藏北沉鱼湖—向阳湖一带石坪顶组火山岩特征、形成时代及环境

TIME AND ENVIRONMENT OF FORMATION AND GEOCHEMICAL CHARACTERISTICS OF THE CHENYUHU TO XIANGYANGHU SHIPINGDING GROUP VOLCANIC ROCKS IN NORTHERN TIBET

沉鱼湖—向阳湖一带的石坪顶组火山岩大地构造位置属巴颜喀拉-可可西里地块和南部的若拉岗日裂谷带,岩石结构类型比较简单,以粗面安山岩为主,粗面岩、玄武粗安岩、粗面英安岩次之,以钾质太平洋型钙碱性系列为主.火山岩轻、重稀土分馏程度均较高,重稀土分馏程度比轻稀土稍低一些,具轻稀土富集,重稀土亏损的特点,时代属中新世.K2O/Na2O>1,说明成矿物质为深部幔源物质混合了壳源物质,属大陆板内造山晚期演化的火山岩类型.

The Chenyuhu to Xiangyanghu Shipingding group volcanic rocks are located north of the Hoh Xil Mountains-Bayan Har massif and south of the Ruolagangri Rift Valley Belt. Rock types are simple： trachyandensite, the trachyte, basalt-trachyte, trachyandensite and are typical of the Pacific Ocean calcium alkali series. The volcanic rock is light; the degree of heavy rare earth fractionation is all high and compared to the light rare earth is slightly lower; has light rare earth concentrates and; the heavy rare earth loses are characteristic. The age is Miocene Epoch. K2O/Na2O is greater than 1 and the ore forming material consists of deep seated mantle derived material mixed with crust-derived material. The volcanic rocks formed and evolved during continent intraplate orogeny.