北祁连造山带东段查巴峡早寒武世蛇绿混杂岩带的确定及其构造意义
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摘要
在北祁连造山带东段的青海省门源县南门峡镇查巴峡一带新识别出一条蛇绿混杂岩带,其物质组成复杂,构造岩块包括变质橄榄岩、基性岩墙、变质基性熔岩、中性侵入岩、变质中基性火山岩和外来地层。基性岩墙和变质基性熔岩具有向右缓倾、轻稀土元素略富集的稀土元素配分模式,富集大离子亲石元素Ba和U,高场强元素Nb、Ta、Zr、Ti基本不显示异常,总体地球化学特征与富集型洋中脊玄武岩(E-MORB)相似。对蚀变辉长岩进行LA-ICP-MS锆石U-Pb测年,获得~(206)Pb/~(238)U年龄加权平均值为522.6±9.7Ma。结合前人的研究成果,认为查巴峡蛇绿混杂岩形成于早寒武世北祁连洋盆扩张的构造环境。查巴峡蛇绿混杂岩的确定扩大了北祁连造山带蛇绿岩南带向南东方向的延伸范围,进而扩大了北祁连造山带早期洋盆向南东方向的分布范围。
The ophiolitic melange belt was identified in Chabaxia area, Menyuan County of Qinghai Province, along the North Qilian orogenic belt. Its physical composition is complex, and the tectonic blocks involved in the belt include metamorphic peridotite, mafic dyke, metamorphic basic lava, intermediate intrusive rock, metamorphic intermediate acid volcanic rock and exotic strata. The mafic dykes and metamorphic basic lava have the REE distribution patterns which are slightly right-inclined and slightly enriched in LREE. They also show enrichment of LILES such as Ba and U, whereas HFSE such as Nb, Ta, Zr and Ti do not show anomalies. These geochemical characteristics are similar to features of E-MORB. LA-ICP-MS zircon U-Pb dating of alteration gabbro yielded~(206)Pb/~(238)U weighted average age of 522.6±9.7 Ma. In combination with the previous research results, the authors infer that Chabaxia ophiolite was formed in the tectonic environment of of northern Qilian basin expansion in Early Cambrian. The identification of Chabaxia ophiolite melange suggests that south ophiolite belt of North Qilian orogenic belt expanded and extended southeastward, and thus early ocean basin of North Qilian orogenic belt expanded southeastward.
The ophiolitic melange belt was identified in Chabaxia area, Menyuan County of Qinghai Province, along the North Qilian orogenic belt. Its physical composition is complex, and the tectonic blocks involved in the belt include metamorphic peridotite, mafic dyke, metamorphic basic lava, intermediate intrusive rock, metamorphic intermediate acid volcanic rock and exotic strata. The mafic dykes and metamorphic basic lava have the REE distribution patterns which are slightly right-inclined and slightly enriched in LREE. They also show enrichment of LILES such as Ba and U, whereas HFSE such as Nb, Ta, Zr and Ti do not show anomalies. These geochemical characteristics are similar to features of E-MORB. LA-ICP-MS zircon U-Pb dating of alteration gabbro yielded~(206)Pb/~(238)U weighted average age of 522.6±9.7 Ma. In combination with the previous research results, the authors infer that Chabaxia ophiolite was formed in the tectonic environment of of northern Qilian basin expansion in Early Cambrian. The identification of Chabaxia ophiolite melange suggests that south ophiolite belt of North Qilian orogenic belt expanded and extended southeastward, and thus early ocean basin of North Qilian orogenic belt expanded southeastward.
引文
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