Triassic convergence and tectonic evolution of the West Qinling orogen: Constraints from reflection-seismology imaging

Abstract

Although it is well known that the West Qinling orogen was created by the convergence and collision between the North China block (NCB) and the South China block (SCB), the process of the microplate convergence in the West Qinling orogen and its adjacent blocks remains poorly understood. Here we address this question by analyzing ∼ 400 km seismic-reflection-profile data to constrain the subsurface structure of the orogenic system. Our data reveal two north-dipping reflection sets sandwiched between a sub-horizontal Moho (16 s to 18 s, t.w.t.) and a decollement zone (∼6 s, t.w.t.) that separates the upper and mid-lower crusts. In detail, two sets of north-dipping reflectors occur beneath the Zoige basin (CDP 3000–4500, NR-1) and the southern West Qinling orogen (CDP 7000–10500, NR-2), which correlate to south-directed thrusts and are best interpreted as the result of the closure of the Paleo-Tethys Mianlue ocean in the early Triassic. This interpretation is consistent with the presence of an ocean separating the southern West Qinling orogen (S-WQO) from the northern West Qinling orogen (N-WQO). The origin of the required ocean is likely to be a branch of the Paleo-Tethys Mianlue ocean.