内蒙古昭盟地区中生代火山岩中斜长石环带特征及其地质意义

在内蒙古东部昭盟地区中生代的安山岩和某些花岗岩类岩石中的斜长石具有环带构造。本文研究了该斜长石环带的成份、特征,并初步分析其成因,这对研究该区岩石成因及了解岩浆的动态具有一定意义。

CHARACTERISTICS OF THE ZONING IN PLAGIOCLASE FROM THE MESOZOIC VOLCANIC ROCKS FROM ZHAOMENG DISTRICT, INNER MONGOLIA, AND ITS IMPLICATIONS

The zoning in plagioclase from The Meso.zoic igeneous in Zhaomeng district, Inner Mongolia is studied. The composition of zones has been analysed by electron micro-probe. It shows normal oscillatory zoning in granites and reverse one in andesites. The oscillatory amplitude is usually about 10%. The numbers of zones are usually 5-6. There are a lot of inclusions. Sometimes, there is a resorped core of the zoning plagiocla-se in the mica-pyroxene andesites, but there is no anyone in amphibolemica andesites.The genesis of normal oscillatory zoning can be interpreted by using the Ab-An phase diagram during slow cooling of intrusion. The reverse osscillatory zoning is explained that the water and volatiles in the magma had repeatedly been changed during the rise process of magma so that it could lead to different pressure and temperature in their crystalline process.From the characteristics of the zoning in volcanic rocks, it may be considered that the primary magma under the decreasing pressure was going to a process from stable, through oscillatory to extrusive. But the oscillatory amplitudes are different everywhere.The characteristics of zoning in plagioelase from andesites in southern part obviously differ from those in northern part. It shows that magma depth, contents of volatiles and forming-stage of plagioclases in the two part are quite different.