石尖山花岗岩体的锆石U——Pb年代学意义——对古亚洲洋闭合时间的制约

UPb Zircon Chronology of Shijianshan Granite——Constraints to Closing Time of the Paleo-Asian Ocean

摘要:

古亚洲洋通过板块俯冲而闭合后，形成规模巨大的中亚造山带，石尖山花岗岩体位于中亚造山带东段中部，是石尖山地区出露面积最大的侵入岩体，为了研究该地区构造演化特征，探讨该地区古亚洲洋的闭合时间，本次研究应用激光剥蚀-电感耦合等离子体质谱法，对石尖山花岗岩体进行了锆石UPb同位素测年，获得岩体同位素年龄（230.9±2.6）Ma和（231.5±2.5）Ma；同时，作者对该花岗岩体的地球化学特征及形成的构造环境进行了分析探讨，分析表明石尖山花岗岩形成于造山晚期-造山后过渡的拉伸环境。综合上述研究，石尖山花岗岩体为中三叠世结晶成岩，是造山活动末期的拉伸环境产物，反映了内蒙古石尖山地区古亚洲洋最可能闭合于晚二叠世—早三叠世。

Abstract:

Shijianshan granite is located in the middle of east part of the Central Asian orogenic belt. It is the largest intrusive rock in Shijianshan area. In order to study the tectonic evolution and the closure time of Paleo-Asian Ocean in the area, by using the laser ablation inductively coupled plasma mass spectrometry, zircon U Pb isotopic dating of Shijianshan granite has been carried out. The isotopic ages of the granite body are （230.9±2.6）Ma and （231.5±2.5）Ma. Meanwhile, geochemical characteristics and tectonic setting of the granite body have been discussed. As showed by the analysis, Shijianshan granite is formed in the extensional environment of late orogenic post orogenic transition. Based on the above study, Shijianshan granite is a product of extensional environment at the end of orogeny, which indicates that Paleo-Asian Ocean in Shijianshan area of Inner Mongolia is most likely closed in late Permian—early Triassic.