Geology and petrology of three plutons (the Epilchik, Machevna and Tigil) in the southern Olyutor Range of Northeastern Kamchatka (USSR) are briefly summarized in this paper. The Upper Cretaceous volcano-sedimentary rocks in the range consititute a prolongation of the submarine Shirshov ridge, that separates the Aleutian passive back arc basin from the Komandorsky basin. Many ultramafic and mafic to intermediate plutons of Paleogene age are distributed in the Upper Cretaceous rocks.
The Epilchik ultramafic pluton shows a concentric structure: the dunitic core passes progressively into wehrlite and clinopyroxenite of the rim, and into a discontinous margin of gabbro. The common presence of diopside and chromian spinel and the absence of orthopyroxene in the ultramafic pluton are characteristics recognized universally in Alaskan-type ultramafic complexes.
The Machevna pluton comprises North and South plutons. The two plutons are both zoned, with gabbroic rim and quartz dioritic core, accompanied by a small amount of clinopyroxenite. The northeastern contact of the North Machevna pluton is characterized by a complicated zone of gabbro and basalt, both the rocks have metamophosed to the amphibolite facies, presumably by synshear, hydrothermal fluid infiltration. The Tigil pluton is composed mainly of gabbro and quartz gabbro. The constituent rocks of the Machevna and Tigil plutons are characterized by low abundances in Ti, Zr and Rb, and by high magnetic susceptibility (30-200×10^-3SI unit). These features are similar to those of plutonic rocks formed in intraoceanic island arcs, such as the Aleutian arc and Papua New Guinea etc..
The constituent rocks of the three plutons and their country rocks have suffered pervasive low-grade metamorphism, commonly up to the greenschist facies. To clarify the petrogeneses of three plutons in detail, further studies from both sides of igneous and metamorphic petrology are wanted.

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Chemical compositions of 32 Paleogene sedimentary rock samples and three basement rock samples from Northern Kyushu, Japan are presented.
Good inverse correlations are found between SiO₂ content and Al₂O₃, Fe₂O₃+FeO, and MgO contents. K₂O/Na₂O and Al₂O₃/Na₂O ratios generally change from the basal formation to the upper formations in respective areas. A-C-F diagram indicates the interrelationship between the chemical composition of Paleogene rocks with that of the basement rocks. The composition also shows their variations between the basins.
The obtained data show the effects of grain size, maturation, and source rocks on the chemical composition of Paleogene sandstones and shales. This fact is consistent with the previous geological and sedimentological views that Paleogene sedimentation in each separated small basin was strongly influenced by the surrounding local geological conditions.

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K-Ar dating and petrologic description were carried out on the Inase valcanic rocks from eastern part of the Kitakami district of Iwate Prefecture, Northeast Japan. We obtained K-Ar whole rock ages of 15.1±0.4 Ma and 15.5±0.4 Ma for two andesites. The results of the present and previous K-Ar age detamination indicate that the volcanic activities in the Inase district took place in the range of 15.5-13.2 Ma. The chemical compositions of representative 32 andesitic samples were determined by XRF technique. The upper Inase volcanics composed of tholeiitic andesites with SiO₂ of 53.61-60.61% have chemical characters similar broadly to those of the Quaternary andesites from the NE Japan arc, whereas the lower Inase ones composed also of tholeiitic andesites with SiO₂ of 53.86-55.28% are characterized by high contents of HFS elements such as P, Ti, Nb, Y and Zr, suggesting that the latter are different in chemical compositions from the typical island arc andesites. We estimated the trace element composition of the primary magmas of the lower and upper Inase volcanics using the method of Sakuyama and Nesbitt (1986) and Yoshida and Aoki (1988). The process identification diagram for the primary magma compositions of the Inase volcanics and the Quaternary volcanics in the NE Japan arc and the surrounding areas suggests that the upper Inase primary magma may be derived from the magma source chemically similar to the present sub-continental mantle beneath the NE Japan arc, while the lower Inase primary magma may be derived from the magma source which is more enriched in HFS element contents than the sub-continental mantle.

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