This ppt explaining the geodynamic evolution of Himalayas in Geologic history.

1. GEOLOGY PRESENTATION
TOPIC- GEODYNAMIC EVOLUTION OF HIMALAYA
Prepared by- Ritik
Contact Info- raoritikyadavnkt@gmail.com

2. 1 . Emergence and Evolution of Himalaya
Contents
2 . Bending and Bulging up of Leading Edge
3 . Sagging of ITS Zone
4 . Breaking of Himalayan Crust
5 . Domal Structures in Tethys Terrane
6 . Metamorphism in Himadri (Great Himalaya) Terrane
7 . Anatexis and Emplacement of Leucogranites
8 . Development of Lesser Himalayan Terrane
9 . Evolution of Syntaxial Bends
10 . Oblique Thrust Ramps

3. Emergence and Evolution of Himalaya
1 Amalgamation of India with Eurasia
• The Kohistan island arc in the frontal part of
the Indian plate docked with mainland
Asia, as already stated, around 65 Ma, and
the suturing or welcing of the two
continents was complete by 50–55 Ma. The
frontal part of the Indian plate bent—
the continental margin—down, was cut by
deep steep faults and compressed into
a series of folds, giving rise to a huge
synclinorium in the terrane known as the
Tethys Himalaya.
• Even the pillow lavas and underlying dyke
swarms along with the substratum.
• The mixed suite of rocks melange was
sheared, shattered and uprooted in the zone
of welding of the two continents. This zone of
welding is known as Indus-Tsangpo Suture.

4. 2 Bending and Bulging up of Leading Edge
2.1 Deformation
Most scientists believe that the leading edge of the northward-moving Indian
plate plunged and slid under the Eurasian plate
Being 20% less dense than the mantle , the Indian mass stopped sliding and
buckled up into a domal .
2.2 Metamorphism
Shortly after the docking, the rocks of the junction zone
were deformed and metamorphosed.Pressures locally as
strong as 11–9 kbar and the temperatures rather as
low as (420–350 °C) converted the ophiolites in many
places into blue schists which
are made up of glaucophane, jadeite, lawsonite with or
without phengite
Coesite-bearing eclogite in the Kaghan Valley in northern
Pakistan indicates ultrahigh-pressure metamorphism at 46 Ma

5. 3 Sagging of ITS Zone
3. 1 Sedimentation
Even as the northern edge of the Indian plate bulged up, the zone of welding of India and Asia sagged
down. This happened in the Late Eocene time, 34–30 million years ago. A 2000-km-long and 60–100-
km-wide depression was formed along what is today occupied by the valleys of the Sindhu and Tsangpo
rivers.The depression is described as the Sindhu Basin
4 Breaking of Himalayan Crust
4.1 Main Central Thrust
Earlier formed folds were further tightened and overturned, some of
them toppling over southwards. Many of the tightened folds were split by faults
along their axial planes and subsequently displaced or thrust southwards as much
as 30–80 km There was continuous build-up of compressive
strain, and the buckled-up Himalayan crust broke up at 21 ± 2 Ma along what
was to become the Main Central Thrust (MCT), first recognized by A. Heim and
A. Gansser in 1939 in the Uttarakhand sector. The broken-up crustal block
moved up and southwards along gently (30°–45°) inclined thrust plane all along
its 2000 km stretch—from the Kishtwar in the north-west to the Siang valley in
the east to produce the great Himalaya delimited at the base by the Main Central
Thrust(MCT).
The MCT ends against the Indus– Tsangpo Suture which is in Pakistan, where it is described as the Main
Mantle Thrust

6. MCT is thus a terrane -defining tectonic plane bringing the Great Himalayan highgrade
metamorphic rocks that are intruded by Miocene granites, onto and over the
Lesser Himalayan lower-grade metamorphic rocks intimately associated with the
Proterozoic granites.
The MCT ends against the Indus– Tsangpo Suture which is in Pakistan, where it is described as
the Main Mantle Thrust
In Nepal, the MCT zone is a 2- to 3-km-thick zone of strain that developed
during two or more episodes of movement concentrated along Chomrong Thrust,

7. 4.2 Trans-Himadri Detachment Fault
Tethyan sedimentary cover was detached from the hard unyielding crystalline basement making the Great Himalaya .
The plane of detachment represents normal gravity fault (whose inclination varies from sector to sector) which was first
described as the Malari Fault Thrust in the valleys of Dhauli,Gori and Kali and later named the Trans-Himadri
Detachment Fault
The movements of the Trans- Himadri Fault in Uttaranchal are dominantly dip slip. The T-H- F is discernible in Lahaul,
and Spiti and Kullu valleys in Himachal Pradesh
5 Domal Structures in Tethys Terrane
All along the northern zone of the Himalaya province, high points or domal structures
of large dimension occur within the sedimentary expanse of the Tethys terrane.
In south-eastern Ladakh , the Tso Morari Dome in the surrounding of Later Precambrian to Cretaceous succession.
These were formed by shearing of the upper crust metamorphic rocks.
South of Mount Kailas is the gneissic Gurla
Mandhata Dome, the development
of which is related to the tectonics of the Indus–
Tsangpo Suture

8. The Main Boundary Thrust (MBT) represents the southwards migration of Himalayan
deformation from the site of MMT. From northeast to southwest, it extends along the front of the
northern fold and thrust belt around Hazara-Kashmir Syntaxes. It carries the per-collision
Paleozoic and mesozoic sedimentary rocks of northern deformed fold and thrust belt in its
hanging wall and post- collision folded Miocene foreland- basin deposits in its footwall.
Main Boundary Thrust ( MBT)
Himalayan Frontal Thrust (HFT)
The Siwalik foothills were uplifted approximately one million years ago along high angle
reverse faults (still active) , called Himalayan Frontal Fault (or thrust ) and first mapped in
India and Nepal by the Japanese Geologist T. Nakata in 1972 . The Himalayan Frontal Fault
marks the boundary between Siwalik Range and northern Indian plains. The Himalayan
Frontal Fault is a series of blind faults ( the fault plane is not visible at the surface ), and can be
mapped from the topography features they have created . These faults are often under an apron of
debris from the hillsides.

10. 6 Metamorphism in Himadri (Great Himalaya) Terrane
Metamorphic mineral assemblages characterized by staurolite, kyanite and sillimanite
indicate that the Himadri metamorphic rocks evolved at the depth of30–35 km where the temperature was
higher than 600 °C and the pressure more than 7–8 kbar
6.2 Inverted Metamorphism
First noticed in the Darjeeling Hills, the abnormal succession of metamorphic grades was described by F.R.
Mallet in 1884.
The inversion of metamorphism is only apparent and is related to repeated thrusting. Another view is that
Intracontinental underthrusting along the MCT and bowing down of the isotherms resulted in the inversion of
metamorphic grades.
 Apparent inversion of metamorphic grades is interpreted in different ways. a effect of deformation of
a normal metamorphic sequence across a broad shear zone and b differential denudation of the metamorphic zones as a
consequenceof imbricated thrusting
6.3 Date of Metamorphism
In the Zanskar range 37.3 Ma is the time of
metamorphism before deformation .In north
eastern Nepal, the hanging wall rocks above the
MCT were metamorphosed during the thrust
movement at 21 Ma

11. 7 Anatexis and Emplacement of Leucogranites
7.1 Mode of Occurrence
In the Himadri domain, the pressure and temperature had risen so high in the Early Miocene that susceptible parts
of the metamorphic rocks melted differentially or partially, giving rise to molten material of granitic composition.
Minerals such as sillimanite, cordierite and garnet, so common in metamorphic rocks, occur profusely in these
anatectic granites. The granites are leucocratic all along the Himadri expanse. The anatectic magmas were
emplaced in the form of batholiths ,stocks , laccoliths, sills, dykes and veins
7.2 Causes of Anatexis
The shear zone stress on thrusts and faults at the base and at the top of the Himadri succession must have
decreased, resulting in decompression melting . In the southern part of the Nanga Parbat massif, the 22–16 Ma
leucogranites occur adjacent to the Rupal Shear Zone .In the Kishtwar region, it was formed due to frictional
heating along the MCT

12. 8 Development of Lesser Himalayan Terrane
8.1 Northern Duplex Zone
Repeated translation or thrusting of the Himadri rock pile threw more than 7000-m-thick Lesser Himalayan sedimentary and
metasedimentary successions into a series of folds. Close to the MCT, the squeezing and tightening of folds resulted in
southward overturning and toppling over of folds, accompanied by their splitting by a multiplicity of faults along axial
planes . This gave rise to a duplex or schuppen zone comprising imbricating lithotectonic stacks as seen in the tract between
Alaknanda and Yamuna in Uttarakhand
8.2 Far-Travelled Nappes
Increasing compression resulted in the uprooting of the entire folded pile under the MCT and their 80 to 125 km
displacement southwards in the form of thrust sheets or nappes . There are two principal lithologically and structurally
distinctive nappes. The structurally lower Ramgarh–Chail Nappe is made up of lowgrade metamorphic rocks integrally
associated with 1900 ± 100 Ma mylonitized porphyritic granite and porphyry. In western Nepal, the Ramgarh thrust
sheet—0.2 to 2.0 km in thickness .
The structurally upper Almora/Munsiari–Jutogh
Nappe comprises medium-grade metamorphic
rocks intruded by 500 ± 25 Ma granit granodiorite
plutons.

13. 9 Evolution of Syntaxial Bends
9.1 Impact of Projecting Promontories
The WNW–ENE-oriented Himalaya mountain arc, with all its rock formations and structures including fold belts and
thrust systems, abruptly bends southwards, making acute angles, at its two extremities . Theses pectacular features,
resembling knee bends, are known as the syntaxial bends north-western syntaxial bends were formed due to strong
impact of the projecting promontories—points of highland jutting of the Indian Shield.
9.2 Nanga Parbat Syntaxial Bend
The Nanga Parbat Syntaxis is a northwardly plunging antiformal structure, in the core of which occur Proterozoic
gneisses. The gneisses give way outwardly to mylonitized and sheared rocks of marginal shear zones, thrusts,
and dextral faults, particularly in the west. It has also been interpreted as a feature that resulted from interference of
structures of two thrust systems.
9.3 Hazara Syntaxis
In the Hazara Syntaxis, the entire succession of NW–SE-trending rock formations with intervening thrust zones bends
around southwards, making an angle of 40°. The western flank of the syntaxis behaved differently. The syntaxis thus
resulted from an early set of nappe units thrust southwards, followed by the formation of large shear zones and finally
transportation of overthrust units southwards
9.4 Siang Syntaxis
In the eastern Himalaya, the Siang Syntaxis was formed due to compressive movements on continental conjunction
which led to northward displacement of the Arunachal block and Myanmar landmass relative to the Tibet–Shan
States–Malaysia block of the Asian plate .

14. Formation of the Hazara–Kashmir syntaxis: a initial overthrust geometry, b rotation
of overthrust units and formation of shear zones and c further rotation of overthrust units, leading to present-day
geometry of the syntaxis
• Sketch map shows the lithological units
and tectonic boundaries in the Nanga
Parbat syntaxial antiform.
• Siang syntaxis in eastern Himalaya. The
eastern Arunachal Pradesh flank is delimited
by the NW–SE-trending Tidding–Tuting
Shear Zone, representing the Indus–Tsangpo
Suture

15. 10 Oblique Thrust Ramps
The Himalaya province is cut by wrench faults trending transverse to the general trend of the Himalaya,
forming NNW–SSE- and N/NNE–S/SSW-oriented conjugate fault systems . Some of these faults,
coinciding with the older thrusts, have been interpreted as oblique thrust ramps .
The Kaurik–Chango fault system, defining the Leopargial horst in the Himadri terrane in north-eastern Himachal
Pradesh, provides an example of the oblique ramp thrusts .
The Karakoram Fault, developed sometime after 17 Ma, accommodated the evolution of the Tibetan Plateau.
The Karakoram Shear Zone is characterized by mylonitic rocks .
References
In K. S. Valdiya , Geological Survey of India, 24(II), 71–90.
Anczkiewicz, R., Burg, J. P., Villa, I. M., & Meier, M. (2000). Late Cretaceous blueschist metamorphism
in the Indus Suture Zone, Shangla region, Pakistan Himalaya. Tectonophysics,
324, 111–134.
Argles, T. W., & Edward, M. A. (2002). First evidence for high-grade Himalayan-age synconvergent
extension recognized within the western syntaxis—Nanga Parbat, Pakistan. Journal of
Structural Geology, 24, 1327–1344.
Bahuguna, V. K., & Saklani, P. S. (1988). Tectonics of the Main Central Thrust in Garhwal
Himalaya. Journal of the Geological Society of London, 31, 197–209.
Bhakuni, S. S. (1995). The structure of the Great Himalaya in Chamoli and Uttarkashi districts,
Kumaun Himalaya. Geoscience Journal, 16