内蒙古科尔沁右翼中旗三叠纪花岗质岩锆石U-Pb年龄、地球化学特征及其地质意义

笔者对内蒙古科尔沁右翼中旗代钦塔拉地区出露的花岗质岩进行了锆石U-Pb定年和岩石地球化学研究,旨在探讨该区花岗岩成因类型和区域构造演化。研究区的花岗质岩主要以黑云母花岗岩和花岗闪长岩为主,岩石明显富SiO2、Al2O3和碱质,属于过铝质高钾钙碱性系列的S型花岗岩;稀土元素标准化配分图总体呈轻稀土富集、重稀土亏损特点,LREE/HREE的值为3.12~16.17,平均为10.07;LaN/YbN为2.72~28.71,具中等程度的负Eu异常;岩石富集大离子亲石元素Rb、K、Pb,亏损高场强元素Nb、Ta、Zr、Ce、Ti,具碰撞型花岗岩的特征。依据地球化学特征可将花岗岩划为低Sr低Yb型,说明花岗岩可能是在较高的压力下形成的。锆石U-Pb年龄为(242.6±2.5)Ma,表明该区古亚洲洋的俯冲碰撞发生在三叠纪,花岗岩体的形成与碰撞拼合有关。

Zircon U Pb Age,Geochemical Characteristics and Geological Significance of the Triassic Granite in Keerqinyouyizhongqi,Inner Mogolia

Based on the Zircon U Pb dating and geochemical data obtained for the granite in Keerqinyouyizhongqi Inner Mongolia,we discussed the granite types and regional tectonic evolution. The biotite granite and granodiorite are mainly developed in the area.They are enriched in SiO2 ,Al2 O3 , and alkali,and belong to high potassium peraluminous calc-alkaline series of S type granite.The rare earth element normalized distribution diagram shows that LREE are highly concentrated,while HREE are relatively depleted with the ratio of LREE/HREE between 3.12 and 1 6.17,an average of 10.07;the ratio of LaN and YbN is between 2.72 and 28.71,Eu anomaly is moderate negative;enrichment of rock large ion lithophile Rb,K and Pb,depletion of high field strength elements Nb,Ta,Zr,Ce,Ti,the feature of collision type granite.These granitics could be distinguished by their low-Sr and low-Yb based on the geochemical characteristics,which shows that the granitics are likely formed under high pressure. The Zircon U Pb age (242.6 ± 2.5 )Ma,suggests that the paleo Asian Ocean subduction collision occurred in Triassic period,the formation of granite rock mass related to the collision split.