从矿物包裹体类型、特征探讨“三江”地区川西段花岗岩的成因

DISCUSSING ON THE GENESIS OF THE GRANITES IN THE NUJIANGLANCANG-JINSHA RIVERS AREA OF W.SICHUAN BASED ON THE MINERAL INCLUSION

本文通过对"三江"地区川西段花岗岩类三个构造岩浆岩带内的花岗岩中包裹体类型、特征及成岩温度的研究,进一步探讨上述各带花岗岩的不同成因。东带侵入岩中以晶质熔融包裹体为主,流纹岩中以玻璃包裹体为主,说明东带为壳幔混源的同熔型花岗岩。中带以陆壳改造型花岗岩为主,除熔融包裹体外,出现大量气液包裹体,对成矿有利。在含锡钾长花岗岩和二长花岗岩中,气体包裹体和液体包裹以及高盐度含 NaCl子矿物包裹体常常共存且均一温度接近。表明该地区锡(多金属)成矿作用来自于含矿热液流体的多次沸腾。中带措莫隆岩体中黑云斑状花岗岩石英中的副矿物锆石同时捕获先形成的浑圆状锆石和结晶完好的锆石作为包裹体,充分说明该岩体为陆壳改造型花岗岩。西带花岗岩为花岗岩化交代成因。包裹体类型以液体包裹体为主。其均一温度为花岗岩化形成的典型岩石的成岩温度。

The Renesis of the granites is herein addressed on the basis of the study of inclusion types,characteristics and diagenetic temperatures ot the granites from three tectonic-magmatic zones in the Nujiang-Lancang-Jinshan rivers area of western Sichuan.The crystalline melting in- clusions predominate in the intrusive rocks,and the glass inclusions appear mostly in the rhyolites in the eastern zone.In the middle zone,abundant fluid inclusions,besides the melting inclusions, occur in the continental crust-reworking granites,which is believed to be favourable for minera- lization.The gas inclusions,fluid inclusions and high-salinity NaCl-bearing daughter mineral inclu- sions often coexist in the Sn-bearing moyite and adamellite,with approximate homogenization tem- peratures.It is implied that the Sn(polymetallic)mineralizantion resulted mainly from the multi- stage boiling of the ore-bearing hydrothermal fluids.The pre-existing well-rounded zircon and well-crystallized zircon are simultaneously trapped as the inclusions in the accessory mineral zir- con from biotite porphyritic granites in the Comolong rock body.It is indicated indicating that the rock should be described as the continental crust-reworking granites;the granites were granitized replacement origin in the western zone,and mainly comprise the fluid inclusions whose homoge- nization temperatures are characteristic of the rock formed through granitization.