湘南西山花岗质火山-侵入杂岩形成时代的确定

The Determination of the Formation Ages of the Xishan Volcanic-Intrusive Complex in Southern Hunan Province

湖南南部西山火山 侵入杂岩中 3个代表性岩石单元 (花岗岩、碎斑熔岩和流纹岩 )的产状、岩石化学、微量元素和同位素地球化学特征显示 ,它们同空间、同物质来源。全岩Rb Sr定年结果表明 :花岗岩、碎斑熔岩和流纹岩的形成时代分别为15 6± 6Ma、15 9± 2Ma和 15 4± 11Ma ,87Sr/86Sr初始值分别为 0 .71779、0 .71738和 0 .71774 ,其中碎斑熔岩的锆石SHRIMP定年结果为 15 6± 2Ma ,它们在误差范围内基本相同 ,为中侏罗世晚期同一构造岩浆事件中陆壳活化的产物。

The occurrences, geochemistry and trace element and isotopic characteristics of three representative rock units, namely granite, clastoporphyritic lava and rhyolite, in Xishan granitic volcanic-intrusive complex of southern Hunan, indicate that they have identical space and material resources. The whole rock Rb-Sr dating shows that the ages of these three units are 156±6 Ma,159±2 Ma and 154±11 Ma, respectively, and the zircon SHRIMP age of the clastoporphyritic lava is 156±2 Ma. These age data show that the Xishan complex was formed almost at the same time, and might have been the late stage product of the Middle Jurassic magmatism.