Origin and Generation Process of High Mg# Peridotites

本文讨论了上地幔高Mg橄榄岩的成因，认为它们是玄武质岩浆部分熔融过程中提取后的残留地幔物质、玄武质岩浆结晶形成的堆晶岩和沟道熔体与壁面橄榄岩相互作用后的自生橄榄岩。在这里，我们专注于高Mg#橄榄岩的Horoman和Oku-Niikappu超镁铁质杂岩，日高变质带，并在岩内岳橄榄岩，Kamuikotan蛇绿岩带，北海道。通过对高Mg#橄榄岩在上地幔物质中的产出方式、岩石和组分矿物的化学成分特征、岩浆通道系统的重建（包括岩浆作用和岩浆壁橄榄岩相互作用）的研究，结果表明，高Mg#橄榄岩总是在上地幔橄榄岩内部的岩浆通道中生成，在与通道接触处与反应区（替换带）紧密相连。在霍罗曼橄榄岩杂岩中，观察到两种不同的岩浆通道模式。一种是岩浆通道作用，熔体从壁面橄榄岩中流出;另一种是岩浆通道作用，熔体从通道喷口中流出。这种高Mg#橄榄岩如纯橄榄岩和铬铁矿也主要形成于奥新浦和岩内岳蛇绿橄榄岩杂岩的高度亏损方辉橄榄岩中。

Origin of high Mg# peridotites derived from upper mantle has been discussed as residual mantle materials after basaltic magma extraction during partial melting, cumulates crystallized from basaltic magma, and replacive peridotites after interactions between channeling melt and wall peridotites. Here, we focused on high Mg# peridotites in the Horoman and Oku-Niikappu ultramafic complexes, Hidaka metamorphic belts, and in the Iwanai-dake peridotites, Kamuikotan ophiolite belt, Hokkaido. This is to understand (1) modes of occurrence of high Mg# peridotites in upper mantle materials, (2) characteristics of chemical composition for the bulk rocks and the constituent minerals, and (3) reconstruction of the magma channeling systems in cluding the magmatic processes and the magmawall peridotite interactions.The results indicate that the high Mg# peridotites always generate in magma channels within upper mantle peridotites, in close association with reaction zones (replacement bands) at the contact with the channels. In the Horoman peridotite complex, two different modes of magma channeling were observed. One is magma channeling with melt extractions from the wall peridotites, and the other is magma channeling with melt addition from the channeling magma vents. Such a high Mg# peridotite as dunite and chromitite are also formed dominantly in highly depleted harzburgites of the Oku-Niikappu and Iwanai-dake ophiolitic peridotite complexes.