MESOZOIC EXTENSIONAL STRUCTURES OF THE FANGSHAN TECTONIC DOME AND THEIR SUBSEQUENT REWORKING DURING COLLISIONAL ACCRETION OF THE NORTH CHINA BLOCK

Abstract

The Fangshan area, SW of Beijing, lies at the junction of the NNE-trending Taihang mountain range and the southeastern portion of the Yanshan intraplate orogenic belt and has undergone at least five stages of deformation. Mid- to late Triassic extensional deformation (D1) is represented by the formation of the Fangshan tectonic dome during SE-directed extensional tectonics. This deformation was later modified by NNW-directed thrusting in the late Triassic (D2) and WNW-directed thrusting in the late Jurassic (D3). These D1-D3 structures were deformed by the arcuate Beiling syncline (D4), which formed during the intrusion of the 133-128 Ma Fangshan pluton. D5 deformation is represented by Cretaceous to Quaternary NNE-striking high-angle normal faults. The ages of these events demonstrate that the principal ENE-trending tectonic framework of the Yanshan intraplate orogenic belt was established mainly in the mid- to late Triassic (the Indosinian event). The Jurassic to Cretaceous Yanshanian deformation with thick-skinned thrusting was associated with intrusion of numerous plutons, and strongly modified the older structures. The tectonic evolution of the Fangshan tectonic dome was linked genetically with the collision of the North China Block and the Siberian Craton, and the later collision of the North and South China blocks.