鄂尔多斯盆地变质基底中碎屑锆石的 LA-ICP-MS U-Pb 年龄及其构造意义

摘要

根据鄂尔多斯盆地东北部钻孔的资料显示，鄂尔多斯盆地基底主要由一套变质沉积岩组成，对其中的二云母斜长片麻岩和矽线石片麻岩样品进行 LA-ICP-MS 锆石 U-Pb 年代学研究，两件样品单颗粒碎屑锆石共获得96个具有地质意义的年龄资料。二云母斜长片麻岩的部分锆石显示清晰的韵律环带，具有岩浆锆石的特征，其获得的207 Pb／206 Pb 年龄介于1898．2～2047．2Ma 之间，综合前人的研究数据，显示鄂尔多斯盆地基底东北部在古元古代2．0～2．1Ga 左右曾有岩浆活动。二云母斜长片麻岩的部分锆石和矽线石片麻岩的锆石具有变质锆石特征，获得的变质锆石年龄数据支持鄂尔多斯盆地东北部在古元古代发生过两期变质作用，早期的变质作用峰值年龄约为1．83Ga，代表着东部陆块和西部陆块碰撞拼合这期构造事件；晚期变质作用发生在约1．78Ga，可能记录了这一阶段的拉张抬升事件。%Basement rocks from drill cores at the northeastern margin of the Ordos Basin are mainly composed of meta-sedimentary rocks.LA-ICP-MS U-Pb zircon dating was conducted on two basement metamorphic rocks and yielded 96 valid data.A two-mica plagiogneiss yielded a restricted range of the magmatic zircon ages from 1898.2 Ma to 2047.2 Ma,which suggest the possible existences of a Paleoproterozoic intensive magmatic episode.A two-mica plagiogneiss and a sillimanite gneiss were overprited by two metamorphic events at ca.1.83Ga and ca.1.78Ga.The ages and characters of the zircons indicate that the basement of the northeastern Ordos Basin had undergone two metamorphic events at Late Paleoproterozoic.The ca. 1.83Ga metamorphic event indicates the northeastern Ordos Basin joined the final amalgamation of the NCC,while the ca.1.78Ga was probably a result of terrane uplift or regional extension.