Category Archives: Himalaya/Tibet

Article on the South Lunggar rift, western Tibet, accepted in Tectonics

A big part of my PhD was the exploration of a large, but essentially unknown, active rift in southwest Tibet, the South Lunggar rift.  We mapped the rift, and did a solid amount of zircon (U-Th)/He thermochronology, combined with thermal modeling using Pecube, and did some ancillary zircon U-Pb geochronology as well.

The rift itself is a central horst bound by two rift basins, with major, active normal faults between the horst and the rift.  Structural and thermal observations and modeling suggest a total of 10-21 km extension since ~10-12 Ma, at modern rates of ~1-3 mm/yr.  There is pretty good evidence for an rapid increase in extension rate at 8 Ma, on the most significant fault in the rift, the low-angle South Lunggar Detachment.

We have just gotten a paper accepted in Tectonics that covers most of what is known about the rift.  The official Tectonics page is here, although the PDF that they host has some serious formatting errors and the figures are atrociously pixelated and distorted; this will be fixed in the future, I assume.  The ungated Word-style formatted PDF with correct figures is here, from my ResearchGate page.  The paper itself is pretty big; 90 something manuscript pages; it’ll probably be 30+ pages once formatted.

The paper is pretty broad in scope, and represents quite a bit of work.  As I mentioned above, the rift was basically unknown before we went there, though there was a M ~6.8 normal faulting event in late August 2008 that was studied by John Elliott (paper here) and in more detail by Isabelle Ryder (here).  Both of these papers simply studied the earthquake itself, from remotely-collected geophysical data.  Our study here represents about a month of mapping and sample collection over two campaigns, as well as ~35 new zircon (U-Th)/He cooling ages, 2 zircon U-Pb crystallization ages, and a ton of thermal modeling (~25,000 Pecube runs).  The goal was to have one single, thorough paper that presents all of our observations, data, modeling, interpretations–almost like a treatise on the rift.  It might have been wiser to break it down into several shorter papers, but that’s just not how it went…

In any case, it’s finally out.  Enjoy!

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HimaTibetMap now on GitHub

edit 9 June 2013: HimaTibetMap repo on GitHub updated to new address

I maintain HimaTibetMap, an open-source database of active faults in the Indo-Asian collision zone.  While I was in phd school, we hosted the data on KU’s proprietary HawkDrive system, which performed adequately but wasn’t super accessible for other things than downloading.  Furthermore, it was not clear if I would still have access to the site now that I’ve graduated.

So I  have made a HimaTibetMap page on GitHub, the new standard in collaboration websites.  This is where the version I maintain will be.  After discussion with collaborators, I may move the Active Tectonics of the Andes database there as well.

Ideally, this move will make it easier for others to contribute to the database as well.  So if you have anything to contribute, don’t hold back!

Great BBC documentary on Youtube of mountain building and collapse highlighting Tibet

I was sent a great BBC video entitled ‘Roof of the World’  that does a nice job of outlining many of the modern concepts of mountain building (orogeny) and related collapse (taphrogeny), with emphasis on the Tibetan/Himalayan system and Greece, keeping the tools of the trade central to the story.  There is a lot of gorgeous footage of the dramatic mountain scenery, featuring many of the rock stars of the contemporary academic regime (e.g., P. England, J.-P. Avouac, M. Searle, P. Molnar).  Despite being almost 15 years old, many of the ideas presented here are still driving the science.  The film isn’t as ‘dated’ as some of the commenters would have one believe.  With respect to Tibet and the Himalaya, the only Big Ideas not discussed are the channel flow models of the Himalaya (south-directed, a la Beaumont) and of Tibet (east-directed, a la Clark and Royden), which were published a few years after the movie came out.  There is also not much discussion of the effect of India’s underthrusting of Tibet, either; the situation is presented as a vertically-homogeneous collision, which of course is a problematic approximation.

While I think my favorite part is the scenery, I am very impressed by the ease with which the theories are communicated and the fluidity with which the field and analytical techniques are integrated into the narrative.  The animations definitely help, but a big part of it is simply that many of the modern, cutting-edge concepts in tectonics aren’t actually that complicated.  The treatment of lithosphere as a viscous fluid, the effects of mantle delamination, gravitational collapse, etc., are fairly simple and intuitive concepts.

The genius involved in this kind of work isn’t the mental power and agility necessary to get one’s mind around these ideas, it is the mental power and agility required to look at an enormous pyramid of granite and think of fluid dynamics–actually deriving these concepts from the observation is the hard part.  Well, it’s one of the hard parts.  Figuring out how to quantify and test these concepts (which are hypotheses, of course) against observational data, and to refine, reject and replace them if necessary, is an often harder part.  It’ll be interesting to see what the science looks like in another 15 years–I have some predictions on what will stand, fall, or rise, but these will be tested as well.

HimaTibetMap-1.1: An expanded and updated version of the Database of Active Faults from the Indo-Asian Collision Zone- for ArcGIS, GMT, and Google Earth

Edit 3 May 2013: HimaTibetMap is now on GitHub!

I am pleased to announce the updated version of HimaTibetMap-1.1. HimaTibetMap is a database of active faults from the Indo-Asian collision zone, spanning from Iran to Myanmar, and India to Siberia, and contains over 1000 structures.  The area covered is approximately the same size as the contiguous US.  It was originally compiled by Mike Taylor and An Yin based on their field observations, remote sensing analysis, and reviews of the literature, as described in Taylor and Yin (2009). It was since updated slightly by Mike and myself, and released to the public as outlined in our Eos article from May 2010.

Map showing the extent of HimaTibetMap-1.1 made in ArcMap with topography from SRTM.

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How to create topographic profiles in ArcGIS with x,y coordinates, and plot them with projected sample locations in Python

I have been getting a lot of zircon (U-Th)/He cooling data these past couple of weeks from my South Lunggar project, and placing that data in a proper structural context for interpretation.  This involves drawing cross-sections and projecting my sample locations onto those cross-sections, which requires a topographic profile (drawn with no vertical exaggeration) that has proper geographic or projected coordinates.  Though this is a task that most geologists (especially structure/tectonics types) will have to do at some point, there is not a lot of information out there for doing it with modern tools.
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Int’l geology field campaign checklist

It’s getting close to summer, and various geologists around me are gearing up for field campaigns to exotic locations.  Doing this while trying to get the normal semester’s work done ahead of time is pretty hectic, and there is a constant danger of forgetting something.  Here is my list of things to bring for my last Tibetan field campaign; hopefully it’ll be of use to others.

As a qualifier, this was 2 month field geology trip that involved mapping, bedrock sampling, and cosmogenic sampling (mostly digging 2 m depth profiles).  Weather was anything from 40°C (Beijing in July) to -10° C (?  didn’t have a thermometer, although one of these would be sweet; maybe a little portable weather station?) w/ all forms of wind and precip.  We camped in the field, but most food preparation was handled by the drivers while we worked.  It was basically car camping, with big propane stoves and ‘indoor’ cookware, so that is not included in this list in detail.  The list for more specialized work (e.g., GPS campaigns) is a bit different; that might be covered in a later post.

Northwest camp, South Lunggar Rift. Footwall of the South Lunggar Detachment in background.

If anyone has anything to contribute, that’d be great.  Logistics stuff could also be good, especially sample shipping, dealing with permits and vehicles, etc.

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Himalayan arc-parallel extension from variably-oblique convergence

Here is a summary of the first paper of my dissertation, which has been accepted to Geosphere (all figures are slightly modified from that manuscript):

Although the Himalayan arc is dominantly a contractile thrust belt, significant amounts of arc-parallel extension and translation have taken place since the Miocene.  We (myself, Mike Taylor, Mike Murphy) test the prominent models for arc-parallel extension and translation, and find that the along-strike variations in convergence obliquity between India and the Himalaya best predicts the geologic and GPS geodetic observations.

Active structures and focal mechanisms of the Himalaya and Tibet.

Over the past 25 years, there has been significant recognition of major, active arc-parallel extensional structures in the Himalaya, dominantly the Leo Pargil, Gurla Mandhata, Thakkhola, Kung Co, Ama Drime, and Yadong Gulu rifts.  Some of these (LP, GM, AD) are the Himalayan/Tibetan version of metamorphic core complexes (and the differences between these and the Cordilleran version will be discussed here in the future); the others are major graben cutting the High Himalaya.  The western ones (LP, GM, Thakkhola(?)) bear some relationship to the Karakoram Fault, a sub-orogen-scale strike-slip fault that accommodates dextral shear between the NW Himalaya and the western Tibetan Plateau.  In particular, right slip along the KF seems to step south at GM and into the High Himalaya; this interpretation (spearheaded by Mike Murphy) has GM being a releasing structure on the KF-Humla fault system, and probably accommodating the ~30 km slip differential between the those faults.  Importantly, offsets along the KF decrease systematically from ~150 km in the NW to ~50 km in the SE near Mt. Kailash; the Himalaya to the SW is extending, but Tibet to the NE is not (in the vicinity of the fault).  This indicates that the KF is accommodating differential extension of the Himalaya relative to Tibet.

Active structures of the Himalaya and south Tibet. Numbers indicate magnitude of fault slip (km).

It is also clear from published GPS data that the convergence direction between India and the Himalaya remains pretty consistent, even though the strike of the Himalaya changes dramatically (by about a radian) over its ~2500 km length.  A look at the arc-parallel component of the GPS vectors (Eurasia-relative) shows dramatic arc-parallel spreading away from the center of the range (suspiciously close to Everest).  This also leads to an increase in arc-parallel dextral shear from the central Himalaya to the NW, though the picture is complicated by plate boundary changes to the east.  Shortening across the range somehow manages to stay pretty consistent along strike, even though the magnitude of the velocities involved decreases by a factor of two from Everest to the NW.

Arc-parallel GPS velocities (relative to Eurasia) from a variety of sources.

The major models explaining aspects of Himalayan and Tibetan deformation that we tested are radial spreading of south Tibet, variably-oblique convergence between India and the Himalaya, oroclinal bending of the Himalaya, and east-directed, lateral extrusion of a quasi-rigid Tibet.  The only hypothesis not rejected by fundamental observations was the variably-oblique convergence model, as suggested by McCaffrey and Nabelek (1998). Radial spreading isn’t supported by the N-S contraction of the entire Himalaya and Tibet observed geodetically, and lack of mapped structures capable of accommodating this deformation (the South Tibetan Detachment is cut by the structures accommodating arc-parallel extension, and its activity coincided with Main Central Thrust activity, so it could not have contributed to an areal increase in the Tibetan Plateau).  Active oroclinal bending requires E-W contraction of the Himalayan hinterland and S. Tibet and/or left-lateral shear in the western Himalaya/S. Tibet and right-lateral shear in the east (flexural folding); the opposite shear sense is observed in both cases.  And finally, lateral extrusion requires active dextral shear across the whole northern margin of the Himalaya, at a fairly good clip, and this is simply not observed east of the KF.

Questions and comments are welcome.  I can send a copy of the manuscript although I’m not sure if I’m allowed to put a link to it.

–Richard