青藏高原祁漫塔格古生代以来主要岩浆活动及其意义

采用LA-ICP-MS方法对青藏高原祁漫塔格山西部枯草沟地区花岗岩和闪长岩进行锆石U-Pb测年,获得405.7±1.3Ma、420.8±1.6Ma、423.9±1.5Ma和421.0±1.7Ma四个年龄,属于晚志留世—早泥盆世。这些锆石具有高Th/U值,是典型的岩浆锆石,其结晶年龄代表岩石形成年龄。综合统计目前已有锆石U-Pb年龄数据表明,该地区主要存在2期岩浆活动:350~500Ma和200~350Ma,分别对应早古生代和晚古生代—早中生代。祁漫塔格早古生代岩浆活动年龄数量占统计的60%以上,为主要岩浆活动期,主要分布于祁漫塔格北部和西部。东昆仑晚古生代—早中生代的岩浆约占古生代以来岩浆总量的77%以上,为东昆仑主要岩浆活动期。祁漫塔格晚古生代—早中生代岩浆活动主要分布于其东南部,靠近东昆仑山,暗示其可能受东昆仑主要岩浆活动的影响。以上结果暗示,早古生代期间祁漫塔格洋的活动性强于东昆仑洋的活动性,祁漫塔格和东昆仑可能自晚古生代以来才逐步形成统一的造山带。

The major magmatic events in the Qimantag Mountain of Tibeatan Plateau since Paleozoic and its implications

In this study, four LA-ICP-MS zircon U-Pb ages (405.7±1.3Ma, 420.8±1.6Ma, 423.9±1.5Ma and 421.0±1.7Ma) were obtained in Kucaogou area, Qimantag Mountain, suggesting Late Silurian to Early Devonian. These zircons with high Th/U ratios are typical magmatic zircons, so these ages can present the granite and diorite petrogenetic ages. In combination with previously published results, the authors hold that two major magmatic events occurred respectively in 350~500Ma and 200~350Ma, corresponding to Early Paleozoic and Late Paleozoic-Early Mesozoic, respectively. The Early Paleozoic magma is the major mag-ma (> 60%), which is distributed in the north and west of the Qimantag Mountain. The major magma in the East Kunlun Mountains, which accounts for over 77% of the magma formed since Paleozoic, occurred during Late Paleozoic-Early Mesozoic. The magma formed during Late Paleozoic-Early Mesozoic and distributed in the southeast Qimantag Mountain is close to the East Kunlun Mountains, which means that this magmatic activity was probably influenced by the magmatic activity of East Kunlun Mountains. These results also imply that the activity of the Qimantag Ocean was stronger than that of the East Kunlun Ocean during Early Paleozoic, and the Qimantag Mountain and East Kunlun Mountains gradually formed a united orogenic belt since Late Paleozoic.