| 柴北缘鱼卡河榴辉岩围岩的变质时代及其地质意义 |
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| 引用本文： | 陈丹玲,孙勇,刘良.柴北缘鱼卡河榴辉岩围岩的变质时代及其地质意义[J].地学前缘,2007,14(1):108-116. |
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| 作者姓名： | 陈丹玲 孙勇 刘良 |
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| 作者单位： | 西北大学,大陆动力学国家重点实验室,西北大学,地质学系,陕西,西安,710069 |
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| 基金项目： | 国家自然科学基金
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教育部科学技术研究重点项目 |
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| 摘 要： | 利用阴极发光和LA-ICP-MS原位分析方法,对柴北缘鱼卡河超高压榴辉岩的直接围岩——石榴石白云母角闪钠长片麻岩和含蓝晶石的石榴石云母片岩进行了详细的锆石微量元素和U-Th-Pb同位素分析。结果表明,石榴石白云母角闪钠长片麻岩中的锆石主体呈浑圆状形态,内部结构以扇状和冷杉树状为主,稀土总量和重稀土含量均较低,重稀土富集程度低,具明显正Eu异常,Th/U比值均小于0.1,指示其形成在与石榴石平衡共生而不含斜长石的变质条件下。而含蓝晶石的石榴石云母片岩中的锆石显示明显的核-边结构,核部显示碎屑锆石特征,边部为与石榴石共生的变质新生锆石。LA-ICP-MS原位定年获得两种围岩的峰期变质年龄分别为(431±3)Ma和(432±19)Ma。这两组年龄在误差范围内一致,而且与已获得的紧邻的两类超高压榴辉岩的变质年龄((436±3)Ma和(431±4)Ma)以及带内指示大陆深俯冲作用时代的都兰含柯石英副片麻岩锆石的柯石英微区年龄(424~432Ma)完全一致。参考这两类岩石与超高压榴辉岩的野外产状关系、含蓝晶石的石榴石云母片岩的原岩特征以及榴辉岩中超过变质年龄达300Ma的原岩残核的存在,共同表明,柴北缘鱼卡河超高压变质地体是典型的大陆深俯冲碰撞作用的产物,本区大陆深俯冲发生的时代为430~435Ma的早古生代。
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| 关 键 词： | 超高压变质岩片 榴辉岩围岩 LA-ICP-MS锆石U-Pb定年 鱼卡河 柴北缘 |
| 文章编号： | 1005-2321（2007）01-0108-09 |
| 收稿时间： | 2006-10-18 |
| 修稿时间： | 2006-12-10 |
The metamorphic ages of the country rock of the Yukahe eclogites in the North Qaidam and its geological significance |
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| Chen Danling,Sun Yong,Liu Liang.The metamorphic ages of the country rock of the Yukahe eclogites in the North Qaidam and its geological significance[J].Earth Science Frontiers,2007,14(1):108-116. |
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| Authors: | Chen Danling Sun Yong Liu Liang |
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| Abstract: | Using cathodoluminescence (CL) imaging, LA-ICP-MS in situ trace element analysis and U-Pb dating, we have comprehensively studied zircon grains from garnet-bearing muscovite-amphibole-albite gneiss and kyanite-bearing garnet-mica schist. These are the country rocks of the ultrahigh-pressure (UHP) eclogites in Yukahe Area in the North Qaidam Basin. Zircons from garnet-bearing muscovite-amphibole-albite gneiss mainly exhibit a rounded crystal habit with internal sector and zoning, low Th/U ratio, low content of REE and HREE, weak HREE enrichment and positive Eu anomaly. This indicates that these zircons were formed under garnets stable and plagioclases unstable metamorphic conditions. Zircons from kyanite-bearing garnet-mica schist display a core-rim internal texture. The core shows features of detrital origin, whereas the rim exhibit metamorphic characteristics, as indicated by the low Th/U ratio and weak HREE enrichment and Eu anomaly.LA-ICP-MS U-Pb dating yields the peak metamorphic ages of (431±3) Ma and (432±19) Ma for these two rocks. These ages are consistent within errors with each other and also with the metamorphic age of the UHP eclogites ((436±3) Ma and (431±4) Ma) as well as the coesite-bearing pelitic schist (424-432 Ma) in Yematan Area. The concordant metamorphic ages of UHP eclogites and their country rocks, together with their field relationships and the features of the protolith of kyanite-bearing garnet-mica schist, allow us to conclude that the Yukahe UHP metamorphic block is the result of a typical continental deep subduction-collision process, formed during 430-435 Ma in the early Paleozoic. |
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| Keywords: | UHP metamorphic belt country rocks of UHP eclogites eclogites LA-ICP-MS zircon dating Yukahe the North Qaidam |
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