Revisiting of the Yanshanian basins in western and northern Beijing, North China

Abstract

We present new laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) zircon U–Pb ages and provenance data for the Yanshanian basins in western and northern Beijing, North China, with the aims of demonstrating the relationship between basin evolution and “Yanshanian tectonism” and constraining the Late Jurassic–Early Cretaceous tectonic evolution of the region. The inherited Yanshanian basin in western Beijing has a Late Jurassic–Early Cretaceous tectonic history similar to that of typical Yanshanian basins in the Yanshan Fold–Thrust belt (YFTB), and it became inactive at ∼138 Ma. The Qianjiadian basin (QJB) in northern Beijing is only infilled by the sediments of the Tuchengzi Formation. Our new zircon U–Pb ages (160–156 Ma) for the pyroclastic and volcanic rocks of the Tuchengzi Formation suggest that formation of the QJB commenced at ∼160 Ma, consistent with the main episode of “Yanshanian tectonism”. The QJB developed in the footwall of the Pingquan-Gubeikou thrust fault (PGF), and records the syn-tectonic unroofing and erosion of the hanging wall of that fault. It was later reformed by the post-depositional Qianjiadian thrust fault (QJF) along the western margin. The formation and development of the QJB in northern Beijing and the inherited Yanshanian basin in western Beijing were related to the “Yanshanian tectonism”, especially at ca. 160 Ma, when the intense deformation and large-scale magmatism occurred. The tectonic transition from N–S to NW–SE shortening is attributed to the northwest-ward subduction of the Paleo-Pacific Plate, and is constrained to ∼156–135 Ma in the YFTB and eastern China.