浅议临澧县白土坡玻屑凝灰岩的岩石学特征

An Elementary opinion about the petrologic Characteristics ofthe Vitric Tuff in Baitupo,Linli County

临澧县白土坡玻屑凝灰岩（或半固结火山灰）赋存在第四系下更新统，层状或似层状，岩石松散，镜下具典型的玻屑凝灰结构。主要由流纹质火山玻屑，少量斜长石、石英及黑云母晶屑以及粘上矿物等组成。流纹质火山玻璃的电子探针分析平均值（％）：ＳｉＯ＿２７４．９７、Ａｌ＿２Ｏ＿３１４．０４６、ＣａＯ０．３２６、ＫｚＯ６．９３３、Ｎａ＿２Ｏ２．５３６、ＦｅＯ０．５１，总量９９．５２。

The vitric tuff(or partly consolidated volcanic ash)occurs in Iower Pleistocene series in Baitupo, Linli asaloose layer orastratoid,which has a typical texture of vitric tuff under micro-scope. And it is composed predominantly of clasts of rhyolitic volcanic glass,minor crystal clasts of plagiclase,quartz and bio- tite, and less clay minerals etc. Average compositions of rhyolitic glass analyzed by electronic microprobe are; SiO_2 74.97, Al_2O_3 14.046,CaO 0.326,K_2O 6.933,Na_2O 2.536,FeO 0.51,totaliy 99.52(in wt%)。