新疆库鲁克塔格新元古代花岗岩年龄和地球化学

本文报道了新疆塔里木北缘库鲁克塔格地区新元古代孤山岩体(或太阳岛岩体)的岩石学、锆石U-Pb年龄及地球化学组成。研究表明:该岩体主要由英云闪长岩、奥长花岗岩及正长花岗岩组成,结晶的时间为795 Ma。其地球化学特征表现为富Na、LREE、LILE及亏损HREE、HFSE,因此具有高的(La/Yb)N及Sr/Y比值,与现代的艾达克岩相似。然而该岩体具有低的Nd初始值及太古代的Nd模式年龄,因此推测其岩浆来自太古代基性下地壳的重熔。鉴于在库鲁克塔格地区发育有800 Ma左右的蛇绿岩,因此我们推测该岩体是碰撞造山引起的加厚的下地壳重熔的结果,代表了塔里木地块前寒武纪基底的最终形成。

Age and geochemistry of Neoproterozoic granite from Kuruketage in the north of Tarim,Xinjiang

Petrography,SHRIMP U-Pb zircon age and systematic geochemistry were studied for the Gushan Neoproterozoic granite from Kuruketage in the north of Tarim Block.The results show that the Gushan pluton is mainly consisted of quartz-biotitediorite,trondhjemite and orthoclase granite,SHRIMP U-Pb zircon dating indicates that the pluton was crystallized at 795 Ma.The rocks are enriched in Na,LREE,LILE and depleted in HREE and HFSE,which led to high LREE/HREE and Sr/Y ratios,showing that they are similar with the modern adakites in characteristics of main and trace elements.Since the rocks have low initial Nd values and Archean Nd model age,the magma is likely derived from the partial melting of Archaean mafic rocks of the lower crust.Considering the occurrence of ophiolites with the age of 800 Ma in this area,it is inferred that the Gushan pluton was formed by thickened lower crust remelting resulted from collision orogenic movement and represents the solidification of the Precambrian basement of the Tarim Block.