. 48, 2011


Plains in the Late Cretaceous was controlled largely by, and     large enough (i.e., > 40 mm across, see as follows) for laser
derived from, the active Cordillera to the south and west        ablation analyses. In contrast, the much finer grained Impe-
(Dixon 1999).                                                    rial samples yielded a smaller fraction of zircons that were
                                                                 sufficiently large for analysis. Selected grains were, as
U–Pb geochronology                                               much as possible, free of fractures, inclusions, and altera-
                                                                 tion. U–Pb geochronology of zircons was conducted by
Sample description and analytical procedures                     LA–MC–ICP–MS at the Radiogenic Isotope Facility at the
   This study presents U–Pb geochronological results for         University of Alberta, Edmonton, Alberta, using analytical
four samples from the Devono-Mississippian clastic succes-       procedures described by Simonetti et al. (2005). The analy-
sion in the Peel Region, two from the Imperial Formation         ses involved ablation of zircons using a 40 mm diameter la-
(samples 07TH33B and 07WZ020A), and two from the Tut-            ser spot size for 30 s. A ‘‘standard-sample-standard’’ method
tle Formation (samples 07WZ019A and 06YHL046B); their            was used to correct instrumental drift during a single laser
geographic locations are shown in Fig. 2 and given in            ablation session and involved analysis of an internal stand-
Table 1.                                                         ard after every 12 unknown grains; this protocol was devel-
   Sample 07TH33B was collected at the type section of Im-       oped for provenance studies focusing on the dating of a
perial Formation (Fig. 2). Located near the eastern erosional    large number of detrital zircon grains (Simonetti et al.
edge of Imperial Formation, the type section preserves the       2005) The collector configuration allows for the simultane-
oldest strata of Imperial Formation, which were deposited        ous measurement of ion signals ranging in mass from 238U
as a shallow shelf-like accumulation of sediment that pro-       to 203Tl. Periodically, a 30 s blank measurement was per-
graded southwestward into a generally westward-deepening         formed, which included correction for the 204Hg contribu-
basin (Hadlari et al. 2009). The sampled interval consists of    tion; ion-counter bias was also determined using a mixed
fine-grained cross-stratified sandstone from the locally de-     solution of Pb and Tl. Common Pb correction was applied
veloped shallow-marine facies.                                   using an initial Pb composition taken from Stacey and
   West of Imperial River, the Imperial Formation is inter-      Kramers (1975).
preted as a succession of submarine fan and slope sand-
stones and shales exceeding 500 m in thickness that, based       Results of U–Pb analysis
upon paleocurrent and seismic data, are interpreted to have         The results are presented in Table 1 (with uncertainties at
been deposited by a system that prograded in a west-south-       the 2s level) and shown in relative age–probability diagrams
west direction (Hadlari et al. 2009). Tuttle Formation is gen-   (from Ludwig 2003) in Fig. 5. The diagrams present the sum
erally Famennian to Tournasian in age (Allen et al. 2009),       of all ages from a sample as a normal distribution based on
overlies the Imperial Formation, is partly defined by me-        the age and uncertainty of each analysis, the areas under
dium sand and coarser grain sizes, and represents a rejuve-      each curve are equal. Interpretations for <1000 Ma grains
nation of sand-grade siliciclastic input to the basin from the   are based on 206Pb/238U ages, which yield more precise re-
northeast (Hadlari et al. 2009). Based upon the depositional     sults given the low concentration of 207Pb in younger zir-
system, the three remaining samples are significantly            cons. For grains >1000 Ma, analyses are based on 207Pb/
younger than 07TH33B because they are located over               206Pb ages. To reduce the effect of discordance, possibly re-

100 km west of Imperial River. Considering their mutual          sulting from isotopic disturbance and (or) inheritance, analy-
proximity, we have placed the three western samples in or-       ses that are >5% discordant or >5% reverse discordant
der by the stratigraphic level that was sampled within the       (italics in Table 1) have been excluded from further consid-
combined Imperial–Tuttle formation section. Sample               eration.
07WZ020A, a massive fine-grained sandstone, was collected           A total of 67 zircons were analyzed from sample
a few metres above the Canol–Imperial contact along a trib-      07TH33B (Imperial Formation), of which 54 were consid-
utary of the Snake River near the western edge of the study      ered (Fig. 5; Table 1). A significant number of zircons
area. From the middle part of the section, sample                yielded age clusters between 380 and 711 Ma (n = 26),
06YHL046B was collected from a *150 m high bluff of              with peaks evident at 390, 555, and 670 Ma. Twenty-five
conspicuously hard and massive, medium- to coarse-grained,       zircons yielded Proterozoic dates, with the most dominant
quartz-rich sandstone sharply overlying shale and siltstone      peaks at 1100, 1350, 1670, and 1950 Ma; only one zircon
west of Cranswick River (Fig. 4). Although the bluff was         falls in the interval 2100–2500 Ma. Three Archean zircons
mapped as Imperial Formation by Norris (1982), the grain         were documented (i.e., 2625, 2796, and 2820 Ma).
size is clearly atypical of Imperial Formation, and is inter-       Ninety-one zircons extracted from the westernmost sam-
preted here as part of Tuttle Formation. Sample 07WZ019A         ple of the Imperial Formation (07WZ020A) were analyzed,
is conglomerate of Tuttle Formation from the top of the Im-      of which 61 are within 5% of the concordia. This sample
perial–Tuttle section at Flyaway Creek; the section exposes      has a dominant zircon age population (n = 46) between
a thin interval, *50 m thick, of sandstone and conglomerate      *1000 and 2100 Ma, with major peaks at 1130, 1660, and
overlying *600 m in thickness of Imperial Formation (Ha-         1860 Ma, and subordinate age groups at 1300–1550, 1730–
dlari et al. 2009). The entire sample of quartz clast conglom-   1800, 1900–2100 Ma. The sample also includes (i) four
erate with sandstone matrix was crushed for analysis.            lower Paleozoic zircons at 424, 432, 438, and 505 Ma; (ii)
   Each sample yielded euhedral to anhedral, colourless to       four Neoproterozoic grains at 570, 597, 645, and 855 Ma;
pink or yellow, generally well-rounded zircons consistent        and (iii) seven Archean zircons between 2614 and 2806 Ma.
with a detrital origin. Samples from the Tuttle Formation        There is a gap between 2100 and 2600 Ma.
were sufficiently coarse grained to yield abundant zircons          Ninety-one zircon were analyzed from sample

                                                                                                  Published by NRC Research Press
Lemieux et al.                                                                                                                      521


Fig. 4. (a) Field photograph showing the contact between the Imperial Formation and overlying Tuttle Formation in the Cranswick River
area. The bluff (in the middle ground) was mapped as Imperial Formation by Norris (1982). View to northeast; field of view in middle
ground is *4 km. (b) Close-up of approximate contact (dashed line) between the Imperial and Tuttle formations. Geologist for scale. See
Fig. 2 for location of photographs.




06YHL046B (Tuttle Formation); 18 zircon have not been                 1512 Ma (n = 2), and 1597–1731 Ma (n = 5). One grain
considered further. A 440 Ma Silurian-age peak is evident,            yielded a Neoproterozoic date (940 Ma).
represented by seven grains between 428 and 444 Ma. The                 A total of 112 zircons were analyzed from sample
sample yielded 45 grains between *1800 and 2800 Ma,                   07WZ019A (Tuttle Formation), of which 99 were consid-
with dominant age peaks at 1860 and 2780 Ma, and subordi-             ered. A 1937 Ma Paleoproterozoic age peak is evident in
nate age groups between *2000 and 2700 Ma. Twenty zir-                the zircon population, with 50 grains falling in the interval
cons fall in the intervals 1038–1366 Ma (n = 13), 1494–               1792–2000 Ma; a subordinate age cluster occurs at 430 Ma,

                                                                                                          Published by NRC Research Press
522
                                  Table 1. U–Pb data of detrital zircons.

                                                          Isotopic ratios                                                   Apparent ages (Ma)
                                             206Pb
                                                           206
                                                                 Pb         207
                                                                                  Pb            206
                                                                                                      Pb
                                                                                                                    Err.    206
                                                                                                                                  PbÃ
                                                                                                                                        ±        207
                                                                                                                                                       Pbà           207
                                                                                                                                                                            PbÃ
                                                                                                                                                                                           Disc.
                                  Grain #    (cps)         204
                                                                 Pb         235
                                                                                  U    ± (2s)   238
                                                                                                      U    ± (2s)   corr.    238
                                                                                                                                   U    (2s)      235
                                                                                                                                                        U    ± (2s)   206
                                                                                                                                                                            Pbà   ± (2s)   (%)
                                  Sample 07TH33B (UTM ZONE 9N, N7221831, E553690)
                                  1        217352   Infinite   0.4578     0.012                 0.0607     0.002    0.96    380         15       383         10       368         25       –3.1
                                  2        266037   29559.7    0.4382     0.008                 0.0585     0.001    0.92    366         13       369         7        370         32       0.8
                                  3        97534    Infinite   0.4601     0.006                 0.0600     0.001    0.93    376         12       384         5        393         27       4.3
                                  4        141527   Infinite   0.4855     0.010                 0.0629     0.001    0.91    393         14       402         8        409         34       3.8
                                  5        105463   Infinite   0.4873     0.009                 0.0629     0.001    0.90    393         13       403         7        409         34       3.8
                                  6        116583   Infinite   0.4960     0.012                 0.0644     0.001    0.95    402         15       409         10       413         27       2.6
                                  7        87935    Infinite   0.4998     0.014                 0.0649     0.002    0.91    405         15       412         11       416         37       2.6
                                  8        57814    Infinite   0.5677     0.013                 0.0724     0.002    0.94    451         16       457         10       422         29       -6.8
                                  9        57549    Infinite   0.5629     0.011                 0.0716     0.001    0.93    446         15       453         9        425         29       –4.8
                                  10       191304   Infinite   0.5751     0.009                 0.0734     0.001    0.95    457         15       461         7        451         23       –1.2
                                  11       204407   Infinite   0.4615     0.013                 0.0582     0.002    0.95    365         15       385         11       476         29       23.4
                                  12       325769   Infinite   0.6521     0.015                 0.0809     0.002    0.95    501         19       510         12       518         26       3.3
                                  13       61741    Infinite   0.7202     0.019                 0.0883     0.002    0.96    545         22       551         15       521         26       –4.6
                                  14       193746   Infinite   0.7096     0.016                 0.0863     0.002    0.94    533         20       544         12       556         29       4.0
                                  15       109660   Infinite   0.7400     0.016                 0.0897     0.002    0.96    554         20       562         12       559         24       1.0
                                  16       202468   Infinite   0.7514     0.022                 0.0907     0.003    0.97    560         24       569         17       564         24       0.8
                                  17       340492   Infinite   0.7230     0.014                 0.0878     0.002    0.93    542         19       552         11       567         28       4.3
                                  18       141712   4571.37    0.6721     0.039                 0.0810     0.004    0.92    502         30       522         30       575         57       12.7
                                  19       134699   33674.67   0.7638     0.021                 0.0917     0.002    0.94    565         22       576         16       584         29       3.3
                                  20       296319   Infinite   0.7744     0.014                 0.0931     0.002    0.95    574         20       582         10       593         24       3.2
                                  21       229189   Infinite   0.7777     0.017                 0.0931     0.002    0.95    574         21       584         13       596         25       3.6
                                  22       278753   25341.2    0.6959     0.020                 0.0830     0.002    0.93    514         20       536         15       605         32       15.0
                                  23       417489   Infinite   0.7199     0.016                 0.0863     0.002    0.96    534         20       551         12       606         23       11.9
                                  24       365918   Infinite   0.9035     0.017                 0.1043     0.002    0.94    640         22       654         12       670         25       4.5
                                  25       203291   Infinite   0.8012     0.020                 0.0918     0.002    0.93    566         21       598         15       670         30       15.5
                                  26       100302   Infinite   0.9362     0.022                 0.1071     0.002    0.94    656         24       671         16       675         29       2.8
                                  27       273595   Infinite   0.9270     0.025                 0.1091     0.003    0.96    667         27       666         18       677         23       1.4
                                  28       188263   Infinite   0.9401     0.020                 0.1078     0.002    0.95    660         24       673         14       679         25       2.8
                                  29       227461   10831.45   0.9981     0.052                 0.1146     0.005    0.91    699         39       703         37       684         54       –2.2




                                                                                                                                                                                                   Can. J. Earth Sci. Vol. 48, 2011
                                  30       278435   Infinite   0.9515     0.017                 0.1096     0.002    0.96    670         23       679         12       698         22       4.0
Published by NRC Research Press




                                  31       312369   Infinite   0.8629     0.033                 0.0991     0.004    0.97    609         30       632         24       702         24       13.2
                                  32       165271   Infinite   0.9856     0.026                 0.1107     0.003    0.96    677         27       696         18       707         24       4.3
                                  33       217427   Infinite   1.0312     0.015                 0.1166     0.001    0.91    711         23       720         11       717         29       0.9
                                  34       227825   28478.1    0.9579     0.023                 0.1031     0.002    0.94    633         24       682         16       819         28       22.8
                                  35       71442    Infinite   1.6142     0.031                 0.1607     0.003    0.93    961         33       976         19       953         27       –0.8
                                  36       102579   Infinite   1.9582     0.060                 0.1866     0.006    0.97    1103        47       1101        34       1059        21       –4.2
                                  37       725341   Infinite   1.4684     0.041                 0.1403     0.004    0.93    846         33       917         26       1084        31       21.9
                                  38       259436   Infinite   1.9815     0.037                 0.1867     0.003    0.95    1103        39       1109        21       1095        22       –0.8
                                  39       198957   Infinite   1.9575     0.051                 0.1833     0.005    0.96    1085        43       1101        28       1097        21       1.1
Lemieux et al.
                                  Table 1 (continued).

                                                         Isotopic ratios                                                     Apparent ages (Ma)
                                             206Pb
                                                         206
                                                               Pb          207
                                                                                 Pb              206
                                                                                                       Pb
                                                                                                                     Err.    206
                                                                                                                                   PbÃ
                                                                                                                                         ±        207
                                                                                                                                                        Pbà           207
                                                                                                                                                                             PbÃ
                                                                                                                                                                                            Disc.
                                  Grain #    (cps)       204
                                                               Pb          235
                                                                                 U     ± (2s)    238
                                                                                                       U    ± (2s)   corr.    238
                                                                                                                                    U    (2s)      235
                                                                                                                                                         U    ± (2s)   206
                                                                                                                                                                             Pbà   ± (2s)   (%)
                                  40         802664      21693.62          1.9697      0.045     0.1865     0.004    0.93    1102        40       1105        25       1106        28       0.3
                                  41         224638      1936.534          1.8174      0.064     0.1809     0.006    0.92    1072        47       1052        37       1118        36       4.1
                                  42         1011788     2007.516          2.4696      0.224     0.2155     0.019    0.98    1258        119      1263        114      1272        33       1.1
                                  43         243064      Infinite          2.1622      0.178     0.1784     0.014    0.97    1058        91       1169        96       1330        38       20.4
                                  44         607082      530.203           2.5457      0.133     0.2178     0.010    0.91    1270        71       1285        67       1333        49       4.7
                                  45         522574      Infinite          2.6736      0.083     0.2244     0.007    0.97    1305        56       1321        41       1341        20       2.6
                                  46         1073922     Infinite          2.6708      0.062     0.2241     0.005    0.96    1304        49       1320        31       1345        20       3.1
                                  47         114935      Infinite          2.8172      0.049     0.2294     0.004    0.93    1332        45       1360        24       1374        25       3.1
                                  48         385586      16764.6           2.7961      0.049     0.2198     0.003    0.91    1281        42       1355        24       1452        27       11.8
                                  49         1398896     Infinite          3.3621      0.044     0.2658     0.003    0.95    1519        50       1496        20       1487        19       –2.1
                                  50         1668858     Infinite          2.6855      0.035     0.1994     0.002    0.93    1172        38       1324        17       1555        22       24.6
                                  51         505990      Infinite          4.3155      0.105     0.3056     0.007    0.97    1719        66       1696        41       1659        19       –3.6
                                  52         1627787     Infinite          3.9893      0.076     0.2831     0.005    0.96    1607        57       1632        31       1670        19       3.8
                                  53         630839      Infinite          4.2327      0.086     0.2952     0.006    0.96    1668        60       1680        34       1688        19       1.2
                                  54         488924      Infinite          4.6379      0.339     0.3078     0.021    0.94    1730        129      1756        128      1727        51       –0.2
                                  55         840928      Infinite          4.6572      0.069     0.3100     0.005    0.95    1741        58       1760        26       1779        19       2.1
                                  56         200124      939.5515          5.5286      0.415     0.3341     0.025    0.97    1858        148      1905        143      1893        33       1.8
                                  57         481859      Infinite          5.7437      0.120     0.3505     0.007    0.96    1937        71       1938        40       1929        19       –0.4
                                  58         673729      2029.306          5.7164      0.107     0.3497     0.006    0.95    1933        68       1934        36       1935        20       0.1
                                  59         933238      Infinite          5.6258      0.080     0.3369     0.005    0.95    1872        62       1920        27       1968        18       4.9
                                  60         966251      Infinite          6.2317      0.095     0.3725     0.006    0.95    2041        69       2009        31       1976        18       –3.3
                                  61         1716228     17693.07          6.2476      0.108     0.3704     0.006    0.94    2031        69       2011        35       2011        22       –1.0
                                  62         883413      Infinite          5.9951      0.114     0.3495     0.007    0.96    1932        68       1975        37       2021        18       4.4
                                  63         322605      1097.296          7.6982      0.196     0.3990     0.010    0.95    2164        83       2196        56       2206        22       1.9
                                  64         1093494     Infinite          11.6411     0.170     0.4771     0.007    0.95    2515        84       2576        38       2625        17       4.2
                                  65         1548221     30964.42          14.8244     0.277     0.5507     0.010    0.96    2828        100      2804        52       2796        17       –1.1
                                  66         390767      Infinite          15.4936     0.348     0.5625     0.013    0.96    2877        108      2846        64       2820        17       –2.0
                                  67         3034842     35704             10.4927     0.353     0.3826     0.013    0.97    2089        94       2479        83       2832        17       26.2
                                  Sample 07WZ020A (UTM Zone 9N, N7277599,             E308503)
                                  1        126733   Infinite    0.5336                 0.015     0.0693     0.002    0.96    432         18       434         12       420         25       –2.8
                                  2        340726   Infinite    0.5227                 0.008     0.0679     0.001    0.95    424         14       427         6        441         23       3.9
Published by NRC Research Press




                                  3        259160   Infinite    0.5501                 0.011     0.0703     0.001    0.96    438         16       445         9        454         24       3.6
                                  4        297800   Infinite    0.4928                 0.007     0.0623     0.001    0.94    390         13       407         6        483         24       19.3
                                  5        699418   Infinite    0.4709                 0.012     0.0584     0.001    0.94    366         14       392         10       516         30       29.1
                                  6        357235   238.9533    0.6515                 0.083     0.0815     0.010    0.97    505         64       509         65       525         70       3.8
                                  7        371429   Infinite    0.5386                 0.013     0.0664     0.002    0.94    414         16       437         10       529         28       21.7
                                  8        256729   Infinite    0.7658                 0.016     0.0925     0.002    0.96    570         21       577         12       582         24       1.9
                                  9        109026   Infinite    0.8092                 0.018     0.0970     0.002    0.94    597         22       602         13       587         28       –1.6
                                  10       433467   Infinite    0.6441                 0.012     0.0775     0.001    0.96    481         17       505         9        595         23       19.2
                                  11       181581   Infinite    0.9039                 0.011     0.1052     0.001    0.95    645         21       654         8        656         23       1.7




                                                                                                                                                                                                    523
524
                                  Table 1 (continued).

                                                         Isotopic ratios                                                   Apparent ages (Ma)
                                             206Pb
                                                         206
                                                               Pb          207
                                                                                 Pb            206
                                                                                                     Pb
                                                                                                                   Err.    206
                                                                                                                                 PbÃ
                                                                                                                                       ±        207
                                                                                                                                                      Pbà           207
                                                                                                                                                                           PbÃ
                                                                                                                                                                                          Disc.
                                  Grain #    (cps)       204
                                                               Pb          235
                                                                                 U    ± (2s)   238
                                                                                                     U    ± (2s)   corr.    238
                                                                                                                                  U    (2s)      235
                                                                                                                                                       U    ± (2s)   206
                                                                                                                                                                           Pbà   ± (2s)   (%)
                                  12         1016871     3697.711          1.3405     0.048    0.1418     0.005    0.96    855         39       863         31       887         26       3.6
                                  13         158487      Infinite          1.6375     0.030    0.1613     0.003    0.95    964         34       985         18       996         22       3.2
                                  14         753417      39653.5           1.7187     0.044    0.1676     0.004    0.96    999         39       1016        26       1044        23       4.3
                                  15         972131      Infinite          1.8740     0.032    0.1789     0.003    0.96    1061        37       1072        18       1091        20       2.7
                                  16         555233      Infinite          1.8900     0.064    0.1790     0.006    0.96    1061        47       1078        36       1097        25       3.3
                                  17         1298874     4071.706          1.8714     0.132    0.1781     0.012    0.94    1056        76       1071        75       1101        53       4.1
                                  18         202173      Infinite          2.0020     0.037    0.1871     0.003    0.94    1106        38       1116        21       1115        24       0.8
                                  19         334811      Infinite          2.0319     0.042    0.1902     0.004    0.96    1122        41       1126        23       1115        21       –0.6
                                  20         85633       Infinite          2.0206     0.036    0.1856     0.003    0.93    1097        37       1122        20       1130        25       2.9
                                  21         433460      Infinite          2.0282     0.043    0.1890     0.004    0.96    1116        41       1125        24       1134        21       1.6
                                  22         135092      Infinite          2.0534     0.056    0.1873     0.005    0.95    1107        44       1133        31       1154        25       4.1
                                  23         393360      19668             2.1728     0.042    0.1995     0.003    0.92    1173        40       1172        23       1161        28       –1.0
                                  24         158101      Infinite          2.2812     0.022    0.2067     0.001    0.93    1211        37       1206        11       1166        24       –3.9
                                  25         457060      Infinite          1.6001     0.087    0.1451     0.008    0.97    874         54       970         53       1168        27       25.2
                                  26         1110968     Infinite          1.6735     0.014    0.1527     0.001    0.94    916         28       999         8        1185        21       22.7
                                  27         1177595     Infinite          2.1699     0.054    0.1985     0.005    0.97    1167        45       1171        29       1185        20       1.5
                                  28         260928      Infinite          2.2472     0.063    0.2032     0.006    0.96    1192        49       1196        33       1186        22       –0.5
                                  29         1078929     Infinite          2.3740     0.104    0.2117     0.009    0.97    1238        64       1235        54       1228        27       –0.8
                                  30         166663      Infinite          2.3208     0.038    0.2022     0.003    0.95    1187        40       1219        20       1237        22       4.0
                                  31         241826      Infinite          2.3165     0.064    0.2031     0.006    0.97    1192        48       1217        34       1243        21       4.1
                                  32         393935      Infinite          2.2663     0.169    0.1945     0.013    0.92    1146        86       1202        90       1279        62       10.4
                                  33         376764      1638.1            2.3487     0.076    0.1995     0.006    0.94    1173        50       1227        40       1304        30       10.0
                                  34         395046      Infinite          2.5778     0.049    0.2173     0.004    0.94    1268        44       1294        25       1330        24       4.7
                                  35         127330      Infinite          2.8597     0.065    0.2341     0.005    0.94    1356        50       1371        31       1366        24       0.8
                                  36         236473      Infinite          2.5301     0.068    0.2065     0.005    0.96    1210        48       1281        34       1383        23       12.5
                                  37         230817      Infinite          3.0753     0.044    0.2455     0.003    0.94    1415        47       1427        21       1402        21       –0.9
                                  38         344399      Infinite          2.9715     0.050    0.2393     0.004    0.94    1383        47       1400        24       1411        22       2.0
                                  39         441807      14726.89          3.2392     0.066    0.2544     0.004    0.91    1461        50       1467        30       1465        29       0.3
                                  40         147977      Infinite          3.2981     0.066    0.2546     0.004    0.91    1462        50       1481        30       1474        28       0.8
                                  41         669286      Infinite          3.3311     0.059    0.2585     0.005    0.95    1482        51       1488        26       1505        20       1.5
                                  42         1296589     Infinite          3.4601     0.056    0.2636     0.004    0.96    1508        51       1518        24       1533        19       1.6




                                                                                                                                                                                                  Can. J. Earth Sci. Vol. 48, 2011
                                  43         491753      1576.13           3.0343     0.278    0.2285     0.019    0.92    1327        118      1416        130      1548        73       14.3
Published by NRC Research Press




                                  44         131575      Infinite          4.1502     0.081    0.2915     0.006    0.95    1649        59       1664        32       1649        20       0.0
                                  45         228486      337.4977          4.3403     0.233    0.3062     0.015    0.94    1722        101      1701        91       1653        38       –4.2
                                  46         321559      Infinite          3.9912     0.130    0.2809     0.009    0.97    1596        71       1632        53       1660        19       3.9
                                  47         1031062     Infinite          4.0686     0.081    0.2883     0.006    0.96    1633        59       1648        33       1664        19       1.9
                                  48         528558      Infinite          4.3359     0.084    0.3050     0.006    0.96    1716        61       1700        33       1669        19       –2.8
                                  49         590211      Infinite          3.0786     0.314    0.2133     0.022    0.99    1246        132      1427        146      1684        30       26.0
                                  50         600365      Infinite          4.3516     0.116    0.3040     0.008    0.97    1711        69       1703        45       1701        19       –0.6
                                  51         593925      Infinite          3.8213     0.069    0.2633     0.005    0.96    1507        53       1597        29       1710        19       11.9
Lemieux et al.
                                  Table 1 (continued).

                                                         Isotopic ratios                                                   Apparent ages (Ma)
                                             206Pb
                                                         206
                                                               Pb          207
                                                                                 Pb            206
                                                                                                     Pb
                                                                                                                   Err.    206
                                                                                                                                 PbÃ
                                                                                                                                       ±        207
                                                                                                                                                      Pbà           207
                                                                                                                                                                           PbÃ
                                                                                                                                                                                          Disc.
                                  Grain #    (cps)       204
                                                               Pb          235
                                                                                 U    ± (2s)   238
                                                                                                     U    ± (2s)   corr.    238
                                                                                                                                  U    (2s)      235
                                                                                                                                                       U    ± (2s)   206
                                                                                                                                                                           Pbà   ± (2s)   (%)
                                  52         728551      3223.678          4.3360     0.792    0.2943     0.053    0.99    1663        306      1700        310      1747        41       4.8
                                  53         386808      16817.72          4.6421     0.095    0.3115     0.006    0.93    1748        62       1757        36       1748        24       0.0
                                  54         624037      Infinite          4.6055     0.058    0.3077     0.004    0.95    1729        56       1750        22       1766        19       2.1
                                  55         2324654     36899.3           4.0873     0.067    0.2723     0.004    0.95    1553        53       1652        27       1793        20       13.4
                                  56         775421      2959.62           4.6605     0.150    0.3029     0.010    0.97    1706        75       1760        57       1825        20       6.5
                                  57         456978      Infinite          4.2560     0.077    0.2740     0.005    0.96    1561        55       1685        31       1832        18       14.8
                                  58         1267941     4103.37           3.6877     0.111    0.2384     0.007    0.95    1378        57       1569        47       1841        23       25.2
                                  59         640904      Infinite          5.2003     0.111    0.3332     0.007    0.96    1854        68       1853        39       1848        18       –0.3
                                  60         842510      Infinite          5.0816     0.084    0.3242     0.005    0.96    1810        62       1833        30       1854        18       2.4
                                  61         449007      Infinite          5.2542     0.072    0.3332     0.005    0.95    1854        61       1861        26       1860        18       0.3
                                  62         178341      Infinite          5.5673     0.102    0.3465     0.006    0.96    1918        67       1911        35       1870        19       –2.6
                                  63         462742      Infinite          5.1635     0.121    0.3234     0.007    0.93    1807        66       1847        43       1875        26       3.7
                                  64         2906290     10416.8           3.8769     0.187    0.2447     0.012    0.98    1411        80       1609        78       1892        18       25.4
                                  65         878581      2670.46           4.1829     0.112    0.2585     0.006    0.93    1482        57       1671        45       1913        27       22.5
                                  66         1133511     4048.255          5.6088     0.427    0.3423     0.023    0.90    1898        141      1917        146      1919        64       1.1
                                  67         954093      Infinite          5.7962     0.078    0.3545     0.005    0.95    1956        64       1946        26       1931        18       –1.3
                                  68         125954      Infinite          5.7371     0.118    0.3456     0.007    0.95    1914        68       1937        40       1934        21       1.0
                                  69         276151      Infinite          5.8263     0.112    0.3524     0.007    0.96    1946        69       1950        37       1937        19       –0.5
                                  70         661599      2584.37           4.8255     0.262    0.2931     0.014    0.91    1657        95       1789        97       1964        46       15.6
                                  71         641871      Infinite          4.9901     0.230    0.2908     0.013    0.98    1646        90       1818        84       2005        19       17.9
                                  72         628332      Infinite          6.2959     0.131    0.3659     0.008    0.96    2010        73       2018        42       2022        18       0.6
                                  73         1454081     Infinite          5.8633     0.124    0.3421     0.007    0.96    1897        69       1956        41       2026        19       6.4
                                  74         569035      Infinite          6.8134     0.148    0.3905     0.008    0.96    2125        79       2087        45       2041        18       –4.1
                                  75         540218      13505.46          6.4420     0.141    0.3624     0.007    0.93    1994        72       2038        45       2072        24       3.8
                                  76         2375359     Infinite          5.9257     0.104    0.3289     0.006    0.96    1833        64       1965        35       2117        18       13.4
                                  77         763478      21813.7           7.6396     0.276    0.3721     0.013    0.97    2039        95       2190        79       2330        19       12.5
                                  78         261215      4213.14           7.7344     0.778    0.3480     0.034    0.97    1925        197      2201        221      2442        42       21.2
                                  79         1196610     10978.1           8.7709     0.263    0.3711     0.011    0.95    2035        85       2314        69       2576        21       21.0
                                  80         1757086     Infinite          10.8700    0.261    0.4452     0.011    0.97    2374        91       2512        60       2607        17       9.0
                                  81         593333      7510.545          12.4287    0.219    0.5121     0.007    0.90    2666        88       2637        46       2614        25       –2.0
                                  82         662851      12747.13          12.1365    0.259    0.5015     0.010    0.95    2620        95       2615        56       2616        20       –0.2
                                  83         416360      Infinite          12.9122    0.260    0.5159     0.010    0.96    2682        97       2673        54       2657        17       –0.9
Published by NRC Research Press




                                  84         252375      Infinite          13.1744    0.276    0.5171     0.011    0.96    2687        98       2692        56       2676        17       –0.4
                                  85         208645      Infinite          11.6138    0.424    0.4548     0.016    0.97    2416        114      2574        94       2678        18       9.8
                                  86         1148347     Infinite          7.6352     0.513    0.3010     0.020    0.99    1696        124      2189        147      2685        20       36.8
                                  87         1089764     6263.011          13.2524    0.216    0.5143     0.008    0.96    2675        91       2698        44       2720        17       1.7
                                  88         808986      3595.492          13.2011    0.297    0.5020     0.011    0.96    2622        98       2694        61       2743        18       4.4
                                  89         2297798     10687.43          14.0788    0.229    0.5194     0.008    0.95    2697        92       2755        45       2806        17       3.9
                                  90         2196173     Infinite          11.3921    0.208    0.4155     0.008    0.96    2240        78       2556        47       2827        17       20.7
                                  91         2605994     Infinite          14.3094    0.171    0.5033     0.006    0.94    2628        84       2770        33       2886        18       8.9




                                                                                                                                                                                                  525
526
                                  Table 1 (continued).

                                                         Isotopic ratios                                                     Apparent ages (Ma)
                                             206Pb
                                                         206
                                                               Pb          207
                                                                                 Pb              206
                                                                                                       Pb
                                                                                                                     Err.    206
                                                                                                                                   PbÃ
                                                                                                                                         ±        207
                                                                                                                                                        Pbà           207
                                                                                                                                                                             PbÃ
                                                                                                                                                                                            Disc.
                                  Grain #    (cps)       204
                                                               Pb          235
                                                                                 U    ± (2s)     238
                                                                                                       U    ± (2s)   corr.    238
                                                                                                                                    U    (2s)      235
                                                                                                                                                         U    ± (2s)   206
                                                                                                                                                                             Pbà   ± (2s)   (%)
                                  Sample 06YHL046B (UTM Zone 9N, N7272396,            E343816)
                                  1        306103    21864.5    0.4471                0.011      0.0586     0.001    0.90    367         13       375         9        412         38       10.8
                                  2        143296    Infinite   0.5353                0.013      0.0686     0.002    0.96    428         16       435         11       439         25       2.6
                                  3        267931    Infinite   0.5415                0.008      0.0698     0.001    0.95    435         15       439         7        449         24       3.1
                                  4        269063    Infinite   0.5246                0.009      0.0667     0.001    0.95    416         14       428         7        450         23       7.5
                                  5        305544    25462.04   0.5388                0.011      0.0690     0.001    0.91    430         15       438         9        452         33       4.8
                                  6        191005    Infinite   0.5527                0.010      0.0706     0.001    0.95    440         15       447         8        452         24       2.8
                                  7        117843    Infinite   0.5512                0.010      0.0696     0.001    0.94    434         15       446         8        453         27       4.3
                                  8        87963     Infinite   0.5519                0.008      0.0697     0.001    0.94    435         14       446         6        457         24       4.9
                                  9        273721    Infinite   0.5580                0.010      0.0712     0.001    0.94    444         15       450         8        461         27       3.8
                                  10       244012    Infinite   0.5268                0.010      0.0673     0.001    0.96    420         15       430         8        464         23       9.4
                                  11       157050    6828.25    0.5478                0.008      0.0693     0.001    0.94    432         14       444         7        476         25       9.3
                                  12       250449    Infinite   0.5569                0.012      0.0701     0.001    0.96    437         16       450         9        488         23       10.5
                                  13       90322     Infinite   0.5830                0.009      0.0726     0.001    0.94    452         15       466         8        488         26       7.4
                                  14       75488     Infinite   0.5878                0.009      0.0735     0.001    0.93    457         15       469         7        489         27       6.5
                                  15       258727    Infinite   0.5517                0.014      0.0694     0.002    0.94    433         17       446         11       489         29       11.6
                                  16       540430    24565      0.4523                0.009      0.0569     0.001    0.91    357         12       379         8        505         33       29.3
                                  17       667919    Infinite   0.5657                0.017      0.0701     0.002    0.97    437         19       455         14       514         23       15.0
                                  18       61977     Infinite   0.5407                0.008      0.0656     0.001    0.91    410         13       439         6        553         30       25.9
                                  19       667782    897.556    1.2921                0.107      0.1382     0.011    0.97    835         72       842         70       946         40       11.7
                                  20       554178    Infinite   1.5739                0.027      0.1571     0.003    0.96    940         32       960         16       987         21       4.7
                                  21       1153240   31168.66   1.7696                0.026      0.1748     0.002    0.93    1038        34       1034        15       1045        24       0.7
                                  22       53008     Infinite   1.9203                0.040      0.1822     0.004    0.95    1079        39       1088        23       1067        24       –1.2
                                  23       827576    Infinite   1.9780                0.036      0.1875     0.003    0.96    1108        39       1108        20       1106        20       –0.2
                                  24       48901     Infinite   2.1117                0.041      0.1952     0.004    0.94    1149        40       1153        23       1106        25       –3.9
                                  25       276073    21236.4    1.8961                0.045      0.1767     0.004    0.93    1049        39       1080        26       1121        28       6.4
                                  26       493272    Infinite   2.0163                0.038      0.1879     0.003    0.96    1110        39       1121        21       1138        21       2.4
                                  27       385501    Infinite   2.1941                0.027      0.2006     0.002    0.95    1179        38       1179        15       1168        20       –0.9
                                  28       391950    23055.89   2.1692                0.031      0.1970     0.002    0.92    1159        37       1171        17       1178        26       1.6
                                  29       862341    16908.65   2.1118                0.040      0.1932     0.003    0.90    1139        38       1153        22       1181        30       3.6




                                                                                                                                                                                                    Can. J. Earth Sci. Vol. 48, 2011
                                  30       329913    Infinite   2.2349                0.035      0.2006     0.003    0.95    1179        40       1192        19       1198        21       1.6
Published by NRC Research Press




                                  31       1542492   23022.28   2.2253                0.039      0.2020     0.003    0.93    1186        40       1189        21       1215        26       2.4
                                  32       963785    19669.07   2.3924                0.042      0.2128     0.003    0.92    1244        41       1240        22       1243        27       –0.1
                                  33       183429    Infinite   2.5816                0.025      0.2189     0.002    0.93    1276        40       1295        13       1302        22       2.0
                                  34       805537    44752.06   2.6900                0.056      0.2234     0.005    0.96    1300        47       1326        28       1366        21       4.9
                                  35       387711    Infinite   2.9232                0.053      0.2292     0.004    0.95    1330        46       1388        25       1468        20       9.4
                                  36       184140    Infinite   3.3213                0.085      0.2559     0.006    0.93    1469        56       1486        38       1494        27       1.7
                                  37       582297    Infinite   3.4728                0.046      0.2661     0.003    0.95    1521        50       1521        20       1512        20       –0.6
                                  38       283821    Infinite   3.1801                0.065      0.2393     0.005    0.95    1383        50       1452        30       1525        21       9.3
                                  39       98480     Infinite   3.8013                0.085      0.2746     0.006    0.95    1564        58       1593        35       1597        22       2.0
Lemieux et al.
                                  Table 1 (continued).

                                                         Isotopic ratios                                                   Apparent ages (Ma)
                                             206Pb
                                                         206
                                                               Pb          207
                                                                                 Pb            206
                                                                                                     Pb
                                                                                                                   Err.    206
                                                                                                                                 PbÃ
                                                                                                                                       ±        207
                                                                                                                                                      Pbà           207
                                                                                                                                                                           PbÃ
                                                                                                                                                                                          Disc.
                                  Grain #    (cps)       204
                                                               Pb          235
                                                                                 U    ± (2s)   238
                                                                                                     U    ± (2s)   corr.    238
                                                                                                                                  U    (2s)      235
                                                                                                                                                       U    ± (2s)   206
                                                                                                                                                                           Pbà   ± (2s)   (%)
                                  40         534604      Infinite          4.1880     0.070    0.2967     0.005    0.96    1675        57       1672        28       1650        19       –1.5
                                  41         774143      3351.27           4.0421     0.059    0.2841     0.004    0.95    1612        54       1643        24       1679        19       4.0
                                  42         271748      Infinite          4.2425     0.065    0.2948     0.004    0.95    1665        56       1682        26       1683        19       1.1
                                  43         1049121     2149.839          4.4244     0.111    0.3093     0.008    0.96    1737        68       1717        43       1731        20       –0.4
                                  44         1083148     16924.2           5.2375     0.104    0.3449     0.006    0.93    1910        67       1859        37       1807        24       -5.7
                                  45         345860      Infinite          5.1241     0.078    0.3283     0.005    0.95    1830        61       1840        28       1837        19       0.4
                                  46         87174       Infinite          5.0542     0.081    0.3175     0.005    0.94    1777        60       1828        29       1844        21       3.6
                                  47         908076      Infinite          4.8886     0.093    0.3145     0.006    0.96    1763        62       1800        34       1848        19       4.6
                                  48         160593      Infinite          5.1285     0.074    0.3232     0.005    0.95    1806        60       1841        27       1850        19       2.4
                                  49         158205      Infinite          5.2452     0.144    0.3314     0.009    0.96    1845        74       1860        51       1855        21       0.5
                                  50         217662      Infinite          5.1917     0.104    0.3269     0.006    0.96    1823        65       1851        37       1855        19       1.7
                                  51         286154      Infinite          5.1969     0.118    0.3299     0.007    0.96    1838        69       1852        42       1858        19       1.1
                                  52         908503      Infinite          5.1060     0.101    0.3245     0.006    0.96    1812        65       1837        36       1881        18       3.7
                                  53         380632      Infinite          5.2275     0.092    0.3266     0.006    0.96    1822        63       1857        33       1882        18       3.2
                                  54         547020      30390.02          5.4287     0.102    0.3397     0.006    0.95    1885        66       1889        36       1884        20       0.0
                                  55         418269      Infinite          5.1815     0.097    0.3247     0.006    0.96    1813        64       1850        35       1886        19       3.9
                                  56         547155      Infinite          5.3779     0.100    0.3358     0.006    0.96    1867        66       1881        35       1887        18       1.1
                                  57         383706      Infinite          5.2456     0.106    0.3247     0.006    0.93    1813        64       1860        37       1899        24       4.5
                                  58         823007      39190.81          5.5397     0.101    0.3455     0.006    0.95    1913        67       1907        35       1905        19       –0.4
                                  59         227125      Infinite          5.7988     0.144    0.3527     0.009    0.97    1948        76       1946        48       1927        18       –1.1
                                  60         415084      29648.85          5.5268     0.086    0.3346     0.005    0.95    1860        62       1905        30       1937        20       3.9
                                  61         863196      Infinite          5.4964     0.070    0.3343     0.004    0.95    1859        61       1900        24       1943        18       4.3
                                  62         568320      33430.6           5.6318     0.112    0.3386     0.006    0.95    1880        67       1921        38       1945        21       3.3
                                  63         301989      Infinite          5.9578     0.228    0.3544     0.013    0.94    1956        91       1970        75       1981        30       1.3
                                  64         1654832     7576.821          5.9299     0.170    0.3536     0.010    0.97    1952        81       1966        56       1989        18       1.9
                                  65         134120      Infinite          6.3813     0.096    0.3660     0.005    0.95    2011        67       2030        30       2014        20       0.2
                                  66         453298      11928.89          6.4458     0.162    0.3719     0.009    0.93    2038        77       2039        51       2028        26       –0.5
                                  67         213612      Infinite          6.2961     0.073    0.3578     0.004    0.95    1972        63       2018        23       2042        18       3.4
                                  68         340590      Infinite          6.9231     0.087    0.3816     0.005    0.95    2084        68       2102        27       2103        18       0.9
                                  69         169094      Infinite          7.2633     0.110    0.3982     0.006    0.95    2161        72       2144        32       2108        18       –2.5
                                  70         254999      1432.578          7.0782     0.224    0.3826     0.011    0.92    2088        86       2121        67       2132        31       2.1
                                  71         288084      10288.7           7.7350     0.149    0.4007     0.006    0.91    2172        74       2201        42       2218        25       2.1
Published by NRC Research Press




                                  72         243308      Infinite          8.2218     0.117    0.4142     0.005    0.92    2234        72       2256        32       2259        22       1.1
                                  73         713263      3114.684          7.9414     0.163    0.4009     0.007    0.91    2173        75       2224        46       2274        26       4.4
                                  74         297895      Infinite          9.1338     0.172    0.4395     0.008    0.96    2349        83       2351        44       2334        18       –0.6
                                  75         627237      36896.29          8.9794     0.166    0.4289     0.008    0.95    2301        81       2336        43       2369        18       2.9
                                  76         588155      Infinite          9.5616     0.116    0.4463     0.005    0.95    2379        77       2393        29       2396        17       0.7
                                  77         744871      Infinite          9.5427     0.175    0.4456     0.008    0.96    2376        83       2392        44       2404        17       1.2
                                  78         688756      Infinite          10.3881    0.132    0.4568     0.006    0.95    2426        79       2470        31       2500        17       3.0
                                  79         315734      Infinite          11.5054    0.202    0.4803     0.008    0.96    2529        88       2565        45       2578        17       1.9




                                                                                                                                                                                                  527
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel
Lemieux et al 2011 devonian d zr peel

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Lemieux et al 2011 devonian d zr peel

  • 1. 515 Detrital zircon geochronology and provenance of Devono-Mississippian strata in the northern Canadian Cordilleran miogeocline1,2 Yvon Lemieux, Thomas Hadlari, and Antonio Simonetti Abstract: U–Pb ages have been determined on detrital zircons from the Upper Devonian Imperial Formation and Upper Devonian – Lower Carboniferous Tuttle Formation of the northern Canadian Cordilleran miogeocline using laser ablation – multicollector – inductively coupled plasma – mass spectrometry. The results provide insights into mid-Paleozoic sediment dispersal in, and paleogeography of, the northern Canadian Cordillera. The Imperial Formation yielded a wide range of de- trital zircon dates; one sample yielded dominant peaks at 1130, 1660, and 1860 Ma, with smaller mid-Paleozoic (*430 Ma), Neoproterozoic, and Archean populations. The easternmost Imperial Formation sample yielded predominantly late Neoproterozoic – Cambrian zircons between 500 and 700 Ma, with lesser Mesoproterozoic and older populations. The age spectra suggest that the samples were largely derived from an extensive region of northwestern Laurentia, including the Canadian Shield, igneous and sedimentary provinces of Canada’s Arctic Islands, and possibly the northern Yukon. The pres- ence of late Neoproterozoic – Cambrian zircon, absent from the Laurentian magmatic record, indicate that a number of grains were likely derived from an exotic source region, possibly including Baltica, Siberia, or Arctic Alaska – Chukotka. In contrast, zircon grains from the Tuttle Formation show a well-defined middle Paleoproterozoic population with dominant relative probability peaks between 1850 and 1950 Ma. Additional populations in the Tuttle Formation are mid-Paleozoic (*430 Ma), Mesoproterozoic (1000–1600 Ma), and earlier Paleoproterozoic and Archean ages (>2000 Ma). These data lend support to the hypothesis that the influx of sediments of northerly derivation that supplied the northern miogeocline in Late Devonian time underwent an abrupt shift to a source of predominantly Laurentian affinity by the Mississippian. ´ ´ ˆ ´´ ´ ´ ´ ` Resume : Des ages U–Pb ont ete determines par spectrometrie de masse a plasma inductif avec multicollecteur apres abla-` ´ ´ ´ tion au laser sur des zircons detritiques provenant de la Formation Imperial (Devonien superieur) et de la Formation Tuttle ´ ` ´ ´ ` ´ (Devonien – Carbonifere inferieur) du miogeoclinal de la Cordillere canadienne septentrionale. Les resultats fournissent des ´ ´ ¨ ´ ´ ` apercus de la dispersion des sediments au Paleozoıque moyen et de la paleogeographie de la Cordillere canadienne septen- ¸ ´ ´ ´ trionale. La Formation Imperial a donne une grande plage de dates sur des zircons detritiques; un echantillon a donne des´ ` ´ ¨ pics dominants a 1130, 1660 et 1860 Ma ainsi que des populations moindres datant du Paleozoıque moyen (*430 Ma), du ´ ´ ¨ ´ ´ ` ´ Neoproterozoıque et de l’Archeen. L’echantillon le plus a l’est de la Formation Imperial a donne des zircons datant surtout ´ ´ ¨ ´ du Neoproterozoıque tardif – Cambrien, soit entre 500 et 700 Ma, avec des populations moindres datant du Mesoprotero- ´ ¨ ˆ ` ´ ´ zoıque et plus anciennes. Les plages d’ages suggerent que les echantillons proviennent surtout d’une region extensive dans le nord-ouest de la Laurentie, incluant le Bouclier canadien, les provinces ignees et sedimentaires des ˆles de l’Arctique ca- ´ ´ ı ´ ´ ´ ¨ nadien et possiblement du nord du Yukon. La presence de zircons datant du Neoproterozoıque tardif – Cambrien, lesquels ´ sont absents des donnees magmatiques laurentiennes, indique qu’un certain nombre de grains proviennent sans doute d’une ´ ´ region source exotique, possiblement de Baltica, de la Siberie ou du terrane Arctic Alaska – Chukotka. Cependant, les zir- ´ ´ ´ ¨ cons provenant de la Formation Tuttle montrent une population bien definie du Paleoproterozoıque moyen avec des pics de ´ ´ ¨ probabilite relative entre 1850 et 1950 Ma. D’autres populations dans la Formation Tuttle datent du Paleozoıque moyen ´ ´ ¨ ´ ´ ¨ ´ ´ (*430 Ma), du Mesoproterozoıque (1000–1600 Ma) ainsi que du Paleoproterozoıque inferieur et de l’Archeen (>2000 Ma). ´ ` ´ ´ Ces donnees supportent l’hypothese que l’influx de sediments provenant du Nord qui a fourni le miogeoclinal septentrional ´ ´ au Devonien tardif a subi un changement abrupt vers une source d’affinite surtout laurentienne vers le Mississippien. ´ [Traduit par la Redaction] Received 23 November 2009. Accepted 26 May 2010. Published on the NRC Research Press Web site at cjes.nrc.ca on 9 February 2011. Paper handled by Associate Editor W.J. Davis. Y. Lemieux and T. Hadlari.3,4 Northwest Territories Geoscience Office, Box 1500, 4601-B, 52 Avenue, Yellowknife, NT X1A 2R3, Canada. A. Simonetti.5 Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada. 1This article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh. 2Northwest Territories Geoscience Office Contribution 0047. Geological Survey of Canada Contribution 20100432. 3Corresponding author (e-mail: thomas.hadlari@nrcan-rncan.gc.ca). 4Present address: Geological Survey of Canada, 3303, 33rd St. NW, Calgary, AB T2L 2A7, Canada. 5Present address: 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556. Can. J. Earth Sci. 48: 515–541 (2011) doi:10.1139/E10-056 Published by NRC Research Press
  • 2. 516 Can. J. Earth Sci. Vol. 48, 2011 Introduction folded miogeoclinal strata are exposed at the mountain front. The area preserves a relatively complete Cambrian to Dev- Despite an increasing number of U–Pb geochronology and onian, rift to post-rift passive-margin succession that lies Nd isotopic studies that provided new perspectives on re- with a pronounced unconformity on a thick succession of gional patterns of sediment dispersal in northwestern Canada Proterozoic sedimentary rock (Fig. 3; Aitken et al. 1982). A and adjacent Arctic region in Paleozoic time (e.g., McNicoll wedge of Cretaceous siliciclastic strata, interpreted to have et al. 1995; Garzione et al. 1997; Gehrels et al. 1999; Patch- been deposited in a foreland basin setting, overlies the Pale- ett et al. 1999; Miller et al. 2006), the tectonic setting and ozoic succession. paleogeography during deposition of the Devono-Mississip- In Cambrian to Middle Devonian time, the northern Cana- pian succession in the northern Canadian Cordilleran mio- dian Cordilleran miogeocline was a continental margin geocline is not well understood. marked by deposition of extensive carbonate platform and Prior to the late Devonian, the northern Cordilleran mar- minor associated siliciclastic rocks (Mackenzie Platform; gin was dominated by an extensive shallow-water carbonate Fritz et al. 1991), and, to the west, deeper water siliciclastic platform thickening markedly westward toward a fine- and minor carbonate succession (Fig. 3; Pugh 1983). Detrital grained basinal succession (e.g., Fritz et al. 1991). The plat- zircon ages from Cambrian sandstone in east-central Alaska form was flanked to the east by the Laurentian Precambrian suggest provenance largely from regions of the Canadian Shield, which provided most of the sediment for the clastic Shield (Gehrels et al. 1999). deposits (Gordey et al. 1991). By the late Devonian, an in- In the late Devonian, passive-margin sedimentation was flux of fine siliciclastic sediment blanketed the northern interrupted by a major change in tectono-sedimentological shelf and platform, marking a profound change in depositio- elements with uplift of clastic sourcelands north and west of nal regime and tectonic setting along the Cordilleran margin the platform and influx of thick wedges of coarse and fine (Morrow and Geldsetzer 1988). In northern Yukon and clastic sediments (Pugh 1983; Gordey et al. 1991). The Northwest Territories, the Middle Devonian to Early Car- Upper Devonian Imperial Formation (Bassett 1961), mark- boniferous Imperial Assemblage, including the Hare Indian, ing the transition from carbonate to sand-grade siliciclastic Canol, Imperial, Tuttle, and Ford Lake formations, was in- deposition in the northern miogeocline (e.g., Gordey et al. terpreted by Gordey et al. (1991) to have been derived from 1991), includes a thick sequence of marine shale, siltstone, an uplifted region in northern Yukon. On the basis of Nd and very fine- to fine-grained sandstone that overlies black isotopic constraints, Garzione et al. (1997) and Patchett et siliceous shale of the Canol Formation. Within the study al. (1999) argued that the Imperial Assemblage was likely derived from Ordovician to Early Carboniferous orogenic area, the Imperial Formation has been interpreted as Fras- systems in Greenland and the Canadian Arctic, as proposed nian–Famennian shelf sandstones and basinal turbidites with by Embry and Klovan (1976). More recently, detailed sedi- an eastward or northeastward sediment source inferred from mentology of the Upper Devonian Imperial Formation and outcrop studies (Braman and Hills 1992), and as a west- to Tuttle Formation (Hadlari et al. 2009) indicated derivation southwestward-prograding submarine slope and fan complex from a northeastern and eastern source region. (Hadlari et al. 2009). To the north and west, the Imperial Formation is composed of turbidites interpreted to have Paleozoic sediment dispersal in the northern Cordillera been derived largely from northern source regions (Gordey can be better constrained with detrital zircon geochronology et al. 1991; Braman and Hills 1992). Seventeen single zircon data. Few U–Pb detrital zircon studies have been carried out dates from the Imperial Formation in northwestern Yukon in strata of the miogeocline in the northern Canadian Cordil- (C. Garzione, G. Ross, J. Patchett, and G. Gehrels unpub- lera (e.g., Beranek et al. 2010). In this paper, we present lished data, discussed in Gehrels et al. 1999) indicated a new U–Pb detrital zircon dates obtained using laser ablation dominance of >1.8 Ga detritus, consistent with derivation – multicollector – inductively coupled plasma – mass spec- from Canadian Shield sources, with a subordinate population trometry (LA–MC–ICP–MS) from the Upper Devonian Im- of mid-Paleozoic (400–450 Ma) grains. Single zircon grains perial Formation and Upper Devonian – Lower Carboniferous Tuttle Formation exposed in the northern from a Late Devonian sandstone-bearing unit in east-central Mackenzie Mountains (Figs. 1, 2). The purpose of the study Alaska yielded chiefly 430 Ma, Paleoproterozoic (>1.8 Ga), is to constrain the provenance of sandstones within these and Archean grains, consistent with an influx of detritus, in two units to better understand regional patterns of mid-Pale- part, from Laurentian source regions (Gehrels et al. 1999). ozoic sediment dispersal in the northern Cordillera and to Similar results have been reported from Devonian to Car- draw conclusions regarding paleogeography of northern boniferous sandstones of northeastern Yukon Territory (Be- Laurentia. As our data indicate, the zircons from the Impe- ranek et al. 2010). rial and Tuttle formations were likely derived from an ex- East of Arctic Red River (see Fig. 2 for location), Impe- tensive region of northern Laurentia, including the rial Formation is unconformably overlain by wedge of Cre- northwestern Canadian Shield, provinces of Canada’s Arctic taceous clastic sediments deposited in a foreland basin Islands, and Greenland. setting (Aitken et al. 1982); west of Arctic Red River, how- ever, the Imperial Formation is conformably overlain by the Upper Devonian – Lower Carboniferous Tuttle Formation, a Geological setting thick succession of alternating conglomerate, coarse- to fine- The study area lies along the northern margin of the grained sandstone, siltstone, and shale. The contact with the Mackenzie Mountains and encompasses the southern Peel Imperial Formation is interpreted as a facies boundary and, Plateau and Plain (Peel Region) of the northern Interior therefore, is diachronous (Pugh 1983). Hills and Braman Plains (Figs. 2); it occupies a region where imbricated and (1978) and Braman and Hills (1992) interpreted the Tuttle Published by NRC Research Press
  • 3. Lemieux et al. 517 Fig. 1. Tectonic assemblage map of Yukon Territory, Northwest Territories and Nunavut showing location of study area and Fig. 2. Geol- ogy after Wheeler et al. (1996), paleocurrent data from Embry and Klovan (1976) and Hadlari et al. (2009). Formation as a southward-advancing turbidite succession. In The sub-Cretaceous unconformity marks a hiatus in the contrast, Pugh (1983) viewed the unit as a deltaic depositio- sedimentary record as Late Carboniferous to Jurassic strata nal system and interpreted the shale-out to the west as indi- are absent from the northern Interior Plains. The end of con- cating southwest-prograding deposition despite a progressive tinental margin sedimentation and beginning of widespread southward decrease in grain size and trend to better sorting. compressional deformation in the northern Cordillera in By the mid-Mississippian, marine clastic and carbonate dep- Mesozoic time (e.g., Berman et al. 2007) influenced the de- osition with sediment derivation from the craton to the east velopment of foreland basins adjacent to the mountain front was re-established (Gordey et al. 1991). (Dixon 1999). Clastic sedimentation in the northern Interior Published by NRC Research Press
  • 4. Fig. 2. Simplified geological map (modified after Hadlari et al. 2009) of southern Peel Plateau and Peel Plain, and the northern Mackenzie Mountains showing seismic line traces and 518 clinoform progradation directions, turbidite paleocurrents, and locations of the detrital zircon samples. Geology after Wheeler et al. (1996). Published by NRC Research Press Can. J. Earth Sci. Vol. 48, 2011
  • 5. Lemieux et al. 519 Fig. 3. Schematic stratigraphic section for the southern Peel Plateau and Peel Plain and northern Mackenzie Mountains. Modified after Morrow et al. (2006). Published by NRC Research Press
  • 6. 520 Can. J. Earth Sci. Vol. 48, 2011 Plains in the Late Cretaceous was controlled largely by, and large enough (i.e., > 40 mm across, see as follows) for laser derived from, the active Cordillera to the south and west ablation analyses. In contrast, the much finer grained Impe- (Dixon 1999). rial samples yielded a smaller fraction of zircons that were sufficiently large for analysis. Selected grains were, as U–Pb geochronology much as possible, free of fractures, inclusions, and altera- tion. U–Pb geochronology of zircons was conducted by Sample description and analytical procedures LA–MC–ICP–MS at the Radiogenic Isotope Facility at the This study presents U–Pb geochronological results for University of Alberta, Edmonton, Alberta, using analytical four samples from the Devono-Mississippian clastic succes- procedures described by Simonetti et al. (2005). The analy- sion in the Peel Region, two from the Imperial Formation ses involved ablation of zircons using a 40 mm diameter la- (samples 07TH33B and 07WZ020A), and two from the Tut- ser spot size for 30 s. A ‘‘standard-sample-standard’’ method tle Formation (samples 07WZ019A and 06YHL046B); their was used to correct instrumental drift during a single laser geographic locations are shown in Fig. 2 and given in ablation session and involved analysis of an internal stand- Table 1. ard after every 12 unknown grains; this protocol was devel- Sample 07TH33B was collected at the type section of Im- oped for provenance studies focusing on the dating of a perial Formation (Fig. 2). Located near the eastern erosional large number of detrital zircon grains (Simonetti et al. edge of Imperial Formation, the type section preserves the 2005) The collector configuration allows for the simultane- oldest strata of Imperial Formation, which were deposited ous measurement of ion signals ranging in mass from 238U as a shallow shelf-like accumulation of sediment that pro- to 203Tl. Periodically, a 30 s blank measurement was per- graded southwestward into a generally westward-deepening formed, which included correction for the 204Hg contribu- basin (Hadlari et al. 2009). The sampled interval consists of tion; ion-counter bias was also determined using a mixed fine-grained cross-stratified sandstone from the locally de- solution of Pb and Tl. Common Pb correction was applied veloped shallow-marine facies. using an initial Pb composition taken from Stacey and West of Imperial River, the Imperial Formation is inter- Kramers (1975). preted as a succession of submarine fan and slope sand- stones and shales exceeding 500 m in thickness that, based Results of U–Pb analysis upon paleocurrent and seismic data, are interpreted to have The results are presented in Table 1 (with uncertainties at been deposited by a system that prograded in a west-south- the 2s level) and shown in relative age–probability diagrams west direction (Hadlari et al. 2009). Tuttle Formation is gen- (from Ludwig 2003) in Fig. 5. The diagrams present the sum erally Famennian to Tournasian in age (Allen et al. 2009), of all ages from a sample as a normal distribution based on overlies the Imperial Formation, is partly defined by me- the age and uncertainty of each analysis, the areas under dium sand and coarser grain sizes, and represents a rejuve- each curve are equal. Interpretations for <1000 Ma grains nation of sand-grade siliciclastic input to the basin from the are based on 206Pb/238U ages, which yield more precise re- northeast (Hadlari et al. 2009). Based upon the depositional sults given the low concentration of 207Pb in younger zir- system, the three remaining samples are significantly cons. For grains >1000 Ma, analyses are based on 207Pb/ younger than 07TH33B because they are located over 206Pb ages. To reduce the effect of discordance, possibly re- 100 km west of Imperial River. Considering their mutual sulting from isotopic disturbance and (or) inheritance, analy- proximity, we have placed the three western samples in or- ses that are >5% discordant or >5% reverse discordant der by the stratigraphic level that was sampled within the (italics in Table 1) have been excluded from further consid- combined Imperial–Tuttle formation section. Sample eration. 07WZ020A, a massive fine-grained sandstone, was collected A total of 67 zircons were analyzed from sample a few metres above the Canol–Imperial contact along a trib- 07TH33B (Imperial Formation), of which 54 were consid- utary of the Snake River near the western edge of the study ered (Fig. 5; Table 1). A significant number of zircons area. From the middle part of the section, sample yielded age clusters between 380 and 711 Ma (n = 26), 06YHL046B was collected from a *150 m high bluff of with peaks evident at 390, 555, and 670 Ma. Twenty-five conspicuously hard and massive, medium- to coarse-grained, zircons yielded Proterozoic dates, with the most dominant quartz-rich sandstone sharply overlying shale and siltstone peaks at 1100, 1350, 1670, and 1950 Ma; only one zircon west of Cranswick River (Fig. 4). Although the bluff was falls in the interval 2100–2500 Ma. Three Archean zircons mapped as Imperial Formation by Norris (1982), the grain were documented (i.e., 2625, 2796, and 2820 Ma). size is clearly atypical of Imperial Formation, and is inter- Ninety-one zircons extracted from the westernmost sam- preted here as part of Tuttle Formation. Sample 07WZ019A ple of the Imperial Formation (07WZ020A) were analyzed, is conglomerate of Tuttle Formation from the top of the Im- of which 61 are within 5% of the concordia. This sample perial–Tuttle section at Flyaway Creek; the section exposes has a dominant zircon age population (n = 46) between a thin interval, *50 m thick, of sandstone and conglomerate *1000 and 2100 Ma, with major peaks at 1130, 1660, and overlying *600 m in thickness of Imperial Formation (Ha- 1860 Ma, and subordinate age groups at 1300–1550, 1730– dlari et al. 2009). The entire sample of quartz clast conglom- 1800, 1900–2100 Ma. The sample also includes (i) four erate with sandstone matrix was crushed for analysis. lower Paleozoic zircons at 424, 432, 438, and 505 Ma; (ii) Each sample yielded euhedral to anhedral, colourless to four Neoproterozoic grains at 570, 597, 645, and 855 Ma; pink or yellow, generally well-rounded zircons consistent and (iii) seven Archean zircons between 2614 and 2806 Ma. with a detrital origin. Samples from the Tuttle Formation There is a gap between 2100 and 2600 Ma. were sufficiently coarse grained to yield abundant zircons Ninety-one zircon were analyzed from sample Published by NRC Research Press
  • 7. Lemieux et al. 521 Fig. 4. (a) Field photograph showing the contact between the Imperial Formation and overlying Tuttle Formation in the Cranswick River area. The bluff (in the middle ground) was mapped as Imperial Formation by Norris (1982). View to northeast; field of view in middle ground is *4 km. (b) Close-up of approximate contact (dashed line) between the Imperial and Tuttle formations. Geologist for scale. See Fig. 2 for location of photographs. 06YHL046B (Tuttle Formation); 18 zircon have not been 1512 Ma (n = 2), and 1597–1731 Ma (n = 5). One grain considered further. A 440 Ma Silurian-age peak is evident, yielded a Neoproterozoic date (940 Ma). represented by seven grains between 428 and 444 Ma. The A total of 112 zircons were analyzed from sample sample yielded 45 grains between *1800 and 2800 Ma, 07WZ019A (Tuttle Formation), of which 99 were consid- with dominant age peaks at 1860 and 2780 Ma, and subordi- ered. A 1937 Ma Paleoproterozoic age peak is evident in nate age groups between *2000 and 2700 Ma. Twenty zir- the zircon population, with 50 grains falling in the interval cons fall in the intervals 1038–1366 Ma (n = 13), 1494– 1792–2000 Ma; a subordinate age cluster occurs at 430 Ma, Published by NRC Research Press
  • 8. 522 Table 1. U–Pb data of detrital zircons. Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) Sample 07TH33B (UTM ZONE 9N, N7221831, E553690) 1 217352 Infinite 0.4578 0.012 0.0607 0.002 0.96 380 15 383 10 368 25 –3.1 2 266037 29559.7 0.4382 0.008 0.0585 0.001 0.92 366 13 369 7 370 32 0.8 3 97534 Infinite 0.4601 0.006 0.0600 0.001 0.93 376 12 384 5 393 27 4.3 4 141527 Infinite 0.4855 0.010 0.0629 0.001 0.91 393 14 402 8 409 34 3.8 5 105463 Infinite 0.4873 0.009 0.0629 0.001 0.90 393 13 403 7 409 34 3.8 6 116583 Infinite 0.4960 0.012 0.0644 0.001 0.95 402 15 409 10 413 27 2.6 7 87935 Infinite 0.4998 0.014 0.0649 0.002 0.91 405 15 412 11 416 37 2.6 8 57814 Infinite 0.5677 0.013 0.0724 0.002 0.94 451 16 457 10 422 29 -6.8 9 57549 Infinite 0.5629 0.011 0.0716 0.001 0.93 446 15 453 9 425 29 –4.8 10 191304 Infinite 0.5751 0.009 0.0734 0.001 0.95 457 15 461 7 451 23 –1.2 11 204407 Infinite 0.4615 0.013 0.0582 0.002 0.95 365 15 385 11 476 29 23.4 12 325769 Infinite 0.6521 0.015 0.0809 0.002 0.95 501 19 510 12 518 26 3.3 13 61741 Infinite 0.7202 0.019 0.0883 0.002 0.96 545 22 551 15 521 26 –4.6 14 193746 Infinite 0.7096 0.016 0.0863 0.002 0.94 533 20 544 12 556 29 4.0 15 109660 Infinite 0.7400 0.016 0.0897 0.002 0.96 554 20 562 12 559 24 1.0 16 202468 Infinite 0.7514 0.022 0.0907 0.003 0.97 560 24 569 17 564 24 0.8 17 340492 Infinite 0.7230 0.014 0.0878 0.002 0.93 542 19 552 11 567 28 4.3 18 141712 4571.37 0.6721 0.039 0.0810 0.004 0.92 502 30 522 30 575 57 12.7 19 134699 33674.67 0.7638 0.021 0.0917 0.002 0.94 565 22 576 16 584 29 3.3 20 296319 Infinite 0.7744 0.014 0.0931 0.002 0.95 574 20 582 10 593 24 3.2 21 229189 Infinite 0.7777 0.017 0.0931 0.002 0.95 574 21 584 13 596 25 3.6 22 278753 25341.2 0.6959 0.020 0.0830 0.002 0.93 514 20 536 15 605 32 15.0 23 417489 Infinite 0.7199 0.016 0.0863 0.002 0.96 534 20 551 12 606 23 11.9 24 365918 Infinite 0.9035 0.017 0.1043 0.002 0.94 640 22 654 12 670 25 4.5 25 203291 Infinite 0.8012 0.020 0.0918 0.002 0.93 566 21 598 15 670 30 15.5 26 100302 Infinite 0.9362 0.022 0.1071 0.002 0.94 656 24 671 16 675 29 2.8 27 273595 Infinite 0.9270 0.025 0.1091 0.003 0.96 667 27 666 18 677 23 1.4 28 188263 Infinite 0.9401 0.020 0.1078 0.002 0.95 660 24 673 14 679 25 2.8 29 227461 10831.45 0.9981 0.052 0.1146 0.005 0.91 699 39 703 37 684 54 –2.2 Can. J. Earth Sci. Vol. 48, 2011 30 278435 Infinite 0.9515 0.017 0.1096 0.002 0.96 670 23 679 12 698 22 4.0 Published by NRC Research Press 31 312369 Infinite 0.8629 0.033 0.0991 0.004 0.97 609 30 632 24 702 24 13.2 32 165271 Infinite 0.9856 0.026 0.1107 0.003 0.96 677 27 696 18 707 24 4.3 33 217427 Infinite 1.0312 0.015 0.1166 0.001 0.91 711 23 720 11 717 29 0.9 34 227825 28478.1 0.9579 0.023 0.1031 0.002 0.94 633 24 682 16 819 28 22.8 35 71442 Infinite 1.6142 0.031 0.1607 0.003 0.93 961 33 976 19 953 27 –0.8 36 102579 Infinite 1.9582 0.060 0.1866 0.006 0.97 1103 47 1101 34 1059 21 –4.2 37 725341 Infinite 1.4684 0.041 0.1403 0.004 0.93 846 33 917 26 1084 31 21.9 38 259436 Infinite 1.9815 0.037 0.1867 0.003 0.95 1103 39 1109 21 1095 22 –0.8 39 198957 Infinite 1.9575 0.051 0.1833 0.005 0.96 1085 43 1101 28 1097 21 1.1
  • 9. Lemieux et al. Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 40 802664 21693.62 1.9697 0.045 0.1865 0.004 0.93 1102 40 1105 25 1106 28 0.3 41 224638 1936.534 1.8174 0.064 0.1809 0.006 0.92 1072 47 1052 37 1118 36 4.1 42 1011788 2007.516 2.4696 0.224 0.2155 0.019 0.98 1258 119 1263 114 1272 33 1.1 43 243064 Infinite 2.1622 0.178 0.1784 0.014 0.97 1058 91 1169 96 1330 38 20.4 44 607082 530.203 2.5457 0.133 0.2178 0.010 0.91 1270 71 1285 67 1333 49 4.7 45 522574 Infinite 2.6736 0.083 0.2244 0.007 0.97 1305 56 1321 41 1341 20 2.6 46 1073922 Infinite 2.6708 0.062 0.2241 0.005 0.96 1304 49 1320 31 1345 20 3.1 47 114935 Infinite 2.8172 0.049 0.2294 0.004 0.93 1332 45 1360 24 1374 25 3.1 48 385586 16764.6 2.7961 0.049 0.2198 0.003 0.91 1281 42 1355 24 1452 27 11.8 49 1398896 Infinite 3.3621 0.044 0.2658 0.003 0.95 1519 50 1496 20 1487 19 –2.1 50 1668858 Infinite 2.6855 0.035 0.1994 0.002 0.93 1172 38 1324 17 1555 22 24.6 51 505990 Infinite 4.3155 0.105 0.3056 0.007 0.97 1719 66 1696 41 1659 19 –3.6 52 1627787 Infinite 3.9893 0.076 0.2831 0.005 0.96 1607 57 1632 31 1670 19 3.8 53 630839 Infinite 4.2327 0.086 0.2952 0.006 0.96 1668 60 1680 34 1688 19 1.2 54 488924 Infinite 4.6379 0.339 0.3078 0.021 0.94 1730 129 1756 128 1727 51 –0.2 55 840928 Infinite 4.6572 0.069 0.3100 0.005 0.95 1741 58 1760 26 1779 19 2.1 56 200124 939.5515 5.5286 0.415 0.3341 0.025 0.97 1858 148 1905 143 1893 33 1.8 57 481859 Infinite 5.7437 0.120 0.3505 0.007 0.96 1937 71 1938 40 1929 19 –0.4 58 673729 2029.306 5.7164 0.107 0.3497 0.006 0.95 1933 68 1934 36 1935 20 0.1 59 933238 Infinite 5.6258 0.080 0.3369 0.005 0.95 1872 62 1920 27 1968 18 4.9 60 966251 Infinite 6.2317 0.095 0.3725 0.006 0.95 2041 69 2009 31 1976 18 –3.3 61 1716228 17693.07 6.2476 0.108 0.3704 0.006 0.94 2031 69 2011 35 2011 22 –1.0 62 883413 Infinite 5.9951 0.114 0.3495 0.007 0.96 1932 68 1975 37 2021 18 4.4 63 322605 1097.296 7.6982 0.196 0.3990 0.010 0.95 2164 83 2196 56 2206 22 1.9 64 1093494 Infinite 11.6411 0.170 0.4771 0.007 0.95 2515 84 2576 38 2625 17 4.2 65 1548221 30964.42 14.8244 0.277 0.5507 0.010 0.96 2828 100 2804 52 2796 17 –1.1 66 390767 Infinite 15.4936 0.348 0.5625 0.013 0.96 2877 108 2846 64 2820 17 –2.0 67 3034842 35704 10.4927 0.353 0.3826 0.013 0.97 2089 94 2479 83 2832 17 26.2 Sample 07WZ020A (UTM Zone 9N, N7277599, E308503) 1 126733 Infinite 0.5336 0.015 0.0693 0.002 0.96 432 18 434 12 420 25 –2.8 2 340726 Infinite 0.5227 0.008 0.0679 0.001 0.95 424 14 427 6 441 23 3.9 Published by NRC Research Press 3 259160 Infinite 0.5501 0.011 0.0703 0.001 0.96 438 16 445 9 454 24 3.6 4 297800 Infinite 0.4928 0.007 0.0623 0.001 0.94 390 13 407 6 483 24 19.3 5 699418 Infinite 0.4709 0.012 0.0584 0.001 0.94 366 14 392 10 516 30 29.1 6 357235 238.9533 0.6515 0.083 0.0815 0.010 0.97 505 64 509 65 525 70 3.8 7 371429 Infinite 0.5386 0.013 0.0664 0.002 0.94 414 16 437 10 529 28 21.7 8 256729 Infinite 0.7658 0.016 0.0925 0.002 0.96 570 21 577 12 582 24 1.9 9 109026 Infinite 0.8092 0.018 0.0970 0.002 0.94 597 22 602 13 587 28 –1.6 10 433467 Infinite 0.6441 0.012 0.0775 0.001 0.96 481 17 505 9 595 23 19.2 11 181581 Infinite 0.9039 0.011 0.1052 0.001 0.95 645 21 654 8 656 23 1.7 523
  • 10. 524 Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 12 1016871 3697.711 1.3405 0.048 0.1418 0.005 0.96 855 39 863 31 887 26 3.6 13 158487 Infinite 1.6375 0.030 0.1613 0.003 0.95 964 34 985 18 996 22 3.2 14 753417 39653.5 1.7187 0.044 0.1676 0.004 0.96 999 39 1016 26 1044 23 4.3 15 972131 Infinite 1.8740 0.032 0.1789 0.003 0.96 1061 37 1072 18 1091 20 2.7 16 555233 Infinite 1.8900 0.064 0.1790 0.006 0.96 1061 47 1078 36 1097 25 3.3 17 1298874 4071.706 1.8714 0.132 0.1781 0.012 0.94 1056 76 1071 75 1101 53 4.1 18 202173 Infinite 2.0020 0.037 0.1871 0.003 0.94 1106 38 1116 21 1115 24 0.8 19 334811 Infinite 2.0319 0.042 0.1902 0.004 0.96 1122 41 1126 23 1115 21 –0.6 20 85633 Infinite 2.0206 0.036 0.1856 0.003 0.93 1097 37 1122 20 1130 25 2.9 21 433460 Infinite 2.0282 0.043 0.1890 0.004 0.96 1116 41 1125 24 1134 21 1.6 22 135092 Infinite 2.0534 0.056 0.1873 0.005 0.95 1107 44 1133 31 1154 25 4.1 23 393360 19668 2.1728 0.042 0.1995 0.003 0.92 1173 40 1172 23 1161 28 –1.0 24 158101 Infinite 2.2812 0.022 0.2067 0.001 0.93 1211 37 1206 11 1166 24 –3.9 25 457060 Infinite 1.6001 0.087 0.1451 0.008 0.97 874 54 970 53 1168 27 25.2 26 1110968 Infinite 1.6735 0.014 0.1527 0.001 0.94 916 28 999 8 1185 21 22.7 27 1177595 Infinite 2.1699 0.054 0.1985 0.005 0.97 1167 45 1171 29 1185 20 1.5 28 260928 Infinite 2.2472 0.063 0.2032 0.006 0.96 1192 49 1196 33 1186 22 –0.5 29 1078929 Infinite 2.3740 0.104 0.2117 0.009 0.97 1238 64 1235 54 1228 27 –0.8 30 166663 Infinite 2.3208 0.038 0.2022 0.003 0.95 1187 40 1219 20 1237 22 4.0 31 241826 Infinite 2.3165 0.064 0.2031 0.006 0.97 1192 48 1217 34 1243 21 4.1 32 393935 Infinite 2.2663 0.169 0.1945 0.013 0.92 1146 86 1202 90 1279 62 10.4 33 376764 1638.1 2.3487 0.076 0.1995 0.006 0.94 1173 50 1227 40 1304 30 10.0 34 395046 Infinite 2.5778 0.049 0.2173 0.004 0.94 1268 44 1294 25 1330 24 4.7 35 127330 Infinite 2.8597 0.065 0.2341 0.005 0.94 1356 50 1371 31 1366 24 0.8 36 236473 Infinite 2.5301 0.068 0.2065 0.005 0.96 1210 48 1281 34 1383 23 12.5 37 230817 Infinite 3.0753 0.044 0.2455 0.003 0.94 1415 47 1427 21 1402 21 –0.9 38 344399 Infinite 2.9715 0.050 0.2393 0.004 0.94 1383 47 1400 24 1411 22 2.0 39 441807 14726.89 3.2392 0.066 0.2544 0.004 0.91 1461 50 1467 30 1465 29 0.3 40 147977 Infinite 3.2981 0.066 0.2546 0.004 0.91 1462 50 1481 30 1474 28 0.8 41 669286 Infinite 3.3311 0.059 0.2585 0.005 0.95 1482 51 1488 26 1505 20 1.5 42 1296589 Infinite 3.4601 0.056 0.2636 0.004 0.96 1508 51 1518 24 1533 19 1.6 Can. J. Earth Sci. Vol. 48, 2011 43 491753 1576.13 3.0343 0.278 0.2285 0.019 0.92 1327 118 1416 130 1548 73 14.3 Published by NRC Research Press 44 131575 Infinite 4.1502 0.081 0.2915 0.006 0.95 1649 59 1664 32 1649 20 0.0 45 228486 337.4977 4.3403 0.233 0.3062 0.015 0.94 1722 101 1701 91 1653 38 –4.2 46 321559 Infinite 3.9912 0.130 0.2809 0.009 0.97 1596 71 1632 53 1660 19 3.9 47 1031062 Infinite 4.0686 0.081 0.2883 0.006 0.96 1633 59 1648 33 1664 19 1.9 48 528558 Infinite 4.3359 0.084 0.3050 0.006 0.96 1716 61 1700 33 1669 19 –2.8 49 590211 Infinite 3.0786 0.314 0.2133 0.022 0.99 1246 132 1427 146 1684 30 26.0 50 600365 Infinite 4.3516 0.116 0.3040 0.008 0.97 1711 69 1703 45 1701 19 –0.6 51 593925 Infinite 3.8213 0.069 0.2633 0.005 0.96 1507 53 1597 29 1710 19 11.9
  • 11. Lemieux et al. Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 52 728551 3223.678 4.3360 0.792 0.2943 0.053 0.99 1663 306 1700 310 1747 41 4.8 53 386808 16817.72 4.6421 0.095 0.3115 0.006 0.93 1748 62 1757 36 1748 24 0.0 54 624037 Infinite 4.6055 0.058 0.3077 0.004 0.95 1729 56 1750 22 1766 19 2.1 55 2324654 36899.3 4.0873 0.067 0.2723 0.004 0.95 1553 53 1652 27 1793 20 13.4 56 775421 2959.62 4.6605 0.150 0.3029 0.010 0.97 1706 75 1760 57 1825 20 6.5 57 456978 Infinite 4.2560 0.077 0.2740 0.005 0.96 1561 55 1685 31 1832 18 14.8 58 1267941 4103.37 3.6877 0.111 0.2384 0.007 0.95 1378 57 1569 47 1841 23 25.2 59 640904 Infinite 5.2003 0.111 0.3332 0.007 0.96 1854 68 1853 39 1848 18 –0.3 60 842510 Infinite 5.0816 0.084 0.3242 0.005 0.96 1810 62 1833 30 1854 18 2.4 61 449007 Infinite 5.2542 0.072 0.3332 0.005 0.95 1854 61 1861 26 1860 18 0.3 62 178341 Infinite 5.5673 0.102 0.3465 0.006 0.96 1918 67 1911 35 1870 19 –2.6 63 462742 Infinite 5.1635 0.121 0.3234 0.007 0.93 1807 66 1847 43 1875 26 3.7 64 2906290 10416.8 3.8769 0.187 0.2447 0.012 0.98 1411 80 1609 78 1892 18 25.4 65 878581 2670.46 4.1829 0.112 0.2585 0.006 0.93 1482 57 1671 45 1913 27 22.5 66 1133511 4048.255 5.6088 0.427 0.3423 0.023 0.90 1898 141 1917 146 1919 64 1.1 67 954093 Infinite 5.7962 0.078 0.3545 0.005 0.95 1956 64 1946 26 1931 18 –1.3 68 125954 Infinite 5.7371 0.118 0.3456 0.007 0.95 1914 68 1937 40 1934 21 1.0 69 276151 Infinite 5.8263 0.112 0.3524 0.007 0.96 1946 69 1950 37 1937 19 –0.5 70 661599 2584.37 4.8255 0.262 0.2931 0.014 0.91 1657 95 1789 97 1964 46 15.6 71 641871 Infinite 4.9901 0.230 0.2908 0.013 0.98 1646 90 1818 84 2005 19 17.9 72 628332 Infinite 6.2959 0.131 0.3659 0.008 0.96 2010 73 2018 42 2022 18 0.6 73 1454081 Infinite 5.8633 0.124 0.3421 0.007 0.96 1897 69 1956 41 2026 19 6.4 74 569035 Infinite 6.8134 0.148 0.3905 0.008 0.96 2125 79 2087 45 2041 18 –4.1 75 540218 13505.46 6.4420 0.141 0.3624 0.007 0.93 1994 72 2038 45 2072 24 3.8 76 2375359 Infinite 5.9257 0.104 0.3289 0.006 0.96 1833 64 1965 35 2117 18 13.4 77 763478 21813.7 7.6396 0.276 0.3721 0.013 0.97 2039 95 2190 79 2330 19 12.5 78 261215 4213.14 7.7344 0.778 0.3480 0.034 0.97 1925 197 2201 221 2442 42 21.2 79 1196610 10978.1 8.7709 0.263 0.3711 0.011 0.95 2035 85 2314 69 2576 21 21.0 80 1757086 Infinite 10.8700 0.261 0.4452 0.011 0.97 2374 91 2512 60 2607 17 9.0 81 593333 7510.545 12.4287 0.219 0.5121 0.007 0.90 2666 88 2637 46 2614 25 –2.0 82 662851 12747.13 12.1365 0.259 0.5015 0.010 0.95 2620 95 2615 56 2616 20 –0.2 83 416360 Infinite 12.9122 0.260 0.5159 0.010 0.96 2682 97 2673 54 2657 17 –0.9 Published by NRC Research Press 84 252375 Infinite 13.1744 0.276 0.5171 0.011 0.96 2687 98 2692 56 2676 17 –0.4 85 208645 Infinite 11.6138 0.424 0.4548 0.016 0.97 2416 114 2574 94 2678 18 9.8 86 1148347 Infinite 7.6352 0.513 0.3010 0.020 0.99 1696 124 2189 147 2685 20 36.8 87 1089764 6263.011 13.2524 0.216 0.5143 0.008 0.96 2675 91 2698 44 2720 17 1.7 88 808986 3595.492 13.2011 0.297 0.5020 0.011 0.96 2622 98 2694 61 2743 18 4.4 89 2297798 10687.43 14.0788 0.229 0.5194 0.008 0.95 2697 92 2755 45 2806 17 3.9 90 2196173 Infinite 11.3921 0.208 0.4155 0.008 0.96 2240 78 2556 47 2827 17 20.7 91 2605994 Infinite 14.3094 0.171 0.5033 0.006 0.94 2628 84 2770 33 2886 18 8.9 525
  • 12. 526 Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) Sample 06YHL046B (UTM Zone 9N, N7272396, E343816) 1 306103 21864.5 0.4471 0.011 0.0586 0.001 0.90 367 13 375 9 412 38 10.8 2 143296 Infinite 0.5353 0.013 0.0686 0.002 0.96 428 16 435 11 439 25 2.6 3 267931 Infinite 0.5415 0.008 0.0698 0.001 0.95 435 15 439 7 449 24 3.1 4 269063 Infinite 0.5246 0.009 0.0667 0.001 0.95 416 14 428 7 450 23 7.5 5 305544 25462.04 0.5388 0.011 0.0690 0.001 0.91 430 15 438 9 452 33 4.8 6 191005 Infinite 0.5527 0.010 0.0706 0.001 0.95 440 15 447 8 452 24 2.8 7 117843 Infinite 0.5512 0.010 0.0696 0.001 0.94 434 15 446 8 453 27 4.3 8 87963 Infinite 0.5519 0.008 0.0697 0.001 0.94 435 14 446 6 457 24 4.9 9 273721 Infinite 0.5580 0.010 0.0712 0.001 0.94 444 15 450 8 461 27 3.8 10 244012 Infinite 0.5268 0.010 0.0673 0.001 0.96 420 15 430 8 464 23 9.4 11 157050 6828.25 0.5478 0.008 0.0693 0.001 0.94 432 14 444 7 476 25 9.3 12 250449 Infinite 0.5569 0.012 0.0701 0.001 0.96 437 16 450 9 488 23 10.5 13 90322 Infinite 0.5830 0.009 0.0726 0.001 0.94 452 15 466 8 488 26 7.4 14 75488 Infinite 0.5878 0.009 0.0735 0.001 0.93 457 15 469 7 489 27 6.5 15 258727 Infinite 0.5517 0.014 0.0694 0.002 0.94 433 17 446 11 489 29 11.6 16 540430 24565 0.4523 0.009 0.0569 0.001 0.91 357 12 379 8 505 33 29.3 17 667919 Infinite 0.5657 0.017 0.0701 0.002 0.97 437 19 455 14 514 23 15.0 18 61977 Infinite 0.5407 0.008 0.0656 0.001 0.91 410 13 439 6 553 30 25.9 19 667782 897.556 1.2921 0.107 0.1382 0.011 0.97 835 72 842 70 946 40 11.7 20 554178 Infinite 1.5739 0.027 0.1571 0.003 0.96 940 32 960 16 987 21 4.7 21 1153240 31168.66 1.7696 0.026 0.1748 0.002 0.93 1038 34 1034 15 1045 24 0.7 22 53008 Infinite 1.9203 0.040 0.1822 0.004 0.95 1079 39 1088 23 1067 24 –1.2 23 827576 Infinite 1.9780 0.036 0.1875 0.003 0.96 1108 39 1108 20 1106 20 –0.2 24 48901 Infinite 2.1117 0.041 0.1952 0.004 0.94 1149 40 1153 23 1106 25 –3.9 25 276073 21236.4 1.8961 0.045 0.1767 0.004 0.93 1049 39 1080 26 1121 28 6.4 26 493272 Infinite 2.0163 0.038 0.1879 0.003 0.96 1110 39 1121 21 1138 21 2.4 27 385501 Infinite 2.1941 0.027 0.2006 0.002 0.95 1179 38 1179 15 1168 20 –0.9 28 391950 23055.89 2.1692 0.031 0.1970 0.002 0.92 1159 37 1171 17 1178 26 1.6 29 862341 16908.65 2.1118 0.040 0.1932 0.003 0.90 1139 38 1153 22 1181 30 3.6 Can. J. Earth Sci. Vol. 48, 2011 30 329913 Infinite 2.2349 0.035 0.2006 0.003 0.95 1179 40 1192 19 1198 21 1.6 Published by NRC Research Press 31 1542492 23022.28 2.2253 0.039 0.2020 0.003 0.93 1186 40 1189 21 1215 26 2.4 32 963785 19669.07 2.3924 0.042 0.2128 0.003 0.92 1244 41 1240 22 1243 27 –0.1 33 183429 Infinite 2.5816 0.025 0.2189 0.002 0.93 1276 40 1295 13 1302 22 2.0 34 805537 44752.06 2.6900 0.056 0.2234 0.005 0.96 1300 47 1326 28 1366 21 4.9 35 387711 Infinite 2.9232 0.053 0.2292 0.004 0.95 1330 46 1388 25 1468 20 9.4 36 184140 Infinite 3.3213 0.085 0.2559 0.006 0.93 1469 56 1486 38 1494 27 1.7 37 582297 Infinite 3.4728 0.046 0.2661 0.003 0.95 1521 50 1521 20 1512 20 –0.6 38 283821 Infinite 3.1801 0.065 0.2393 0.005 0.95 1383 50 1452 30 1525 21 9.3 39 98480 Infinite 3.8013 0.085 0.2746 0.006 0.95 1564 58 1593 35 1597 22 2.0
  • 13. Lemieux et al. Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 40 534604 Infinite 4.1880 0.070 0.2967 0.005 0.96 1675 57 1672 28 1650 19 –1.5 41 774143 3351.27 4.0421 0.059 0.2841 0.004 0.95 1612 54 1643 24 1679 19 4.0 42 271748 Infinite 4.2425 0.065 0.2948 0.004 0.95 1665 56 1682 26 1683 19 1.1 43 1049121 2149.839 4.4244 0.111 0.3093 0.008 0.96 1737 68 1717 43 1731 20 –0.4 44 1083148 16924.2 5.2375 0.104 0.3449 0.006 0.93 1910 67 1859 37 1807 24 -5.7 45 345860 Infinite 5.1241 0.078 0.3283 0.005 0.95 1830 61 1840 28 1837 19 0.4 46 87174 Infinite 5.0542 0.081 0.3175 0.005 0.94 1777 60 1828 29 1844 21 3.6 47 908076 Infinite 4.8886 0.093 0.3145 0.006 0.96 1763 62 1800 34 1848 19 4.6 48 160593 Infinite 5.1285 0.074 0.3232 0.005 0.95 1806 60 1841 27 1850 19 2.4 49 158205 Infinite 5.2452 0.144 0.3314 0.009 0.96 1845 74 1860 51 1855 21 0.5 50 217662 Infinite 5.1917 0.104 0.3269 0.006 0.96 1823 65 1851 37 1855 19 1.7 51 286154 Infinite 5.1969 0.118 0.3299 0.007 0.96 1838 69 1852 42 1858 19 1.1 52 908503 Infinite 5.1060 0.101 0.3245 0.006 0.96 1812 65 1837 36 1881 18 3.7 53 380632 Infinite 5.2275 0.092 0.3266 0.006 0.96 1822 63 1857 33 1882 18 3.2 54 547020 30390.02 5.4287 0.102 0.3397 0.006 0.95 1885 66 1889 36 1884 20 0.0 55 418269 Infinite 5.1815 0.097 0.3247 0.006 0.96 1813 64 1850 35 1886 19 3.9 56 547155 Infinite 5.3779 0.100 0.3358 0.006 0.96 1867 66 1881 35 1887 18 1.1 57 383706 Infinite 5.2456 0.106 0.3247 0.006 0.93 1813 64 1860 37 1899 24 4.5 58 823007 39190.81 5.5397 0.101 0.3455 0.006 0.95 1913 67 1907 35 1905 19 –0.4 59 227125 Infinite 5.7988 0.144 0.3527 0.009 0.97 1948 76 1946 48 1927 18 –1.1 60 415084 29648.85 5.5268 0.086 0.3346 0.005 0.95 1860 62 1905 30 1937 20 3.9 61 863196 Infinite 5.4964 0.070 0.3343 0.004 0.95 1859 61 1900 24 1943 18 4.3 62 568320 33430.6 5.6318 0.112 0.3386 0.006 0.95 1880 67 1921 38 1945 21 3.3 63 301989 Infinite 5.9578 0.228 0.3544 0.013 0.94 1956 91 1970 75 1981 30 1.3 64 1654832 7576.821 5.9299 0.170 0.3536 0.010 0.97 1952 81 1966 56 1989 18 1.9 65 134120 Infinite 6.3813 0.096 0.3660 0.005 0.95 2011 67 2030 30 2014 20 0.2 66 453298 11928.89 6.4458 0.162 0.3719 0.009 0.93 2038 77 2039 51 2028 26 –0.5 67 213612 Infinite 6.2961 0.073 0.3578 0.004 0.95 1972 63 2018 23 2042 18 3.4 68 340590 Infinite 6.9231 0.087 0.3816 0.005 0.95 2084 68 2102 27 2103 18 0.9 69 169094 Infinite 7.2633 0.110 0.3982 0.006 0.95 2161 72 2144 32 2108 18 –2.5 70 254999 1432.578 7.0782 0.224 0.3826 0.011 0.92 2088 86 2121 67 2132 31 2.1 71 288084 10288.7 7.7350 0.149 0.4007 0.006 0.91 2172 74 2201 42 2218 25 2.1 Published by NRC Research Press 72 243308 Infinite 8.2218 0.117 0.4142 0.005 0.92 2234 72 2256 32 2259 22 1.1 73 713263 3114.684 7.9414 0.163 0.4009 0.007 0.91 2173 75 2224 46 2274 26 4.4 74 297895 Infinite 9.1338 0.172 0.4395 0.008 0.96 2349 83 2351 44 2334 18 –0.6 75 627237 36896.29 8.9794 0.166 0.4289 0.008 0.95 2301 81 2336 43 2369 18 2.9 76 588155 Infinite 9.5616 0.116 0.4463 0.005 0.95 2379 77 2393 29 2396 17 0.7 77 744871 Infinite 9.5427 0.175 0.4456 0.008 0.96 2376 83 2392 44 2404 17 1.2 78 688756 Infinite 10.3881 0.132 0.4568 0.006 0.95 2426 79 2470 31 2500 17 3.0 79 315734 Infinite 11.5054 0.202 0.4803 0.008 0.96 2529 88 2565 45 2578 17 1.9 527