内蒙古突泉—科尔沁右翼中旗地区中生代花岗岩锆石U-Pb年龄及其地质意义

Zircon U-Pb Ages and Its Geological Implication of Mesozoic Granites in Tuquan-Keerqin Youyizhongqi Region

内蒙古突泉—科尔沁右翼中旗地区位于大兴安岭中南段,中生代岩浆活动较为频繁,岩浆作用形成的岩石类型主要包括花岗闪长岩、正长花岗岩、二长花岗岩和花岗斑岩等。鉴于目前研究区地质资料缺乏对整个突泉—科右中旗地区中生代花岗岩较为完善的研究和论述,笔者旨在对全区范围内的中生代花岗岩进行LA-ICP-MS锆石U-Pb年龄测定,同时在总结前人资料的基础上划分该地区不同的中生代岩浆作用期次,进而讨论本区不同花岗岩所代表的地质意义。花岗岩锆石U-Pb年龄测试结果表明,孟恩陶勒盖花岗闪长岩的形成时代为(241.2±2.8)Ma,杜尔基镇南部正长花岗岩的形成时代为(148.2±1.0)Ma,宝格吐岩体的花岗闪长岩的形成时代为(226.0±1.1)Ma,马家屯花岗斑岩的形成时代为(124.6±1.1)Ma,这与广泛分布于本区中生代火山岩的形成时代较为一致。结合前人研究成果以及邻区的地质资料,认为本区岩浆活动可以划分为中—晚三叠世、晚侏罗世和早白垩世;中—晚三叠世花岗岩可能属于古亚洲洋闭合造山后岩石圈伸展作用的产物,而晚侏罗世花岗岩的形成可能与中侏罗世蒙古—鄂霍茨克洋闭合后岩石圈伸展作用有关,早白垩世花岗岩可能反映了板内拉张的构造背景。

Tuquan-Keerqin Youyizhongqi of Inner Mongolia is located in the central and southern Da Hinggan Range,where the Mesozoic magmatic activity was frequent.The rocks are mainly composed of granodiorite,syenite,monzonitic granite,and granite porphyry etc.We studied the Mesozoic granites in the whole area to obtain the related geological data,tested the LA-ICP-MS zircon U-Pb age,divided the different Mesozoic magmatism periods on the basis of the predecessors’ data,and then discussed the geological significance of the different granites in this area.Several samples of the three magmatic intrusive rocks from this region were dated by the LA-ICP-MS technique.The result indicates that the granodiorite of Mengentaolegai pluton was emplaced at（241.2±2.8）Ma,the syenite in the southern Duerji was emplaced at（148.2±1.0）Ma,the monzonitic granite of Baogetu pluton was emplaced at（226.0±1.1）Ma,and the granite porphyry of the Majiatun pluton was emplaced at（124.6±1.1）Ma,corresponding to the ages of the volcanic rocks respectively.Combining with the previous and adjacent geological data,we divided the magmatic activity into three periods： Middle-Late Triassic,Late Jurassic,and Early Cretaceous.We conclude that the Middle-Late Triassic granites may be the product of the post-orogenic lithospheric extension of the Paleo-Asian Ocean closure,and the formation of the Late Jurassic granites may be related to the Mongol-Okhotsk Ocean closure;while the Early Cretaceous granites might reflect the extensional tectonic setting.