The present study reports the geochemical characteristics and new precise zircon U-Pb age of alkali basalt to trachyte that form the basement of the reef limestones of the Akiyoshi Terrane, Southwest Japan. The rocks of the Yamano Group (part of the Permian Maizuru Terrane) in the Yakawa area, eastern Hiroshima Prefecture are unconformably overlain by the Inakura Formation of the Cretaceous Kanmon Group. The latter contains limestone blocks and is accompanied by underlying volcanic rocks that are extremely vesicle-rich and highly altered. We carried out detailed petrographic studies on one trachytic rock, and three basaltic rock samples from the Yakawa area. Apart from that, we also have studied two basaltic samples from the Akiyoshi-dai area, one from the Atetsu-dai area, one from the Oga-dai area, and one associated with the Hina Limestone. Geochemically, except for one trachyte-phonolite sample, all other samples from Yakawa, Hina Limestone, Oga-dai, and Atetsu-dai areas are alkali basalt, while samples from Akiyoshi-dai are basalt. The U-Pb zircon age of the trachytic sample from the Yakawa area yielded a crystallization age of 335.8 ± 1.6 Ma. The tectonic discrimination diagram indicates that the samples of the Yakawa area and Hina Limestone are of French-Polynesia-type superplume origin, while the rest are of normal hotspot region affinity. Zircon geochemistry also corroborates the fact that their origin was in the hotspot-type oceanic island.

Imayoshiite, Ca₃Al(CO₃)[B(OH)₄](OH)₆·12H₂O, is a rare mineral belonging to the ettringite group. The imayoshiite discussed in this paper was discovered in hydrothermally altered pockets at the Shijiangshan mine, Hexigten Banner, Chifeng City, Inner Mongolia, China. Before its discovery at the Shijiangshan mine, the only known locality for this mineral was Suisho-dani, Ise City, Mie Prefecture, Japan. The formation of Shijiangshan imayoshiite relates to the low-temperature hydrothermal processes during the late skarn stage. Its euhedral crystals exhibit a combination of hexagonal dipyramid {10-12} and hexagonal prism {10-10}. The empirical chemical formula of the sample is Ca₃(Al_0.78Si_0.11Fe_0.01)_∑0.90{[B(OH)₄]_0.91(CO₃)_0.60(SO₄)_0.45}_∑1.96(OH)_5.80·12.39H₂O, with Z = 2 (based on Ca_apfu = 3). Due to its disordered structure and specific crystal-chemical features, the crystal’s structure was solved and refined with a higher symmetry space group (P6₃/mcm) compared to the previously reported (P6₃). Using this space group and unit-cell parameters of a = 11.0663(6) Å, c = 10.6387(6) Å, and V = 1128.30(14) ų, the refinement converged to R = 0.0492. X-ray photoelectron spectroscopy (XPS) showed that all S atoms are present as SO₄²⁻. This study presents new data on the high-symmetry variety of imayoshiite, i.e., imayoshiite-P6₃/mcm, and summarizes the complex ligand morphology resulting from disorder in the ettringite group.

A Middle Miocene picritic dolerite sill is exposed to the southwest of the Sado Island, the largest island in the Sea of Japan. This picrite has two types of phenocrystic olivine: high-Fo and -Ca normally zoned olivine with abundant Cr-spinel inclusions (type-1) and low-Fo and -Ca reverse-zoned olivine without Cr-spinel inclusions (type-2). Type-1 olivine and type-2 olivine mantle are in equilibrium with the chilled margin of the sill, but the type-2 olivine core is clearly in disequilibrium with that. This suggests that the types-1 and -2 olivine crystals may be autocrysts and antecrysts, respectively. These two types of olivines contain multiphase solid inclusions in their cores. These inclusions are also classified into the following two types based on the mineral assemblage and average bulk composition: plagioclase + clinopyroxene + hornblende assemblage with basaltic composition (O1-type) and orthopyroxene + clinopyroxene + hornblende (± plagioclase) assemblage with high-magnesian andesitic composition (O2c-type). The composition of glasses coexisting with plagioclase in multiphase solid inclusions indicates that plagioclase crystallized at the early stage of crystallization in the O1-type inclusions but did not crystallize until the last stage in the O2c-type. The mineral assemblages suggest that the O1- and O2c-types multiphase solid inclusions represent the trapped basaltic and high-Mg andesitic melts, respectively. Our results suggest that the type-1 olivine is autocrysts crystallized from a primitive basaltic magma and the type-2 olivine core is antecrysts crystallized from an H₂O-rich high-Mg andesitic magma. After the type-2 olivine core crystallized at the deeper parts (>130-190 MPa), it was then incorporated into the primitive basaltic magma. Consequently, the high-Fo and -Ca olivine mantles grew around the type-2 olivine cores under the condition of moderate undercooling at a shallower depth. The high-Mg andesitic magmatism inferred from the O2c-type multiphase solid inclusions in the picrite suggest that the highly depleted oceanic mantle infiltrated by slab-derived melts/fluids may have existed ubiquitously under the back-arc basin during the Miocene back-arc opening of the Japan Sea.

Many large-scale volcanic ash deposits of different eruption ages and origins are widely distributed in the southern Kyushu region of Japan. Among these volcanic ash deposits, allophanes Kp and Op were collected from the Kikai Akahoya ash fall deposit and the Osumi pumice fall deposit, respectively. The mineralogical characteristics of the allophanes were examined using X-ray diffraction, X-ray fluorescence analysis, attenuated total reflectance Fourier-transform infrared absorption spectroscopy, scanning electron microscopy, and differential thermal and thermogravimetric analysis. In addition, acid-base titration and ion adsorption experiments were conducted to verify the surface charge characteristics and adsorption properties for major ions in the biosphere, such as K⁺, NH₄⁺, NO₃⁻, and SO₄²⁻. Chemical analysis showed that allophanes Kp and Op had Al/Si = 1.72 and 1.23, and Fe³⁺/Si = 0.19 and 0.10, respectively, indicating that allophane Kp was relatively enriched in Al and Fe³⁺, whereas allophane Op was enriched in Si compared to allophane Kp. Acid-base titration experiments revealed that allophanes Kp and Op exhibited the point of zero charge at pH 6.5 and 5.1, respectively. The surface charge characteristics of each allophane were consistent with their different chemical compositions. Ion adsorption experiments demonstrated that allophane Kp tended to adsorb fewer cationic species (K⁺ and NH₄⁺) and more anionic species (NO₃⁻ and SO₄²⁻) than allophane Op, which were in good agreement with their surface charge characteristics. Furthermore, these allophanes adsorbed more NH₄⁺ than K⁺ and considerably more SO₄²⁻ than NO₃⁻. The adsorption behaviors of K⁺, NH₄⁺, NO₃⁻, and SO₄²⁻ on the surfaces of allophanes Kp and Op were similar to those on kaolinite and Fe- and Al-oxide minerals reported previously.

The Maizuru Belt in Southwest Japan is a Permian island arc-back-arc basin system that includes fragments of continental massifs ranging in age from the Neoarchean to Triassic. The Northern Zone of the Maizuru Belt is composed mainly of fragmented granitic rocks with subordinate pelitic/psammitic metamorphic rocks, and their geochronological and geochemical characteristics are key for defining the tectonic correlation between the Maizuru Belt and Northeast Asian continents. Previously, occurrences of the Northern Zone of the Maizuru Belt have been restricted to two identified localities; however, we have identified a new Paleozoic igneous-sedimentary rock unit in the Kume area of northern Okayama, and it is confirmed to be part of the Northern Zone of the Maizuru Belt. The weighted mean zircon ²⁰⁶Pb/²³⁸U ages of the tonalite mylonite in this unit are 487.8 ± 2.5 Ma, and those of the granite mylonites are 449.3 ± 3.6, 323.0 ± 3.2, 312.2 ± 2.7, and 299.6 ± 2.6 Ma, respectively; these ages represent the timing of magmatism based on the oscillatory zoned texture of the zircon grains. Geochemically, these granitic mylonites commonly show an arc affinity. The detrital zircon U-Pb age of the pelitic slate in the same unit shows a youngest age of ∼ 278 Ma with two major age clusters of ∼ 380-280 (∼ 67%) and ∼ 530-430 Ma (∼ 28%) with very minor Precambrian detrital zircon grains. These age populations are strongly correlated with the magmatic ages of the granitic mylonites in the same unit and further represent the overall magmatic episodes of the unit. These new data indicate that the timing of magmatism in the Kume area is correlated with that of the Khanka-Jiamusi Massif, suggesting their common evolutionary history along with the Maizuru-Oe area of the Northern Zone of the Maizuru Belt.

Miyawakiite-(Y), a newly discovered mineral having the ideal formula □Y₄Fe₂(Si₈O₂₀)(CO₃)₄(H₂O)₃ of a new structure type, was found in a granitic pegmatite from Suishoyama, Kawamata Town, Fukushima Prefecture, Japan. It is composed of tiny crystals of granular, plate-like, or columnar shape up to 0.8 mm with a pale-yellow color. It is transparent with a vitreous luster, occurring as a secondary mineral in a cavity in an aggregate composed of allanite-(Y) and britholite-(Y). The Mohs hardness is 3-4. Its tenacity is brittle, and its calculated density is 2.95 g·cm⁻³. Under plane-polarized light, the mineral is pleochroic with O = colorless and E = pale yellow. It is uniaxial (+), with refractive indices of ω = 1.593(3) and ε = 1.654(2) (white light). Dispersion is weak. The empirical formula, calculated on the basis of 4 C and 8 Si atoms per formula unit, is (□_0.70K_0.30)_Σ1.00(Y_2.95Dy_0.21Yb_0.12Er_0.10Gd_0.08Sm_0.02Tb_0.01Ca_0.33)_Σ3.82(Fe²⁺_1.14Mg_0.48Mn_0.24)_Σ1.86Si₈C₄O_31.42[(H₂O)_2.70(OH)_0.30] after electron microprobe, Raman spectroscopic, and crystal structure analyses. The refined unit-cell parameters determined by single-crystal X-ray diffraction are a = 17.53637(9), c = 9.55702(8) Å, V = 2939.02(4) ų, and Z = 4 in conjunction with the I4/mcm (#140) tetragonal space group. The structure is quite unique: the Y- and Fe-centered polyhedral arrangement with CO₃ triangles forms a prismatic framework, with channels leading in the c-axis direction. The SiO₄ tetrahedral networks are developed in this channel, forming a zeolite-like framework with K sites inside. The correlation between the OH/H₂O and K contents results in a solid-solution series of □Y₄Fe₂(Si₈O₂₀)(CO₃)₄(H₂O)₃-KY₄Fe₂(Si₈O₂₀)(CO₃)₄[(H₂O)₂(OH)].

To understand fluid activity around a granitic pluton, a petrological study combined with U-Th-total Pb chemical dating of accessory U-Th oxides was conducted on a zoned calcsilicate vein from the contact aureole of the Cretaceous Kaizukiyama granite, Japan. The vein exhibits distinct zoning with the following sequence of major assemblages from the host rock (dolomitic marble) to the vein center: Zone 1 (comprising three mineral assemblages in order away from the host rock: clinohumite + calcite, forsterite + calcite, and diopside + forsterite + calcite), Zone 2 (clintonite + spinel + Al-rich clinopyroxene or pargasite + calcite), and Zone 3 (grossular + anorthite + clinopyroxene + calcite). Additionally, various U-, Th-, and REE-rich accessory minerals occur in Zones 2 and 3. Grossular and anorthite in Zone 3 are extensively replaced by later-stage minerals (clinozoisite or prehnite + muscovite). Zone 1 is likely a metasomatic reaction vein formed by interactions between the host dolomitic marble and aqueous silica in the infiltrating fluid. The mineral assemblage in Zone 2 likely resulted from interactions between Zone 1 and a fluid enriched in alumina. Thorianite grains in Zone 2 yield a chemical age of 97.0 ± 1.1 Ma, contemporaneous with the emplacement age of the Kaizukiyama granite. The primary minerals in Zone 3 probably formed during a crack-sealing process associated with new fluid infiltration, which also slightly interacted with Zone 2. The later-stage minerals in Zone 3 are attributed to low-temperature hydrothermal alteration. Uraninite grains in Zone 3 yield a chemical age of 88.1 ± 0.8 Ma, likely related to the hydrothermal alteration stage. Combining these results with the previously established cooling history of the Kaizukiyama granite suggests that low-temperature hydrothermal activity may have continued for a long period (∼ 6 Myr) in the surrounding area after the rapid initial cooling of the pluton.

Descriptive mineralogical studies, including single-crystal structure analysis, were conducted on aluminosugilite and norrishite, two rare minerals from the Funakozawa mine. Aluminosugilite occurs in the quartz layer spread along the schistosity of the slate as foliated reddish-light purple crystals up to 1 mm in diameter and 50 µm thick. The cleavage is indistinct, and the Mohs hardness is 6. Aluminosugilite coexists with aegirine and amphibole. In the outcrop, aluminosugilite often transforms into swinefordite with its texture retained. The representative chemical composition of aluminosugilite from a boulder sample was K_0.98Na_1.93(Al_1.31Fe_0.44Mn_0.17)_Σ1.91Li₃Si₁₂O_29.82, and single-crystal X-ray data yielded a hexagonal P6/mcc lattice with a = 9.9894(7) Å, c = 13.9527(9) Å, and V = 1205.77(14) ų. The structure refinement converged to R₁ = 2.67%. The structure may limit the accommodation of the Jahn-Teller cation, Mn³⁺, due to symmetry. Norrishite is one of the most abundant constituent minerals in slate and coexists with aegirine and amphibole. In thin sections, norrishite is observed to be surrounded by quartz. Norrishite is brown to black and is in the form of irregularly shaped foil-like to plate-like crystals that exhibit perfect cleavage at {001} planes. Norrishite is also pleochroic and highly polychromatic with color variation from yellow to brown to green. The representative chemical composition of norrishite from a boulder was K_0.99(Mn_1.97Mg_0.09Ti_0.03Li_0.92)_Σ3(Al_0.22Si_3.78)_Σ4O_11.95, which represents an absolutely Fe-free composition. Single-crystal X-ray data yielded a monoclinic C2/m lattice with a = 5.3024(2) Å, b = 8.9520(4) Å, c = 10.0812(5) Å, β = 98.191(4)°, and V = 473.65(4) ų as the 1M polytype. The structure refinement converged to R₁ = 4.30%. The structure is sufficiently flexible to accept the Jahn-Teller cation, Mn³⁺, but then its ability to form a solid solution with other components is limited.

Opal from the Shikaribetsu area, Shikaoi, Hokkaido, Japan exhibits visible photoluminescence. The opal is characterized using powder X-ray diffraction (XRD) measurements, fluorescence spectroscopy, and fluorescence lifetime measurements. The XRD pattern of the powdered sample indicates that the opal is amorphous opal-A. The dried powdered opal exhibits broad emission spectra ranging from 450 to 750 nm with the maximum at approximately 590 nm. The emission decay curve is fitted with the multi-exponential decay function. The average emission lifetime is shorter than 10 ns, and the emission is ascribed to fluorescence. The d-d transition of transition metal ions and the f-f transition of lanthanide ions are forbidden according to the Laporte selection rule, and their emission lifetime should be much longer than that observed in this study. Therefore, the transition metal ions or lanthanide ions are not the origin of the photoluminescence of the opal. The fluorophore can be extracted from the opal to organic solvents, and the fluorescence color changes from orange to bright cyan in the solvent. The fluorescence and fluorescence excitation spectra show the narrow bands which can be ascribed to the vibronic transition of organic molecules. The typical fluorescence lifetime is approximately 8 ns. These results suggest that the fluorophore in the opal is polyaromatic hydrocarbon molecules. It is also demonstrated that the solvent extraction is a useful method to study the origin of the fluorescence and to analyze ingredients in the opal.

Low-molecular-weight organic acids are the predominant biological molecules released by microbes in the earth’s surface environments. To elucidate the effect of the molecules on the formation and polymorphism of calcium carbonate (CaCO₃) minerals in hot water environments, we studied the formation of CaCO₃ minerals in systems containing citric acid, malic acid, or acetic acid at 40, 60, and 80 °C for 24 h. Each system contained 5.0 mmol/L Ca²⁺, 20.0 mmol/L total carbonate ions, and 0.0, 0.01, 0.05, 0.1, 0.5, and 1.0 mmol/L organic acids. Our results demonstrated that citric acid considerably suppressed aragonite formation and promoted rhombohedral calcite formation with increasing citric acid concentration at temperatures up to 80 °C. Malic acid showed a similar effect on CaCO₃ polymorphism to a slightly lesser extent than citric acid, whereas acetic acid exhibited a much lower effect than the other two organic acids. Moreover, the rhombohedral calcite crystals changed to a polyhedral morphology, and then to polyhedral crystals elongated along the c-axis with increasing citric acid concentration at 40 °C. However, very little or no significant effect on the calcite morphology was observed in the systems containing malic acid and acetic acid. The greater effect of citric acid on the CaCO₃ polymorphism is likely due to the stronger adsorption affinity of citric acid for the aragonite surface compared to that of malic acid and acetic acid. In the morphology of calcite, citric acid is likely to preferentially adsorb on the {hk0} faces such as {110} and {100} of calcite crystals at 40 °C, resulting in the inhibition of crystal growth in the direction perpendicular to the c-axis and promotion of growth in the direction parallel to the c-axis.

Granitic rocks (sensu lato) represent unerupted felsic magmas crystallized in the crust. In this study, we estimate water contents of melts and crystallization pressures of zircons in granitoid magma using melt inclusions in zircon, a ubiquitous accessory mineral in granitoids. Homogenization experiments of polymineralic inclusions hosted in zircon have been conducted for a granitoid sample from the Cretaceous Gamano granodiorite in Yashiro-jima Island, southwest Japan, using a piston-cylinder high-pressure-high-temperature apparatus. SEM-EDS analysis reveals that the homogenized melt inclusions have high water contents (6.4-11.3 wt%) and high SiO₂ contents (76-78 wt% anhydrous basis) implying that they represent fractionated interstitial hydrous melts trapped in growing zircon crystals. A recently proposed machine learning-based melt-phase assemblage geobarometer yields pressures ranging from 563 to 266 MPa interpreted as crystallization pressures of the zircons. The results of this study suggest high water activity of the interstitial melts within the Gamano granodiorite magma at the time of zircon crystallization. The melt inclusions in zircons record a wide range of pressures, from intrusion of the magma into the deeper crustal levels (∼ 563-509 MPa) to final solidification at shallower levels (∼ 266 MPa).

The chemical composition of swedenborgite sample obtained from the type locality, Långban, Värmland, Sweden, was determined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that swedenbolgite crystals possess both Ca-free and Ca-containing zones. The crystal structures of swedenborgite [space group P6₃mc, a = 5.4402(10) Å c = 8.8690(9) Å, Z = 2] was refined to R1 = 0.012 using 1573 unique reflections. In addition, the threshold energy of the Sb K-edge XANES spectrum of swedenborgite was found to be higher than that of Sb₂O₃, but almost the same as that of Sb₂O₅. These results indicated that the oxidation state of Sb in swedenborgite was almost pentavalent, although the presence of a small amount of trivalent Sb is also suggested. It was therefore assumed that the following substitution relationship exists: 2Na⁺ + Sb⁵⁺ ⇄ 2Ca²⁺ + Sb³⁺, and that the charge balance of Ca occupation is achieved by reduction of some Sb⁵⁺ ions in the Ca-containing zone. The general formula of swedenborgite was therefore expressed as (Na_1−xCa_x)Be₄Sb⁵⁺_1−0.5xSb³⁺_0.5xO₇ (x = 0.0 or 0.05-0.07). The distortions of the Be-O distances along the c-axis and O-Be-O angles of BeO₄ trigonal pyramid in swedenborgite were significantly larger than those in BeO bromellite. Opposite coordinate shifts between cations and anions along the c-axis occur because of the asymmetric arrangement around the NaO₁₂ tetradecahedra with upper face sharing and lower edge sharing. The structure of swedenborgite therefore exhibits a biased arrangement of cations and anions parallel to the c-axis, which induces spontaneous polarization.

Shiranuiite, a newly-discovered platinum-group mineral in the carrollite-type thiospinel group with an ideal formula of Cu⁺(Rh³⁺Rh⁴⁺)S₄, was discovered at Haraigawa, Misato machi, Kumamoto Prefecture, Japan. This mineral was named after the ancient name for Kumamoto Prefecture, ‘Land of Fire’, which appeared in an anecdote about Emperor Keiko’s pilgrimage to Kyushu recorded in the Nihon Shoki: ‘the fire that everyone does not know about (= SHIRANUI, in the Japanese historical kana orthography)’. Shiranuiite occurs as the most abundant mineral in nubs accompanied by isoferroplatinum-based grains and is occasionally associated with bowieite, cuprorhodsite, michitoshiite-(Cu), and oxidized platinum-group minerals. Shiranuiite is opaque and has a metallic luster with a bluish gray color in reflected light. The Mohs hardness of this mineral was estimated to be 5 according to the analogous thiospinel-group minerals, and a density of 5.78 g·cm⁻³ was calculated from the empirical formula and powder X-ray diffraction data. The empirical formula, on the basis of 7 apfu is (Cu⁺_0.95Fe³⁺_0.04Ni²⁺_0.01)(Rh³⁺_1.20Rh⁴⁺_0.77Ir⁴⁺_0.06Pt⁴⁺_<0.01)S_3.99. Powder X-ray diffraction measurements indicated that the mineral has the spinel structure and belongs to the space group Fd3m with lattice parameters of a = 9.757(2) Å and V = 928.9(5) ų (Z = 8). Evidence for a spinel structure was also provided by Raman spectroscopy. Both shiranuiite and cuprorhodsite are altered products of bowieite and are highly immiscible in the Cu-Fe system. There is evidence suggesting that shiranuiite formed at a later stage than cuprorhodsite, i.e., these two minerals may form at different stages.

Knowledge of the viscosity of melts and liquids at high pressure conditions is essential to understand the mobility of magmas and other liquids in the Earth’s interior. The falling sphere viscosity measurement in large volume press using synchrotron X-ray imaging is one of the most powerful techniques for investigating the viscosities of melts and liquids at high pressure and high temperature conditions. Despite capability of the in-situ X-ray radiography falling sphere viscosity measurement strongly depends on the speed of X-ray imaging, common imaging setups are limited to speed of ∼ 30-60 frames/second (fps), which hamper proper viscosity measurements on low viscous melts and liquids. In this study, we developed a new high-speed X-ray imaging setup up to 5000 fps combined with 1500-ton multi-anvil press at the BL04B1 beamline in the SPring-8. By using the high-speed X-ray imaging with the frame rate of 1000 fps, we succeeded to determine low viscosity value of 0.0081 (±0.0011) Pa s in calcite (CaCO₃) liquid at ∼ 4.7 GPa and ∼ 1925 °C. The high-speed X-ray imaging combined with 1500-ton multi-anvil press at the BL04B1 beamline would expand capability of falling sphere viscosity measurement of low viscous liquids at high pressure conditions of deep mantle.

Clinopyroxene (Cpx)-rich peridotites have been observed at the base of mantle section from northern to southern massifs in the Oman ophiolite. We present Nd isotopic ratios of Cpx grains separated from the Cpx-rich peridotites of the central Sarami massif and compared them with published Nd isotopic ratios of Cpx grains from the northern Fizh and the southern Wadi Tayin Cpx-rich peridotites. The Nd isotopic data combined with spinel Cr# suggest that fertile Cpx-rich peridotites (spinel Cr# < 0.3) from the northern and the central massifs preserved a simple melt extraction event, whereas relatively refractory Cpx-rich peridotite (spinel Cr# = 0.33) from the southern massif and harzburgite (spinel Cr# = 0.55) from the northern Hilti massif recorded a further melt extraction event with an influx of a mid-ocean ridge basalt like melt.

Hydrogenation of iron sulfide (FeS) under high-pressure and high-temperature conditions has attracted attention because hydrogen and sulfur are promising candidates as light elements in the cores of the Earth and other terrestrial planets. In earlier reports describing the hydrogenation of FeS, the chemical compositions of starting materials were not fully clarified. This study reports in-situ neutron and X-ray diffraction measurements under high-pressure and high-temperature conditions of an Fe-S-H system using a stochiometric Fe_1.000S (troilite) as a starting material. The site occupancies of hydrogen atoms in FeS, estimated by Rietveld refinement of neutron diffraction patterns collected at about 5 GPa, were 0.014(2) at 700 K and 0.024(2) at 1000 K. The hydrogen occupancy at 900 K and 18.2 GPa was estimated as 0.067(6) from the unit-cell volume determined by X-ray diffraction using the hydrogen-induced volume expansion calculated from first-principles calculations. These occupancies were significantly lower than those reported from earlier studies, indicating that the hydrogenation of FeS can be affected strongly by the stoichiometry of iron sulfide.

We performed a cathodoluminescence (CL) study of Ca-rich plagioclase (An_85-86Ab₁₄Or_<1) in Stillwater gabbronorite experimentally shocked at 20.1, 29.8, and ∼ 41 GPa, for characterization of the shock effects. Chroma CL image of unshocked plagioclase showed the homogeneous red CL emission. In contrast, experimentally shocked plagioclase showed the heterogeneous CL emission colors in red and blue. The Raman spectra analysis identified that the red and blue portions correspond to plagioclase and maskelynite, respectively. In our observation, plagioclase experimentally shocked at 20 GPa was partially converted into maskelynite. At 30 GPa, most of plagioclase were converted into maskelynite. At 40 GPa, plagioclase was fully converted into maskelynite. Our observations of Ca-rich plagioclase indicated that the maskelynization starts at a slightly lower pressure and completes at a higher pressure than those in the previous studies (∼ 24 and ∼ 28 GPa, respectively). These pressure differences may be due to the high sensitivity of CL, which allows for the detection of small (a few µm in size) and rare phases that may have been overlooked in the traditional methods. The CL spectra of plagioclase showed a continuous change with increasing shock pressure. Hence, the CL imaging method using plagioclase and maskelynite is found to be very effective to estimate precisely shock pressure. In particular, there was a marked decrease in the CL intensity of Mn²⁺ and Fe³⁺ centers. Furthermore, the shock-induced center around the UV region was observed in experimentally shocked plagioclase and maskelynite. These CL features reflect the destruction of the framework structure to varying extents depending upon shock pressure. Combined with the Fourier transform infrared spectroscopy (FTIR) analysis in the present study, the transition of plagioclase to maskelynite was clearly illustrated in spectra. The reflectivity decreased continuously with increasing shock pressures during maskelynization. Additionally, the absorption at ∼ 8.6 µm observed in plagioclase was absent in maskelynite. This feature can be used as a diagnostic feature to characterize plagioclase and maskelynite by FTIR. The combination of detailed petrology using CL and FTIR spectra provides valuable insights into the shock scale for achondrites and planetary materials rich in shock-experienced plagioclase.

The Southern Granulite Terrain of peninsular India consists of a wide range of metamorphic rocks with formation ages that span the late Archean Era to the Cambrian Period. It consists of numerous tectonic blocks dissected by deep crustal-scale shear zones. The Madurai Block is the largest crustal block, comprising Neoarchean to Ediacaran-Cambrian gneisses that include charnockite, hornblende-biotite gneiss, mafic granulite and metapelite, amongst other lesser rock types. This study focuses on the geochemistry of granulite-facies rocks from the western part of the Madurai Block, how these rocks correlate with similar types in other tectonic blocks of the Southern Granulite Terrain, and the implication of such correlations for East Gondwana tectonics. The geochemistry of the various granulite-facies rocks from the western Madurai Block reveals metaluminous to slightly peraluminous, calcic to alkalic, and ferroan to magnesian signatures. Geochemical tectonic discrimination diagrams indicate both A-type granitoid and Cordilleran affinities, consistent with petrogenesis in active continental margin and extensional tectonic settings, with chemical variation also generated through magmatic differentiation. Similar lithological, geochronological and geochemical features have been reported from granulites of the Antananarivo Block of Madagascar, based on which a correlation can be made with the western Madurai Block that predates Gondwana assembly.

Grain growth experiments were performed on rhombohedral camphor as a rock analogue at 24 °C [i.e., room temperature (RT)] and higher temperatures of 31, 35, 43, and 50 °C. The experiments were very simple compared with those on rocks, which require special apparatuses. The ground sample of camphor was pressed on a glass slide, and a thermometer was set next to the sample. The two-dimensional see-through experiment was performed at RT under a polarizing microscope. The evolving microstructures were clearly observable and showed real-time grain boundary migration by grain growth and the consumption of smaller grains by neighboring larger grains. The result was a consistent increase in grain size from ∼ 10 to ∼ 40 µm in 2 h. The higher-temperature experiments were performed on a hot plate. A glass slide and a weight that had been preheated on the hot plate were placed on top of the glass slide that contained the pressed sample and thermometer. The increase in grain size was controlled by increasing the temperature, with the temperature being held for the same durations. The grain size data in the case of grain growth were analyzed with the grain growth law of dⁿ − d₀ⁿ = k₀ exp(−Q/RT)t, where d (µm) is the grain size at time t (s), d₀ (µm) is the initial grain size, n is the grain growth exponent, k₀ (µmⁿ/s) is a constant, Q (kJ/mol) is the activation energy, R is the gas constant, and T is the temperature in Kelvin. The determined parameters were n = 3.7 ± 0.2, k₀ = 10^−12.7±0.1, and Q = 60.4 ± 6.1.

A WNW-ESE-trending mafic dyke intruding across major structures in high-grade metamorphic rocks was found at Niban Iwa (translated as ‘Number Two Rock’) in the Proterozoic Lützow-Holm Complex of East Antarctica. It is holocrystalline and aphyric, and comprises biotite, hornblende, plagioclase, orthoclase, quartz, apatite, and titanite. Chemically the dyke rock is alkali basalt with high K₂O/Na₂O and total Fe contents, and low Cr and Ni contents, indicating that it was formed by the differentiation of olivine from a primary alkali basaltic magma derived from the subcontinental mantle. The Rb-Sr mineral isochron age was obtained of 487 ± 15 Ma with Sr_IR = 0.70486 ± 0.00007. Considering that the metamorphic age of the gneisses at Niban Iwa was estimated to be 532 Ma, the dyke probably intruded after metamorphism as part of the post-orogenic igneous activity following the collision of East and West Gondwana.

Ezochiite, a newly-discovered platinum-group mineral in the thiospinel group having the ideal formula Cu⁺(Rh³⁺Pt⁴⁺)S₄, was discovered in samples from the Tomamae coast near Tomamae town, Hokkaido, Japan. Additional specimens were later found in the Shosanbetsu river, Ainusawa river and Obira coast, Hokkaido. Ezochiite crystallized in melt pockets trapped in isoferroplatinum grains, occurring in the form of anhedral grains less than 5 µm in length. Ezochiite is associated with sulfide minerals such as braggite, cooperite, torryweiserite, and chalcopyrite. It is opaque and has a metallic luster with a bluish gray color in reflected light. The Mohs hardness of this mineral was estimated to be 5 by analogy with related thiospinel group minerals and a density of 6.66 g·cm⁻³ was calculated from the empirical formula and powder X-ray diffraction data. The empirical formula, on the basis of 7 apfu was (Cu⁺_0.85Fe³⁺_0.15)_Σ1.00(Rh³⁺_1.09Pt⁴⁺_0.78Ir³⁺_0.08Pt²⁺_0.05)_Σ2.00S_4.00 for a specimen obtained from the Tomamae coast. The powder X-ray diffraction study indicated that the mineral exhibits the spinel structure, space group Fd3m, with lattice parameters a = 9.8559(14) Å and V = 957.4(4) ų (Z = 8). Evidence for a spinel structure was also provided by Raman spectra. Data from samples of ezochiite and cuprorhodsite from samples sourced in Hokkaido showed a compositional relationship based on coupled Fe³⁺_0.5Rh³⁺-Cu⁺_0.5Pt⁴⁺ substitution. Ezochiite is not rare. It is also found various other geological environments, including in ophiolites, Ural-Alaskan intrusions and mafic-ultramafic intrusions.

The 2021 eruption of Fukutoku-Oka-no-Ba (FOB), which is a submarine volcano located at the southern end of the Izu-Ogasawara arc, produced a large number of pumice clasts that drifted to many places in the islands of Japan and eastern Asia. Amongst the typical gray pumice clasts, several peculiar clasts have been discovered, such as those with a black coloration and containing mafic enclaves. This study found a mostly bimineralic enclave consisting of plagioclase phenocrysts and an alkali feldspar matrix, with minor cristobalite, TiO₂ minerals (anatase and rutile), and Fe sulfide. The chemical composition of the plagioclase phenocrysts is similar to that reported from the FOB pumice, and the tie line of the alkali feldspar and plagioclase in a Ca-Na-K ternary diagram indicates that they originated from melt extracted from the crystal mush of the FOB magma reservoir. The cristobalite occurs in the voids in the matrix, in which surrounding alkali feldspar compositions changed gradually along the ternary feldspar solvus of ∼ 850 °C. The formation of a cristobalite-bearing bimineralic enclave can be explained by (1) the melt was extracted and accumulated at the shallow part of the magma reservoir, which crystallized as syenitic rocks; (2) subsequent degassing-related alteration within the volcanic conduit that caused plagioclase breakdown and cristobalite crystallization; and (3) entrainment of the syenitic rock fragment by the nanolite-bearing magma being erupted from the conduit.

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.