Deep Subduction Erosion Model for Continent-Continent Collision of the Sulu HP-UHP Metamorphic Terrain
摘要
By the construction for the HP-UHP metamorphic rocks, containing eclogite, feldspar amphibolite, paragneiss and granitic gneiss, it is revealed that their protoliths were continental basaltic rocks, gabbros, supracrustal rocks and granites formed under extensional environment at the Yangtze passive continental margin. New zircon SHRIMP U-Pb dating for the protoliths of the south Sulu UHP metamorphic rocks reflects the Neoproterozoic (700-800 Ma) granitic-mafic mag-matism events induced by the Rodinia supercontinental breakup. Detailed zircon SHRIMP U-Pb dating for granitic gneiss in the N. Sulu (Qingdao-Weihai) area shows its oldest metamorphic basement being age of2 400 Ma and was overprinted by metamorphisms of 1700-1800 Ma and to 200 Ma. Therefore, above-mentioned age dating together with previous chronologic data led us to conclude that the Sulu HP-UHP nappes have two basements: the Early-Middle Protrozoic (≥2 400 Ma) basement in the N. Sulu and the Neoprotrozoic (700-800 Ma) basement in the S. Sulu. The basement ages in the N. Sulutogether with its western part of the no-UHP metamorphic area (Laiyang-Penglai) are similar and named by the Jiao-Liao-Korea block (JLKB) belong to the NCR Besides, the boundary between both of the S. Sulu UHP area and JLKB is along north Wulian and south Haiyangsuo. New zircon SHRIMP U-Pb dating for coesite-bearing quartzite of the N. Sulu shows the UHP peak metamorphism being age of 238 Ma and retrograde metamorphism being age of 215 Ma, which indicates both basements of the Sulu UHP metamorphic terrain have undergone UHPM simultaneously. Based on occurrences of the two different basements of the Sulu HP-UHP metamorphic terrain, a new dynamic model of deep subduction erosion for continent-continent collision is proposed in this study. That means during the deep subduction of YZP at 240-220 Ma, the part of JLKB had been dragged downward to be 100 km depth and a wedge subduction erosion body was formed on the upper part of the Yangtze