水溪庙花岗伟晶岩脉的成因研究

A STUDY ON THE GENESIS OF SHUIXIMIAO GRANITIC PEGMATITE DIKES

水溪庙花岗伟晶岩脉的地质及地球化学特征的研究结果表明：京汉庙花岗伟品岩脉是一典型的内部具有明显不对称带状结构分布特征、与花岗岩体呈过江关系的层状伟晶岩，也是在我国首次详细研究的层状花岗伟晶岩．温过研究，作者论证了水没庙花岗质社体结晶演化至岩浆一热液过渡阶段时熔体结晶的产物．脉体内部的不对林带状分布结构是岩浆结晶分异演化作用过程中，体系内挥发份由不饱和到过饱和的渐变过程中结晶形成的。

The grndic pegmatite dikes of Shuiximiao mine are found as upward branches from the fine -grained albite -topaz granite cupola.The albite-topaz grace is characteral by the development of'snow ball'texture of quartz and K -feldspar phenocrysts,existence of melt-amour inclnylonS in qtz and ta etc. minerall,enrlchmeot of Na, Li, F, Ta, Nb,Sn,W etc.elements and depletion of REE.All these features indicate its crystallization from a residals melt of hashly evolved graphic mngmatic system.The pegmatite daaes are steep to gentle in attitude,tallufor in shape,up to 200 m lOng,90 m deep and 2-15 m thank. In the interal structure,tyey are asymmetriCally layered. The lOwer layers are mostly dominated by the aiblte-rich aplitel the upper layers are mostly domlhated by the K feklspar-rich pcamatlte I the middle layerS are maltly the alternating bands of sodic aplite and potasslC pegmatite.TranSition between these layers is grsdatioflai. From the lOwer acs upwbos,these is a tendency Of syStematiC increase Of SiOZ,KZO and decrease of Al2O3,Na2O, FeO,CaO,MgO.Based on the comprehensive geological, petrological and geochemical study,it is evidenced that the initial silicate melt responsible for formation of pegmatite-aplite daaes was derived horn the aiblte-topaz grndee cupola. The discs were formed at the mngmatic-hydrothermat transitional stage of evolution and differentiation of the volatile aam F-rich granitic melt when the silicate melt phase,crystal Phase the free fluid phase coexist.Their asymmetrically forred structure was dewloped in the Crystallizing system wherethe volatile concentration in the melt changed from the undersaturated towards the oversaturated.