武当地块西部席状基性侵入岩群地球化学特征:南秦岭古生代底侵作用的依据  

Geochemistry of the basic sills in the western Wudang block: the evidences of the Paleozoic underplating in south Qinling.

作　　者：赵国春[1] 胡健民[2] 孟庆任[3] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质科学院地质力学研究所 [3]中国科学院地质与地球物理研究所,北京100101

出　　处：《岩石学报》2003年第4期612-622,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金(批准号:49972066;40272097)

摘　　要：武当地块西部顺层侵位了大量的基性岩席。本文对其进行的岩石学、地球化学和Sr、Nd同位素等特征研究表明,该基性岩席群的岩浆属于大陆拉斑玄武岩系列,来源于混合异常大陆岩石圈地幔型源区,为武当地块裂解和中古生代时南秦岭地区曾发生大规模的地幔岩浆底侵及壳幔相互作用重要标志之一。此外,该基性岩席群的岩石地球化学特征与勉略地区玄武岩及变辉绿岩总体的特点具有较大的一致性,结合该基性侵入岩席群的形成时代(401～407 Ma)、武当地块伸展构造(425～260 Ma)与勉略带火山岩(230Ma)同位素年代学的差异,武当地块西部基性岩席群很可能是由于勉略洋拉开前地幔柱活动使大陆岩石圈拉伸减薄发生拆离、深部岩浆上涌的结果。因此,它们应该是勉略洋打开的早期阶段在武当地块区的响应。There are a lot of the Paleozoic basic sills in the western Wudang terrain in south Qinling structural zone. The study on petrology, geochemistry and isotopic composition of Sr and Nd in this paper shows that the magma of the basic sills belongs to the tholeiite series and is from a mixed and abnormal continental lithospheric mantal-type magma resource. The basic sill swarm is one of the marks of the rifting of Wudang terrain and the middle Paleozoic underplating of mantal magma and interplayting between the mantal and crust. In addition to it, the geochemistry of basic sills is very similar to that of the tholeiite and meta-diabases in Mianlue ophiolite. Considering the differences in isotopic age of the basic sills (401similar to407 Ma), the extension of Wudang terrain (425similar to260 Ma) and the basic volcanic rocks in Mianlue suitural zone (230 Ma), the authors believe that the basic sills in the western Wudang terrain are the result from the extension and the thinning of the continental lithosphere caused by the activation of the mantal plume, and upwelling of the deep magma. So the basic sills should be a response of the early stage of opening of the Mianlue ocean.

关 键 词：基性岩席群 底侵作用 伸展构造 武当地块 秦岭造山带 

分 类 号：P588.124[天文地球—岩石学] P597[天文地球—地质学]