Origin and Generation Process of High Mg# Peridotites

上地幔高镁橄榄岩是部分熔融过程中玄武岩岩浆提取后残留的地幔物质、玄武岩岩浆结晶后的堆积物、通道熔体与壁面橄榄岩相互作用后置换橄榄岩的成因。在这里，我们重点研究了Hidaka变质带Horoman和Oku-Niikappu超镁铁质杂岩以及北海道Kamuikotan蛇绿岩带Iwanai-Dake橄榄岩中的高Mg#橄榄岩。这是为了了解(1)高镁橄榄岩在上地幔物质中的赋存方式，(2)块体岩石和组成矿物的化学成分特征，以及(3)岩浆通道系统的重建，包括岩浆过程和岩浆壁橄榄岩相互作用。结果表明，高镁橄榄岩总是在上地幔橄榄岩内部的岩浆通道中产生，与通道接触处的反应带(交代带)密切相关。在霍罗曼橄榄岩杂岩中，观察到了两种不同的岩浆通道模式。一种是从壁面橄榄岩中提取熔体的岩浆通道作用，另一种是通过通道岩浆喷口的熔体添加作用的岩浆通道作用。在Oku-Niikappu和Iwanai-Dake蛇绿橄榄岩杂岩的高度亏损的方辉橄榄岩中，也主要形成了纯橄榄岩和铬铁矿等高镁橄榄岩。

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.