大兴安岭扎兰屯地区晚奥陶世石英闪长岩体岩石地球化学特征及其地质意义

扎兰屯音河岩体被音河水系分为南、北两部分,研究发现南、北岩体形成年代不同,选取南部岩体(称为二村岩体)进行研究。二村岩体主要由石英闪长岩-英云闪长岩组成,石英闪长岩的LA-ICP-MS锆石U-Pb年龄为444.0±4.6Ma,时代为晚奥陶世。岩石化学组成相对富钠、贫钾,Na2O/K2O值大于1(1.73~3.17),属中钾钙碱性系列。岩石富含轻稀土元素、亏损重稀土元素,富集大离子亲石元素Rb、Ba、K,显著亏损Nb、Ta、P、Ti等高场强元素。矿物组成及岩石地球化学特征指示其为I型花岗岩。岩体的形成时代、构造背景与多宝山岛弧火成岩相似,为区域多宝山岛弧西南向延伸提供了新的制约。

Petrogeochemistry of the Late Ordovician quartz diorite in Zhalantun area of Da Hinggan Mountains and its geological significance

Yinhe rock mass is divided into two parts (north and south)by the Yinhe River system, and the age of southern rock mass (named Ercun rock mass) is different from that of the northern rock mass. The Ercun intrusive body is mainly composed of quartz di-orite-tonalite. The LA-ICP-MS zircon U-Pb age of the quartz diorite is 444.0 ±4.6Ma, suggesting Late Ordovician. The chemi-cal composition of the rock is relatively rich in sodium and poor in potassium, and Na₂O/K₂O ratio is higher than 1 (1.73~3.17), sug-gesting the potassium calc-alkaline series. The rocks are rich in LREE, depleted in HREE, and enriched with LILE, Rb, Ba, and K, with significant losses of HFSE such as Nb, Ta, P and Ti. Mineral composition and petrological geochemical characteristics indicate that it should belong to type I granite. The age and tectonic setting of the rock mass is similar to that of the Duobaoshan island arc ig-neous rock, which provides a new constraint for the southwest extension of the Duobaoshan island arc.