北海道の東部,知床半島の知床岬海岸において,花崗岩類の礫を見いだした。これらは径5～20cmの円礫～亜円礫をなす。これらの花崗岩礫の岩石学的記載,主成分全岩化学分析, K-Ar法による年代測定を行った。知床岬の花崗岩礫は,アダメロ岩,花崗閃緑岩および石英モンゾニ岩からなる。これらの多くは半自形粒状組織を呈するが,石英モンゾニ岩と花崗閃緑岩の一部は圧砕組織を呈する。アダメロ岩中の黒雲母は191.8 ± 4.5 Ma, 圧砕花崗閃緑岩中のカリ長石は114.6 ± 2.5 Ma, 圧砕石英モンゾニ岩中の白雲母は124.2 ± 2.7 MaのK-Ar年代を示した。知床岬の花崗岩礫の岩石学的性質とK-Ar年代は,オホーツク海からドレッジされた花崗岩類に似ており,それらはオホーツク海域の大陸地殼を構成する花崗岩類の一部である可能性が高い。

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The Yurappu-dake plutonic complex in the central Oshima Peninsula can be divided into two series; a northern gabbroic body of 5 × 1km and a southern granodioritic body of 14 × 10km. The former consists of coarse gabbro, fine quartz gabbro, coarse quartz gabbro, fine tonalite, and porphyritic granodiorite, and the latter includes tonalite, granodiorite 1, granodiorite 2, and garnet bearing granite. Based upon the field observations, the following order of intrusion of this complex is proposed: 1) successive intrusions in the gabbroic body from early coarse gabbro to late porphyritic granodiorite, and 2) an intrusion of the main granodioritic body followed by a minor intrusion of the garnet bearing granite. The main granodioritic body shows continuous reverse zoning from two tonalitic cores to a felsic margin of the granodiorite 1 and 2. This reverse zoning appears to be the product of in situ crystal accumulation. Rapid solidification may have promoted to preserve the configuration of inward concentration of early-formed minerals due to magmatic convection. The gabbroic rocks and granodioritic ones exhibit continuous variation patterns in the bulk chemistry and mineralogy, indicating a close genetic relationship between the two rocks.

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Musa volcano is situated at the central part of the Akan-Shiretoko volcanic chain, which belongs to the Kurile arc, eastern Hokkaido. In this region, Pliocene subaqueous volcanism (Yunosawa, 574m highland, and 626m-peak volcanoes) has changed to terrestrial one (Musa volcano) in early Pleistocene. Musa volcano is composed of a cluster of several stratovolcanoes and lava domes, and is topographically divided into two stages, older and younger. K-Ar age of the andesite from the younger stage has been obtained to be 0.48 ± 0.19 Ma.
The eruptive rocks of Musa volcano ranges from basaltic andesite to dacite, and are defined as low-K series of Gill (1981). K₂O content of the rocks increases from the volcanic front (Musa and Mashu volcanoes) to the back arc side (Shari, Shiretoko-Iwo volcanoes). The zonal distribution of lava chemistry (eg. K₂O) in the southern part of the Kurile arc transverses the echelon arrangement of the volcanoes.

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ディオプサイド (CaMgSi₂O₆)-アクマイト (NaFeSi₂O₆) 系の低酸素分圧下 (fO₂=10^-8, 10^-10,10^-12 atm) における相平衡関係を1000～1400°Cの温度範囲において検討した。各酸素分圧下における平衡状態図は基本的には変わらず, 1000°C以下では2つの端成分の間に輝石固溶体の単相領域が存在する。アクマイト組成50%以上の領域では輝石固溶体は磁鉄鉱＋液 (fO₂=10^-8, 10^-10) かウスタイト+液に分解熔融する。一方ディオプサイド成分に富む領域の初晶は輝石固溶体である。X線回折データから判断するに,高温低酸素分圧下で形成される輝石固溶体はディオプサイド,アクマイト成分のほかにヘデンベルグ輝石成分をも含む。

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Twenty eight major, minor and trace element contents in the nine rock reference samples of the “Sedimentary rock series” issued by the Geological Survey of Japan; lake sediment JLk-1, stream sediments JSd-1, to JSd-3, slates JSl-1 and JSl-2, chert JCh-1, limestone JLs-1, dolomite JDo-1, have been determined by wet chemical techniques, atomic absorption spectrometry, flame emission spectrometry, spectrophotometry, ion-electrode method, and photon activation analyses. It is difficult to determine accurately for trace amounts of Na₂O and K₂O in JLs-1 and JDo-1 because of contamination in analytical process, and for P₂O₅ in the all rock reference samples of the “Sedimentary rock series” because of presence of organic carbon in them.

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