Brian Zurek - Seeing the Roots of Mountains, Imagining the Crust of Tibet

Brian Zurek, Stephane Sol, Anne Meltzer and Peter Zeitler
Dept of Earth and Environmental Sciences
Our research focuses on how the continental crust evolves and is modified during continental collisions. Some fundamental questions that we are addressing are what generates anomalously tall mountains, how rocks are modified and what role erosion plays during process of continental collisions. Specifically this study is testing the hypothesis that the combination of an elevated flat surface, such as a plateau, a crust that buoyantly floats on the mantle and large erosive rivers can generate mountains that stand significantly higher then the surrounding landscape.
To test this hypothesis we are going to use the eastern end of the Himalaya where the large Tsangpo River incises into and drains the Tibetan plateau. Coincident with this location are the high standing 7,782 m Namche Barwa and 7,294 Gyala Peri massifs. These two peaks are located roughly 20 km apart yet are separated by the Tsangpo river which cuts through them at roughly an elevation of 2700m.
To test the hypothesis that these two peaks are being buoyantly uplifted by the erosive unloading of mass by the Tsangpo river we compare the thickness of the crust to the surface elevation and see if it matches predictions for a buoyantly stable crust. We will use seismology, or the study of acoustic and elastic waves that travel through the earth to measure the thickness of the crust. In the case of the crust mantle boundary we will be identifying the sharp density contrast that occurs at this compositional boundary. The data for this study comes from a two temporary networks of seismometers in southeast Tibet. One of which is a 70-instrument network that we installed and operated in southeast Tibet for 15 months.
To first order we observe a crust that goes from ~75 km thick at the plateau to 45 km at the margins. This thickness correlates strongly with a mean surface elevation that has been averaged (smoothed) over a wavelength of 200-300 km. When we examine the region where the low-lying Tsangpo River is transecting the high standing Namche Barwa and Gyali Peri massifs, we see that the lower river valley dominates the topography resulting in a mean elevation that is lower then the surrounding plateau. Coincident with this low-lying region is a thinner crust. Suggesting that the Tsangpo River is erosively removing mass from the region, which is causing the region to buoyantly uplift, raising the base of the crust and leaving behind the high standing Namche Barwa and Gyali Peri massifs.
Further reading:
Zeitler, P.K., Meltzer, A.S., Koons, P.O., Craw, D., Hallet, B., Chamberlain, C.P., Kidd, W.S.F., Park, S.K., Seeber, L., Bishop, M., and Shroder, J., 2001, Erosion, Himalayan geodynamics, and the geomorphology of metamorphism: GSA Today, v. 11, p. 4-9.
Brian Zurek's research  focuses on using seismology to image the interior of the earth to gain a better understanding of how the landscape evolves from subsurface processes. Using the Tibetan plateau as a natural laboratory, his current work is focused on how the strength of rocks influences how continents deform during collision. Brian obtained a MS in seismology from the University of Wyoming. His thesis looked at how the continental lithosphere of the southern Rocky Mountains stabilized after assembly and how mantle processes such as the Yellowstone hotspot have modified the lithosphere over time. Brian earned a BA in Physics from the University of Colorado – Boulder.