西秦岭造山带北部早古生代麻粒岩相变质作用及深熔作用:锆石和独居石U-Pb年代学的制约

发布时间：2018-05-30 05:52

本文选题：西秦岭 + 麻粒岩　；参考：《中国科学:地球科学》2017年05期

【摘要】：西秦岭造山带北部的秦岭杂岩中新识别出麻粒岩相岩石,它们由角闪二辉麻粒岩和石榴夕线黑云片麻岩组成,并具有强烈的混合岩化特征.本文选择3个麻粒岩相岩石和1个深熔浅色体样品进行SHRIMP、LA-ICPMS锆石和独居石的U-Pb年代学分析,一个麻粒岩相变泥质岩样品中的锆石给出了加权平均年龄为(430±4)Ma(MSWD=0.88),另一个麻粒岩相变泥质岩的独居石给出了(433±4)Ma(MSWD=0.27)的加权平均年龄,两者在误差范围内一致,结合岩相学观察及锆石特征,认为其代表了变泥质岩麻粒岩相变质时代;角闪二辉麻粒岩中的变质锆石分别给出了(424±3)Ma(MSWD=0.45)和(402±3)Ma(MSWD=1.4)的2个加权平均年龄值,结合岩相学特征,认为前者代表麻粒岩相的变质年龄,而后者可能为麻粒岩相变质作用之后的退变质作用改造的时代;混合岩中浅色体中的锆石给出了(426±2)Ma(MSWD=0.3)加权平均年龄,代表了深熔脉体的结晶年龄.因此,与东秦岭造山带相似,西秦岭造山带北部同样记录了早古生代晚期麻粒岩相变质作用及深熔作用,其形成于商丹洋向北俯冲的岩浆弧背景还是与早古生代的碰撞造山有关仍需进一步确定.
[Abstract]:Granulite facies rocks are newly identified from the Qinling complex in the northern part of the West Qinling orogenic belt. They are composed of hornblende androxenite and pomegranate nigrite gneiss with strong mixed lithologic characteristics. In this paper, three granulite facies rocks and one submersible light-colored sample are selected for U-Pb chronological analysis of shrimp LA-ICPMS zircon and monazite. The weighted mean age of zircon in one granulite phase change argillite sample is given, the weighted mean age is 0.88 ~ 0.88, and the weighted mean age of the monazite of another granulite phase change argillite is 433 卤4 ~ 4 Ma-MSWDN _ (0.27), which is consistent in the error range. Combined with petrographic observation and zircon characteristics, it is considered that the metamorphic zircon represents the age of granulite metamorphism in argillaceous rocks, and the metamorphic zircon in amphibolite is given two weighted mean ages of 424 卤3 Ma-MSWD0. 45) and 402 卤3 Ma-MSWD1. 4), which are combined with the lithofacies characteristics. It is considered that the former represents the metamorphic age of granulite facies, while the latter may be the retrograde metamorphic age after granulite metamorphism, and the zircon from the paleochromatic body in the migmatite gives a weighted mean age of 426 卤2 MaMSWD0. 3). It represents the age of crystallization of the deep melting vein. Therefore, similar to the East Qinling orogenic belt, the northern part of the West Qinling orogenic belt also recorded the late early Paleozoic granulite facies metamorphism and deep melting. The background of magmatic arc which subducted northward in Shangdan Ocean is related to the collision orogeny of early Paleozoic.
【作者单位】：中国地质科学院地质研究所;北京大学地球与空间科学学院;中国海洋大学海洋地球科学学院海底科学与探测技术教育部重点实验室;青岛海洋科学与技术国家实验室海洋地质功能实验室;天津大学表层地球系统科学研究院;
【基金】：国家自然科学基金项目(批准号:41630207,41572180) 中国地质调查局项目(编号:12120115027001)资助
【分类号】：P588.3;P597.3

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