Global Positioning System Bound on the Rate and Duration of Crustal Shortening Across the Tien Shan, Kyrgyzstan and Kazakhstan

The Tien Shan, the high, seismically active intracontinental belt 1000-2000 km north of the Himalaya, has grown as a result of India's penetration into the rest of Asia1. Yet, whereas the crustal shortening (~200 ± 50 km, refs. 2,3) and thickening that built the belt has accommodated only a small fraction of India's 2000-3000 km penetration since India and Eurasia collided, we report Global Positioning System (GPS) geodetic measurements that indicate a current shortening rate that is nearly half of India's 44 mm yr-1 convergence rate with Eurasia in this area4. Measurements demonstrate 13 ± 2 mm yr-1 of shortening across the segment of the Tien Shan in Kyrgyzstan and Kazakhstan, ~70% of its width. Extrapolation across the remaining, highest, part suggests a total shortening rate of ~20 mm yr-1, which is roughly twice average rates inferred previously from extrapolating Holocene slip rates3 and from displacements associated with earthquakes in this century5. Insofar as this rate applies to late Cenozoic time, it suggests that the rate of mountain building in the Tien Shan has accelerated several fold since the collision at ~ 50-55 Ma (refs. 6,7). An extrapolation of the current rate suggests that most of the belt has been constructed in the last 10 Myr, perhaps following an apparently abrupt 1-2.5 km rise of the Tibetan Plateau8,9, and in response to an increased horizontal force applied by a higher plateau to the Tien Shan.