Wollastonite of variable cathodoluminescence (CL) intensity was found in a skarn xenolith from Tadano, Fukushima Prefecture, Japan. Electron microprobe analysis revealed bright-blue and faint-blue CL spots in crystals. Panchromatic CL images revealed that individual wollastonite grains often include bright and dark CL regions of bright- and faint-blue CL, respectively. The TiO₂ contents of bright CL regions (0.055-0.110 wt%) were higher than those of dark CL regions (<0.008-0.013 wt%). The blue CL intensity gradually increased from <0.008 to 0.102 wt% TiO₂, and that with 0.102 and 0.110 wt% TiO₂ was almost the same. The results indicated a positive correlation of Ti content with blue CL intensity.

Shimane Peninsula in the San’in region, SW Japan, has preserved a wide distribution of igneous rocks related to back-arc rifting in the Miocene. We investigated the petrography, geochemistry, and Sr-Nd isotope systematics of rhyolite lavas (Josoji rhyolite: 18-15 Ma) and basaltic to dacitic intrusions of Stage I (∼ 14 Ma) and II (∼ 13 Ma) intrusive rocks. They are classified as medium-K magma series. The Josoji rhyolite and Stage I rocks show chemical compositions of arc-type signatures, whereas the Stage II rocks show elevated Nb and Ta abundances suggesting weaker arc signatures. The geochemical characteristics indicate that the Josoji rhyolite was produced by partial melting of arc-type basalt under lower to middle crustal conditions. The arc signatures of the Stage I rocks were inherited from a remnant metasomatized lithosphere formed by the subduction of the Pacific Plate before the opening of the Japan Sea. The Stage II rocks were formed from a fertile magma that might be produced by the melting of upwelling asthenospheric mantle. We conclude that various magmatic processes took place during and just after the back-arc rifting development in the San’in region.

Feldspar internal textures in a pyroclastic trachyte from Oki-Dogo, Sea of Japan, were examined to expand the understanding of feldspar reactions during the cooling through magmatic to hydrothermal stages, beyond the previous information of feldspars in Oki-Dogo alkaline lava and sheet rocks, using the methods of an electron microprobe and cathodoluminescence. Two types of micron-size internal microtextures were found to coexist in individual feldspar phenocrysts: clear domain textures, formed during a high-temperature magmatic stage, and turbid microperthitic textures, formed during a low-temperature subsolidus stage. The both microtextures are products of metasomatic replacement reactions. In addition, nano-size fluorite grains are aligned across the microtextures. The fluorite occurrence records the behavior of fluorine related to feldspar reactions. The first account of metasomatic microtextures crosscut by fluorite alignments in volcanic alkali feldspars expands our knowledge of feldspar reactions during the cooling and fluorine behaviors related to them in igneous rocks and shows the significance of the careful analysis of feldspar internal microtextures.

The fine structure of goldfish (Carassius auratus) asterisci, which consists of vaterite—a metastable polymorph of anhydrous calcium carbonate—has been investigated and compared with inorganically synthesized vaterites, using electron microscopy. This is as a first step in elucidating the mechanism of polymorph selection of calcium carbonate in the biomineralization of otoliths. X-ray and electron diffraction analyses suggested that there was no marked difference in the unit cell parameters, supercell structure, or stacking disorder features between the asteriscus vaterite and the synthesized vaterites. Although the sizes of the vaterite single crystals in the asteriscus are considerably larger than those in the synthesized ones, both show mosaicity, or crystal aggregates with small misorientations, implying that this character is an intrinsic property of the vaterite structure. The asteriscus consists of slender elements radiating from the central region of the asteriscus, with the elements extending normal to the c-axis, suggesting that the polymorph was selected at the asteriscus initial growth stage.

Understanding the crustal evolutionary dynamics of island arc-trench systems requires a thorough evaluation of magma chamber processes, and especially of shallow crustal granitic magma intrusion and emplacement processes. To address this, we studied the petrography and geochronology of the Kuki granite, Kitakami Mountains, northeast Japan, as an example of a non-adakitic granite at the magmatic flare-up stage. Analysis of paired crystallization temperatures and pressures of hornblende grains reveals the temperature-pressure (i.e., depth) history of the granitic magma. The pressure and temperature history of the Kuki granite indicates no change in the magma depth with cooling from 800 to 730 °C, and geobarometric calculations indicate the emplacement of magma at a depth of approximately 9-10 km. Simultaneous determination of the zircon U-Pb age, Ti concentration, and Th/U yields 1) the time-temperature history of granitic magma before its solidification, and 2) the correlation between temperature and Th/U in the magma. The magma chamber cooled from ∼ 900 to 700 °C at approximately 125 Ma. The change in Th/U with temperature indicates the progression of fractional crystallization in the cooling magma chamber, and greater fractional crystallization in the magma chamber at temperatures above 800 °C than below 800 °C.

Shock recovery experiments on the single crystal rutile and the powdered rutile were performed using a single-stage propellant gun to investigate the effects of porosity (i.e., temperature effect) on the formation of shock-induced deformation microstructures. X-ray diffraction and transmission electron microscopy analyses of the shocked single crystal rutile revealed the occurrence of a high-density stacking fault in the {101} plane of rutile. This defect suggests that the dominant slip system causing the plastic deformation of the crystal was {101}<101> at lower temperatures, forming stacking faults. Additionally, part of the crystal exhibited intergrowth with the α-PbO₂ structure in a topotaxial relationship: <100>_Rutile // <001>_α-PbO2. Topological analysis suggests that the single crystal rutile transforms into the α-PbO₂ structure concomitantly with the shear deformation via the fluorite structure. In contrast, the shocked powdered rutile primarily comprises particles with pervasive entangled dislocations and recrystallized particles, where the α-PbO₂ structure was not observed at all. Considering the absence of stacking faults, the dominant slip system in the shocked powdered rutile should have been {110}<001>, which is expected to work more actively at higher temperatures. These contrasting results on shocked rutile indicate that the shock heating effect and the initial porosity significantly influenced the deformation microstructures and high-pressure phase transformations of rutile in shocked meteorites as well as in impact crater rocks.