藏东类乌齐地区始新世钾玄质侵入岩特征及构造环境

往过同岩体位于藏东类乌齐地区往过同,岩石类型为斑状中粒黑云母二长花岗岩,黑云母K-Ar同位素年龄为35 Ma,时代为始新世。往过同花岗岩富硅、铝、碱,高钾贫钛,低铁、镁、钙,在SiO2-K2O和K2O-Na2O图解中样品均落在钾玄岩系列区,岩石系列为钾玄质花岗岩。岩石富集大离子亲石元素和轻稀土元素,负Eu异常;在原始地幔蛛网图上Th强烈富集,Sr呈现低谷负异常,高场强元素Nb、Ta、Ti亏损,表现出钾玄岩的地球化学特征。经分析,并应用构造环境判别图解,往过同花岗岩形成于后碰撞的构造环境。

Characteristics and tectonic environment of Eocene shoshonitic intrusive rocks in Leiwuqi region of eastern Tibet, China

Wangguotong Pluton is located in Wangguotong,Leiwuqi region of eastern Tibet.The rock type is porphyritic biotite adamellite,the biotite K-Ar isotopic age is 35 Ma,and the rock is Eocene in age.Wangguotong granite is rich in silicon,aluminum and alkali,has high potassium and poor titanium content,and low in iron,magnesium and calcium.In the diagram of the SiO2-K2O and K2O-Na2O,the samples all belong to the series of shoshonitic rocks,shoshonitic granite in rock series.The rock shows high concentration of large ion lithophile elements and light rare earth elements,and negative Eu abnormality,and it also shows Th strong concentration on the original cobweb diagram,Sr low negative abnormality,and losses of high-field strength elements Nb,Ta and Ti.These all indicate the geochemical characteristics of shoshonitic rock.By using the discrimination diagram of tectonic environment,it is proved that the Wangguotong granite is formed in post-collisional tectonic environment.