内蒙古东乌旗地区满克头鄂博组流纹岩年代学、地球化学特征及其地质意义

为确定内蒙古东乌旗地区满克头鄂博组火山岩地层的时代归属和形成构造背景,对满克头鄂博组流纹岩进行了年代学、地球化学特征等研究。流纹岩的LA-ICP-MS锆石U-Pb年龄为150.9±4.2Ma,时代归属晚侏罗世。满克头鄂博组流纹岩属于高钾钙碱性系列岩石,且具有高硅、富碱、高铝、贫钙贫镁的特征。稀土元素总量变化较大,配分曲线右倾,具有负Eu异常;富集大离子亲石元素(LILE)Rb、K、Th和轻稀土元素,亏损Sr和Nb、Ti、P;基性相容元素Cr、Co、Ni和Mg~#值较低,岩浆来源于下地壳岩石的部分熔融。根据元素地球化学特征,流纹岩具有A型花岗岩特征,结合相关构造判别图解,表明东乌旗地区在晚侏罗世处于伸展构造环境,可能与蒙古-鄂霍茨克洋闭合造山后伸展作用体制有关。

Geochronological and geochemical characteristics of rhyolite in the Manketou'ebo Formation of Dong Ujimqin Banner, Inner Mongolia, and its geological implications

In order to determine the age attribution and tectonic setting of the volcanic strata of the Manketou''ebo Formation in Dong Ujimqin Banner of Inner Mongolia, the authors studied the geochronological and geochemical characteristics of the rhyolite from the Manketou''ebo Formation. The weighted age of rhyolite by LA-ICP-MS zircon U-Pb dating is 150.9±4.2Ma, suggesting Late Jurassic. The rhyolite in the Manketou''ebo Formation belongs to the high-potassic calc-alkaline series of rocks and is characterized by high silicon, rich alkali, high aluminum, low calcium and depleted magnesium. The total amount of rare earth elements changes greatly, the distribution curve is right-inclined, and there is negative anomaly of Eu. The rocks are enriched in large ion lithophile elements of Rb, K, Th, and LREE, and simultaneously depleted in elements of Sr, Nb, Ti and P. The basic compatible elements Cr, Co, Ni and Mg^# are relatively low, and the magma was derived from the partial melting of the lower crust rocks. According to element geochemical characteristics, rhyolite has A-type granite characteristics. Combined with the related structural discriminant diagrams, the authors hold that the Dong Ujimqin Banner area was in an extensional tectonic setting in the Late Jurassic, and may be related to the extensional system of the Mongolian-Okhotsk Ocean after the closure of the ocean.