Process of magma channel formation in the upper mantle

在来自上地幔的橄榄岩中，可以辨认出高温岩浆穿过上地幔形成的通道的痕迹。造山二辉橄榄岩中的纯橄榄岩脉和蛇绿橄榄岩中不协调的纯橄榄岩-铬铁矿组合是上地幔岩浆通道的代表性样品。通道的赋存方式、岩石结构和岩石结构，以及北海道的Iwanai-Dake橄榄岩和Horoman橄榄岩杂岩的通道样品，以及土耳其西南部的Fethiye蛇绿岩和巴基斯坦北部的Malakand蛇绿岩的通道样品，都进行了研究。在岩浆通道上进行了系统的采样，以检测通道岩浆/橄榄岩壁相互作用的影响。用电子探针分析了橄榄石、斜辉石、单斜辉石和尖晶石等主要成分矿物，并用LA-ICPMS进行了微量元素分析，以确定熔体成分和通道岩浆的类型。Iwanai-Dake橄榄岩杂岩的纯橄榄岩-铬铁矿通道具有极高的Mg#和Cr#特征，表明通道形成的岩浆类型是高镁安山岩或板岩岩浆。包裹铬铁矿层的纯橄榄岩可解释为岩浆在壁方辉橄榄岩中流出时，熔体/壁橄榄岩相互作用形成的复制性纯橄榄岩。在霍罗曼橄榄岩杂岩中，寄主方辉橄榄岩和二辉橄榄岩中发现了大量以岩浆通道群形式存在的纯橄榄岩墙。在霍罗曼橄榄岩中发现了几种岩浆类型，如MORB型玄武岩和更难熔的玄武岩。

Traces of channels formed by high temperature magma channeling through the upper mantle can be recognized in peridotites derived from the upper mantle. Dunite dykes in orogenic Iherzolites and discordant dunite-chromitite associations in ophiolitic peridotites are representative samples of magma channels formed in the upper mantle.Mode of occurrence of channels, structures and textures of rocks, and the constituent minerals ware examined on the channel samples from the Iwanai-dake peridotite and the Horoman peridotite complexes in Hokkaido, together with those from the Fethiye ophiolite of SW Turkey and the Malakand ophiolite of Northern Pakistan. The sampling were performed as a systematic one across the magma channels to detect the effect of 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 the 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 baninite magma for the magma type of the channel formation. The dunite enveloping the chromitite layer can be explained as replasive dunite formed by a melt/wall peridotite interaction during the magma channeling in the wall harzburgite. A number of dunite dykes were found as magma channel swarm in the host harzburgite and Iherzolite 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.