REPORT ◥ GEOMORPHOLOGY Tectonic control of Yarlung Tsangpo Gorge revealed by a buried canyon in Southern Tibet Ping Wang, 1 Dirk Scherler, 2 *† Jing Liu-Zeng, 1 Jürgen Mey, 3 Jean-Philippe Avouac, 2 ‡ Yunda Zhang, 4 Dingguo Shi 4 The Himalayan mountains are dissected by some of the deepest and most impressive gorges on Earth. Constraining the interplay between river incision and rock uplift is important for understanding tectonic deformation in this region. We report here the discovery of a deeply incised canyon of the Yarlung Tsangpo River, at the eastern end of the Himalaya, which is now buried under more than 500 meters of sediments. By reconstructing the former valley bottom and dating sediments at the base of the valley fill, we show that steepening of the Tsangpo Gorge started at about 2 million to 2.5 million years ago as a consequence of an increase in rock uplift rates. The high erosion rates within the gorge are therefore a direct consequence of rapid rock uplift. T he topographic evolution of mountain ranges results from the competition be- tween tectonic and erosive forces (1–3) and controls the organization of drainage and atmospheric-circulation systems (4–6). Al- though tectonics and erosion act in opposing directions, there may be feedbacks that couple the two (7, 8). Prominent candidates for such coupling comprise the syntaxes regions (9, 10), at either end of the Himalaya, where the two biggest rivers draining Tibet, the Indus and Yarlung Tsangpo, have cut deep gorges into very young metamorphic massifs ( F1 Fig. 1A) (11–17). In the so-called tectonic aneurysm model, it has been proposed that rapid incision within these gorges has thermally weakened the crust and now sustains a positive feedback between uplift and erosion (9, 10), but how and when this happened remains elusive. Deeply incised gorges exist along the entire Himalaya and always coincide with very steep river gradients that have been related to zones of rapid rock uplift and incision (18–20). The most spectacular and emblematic gorge in the Himalaya, and probably on Earth, is the Tsangpo Gorge, where the Yarlung Tsangpo drops by 2 km in elevation as it cuts through the ~50-km-wide eastern Himalayan syntaxis where erosion rates are exceptionally high ( F2 Fig. 2B). The contorted and generally steep course of the gorge is often considered evidence for relatively young cap- ture of the Yarlung Tsangpo by the headward incising Brahmaputra River, from a former course connecting it to the Parlung and Yigong RESEARCH SCIENCE sciencemag.org 00 MONTH 2014 • VOL 000 ISSUE 0000 1 1 State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, P. R. China. 2 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA. 3 Institute of Earth and Environmental Sciences, University Potsdam, 14476 Potsdam, Germany. 4 Chengdu Engineering Corporation, Chengdu 610072, P. R. China. *Corresponding author. E-mail: scherler@caltech.edu †Present address: GFZ German Research Centre for Geosciences, Section 3.4, Telegrafenberg, D-14473 Potsdam, Germany. ‡Present address: Department of Earth Sciences, University of Cambridge, Cambridge, UK 96°E 95°E 94°E 93°E 30°N 29°N NB GP Indus - Y arlu n g T s a n g p o S u t ure Zone Jiali Fault Zone Tsangpo gorge Tsangpo gorge Tsangpo gorge Brahmaputra River Yarlung Tsangpo River Nyang River Parlung River Yigong River Fig.1b Pasighat 3 3 2 2 1 1 4 4 5 5 Elevation a.s.l. (km) 5.0 4.5 3.5 2.5 1.5 Estimated valley fill thickness (m) 863 0 0 100 Kilometers Namche Barwa (7,756 m) Gyala Peri (7,294 m) Yarlung Tsangpo ~4 km 100°E 90°E 70°E 60°E 80°E 30°N Tibetan Plateau Tibetan Plateau Indus-Yarlung Tsangpo Suture Zone Indus Ganges Brahmaputra IG TG Fig. 1. River gorges in the Himalaya. (A) Geographical overview of Tibet and the Himalaya, with internally drained areas (horizontally hatched), major rivers, and gorges (red and black points) located within steep mountainous areas—i.e., where 5-km-radius local relief is >2 km (red). Black polygons show the mountainous drainage basins of the Indus River in the west and the Yarlung Tsangpo-Brahmaputra River in the east. The Indus-Yarlung Tsangpo Suture Zone separates the Eurasian (north) from the Indian plate (south) and is strongly distorted in the Indus Gorge (IG) and Tsangpo Gorge (TG). (B) Oblique northeastward aerial view of the Yarlung Tsangpo upstream of the Tsangpo Gorge (from Google Earth, www.google.com/earth). (C) Map of the Eastern Himalayan syntaxis with the studied valley fill and drill core locations (red points). Contour lines show rapidly exhuming areas with young (<2 Ma) Zircon U/Th-He (orange), and Biotite 40 Ar/ 39 Ar ages (yellow) centered on the Tsangpo Gorge (16), which is marked by a red line. MS no: RE1259041/CJH/GEOCHEM PHYS