冲绳海槽碱性玄武岩浆的起源及演化
Origin and evolution of the alkali basaltic magma in the Okinawa Trough
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摘要: 利用电子探针对冲绳海槽133站位玄武岩的斑晶矿物、基质以及斑晶矿物中关晶石包体和岩浆包裹体作了化学主成分分析,结果表明,该站位玄武岩属橄榄玄武岩,岩石中斑晶矿物由培长石、普通辉石、贵橄榄石和磁铁矿组成,尚见有少量外来的脉石英碎块,基质成分由拉长石微晶和玻璃组成。培长石和贵橄榄石中含有玻璃质岩浆包裹体和铬镁尖晶石或铬镁铁尖晶石包体。尖晶石的化学成分证明它是地幔部分熔融成因的。岩浆包裹体代表了一种原生的碱性橄榄玄武岩浆,其化学成分相当于橄榄辉长岩。该站位的玄武岩浆起源于上地幔尖晶二辉橄榄岩的部分熔融,并沿着“碱性橄榄玄武岩浆-粗面玄武岩浆-玄武质粗面岩浆-粗面岩浆”方向演化,每一阶段的岩浆在上升过程中都不同程度地受到地壳物质的同化和混染作用。Abstract: The contents of major clement composition of the phenocrysts and matrix glass as well as spinel inclusions and melt inclusions in the phenocrysts of the basalt dredged from 133 site of the Okinawa Trough are determined by electron microprobe.The results show that the basalt is a dorgalite consisting of phenocrysts of bytownite,chrysolite,clinopyroxene and magnetite as well as labradorite microcrystal and matrix glass as well as a few bits of broken vein quartz.Glassy melt inclusions and chromohercynite or chrompleonaste exist in bytownite and chrysolite.The formation of spinels is related to fraction melting of the mantle.The melt inclusions stand for a primary alkali olivine basaltic magma,whose composition corresponds to olivine gabbro.The basaltic magma generated in fraction melting of spinel-lherzoliteof the upper mantle and evolved in a process of "alkali olivine basaltic magma→trachy-basahitic magma→basaltic trachyte magma→trachytic magma".Assimilation and contamination of crustal material may present during magma upwelling in every evolutionary stage.
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Key words:
- Basalt /
- spinel /
- melt inclusion /
- magmatic origin /
- magma evolution
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