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.