东昆仑前寒武纪基底变质岩系的锆石SHRIMP年龄及其构造意义

东昆仑地区有一系列前寒武纪变质基底岩系出露 ,这些基底岩块可以划分为两类 :北部基底以太古宙—古元古代的白沙河岩群和中元古代的小庙岩群为代表 ,南部基底以古、中元古代苦海杂岩为代表。对北部基底岩系小庙岩群变质碎屑岩系的锆石U PbSHRIMP年龄分析结果显示小庙岩群(Pt2 x)碎屑物源区是年龄大于 2 4亿年的岩石 ,2 4～ 2 5亿年的碎屑锆石的群组年龄很可能反映了小庙岩群源区的一期变质作用时间。个别 32亿年的碎屑锆石年龄指示源区存在古太古代的陆核。变质锆石及深熔成因的锆石给出的 10 35～ 10 74Ma群组年龄是小庙岩群的主期构造热事件时间 ,反映以清水泉蛇绿岩为代表的中元古代洋盆的闭合和南北不同基底块体的愈合 ,是Rodinia大陆聚合事件在东昆仑地区的表现。

Zircon SHRIMP ages of Precambrian metamorphic basement rocks and their tectonic significance in the eastern Kunlun Mountains, Qinghai Province, China

There are some fragmentary Precambrian basement rocks exposed in the Eastern Kunlun Mountains, which can be divided into two different kinds of basement blocks. The north basement is composed of Archean-Paleoproterozoic Baishahe Group and Mesoproterozoic Xiaomiao Group, and the south basement is composed of Paleoproterozoic-Mesoproterozoic Kuhai Group. The U-Pb SHRIMP age dating to the metamorphic detrital rocks of the Xiaomiao Group in the north basement shows that the provenances of the detrital rocks of the Xiaomiao Group are older than 2 400 Ma. The age dating gives a peak age of about 2 400～2 500Ma, reflecting a metamorphic thermal event in the source area. One detrital zircon yields~(207)Pb/~(206)Pb age of (3 206±14) Ma, showing the existence of Paleoarchean continental nucleus in the source area. The metamorphic zircon and anatectic zircon give an age group of 1 035～(1 074) Ma, showing the principal metamorphism and extensive tectonic-thermal event of the Xiaomiao Group and reflecting the collision event of the north and south blocks during the sealing of the Mesoproterozoic ocean, which is implied by the Qingshuiquan ophiolite. This event is accordant with the formation of the Rodinia supper continent, suggesting that the extensive ductile shearing and anatexis of the basement rocks in the Eastern Kunlun are the representation of the convergence of the Rodinia continent.