北秦岭西段冥古宙锆石(4.1～3.9Ga)年代学新进展  

In situ U-Pb geochronology of Hadean zircon xenocryst(4.1～3.9Ga) from the western of the Northern Qinling Orogenic Belt

作　　者：第五春荣[1] 孙勇[1] 董增产[1] 王洪亮[1] 陈丹玲[1] 陈亮[1] 张红[1] 

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,西安710069

出　　处：《岩石学报》2010年第4期1171-1174,共4页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40773044;40902056);西北大学大陆动力学国家重点实验室科技部专项联合资助

摘　　要：2007年王洪亮等报道在北秦岭西段火山岩中获得一粒年龄为4079±5Ma的冥古宙捕虏锆石。之后,对这一发现开展了深入的调查研究,我们除利用SHIMP技术方法对原4079Ma的锆石进行验证外,新获得了两粒^(207)Pb/^(206)Pb年龄为4007±29Ma和3908±45Ma捕获的变质成因锆石,表明早在4.0Ga已经有变质作用的发生,这或许说明在冥古宙时期地球已经具有相当规模和厚度的地壳。同时开展的岩石学研究表明,蕴含古老锆石的母岩属于火山碎屑熔岩类而不是火山熔岩。One zircon xenocryst with a concordant ^(207)Pb/^(206)Pb age of 4079±5Ma was reported by Wang et al.(2007) from volcanic rocks in the western of the Northern Qinling Orogenic Belt.In recent study on those old xenocrysts,about 3,000 zircon grains are separated from the same rock outcrop and have been analyzed by LA-ICPMS.Two metamorphic zircon xenocrystic cores gave concordant ^(207)Pb/^(206)Pb ages of 4008±29Ma and 3908±45Ma,respectively.The occurrence of 4.0Ga metamorphic zircon provided evidence that the metamorphism occurred as old as 4008Ma.The lithologic characteristics of the host rocks contain Hadean zircons are clearly defined as pyroclastic lava,not volcanic lava,as previously believed.

关 键 词：冥古宙 锆石 火山岩 北秦岭造山带 变质作用 

分 类 号：P597.3[天文地球—地球化学]