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在1∶25万区域地质调查工作的基础上,对出露于西盟县新厂乡一带的曼亨花岗岩进行了岩石地球化学和精确的成岩年代学研究。岩石中w(Si O2)为72.73%~77.24%,w(K2O+Na2O)=4.28%~9.01%(平均7.38%),w(K2O)/w(Na2O)=0.65~20.84(平均2.67),显示高硅和富碱的特点。标准矿物计算结果具较高q值,并出现较高c分子,标准矿物组合为c+q+or+ab+an+hy,属于铝、硅过饱和系列。岩石的A/NCK为1.05~2.66(平均1.29),属S型花岗岩。LA-ICPMS锆石U-Pb测年结果,显示曼亨花岗岩结晶年龄为446.1±2.5 Ma,表明该岩体形成于晚奥陶世。综合研究认为该期花岗岩具有同碰撞岩浆活动的特征,是泛非运动晚期冈瓦纳大陆汇聚过程其外围地区板块持续相互碰撞、造山作用的产物。
Based on 1: 250,000 regional geological survey work, petrological and precise diagenetic geochronology of manhng granite exposed in Xinchang Township, Ximeng County was conducted. (Si02) is 72.73% ~ 77.24%, w (K2O + Na2O) is 4.28% ~ 9.01% (average 7.38%) and w2O5 is 0.65 ~ 20.84 (average 2.67) High silicon and alkali-rich features. The standard mineral calculation results have higher q values and higher c molecules, and the standard mineral combination is c + q + or + ab + an + hy, belonging to the supersaturated series of aluminum and silicon. Rock A / NCK 1.05 ~ 2.66 (average 1.29), is a S-type granite. LA-ICPMS zircon U-Pb dating results show that the Manchurian granite age is 446.1 ± 2.5 Ma, indicating that the rock body formed in the Late Ordovician. The comprehensive study shows that the granites in the period have the characteristics of co-collision magmatism and are the products of continuous collisions and orogenies in the peripheral areas of the Gondwanaland during the Pan-African Movement.