Tethyan Himalaya And Trans Himalaya

What is the difference between Tethyan Himalaya and Trans Himalaya?

I've seen the two terms being used interchangeably, but geologists recognize them as geologically distinct terrains. Their geographic locations and geologic context has been annotated in the satellite imagery below. 

The Indus Suture is the zone of collision between the Indian and Asian tectonic plates. It contains broken pieces of  oceanic crust and deep sea sediments which were uplifted and jammed between the colliding continents, forming a sort of a geologic no-man's land. The Tethyan Himalaya are the ranges immediately south of the Indus Suture. They are the deformed rocks of the Indian plate. The Trans Himalaya are the ranges north of the Indus Suture made up of a variety of rocks of the Asian plate.

The Tethyan Himalaya is a pile of Paleozoic and Mesozoic sedimentary rocks which was deformed into a fold and thrust belt during the early stages (45-35 million years ago) of the India Asia collision. At places, the sedimentary cover has been stripped away by erosion and high grade metamorphic rocks formed deep in the crust have been exposed. These 'windows' are known as gneiss domes since the sedimentary cover rocks have been arched up during uplift and exhumation of the high grade rocks. The area around the famous Tso Moriri lake is one of the best examples of a gneiss dome.

If your are traveling in Zanskar, Spiti, Lahaul, upper reaches of Kinnaur, and near about Milam and Panchachuli Glaciers,  you are in the Tethyan Himalaya. 

In the late Cretaceous (100 million  years ago), the leading edge of the Indian plate began subducting underneath Asia. As the plate dove deeper it heated up and released water, which triggered the formation of magma in the upper mantle of the Asian plate. This magma rose and assimilated rocks from the Asian lower crust. It then intruded older sedimentary and metamorphic rocks of the Asian crust and solidified as giant bodies of granites and granodiorites (containing calcium rich feldspars). These large granitic intrusions or 'batholiths' range in age from 100 million years to about 50 million years ago. One example is the Ladakh Batholith on which the town of Leh sits. Some of this magma also erupted on the surface through volcanoes. The rocks of Khardungla Pass are remnants of this ancient volcanic terrain. 

A similar situation today is along the western South American margin. There, subduction of the Nazca Plate underneath South America has triggered large scale magmatism and formation of giant batholiths of the Andes Mountains. 

Another impressive geologic feature of the Trans Himalaya is the Karakoram Fault Zone. It is a NW-SE aligned right lateral strike slip fault where crustal blocks have been sliding past each other since about 18 million years ago, resulting in a 150 km of offset of rocks. There has been some vertical movement also along this fault and this uplift has resulted in the formation of the Pangong Ranges where high grade metamorphic rocks have been exhumed from a deeper crustal level. The Pangong Lake is a drowned river valley formed by the damming of the river on its western end due to fault uplift. 

Strike slip faults have been in the news recently. The devastating earthquake in Turkey and Syria was caused by movement along the left lateral strike slip East Anatolian Fault. 

The India Asia collision resulted in the partial melting of deeply buried rocks of the Asian crust in the Miocene (21-16 million years ago) and the resulting granitic magmas have intruded the upper levels of the crust as dikes and sills. These melt channels also coalesce to form plutons and batholiths. Granitic intrusions of Miocene age which formed as crustal melts differ in their composition from the older Ladakh batholith which has a mixed mantle and crustal origin. There is a lot of interesting and complicated geology in the Trans Himalaya too! 

There are lots of technical papers on this topic. For good popular style book I recommend Mike Searle's Colliding Continents: A Geological Exploration of the Himalaya, Karakoram and Tibet. 

If you want a short answer to the question I posed, it is this: The Himalaya (including the Tethyan Himalaya) is the deformed northern edge of the India Plate. The Trans Himalaya is the deformed southern edge of the Asian Plate.
 

Papers: Tectonics And Physical Volcanology Of Deccan Traps

There are plenty of research papers on the geochemistry of the Deccan Basalts. But nature lovers and trekkers like me come face to face not with chemistry but with the physical forms of lava and the structural elements of the volcanic pile.

I found this list of papers most useful. They have helped me sort out my confusions regarding lava morphology and taught me something about the structural fabric of the western margin of the Deccan Volcanic Province.

1) Near N–S paleo‑extension in the western Deccan region, India: Does it link strike‑slip tectonics with India–Seychelles rifting? - Achyuta Ayan Misra Gourab Bhattacharya, Soumyajit Mukherjee, Narayan Bose

This is a structural analysis of the fracture systems that cut across the western margin of the Deccan province.  The area of study is the coastal plains, about 100 km north and south of Mumbai. The Indian western margin is a rifted margin i.e. it formed by the breakup of India with Madagascar (88 million years ago) and then Seychelles (64 million years ago). This type of margin is formed by tensional forces splitting apart continents and so you would expect normal faults, wherein blocks of crust have moved down along inclined fault planes.  Except here, the researchers find evidence of strike slip movement along sub-vertical fault planes. This means crustal blocks slid past each other. This implies oblique rifting with components of both extension and transverse movement between India and Seychelles. There are some really revealing field photos of this transverse (strike slip) movements.

2) Geology of the Elephanta Island fault zone, western Indian rifted margin, and its significance for understanding the Panvel flexure- Hrishikesh Samant, Ashwin Pundalik, Joseph D’souza, Hetu Sheth, Keegan Carmo, LoboKyle D’souza, Vanit Patel

Wait a minute. There are normal faults with downthrown blocks in this region too. And from the famous Elephanta Island. The fault planes dip eastwards producing easterly downthrows. That means the easterly crustal block has moved down. Again, some good field photos of fault planes and slickensides ( fault surfaces which get a polished striated appearance due to the frictional movement of rocks). These faults with easterly downthrows are found all along the west coast.  There is one near the proposed site of the nuclear power plant at Jaitapur in southern Maharashtra, which shows signs of intermittent movement over the past fifty thousand years. So, there is a very practical reason for understanding these faults.

3) Deccan Plateau Uplift: insights from parts of Western Uplands, Maharashtra, India- Vivek. S Kale, Gauri Dole, Devdutta Upasani and Shilpa Patil Pillai

This is a study of part of the Deccan plateau. I visited this region a few weeks back.  Very useful information of the various fracture systems that cut across the stacks of lava and their significance in terms of recent (Quaternary) crustal movements and controls on the drainage systems. Well thought out block diagrams illustrate the authors ideas very clearly.

4) Pahoehoe–a'a transitions in the lava flow fields of the western Deccan Traps, India-implications for emplacement dynamics, flood basalt architecture and volcanic stratigraphy-  Raymond A. Duraiswami, Purva Gadpallu, Tahira N. Shaikh, Neha Cardin

Good explanations of the morphology of basalt lava flows.  I really liked the sketches showing the internal structure of lava flows and the emplacement of pahoehoe lava fields with its transformation into transitional and a'a type lavas. Very useful guide for my next outing into the Deccan basalts!

Cartosat 1 DEM- Two Strike Slip Faults

My two favorite strikes slip faults in India as rendered by Cartosat 1 Digital Elevation Model-

1) Yamuna Left Lateral Fault-

Source: Cartosat 1 DEM National Remote Sensing Center, ISRO

You can see that the Siwalik hills are breached by the Yamuna and dislocated in a left lateral sense, i.e. one would have to turn left to follow the narrow marker rock bed across the fault.

From a previous post on this fault-

Miocene onwards a thick wedge of fluvial sediments filled up a foreland basin that formed in front of rising thrust sheets uplifted along the active Main Boundary Thrust (MBT). That phase ended about 0.5 to 1 mya.

This fluvial wedge over the last half a million years has been deformed into the Siwalik mountains. These mountains form broad synclines and tight anticlines cut by north dipping thrust faults, a result of the continuing compression of the sediment wedge. The southernmost of these thrusts which brings into tectonic contact the anticlinal Frontal Range of the Siwaliks over the alluvial plains in called the Himalayan Frontal Thrust (HFT).

The HFT is broken into segments and the amount of displacement along these segments or thrust blocks is unequal. For example the blocks west of the Yamuna and east of the Ganga have moved southwards with an opposite sense of movement relative to the central block known as the Dun block. To view this, turn on labels and pan southeastwards in embeddable map below until the town of Haridwar where the Ganga enters the plains.

Thus the Yamuna fault has a left lateral sense of movement while the Ganga fault has a right lateral sense of movement. These faults can be thought of as lateral ramps of the HFT accommodating the displacement caused by the southwards movement of the HFT blocks. 

Structural considerations indicate that during the last 0.5 my there has been about 8 km of displacement along the Yamuna and Ganga faults, a slip rate of approx. 16 mm year. - See more at: http://suvratk.blogspot.in/2010/12/remotely-india-3-left-lateral-yamuna.html#sthash.H9K4tfrI.dpuf

 Miocene onwards a thick wedge of fluvial sediments filled up a foreland basin that formed in front of rising thrust sheets uplifted along the active Main Boundary Thrust (MBT). That phase ended about 0.5 to 1 mya.

This fluvial wedge over the last half a million years has been deformed into the Siwalik mountains. These mountains form broad synclines and tight anticlines cut by north dipping thrust faults, a result of the continuing compression of the sediment wedge. The southernmost of these thrusts which brings into tectonic contact the anticlinal Frontal Range of the Siwaliks over the alluvial plains in called the Himalayan Frontal Thrust (HFT).

The HFT is broken into segments and the amount of displacement along these segments or thrust blocks is unequal. For example the blocks west of the Yamuna and east of the Ganga have moved southwards with an opposite sense of movement relative to the central block known as the Dun block. To view this, turn on labels and pan southeastwards in embeddable map below until the town of Haridwar where the Ganga enters the plains.

Thus the Yamuna fault has a left lateral sense of movement while the Ganga fault has a right lateral sense of movement. These faults can be thought of as lateral ramps of the HFT accommodating the displacement caused by the southwards movement of the HFT blocks.

Structural considerations indicate that during the last 0.5 my there has been about 8 km of displacement along the Yamuna and Ganga faults, a slip rate of approx. 16 mm year.

The Digital  Elevation Model also brings out beautifully the Quaternary alluvial fans with tiers of river terraces deposited in the valley between the Siwaliks and the Lesser Himalayas and the intricate drainage on the southern slopes of the Siwalik frontal range.

2) Gani Kalava Fault-

This too has a left lateral movement and has a prolonged history of being reactived during different phases of sedimentation in the Proterozoic Cuddapah Basin of south India.  I  did my M.Sc dissertation on this area, concentrating on the asymmetric anticline with a gentler dipping southern limb and a nearly vertical dipping northern limb located south of Gani village.

Source: Cartosat 1 DEM, National  Remote Sensing Center, ISRO

From a previous post on this fault-

The feature is an ENE plunging asymmetric anticline with spectacular dip slopes of quartz arenites making up the southern limb of the fold and left-lateral movement along a regional fault steepening the northern limb of the fold. There is some copper mineralization along the fault. The Cuddapah basin is an intra-cratonic basin which was filled up in several depositional mega cycles. Sections of two of these mega cycles are exposed in this area. The older mega cycle comprising the Cuddapah subgroup is exposed in the core of the anticline. An angular unconformity separates the older cycle from the younger Kurnool cycle (sub group) which is exposed along the limbs.

Brown arrows shows the offset marker beds (grey arrows show sense of movement) of the oldest sedimentary formation of the Cuddapah basin, the early Proterozoic Gulcheru Quartzites and Vempalle limestones of the Papaghani Group. These lie unconformably on the Archean Peninsular  Gneiss which is the fawn colored peneplain in the left part of the DEM. The very distinct dip slopes of  the Gani anticline (south of Gani village) are made up of a much younger sedimentary unit, the Banganpalle  Quartzites of the Kurnool Group. They were deposited in energetic shallow seas, forming a vast sand shelf, wherein waves and currents winnowed out unstable minerals, leaving behind a nearly pure well sorted and rounded quartz sand. The quartz grains are polycyclic, meaning they show evidence of being derived by weathering of older sandstones, the most likely source being the Gulcheru Quartzites.

Remember this is a Digital Elevation Model,  same color means the same altitude range and not mineral composition.

Remotely India # 3: Left Lateral Yamuna Fault

One of India's great rivers, the Yamuna, leaves the Himalayas and comes rushing on to the plains through a great tear in the Himalayan frontal ranges of the Siwalik mountains.

That breach in the mountains is a dislocation along the Yamuna fault. The sense of movement is left lateral, which means if you are following a rock formation across the fault, you will have to turn left as you cross the fault to trace the same rock formation.

Miocene onwards a thick wedge of fluvial sediments filled up a foreland basin that formed in front of rising thrust sheets uplifted along the active Main Boundary Thrust (MBT). That phase ended about 0.5 to 1 mya.

This fluvial wedge over the last half a million years has been deformed into the Siwalik mountains. These mountains form broad synclines and tight anticlines cut by north dipping thrust faults, a result of the continuing compression of the sediment wedge. The southernmost of these thrusts which brings into tectonic contact the anticlinal Frontal Range of the Siwaliks over the alluvial plains in called the Himalayan Frontal Thrust (HFT).

The HFT is broken into segments and the amount of displacement along these segments or thrust blocks is unequal. For example the blocks west of the Yamuna and east of the Ganga have moved southwards with an opposite sense of movement relative to the central block known as the Dun block. To view this, turn on labels and pan southeastwards in embeddable map below until the town of Haridwar where the Ganga enters the plains.

Thus the Yamuna fault has a left lateral sense of movement while the Ganga fault has a right lateral sense of movement. These faults can be thought of as lateral ramps of the HFT accommodating the displacement caused by the southwards movement of the HFT blocks. 

Structural considerations indicate that during the last 0.5 my there has been about 8 km of displacement along the Yamuna and Ganga faults, a slip rate of approx. 16 mm year.

Interactive:


View Larger Map

Remotely India # 1: A New Series On Indian Geology

I'm experimenting with a new series. The idea is to put up a satellite image of an interesting geological feature from India along with a brief explanation. I'm going into this without much preparation. I have about 5 locations ready but will have to actively look for more features to put up.

Which imaging service should I use? Google Maps and Bing Maps are the easily accessible choices,  but in honor of India's Remote Sensing Program which has been a credit to the country, wherever possible I will be putting up an image from an Indian Remote Sensing Satellite as well. I'm going to be using the public domain web mapping service Bhuvan as the source of the images taken from Indian satellites. The resolution allowed for unrestricted use of imagery via services like Bhuvan is a maximum of 5.8 meters, and so I will supplement that with an embeddable Google Maps frame for higher resolution images and a more interactive experience.

The inaugural image is a sentimental choice from my first solo mapping project in the Proterozoic Cuddapah Basin of Andhra Pradesh, south India, located between the towns of Kurnool and Nandyal.

Gani Kalva Anticline

Source: Resourcesat 1

The feature is an ENE plunging asymmetric anticline with spectacular dip slopes of quartz arenites making up the southern limb of the fold and left-lateral movement along a regional fault steepening the northern limb of the fold. There is some copper mineralization along the fault. The Cuddapah basin is an intra-cratonic basin which was filled up in several depositional mega cycles. Sections of two of these mega cycles are exposed in this area. The older mega cycle comprising the Cuddapah subgroup is exposed in the core of the anticline. An angular unconformity separates the older cycle from the younger Kurnool cycle (sub group) which is exposed along the limbs.

Interactive:


View Larger Map

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