The Structural Analysis Of The Yiwulvshan Metamorphic Core Complex, West Liaoning Province

As a main form of extension structure, from 80 decade of last century, many MCC(metamorphic core complex) has been found in China. The Yiwulvshan MCC lies in the east segment of the Yanshan orogene. The complex regional geology background made the research very significant.The Yiwulvshan MCC consists of a crystalline metamorphic core, a detachment fault and a cover layer. The center of the Yiwulvshan MCC is Yiwulvshan Early Yanshanian adamellite. The metamorphic core consists of Archaean metamorphic rock which represents ductile deformation in deep crust and surrounds the Yiwulvshan adamellite. The lower part of the cover layer consists of Middle Proterozoic, Spreads in northern and eastern part of the metamorphic core and connects with the metamorphic core by a detachment fault. It is cut by Sunjiawan-Shaohuyingzi normal fault in the west of the metamorphic core. The Yiwulvshan MCC is resemble of the Fangshan MCC, and different from Cordilleran MCC. Between the cover layer of brittleness break and bottom of ductile deformation, a series of rheological stratification of Middle Proterozoic Erathem is developed in the lower part of the cover layer.The Yiwulvshan MCC is symmetric type metamorphic core complex. The dip and the movement direction represented by the deformation schistosity, lineation, are opposite in the ductile shear zone of both sides of the MCC.Through chemical analysis, it can be considered that the Yiwulvshan adamellite is a"S"type granite by crust's remelting at the synorogenic stage. The MCC developed as follows:(1) The Archean strata was metamorphosized in the area at the end of Archean era(2500Ma±). Then, it had been eroding till the craton doposition began during the Middle Proterozoic. This stable tectonic evolvement had lasted for a long time and ended at the middle Triassic. Since then, the Indosinian movement had exerted its influence in this region and induced the local melting in the deep crust.(2) In the late of middle Jurassic(162.8-159.1Ma), the Yiwulvshan adamellite had been intruded.(3) During the Early Cretaceous period(127～116Ma), the regional extending became more stronger, the Yiwulvshan fault block arised, while the fault basin developed in both sides of it. At the same time, the detachement and the MCC formed by plastic deformation in the deep crust.(4)The MCC have sufferd denudation and emergenced the earth's surface when the Sunjiawanian formation was formed.