|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1991 : ¥200,000 (Direct Cost : ¥200,000)
Fiscal Year 1990 : ¥2,000,000 (Direct Cost : ¥2,000,000)
Petrological characteristics of the upper mantle-lower crust beneath the Japan arcs can be deduced from xenoliths as follows. (1) Rocks constituting the upper mantle-lower crust beneath the Japan arcs are very heterogeneous in terms of thickness of cumulus mantle (Group I ultramafic rocks), degree of refractoriness of mantle peridotites, degree of accretion of young Fe, Al-rich rocks (Group II), and degree of hydration. (2) Deep-seated rocks can be selectively incorporated into host magmas. Uprising magmas may tend to selectively pass through young dikelets and may not catch wall rocks of the dikelets. (3) The heterogeneity of degree of refractoriness of mantle peridotites may be controlled by abundance of associated cumulative ultramafic rocks, especially of dunites. Mantle peridotite xenoliths which are associated with large amounts of dunite xenoliths are usually harzburgite or refractory lherzolite with high-Cr spinel. Formation of dunites within the mantle peridotites makes depletion aureoles around the dunites, enhancing the heteorgeneity of the mantle peridotites. (4) The deep part of the Japan arcs is composed of, in an an ascending order, mantle peridotites (harzburgite and/or Iherzolite), dunite-websterites, olivine gabbros (oe thier metamorphosed equivalents, spinel websterites), and pyroxene-gabbros (mafic granulites). Part of them have been later hydrated to be hornblendebearing peridotites, harnblende websterites and hornblende gabbros (or amphibolites).