苏鲁高压—超高压变质地体的陆—陆碰撞深俯冲剥蚀模式

中国苏鲁高压—超高压变质地体由2个不同时代的变质基底组成.南苏鲁(临沭—连云港地区)中不同类型高压—超高压变质岩石的原岩形成于由大陆玄武质岩石、辉长岩、表壳岩和花岗岩组成的被动大陆边缘拉伸构造环境.研究表明南苏鲁高压—超高压变质岩石的原岩所代表的花岗岩浆和基性岩浆作用为罗迪尼亚超大陆形成后的新元古代(780-700Ma)裂解事件的响应.北苏鲁(青岛—威海)超高压变质地区的花岗质片麻岩锆石SHRIMPU-Pb定年表明,变质基底的年龄是2400Ma(或 & 2400 Ma),并经历了1800-1700Ma和-200Ma的变质事件,研究表明苏鲁高压—超高压变质地体由2个不同时代变质基底组成,北苏鲁的变质基底属于北中国板块胶辽朝地块的一部分,形成时代比南苏鲁基底老得多,其与南苏鲁地块之间的界限位于五莲以北到海阳所以南一线.由于在北苏鲁含柯石英的透辉石石英岩锆石SHRIMPU-Pb定年获得精确超高压峰期变质年龄为(234.1±4.2)Ma,退变质年龄为(218.2±1.5)Ma,表明南、北苏鲁2个不同时代基底地块同时经历了超高压变质作用.根据上述事实,提出苏鲁高压—超高压变质地体的陆—陆碰撞俯冲剥蚀新模式,即扬子板片在240-220Ma的深俯冲作用中拽动上部胶辽朝板片的—部分老变质基底岩石向下俯冲至大于100km的深度,并形成楔形俯冲剥蚀体,之后又与南苏鲁俯冲板片一起快速折返上来。 

Deep Subduction Erosion Model for Continent-Continent Collision of the Sulu HP-UHP Metamorphic Terrain

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-marie magmatism 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 of〉2 400 Ma and was overprinted by metamorphisms of 1 700-1 800 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. Sulu together 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 NCP. 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 subducted slab. Then both of them were exhumed rapidly.