湖南九嶷山复式花岗岩体SHRIMP锆石定年及其地质意义

应用SHRIMP锆石U-Pb法获得九嶷山复式花岗岩中的主要岩体形成年龄为:雪花顶花岗岩(432±21)Ma、金鸡岭花岗岩(156±2)Ma、砂子岭花岗岩(157±1)Ma和西山火山-侵入杂岩(156±2)Ma。结果显示砂子岭岩体属燕山早期而非印支期;西山火山-侵入杂岩属燕山早期而非燕山晚期。花岗岩中继承锆石复杂,其形成时代为1579Ma、2108Ma和2669Ma,提供了九嶷山地区存在古-中元古代,甚至太古代基底的年龄信息。新元古代(912Ma)锆石的大量出现为扬子陆块和华夏陆块碰撞带通过本区的认识提供了一个间接证据。

SHRIMP U- Pb ZIRCON DATING OF THE JIUYISHAN COMPOSITE GRANITE IN HUNAN AND ITS GEOLOGICAL SIGNIFICANCE

The SHRIMP (sensitive high resolution ion microprobe) zircon U-Pb method was used to determine the ages of main rock masses in the Jiuyishan composite granite, Hunan Province. The Xuehuading granite was dated at 432±21 Ma, the Jingjiling granite, 156±2 Ma, the Shaziling granite, 157±1 Ma, and the Xishan volcanic-intrusive complex, 156±2 Ma. The results show that the Xuehuading granite and the Jingjiling granite belong to Caledonian epoch and early Yanshanian epoch, respectively, and the Shaziling granite and the Xishan volcanic-intrusive complex, which were originally considered to be of Indosinian epoch and late Yanshanian epoch, respectively, actually belong to the early Yanshanian epoch, too. The inherited zircons of 1579 Ma, 2108 Ma and 2669Ma suggests that there were derived from the Paleo-Mesoproterozoic or Archean basement crust. The formation event of lots of early Neoproterozoic (912 Ma) zircons is an indirect evidence that the collisional belt between the Yangtze block and the Cathaysia block passed through the studied area.