衡山地洼花岗岩的断裂重熔成因

DIWA-TYPE GRANITE OF HENSHAN:ORIGIN BY FRACTURAL MELTING

衡山复式花岗岩由南岳岩体和白石峰岩体组成,形成于西缘大断裂的剪切阶段,并与韧性变形变质岩、断裂混合岩构成了紧密共生的(两期)三位一体组合。研究表明,白石峰岩体是由早期眼球状混合岩高程度熔融而成的,南岳岩体则是高变质相韧性断层岩重熔的产物,二者均属断裂重熔。重熔过程是一种流体开放体系,重熔作用沿断裂呈线带状发生,与深部高温热流体沿断裂带的注入、聚集有关。断裂重熔是地洼花岗岩的形成方式之一,其实质是地洼块断(造山作用)重熔。

Heushan composite granite, consisting of Nanyue body and Baishifeng body, was repeatedly intruded during shear stage of deep fault on its west margin. A close relationship with ductile deformation-metamorphic rocks and fractural migmatites, named triad association, is recognized. It is suggested that the Baishifeng granite was derived from high-grade anatexis of early ocular migmatite and the Nanyue granite from the anatexis of ductile fault rocks with high metamorphic phase. Both are the product of fractural melting, which was a fluid open-system melting. Melting along the fault zone was mainly caused by the injection and storage of deep-derived high temperature fluid through the fault zone. Fractural melting is one of the formation ways of diwa-type granites. Its tectonic background is assumed to be block-fault orogenesis in diwa stage.