A three‐dimensional Moho depth model for the Tien Shan from EGM2008 gravity data

Abstract

The Tien Shan in Central Asia is the largest intracontinental mountain range in the world, but it is 1500 km away from the collision zone between the Indian and Eurasian plates. This region has been and still is the focus of numerous geoscientific studies, mainly because of its evolutionary history and its unique position in the Eurasian lithosphere plate. So far, mainly seismological data have been used to explore the origin of and ongoing seismic activity in this region, but only one study has investigated terrestrial gravity data. In this study, a new gravity data set, EGM2008, is used to determine the crust‐mantle boundary (Mohorovičić discontinuity, Moho) of the Tien Shan using inversion of gravity data. In addition, an isostatic Moho is calculated from topographic data, which by comparison to the results of the gravity inversion illuminates the effects of isostatic compensation. The results of the gravity inversion generally agree with results of previous seismic studies and indicate that the Tien Shan has a mountain root with a thickness of about 75 km. Furthermore, the Moho is shallow under the basins, e.g., in the Tarim and Ili basins. The comparison with the isostatic Moho indicates an over‐compensation of the orogen and an under‐compensation of the basins. The over‐compensation results from the former subduction of the Tarim Basin terrane in the south. The under‐compensation of the Tarim Basin is generated by support of the terrane between the Tien Shan in the north and the Pamir mountains, Tibet and Himalayas in the south.