STRUCTURAL CHARACTERISTICS, ORIGIN AND EVOLUTION OF METAMORPHIC CORE COMPLEX IN CENTRAL BASEMENT UPLIFT AND XUJIAWEIZI FAULTED DEPRESSION IN SONGLIAO BASIN, NORTHEAST CHINA
ZHANG Xiao dong 1, YU Qing 2, CHEN Fa jing 2, WANG Xin wen 2(1 Research Institute of Exploration and Development, Daqing Oil Field Inc, Daqing 163712, China; 2 China University of Geosciences, Beijing 100083,China)
The structural characteristics, origin and evolution of the metamorphic core complex of the central basement uplift and Xujiaweizi faulted depression in northern Songliao basin are discussed and several points have been emphasized as follows: (1) The central basement uplift metamorphic core complex displays many of the structural characteristics of Cordillerian metamorphic core complex; (2) Multi layered low angle ductile detachment systems which consist of the central basement uplift are recognized, and they have been the main factors enabling middle grade metamorphic rocks to be brought from middle crust to upper crust;(3) The volcanic dome shaped platform were formed during the Late Jurassic (145.7±6.2)Ma, the extensional faulted depressions controlled by top detachment fault were formed the Early Cretaceous (133～120 Ma), while the age of mylonites near top detachment fault in Well Fang deep 3 is (126.7±1.54)Ma. These imply doming and exhumation of the central basement uplift were also generated since the Late Jurassic. Progressive extension tectonics was associated with upwarping of the deeper parts of this core complex to the surface during the Early Cretaceous. It is suggested that doming and exhumation of this core complex, formation of extensional faulted depression, are driven by mantle delamination, magmatic underplating of mantle and extensional collapse following the continental collision of Izanazi plate and Asia plate.