The Kuroze Formation in the upper part of the Miocene Hokusetsu Subgroup contains several conglomerate beds with channel structures. Based on thin section observations, the conglomerate clasts are mainly volcanic rock and chert, with minor tuff, tuff breccia, granitoid, quartzite, siliceous mudstone, mudstone, sandstone, and mylonite. Radiolarian fossils in the siliceous mudstone clasts indicate a Middle Jurassic age. In the lower part of the succession, sediments were supplied from the Ryoke granitic and metamorphic basement rocks, whereas in the upper part of the succession, they were derived from more extensive Jurassic and older strata.

The Shimanto accretionary complex in Shikoku, which was exhumed from seismogenic depths, contains many calcite veins. These veins may be studied to better understand the origin of various fluids in the deep sections of a subduction zone. For example, fluid sources may be inferred from comparison of the isotopic ratio of the calcite and its depositional temperature. This study obtained δ¹⁸O_VPDB and δ¹³C_VPDB measurements from 74 samples of calcite veins in the Yokonami Melange and surrounding rocks, which had been exposed to peak temperatures of 140°C to 250°C, comparable to seismogenic thermal conditions in the Nankai subduction zone.

The study results show that the isotopic ratio of calcite is related to the paleo-temperature of the host rock. The lowest δ¹³C_VPDB value for calcite from several measurements obtained for a single location is dependent on the paleo-temperature of the host rock. In addition, the calcite samples from the higher paleo-temperature areas have the lowest δ¹³C_VPDB values. This suggests that crack-seal veins acted as conduits for fluid flow at various stages, and calcite samples with the lowest δ¹³C_VPDB values in an area were deposited during the peak temperature stage. The fluid source of calcite may be inferred from δ¹⁸O_SMOW values and depositional temperature. It is revealed that the calcite veins might be deposited from metamorphic fluid. This implies that in-situ fluid flows within the main body of the accretionary prism, free of exotic fluid from shallow or deep sections along the plate boundary fault.

Forearc basin fills in southwest Japan feature mud diapirs and many associated clastic dikes. The orientations of the clastic dikes allow estimates to be made of the regional tectonic paleostress field at the time of intrusion, although local and episodic changes in stress states may have been induced by the mud diapir intrusions. In this study, regional and local stresses were resolved from the analysis of clastic dike orientations in the Miocene Tanabe Group, southwest Japan. A normal-faulting stress with a WNW-ESE tension axis was common to all sub-areas, suggesting that the stress was regional and had a tectonic origin. This stress is broadly consistent with the N-S-trending maximum horizontal compression axis along the forearc of southwest Japan that prevailed in the early Middle Miocene.

Well-crystallized groundmass fractions are commonly used to obtain reliable K-Ar ages for volcanic rocks, as phenocrysts potentially contain excess ⁴⁰Ar. In general, phenocrysts are removed by magnetic separator, heavy liquid separation, and hand picking. Heavy liquid separation utilizes sodium polytungstate (SPT) solution, which replaced toxic heavy liquids such as bromoform in the 1980s. Recently, a vacuum pump has been used to reduce the filtration time for heavy liquid separation using SPT solution, which has a high viscosity. This note describes the separation procedure for gentle suction filtration using a hand vacuum pump, which can be safely completed in 50-60 minutes per sample. The procedure was tested on andesite and basalt samples from Hakusan, Miyakejima, and Etna Volcanos. Separation of the groundmass fraction from the phenocryst fraction was successful for all andesite samples, whereas separation was incomplete in some of the basalt samples, probably because the gravity of groundmass grains was heavier than the maximum gravity of the SPT solution (3.11 g/cm³).

Gneissose rocks exposed at the Yodoe area, northwestern flank of Mt. Daisen, Tottori Prefecture have been considered as western extension of the Hida metamorphic rocks in the Hida Mountains. We describe a new occurrence of hercynite [(Fe²⁺,Mg,Zn,Mn)(Al,Fe³⁺)₂O₄] in garnet-bearing felsic gneiss from the Yodoe area. Green hercynite occurs exclusively as inclusions in garnet, and is not in direct contact with quartz. The Fe²⁺/(Fe²⁺ + Mg + Zn + Mn) and Al/(Al + Fe³⁺) values of the hercynite are 0.84-0.85 and 0.91-0.92, respectively. The hercynite is characterized by low ZnO content (2.21-2.41 wt%).