大兴安岭中部乌兰浩特地区中生代花岗岩的锆石U-Pb年龄及地质意义

Zircon U-Pb ages and its significance of the Mesozoic granites in the Wulanhaote region, central Da Hinggan Mountain.

大兴安岭中生代花岗岩浆作用的时间和期次的确定对讨论东北地区中生代的构造-岩浆演化具有重要意义。本文采用激光ICP-MS技术进行锆石U-Pb年龄测定的结果表明,大兴安岭中部乌兰浩特-索伦地区的中生代花岗岩浆活动可以划分为3期:中-晚三叠世花岗岩岩浆侵位结晶年龄为235-225Ma;早-中侏罗世花岗岩岩浆侵位结晶年龄为182-175Ma;早白垩世花岗岩岩浆侵位结晶年龄为140-125Ma,与该区广泛分布的中生代火山岩时代一致。该区花岗岩的年代学格架与松辽盆地东缘的张广才岭-小兴安岭地区完全可以对比。花岗岩中的捕获锆石具有与额尔古纳地块新元古代花岗岩一致的的年龄信息(-800Ma),反映该区曾经具有前寒武纪结晶基底。结合岩石学特征和邻区的其它地质资料,该区三叠纪花岗岩的形成可能与古亚洲洋闭合造山后的岩石圈伸展体制有关,侏罗纪花岗岩可能是佳木斯地块西缘洋壳俯冲及与松嫩地块拼合作用的产物,而早白垩世花岗岩的形成则与板内拉张性构造体制有关。

The timing and stages of the Mesozoic granites in the Da Hinggan Mountain is the key to the tectonic and magmatic evolution of Northeast China. In this paper, we present new zircon U-Pb age data of granites using laser ablation ICP-MS technique.The result shows three stages of granites in the Wulanhaote-Suolun region, central Da Hinggan Mountain, i. e. , Middle to Late Triassic granites （235 -225 Ma） , Early to Middle Jurassic granites （ 182 - 175 Ma） and Early Cretaceous granites （ 140 - 125 Ma） , which are consistent with the stages of volcanic rocks. This geochronological framework is also comparable to that in the Zhangguangcai-Lessor Hinggan Mountain in the east to the Songliao Basin. The identification of -800 Ma inherited zircons, consistent with Neoproterozoic granites in Eguna block, suggests that there existed Precambrian basement in this region. Considering their petrography and geological data of adjacent regions, we propose that the formation of Triassic granites is related to post-orogenic lithospheric extension after closure of the Paleo-Asian Ocean, Jurassic granites are results of subduction of oceanic plate in the western Jiamusi block and assembly of Jiamusi and Songnen blocks, while, Early Cretaceous granites are product of intra-plate extension.