Liaonan-Wanfu Metamorphic Core Complexes And Their Regional Tectonic Implication

This research summarized the constitution, structure and evolution of the Liaonan metamorphic core complex(mcc). Revealed the existence of the Wanfu mcc and made it certain that Wanfu mcc and Liaonan mcc form a mcc pair, and expatiated their'exhumation mechanism. Combination with analysis of the regional extensional structures characteristics in East China, far east of Russa and eastern Mogolia, illustrated that mcc pair is very important to the regional lithospheric thinning. The results of this research list below:(1) Liaonan metamorphic core complex has a three-layer structure and is constituted by five parts. Different types of fault rocks(from mylonitic gneissto pseudotachylites) giving clues to the evolution of the detachment fault zone. The detachment fault of Liaonan mcc is characterized by typical corrugation, the emplacement of granitic plutons contributed to the development of the corrugation.(2) This research reveals the existence of a new metamorphic core complex (mcc), i.e. the Wanfu mcc for the first time. The Wanfu mcc has a three-layer structure. Stretching lineation indicate uniform top-to-SEE shearing along the main detachment fault zone.(3) The zircon U-Pb dating results of Five samples from different part of the two mccs indicate that the volcanic rocks form in two periods: pre-tectonic type(SL0530,169±8 Ma)and syn tectonic type(SL0585,123±7 Ma) magmatic activities; granites in three periods: pre-tectonic type(SL05103,166±4 Ma), syn-tectonic type(SL0543,124±3 Ma) and post- tectonic magmatic activities. The extraordinary same age of pre-tectonic type and syn-tectonic type vocalnic and granite rocks make us know that the time of the magmatic events is coincident.(4) The Wanfu mcc and Liaonan mcc form a mcc pair. They share many common features. The occurrence of the mcc pair and some suspected mcc's to the east of Wanfu area provide new evidences for discussion on the mechanical and rheological behavior and thinning processes of the North China plate in late Mesozoic.(5) The evolution geochronological framework of Liaonan-Wanfu mcc pair provides important evidence to the lithospheric extension and thinning of North China craton. We considered that the emplacement of Zhaofang intrusion(113 Ma) marks the termination of a series of tectono-magamtic activities during regional extension.(6) Liaonan, Wanfu mcc have unification with extensional structures of other aeras in deformation time and movement regularity. It reveals the lithosphere in the whole east Asia experienced intense extension and lithosphere thinning during late Mesozoic. Shearing was the dominant mechanism of the regional extension and the detachment mainly occurred in shallow to middle crust.