藏西措勤含铜岩系的物质来源与成因

The Material Source and Genesis of Copper-Bearing Bimodal Rock Series in Coqin County, Western Tibet

青藏高原中西部措勤县城东南（约100km）的日阿铜矿区发育两种矿化类型,一种是与二长花岗斑岩岩株有关的夕卡岩型铜矿化,另一种是与辉绿玢岩岩脉有关的细脉浸染型铜矿化。Nd、Sr同位素分析表明,它们以高87Sr/86Sr比值,低^143Nd/^144Nd比值和负εNd（t）为特征,清楚地显示出地壳组分的特点;Pb同位素则以富含放射性成因Pb为特征,^206Pb/^204Pb,^207Pb/^204Pb,^208Pb/^204Pb比值分别为18.672~18.926,15.630~15.685和39.018~39.432,显示出俯冲板片组分在岩浆形成过程中的作用。Nd、Sr、Pb同位素分析表明,它们形成于碰撞后伸展环境。在该环境下,富集的大陆岩石圈地幔发生部分熔融形成的具OIB特征的镁铁质岩浆底侵与地壳岩石相互作用形成了措勤含铜岩系。这个岩系产生于拉萨地块内,从俯冲带演化历史来看,它与南部的印度河-雅鲁藏布江洋壳的俯冲无关,而是北部班公湖-怒江洋壳向南俯冲的结果。

Ri＇a copper deposit southeast （about 100km） of Coqin county in western central Tibetan plateau includes two mineralization types. One is skarn-type copper mineralization related to adamellite stocks, and the other is veinlet-disseminated copper mineralization related to diahase dyke. They are copperbearing bimodal rock series. Nd and Sr isotope analysis shows that they are characterized as high ^87 Sr/^86 Sr ratio, low ^143Nd/^144 Nd ratio and negative εnd （t）, which clearly indicate crustal component feature. Pb isotope is characterized as rich radioactive Pb, and ^206Pb/^204 Pb,^207 Pb/^204 Pb,^208Pb/^204 Pb ratios are respectively 18. 672~18. 926,15. 630~15. 685 and 39. 018~39. 432, which indicate the role of subduction component during magmatic process. Nd, Sr and Pb isotope analysis shows that these bimodal series is formed under post-collisional extensional environment. Rich continental lithosphere mantle was subjected to partially melting to generate mafic magma with OIB features. The mafic magma intruded and interacted with crustal rocks at different depth to form Coqin copper-bearing bimodal rocks. These bimodal series is located in Lhasa terrain. Seeing from the evolution histories of suhduction zones, the author thinks that these bimodal series is not related to the subduction of southern India-Yaluzangbu ocean crust, but related to south subduction of Bangonghu-Nujiang ocean crust beneath the Lhasa terrane.