Petrology Study Of Heilongjiang Metamorphic Complex In Yilan District And Its Lithofacies Palaeogeographic Significance

With detailed studies on mineralogy, petrology and geochronology together with previous research results and the latest exploration data, this paper presents the new data of mineral petrology and geochronology of rocks from the Heilongjiang complex in the Yilan district, Heilongjian province, and provides new insight to geological implications for the Heilongjiang complex.Metamorphism and deformation characteristics of the Heilongjiang metamorphic complex shows that rocks investigated experience multi-metamorphic stages including re-crystallization process. A representative rock stilpnomelane schist, was formed in the process of the Jiamusi block westward subduction jointing together with the Songnen block during the late-stage of blue-schist metamorphism, and formed when pressure slightly declined and temperature slightly increased during blue-schist facies transformation into green-schist facies under P-T conditions of 250-400℃and 6-9 Kbar. Studies on LA-ICP-MS zircon U-Pb dating of the typical rocks of the Heilongjiang complex together with the formation age of same collision volcanic arc granite on the Jiamusi massif and the chronological study of other rocks indicate that the oceanic crust subduction is inferred between the Jiamusi Massif and its western margin of the Songnen Block, and subsequently continent-continent collision occurred at about 317-220Ma, whileas blue-schist facies metamorphism of the Heilongjiang complex may occur before 254 Ma. Petrological and geochemical characteristics also suggest the geological background of the subduction and afterward collision of the Jiamusi Massif and the Songnen Block. Combined with isotope study, paleontological research and geological background of the Jiamusi Massif, this study concludes a formation and evolution model of the Heilongjiang complex, and develops a lithofacies palaeogeography diagram of late Carboniferous to early Permian in the northeast region, China, providing basic theory and practical significance for oil exploration. The Late Paleozoic strata in depth of this district may bring new breakthrough in oil exploration, and provide oil vision evaluation of the northeast region of China.