Rare-earth elements in rock reference samples were analysed by ion chromatography using α-hydroxyisobutyric acid (α-HIBA) as an eluent. The technique employs the chelating agents to permit the separation of individual REEs as cationic complexes. Use of α-HIBA is more appropriate for the elution of REEs than of oxalic acid. The reasons are as follows: 1) The heavier REE abundance in geologic samples is lower than lighter one, so for the purpose of decreasing the tailing, it is important to elute REE in order of the lower abundance i.e. heavy REE. 2) The baseline is steadier, and 3) the separation of individual REEs is better than that by the techniques using oxalic acid. By this method, however, it is impossible to obtain data for Dy, due to interference by Y.
     Providing that more sufficient care is taken over preparations of standard solution and eluent in purpose of separation of individual REEs, the accuracy will be improved and ion chromatography can be one of the available techniques for REE analysis of geological samples.

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Northern Hokkaido is situated in the back arc region behind the arc-arc junction of the Kurile and Northeast Japan arc. The district is unique because it is located between two back-arc basins, Kurile and Japan basins. Tertiary small-scale shield-like volcanoes (flat lavas) and volcaniclastic formations are widely distributed in this district. 9 K-Ar ages and 148 major element chemistries for these volcanic rocks were determined to clarify their petrological features and tectonic evolution of this district.
     The newly determined and previously reported K-Ar ages indicate that the vigorous volcanic activity took place during a short period from 14 to 9 Ma in the district. Total volume of the volcanic rocks is more than 650 km³. The volume of the volcanic rocks decreases from east (Sea of Okhotsk side) to west (Japan Sea side), suggesting that the volcanism took place mainly in eastern to central part. Most of the volcanic rocks are calc-alkaline and low-K to medium-K tholeiitic andesites, common in island arc setting. However, high TiO₂ andesites and icelandite-like dacites also occur along the Sea of Okhotsk. In addition, the volcanic rocks in northern Hokkaido show no systematic across-arc lateral variation in K₂O content.
     The spatial variation in the chemical composition suggests that the Tertiary volcanism in northern Hokkaido was not caused by subduction of the Pacific plate. We presume that the volcanism was due to the episodic uprising of heat source (asthenospheric mantle?) which should be related to the opening of the Kurile basin.

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Orbicular rock from Inusotoba, Shiroishi, Miyagi Prefecture was studied by optical and chemical methods. The orbicules, which are 5∼20 cm in diameter, are divided into two parts, — core and shell. The core is ball-shaped and dark-colored, and consists mainly of fibrous hornblende and chlorite. The shell, which surrounds core, is light-colored and consists of coarse radial anorthite crystals less than l cm long, which are elongated to a-axis. These radial crystals are characterized by micro subgrains of albite twin and parallel-growing crystals. The other type of orbicule is also known, whose shell consists of several alternate layers of mafic and felsic minerals. This latter type of orbicules is never produced together with the former radial type. The matrix, solidified among orbicules, has a heterogeneous texture, which consists of the dark-part of poikilitic hornblende and the light-part rich in euhedral plagioclase.
     The forming environment of orbicular rocks is featured by many close-packed orbicules, the flow structure of felsic mineral assembledge in matrix and unmixing of magma including orbicules with the other magma containing plagioclase spherulites. It is considered that orbicules were formed in supercooling magma possibly due to income of another magma.

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