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Magma channels in the Upper Mantle : Origin of dunite-chromitite channels

上地幔中的岩浆通道：纯铜矿-铬铁矿通道的起源

基本信息

批准号：
15540453
负责人：
NIIDA Kiyoaki
金额：
$ 2.3万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15540453/
关键词：
upper mantle ophiolitic peridotite basaltic magma dunite chromitite harzburgite olivine spinel

项目摘要

A trace of channels formed by high temperature magma channeling through the upper mantle can be ovserved in peridotites derived from the upper mantle. Dunite dykes in orogenic lherzolites and discordant dunite-chromitite associations in ophiolitic peridotites are representative samples for magma channels formed in the upper mantle.Modes of occurrence of channels, structures and textures of rocks, and the constituent minerals were examined on the channel samples from the Iwanai-dake peridotite and the Horoman peridotite complexes in Hokkaido. The sampling were performed systematically across the channels to detect the channeling magma/peridotite wall interactions. The major constituent minerals such as olivine, orthopyroxene, clinopyroxene, and spinel, were analyzed by EPMA for major elements and also by LA-ICPMS for trace elements to detect the melt components and to characterize the type of channeled magmas.The dunite-chromitite channels from the Iwanai-dake peridotite complex are characterized by minerals with extremely high Mg# and Cr# signatures, suggesting a high-Mg andesite or a boninite magma for the magma type. The dunite enveloping the chromitite layer can be explained as replacive dunite formed by a melt/wall peridotite interactions during the magma channeling in the wall harzburgite. A number of dunite dykes were found as magma channel swarm in the host harzburgite and lherzolite in the Horoman peridotite complex. Several kinds of magma types such as MORB-type basalt and a more refractory basalt were detected for magmas channeled in the Horoman peridotites.

在上地幔橄榄岩中可观察到高温岩浆穿流上地幔形成的通道痕迹。造山二辉橄榄岩中的纯橄榄岩脉和蛇绿橄榄岩中的不整合纯橄榄岩-铬铁矿组合是上地幔岩浆通道的代表性样品，本文对北海道岩内岳橄榄岩和钟落橄榄岩杂岩中的通道样品进行了通道产状、岩石结构和组成矿物的研究。在通道中系统地进行采样，以检测通道岩浆/橄榄岩壁的相互作用。通过EPMA和LA-ICPMS分析了岩石中橄榄石、斜方辉石、单斜辉石和尖晶石等主要成分矿物的主量元素和微量元素，研究了岩石熔体成分和通道岩浆的类型。岩内岳橄榄岩杂岩中纯橄榄岩-铬铁矿通道的特征是矿物具有极高的Mg#和Cr#特征，岩浆类型为高镁安山岩或玻安岩岩浆。包裹铬铁矿层的纯橄榄岩可解释为岩浆在壁面辉橄榄岩中窜流时，熔体/壁面橄榄岩相互作用形成的孤立纯橄榄岩。在寄主方辉橄榄岩和霍罗曼橄榄岩杂岩的二辉橄榄岩中发现了大量纯橄榄岩脉作为岩浆通道群。在霍罗曼橄榄岩中发现了多种岩浆类型，如MORB型玄武岩和一种更难熔的玄武岩。