Palaeozoic tectonic transition of the North Qilian Belt in the northern margin of the Tibetan Plateau, NW China: Insights from detrital zircon U–Pb geochronology and sedimentology

Abstract

This study presents new integrated stratigraphic, sedimentary, and geochronological data for Silurian to Devonian sedimentary rocks in the central North Qilian Belt (NQB), NW China. These data constrain the timing and processes involved in the Palaeozoic tectonic transition from compression to extension in the NQB. This study indicates that the Angzanggou Formation probably formed in a foreland basin setting during 439–430 Ma compression associated with the closure of the North Qilian Ocean. The terrestrial sedimentary rocks overlying the formation were most likely deposited in a superimposed basin at 409–388 Ma as a result of the post‐orogenic extension of the NQB, an event that involved initial post‐orogenic extension‐related sedimentation. Silurian–Devonian sediments were derived from multiple sources, including the NQB, Central Qilian Block (CQB), and Alxa and Dunhuang blocks. Convergence between the CQB and the Alxa Block propagated westward, leading to the scissor‐like closure of the North Qilian Ocean during the Middle to Late Silurian and the oblique docking and collision of these two blocks. This is evidenced by a lack of middle–upper Silurian sedimentary rocks in the middle and eastern NQB compared with the well‐developed and well‐preserved sedimentary strata in the western segment. Devonian retrogradation and intracontinental extension‐related magmatism in the NQB also provide evidence of long‐lived tectonic extension of the lithosphere. Combining these new data with previously published data for the NQB and the wider region suggests that the Devonian terrestrial strata were deposited in a post‐orogenic extensional setting similar to that in the North Qaidam and East Kunlun belts, indicating that the Palaeozoic large‐scale tectonic transition from compression to extension in these three belts most likely started during the Early Devonian.