Geology 104

3. Dianne Meltzer, MS Student of Geology Fall 2011 High peaks Forty-six of the tallest mountains are considered "The 46" Adirondack High Peaks—those over 4,000 ft. (1,219 m), as surveyed at the beginning of the twentieth century. Since that time, better surveys have shown that four of these peaks (Blake Peak, Cliff Mountain, Nye Mountain, and Couchsachraga Peak) are in fact just under 4,000 ft. (1,200 m), and one peak just over 4,000 ft. (MacNaughton Mountain) was overlooked. 10/31/11

4. Mount Marcy, the Adirondacks highest peak, looking across Panther Gorge from Mount Haystack. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11

5. Dianne Meltzer, MS Student of Geology Fall 2011 The highest peak, Mount Marcy (sometimes also called Tahawus), at 5,344 ft. (1,629 m), is near the eastern part of the group. Other noted High Peaks include: Algonquin Peak (formerly Mt. McIntyre); 5,114 ft. (1,559 m) Haystack; 4,960 ft. (1,512 m) Skylight; 4,926 ft. (1,501 m) Whiteface; 4,867 ft. (1,483 m) Dix; 4,857 ft. (1,480 m) Giant; 4,627 ft. (1,410 m) There are over one hundred summits, ranging from under 1,200 to over 5,000 feet (370 m to 1500 m) in altitude. 10/31/11

7. Dianne Meltzer, MS Student of Geology Fall 2011 The Grenville Orogeny, is a mountain building event that included parts of the Adirondacks. Actually, the Adirondacks are a small outcrop area of the Grenville orogeny (mountain belt). Grenville rocks extend for 3,100 miles (5,000 km) underground from the eastern United States to Mexico and from northern Lake Huron across Ontario to Labrador, southern Greenland, and areas now separated form North America. 10/31/11

8. Dianne Meltzer, MS Student of Geology Fall 2011 The Grenville orogeny was an early stage in the assembly of the supercontinent Rodinia. No record of the next 550 million years is known in this region, but this time included erosion of the Grenville mountains and the removal of 19-25 miles (30-40 km) of Grenville rock down to about its present level. It is unknown where the sediment eroded from the Adirondack Mountains and Hudson Highlands in the Grenville belt was deposited. 10/31/11

9. Dianne Meltzer, MS Student of Geology Fall 2011 The Adirondacks are not an elongate mountain belt but are a circular dome caused by then unwarping of continent basement and erosion of overlying younger rocks. 10/31/11

10. Dianne Meltzer, MS Student of Geology Fall 2011 It is possible that the southwestern Hudson Highlands lay near a collision zone between ancestral North America and a continent that included much of South America. This collision may have produced the Grenville orogeny and the rocks of the Adirondacks and Hudson Highlands. The Adirondack Mountains are very different in shape and content from other mountain systems. The Adirondacks form a circular dome, 160 miles wide and one mile high. Although the dome as we know it today is a recent development of five million years ago, its made of ancient rock more than 1,000 million years old. Hence the Adirondacks are new mountains from old rocks. . Zircons (reworked), with 2,075 mya and 1,500 mya ages are best known in the northern Amazon Basin. These data suggest that Amazonian rocks were eroded to supply the zircons. The following illustration shows why it is common to include the Adirondack in various accounts of mountain building events, throughout the ages. The gathering of mountains in a circular area may be evidence of the multiple impacts and additions to its landscape over the ages, that included powerful folding events and subduction of lower density crustal surface. 10/31/11

12. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11

13. The Grenville orogeny was an early stage in the assembly of the supercontinent Rodinia. No record of the next 550 million years is known in this region, but this time included erosion of the Grenville mountains and the removal of 19-25 miles (30-40 km) of Grenville rock down to about its present level. It is unknown where the sediment eroded from the Adirondack Mountains and Hudson Highlands in the Grenville belt was deposited. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11

14. Dianne Meltzer, MS Student of Geology Fall 2011 The craton includes the sedimentary rocks that overlie the Adirondack basement and extend into Ontario, Quebec, and the Lake Champlain valley and that underlie all areas south of the Adirondacks and west of the Hudson-Wallkill River valley. The craton south of the Mohawk-Lake Ontario Lowlands lies at the north end of the Allegheny Plateau, an upland east of the Appalachians that extends to Alabama and into the Midwest. 10/31/11

16. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11

17. Dianne Meltzer, MS Student of Geology Fall 2011 Repeated episodes of folding and faulting by orogenic (mountain-building) processes, the craton changes east of the Wallkill-Hudson-Lake Champlain Lowlands into the Appalachian Mountain belt of easternmost New York State. This geological region of the state features New England-type geology. In this area, Adirondack-type basement was uplifted on faults (Hudson Highlands), and deep-water, continent-martin rocks of the Taconic slate belt were pushed into New York from their original position in the Connecticut River Valley region. 10/31/11

19. Dianne Meltzer, MS Student of Geology Fall 2011 The Adirondacks are largely composed of such metamorphic rocks as gneiss (feldspar-, quartz-, and mica-rich rocks with minerals segregated into layers) and minor marble (metamorphosed limestone). These rocks are composed of minerals formed at temperatures and pressures associated with burial to 19-25 miles (30-40 km). Such depths of burial are produced in continent-continent collisions where one continent overrides another. 10/31/11

20. Dianne Meltzer, MS Student of Geology Fall 2011 In the following map of the southern Adirondack to Mohawk Valley region (modified from Hay and Cisne, 1988), the major fault in the area is referred to as the "Thrust Fault" and although there are some minor examples of thrust faults in areas to the west, the most predominant thrust faults in the region are in eastern New York State. The fault bounded areas are shaded in dark gray and are labeled as the Taconic Front. These rock units are part of the "Taconic Melange" and represent materials that were pushed up over the top of the ancestral margin of eastern Laurentia during the Taconic Orogeny. It was the thrust faulting of these same rocks that helped to form the Taconic Foreland Basin which resulted in the deposition of the Trenton Group. 10/31/11

21. Image Modified from: Hay and Cisne, 1988 "Deposition in the Oxygen-Deficient Taconic Foreland Basin, Late Ordovician"

23. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11

24. Mountain building Adirondacks when continents collide; they are the calling cards of orogenies, mountain-building events. In this case, the mountains that were built were called the Grenville Mountains, and they were piled up when the Congo craton collided with ancestral North America (sometimes called "Laurentia") and smeared out a block of crust between the two. This collision, which added a large block of new crust to the eastern edge of North America, completed the assembly of a supercontinent geologists call "Rodinia”. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11

28. Dianne Meltzer, MS Student of Geology Fall 2011 Glaciers A quarter of a million years ago, the snow which fell in the winter did not melt over the summer. As it accumulated over a millennia, its enormous weight compressed the lower layers of snow into ice, eventually becoming thousands of feet thick. The increased pressure softened the lower ice, causing it to flow like thick molasses. The glacier pulverized boulders into pebbles, carrying debris as it moved. As the ice sheets thickened, the glacier crept over hills and eventually, over the highest mountains, breaking and lifting rocks as it rounded their summits. When the ice sheets melted these rocks called erratic's, were deposited throughout the Adirondacks, where they can be seen today in fields, along forest trails, and scattered on mountaintops. 10/31/11

29. Glacial erractics deposited throughout the Adirondacks. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11

32. Dianne Meltzer, MS Student of Geology Fall 2011 10/31/11