CAJ | 학술논문

根据矿物结构可以有效的识别开放性体系内的各种岩浆过程，在岩相学研究基础上，对全新世喷发的Ruapehu火山Whakapapa组安山岩内的辉石斑晶进行了系统的矿物学分析。所研究样品中辉石斑晶以普通辉石及顽火辉石为主，具多样结构与形态，根据其结构和成分特征可分为3类：（1）骸晶状的辉石（SP型），具有破碎的、筛孔状外形，核部具有异常高的FeOT含量，可能为壳源捕掳晶；（2）具均一结构及成分的辉石（HP型），其内部未显示明显的熔融结构，形成于岩浆房的内部，基本未受基性岩浆混合的影响；（3）具核-幔-边结构的“绿核”辉石（GCP型），其幔部相比核部及边部具有更高的En、Mg#、CaO、MgO和Cr2O3含量以及更低的FeOT、TiO2含量。且GCP辉石边部相比核部更加富CaO、MgO而贫FeOT、TiO2。GCP型辉石幔部（边部）与核部形成明显的反环带结构，两者界线清晰，成分上存在突变，是偏基性岩浆注入岩浆房边界层时，岩浆发生大规模扩散、混合之前形成于脉状岩浆“通道”内；而GCP辉石边部则结晶于混合后的岩浆之中。辉石的结构及岩相学特征暗示，安山岩在喷发前经历了岩浆混合及地壳物质的混染，混合过程主要发生于地壳浅部岩浆房的边界层及粥状层内，且这种混合过程可能是诱发火山喷发的重要机制之一。
근거광물결구가이유효적식별개방성체계내적각충암장과정，재암상학연구기출상，대전신세분발적Ruapehu화산Whakapapa조안산암내적휘석반정진행료계통적광물학분석。소연구양품중휘석반정이보통휘석급완화휘석위주，구다양결구여형태，근거기결구화성분특정가분위3류：（1）해정상적휘석（SP형），구유파쇄적、사공상외형，핵부구유이상고적FeOT함량，가능위각원포로정；（2）구균일결구급성분적휘석（HP형），기내부미현시명현적용융결구，형성우암장방적내부，기본미수기성암장혼합적영향；（3）구핵-만-변결구적“록핵”휘석（GCP형），기만부상비핵부급변부구유경고적En、Mg#、CaO、MgO화Cr2O3함량이급경저적FeOT、TiO2함량。차GCP휘석변부상비핵부경가부CaO、MgO이빈FeOT、TiO2。GCP형휘석만부（변부）여핵부형성명현적반배대결구，량자계선청석，성분상존재돌변，시편기성암장주입암장방변계층시，암장발생대규모확산、혼합지전형성우맥상암장“통도”내；이GCP휘석변부칙결정우혼합후적암장지중。휘석적결구급암상학특정암시，안산암재분발전경력료암장혼합급지각물질적혼염，혼합과정주요발생우지각천부암장방적변계층급죽상층내，차저충혼합과정가능시유발화산분발적중요궤제지일。
Mineral textures and zoning provide a way to investigate the evolution process of an open magmatic system. In this study, petrographic and EMPA mineral analysis have been taken in the pyroxene phenocrysts from Holocene Ruapehu andesite. These pyroxenes are augite and enstatite, and can be divided into three types based on their texture and compositional features, including homogeneous pyroxenes (HP), green-core pyroxenes (GCP) and skeletal pyroxenes (SP). HP pyroxenes are crystallizing in a steady, showing homogeneous composition from core to rim, and lacking any dissolution texture. GCP exhibit the core-mantle-rim texture. Comparing with the core and the rim, the mantle zones show higher En, Mg#, CaO, MgO and Cr2O3 contents, while lower FeOT, TiO2 contents, displaying clearly reverse zoning. Broken cellular core of SP show similar compositions to the crustal meta-igneous xenolith, indicating a xenocrystic origin for the SP and crustal contamination during magma ascent. The reverse zoning of pyroxenes and other petrographic features suggest that the mixing mainly take place in the rigid and mush zone of shallow magma chamber, and just prior to the eruption.