|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1996 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1995 : ¥1,600,000 (Direct Cost : ¥1,600,000)
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.