内蒙古西部苦楚乌拉—英巴地区花岗岩锆石U-Pb定年及地球化学特征

锆石U?Pb定年结果表明,内蒙古西部苦楚乌拉—英巴地区花岗岩包括晚泥盆世二长花岗岩((371±2)Ma)、中二叠世钾长花岗岩((271±1)~(270±1)Ma)和早白垩世二长花岗岩((133±1)Ma)。结合前人资料,将研究区晚古生代以来的酸性岩浆活动分为4期:晚泥盆世(~371 Ma)、晚石炭世(313~311 Ma)、早—中二叠世(282~270 Ma)和早白垩世(133~130 Ma)。地球化学组成上,晚泥盆世二长花岗岩属于非典型的S型花岗岩,反映了一种后碰撞的构造背景,一方面说明珠斯楞—杭乌苏构造带在石炭纪之前已经开始出现岩浆活动,另一方面可能也恰好反映了哈萨克斯坦+塔里木+华北板块与西伯利亚板块拼合时间的下限;中二叠世钾长花岗岩则属A型花岗岩,反映了地壳伸展减薄的构造背景,与同时期区域强烈的拉张构造背景具有良好的对应关系;早白垩世二长花岗岩与晚泥盆世二长花岗岩具有相似的地球化学特征,同样反映了一种后碰撞的构造背景,与同时期区域后碰撞的拉张构造背景一致。

Zircon U-Pb dating and geochemical characteristics of the granites in Kuchuwula-Yingba area of western Inner Mongolia

Zircon U-Pb dating indicates that the granite samples collected from the Kuchuwula-Yingba area of western Inner Mongolia includes the Late Devonian monzonitic granite((371±2)Ma),Middle Permian K-feldspar granite((271±1)-(270±1)Ma)and Early Cretaceous monzonitic granite((133±1)Ma).In combination with the data available,the acidic magmatic activity can be divided into 4 stages:Late Devonian(-371 Ma),Late Carboniferous(313-311 Ma),Early-Middle Permian(282-270 Ma)and Early Cretaceous(133-130 Ma).Geochemically,the Late Devonian monzonitic granites belong to the typical S-type granites,which reflects a post-collisional tectonic setting.On the one hand,these data indicate that magmatic activities occurred before the Carboniferous period in the Zhusileng-Hangwula tectonic zone;on the other hand,they probably exactly reflect the lower limit of the time when Kazakhstan+Tarim+North China plate collided with the Siberian plate.The Middle Permian K-feldspar granites belong to the A-type granites,which reflects a tectonic setting of the crustal extension,having a good correspondence with the strong extension environment of this region in the same period.The geochemical characteristics of the Early Cretaceous monzonitic granites are similar to the features of Late Devonian monzonitic granite,also suggesting a post-collisional tectonic setting in accord with the post-collisional and extensional environment of this region in the same period.