The Evolution Of The Lithosphere In The East Part Of Heilongjiang Province

Abstract: The studied region is located in the east part of Heilongjiang province. Geotectonically, it belongs to the east part of the Central Asian orogenic belt between the North China plate and the Siberia plate, east to the Pacific plate. There exist not only microplate, ophiolite complex, and terrane, representing the evidences of lateral accretional of continent, but also magmatic rock belt and extensional basin-range system, showing evidences of vertical accretion and transformation of continent. The area is a typical place where the structure frames dominated by E-W and S-N trends were reworked by N-E trend structures later. Such three groups of structures reflect the basic structural features on evolution of the continental margin of Northeast Asia , which formed in Paleozoic, early Mesozoic and late Mesozoic respectively. They represent the geodynamical evolutions of Paleo-Asian, Paleo-Pacific, Pacific structural domains respectively. Therefore, this area is an ideal region to study the geodynamic evolution of continental margin of Northeast Asia .The Jiamusi microplate and Nadanhada terrane are two important geological units in the east part of Heilongjiang province. Based on Jiamusi microplate, Yuejinshan rock series and Nadanhada (Raohe, Wandashan) terrane, we selected the deep texture as our topic in order to study the deep texture, structural characteristics of Jiamusi microplate and Nadanhada terrane and their amalgamation from lithosphere scale. Contacting the lateral accretion of continent growth, lithospheric mantle-crust interreaction with vertical accretional process of continental material, combining lithospheric geometry, crustal petrology, structural geology and geochemistry, we built the three-dimensional lithospheric texture and geodynamical process. The general situation of peripheral geological body or marginal convergent belt was introduced in the researching area firstly, i.e. Songnen massif, Xingkai, Xikhote-Aline terrane, Jiayin-Mudanjiang convergent belt, Mudanjiang-Muling convergent belt, Zhangguangcailing granite, North marginal convergent belt of North China plate and so on. After analyzing basic crustal geology of Jiamusi microplate, Yuejinshan rock series and Nadanhada terrane, and collecting isotopic data of recent years, we found an 510~520Ma granulite facies metamorphism and 255~270Ma magmatic intrusion in Jiamusi microplate. Thus it is proved that Jiamusi massif was a foreign microplate which underwent an independent evolution process, and the amalgamation time was late stage of Paleozoic or early stage of Mesozoic.According to the MT deep sounding section of Huanan-Raohe, we understood the lithospheric texture characteristics of Jiamusi massif, Yuejinshan rock series and Nadanhada terrane. And we determined that the boundaries of east part of Jiamusi massif were different in the deep and superficial parts, i. e. the superficial boundary is located 30km to the east of Baoqing and the deep one is under Baoqing. And it suggested that accretional event occurred to the west of Jiamusi micoplate ,which related to oceanic crust.Based on the above analysis, it was suggested that Jiayin-Yilan-Mudanjiang suture between Xiaoxinganling-Zhangguangcailing magmatic belt and Jiamusi microplate was formed in the end of Late Paleozoic to the beginning of Mesozoic, and Tongjiang-Baoqing-Mishan convergent belt between Jiamusi microplate and Nadanhada terrane was formed in late Mesozoic.