幌満岩体は3種類の異なる起源のかんらん岩系列一とけ残り物質である Main Harzburgite-Lherzolite (MHL) 系列および各々異なるマグマからの集積岩起源である Spinel-rich Dunite-Wehrlite (SDW) 系列, Banded Dunite-Harzburgite (BDH) 系列一から構成されている。 MHL系列は岩体の大部分を占め漸移境界をもつハルツバージャイト～斜長石レールゾライトの層状の岩塊である。ざくろ石の分解物でめると考えられている輝石-スビネル・シンプレクタイトはスピネル～斜長石レールゾライト中にのみ産する。ほとんどのハルツバージャイトの中心にはシャープな境界をもつ層状のSDW系列の岩石が存在する。産状,化学組成の検討からSDW系列はMHL系列岩石から分離したメルトからの結晶集積により形成されたことが判明した。メルトの分離はクラックの形成によって引き起こされた可能性が高い。BDH系列は高Mgマグマからの集積岩であり, MHL系列にとりこまれた異質岩塊である可能性が高い。

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Rb-Sr chronological study has been carried out on the Miyamoto tonalitic complex to the east of Iwaki city, Fukushima prefecture, northeastern Japan. The rock facies of the complex can be grouped into three in terms of petrological understanding: they are gabbro group, tonalite group, and adamelite group in order of intrusion. The Rb and Sr abundances and Sr isotopic compositions were analyzed for gabbro group rocks (14), tonalite group rocks (8), and adamelite group rocks (5). The mineral separates from one of the gabbro group rocks were also analyzed.
The Rb-Sr age of the tonalite group is 120 Ma, and the initial ⁸⁷Sr/⁸⁶Sr ratio is 0.7052; the results are similar to those of the tonalitic plutonic complexes distributed nearby. The adamelite group yielded 119 Ma as the solidification age with teh inital ⁸⁷Sr/⁸⁶Sr ratio 0.7049. The age is identical to that of the tonalite group, but the initial ⁸⁷Sr/⁸⁶Sr ratio is different between them. Although the tonalite and adamelite group magmas intruded successively and solidified, the origin could largely differ between the two groups.
The gabbro group gave no consistent whole-rock age, and neither did the mineral separates. Excluding biotite, the remaning mineral separates, plagioclase, hornblende, and the whole rock make an isochron with an angle indicating the age of 100 Ma with an uncertainty of 13 Ma. The significance of the obtained mineral age, however, is unclear. The Rb-Sr system of the gabbro group seems considerably disturbed by alteration.

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Various mineral assemblages are observed in the Mineoka metamorphic rocks of basic and siliceous compositions from Byobu-jima, Kamogawa fishing port. Major basic schists are divided into two groups, hematite-bearing and ilmenite-pyrrhotite-bearing. These rocks often contain a rutile-sphene-quartz-calcite sub-assemblage in common, which may have been a buffer of CO₂ and thereby H₂O fugacities in these graphite-free rocks during metamorphism (estimated X_CO2 is around 0.3). The hematite-bearing rocks have a mineral assemblage defining the epidote-amphibolite facies whereas the ilmenite-pyrrhotite-bearing rocks the amphibolite facies, showing the great effect of oxygen fugacity on the silicate mineral mineral assemblages in basic schists. The aegirinaugite-bearing sillceous schists always contain a small amount of K-feldspar in addition to albite, while the epidote-bearing rocks are free of K-feldspar. Thus the occurrence of aegirinaugite is restricted to the rocks deficient in alumina. Some of the aegirinaugite-bearing rocks contain piedmontie and biotie rich in copper and manganese, indicating extremely high oxygen and very low sulfur fugacities in these rocks during metamorphism. Minor psammitic schist occasionally includes pebbles of (alkali) granite, offering a new insight into the sedimentary environment of the original rocks of the Mineoka metamorphi rocks.
Estimated metamorphic pressure and temperature are 5 kb and 500-550°C, respectively.

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