内蒙古苏尼特左旗北部阿登锡勒大队一带早石炭世高分异I型花岗岩的发现及地质意义

The Discovery of Monzogranite and Its Geologic Implication in Adenxile,Sonid Zuoqi,Innner Mongolia

本文对内蒙古苏尼特左旗北部阿登锡勒大队一带二长花岗岩进行了LA-ICP-MS锆石U-Pb测年,年龄为335.9±1.3Ma。岩石地球化学具有高硅、富碱,贫TFe O、Mg O特征,铝饱和指数A/CNK介于1.03-1.15之间,TFe O/Mg O=6.58-10.13。稀土总量偏低,轻稀土分馏程度相对较高,重稀土不分馏,δEu=0.25-0.69。大离子亲石元素Rb、Th等相对富集,高场强元素Sr、P、Ti表现为强烈亏损,而元素Nb、Ta则表现为相对亏损。属弱过铝质高分异I型花岗岩,形成于俯冲构造环境。通过区域对比分析,与近两年在二连浩特—东乌珠穆沁旗地区新发现的早石炭世二长花岗岩、花岗闪长岩、石英闪长岩、安山岩、英安岩共同构成了早石炭世贺根山洋盆向北俯冲形成的早石炭世岩浆弧。

This paper carries out some geochemical analysis on a monzogranite in the Adenxile village,Sonid Zuoqi,Inner Mongolia. The age of this pluton is around 335. 9 ± 1. 3 Ma according to the U-Pb dating by LA-ICPMS. The analyzed samples are riched in Si O2,Na2 O and K2 O,but poored in Mg O and TFe O. Their TFe O / Mg O ratio ranges from 6. 58 - 10. 13. The Al saturation index（ A / CNK） varies between 1. 03 and 1. 15. The LREE of these samples are highly differentiated,but the HREE present flat distributions. The element of Eu displays obvious negative anomaly with the δEu between 0. 25 and 0. 69. In the spider diagram,these rocks are highly enriched in Rb,Th and LILE and depleted in Sr,P,Ti,Nb and Ta. All the geochemical features above define this monzogranite as the highly differentiated peraluminum I-type granite,and they were formed in the settings related to subduction. This monzogranite,together with other Early Carboniferous arc-related felsic magmatic rocks in the Erenhot—East Ujimqin Banner region, constitute the magmatic arc caused by the northward subduction of Hegenshan Ocean.