太白岩基巩坚沟变形侵入体LA-ICPMS锆石U-Pb测年及大地构造意义——吕梁运动在北秦岭造山带的表现初探

LA-ICPMS Dating of Zircon U-Pb and Tectonic Significance of Gongjiangou Deformation Intrusions of Taibai Rock Mass,Shaanxi Province— the Primary Study on the Response in North Qinling Orogenic Belt to Lüliang Movement

太白岩基北部的巩坚沟变形侵入体—片麻状中细粒二长花岗岩中获得1741±12Ma的LA-ICPMS单颗粒锆石微区U-Pb同位素年龄;岩石地球化学资料研究证明,巩坚沟片麻状中细粒二长花岗岩形成于板块边缘的俯冲-碰撞构造环境,岩浆源于部分熔融的中上地壳物质。该变形侵入体所代表的热-构造事件与我国的吕梁运动时代大体相当,可能与Columbia超大陆的形成有一定的成因联系。这一新的资料,对研究北秦岭造山带元古宙大地构造格局、构造演化及中国大陆动力学具有重要意义。

Taibai Granitoid Intrusions lying in the northern Shangxian-Danfeng structural belt in North Qiling is a deep and multiple rock mass formed in different ages. The host rocks of Gongjiangou Deformation Intrusions in the north of Taibai rock mass are gneissic adamellites, which intruded into the high-grade basement of Palaeoproterozoic （Qinling rock group）. U-Pb isotope of zircons from gneissic adamellites are determined by LAICPMS in the key laboratory of continental dynamics of Northwest University ,China,and yielded a zircon U-Pb age of 1741 ± 12Ma. The CL characteristics and the ratio of ^207Pb/^206Pb reveal that all zircons came from the same magma. The formed age of gneissic adamellites should be early Mesoproterozoic. According to petrologic and lithogeochemical characteristics,the characteristics of Gongjiangou Deformation Intrusions are most similar to subduction-syncollision granite, and the lithogenous matter might come from the upper crust. Evidences above show that there is a very strong event of thermo-movement early Mesoproterozoic in North Qinliing orogenic belt. The thermo-movement may be the response to I.tiliang Orogen by which the North China Craton formed. This new information is very significant to restudy the geotectonic situation and structure evolvement of Qinliing orogenic belt, and the dynamic mechanism of China continent of proterozoic. It is also very significant for researching the relationship between North Qiling Orogenic Belt and Columbia super continent.