内蒙古苏左旗地区闪长-花岗岩类SHRIMP年代学

SHRIMP Dating of Diorites and Granites in Southern Suzuoqi,Inner Mongolia

本文对内蒙古苏左旗地区的闪长 -花岗岩类进行了精确的 SHRIMP定年研究。研究表明 ,富钠的白音宝力道岩体是一个多期次侵入的复合岩体 ,主体可能是 4 90～ 4 6 4 Ma之间侵位的 ,推测是洋壳俯冲的产物 ;随后在 4 2 4 Ma左右该地区发生了板块的碰撞事件 ,产生具高钾钙碱性系列的花岗岩。该区富钾的包尔汗喇嘛庙岩体本次得到的 SHRIMP年龄为 2 2 2～ 2 0 4 Ma,表明其在晚三叠世侵位 ,可能代表了造山期后的岩石圈拆沉事件。

High-precision SHRIMP U-Pb zircon dating of the Suzuoqi diorites and granites are reported. The analysis indicate that the Baiyinbaolidao Na-rich granitoids were formed at 464±8Ma ～ 479±8Ma. The geochemical characteristics of the Baiyinbaolidao Na-rich granitoids are similar to those of typical adakites that may represent the subduction of the oceanic crust. It is suggested that the subduction event of the Inner Mongolia took place in the Early Ordovician. The Baiyinbaolidao high-K granites whose geochemical characteristics are similar to those of the post-collisional high-K granites were formed at 423±8Ma ～ 424±10Ma, the results indicate that the collisional event of the Inner Mongolia took place in the Early Silurian after the subduction event in the Early Ordovician. The formation of Baoerhanlabamiao high-K granites in the Late Triassic (220Ma～204Ma) was related to post-orogenic processes, most probably due to lithospheric delamination.