北大巴基性岩墙群地球化学特征、LA-ICP-MS锆石U-Pb定年及其大地构造意义

北大巴地区广泛分布了呈北西-南东向产出的基性岩墙群，主要侵位于下古生界。对该套岩系的地球化学分析表明，w（K2O＋Na2O）、w（TiO2）高，总稀土元素质量分数高并呈轻稀土元素富集型，大离子亲石元素明显富集，Ta、Nb的质量分数远高于洋中脊玄武岩，具大陆裂谷玄武岩的地球化学特征。采用LA-ICP-MS法对北大巴基性岩墙中的岩浆锆石进行了U—Pb同位素定年，获得岩体结晶年龄为（431．0＋3．2）Ma。地球化学及年代学数据表明，北大巴基性岩墙群具有大陆裂谷玄武岩的地球化学特征，表明北大巴早古生代伸展构造受到扬子板块北缘的幔源裂谷作用制约。在裂谷演化过程中，上地幔物质上涌造成岩石圈板块拉伸减薄，使北大巴地区中上地壳发生强烈构造伸展并形成大面积呈线状分布的基性岩墙群，并且该处（431．0±3．2）Ma的年龄值代表了在早志留世北大巴裂谷盆地的伸展裂陷幅度达到最大。

Geochemistry and LA-ICP-MS Zircon U-Pb Age of Basic Dike Swarms in North Daba Mountains and Its Tectonic Significance

Basic dike swarms are widely distributed NW-SE,intruding the Early Paleozoic strata in North Daba Mountains.The geochemistry analysis show that this rock series share similar characteristics of the average mass fraction of continental rift basalt.It is sound that K 2O+Na 2O is concentrated in the major elements with high TiO 2 and rare-earth content.Also the general high rare-earth content is associated with high concentration of light rare-earth and the incompatible large-ion lithophile elements,while the ...