酸性熔岩的塑性流变

一、前言在河北省北部,广泛分布着中生代陆相火山岩系地层,呈北北东、北东或北东东向,集中出露于宽城—兴隆—昌平—涞源以北广大地区。根据岩性、岩相、接触关系、生物化石、同位素年龄等资料,自下而上可分为六个火山岩组,即南大岭组、髫髻山组、白旗组、张家口组、大北沟组、花吉营组。从火山岩岩石学而论,主要为基性、中性熔岩及其喷发岩只有上侏罗统张家口组以酸性熔岩及其火山碎屑岩为主,并且广泛分布在张家口—沽源火山岩区及承德—围场火山岩区内。作者在该区的区调工作中,积累一些酸性熔岩的塑性流变资料,借此探讨一下有关塑变熔岩与熔结凝灰岩的问题。

PLASTIC FLOWAGE DEFORMATION OF ACID LAVAS

The final product of evolution of acid and alkaline magmas is the highviscosity,low-eutectic point melts. The rocks formed by them show a well-developed structure of plastic flowage deformation. In order to distinguish between lavas with this structure and ignimbrites,the author proposes theterms rhyolite of plastic deformation,glassy rocks of plastic deformation and trachyte of plastic deformation for the former;while the latter specifically fers to rocksformed by fusion of pyroclasts,with the exception of the "ignimbrite"formed by plastic deformation and liquation of melts.