| Research Abstract |
Mantle materials in the oceanic and Island-arc regions have been studied in this project. The mantle materials are nodules in alkali basalts in Salt Laice Crater, Hawaii, and in Shingitumura, central Shikoku, as representatives of the coeanic and Island-arc regions, respectively. The mantle materials in Salt Lake Crater are various in rock-type ranging from plagioclase to garnet lherzolite. Pressure and temperature conditions are 31cb at 74OoC for the plaulioclase lherzolite and 20 kb at 1070ﾟC for the garnet lherzolite. These data show that the geotherm xinderiieath the Hawaiian Islands are quite high, probably due to heating by continuius uplift of basaltic materials, i.e, mantle plume. There are two types of pyroxenites;garnet and spinel pyroxenites. These pyroxenites are cumulus products at pools in the lherzolites. The garnet in the garnet pyroxenite was formed by the reaction of spinel and pyroxenes during lateral movement of the oceanic plate.
On the other hand, mantle materials in Shinguu-mura are various in rock-type, but pressure and temperature conditions are restricted around 9 kb at 900ﾟC. All the ultramafic and mafic nodules belong to the granulite facies conditions, hence calcic plagioclase and olivine assemblage, found in cumulate, are not stable to form spinel and pyroxenes at the contact. Such cumulus rock-types are common in the alkali basalt and their temperature are similar to those of the lherzolite. The alkali basalt also included metamorphic rocks similar to the country rocks of the Singuu-mura. Although intermediate rock between the metamorphic and ultramafic-mafic rocks has not been recognisible, lower crust and upper mantle under Shinguu-mxira are highly complex due to intrusions of basaltic materials and subsequent coolings and reactions.
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