内蒙古莫古吐花岗岩年代学、地球化学与地壳伸展-减薄作用

莫古吐花岗岩体位于大兴安岭南段黄岗梁—甘珠尔庙锡多金属成矿带西南端,其岩性主要以黑云母钾长花岗岩为主。文章通过LA?ICP?MS锆石U?Pb定年及岩石地球化学研究分析,探讨莫古吐花岗岩的成因类型、岩浆源区及成岩构造背景。锆石U?Pb年代学研究表明,莫古吐岩体形成于148.8~152.7 Ma,属晚侏罗世岩浆产物。岩石学及地球化学特征显示,莫古吐花岗岩属于碱性—弱过铝质系列,具有富SiO2(73.64%~80.86%),富K2O(2.6%~6.0%),贫Al2O3(10.57%~13.88%)的特点,富集Rb、U、Th等大离子亲石元素,亏损P、Ti、Ba、Sr等元素,稀土配分型式呈燕式分布,δEu值为0.10~0.27,负Eu异常明显,锆石饱和温度较高,为795~911℃,属于高演化A型花岗岩。结合年代学、地球化学数据及前人研究成果,认为莫古吐花岗岩体的岩浆源区较浅,成岩物质主要以壳源物质为主,岩体形成于地壳伸展?减薄的构造环境中,与蒙古—鄂霍茨克洋构造体制的关系更为密切。

Chronology and geochemistry of Mogutu granite in Inner Mongolia and its effect of crustal extension and thinning

The Mogutu granite pluton is emplaced in the southwest Huanggangliang to Ganzhuermiao tin-polymetal metallogenic belt in Southern Da Hinggan Mountains,which is mainly composed of biotite moyite.The genetic type,magmatic source region and diagenetic tectonic setting of the Mogutugranite were studied by U-Pb dating of zircon in LA-ICP-MS and petrogeochemical analysis.Zircon LA?ICP?MS dating of the biotite moyite yields a concordant age of 148.8-152.7Ma,which means that the Mogutu granite pluton was formed in Late Jurassic.The Mogutu granites is characterized by weak peraluminous and alkaline,high content of SiO2(73.64%-80.86%),K2O(2.6%-6.0%),but low content of Al2O3(10.57%-13.88%),depletion in P、Ti、Ba、Sr,and enrichment Rb、U、Th.The chondrite-normalized patterns of REE are in seagull forms,with strong negative Eu anomalies,with 0.10 to 0.27 ofδEu,and higher zircon saturation temperatures(795-911℃),which indicates that the Mogutu pluton is similar to A?type granite.Therefore,the Moguto granites shows highly fractionated A?type granite affinity.Based on the previous research results,it is inferred that the depth of magma source of Mogutu granite pluton is shallow,the magmatic substance was derived from the crust,and the granite pluton was emplaced in the tectonic setting of crustal extension and thinning more likely related to the closure of the Mongol?Okhotsk tectonic belt.