Comparative study of oceanic mantle and Island-arc mantle

该项目研究了大洋区和岛弧区的地幔物质。地幔物质是夏威夷盐Laice火山口和四国中部Shingitumura的碱性玄武岩中的结核，分别代表了大洋和岛弧地区。盐湖火山口地幔物质岩石类型多样，从斜长石到石榴二辉橄榄岩。压力和温度条件为31 cb在740 ℃的榴辉岩二辉橄榄岩和20 kb在1070 ℃的石榴石二辉橄榄岩。这些数据表明，夏威夷群岛的地热系数相当高，可能是由于玄武岩物质的持续抬升（即地幔柱）加热所致。辉石岩有两种类型：石榴石辉石岩和尖晶石辉石岩。这些辉石岩是在lherzegli池积云的产物。石榴辉石岩中的石榴子石是在大洋板块横向运动过程中由尖晶石和辉石反应形成的。另一方面，新国村的地幔物质岩石类型多样，但压力和温度条件仅限于900 ℃时的9 kb左右。所有的超镁铁质和镁铁质结核都属于麻粒岩相条件，因此，堆晶岩中的钙斜长石和橄榄石组合不稳定，在接触处形成尖晶石和辉石。这种堆晶岩类型在碱性玄武岩中很常见，其温度与二辉橄榄岩相似。碱性玄武岩还包括类似于新国村围岩的变质岩。虽然介于变质岩和超镁铁质-镁铁质岩石之间的中间岩尚未被分解，但由于玄武质物质的侵入以及随后的冷却和反应，Shinguu-mxira下的下地壳和上地幔非常复杂。

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.