阿尔金江尕勒萨依榴辉岩和围岩锆石LA-ICP-MS微区原位定年及其地质意义  

Implications based on LA-ICP-MS zircon U-Pb ages of eclogite and its country rock from Jianggalesayi area, Altyn Tagh

作　　者：刘良[1] 张安达[1] 陈丹玲[1] 杨家喜[1,2] 罗金海[1] 王超[1] 

机构地区：[1]西北大学大陆动力学国家重点实验室,西北大学地质学系 [2]长安大学地球科学与国土资源学院,陕西西安710054

出　　处：《地学前缘》2007年第1期98-107,共10页Earth Science Frontiers

基　　金：国家自然科学基金项目(40372088;40572111;40472043);教育部科学技术研究重大项目(306021);国家重点基础研究发展计划"973"项目(G1999075508)

摘　　要：阿尔金江尕勒萨依榴辉岩及其直接围岩——石榴子石黑云母片麻岩锆石的阴极发光图像、微区原位LA-ICP-MS微量元素分析研究表明,榴辉岩锆石内部结构比较均匀,少数颗粒保留斑杂状残核;位于锆石斑杂状残核测点的重稀土相对富集,Th/U比值多大于0.4,为岩浆锆石的特征;位于锆石边部与内部结构均匀颗粒上的测点显示HREE近平坦型或弱亏损型的稀土配分模式,显示了与石榴石平衡共生的变质锆石特征;而石榴子石黑云母片麻岩的锆石具有核-幔-边结构,核部为碎屑锆石,幔部则为与石榴石平衡共生的变质锆石。LA-ICP-MS微区定年获得榴辉岩的变质年龄为(493±4.3)Ma,其原岩形成年龄为(754±9)Ma;石榴子石黑云母片麻岩的变质年龄为(499±27)Ma。榴辉岩的变质年龄滞后于其原岩的形成年龄约250Ma,并且榴辉岩与其直接围岩副片麻岩的变质年龄几乎完全一致,充分表明该超高压榴辉岩的形成是陆壳深俯冲作用的产物。Based on Cathodo-luminescence （CL） and LA-ICP-MS in situ trace element analyses and dating, this paper presents new zircon U-Pb data for the eclogite and its country rock （garnetbiotite gneiss ） from the Jianggalesayi Area, Altyn Tagh, reveal interesting gcodynamic implications. The zircon grains in the eclogite mainly display homogeneous internal texture, with residual cores being found in a few grains. These residual cores show that they are typical magmatic products, characterized by the enrichment in HREE and high ratio of Th/U （mostly is larger than 0. 4）. On the other hand the rims of these zircons and the homogeneous zircon grains show flat REE or slightly depleted HREE patterns, which are typical for metamorphic zircons coexisting with garnet. The zircon grains of the garnet-biotite gneiss display a core-mantle-rim internal structure. The cores show the features of detrital zircons, whereas the mantles show metamorphic features of coexisting with garnet. LA-ICP-MS in situ dating yields the metamorphic ages of （493±4. 3） Ma and （499±27） Ma respectively for the eclogite and garnet-biotite gneiss, and yields a protolith age of （754±9） Ma for the eclogit. The metamorphic age of eclogite is almost the same as that of the country rock paragneiss and is about 250 Ma later than its protolith age, which indicates that the UHP eclogite is the product of continental crust deep subduction.

关 键 词：榴辉岩 榴辉岩围岩——石榴子石黑云母片麻岩 LA-ICP-MS锆石定年 江尕勒萨依 阿尔金 

分 类 号：P597[天文地球—地球化学] P588.34[天文地球—地质学]