酸性喷出岩球状组构的成因及研究意义  

Genesis and significances of high-temperature crystallization domains in acidic eruptive rocks

作　　者：马强[1] 郭建芳 郑建平[1] MA Qiang;GUO Jian-fang;ZHENG Jian-ping(State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,China)

机构地区：[1]中国地质大学(武汉)地球科学学院,地质过程与矿产资源国家重点实验室,武汉430074

出　　处：《矿物岩石地球化学通报》2023年第5期988-997,I0003,共11页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金资助项目(41973050,42288201)。

摘　　要：球状组构(包括球粒和石泡)是流纹岩和流纹质熔结凝灰岩的特殊原生构造。基于中国东部的有关研究报道,本文综述了这种高温结晶球状组构的基本特征、成因和研究意义。球状组构内部常呈同心圈层放射状排列的长英质矿物聚集体,由内到外长石和石英的相对百分含量以及长石的成分都会发生有规律的变化。它们形成于酸性岩浆冷却过程,受岩浆温度、过冷度、熔体中挥发分等因素的控制。球粒结构并不是单一的脱玻化成因,石泡可能也并非简单的气体逃逸体积收缩过程。酸性火山岩(火山碎屑岩)的球状组构提供了自然条件下晶体的生长和成核动力学的直接记录,能提供岩浆挥发分组成与变化的信息,对于认识岩浆结晶动力学过程、酸性火山岩喷发机制及其环境效应具有重要意义。我国东部早白垩世石泡/球粒流纹岩/流纹质熔结凝灰岩分布较广,有待深入研究。High-temperature crystallization domains,including spherulites and lithophysaes,are special original structures often occurred in rhyolites and rhyolitic ignimbrites.Combined with data of spherulitic and lithophysaic rhyolites in eastern China and those reported in the literatures,in this paper,we have summarized features,genesis and significances of the high-temperature crystallization domains.There are often concentric radially arranged felsic mineral aggregates in spheru-litic structures,with regular variations of relative modal compositions of feldspar and quartz,and compositions of feldspar.The high-temperature crystallization domains were formed in the coling process of acidic magma under controlling parame-ters including temperature,supercooling,volatiles and transient tensional stress of the magma.The devitrification is not the only one genesis of spherulies.Lithophysae could not be formed by a simple magmatic volume contraction process due to the gas escape of magma.These high-temperature crystallization domains in acidic volcanic rocks(pyloclastic rocks)can provide direct records regarding to the growth and nucleation kinetics of crystals under natural conditions,and infor-mation about compositions and compositional changes of volatiles of magmas.They are of great significance to understand the dynamic process of magma crystallization,the eruption mechanism and environmental effects of acidic volcanic rocks.We should pay more attention to researches on the high-temperature crystallization domains in the early Cretaceous rhyo-lites and rhyolitic ignimbrites which are relative widely distributed in eastern China.

关 键 词：石泡构造 球粒结构 流纹岩和熔结凝灰岩 结晶 挥发分 

分 类 号：P58[天文地球—岩石学]