Brachiopod shells have been widely used as paleoenvironmental recorders because of their robust preservation in fossil records. However, accurately reconstructing past seawater temperatures from their oxygen (δ18O) and clumped isotope compositions requires identifying shells/shell portions that are minimally affected by kinetic isotope effects (KIE) and diagenetic alteration. This study investigated the potential of Raman spectroscopy as a rapid and non-destructive screening method for shells/shell portions. We conducted Raman spectroscopy on fossil and modern brachiopod calcite shells from Japan and Thailand, focusing on the ν₁ peak center position (peak center) and full width at half maximum (FWHM). The results revealed that intraspecific variations in the peak center and FWHM were relatively small, with each species exhibiting a distinct peak center and FWHM range. The brachiopod shell portions with low Mg and Sr concentrations exhibited peak centers and FWHM values that were closer to those of pure calcite. Depth profile analyses further indicated that shell portions at a 60–90

The Cretaceous high-P/T metamorphic complex such as Sanbagawa schists and Mikabu greenstones is located in the outer zone of the Median Tectonic Line in the Shibukawa area, northwestern Shizuoka Prefecture, central Japan. In this area, a 2 x 1 km Shibukawa ultramafic body, a member of the Mikabu greenstones, occurs within the chlorite zone of the low-grade Sanbagawa schists. The upper part of this ultramafic body is covered by pelitic schists (classified as the Upper unit). The peak temperatures estimated from the Raman spectra of carbonaceous material (CM) in the pelitic schists were 277 degrees C-354 degrees C. The temperatures of the Upper unit range from 277 degrees C to 293 degrees C, which are lower than those of the surrounding Sanbagawa schists, ranging from 295 degrees C to 354 degrees C. Considering the elevation and large-scale structures of the body, the Upper unit is inferred to be a shallow, lower-grade Sanbagawa schist unit preserved in the ultramafic body, as it has a geological structure similar to that of the surrounding schists. This suggests that although the occurrence of the Shibukawa ultramafic body has complicated the geological structure of the Sanbagawa schists, the metamorphic temperature increases toward apparently lower structural levels. In addition to constraining metamorphic temperatures, it shows that the Raman CM geothermometer is a powerful tool for revealing structural characteristics based on geological and thermal relationships within low-grade metamorphic rocks in shallow subduction zones.

The third “Mineral Detection of Neutrinos and Dark Matter” (MDνDM'25) meeting was held May 20-23, 2025 in Yokohama, Japan, hosted by the Yokohama Institute for Earth Sciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). These proceedings compile contributions from the workshop and update the progress of mineral detector research. MDνDM'25 was the third such meeting, following the first in October of 2022 held at the IFPU in Trieste, Italy and the second in January of 2024 hosted by the Center for Neutrino Physics at Virginia Tech in Arlington, USA. Mineral detectors record and retain damage induced by nuclear recoils in synthetic or natural mineral samples. The damage features can then be read out by a variety of nano- and micro-scale imaging techniques. Applications of mineral detectors on timescales relevant for laboratory experiments include reactor neutrino monitoring and dark matter detection, with the potential to measure the directions as well as the energies of the induced nuclear recoils. For natural mineral detectors which record nuclear recoils over geological timescales, reading out even small mineral samples could be sensitive to rare interactions induced by astrophysical neutrinos, cosmic rays, dark matter and heavy exotic particles. A series of mineral detectors of different ages could measure the time evolution of these fluxes, offering a unique window into the history of our solar system and the Milky Way. Mineral detector research is highly multidisciplinary, incorporating aspects of high energy physics, condensed matter physics, materials science, geoscience, and AI/ML for data analysis. Although realizing the scientific potential of mineral detectors poses many challenges, the MDνDM community looks forward to the continued development of mineral detector experiments and the possible discoveries that mineral detectors could reveal.

The quantitative pressure (P)–temperature (T) conditions of low-grade metamorphic rocks, such as pumpellyite–actinolite and greenschist facies, are largely unknown mainly owing to the difficulty in applying thermodynamic methods despite their importance in understanding the protolith and metamorphism within subducting oceanic crusts. In this study, Raman spectroscopy was applied to constrain the peak metamorphic conditions independent of thermodynamic methods for the lowest grade part (chlorite zone) of the Sanbagawa schists in the Shibukawa area, central Japan, where research on metamorphic conditions is limited. The metamorphic peak temperature of the pelitic schists estimated by Raman carbonaceous material geothermometry was 307 ± 27 °C to 395 ± 16 °C, which increased towards the northern fault (Median Tectonic Line). Raman geobarometry using the quartz-inclusions-in-spessartine system on a siliceous schist sample estimated a peak metamorphic pressure of 0.78–0.94 GPa at 360–390 °C. These results suggest that the rocks in the Shibukawa area were subducted to a depth equivalent to that of the garnet zone in central Shikoku and were then exhumed without experiencing further heating. The combination of Raman carbonaceous material geothermometry and Raman geobarometry (Raman geothermobarometry) can be effectively applied to estimate the metamorphic conditions of low-grade metamorphic rocks independent of thermodynamic methods.

This study presents Fourier Transform Infrared (FT-IR) mapping of olivine in mantle xenoliths from the Kaapvaal Craton, introducing methodological innovations for quantifying olivine water content. Our advancements include enabling direct Electron Backscatter Diffraction (EBSD) analysis of FT-IR-measured grains, and developing an automated calculation method to minimize serpentinization effects. This approach enables the calculation of the water content of olivine with high reliability and facilitates a point-to-point correlation between water content and crystallographic orientation. Analysis of garnet lherzolites (100-150 km depth) and spinel peridotites (similar to 60 km depth) revealed our method's effectiveness for olivine water contents above 40 ppm. Olivine in garnet lherzolites contained 40-210 ppm water, while olivine in spinel lherzolites exhibited contents below the detection limit, indicating heterogeneous water distribution in the Kaapvaal Craton mantle. We observed significant water content heterogeneity across multiple scales: intragranular, inter-grain, and xenolithic. Intragranular water content gradients up to 50 ppm were observed, with high-water olivine (>120 ppm) tending to show gradients aligned with crystallographic axes, suggesting anisotropic water incorporation and diffusion processes. Variations in water content between olivine grains within xenoliths and across different microstructures in garnet lherzolites were also noted. This heterogeneity likely results from complex lithospheric mantle processes, including localized metasomatism and deformation. These findings have important implications for understanding cratonic stability, mantle dynamics, and water-related processes in the Earth's mantle, potentially facilitating small-scale metasomatism or deformation without compromising overall cratonic stability.

We evaluated the influence of laser irradiation for Raman spectroscopic analysis of low-grade carbonaceous materials (CMs) using three samples with peak metamorphic temperatures of approximately 200-300 degrees C. In the analysis, spectra were acquired using a 532 nm laser wavelength and a x50 objective lens, which are common analytical conditions in CM Raman geothermometry. As CM is opaque, it is easily heated and damaged when irradiated with a high-power laser. However, an excessively low laser power results in a poor signal-to-noise ratio (SNR), making accurate parameter evaluation difficult. First, we investigated the minimum laser power conditions required to obtain a desirable SNR. The full width at half maximum (FWHM) of the D1-band, which is used as a parameter for metamorphic temperature estimation in CM Raman geothermometry, exhibited a considerably large standard deviation and small SNR at a surface laser power of <0.5 mW. Next, we focused on the influence of high irradiation power on the CM Raman spectra. The results show that the FWHM of the D1-band is sensitive to 'damage', i.e., the irreversible change in the structure of CM by laser irradiation. On the other hand, the peak position of the D1-band is sensitive to 'heat', meaning i.e., the increased surface temperature of CM. In particular, the FWHM of the D1-band increased as the laser power increased to >2.0 mW, which significantly affected the metamorphic temperature estimation. Similar results were obtained for measurements using a x100 objective lens and different types of micro-Raman spectrometers. When the exposure time exceeded 30 s with sufficient laser power (>0.5 mW), the SNR became almost constant. More than three accumulations were efficient at eliminating cosmic-ray interference. Based on these results, we propose that a laser power of 0.5-2 mW and measurements of 10 s x 3 measurements are the optimum laser irradiation conditions for Raman spectroscopic analysis of low-grade CM.

The Sanbagawa belt is a “coherent” oceanic subduction-type metamorphic region representing a rock package predominantly derived from oceanic crust and accreted at depths of 20–80 km (300–700 °C). The thermal structure and lithological layers are complexly deformed but semi-continuous, in contrast to more commonly reported subduction-related domains dominated by mélange. The coeval Shimanto accretionary complex records accretion at depths <15 km and the rocks are primarily terrigenous sediments. The Sanbagawa belt has a greater proportion of mafic rocks than the Shimanto complex, implying progressive peeling-off of oceanic plate stratigraphy with more basaltic oceanic crust slices accreted at deeper levels. Tectonic exhumation can be explained by three separate phases dominated by buoyancy-driven upflow, ductile thinning, and normal faulting.

Serpentinites associated with metamafic and metaplagiogranitic rocks occur sporadically within metasedimentary schists in the Yuli belt. Such metaigneous rocks are considered to represent ophiolitic protoliths and some contain high-pressure (HP) metamorphic minerals or assemblages. However, the origin and metamorphism of these serpentinites have long been a mystery. This study systematically investigates the four major serpentinite-bearing exposures at the Fengtien, Wanjung, Tsunkuanshan, and Chinshuichi. The results reveal that the serpentinites are of two different protoliths on the basis of relict chromian spinel composition. Cr-spinel compositions of the Fengtien and Tsunkuanshan samples are characterised by moderate Cr# [Cr/(Cr + Al)] (0.45-0.57), relatively high Mg# [Mg/(Mg+Fe2+)] (0.59-0.79), but low Fe3+# [Fe3+/(Fe3++Cr+Al)] (0.02-0.06), reflecting an abyssal peridotite type protolith. By contrast, Cr-spinel compositions of the Wanjung and Chinshuichi samples show high Cr# (up to 0.74) and Fe3+# (0.03-0.08), but low Mg# (<0.6), indicating a forearc mantle peridotite origin. Peak metamorphic conditions of the serpentinites are represented by the assemblage of antigorite + magnetite + chlorite + olivine + diopside, which is estimated as up to 550 degrees C but the pressure cannot be constrained quantitatively. Based on field relations, it is inferred that the serpentinites, associated HP metaigneous rocks, and garnet-bearing metasedimentary schists were metamorphosed isofacially. Despite two origins, the peridotitic protoliths were all subjected to hydration and subduction processes. We suggest that precursors of the serpentinites, metaigneous rocks, and metasedimentary schists were juxtaposed and metamorphosed at intermediate to great depths (similar to 35-55 km) of a subduction zone. Therefore, the Yuli belt serpentinites and associated rocks likely represent exhumed materials from a palaeo-subduction interface.

Deep tectonic tremor downdip of the seismogenic zone in warm subduction zones is thought to occur in the region of high fluid pressures. However, the deformation and fluid processes responsible for tremor are poorly understood. We examined the Tomuru metamorphic rocks on Ishigaki Island, southern Ryukyu Arc, deformed at similar to 40 km depth and similar to 450 degrees C under epidote-blueschist metamorphism comparable to the tremor source region in northern Cascadia subduction zone. Here, quartz vein-rich metapelite and metabasite are repeated many times as a result of duplex underplating. The spatiotemporal relationship between clustered quartz veins and the juxtaposition of metapelite and metabasite suggests that quartz vein formation and duplex underplating are contemporaneous. Viscous shear in metapelite is accommodated by dissolution-precipitation creep. Metabasite records heterogeneous dehydration, resulting in rheological heterogeneity characterized by greenschist lenses in the foliated blueschist matrix. Viscous shear in the blueschist matrix was mainly accommodated by dissolution-precipitation creep of glaucophane. Geochemical and strontium-neodymium isotope analyses indicated that quartz veins were derived from sediment dehydration, whereas dehydration from oceanic crust contributed neither to quartz vein formation nor to fluid overpressures. We suggest that high fluid pressure in the deep tremor source region is primarily controlled by dehydration of subducting sediments, and the clustered quartz veins in underplated rocks correlate with the overpressured tremor source in low shear-wave velocity zones. Tectonic tremor is a low-amplitude, noise-like seismic signal. It is typically observed downdip of the locked seismogenic zone in warm-slab environments such as the Cascadia and Nankai subduction zones. Geophysical observations have shown that tremor occurs in the region of high fluid pressure. However, the tremogenic deformation and fluid processes remain unknown. We studied the exhumed metamorphic rocks on Ishigaki Island, southern Ryukyu Arc, which were deformed in a deep subduction zone comparable to the tremor source region in northern Cascadia. Our geological observations show that the tremor source region is represented by multiple stacks of sediments and oceanic crust by duplex underplating and ubiquitous quartz veining as a result of high fluid pressure and silica precipitation. Geochemical analyses indicate that dehydration of subducting sediments, rather than oceanic crust, contributed to the formation of quartz veins and the generation of fluid overpressures. Our results shed new light on the tremor-generating deformation, the fluid source responsible for the high fluid pressure in the tremor source region, and the thickness of the tremor zone, particularly for the regions where the spatial correlation between low shear-wave velocity zone and high tremor activity is observed. Metamorphic rocks exhumed from the deep tremor source region record duplex underplating of quartz vein-rich metapelite and metabasite Sediment dehydration mainly contributed to quartz vein formation and generation of high fluid pressure in the deep tremor source region Clustered quartz veins in underplated rocks may correlate with the overpressured tremor source in the low shear-wave velocity zone

Carbonaceous material (CM) undergoes progressive changes that reflect its thermal history. These changes are in general irreversible and provide valuable information for understanding diagenetic and metamorphic processes of crustal rocks. Among various approaches to quantify these changes, the R2 ratio, area ratio of specific peaks in CM Raman spectra, is widely used to estimate the maximum temperature of intermediate- to moderately high-grade metamorphism. The calculation of the R2 ratio requires peak deconvolution of the original spectrum, and the results depend on the details of how this is carried out. However, a clear protocol for selecting appropriate initial conditions has not been established and obtaining a reliable temperature estimate depends at least in part on the experience and skill of the operator. In this study, we developed a Python code that automatically calculates the R2 ratio from CM Raman spectra. Our code produces R2 ratios that are generally in good agreement with those of Aoya et al. (J Metamorph Geol 28:895–914, 2010, https://doi.org/10.1111/j.1525-1314.2010.00896.x ) for the same Raman data, with much less time and effort than was the case in the previous studies. We have confirmed that the code is also applicable to other previous datasets from both contact and regional metamorphic regions. The overall trend of the recalculated data indicates that samples with R2 greater than 0.7 are not sensitive to the changes in CM maturity and thus should not be used for the calibration of an R2-based geothermometer. We propose a modified geothermometer for contact metamorphism that is strictly applicable to samples with R2 from 0.023 to 0.516, with the proviso that a laser with a wavelength of 532 nm should be used. A slight extrapolation of the newly proposed geothermometer up to R2 of 0.57 provides a temperature estimate that is consistent with the geothermometer of Kaneki and Kouketsu (Island Arc 31:e12467, 2022; https://doi.org/10.1111/iar.12467 ); the boundary between the two geothermometers corresponds to a temperature of 391 °C.

Needle-shaped rutile inclusions occur in garnet within the quartz-eclogite at Mt. Gongen in the Sanbagawa belt, central Shikoku. They are approximately 5-25 mu m along the long axis and are typically oriented along three directions, each intersecting at 120 degrees. This indicates that the needle-shaped rutile is a lamella exsolved from the garnet. Garnet with needle-rutile inclusions is restricted to the quartz-poor domain of the quartz eclogite sample, which consist of quartz, garnet, omphacite, phengite, epidote, kyanite, and hornblende. Garnet grains with rutile lamellae show a composition of the almandine-pyrope series with 14-21 mol% grossular content. Rutile exsolution lamellae were concentrated in the range of 27-34 mol% pyrope of garnet crystals. The garnet host with rutile lamellae has a higher TiO2 content (TiO2 =0.06-0.19 wt%) than those in rutile-free areas. These chemical compositional characteristics suggest that Ti was incorporated into the crystal structure during garnet growth and subsequently partially exsolved as rutile lamellae during the retrograde stage. Rutile lamellae in garnet have generally been regarded as indicators of ultrahigh-pressure metamorphism, but the present report from quartz-eclogite of the Sanbagawa belt, where no coesite has been found, provides evidence in a natural sample that the appearance of rutile exsolution lamellae is not necessarily under ultrahigh-pressure conditions.

Hydrothermal alteration occurs in upper-mantle fault zones and significantly modifies the rheological properties of ultramafic rocks. To understand how hydrothermal alteration affects shear localization and the strength of the fault zones, we conducted simple-shear deformation experiments on water-saturated harzburgite (70 wt% olivine +30 wt% orthopyroxene) gouges sandwiched between three types of shear pistons (tungsten, yttria-stabilized zirconia, and corundum) using two deformation-DIA apparatuses at confining pressures of 1-4 GPa, tempera-tures of 500-580 degrees C, average shear strain rates of 6.1 x 10-6 s- 1 to 1.0 x 10-4 s- 1, and water contents of 4-30 wt %. The harzburgitic gouges with water contents of 10 and 30 wt% exhibited steady-state sliding or strain-hardening behavior, and the shear strength of the latter sample was less than one-third of that of the former sample, possibly reflecting the difference in pore fluid pressure. Olivine/orthopyroxene grains exhibit distributed microfracturing and grain rotation towards P foliation, indicating the operation of cataclastic flow. Shear displacement is also accommodated by the development of serpentine-or talc-bearing multiple shear zones including B, R1, and/or Y shears, where intense cataclasis-related grain size reduction and dissolution/precipi-tation occur. For experimental runs using tungsten and zirconia shear pistons, the serpentine or talc blades that wrap finer-grained and dissolved olivine/orthopyroxene grains form an interconnected network, indicative of frictional sliding or dislocation glide on their basal planes as a dominant deformation mechanism. Raman spectra of the serpentine minerals indicate that they represent antigorite with low crystallinity. These findings suggest that when deep lithospheric fault zones undergo hydrothermal alteration, deformation is controlled by compe-tition between cataclastic flow in olivine/orthopyroxene matrix and slip or glide of antigorite or talc in semi-brittle fault zones, the predominance of which depends on the amount of the hydrous phyllosilicates and the magnitude of pore fluid pressure.

Spectroscopy has been widely used in geology since the 1990s because it is non-destructive and easy to analyze. Raman spectroscopy has generally been used to identify mineral phases in geology, but recent studies have proposed new methods to quantitatively estimate the metamorphic pressure (quartz Raman barometry) and peak temperature (Raman carbonaceous material geothermometry). Studies using infrared spectroscopy are also underway to advance our understanding of hydration processes in subduction zones and mantle through the analysis of water in rocks. In addition to the development of new methods using spectroscopy, new tools are also being developed to analyze huge amounts of data through iterative processing, which will enable the extraction of more informative and quantitative results in a shorter time. This paper introduces examples of spectroscopy applications in geology and examines future developments.

Minerals are solid state nuclear track detectors - nuclear recoils in a mineral leave latent damage to the crystal structure. Depending on the mineral and its temperature, the damage features are retained in the material from minutes (in low-melting point materials such as salts at a few hundred degrees C) to timescales much larger than the 4.5 Gyr-age of the Solar System (in refractory materials at room temperature). The damage features from the $O(50)$ MeV fission fragments left by spontaneous fission of $^{238}$U and other heavy unstable isotopes have long been used for fission track dating of geological samples. Laboratory studies have demonstrated the readout of defects caused by nuclear recoils with energies as small as $O(1)$ keV. This whitepaper discusses a wide range of possible applications of minerals as detectors for $E_R \gtrsim O(1)$ keV nuclear recoils: Using natural minerals, one could use the damage features accumulated over $O(10)$ Myr$-O(1)$ Gyr to measure astrophysical neutrino fluxes (from the Sun, supernovae, or cosmic rays interacting with the atmosphere) as well as search for Dark Matter. Using signals accumulated over months to few-years timescales in laboratory-manufactured minerals, one could measure reactor neutrinos or use them as Dark Matter detectors, potentially with directional sensitivity. Research groups in Europe, Asia, and America have started developing microscopy techniques to read out the $O(1) - O(100)$ nm damage features in crystals left by $O(0.1) - O(100)$ keV nuclear recoils. We report on the status and plans of these programs. The research program towards the realization of such detectors is highly interdisciplinary, combining geoscience, material science, applied and fundamental physics with techniques from quantum information and Artificial Intelligence.

We estimated the protolith age and peak metamorphic temperature of the Yokokawagawa metamorphic rocks (YMR) east of the Itoigawa-Shizuoka Tectonic Line using detrital zircon U-Pb dating and Raman carbonaceous material geothermometry, respectively. U-Pb dating of a psammitic rock yielded a youngest age of similar to 100 Ma, which corresponds to the protolith age. Raman carbonaceous material geothermometry results for five pelitic rock samples give metamorphic temperatures of similar to 350-380 degrees C. The protolith age is consistent with those of the San-bagawa metamorphic rocks (SMR), strongly indicating that the YMR are an extension of the SMR. The increase in peak temperature toward intrusive rocks along the eastern margin of the YMR may indicate that the relatively young ages yielded by previous K-Ar dating of the YMR reflect thermal resetting due to contact metamorphism.

Silicate spherules have been identified from the ca. 3.4 Ga-old Strelley Pool Formation (SPF) in the Pilbara Craton, Western Australia. Their origins and geochemical characteristics, including the Re and platinum-group elements of their host clastic layer and the overlying and underlying microfossil-bearing finely laminated carbonaceous cherts, were examined. The spherules have various morphologies (completely spherical to angular), sizes (∼20 to >500 μm), textures (layered, non-layered, and fibrous), mineralogy (various proportions of microcrystalline quartz, sericite, anatase and Fe-oxides), and chemistry (enriched in Ni and/or Cr), commonly with thin anatase-rich walls. Their host clastic layer is characterized by rip-up clasts, suggesting a suddenly occurring high-energy depositional environment, such as tsunamis. Although various origins other than asteroid impact were considered, none could unequivocally explain the features of the spherules. In contrast, non-layered spherical spherules that occur as individual framework grains or collectively comprise angular-shaped rock fragments appear to be more consistent with the asteroid impact origin. The calculated Re-Os age of the cherts (3331 ± 220 Ma) was consistent with the established age of the SPF (3426-3350 Ma), suggesting that the Re-Os system was not significantly disturbed by later metamorphic and weathering events.

Aluminum-rich and Si-poor calcium amphibole [similar to 3.9 Al atoms per formula unit (apfu) and similar to 5.5 Si apfu for 23 O] occur in the quartz-bearing eclogites from the Donghai area, Sulu ultrahigh-pressure metamorphic belt, eastern China. Most of the aluminous amphibole phases are retrograde products from the exhumation and hydration stage and are texturally divided into a mantle phase around a porphyroblastic garnet and a crack-filling (vein) phase of a garnet. Less aluminous amphibole occurs as symplectite phase with plagioclase after omphacite. The formation process of the aluminous amphibole in the quartz-bearing samples is discussed on the basis of the analytical data by EPMA, FIB-TEM, and EBSD. The mantle amphibole occurs between garnet and symplectite or quartz. A set of plagioclase and aegirinediopside/argirine-hedenbergite thin monomineralic bands forms at the boundary between the mantle amphibole and matrix quartz. However, these monomineralic bands do not occur at the mantle amphibole-symplectite boundary. These textural diferences indicate that the recrystallization of the aluminous amphibole around garnet was controlled by significant local reactions, and the size of equilibrate domains was probably several tens of micrometers or less. The mantle amphibole is composed of inner (garnet-side) and outer (matrix-side) zones. The inner zone is compositionally homogeneous, and its atomic Al/Si value is similar to 0.63-0.66 and similar to that of garnet. Atomic Ca/Si value in the inner zone is also almost uniform and is generally identical to that of garnet. The outer zone exhibits a monotonic decrease in the Al/Si and Ca/Si values outward, and its composition at the outermost margin is similar to that of the symplectitic amphibole. The crack-filling amphibole has a composition similar to the inner zone of the mantle amphibole. The CPO pattern of the crack-filling amphibole is diferent from that of the adjacent mantle amphibole, showing that the crack-filling amphibole is cut by the mantle amphibole. The textural relationship between the mantle and crack-filling amphibole phases and their compositional characteristics imply that: (1) the mantle type is a slightly later stage product than the crack-filling type, and (2) the boundary between the inner and outer zones of the mantle aluminous amphibole probably corresponds to the initial surface of the porphyroblastic garnet. The inner zone is considered to have grown inward by simple substitution of garnet, using the tetrahedral and octahedral cations of the garnet as the basic framework. On the other hand, most of the outer zone of the mantle-type amphibole grew outward in the matrix from the initial surface of the garnet porphyroblast. The mantle amphibole shows a CPO similar to that of amphibole in the adjacent symplectite domain, suggesting that these two types of amphibole formed almost simultaneously, sharing crystallographic orientation with each other. The formation of crack-filling aluminous amphibole was probably promoted by the hydraulic microfracturing process at an early stage of exhumation and hydration. The mantle and symplectitic amphibole phases formation was promoted by the subsequent infiltration of metamorphic fluid. The aluminous amphibole in the SiO2 phase-bearing eclogites probably recrystallized with the formation of a localized SiO2-undersaturated reaction domain because of rapid exhumation and subsequent rapid cooling of the Sulu UHP metamorphic belt.

Carbonaceous material undergoes changes in its maturity mainly in response to its thermal history. Among the various geothermometers based on Raman spectra of carbonaceous material, those proposed by Kouketsu et al. (2014) have been employed to investigate the temperatures experienced by terrestrial rocks that undergo low- to medium-grade metamorphism. Although their geothermometers use spectral parameters that can be determined only by peak deconvolution, criteria for setting the initial conditions for nonlinear least-squares fitting have not been specified, which may generate unnecessary errors in the estimated temperatures owing to differences in fitting results among data analysts. To address this issue, we developed a code that automatically calculates the parameters required for the geothermometers of Kouketsu et al. (2014); that is, the widths of the D1- and D2-bands. Our code yields parameter values consistent with those of Kouketsu et al. (2014) for the same Raman data and is applicable to datasets other than those used to develop it. The geothermometers based on the obtained results show a comparable performance to Kouketsu et al. (2014). Errors in the estimated temperatures caused by variation in Raman systems and the subjective selection of the fitting method are smaller than the uncertainties of the geothermometer itself, so long as the temperature is calculated by following the procedures of the present study. Although this study focused only on geothermometers that require peak deconvolution, the development of those based on fitting-free Raman parameters and on the reaction kinetics of carbonaceous material should be investigated in future studies.

ABSTRACT Residual pressure values of quartz inclusions in host kyanite were estimated using Raman spectroscopy and show that the quartz-inclusions-in-kyanite system can be used as a geobarometer for estimating peak metamorphic conditions. Samples of quartz eclogite, a pelitic high-pressure metamorphic rock composed mainly of garnet, omphacite, and quartz, with subordinate kyanite, were obtained for analysis from the Gongen area in the Sanbagawa metamorphic belt, southwest Japan. Residual pressure in the 236 analyzed quartz inclusions within kyanite grains varies from 0.12 to 0.76 GPa. Values are independent of inclusion size and inclusion aspect ratio, and the distribution of residual pressure within the inclusions is homogeneous, except at inclusion-host interfaces. Numerical calculations based on elastic modeling with the equations of state of quartz and kyanite were applied using the highest residual pressure value of 0.76 GPa, with the calculated isopleth being consistent with previous results obtained by conventional thermodynamic geothermobarometry. We conclude that the quartz-inclusions-in-kyanite system can be used as a reliable new Raman geobarometer.