Present-day crustal motion around the Pamir-Tarim boundary from GPS measurements

Associated with northward convergence of the India continent, the crust around the Pamir-Tarim boundary has experienced complex deformation with reverse, normal, and strike-slip faulting. To better constrain the partitioning pattern of strain among different-type of faults, a campaign GPS network with 37 GPS stations has been deployed around the Pamir plateau and the Tarim basin. From the newly GPS velocity field, it has shown that strike-slip motion is of negligible between the Pamir plateau and the Tarim basin; Whereas, a combined extension-compression deformation is clear across the Pamir-Tarim boundary from Pamir plateau to Tarim basin, with extensional and compressive rate of ~4mm/yr and ~6mm/yr, respectively. By building a two-dimensional viscoelastic finite element model, the coexistence of extension and compression along the same direction across the Pamir-Tarim boundary could be mechanically explained by gravitational collapse which is related to lateral variation of topographic altitude and layered rheology of the lower crust between the Pamir plateau and the Tarim basin. This suggests that around the Pamir-Tarim boundary, strain partitioning perpendicular to the India-Eurasia collisional direction is controlled, at the present time, mainly by gravitational force of the Pamir plateau, resulting in the east-west extension of the Tashkurgan graben along the plateau shoulder, and east-west compression of the western Tarim fold-thrust system out of the Pamir plateau as our newly GPS velocity field documented.