内蒙古克什克腾旗广兴源复式岩体SHRIMP U-Pb定年及地质意义讨论

摘要

广兴源复式岩体位于内蒙古东部西拉木伦河上游地区,岩体主体由二长岩、二长花岗岩、花岗岩和花岗闪长岩构成,边部有少量二长辉长岩和闪长岩出露.岩体地球化学特征表明其属于火山弧环境;对岩体早期的二长岩和侵位于二长岩的花岗闪长岩进行锆石SHRIMP U-Pb定年,分别得到206Pb/238U加权平均年龄为 263.8±2.1Ma和263.3±2.5Ma,属中-晚二叠世.本研究显示中-晚二叠世古亚洲洋东南缘俯冲于华北古板块之下,并在华北板块北缘形成火山-岩浆岩弧环境.至早-中三叠世,华北古板块北缘和西伯利亚古板块南缘发生碰撞造山.%The Guangxingyuan composite pluton is located at the upper reaches of Xar Moron River, Inner Mongolia. It is composed mainly of monzonite, monzogranite, granite, and granodiorite with minor amount of monzogabbro and diorite exposed at edges. Its geochemistry is characterized by the typical volcanic-magmatic arc environment. High-precision SHRIMP U-Pb zircon dating was carried out on early monzonite and granodiorite intruding the monzonite, and yielded 206Pb/238U weighted mean ages of 263.8±2.1Ma and 263.3 ±2.5Ma, respectively, suggesting a Mid-Late Permian age. These data demonstrate that the southeastern margin of the Paleo-Asian Ocean crust subducted southward beneath the North China Craton during the Mid-Late Permian, resulting in a volcanic-magmatic arc environment at the northern margin of the North China Craton, which was followed by collisional orogensis between the northern paleo- North China plate's margin and southern Siberia Craton in Mid-Early Triassic.