南祁连造山带新元古代后碰撞岩浆作用:年代学和地球化学证据

Neoproterozoic Post-collision Magmatism in South Qilian Orogen,China:Evidenced by Geochronology and Geochemistry

南祁连造山带南缘乌北地体中的柯柯沙花岗岩岩浆作用记录了中国西北部响应全球Rodinia超大陆汇聚过程中长时间的后碰撞花岗岩岩浆作用历史。柯柯沙花岗闪长岩和二长花岗岩的LA-ICP-MS锆石U-Pb定年获得其锆石结晶年龄分别为(861±9)^(863±4)Ma和(827±6)^(830±8)Ma,变质锆石年龄为(463±3)Ma。结合先期获得的年龄数据,柯柯沙花岗岩体可能为约860 Ma和810~830 Ma的两阶段岩浆作用产物。花岗闪长岩和二长花岗岩分别呈弱过铝质和弱—强过铝质的高钾钙碱性S型花岗岩特征,其岩浆形成于后碰撞阶段的伸展构造环境,源区岩石主要为变质杂砂岩,岩浆部分熔融温度约为800℃,压力在0.9~1.4GPa之间。综上所述,乌北地体主碰撞阶段结束于860 Ma之前。

The protracted post-collisional magmatism in response to assembly of the global Rodinia supercontinent in Northwest China is recorded by the magmatism of Kekesha granite pluton in North Wulan terrane of South Qilian Orogen,China.LA-ICP-MS zircon U-Pb dating yields crystallization ages of(861±9)-(863±4)Ma and(827±6)-(830±8)Ma for Kekesha granodiorites and monzogranites,respectively,with a metamorphic age of(463±3)Ma.Combined with the previous ages,Kekesha granite pluton may be produced by two stages of magmatism around 860 Ma and 810-830 Ma.The granodiorites and monzogranites are characterized respectively by weakly peraluminous and weakly-strongly peraluminous but totally high potassium calc-alkaline S-type granites,and the precursor magma is formed in the extensional tectonic environment of the post-collision stage,and the source rocks are dominantly meta-graywackes with magmatic partial melting temperature of 800℃and pressures of 0.9-1.4 GPa.In conclusion,the main collision phase of North Wulan terrane ends before 860 Ma.