大兴安岭南部乌拉盖地区满克头鄂博组火山岩年代学、地球化学研究及构造环境分析

【研究目的】通过查明大兴安岭乌拉盖地区火山岩的年龄、地球化学特征，探讨火山岩形成的时代、成因及构造背景，为研究大兴安岭南部地区的岩浆活动和构造演化过程提供依据。【研究方法】选取大兴安岭乌拉盖地区满克头鄂博组火山岩，系统开展LA-MC-ICP-MS锆石U-Pb年代学和岩石地球化学研究。【研究结果】研究区满克头鄂博组火山岩形成于中—晚侏罗世（（154.8±1.2）～(164.96±0.71)Ma），火山岩具有高硅、富碱、富钾、贫镁、贫钙的特征，属于高钾钙碱性系列岩石。所有样品的稀土配分曲线具有相似特征，稀土总量中等，轻重稀土分馏明显，属轻稀土富集型，Eu负异常显著。微量元素特征表现为富集大离子亲石元素（LILE）Rb、K、Th、U，亏损高场强元素（HFSE）Nb、Ta、Ti、P，岩石具有低Sr和较高的Yb含量，表现出与A型花岗岩相似的地球化学特征。【结论】结合区域地质资料及本文研究成果，认为研究区满克头鄂博组火山岩岩浆来源于地壳岩石的部分熔融，产生于造山后伸展构造背景，其形成可能与蒙古—鄂霍茨克洋闭合后的岩石圈伸展作用有关。

Geochronology, geochemistry and tectonic setting of volcanic rocks from Manketouebo Formation in Wulagai area, southern Da Hinggan Mountains

This paper is the result of geological survey engineering.Objective]:By finding out the age and geochemical characteristics of volcanic rocks in Wulagai area of Da Hinggan Mountains, this paper discusses the age, genesis and tectonic background of volcanic rocks, so as to provide a basis for the study of magmatic activity and tectonic evolution in the south of Da Hinggan Mountains.Methods] Our project carried out systematically study the LA-MC-ICP-MS zircon U-Pb chronology and rock geochemistry from the volcanic rocks of Manketouebo Formation in Wulagai area of Da Hinggan Mountains.Results]The volcanic rocks of Manketouebo Formation in the study area were formed in the middle Late Jurassic ((154.8±1.2)-(164.96±0.71)Ma). The volcanic rocks of this region belong to alkali series rocks, with characteristics of high silicon, rich in alkali and potassium, low magnesium and calcium. The rare earth distribution curves of all samples have similar characteristics. The total amount of rare earth is medium, the fractionation of light and light rare earth is obvious, which belongs to light rare earth enrichment type, and the negative Eu anomaly is significant. The rocks are relatively enriched in the large ion lithophile elements Rb, K, Th and U, and have a strong deficit in the high-field strong elements such as Nb, Ta, Ti, P; the volcanic rocks have the characteristics of low Sr, high Yb and A-type granite.Conclusions]The studies on trace elements and rare earth elements indicate that the volcanic magma are derived from the melting of the crust and have the same magmatic source. The volcanic rocks of Manketouebo Formation originated in the post orogenic extensional tectonic background, which was possibly related to the lithosphere extension after the closure of the Mongol-Okhotsk Ocean.Highlights: The volcanic rocks of Manketouebo Formation were formed in the Middle Late Jurassic. The rocks belong to the highk calc alkaline series with A-type granite geochemical characteristics. They were formed in the extensional tectonic environment caused by the closure of the Mongol-Okhotsk Ocean.