东秦岭灰池子花岗岩成岩机制的研究

PETROGENESIS OF HUICHIZI GRANITIC BATHOLITH IN EASTERN QINLING

灰池子岩基定位于东秦岭加里东沟－弧－盆褶皱系内的古岛弧带中，属于原地－准原地改造型花岗岩。其形成机制为：加里东晚期，华北古板块南侧的东秦岭沟－弧－盆体系活动大陆边缘闭合，岛弧带内产生一系列逆冲推覆构造，随着上冲岩片的逆掩叠置，下滑岩片的温度升高而发生强烈的脱水、去碱和去硅作用。在逆冲带强大压力作用下，这些饱含碱和二氧化硅的热流体被从下滑岩片中逐出，升腾至上覆岩片，上覆岩片被浸润而发生深刻的交代－重熔作用，最终形成原地－准原地改造型花岗岩。与华南加里东造山带中的同类型花岗岩相比，灰池子花岗岩岩石地球化学特征方面具有明显不同的特征，其原因在于两造山带内具有不同的岩石建造。源岩的性质影响和制约着由其改造而成的原地－准原地改造型花岗岩的岩石地球化学特征。

The Huichizi batholith,situated in the palaeo-arc belt of the Caledonian Eastern Qinling trench-arc-basin fold system,belongs to the autochthonous-parautochthonous transformation-type granite.During the late Caledonian period,the closure of the eastern Qinling trench-arc-basin system resulted in the formation of a series of northward thrusts in the belt.As the down-going microlithons were overthrusted and superimposed by the up-going microlithons,their temperature rose,resulting in strong dehydration,degasification,dealkalization and desilication of the down-going microlithons and the formation of hydrothermal fluids rich in K,Na,Si and the like.As the hydrothermal fluids rose,the up-going microlithons were metasomated and remelted,leading to the formation of the autochthonous-parautochthonous transformation-type granite.The geochemical features of granite are controlled by those of the down-and up-going microlithons.