Timing of Triassic tectonic division and postcollisional extension in the eastern part of the Jiaodong Peninsula

Abstract

The Jiaodong Peninsula is a key region for researching the interaction between the North and South China Plates. Tectonic relationships between collision, exhumation of ultra-high-pressure (UHP) slabs, strike-slip faulting and gold mineralization, are still ambiguous. The eastern part of the Jiaodong Peninsula (Eastern Jiaodong), which includes Triassic intrusions and is less affected by the Tan-Lu Fault Zone, is a key area to examine exhumation dynamics in detail. Systematic field mapping and zircon U–Pb dating of Triassic intrusions establishes that: (1) The UHP wedge in the eastern part of the Jiaodong Peninsula can be divided into the lateral and frontal ramps of a thrust and nappe system. Dating of samples from Donglinghou (244.7 ± 4.2 Ma) and Qingyutan (233.8 ± 8.1 Ma) areas indicates that the collision happened at or before the Middle Triassic. (2) Postcollisional extension intrusions including the Shidao granitoid (216.2 ± 2.4 Ma), and the Chengshantou granitoid (cut by a dolerite dyke dated at 210.5 ± 1.0 Ma), generally strike NE and occurred in a metamorphic core complex below the Upper Jiashan-Xiangshui detachment (U-JSXS). (3) Regional faults in the Jiaodong Peninsula exploited syncollisional foliations of the UHP wedge, which resulted in faults dipping towards the NW and SE. The reactivation of the Lower Jiashan-Xiangshui shear zone (L-JSXS) and its overprinting upon the Tan-Lu fault system may have caused another major episode of exhumation of the syncollisional wedge, and could have been responsible for an extensional environment that favored gold mineralization.