辽宁北镇地区新太古代变质深成岩地球化学特征及成因探讨

GEOCHEMISTRY AND GENESIS OF THE NEOARCHEAN METAMORPHIC PLUTONIC ROCKS IN BEIZHEN AREA,LIAONING PROVINCE

辽宁北镇地区新太古代变质深成岩是该地区最古老的结晶基底,各侵入岩体普遍发生变质变形,原岩结构构造发生改变.据岩体特征及分布划分为小牵马岭片麻杂岩、白厂门片麻岩两个岩石单位.小牵马岭片麻杂岩Si O2含量在59.69%~76.22%,液相线温度为720~1024℃,岩浆分异程度较高.白厂门片麻岩液相线温度为776~1024℃,岩浆分异指数DI值为68.99~91.68,分异值较高.白厂门片麻岩Ba/Sr比值与小牵马岭片麻杂岩比值接近,稀土配分曲线呈右倾,二者形态基本平行,说明这两种岩石物质来源相似,为铕异常明显的轻稀土富集型.

The Neoarchean metamorphic plutonic rocks in Beizhen area of Liaoning Province are the oldest crystalline basement in the region.With general metamorphism and deformation of plutons,the structures of protolith have changed.The plutonic rocks can be divided into two rock units of Xiaoqianmaling gneiss complex(Ar3xqgnc)and Baichangmen gneiss(Ar3bgn)according to the characteristics and distribution of rock mass.The Si〇2 content in Ar3qgnc is 59.69%-76.22%.The liquidus temperatures of the two rocks are 720-1024℃and 776-1024℃respectively.The Ar3xqgnc is characterized by high degree of magmatic differentiation,while Ar3bgn with high differentiation index(D I)of 68.99-91.68.The Ba/Sr ratios of both rocks are close to each other with approximately parallel right-dipping REE patterns,showing unobvious Eu anomalies with enrichment of LREE s,which indicates that the two rocks are derived from similar material sources.