桐柏地区秦岭岩群中碱性脉岩的锆石U-Pb年龄:对麻粒岩相变质时代的约束  

Zircon U-Pb ages of alkaline dykes from the Qinling Group in the Tongbai area,central China:Constraints on the timing of granulite-facies metamorphism

作　　者：曲玮[1] 刘晓春[1] 胡娟[1] 李怀坤[2] 耿建珍[2] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]中国地质调查局天津地质调查中心,天津300170

出　　处：《岩石学报》2013年第9期3080-3086,共7页Acta Petrologica Sinica

基　　金：国家973计划项目(2009CB825006)资助

摘　　要：由于前人在桐柏地区秦岭岩群高级变质岩石中获得的变质年龄比较分散,所以有关麻粒岩相变质作用的时代问题存在不同的认识。本文使用LA-MC-ICPMS方法对侵入于秦岭岩群中的弱变形和未变形碱性岩脉进行了锆石U-Pb定年,获得其侵位时代分别为429.9±1.5Ma和430.3±1.3Ma。结合区域上已发表的同位素年代学资料,我们推测,秦岭岩群麻粒岩相变质作用发生于约440~430Ma,与华北陆块南缘的弧-陆碰撞作用有关。碰撞后的岛弧岩浆作用主要发生在约430Ma,从而造成了秦岭岩群的缓慢冷却,这可能是麻粒岩相变质锆石的同位素年龄比较分散的主因。Since the age data obtained for metamorphic zircons from high-grade rocks in the Qinling Group, the Tongbai area, are scattered, there has been a debate on the timing of granulite-facies metamorphism. In this paper a weakly deformed and undeformed alkaline dykes intruded in the Qinling Group were dated using LA-MC-ICPMS zircon U-Pb dating method. The emplacement ages obtained for these two dykes are 429.9 ＋ 1.5Ma and 430. 3 ＋ 1.3Ma, respectively. Coupled with the published geochronological data in the area, we infer that granulite-faeies metamorphism in the Qinling Group took place at ca. 440 -430Ma, which is triggered by the arc-continent collision in the southern margin of the North China Block. Post-collisional arc magmatism occurred mainly in ca. 430Ma. This widespread intrusive event may have resulted in the slow cooling of the Qinling Group, and therefore caused scattered age data of granulite-faeies metamorphic zircons.

关 键 词：麻粒岩 碱性脉岩 锆石U-PB年龄 古生代 桐柏地区 

分 类 号：P588.133[天文地球—岩石学] P597.3[天文地球—地质学]