长白山天池火山的岩石矿物学特征——对结晶分异过程和岩浆混合作用的启示

本文对天池火山玄武岩盾,粗面质-碱流质层状锥体以及顶部的粗面质-碱流质碎屑岩类及熔岩的岩石矿物成分做了系统分析,发现在玄武岩类中的主要矿物组合为斜长石、富钙辉石以及富镁橄榄石,而粗面岩-碱流岩类的主要矿物组合为碱性长石、富铁的辉石及橄榄石,并开始出现石英、独居石以及大量的铁钛氧化物,符合结晶分异的演化趋势。同时在玄武岩类及粗面-碱流岩类中均存在不平衡矿物,再结合矿物环带的成分变化、矿物的熔蚀现象及不同特征的岩石条带等,认为天池火山在黑石沟玄武岩、第一、三造锥阶段粗面岩以及千年大喷发的浮岩中均存在岩浆混合作用。根据岩石学及年代学等特征,认为不同时期的玄武质岩浆来自同一地幔源区,经不同程度的结晶分异作用形成,前造锥阶段及造锥阶段的岩石由不同阶段的玄武岩演化而来,全新世的碱流岩类则由造锥阶段粗面岩类演化而来。

Petrological and Mineralogical Characteristics of Tianchi Volcanoe,Changbai Mountain: Implications for Crystallization Differentiation and Magma Mixing

In this study, the authors analyzed lots of rocks and minerals from the whole eruptive sequence. Basalts mainly consist of plagioclase, augite, and olivine, whereas trachyte and comendite mainly consist of alkali-feldspar, ferroaugite, fayalite together with quartz, monazite and plenty of Fe-Ti oxides, which exhibits a crystallization differentiation trend. Meanwhile there are lots of disequilibrium phenomena such as unmatched mineral combination, zonation, and resorption. The authors infer that magma mixing existed in Heishigou basalt, trachyte of the first and third stage cone building and millennium eruption pumice of Tianchi volcanoes. According to the petrologic and chronologic characteristics, the trachytes evolved from different stages of basalts whereas the comenditie evolved from the cone building trachytes. The basalts were formed by partial melting and crystallization differentiation at different depths.