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一、地质和地化背景概述本工作区北起申扎—班戈,南至亚东,火成岩自北往南可分为四个岩带:申扎-班戈岩带、冈底斯岩带、拉轨岗日岩带和喜马拉雅岩带。本区位子冈底斯-念青唐古拉和喜马拉雅两大构造带内。岩体多呈条带状近东西向展布,与区内主要构造线基本一致。其中冈底斯岩带最具代表性,为雅鲁藏布江板块构造俯冲带,广泛发育有岛弧-陆缘型的中基性-酸性为主的钙碱性系列(火山岩系钙碱指数为59.5,岩系指数σ平均为1.8,花岗岩类σ平均为2.3)的火山-深成杂岩体。其北缘局部出现偏碱性系列的杂岩体(岩系指数σ平均为6.2)。岩石组合从玄武安山岩至流纹质岩和从辉长岩至钾长花岗岩。据查佩尔等(B.W.Chappell,1968) 对花岗岩分类,冈底斯岩带的花岗岩类以 I 型为主;拉轨岗日和喜马拉雅岩带以 S 型为主;而申扎-班戈岩带则为过渡型。(表1)
I. Geological and Geochemical Background Overview This work area is divided into four rock zones from north to south: the Xhenza-Bangor rock belt and the Gangdese rock belt , Pull rail Kong Day rock belt and the Himalayan rock belt. This area seat Gangdise - Nyainqentanglha and Himalayan structural belt. Most of the rock mass is nearly strip-shaped east-west distribution, basically consistent with the main tectonic line in the area. The Gangdese rock belt is the most representative for the tectonic subduction zone of the Brahmaputra plate, and widely developed island-continental type of basic-acidic calc-alkaline series (volcanic rock series with a calc-alkaline index of 59.5, The mean value of index σ is 1.8, and the average granite σ is 2.3). The northern margin of the local occurrence of alkaline series of complex rock body (rock index σ average of 6.2). The rock assemblages range from basaltic andesite to rhyolite and from gabbros to k-long granites. According to Chappell et al. (BWChappell, 1968), the granites are classified into granites. Type I is the major granite in the Gangdise zone, S-shaped in the pullback Kong and Himalayan rocks, Belt is a transitional type. (Table 1)