| 柴北缘夹榴辉岩的片麻岩（片岩）地球化学、Sm-Nd和U-Pb同位素研究——深俯冲的前寒武纪变质基底？ |
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| 引用本文： | 张建新,万渝生,孟繁聪,杨经绥,许志琴.柴北缘夹榴辉岩的片麻岩（片岩）地球化学、Sm-Nd和U-Pb同位素研究——深俯冲的前寒武纪变质基底？[J].岩石学报,2003,19(3):443-451. |
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| 作者姓名： | 张建新 万渝生 孟繁聪 杨经绥 许志琴 |
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| 作者单位： | 中国地质科学院地质研究所大陆动力学实验室,100037,北京 |
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| 基金项目： | 国家地质调查项目(200013000170)，国土资源部“十五”重点基础项目(项目批准号:20010201)，国家自然科学基金(40272095,49902018) |
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| 摘 要： | 在柴北缘的鱼卡-锡铁山-沙柳河一带,出露夹有榴辉岩透镜体的花岗质片麻岩(正片麻岩)和副片麻岩(片岩)。地球化学和Sm-Nd同位素数据显示副片麻岩(片岩)与正片麻岩具有类似的地球化学成分和一致的Nd模式年龄(1.88～2.18Ga),结合副片麻岩(片岩)局部包在正片麻岩中的野外关系,正片麻岩可能为副片麻岩(片岩)原地熔融作用的产物。U-Pb锆石测定表明熔融作用产生的正片麻岩的岩浆形成时代为952Ma。另外,这些夹榴辉岩的片麻岩(片岩)也与柴北缘北侧不夹榴辉岩的深变质基底片麻岩和中南祁连地块的变质基底片麻岩有相似Sm-Nd同位素特征和近一致Nd模式年龄(1.87～2.26Ga)。表明它们具有明显的亲缘关系,可能来源于具有古元古代晚期地壳形成年龄的同一变质基底。然而,与柴北缘北 侧和祁连地块的深变质基底岩石不同的是,这套含榴辉岩的片麻岩(片岩)明显遭受了早古生代变质作用的影响,正片麻岩锆石U-Pb测定获得的下交点年龄为478±44Ma,与柴北缘地区榴辉岩的变质锆石的年龄在误差范围内一致;而已在都兰地区副片麻岩锆石中柯石英包体的发现也证明了含榴辉岩的片麻岩(片岩)与榴辉岩一样同样经历了UHP变质作用。因此,我们认为柴北缘含榴辉岩的片麻岩虽然具有与相邻变质基底相似的早期演化历史,但在早古生代又与所夹的榴辉岩
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| 关 键 词： | 柴北缘 夹榴辉岩片麻岩（片岩） Sm-Nd同住素 深俯冲 前寒武纪变质基底 |
| 文章编号： | 1000-0569/2003/019(03)-0443-51 |
| 修稿时间： | 2002年10月30 |
Geochemistry, Sm-Nd and U-Pb isotope study of gneisses (schists) enclosing eclogites in the North Qaidam Monutains--deeply subducted Precambrian metamorphic basement? |
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| ZHANG JianXin,WAN YuSheng,MENG FanCong,YANG JingSui and XU ZhiQin Laboratory of Continental Dynamics.Geochemistry, Sm-Nd and U-Pb isotope study of gneisses (schists) enclosing eclogites in the North Qaidam Monutains--deeply subducted Precambrian metamorphic basement?[J].Acta Petrologica Sinica,2003,19(3):443-451. |
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| Authors: | ZHANG JianXin WAN YuSheng MENG FanCong YANG JingSui and XU ZhiQin Laboratory of Continental Dynamics |
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| Institution: | ZHANG JianXin,WAN YuSheng,MENG FanCong,YANG JingSui and XU ZhiQin Laboratory of Continental Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing,China |
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| Abstract: | Orthogneisses and paragneisses ( schists) enclosing eclogites crop out along the Yuqia-Xitieshan-Shaliuhe of the North Qaidam Mountains ( NQD) . Our geochemical analyses and Sm-Nd isotope data indicate that the Orthogneisses are similar in geochemical composition and Nd model ages( 1. 88 ~ 2. 18Ga) to the paragneisses. In combination of geological relationship that the paragniesses occur as xenolith within the orthogneiss, the Orthogneisses were probably derived through in situ melting of the paragneisses ( schists). Zircon U-Pb data suggest that the magma of the orthogneiss was formed at 952Ma ago . Moreover, the gneisses ( schists) enclosing eclogites also show similar characteristics in Sm-Nd isotope composition and Nd model TDM (1. 87 ~ 2. 26Ga) to those of the high-grade metamorphic rocks enclosing no eclogites ( non-eclogite bearing basement gneisses) in NQD and metamorphic basement rocks of the Qilian block. This implies that they have close affinity, and probably are derived from same metamorphic basement with a crust formation age of late Paleoproterozoic. However, in contrast to the high-grade metamorphic rocks enclosing no eclogites (non-eclogite bearing basement gneisses) in NQD and basement gneisses in the Qilian orogenic belt, the gneisses enclosing eclogites ( eclogite bearing gneisses) were obviously overprinted by early Paleozoic metamorphism as indicated by zircon U-Pb data of a lower intercept age of 478 44Ma which is in agreement with the age of metamorphic zircon from eclogite within error range. In addition, newly reported coesites in paragneisses enclosing eclogites in Dulan area also suggest that the gneiss and enclosed eclogite as a whole underwent early Paleozoic HP-UHP metamorphism. Therefore, although the gneisses enclosing eclogites have similar early evolution histories to adjacent Precambrian high-grade metamorphic basement rocks, they experienced deep subduction together with the enclosed eclogite during early Paleozoic orogeny. |
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| Keywords: | North Qaidam Monutains Gneiss (schist) enclosing eclogite Sm-Nd isotope Deep subduction Precambrianbasement |
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