柴达木盆地南缘金水口群的早古生代构造热事件:锆石U-Pb SHRIMP年龄证据

Early Paleozoic tectono-thermal event of the Jinshuikou Group on the southern margin of Qaidam:Zircon U-Pb SHRIMP age evidence

通过柴达木盆地南缘(东昆仑北缘)原定为金水口群麻粒岩相片麻岩和花岗质岩石中锆石的SHRIMP测定,确定其麻粒岩相变质时代为460Ma±8Ma,而具有深熔成因特征的花岗质岩石深熔作用时间为402Ma±6Ma。这些年龄数据表明,金水口群经历了早古生代与麻粒岩相变质和深熔作用有关的构造热事件,原认为是柴达木地块的前寒武纪变质基底明显在早古生代造山过程中发生了活化作用。花岗质岩石的继承锆石给出了少量太古宙和大量1600～1800Ma之间的年龄,代表了其锆石的主要源区物质年龄,这与祁连—柴达木地区以及扬子地块的地壳形成年龄基本一致,反映柴南缘(东昆仑北缘)的变质基底与扬子克拉通具有明显的亲缘性。

Zircon SHRIMP dating of granulite-facies gneiss and granitic rocks of the original Jinshuikou Group on the southern margin of Qaidam(northern margin of the East Kunlun)yielded age of 460±8Ma for the granulite-facies metamorphism and an age of 402±6Ma for the anatexis of granitic rocks with the features of anatectic genesis.These age data suggest that the Jinshuikou Group underwent the early Paleo-zoic tectono-thermal event associated with granulite-facies metamorphism and anatexis.It is evident that the Precambrian metamorphosed basement of the Qaidam block was activated during the early Paleozoic orogeny.The inherited zircon in granitic rocks gave a few Archean ages and a large number of ages in the range between1600and1800Ma ,which represent the age of the main source region of the zircon and are essentially in agreement with the age of formation the crust beneath the Qilian-Qaidam block and even the Yangtze block.This reflects that the metamorphosed basement of the southern margin of Qaidam(northern margin of the East Kunlun)notably has a close affinity to the Yangtze craton.In addition,the association and age of granulite-facies rocks in the Jinshuikou area may be correlated with those on the south slope of the Altyn Tagh(Altun)Mountains.They might belong to the same early Paleozoic gran-ulite belt and are both the product of early Paleozoic collisional orogeny;later they were cut of the Altyn Tagh strike-slip fault.