Mineralogy of the ejected plutonic blocks of the soufriere volcano St. Vincent: Olivine, pyroxene, amphibole and magnetite paragenesis
Mineralogy of the ejected plutonic blocks of the soufriere volcano St. Vincent: Olivine, pyroxene, amphibole and magnetite paragenesis
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DOI：
10.1007/bf00374766
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发表时间：
1973-02
影响因子：
3.5
通讯作者：
J. Lewis
中科院分区：
文献类型：
--
作者：
J. Lewis
从圣文森特苏弗里埃尔火山喷出的深成岩块由斜长石(An96−An89，平均An93)、橄榄石(Fo79−Fo67，最常见的间隔Fo74−72)、含5-6%Al_2O_3的盐岩、含6%Al_2O_3、4%MgO和7%TiO的磁铁矿组成。铝质玄武岩辉石不仅局限于碱性岩系，还以高温相形式出现在某些钙碱性岩系中。同样，低硅角闪岩具有相对较高的Fe+3+Ti含量，在常见的亚碱性岩石中也很少见。圣文森特区块中的磁铁矿是与区块中其他四个相平衡地沉淀的单一均匀氧化铁相的一个例子。结晶条件与二氧化硅活性在决定相对较浅深度的玄武岩岩浆中分离出的相的组成方面同样重要(Ptot<；8kb)。主要根据晶体化学的依据，认为圣文森特地块的矿物组合可以在相对较高的温度、较高的水蒸气压力和氧逸度条件下，从亚碱性岩浆中结晶出来。
Ejected plutonic blocks from the Soufrière volcano, St. Vincent, consist of the mineral phases plagioclase (An96−An89, average An93), olivine (Fo79−Fo67, most frequent interval Fo74−72), salite containing 5–6 percent Al2O3, hastingsitic amphibole and magnetite containing 6% Al2O3, 4% MgO and 7% TiO2.Aluminous salitic pyroxenes are not confined to alkaline suites but also occur as high temperature phases in certain calc-alkaline suites. Similarly low silica amphiboles with comparatively high Fe+3+Ti contents are unusual in common sub-alkaline rocks. Magnetite in the St. Vincent blocks is an example of a single homogeneous iron oxide phase precipitated in equilibrium with the other four phases in the blocks.Conditions of crystallisation are just as important as silica activity in determining the compositions of phases separating from basaltic magmas at relatively shallow depths (Ptot< 8 kb). It is argued mainly on crystal chemical grounds that the mineral assemblage in the St. Vincent blocks can crystalline from a sub-alkaline magma under conditions of relatively high temperature, high water vapor pressure, and oxygen fugacity.