摘要
基于1：50000区域地质调查工作，在内蒙古乌兰五台地区识别出铝质A型花岗岩。通过研究该套斑状二长花岗岩LA-ICP-MS锆石U-Pb年龄及地球化学特征，分析其成因类型，探讨早一中三叠世该区大地构造环境特征。结果表明：内蒙古乌兰五台地区斑状二长花岗岩单颗粒锆石U—Pb年龄加权平均值为（231．84±0．99）Ma，是印支期岩浆活动的产物，其岩石组合为中细粒、细粒斑状二长花岗岩；岩石地球化学特征属于高钾钙碱性系列，主量元素与微量元素表现为高硅、高碱，w（K2O）／w（Na2O）〉1，A／cNK值为1．01～1．10的特点；Eu负异常明显，Rb、Th、K、Pb相对富集，Sr、Ti亏损；Ba、Nb、Sr、Ti呈现明显负异常，Rb、Th、K、Pb呈现明显正异常，w（Rb）／w（Sr）、w（Rb）／w（Ba）值高，w（Sr）／w（Ba）值低。上述特征显示该花岗岩为中一下地壳脱水部分熔融形成的岩浆侵位，可能形成于后碰撞挤压环境下的局部拉张构造环境，标志着大规模碰撞造山运动的结束和新的板内构造运动演化阶段的开始。
Based on 1 ： 50 000 regional geological surveys, aluminous A-type granite was identified in Wulanwutai area of Inner Mongolia. LA-ICP-MS zircon U-Ph ages and geochemical characteristics of porphyritic adamellite were studied, and the genesis and geotectonic setting characteristics in Early-Middle Triassic were discussed. The results show that the weighted average of single zircon U-Pb age of porphyritic adamellite in Wulanwutai area of Inner Mongolia is （231.84±0.99）Ma; it is a product of Indosinian magmatic activity; the rock is composed of medium fine and fine grained porphyritic adamellites; petrological and geochemical characteristic is high-K calc-alkaline series; major and trace elements have the characteristics of high silica and alkali, w（KzO）/w（Na20） is more than 1, and A/CNK values are 1.01-1. 10; Eu anomaly is obvious negative, Rb,Th, K and Pb are relatively rich, Sr and Ti are loss; Ba, Nb, Sr and Ti anomalies are obvious negative, Rb, Th, K and Pb anomalies are positive; w（Rb）/w（Sr） and w（Rb）/w（Ba） are high, and w（Sr）/w（Ba） is low. These characteristics indicate that the granite is magma emplacement formed by dehydration and partial melting of middle-lower crust, and is partial extension tectonic setting under the postcollisional compression environment; it marks the end of large-scale collision orogenic movement and the start of new intraplate tectonic movement and evolution.
出处
《地球科学与环境学报》
CAS
2015年第6期47-58,共12页
Journal of Earth Sciences and Environment
基金
中国地质调查局地质大调查项目(基[2010]矿评01-19-01)
