豫西地区熊耳群火山岩钠长石化研究及其意义

ALBITIZATION OF THE VOLCANIC ROCKS OF THE XIONG′ER GROUP,WESTERN HENAN,AND ITS IMPLICATIONS

对豫西地区熊耳群火山岩的钠长石化进行镜下观察发现：熊耳群火山岩中的长石有交代作用的痕迹，对长石的电子探针测试结果显示熊耳群中性火山岩中的长石几乎均为钠-更长石，且钠长石占绝对优势，酸性岩中均为较纯净的钠长石（～Ab97），这些钠-更长石是岩石遭受普遍钠长石化的结果。通过熊耳群与后期中基性侵入体的对比，揭示熊耳群火山岩的钠长石化的形成与熊耳群的喷发近于同期，可能主要是岩浆期后蚀变作用所造成，熊耳群喷发晚期海水的灌入可能也对钠长石化有所贡献。蚀变作用导致了熊耳群火山岩碱质（Na2O＋K2O）偏高，其原岩可能为玄武安山岩-安山岩-英安岩-流纹岩组合。

The albitization of the volcanic rocks of the Xiong＇er Group, western Henan, was studied based on rock thin section observations and electron- probe microanalysis （EPMA）. Alteration textures are found through petrographic studies. EPMA results indicate that the feldspars in the intermediate volcanic rocks of the Xiong＇er Group are mainly albite or oligoclase,and dominantly albite ,and the feldspars in the felsic rocks are compositonally pure albite （-Ab97）. These albite-rieh feldspars are the products of widespread albitization processes. The event of albitization possibly took place during the eruption of the Xiong＇er Group,which was revealed through the comparison of the volcanic rocks of the Xiong＇er Group volcanics with the later intermediate intrusions. It is suggested that the albitization might attribute mainly to deuteric alteration,and minor seawater may make contribution also. The alteration processes have somewhat increased the total alkali （Na2O＋K2O） content of the volcanic rocks of the Xiong＇er Group,which may be initially composed of basaltic andesite-andesite-dacite-rhyolite suite.