Forced Cenozoic continental subduction of Tarim craton-like lithosphere below the Tianshan revealed by ambient noise tomography

The possibility that craton-like lithosphere may undergo subduction during convergence of major tectonic plates is still poorly investigated. We addressed this issue using ambient noise tomography of the Tarim Basin and the Tianshan (Central Asia). Our S-wave velocity model reveals a flat-lying high-velocity anomaly beneath the Tarim Basin in the 45–60 km depth range, consistent with intrusion of mafic rocks at the base of the lower crust above a depleted lithospheric mantle, as expected after interaction of the lithosphere with a mantle plume. This high-velocity anomaly can be followed northward, steeply dipping (∼45°) beneath the Tianshan, which indicates that the Tarim craton-like lithosphere was subducted to mantle depths. It is connected with a fast P-wavespeed anomaly in the upper mantle, interpreted as a relict of the South Tianshan Ocean. A long period of tectonic quiescence, after the closure of the South Tianshan Ocean and before the Cenozoic tectonic rejuvenation of the Tianshan, suggests a minor role of oceanic slab pull in controlling continental subduction. The major player is instead the northward push of India within the framework of Cenozoic India-Asia convergence. We conclude that forced subduction can be experienced not only by thinned continental crust but also by a strong craton-like lithosphere.