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Hello Mike,

Thanks for continuing the debate. There is no doubt that the MCT is a major crustal shear zone which exhumes deep-buried high grade rocks. For me at least, and I feel I am not alone in the this view, the issue is why is it active at all and what controls its location and rate of exhumation. The MCT is not just any old fault after all. I would argue that it is located where it is because of the relative rapid exhumation of the Greater Himalayan slab compared to the Lesser Himalaya. This rock uplift is modulated by the rate of erosion at the surface. In other words bands of rainfall intensity control where the rapid exhumation occurs and therefore the location of the MCT (credit to Cam Wobus and Kip Hodges if memory serves me well). I tend to agree with you that the STD works together with the MCT to control the exhumation of the Greater Himalaya but if that is the case then the STD is partly climatically controlled as well. 

As for Nanga Parbat that could be a different kettle of fish. Its seems clear that the Namche Barwe syntaxis is largely achieving its super fast exhumation because of the denudation allowed by the strong monsoon there and the Brahmaputra River, as evidenced by the huge contribution of Namche Barwe to that river. However, the same is not true in the west. Nanga Parbat is in a pretty dry place and does not particularly contribute to the Indus. Its exhumation is much more dominated by the solid Earth in my view, even if erosion does have to lend a hand. Is there any evidence of detachment faulting at Nanga Parbat? Thrusting alone will not result in exhumation, indeed quite the opposite.

The Karakoram exhumation may not be monsoonally controlled but the action of glaciation fed by the monsoon and the westerly jet is clearly critical in allowing that to happen. Without the strong erosion driven by glaciation those high grade rocks would still be at great depth. Perhaps the high grade rocks at Tso Morari are a good example of purely tectonic exhumation?

As for Cherapungi the exhumation rates are lower there than in these other cases because the crust is not very thickened and rock uplift rates are low, like Scotland for example! It is when we have rapid rock uplift plus rainfall that the fun really begins. The solid Earth provides the opportunity for ranges like the Greater Himalaya to form but I would argue that it is the climate that decides where the faults are located and how fast they move, including the STD.

best wishes
Peter



On Nov 13, 2014, at 5:02 AM, MIke Searle <[log in to unmask]> wrote:

Peter,
Bit of a reality check needed here maybe? The Himalayan Main Central 
Thrust and South Tibetan detachment are major crustal-scale ductile 
shear zones, faults that exhume kyanite and sillimanite grade rocks. 
These are entirely tectonic structures and climate cannot possibly have 
any control on their initiation at depths 30km. Once mountains are made by Tectonics, 
then obviously climate changes follow (increased erosion, monsoon etc) 
can take their affect but climate can never induce these type of 
structures. Rainfall cannot suck kyanite gneises out for 12 kbar depths! 
Tectonics, thrust faults brings these rocks up, mountains are formed and 
climate just tags along behind.

Denis is absolutely right to point out the climate differences along the 
Himalaya today. The fastest exhuming bit of real estate and fastest 
erosion rates anywhere on Earth is Nanga Parbat, the west Himalayan 
syntaxis in Pakistan, that exposes Pliocene-Quaternary 
sillimanite-cordierite migmatites and tourmaline leucogranites < 1 
million year old, and it lies in a desert. Similarly the Karakoram to 
the north has little rainfall and has vast area of Miocene - Pliocene 
kyanite and sillimanite rocks, migmatites domes and young leucogranites 
with fast and active rock uplift-exhumation rates and high erosion. The 
wettest place on earth is Cherapungi on the Shillong Plateau in NE India 
where exhumation rates are very low.

Mike Searle
On 10/11/2014 14:19, Peter D Clift wrote:
[log in to unmask]" type="cite" class="">
It should also perhaps be kept in mind that without the erosion along the Himalayan front that the amount of exhumation we have observed in those mountains would be relatively small.  I don’t think many people would agree that all of the Greater Himalayan exhumation is caused by the South Tibet Detachment and that effectively that this mountain belt is an extensional feature.  In any case I’m not entirely convinced that the South Tibet detachment is not climatically modulated anyway. In my opinion that has still yet to be demonstrated. there seem to be good reasons to believe that the Main Central Thrust is climatically controlled so why not South Tibet detachment?

 Peter Clift


On Nov 9, 2014, at 10:14 AM, gapais <[log in to unmask]> wrote:

Some of you should probably keep in mind that the Himalayas is a belt of about 2500 long and that a comparable zonation of exhumed rocks (UHP, Higher Himalayla Crystallinne, and others, crop out all along the belts, despite drastic variations in climate! It rains a lot in central Himalayas as in Nepal during the Monsoon, but the western Ladakh area is a desert! Nepal, althought one of the most visited section, is not representative of the belt in terms of climate, despite outcroping rocks and tectonic features are quite representative of the Himalayan belt. The only common structure all along the belt, that accounts for the exhumation of deep rocks, is the Zanskar and south Tibet detachment, a major tectonic-induced lithospheric structure that has nothing to do with climate. Keep also in mind that the NS-striking Andes cut across nearlly all possible climate environments, and show rather comparable deformation and structural patterns from South Peru down to Patagonia and Tierra de Fuego.

Best regards
Denis

Le 9 nov. 2014 à 06:12, Michael <[log in to unmask]> a écrit :

Dear colleagues,


We would like to draw your attention to the following EGU General Assembly session (TS3.3/CL1.9/GM3.6) to take place between 12th April – 17th April 2015 in Vienna, Austria entitled: “Investigating Tectonism-Erosion-Climate Couplings (iTECC): Himalayan orogenic development and climatic feedbacks from micro- to macro-scale”



Conveners: Guangsheng Zhuang, Michael Kelly, Alessandro Santato, Yani Najman, Jan Wijbrans


This session aims to bring together innovative studies from young and experienced scientists studying the past, present and future implications of the Himalaya-Tibet orogeny from a variety of temporal and special approaches.

Session Description:
A close relationship between tectonics, erosion and climate has been well established over numerous years of research in varying dynamic geological settings and has inspired many rewarding conversations among earth scientists across various fields of research. The Himalaya-Tibet orogen, not only because of its height, extent and rate of uplift, serves as an important natural laboratory for investigating couplings between topographic evolution and climate forces in active mountain belts which are related through surficial processes.

The newly launched Marie Curie Actions Group ‘iTECC’ (Investigating Tectonism-erosion-climate-couplings) program will serve as an excellent podium to inspire discussion and further our understanding of this dynamic geological setting from a wide range of earth science disciplines.

This session aims to bring together innovative studies from young and experienced scientists studying the past, present and future implications of the Himalaya-Tibet orogeny. Himalayan studies from a variety of temporal and special approaches will be presented, ranging from numerical models coupling tectonics, climate and erosion; to quantifying the controls on chemical weathering and physical erosion within the Himalaya by understanding the feedback loops with global atmospheric CO2 levels. Innovative studies utilising compound-level isotopic studies, near- and far-field sedimentary basin records and detrital geochemistry to infer proximal and distal India-Asia collisional tectonics, hinterland exhumation histories of basement rocks and Himalayan evolution are presented. This session will also present studies focusing on Himalayan weathering, erosion and climate through time, as well as, the development and refinement of analytical techniques needed to better interpret the past and present-day records of exhumation, erosion and climate processes within this dynamic orogenic belt.



We welcome oral and poster presentations to this session. Please submit an abstract by following the link: http://meetingorganizer.copernicus.org/EGU2015/session/17980

Abstract deadline is 07 January 2015.

A limited amount of financial support is available through the EGU for students and early career researchers. If you intend to apply for financial support, please submit your abstract by 28th November 2014. More information on financial support can be found at the following webpage
http://www.egu2015.eu/support_and_distinction.html

Please feel free to contact us for any further information (contact details given below). Thank you for your attention.

With best wishes,

Michael Kelly (on behalf of the session organisers)

Guangsheng Zhuang, Lancaster University, UK ([log in to unmask])
Michael Kelly, Cairn India Limited, India ([log in to unmask])
Alessandro Santato, Thermofisher, Germany ([log in to unmask])
Yani Najman, University of Lancaster, UK ([log in to unmask])
Jan Wijbrans, VU University, Amsterdam ([log in to unmask])


Denis Gapais
Géosciences Rennes
UMR 6118 CNRS
Université de Rennes 1
35042 Rennes cedex
France
phone 33 2 23 23 67 36
mobile 33 6 20 01 58 69
fax 33 2 23 23 60 97

 
 
======================
 
Peter D. Clift
Charles T. McCord Chair in Petroleum Geology,
Department of Geology and Geophysics,
E235 Howe-Russell-Kniffen Geoscience Complex
Louisiana State University,
Baton Rouge, LA 70803,
USA
 
Tel: +1 225-578-2153
Fax: +1 225-578-2302
Email: [log in to unmask]
 
http://www.geol.lsu.edu/pclift/pclift/Home.html
 
Attend AGU Chapman meeting "Evolution of the Asian monsoon and its impact on landscape, environment and society”, June 15-19th 2015, Hong Kong
 
http://www.geol.lsu.edu/pclift/Monsoon_AGU_Chapman_Meeting/Welcome.html


-- 
******************************************
Professor Michael P.Searle
Dept. Earth Sciences
Oxford University,
South Parks Road.,
Oxford,   OX1 3AN
England
		Professor of Earth Sciences, and
		Senior Research Fellow, Worcester College, Oxford.

Tel:  +44 1865 272022
Fax:  +44 1865 272072

Mike Searle's Home Page:  http://www.earth.ox.ac.uk/~mikes
	NEW BOOK:-
"Colliding Continents: A Geological Exploration of the Himalaya,
Karakoram and Tibet"  [2013] Oxford University Press, £25.00

http://www.amazon.co.uk/Colliding-Continents-geological-exploration-Karakoram/dp/0199653003
*******************************************

 
 
======================
 
Peter D. Clift
Charles T. McCord Chair in Petroleum Geology,
Department of Geology and Geophysics,
E235 Howe-Russell-Kniffen Geoscience Complex
Louisiana State University,
Baton Rouge, LA 70803,
USA
 
Tel: +1 225-578-2153
Fax: +1 225-578-2302
Email: [log in to unmask]
 
http://www.geol.lsu.edu/pclift/pclift/Home.html
 
Attend AGU Chapman meeting "Evolution of the Asian monsoon and its impact on landscape, environment and society”, June 15-19th 2015, Hong Kong
 
http://www.geol.lsu.edu/pclift/Monsoon_AGU_Chapman_Meeting/Welcome.html