粤西合水、思贺地区花岗质岩石的成因

本区花岗岩的成因问题,存在着三种意见,作者根据区域地质调查获得的新资料,认为它是加里东期同构造花岗岩侵入体,主要依据是:它侵入震旦系云开群变质岩中,接触关系及界线很清楚;岩体有宽大的内部相和很窄的边缘相;岩体外围有角岩类组成的接触变质带。岩石具有同构造碎裂—花岗结构、片麻状构造,岩石化学成分稳定,据各种投影与图解结果,证明它属于岩浆型花岗岩。对晶形完好和浑圆状二种锆石,经分析其化学成分相同;采用 U-Pb法测定的年龄值,分别为469Ma 及461Ma,说明它们均形成时代基本相同。

ORIGIN OF GRANITIC ROCKS IN THE HESHUI-SIHE AREA,WESTERN GUANGDONG

There exist three different views about the origin of granites in theHeshui-Sihe area,western Guangdong.According to the new data obtainedthrough regional geological surveys in recent years,the authors consider thatthey are Caledonian syntectonic granites.The main grounds are as follows:they are intruded into the metamorphic rocks of the Sinian Yunkai Group,both showing a very clear contact relationship and boundary.The intrusionexhibits a wide core facies and very narrow border facies.Around the intrusionthere is a contact metamorphic zone composed of hornfels.The rocks exhibit asyntectonic clastic-granitic texture and a gneissic structure.The petrochemicalcomposition is persistent.Various projections and diagrams demonstrate thatthey belong to magmatic granites.Analysis shows that the perfect zircon crystaland rounded zircon crystal have the same chemical composition.Their agesdetermined by using the U-Pb method are 469 Ma and 461 Ma respectively,suggesting that the two kinds of zircon essentiallyhave the same formation age.