湘西南-桂北交界地区加里东期基性岩的发现及其地质意义

Discovery of Caledonian Mafic Rocks in Southwestern Hunan-northern Guangxi Border Area and Its Geological Significance

湘西南-桂北交界地区属于江南造山带(或称之为钦杭结合带)西南段的重要组成部分,该区与Rodinia超大陆聚合与裂解有关的岩浆活动十分强烈,但至今还没有加里东期基性岩存在的报道。采用LA-ICP-MS锆石U-Pb法对湘西南—桂北交界地区首次发现的加里东期变辉长辉绿岩进行了年代学研究。结果表明,变辉长辉绿岩形成于(421.9±7.8)Ma,为加里东期岩浆活动的产物。该基性岩的发现及其年龄的确定;并结合区域上的研究结果表明,扬子板块和华夏板块结合带(钦杭结合带)西南段可能存在有从新元古代至早古生代的双向洋陆俯冲-碰撞过程。

The southwestern Hunan-northern Guangxi border area is an important ment of Jiangnan orogenic belt （so-called Qinzhou-Hangzhou joint belt）. There is a related to the assembly and break-up of Rodinia supercontinent, but Caledonian mafic part of the southwestern seg- very strong magmatic activity rocks have not been found in this area. Geochronology of Caledonian metamorphic gabbro-diabase discovered firstly in southwestern Hunan-north- ern Guangxi border area was studied by using LA-ICP-MS zircon U-Pb method. The research results showed that the metamorphic gabbro-diabase is developed during （421.9 ＋ 7.8 ） Ma, and it is the product of Caledonian mag- matism activity. The discovery of Caledonian mafic rock and the determination of its era, and in combination with the regional research results, we consider that there was likely a double ocean-continent subduction-collision event occurred during Neoproterozoic to early Paleozoic time.