RELATIVELY RECENT CONSTRUCTION OF THE TIEN SHAN INFERRED FROM GPS MEASUREMENTS OF PRESENT-DAY CRUSTAL DEFORMATION RATES

摘要

THE Tien Shan-a high, seismically active intracontinental mountain belt, 1,000-2,000 km north of the Himalaya-has grown as a result of India's collision with Asia(1). The crustal shortening (similar to 200 +/- 50 km; refs 2, 3) and thickening that gave rise to the Tien Shan accommodates only a small fraction of India's total penetration into Asia (2,000-3,000 km), and the temporal relationship of deformation in this belt to the India-Asia collision remains unclear. Here we report geodetic measurements of the Tien Shan, using the Global Positioning System (GPS), that indicate that the current crustal shortening rate is nearly half of India's convergence rate with Eurasia in this area(4). We infer a total shortening rate for the Tien Shan of similar to 20 mm yr(-1), which is approximately twice that inferred previously from the extrapolation of slip rates in the Holocene(3) and earthquake-induced displacements during this century(5), suggesting that the rate of mountain building in this region has accelerated severalfold since the onset of collision similar to 50-55 Myr ago(6,7). If, as we argue, the current shortening rate can be extrapolated to geological timescales, then our results suggest that most of the Tien Shan has been constructed during the past 10 Myr, perhaps in response to an increased horizontal force following an abrupt rise of the Tibetan plateau(8,9). [References: 38]