Intracontinental convergence accommodated by underthrusting of Tarim Basin beneath central Tian Shan, Central Asia: Insights from Cenozoic upper crust deformation across the western Kepingtage fold-and-thrust belt in the northern Tarim Basin

The way in which intracontinental convergence caused by remote continent-continent collision has been accommodated remains debatable, but it is attributed to either pure shear thickening or continental subduction/underthrusting. Quantification of the deformation architecture of the upper crust and its shortening is vital for testing these competing models. For this purpose, we conducted quantitative analyses of four seismic reflection profiles along the western Kepingtage fold-and-thrust belt of the intracontinental convergence zone between the northern Tarim Basin and the central Tian Shan, a result of the remote India-Eurasia collision, which capture the structures of the upper crust and constrain the amount of shortening in the region. The structural analyses show a thin-skinned style of deformation of the western Kepingtage fold-and-thrust belt, with minimum north−south shortening estimates of ∼71.1 km (∼46.6% strain), ∼76.3 km (∼51.4% strain), ∼67.1 km (∼56.1% strain), and ∼53.0 km (∼49.9% strain), respectively, from east to west. Assuming that coupling shortening occurred across the entire crust and an initial crustal thickness of ∼41−46 km, these shortening ratios would produce a ∼83−95-km-thick crust along the northern Tarim Basin, which is significantly larger than the actual thickness previously reported. This inconsistency leads us to rule out the pure-shear thickening model, which predicts crustal-scale coupling deformation. Alternatively, our results imply that the crust of the northern Tarim Basin was deformed in a decoupling style. These results, combined with those of previous studies, lend support to the intracontinental underthrusting model. We suggest that both the upper crustal fold-and-thrust belts and the lower crustal underthrusting of the northern Tarim Basin accommodated intracontinental convergence.