| 青藏高原拉萨地块西部念青唐古拉岩群的地球化学特征及构造意义 |
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| 引用本文： | 吴勇,马绪宣,张志平,焦世文,段凯,董瀚,王小伟,马涛,李鹏举,梁志勇,曹勇刚,孔垂鹏,马亮.青藏高原拉萨地块西部念青唐古拉岩群的地球化学特征及构造意义[J].地质学报,2016,90(11):3081-3098. |
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| 作者姓名： | 吴勇 马绪宣 张志平 焦世文 段凯 董瀚 王小伟 马涛 李鹏举 梁志勇 曹勇刚 孔垂鹏 马亮 |
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| 作者单位： | 甘肃省地矿局第三地勘院，兰州，730050;,中国地质科学院地质研究所大陆构造与动力学实验室,北京, 100037,甘肃省地矿局第三地勘院，兰州，730050;,甘肃省地矿局第三地勘院，兰州，730051;,甘肃省地矿局第三地勘院，兰州，730052;,甘肃省地矿局第三地勘院，兰州，730053;,甘肃省地矿局第三地勘院，兰州，730054;,甘肃省地矿局第三地勘院，兰州，730055;,甘肃省地矿局第三地勘院，兰州，730056;,甘肃省地矿局第三地勘院，兰州，730057;,甘肃省地矿局第三地勘院，兰州，730058;,甘肃省地矿局第三地勘院，兰州，730059;,甘肃省地矿局第三地勘院，兰州，730060; |
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| 摘 要： | 拉萨地块西部呈断块状沿狮泉河-申扎-嘉黎蛇绿混杂岩带附近分布的念青唐古拉岩群被认为是前寒武纪变质基底。本文对念青唐古拉岩群进行了系统的岩石学、地球化学、同位素年代学及构造地质学研究。研究结果表明片岩-片麻岩-变粒岩含十字石、石榴子石等特征变质矿物,遵循粒度分异规律,其原岩可能为来自冈瓦纳古陆核北缘中新元古代弧盆体系的活动大陆边缘浊积岩。斜长角闪岩具低硅、高铁镁、富钙的基性岩特征,其原岩为岛弧型基性火山岩。念青唐古拉岩群中的花岗伟晶岩锆石LA-ICPMS U-Pb年龄为1150±13Ma,具过铝质S型花岗岩地球化学特征,可能为中元古代(1150±13 Ma)以前就开始沉积的念青唐古拉岩群基底岩石通过部分熔融形成。与花岗伟晶岩渐变过渡接触的二云斜长片麻岩第一组变质重结晶锆石U-Pb年龄为701±15 Ma,结合十字石特征变质矿物,暗示了该地区中温高压变质作用的峰期变质,变质程度达角闪岩相;第二组热液流体锆石UPb年龄为301±8.4 Ma,可能与冈瓦纳大陆北缘古特提斯洋演化过程中的岩浆热液作用有关。
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| 关 键 词： | 拉萨地块 念青唐古拉岩群 花岗伟晶岩 部分熔融 特提斯 前寒武基底 冈瓦纳古陆 |
Geochemical Features of the Nyainqentanglha Group in the Western Lhasa Terrane, Western Tibet and Their Tectonic Significance |
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| WU Yong,MA Xuxuan,ZHANG Zhiping,JIAO Shiwen,DUAN Kai,DONG Han,WANG Xiaowei,MA Tao,LI Pengju,LIANG Zhiyong,CAO Yonggang,KONG Chuipeng and MA Liang.Geochemical Features of the Nyainqentanglha Group in the Western Lhasa Terrane, Western Tibet and Their Tectonic Significance[J].Acta Geologica Sinica,2016,90(11):3081-3098. |
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| Authors: | WU Yong MA Xuxuan ZHANG Zhiping JIAO Shiwen DUAN Kai DONG Han WANG Xiaowei MA Tao LI Pengju LIANG Zhiyong CAO Yonggang KONG Chuipeng and MA Liang |
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| Abstract: | The Nyainqentanglha Group of the western part of the Lhasa terrane, distributed along the Shiquanh-Shenzha-Jiali ophiolite m lange and its vicinity, has been traditionally grouped as the Precambrian metamorphic basement. Detailed petrology, geochemistry, structural geology and zircon U-Pb dating were conducted in this study. The results show that characteristic metamorphic minerals, such as schist, gneiss and leptynite suite follows the granularity differentiation rules, suggesting the protolith of the rocks is likely turbidite deposited in active continental margin of Neoproterozoic arc-basin system in the north margin of Gondwana nucleus. Amphibolites are characterized by low Si, high Fe and Mg and Ca, indicating its island-arc type mafic volcanic rock in origin. Granite pegmatite (P37RZ1) of the Nyainqentanglha Group has a LA-ICPMS U-Pb age of 1150±13 Ma, and is of peraluminous affinity to S-type granite, representing the basement rock of the Nyainqentanglha Group started to deposit due to partial melting before the mesoproterozoic (1150±13 Ma). The formation of the granite pegmatite is considered to be associated with the tectonothermal event during the Grenville orogeny. In contrast, the plagioclase gneiss (P38RZ2) has two types of zircons, namely the recrystallization one and the altered one by hydrothermal melt. The first group zircons yield a weighted mean age of 701±15 Ma, indicating a HP-MT amphibolite facies metamorphism during the disperse of the Rodinia supercontinent and/or the assemblage of the Gondwana landmass. The zircons in the second group yield a weighted mean age of 301±8.4 Ma, which is likely related to with the magmatic hydrothermal process derived from the Paleo-Tethys evolution along the northern margin of the Gondwana landmass. |
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| Keywords: | Lhasa terrane Nyainqentanglha Group granite pegmatite partial melting Tethys Precambrian metamorphic basement Gondwana landmass |
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