蚌埠隆起区花岗岩形成时代及岩浆源区性质:锆石LA-ICPMS U-Pb定年与示踪  

Formation time and magma source of granites in Bengbu uplift: Evidence from LA-ICPMS zircon U-Pb dating and tracing

作　　者：杨德彬[1] 许文良[1] 裴福萍[1] 王清海[1] 柳小明[2] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061 [2]西北大学大陆动力学教育部重点实验室,陕西西安610076

出　　处：《地球化学》2005年第5期443-454,共12页Geochimica

基　　金：国家自然科学基金(40472033;40133020);西北大学大陆动力学教育部重点实验室开放基金~~

摘　　要：蚌埠隆起区西庐山及女山花岗岩中岩浆锆石206Pb/238U加权平均年龄分别为(129.3±4.8)Ma(n=7)和(130.1±3.2)Ma(n=9),这表明岩体的形成时代为早白垩世早期;曹山二长花岗岩和蚂蚁山花岗岩中岩浆锆石206Pb/238U加权平均年龄分别为(110.3±2.8)Ma(n=17)和(115.8±3.1)Ma(n=18),其形成时代为早白垩世晚期。岩体的岩相学和具有震荡环带岩浆锆石的存在表明该类花岗岩均为岩浆结晶的产物,而非混合岩化成因。西庐山和女山花岗岩中新元古代岩浆锆石和印支期变质锆石的存在以及太古宙和古元古代继承锆石的存在暗示岩浆源区既有扬子地块基底物质又有华北地块基底物质,其中某些遭受了超高压变质作用的改造。蚌埠隆起区深部地壳中扬子地块基底物质的存在与扬子地块沿郯庐断裂带于北西方向俯冲于华北地块之下的地质事实相吻合。The granites in the Bengbu uplift were dated using LA-ICPMS zircon U-Pb method to determine their formation time and to trace their magma sources. The results show that the weighted mean ^206Pb/^238U ages of magmatic zircons from the Xilushan and Nǖshan granites in the Bengbu uplift are （129.3±4. 8） Ma （n =7） and （130. 1±3.2） Ma （n = 9）, respectively, which indicates that these granites were formed in the beginning of Early Cretaceous. The weighted mean ^206pb/^238U ages of magmatic zircons from the Caoshan monzonitic granite and the Mayishan granite are （110.3±2.8） Ma （n=17） and （115.8±3.1） Ma （n=18）, respectively, which indicates that they were formed in late period of Early Cretaceous. The petrographic characteristics of these granitic intrusives and the occurrence of magmatic zircons with fine-scale oscillatory zoning rims indicate that they were formed by normal crystallization of felsic melts rather than by migmatization. The coexistence of the Neoproterozoic magmatic inherited zircons, the Indosinian metamorphic inherited zircons, and the Archean and Paleoproterozoic inherited zircons in the Xilushan and Nǖshan granites implies that the magma sources could be involved in both the basements of the Yangtze Block （YB） and the North China Block （NCB）. And some of them were superimposed by the ultrahigh pressure metamorphism. The occurrence of the YB basement in the lower continental crust of the NCB could be resulted from the NWW （or near EW） directed subduction of the YB beneath the NCB along the Tan-Lu fault zone.

关 键 词：花岗岩 锆石 U-PB定年 示踪 岩石成因论 蚌埠 安徽省 

分 类 号：P597[天文地球—地球化学] P581[天文地球—地质学]