Levyne was found in the cavities of biotite-hornblende-orthopyroxene andesite intruding into Paleogene Kuma formation at the Chuyo quarry, Kodono Kuma-cho, Ehime Prefecture. It is colorless with vitreous lusterand forms thin hexagonal plates up to 4 mm in diameter, being frequently associated with epistilbite. Other cavities contain laumontite, ferrierite, mordenite, heulandite, stilbite, chabazite, apophyllite and calcite. Cell dimensions are a=13.35 (3) and c=22.55 (6) Å. Refractive indices are ω1.497 (2) and ε1.486 (2). EPMA analyses yield anhydrous empirical formulae as follows: Ca1.81Na1.63K0.03Mg0.13Sr0.10 (Fe0.013+Al5.31Si12.58) Σ17.90O36 and Ca1.73Na1.96Mg0.01Sr0.03 (A15.33Si12.55) Σ17.88O36 on the basis of O=36. Kodono's material is characterized by highest Si/Al ratio (=2.37) of levynes reported to date.

The basic and ultrabasic metavolcanics, occurring within the about 1.0 Ga Kuanping Group in the Qinling orogenic belt, China, have been investigated for bulk-rock major and trace-element data. Studied rocks fall into three geochemical categories: (1) komatiites, resembling Barberton-type Al-depleted komatiites; (2) OIB-like basalts, spatially associated with and geochemically similar to komatiites; and (3) MORB-like tholeiites, resembling mid-ocean ridge and back-arc basin basalts. Combining our observations and recent high-pressure experimental data, we accordingly considered an unusual pressure condition at the depth of mantle transition zone and a low-degree critical melting (5-6%) event of a majorite mantle source for the generation of komatiitic initial melt. The OIB-like basaltic melt may have been produced by another low degree melting event of the komatiite-derived source or by high-pressure segregation of initial komatiitic magma at the depth greater than 300 km, whereas the MORB-like tholeiite by 15-30% partial melting of a depleted shallow spinel-peridotite source. An unusually hot rising plume would have controlled the generation of komatiitic and basaltic magma and the magmatic evolution. This plume magmatism may have occurred either in a marginal ocean basin where the mantle plume would also controlled the development of the marginal basin, or in a major ocean basin which had developed between the North-China and the South China platform at about 1.2 to 1.0 Ga.

The Amami plutonic rocks occurring in the Amami-O-shima Islands, Kagoshima Prefecture consist of six small bodies; Kasari, Ichi, Kachiura, Koniya, Ankyaba and Uke. These bodies distributed over the islands and mainly composed of adamellite and granodiorite with minor amounts of tonalite, diorite and gabbro. They are divided into peraluminous and metaluminus groups (P and M) based on their mineral assemblage, major and minor chemical compositions, K-Ar ages and Sr isotopic features. Kasari, Ichi, Koniya and Ankyaba bodies comprise the P group, and others the M group. The Kachiura and Uke bodies of the M group gave K-Ar ages of 17.23±0.22 Ma and 110.3±1.2 Ma, respectively. Age from the Kachiura body is similar to that of granitoids in outer zone of southwest Japan (OZSWJ) rather than that of the P group. Mineralogical and geochemical characteristics and the initial Sr ratio of the Kachiura body are similar to those of I-type granitoids of OZSWJ. Muscovite contents and A/CNK ratios in the P group increase continuously from the back arc side to the trench side, and their initial Sr ratios also show the same trend except for the Ankyaba body. The original magmas on the trench side were more affected by pelite-rich continental materials than those on the back arc side. Such spatial variation is also recognized in granitoids of OZSWJ. The Amami plutonic rocks have similar chemical and petrological characteristics to granitoids of OZSWJ, however, ages of the plutonic rocks are different. Common petrological characteristics between both rocks may have resulted from similar tectonic condition.

The Kurohanayama basalt has been referred to as a representative rock of Quaternary basalts in northeast Japan. There has been a significant amount of petrological studies on these rocks, however, the effused age of the Kurohanayama basalt has not been established yet. In this study, we determined the K-Ar ages of rocks from the Kurohanayama basalt, and obtained 5.03±0.50, 5.2±1.2 and 5.64±0.31 Ma in age. From these data, we have shown that basalts of Kurohanayama effused some time between Late Miocene and Early Pliocene (4-6 Ma). Thus, the Kurohanayama basalt is Tertiary in age, and must be genetically separated from the Quaternary Funagata volcano.

Rb-Sr mineral isochron age was obtained for the unmetamorphozed granodiorite from a dike intruded into the Opirarukaomappu gabbroic complex, southern Hidaka metamorphic belt, Hokkaido, Japan. The isochron gives solidification age of 25.5 Ma with an initial Sr isotope ratio of 0.70362. The obtained age is obviously younger than inferred intensive metamorphic age of 56 Ma in the Hidaka metamorphic belt. The young solidification age is in accord with the other evidences. The hornblende geobarometer of the the granodiorite implied that it crystallized in a shallow crust. The granodiorite dike rocks have more evolved nature than the host diorite, but they are not co-magmatic.

Orthopyroxene-bearing basic metamorphic rock occurs as a block enclosed within pelitic-psammitic metamorphic rock in the Ina district of the Ryoke belt. The orthopyroxene is irregular in shape and includes many rounded crystals of calcic amphibole and plagioclase. Orthopyroxene is a representative metamorphic mineral of the granulite facies for rocks of basic composition and a number of metamorphic reactions to produce orthopyroxene have been proposed. However, none of the metamorphic reactions is consistent with the observed textural relationships and the mineral paragenesis of the rock. The author, therefore, suggests that the orthopyroxene was formed by a distinct process. A simple hypothesis to account for the occurrence of the orthopyroxene is that the orthopyroxene was crystallized after a process of partial melting, i.e., melt produced by partial melting was distributed along grain boundaries of calcic amphibole and plagioclase, and this melt precipitated the orthopyroxene. This hypothesis is supported by the following facts: 1) The texture of the orthopyroxene is unusual for a metamorphic mineral. 2) No simple process other than the crystallization from a partial melt fraction can consistently account for the mode of occurrence of orthopyroxene. 3) Recent experimental results suggest that partial melting of basic rock can take place at the temperatures in the high-grade parts of the Ryoke belt, and furthermore that orthopyroxene is a likely product of such partial melting.

The Oshinkoshin Intrusion is a mushroom-shaped, basaltic andesite intrusion of Pliocene age that occurs in the Shiretoko Peninsula, Hokkaido, Japan. The intrusion is 1000 m long and 400 m wide and consists of three concentric zones: inner massive zone, polyhedral jointed zone, and marginal banded zone. The inner massive zone occupies the central part of the intrusion, and is characterized by columnar joints 100 to 250 cm across. The polyhedral jointed zone encircles the inner massive zone, and is characterized by columnar joints 70 to 150 cm across and small polyhedral joints. The small joints outline 10 to 25 cm polyhedra on both longitudinal and transverse surfaces of the columns. The marginal banded zone encircles the polyhedral jointed zone, and shows rhythmic banding parallel to the margins and columnar joints perpendicular to the margins. The rhythmic banding is composed of alternating protruding, more weathering-resistant and recessive, less resistant bands, both of which are a few centimetres thick. Each protruding band characteristically encloses a central vein. Chemically, protruding bands have higher SiO2 and K2O and lower MgO and total Fe contents than recessive bands. Veins in the protruding band have much higher SiO2, TiO2, Na2O, K2O, P2O5, and lower Al2O3, MgO, CaO than the protruding band. The thicknesses of the protruding and recessive bands gradually decrease toward the margin of the intrusion. The concentric zonal structure in the Oshinkoshin Intrusion formed by cooling of a magma which was emplaced in a single intrusive phase into wet, poorly consolidated sediment. The rhythmic banding in the marginal banded zone formed by concentration of residual melt in numerous parallel cooling fractures along the margin of the intrusion, as the rheological behavior of magma changed from ductile to brittle.

The geology and K-Ar geochronology of the Gassan volcano in Northeast Japan were carried out to establish the volcanic history. This volcano is belonging to the Chokai volcanic zone, and composed of several volcanic edifices. On the basis of the field geology and K-Ar dating of the ejecta, the volcanic history is divided into five stages; Stage I (0.88 Ma): the Amamoriyama was formed by dacite volcanism. The dacite lava is composed with hypersthene, augite, hornblende, biotite and quartz phenocrysts. Stage II (0.7 Ma): The Yudonosan, which is composed of a stratovolcano and two lava domes of mainly dacite lava and pyroclastics. Stage III: The volcanism occurred in the north of the Yudonosan. The dacite lava and pyroclastics covered on the basements in the caldera and the lower Yudonosan lava in the Ishihane river. Stage IV (younger than 0.6 Ma): The volcanism of the major stratovolcanoes of central Gassan, the Waratahageyama and the Ubagatake, which are composed of lavas and pyroclastics. The rocks are calc-alkali andesite containing hypersthene, augite, sometimes a small amount of olivine and rarely hornblende. Stage V: The collapse of the northwestern half of Gassan stratovolcano, caused the formation of a horseshoe-shaped caldera and dry avalanche deposits. The rocks of the Gassan volcano are divided into two groups, dacite and andesite in their temporal as spatial distributions.

The Kuma Group, Shikoku, has been referred as Eocene deposits since Nagai (1956). Here we report new fission-track ages from the Kariba Sandstone-Mudstone Formation. Our data indicate that the group is of Early Miocene age.

The Shirakawa pyroclastic flows consist of four pyroclastic flow deposits erupted about 1.3-1.0 Ma in the southern part of Tohoku-Honshu arc. These eruptions are characterized by two different modes of eruption. The eruptions of the older two deposits, the Kumado and Ashino pyroclastic flows, were followed by many numbers of intermittent Plinian eruptions, which persisted for about a few ten thousand years. It is thought that the mode of volcanic eruption corresponds to that of a polygenetic volcano. In contrast, the eruptions of the younger two deposits, the Nishigo and Ten-ei pyroclastic flows, were both single eruption event and no subsequent Plinian eruption was associated. The mode of eruption is similar to that of a monogenetic volcano. The duration of repose between each eruption of pyroclastic flow deposits exceeded a few ten thousand years and is nearly comparable with that of the Aso volcano and longer than that of the Towada volcano (10 or 20 thousand years). The estimated whole life span of the volcanic activity of the Shirakawa pyroclastic flows is about 250 thousand years. It seems to be rather shorter than that of a ordinary Quaternary stratovolcano.