内蒙古布林庙晚石炭世碱长花岗岩的发现及其对古亚洲洋演化的制约

Discovery of the Late Carboniferous alkali-feldspar granite from the Bulinmiao area in Inner Mongolia and its constraints on the evolution of the Paleo-Asian-Ocean

对贺根山蛇绿岩带北缘的布林庙碱长花岗岩体进行了LA-ICP-MS锆石U-Pb定年、岩石地球化学特征研究,以期解释其岩石成因及地质意义。研究表明:碱长花岗岩体的锆石U-Pb年龄为304±1 Ma,为晚石炭世岩浆活动的产物;所有样品的地球化学特征相似,表现为高硅、富碱且相对富钾、弱过铝质的特点,富集Rb、K等大离子亲石元素,贫P、Sr、Ti等元素。结合样品的10000Ga/Al值、TFeO含量、Zr含量、锆石饱和温度等相关指标,认为岩体为高钾钙碱性(钾玄岩)系列的A型花岗岩。岩体形成于贺根山洋盆闭合后,是古亚洲洋造山后伸展阶段早期阶段的产物。

In this paper,LA-ICP-MS zircon U-Pb dating and geochemical characteristics of the Bulinmiao alkali-feldspar granite pluton located in the northern margin of the Hegenshan ophiolite belt are studied in order to explain its petrogenesis and tectonic significance.The study shows that the zircon U-Pb dating give weighted average age of 304±1 Ma,indicating that it is the product of magmatic activity in the Late Carboniferous.The general characteristics of the granite samples are similar,showing the characteristics of high silicon,rich alkali,rich K,and weak peraluminous.Trace elemental data of these rocks show LILE(Rb,K)enrichment,HFSE(P,Sr,Ti)depletion.Combining with the 10000Ga/Al value,TFeO,Zr contents and zircon saturation temperatures of the sample,the pluton is an aluminous A-type granite and belongs to the high-K calc-alkaline series.The granite was the product of the early stage post-orogenic extension after closure of Hegenshan Ocean.