Peridotite xenoliths from the Ichinomegata crater, the Megata volcano, have a wide spread of Cr# (Cr/(Cr+Al) atomic ratio) of chromial spinet, from 0.07 to 0.53. They frequently have secondary hydrous minerals, pargasite and phlogopite, replacing or veining primary minerals. The amount of pargasite is negatively correlated with the amount of clinopyroxene. Phlogopite occurs only in pargasite-rich rocks. The K/(K+Na) ratio of pargasite increases with an increase of degree of hydration of the rocks. Pargasite and phlogopite are depleted in TiO₂ (<1.6 wt. %). Primary minerals have been chemically modified depending on the amounts of the hydrous minerals added ; olivine and pyroxenes have been enriched with Fe (down to Fo₈₃), and chromian spinel, with Al and Fe³⁺. Metasomatic formation of the hydrous minerals was accompanied with addition of, at least, Na, Ti and K. The metasomatism was caused by infiltration of hydrous arc magmas, which consolidated as phlogopite-bearing hornblendite veinlets, into initially anhydrous peridotites. The fluids subsequently released were diffused into the surroundings to produce hydrous minerals.
Peridotite xenoliths from the Sannomegata crater have a very narrow spread of Cr # of chromian spinel, from 0.10 to 0.25; i.e., all is lherzolitic. They usually have pyroxene-spinel symplectite or its coarsened equivalent, with or without relic plagioclase. They are almost free from hydrous minerals and their primary minerals have been devoid of the metasomatic modification.
The petrographical contrast between the Ichinomegata and the Sannomegata peridotites suggests a strong heterogeneity, in terms both of the anhydrous primary mineralogy and of the degree of hydration, for the upper mantle beneath the Northeast Japan arc.

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The late Cretaceous Kwangju volcanic complex is located at southwestern part of Korea and shows a circular distribution pattern. The geology of this region is complicated by syn-volcanic faulting. The volcanic rocks vary from basaltic andesite to rhyolite, and have geochemical characteristics of calcalkaline series with normative quartz. The studied rocks exhibit similar chemical trends each other, implying that these suites may have generated from the same source. However, large variations in incompatible element ratios can not be produced from the single source in closed system. The geochemical modelling suggests that basaltic andesites have assimilated crustal rock concurrently with fractionation to generate the evolved volcanic rocks. Clinopyroxene and Ca-rich plagioclase were dominant fractionation phases during the early stage of evolution, and further fractionation of Na-rich plagioclase, clinopyroxene and magnetite generated rocks of rhyolitic composition.

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CHIME (chemical Th-U-total Pb isochron) ages have been determined for monazites and zircons from the Hikami Granite, granitoid clasts of the “Devonian” Ono Formation and arkosic sandstones of the “Silurian” Kawauchi Formation in the South Kitakami terrane, on the basis of precise electron microprobe analyses. The main results are as follows:
(1) The CHIME ages of zircons from the Hikami Granite in the Ono area are in the range from 340±20 to 360±20 Ma.
(2) The granitoid clasts in the “Devonian” Ono Formation at Higuchi-zawa can be classified into three age groups: 250-260 Ma, 420-450 Ma and 610 Ma. The age data and petrographical features of the clasts do not show their derivation from the Hikami Granite.
(3) The CHIME ages of detrital monazites from the arkosic sandstones of the “Silurian” Kawauchi Formation at Kusayami-zawa concentrate at ca. 430 Ma with a subordinate mode at ca. 500 Ma, and those of detrital zircons range from ca. 250 Ma to as old as ca. 1800 Ma.
(4) Monazites and zircons from the granitoid overlain by the arkosic sandstone at Kusayami-zawa give ca. 250 Ma CHIME ages; they are significantly younger than those from the Hikami Granite in the Ono area.
These CHIME monazite and, zircon ages do not support a current view that the Hikami Granite is pre-Silurian basement. Rather, the CHIME age data require the detailed stratigraphical and sedimentological re-examination of the Ono and Kawauchi Formations.

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