We present trace element compositions of volcanic rocks of Pre-Unzen and Unzen volcanoes. The magma source of those volcanoes are discussed together with major element and Sr isotopic compositions ( Sugimoto et al., 2005; unpublished ). Trace element patterns of primary Pre-Unzen basalts are reproduced by mixing of 90-95% melt from depleted mantle and 5-10% melt from stagnant Pacific slab. In addition, andesites and dacites from Pre-Unzen and Unzen show typical island arc patterns suggesting the contribution of crustal materials.

View full abstract

We investigated U-Pb age of detrital zircons from accretionary complexes in the Amami Oshima Island. Four samples were from the Amami and Naon complexes which attribute to Shimanto and Chichibu complexes, respectively. Similar age distributions of the samples showed the deposition age and provenances are not so different between the samples. Considering the youngest zircon(s), it is thought to be that the accretionary age of at least a part of the Naon Complex is after late Early Cretaceous.

View full abstract

This study considers the use of photographs of shore pebbles to develop a jade identification device and its possible application in assisting in the identification of stones.

This research made use of the TensorFlow machine learning software. The stones used for the learning were pebbles collected along the coast of Itoigawa, a total of roughly 13,000 photographs. These photographs were fed into NASNet as jade and non-jade photos for the purpose of transfer learning.

After 20,000 trials the software achieved a successful identification rate of 96% when working with the teacher data.

View full abstract

We report the mineralogical characteristics of diamond-like grains found in Higo- and Nishisonogi metamorphic rocks. In the former rocks, they occur inside negative crystals in chromite and consist of randomly aggregated nanocrystalline graphite, which may be a pseudomorph after diamond, while in the latter, carbonaceous grains occur as subhedral grains of ~0.5 μm in pore spaces in the phengite matrix. Electron diffraction revealed that they are indeed single crystalline diamond grains.

View full abstract

Ferroan monticellite (or magnesian kirschsteinite) occurs in the Happo ultramafic complex, central Japan. The ferroan monticellite has irregular shapes and replaces primary olivine in serpentinized peridotites. The ferroan monticellite is different from previously reported monticellite compositions in high Fe and Mn contents. Observed textures suggest the coexistence of the ferroan monticellite with antigorite ± diopside. Thermodynamic calculations show that the assemblage is stable at a low-temperature, and low SiO₂ and high Ca²⁺/(H⁺)² activities.

View full abstract

I summarize today's fluid inclusion study containing types of fluid inclusions, instruments, and new discoveries.

View full abstract

Layered ultramafics and MTZ peridotite from the Mersin ophiolite are the cumulates from boninitic magma and reaction products between boninitic magma and depleted harzburgite, respectively. Mantle harzburgite from the mantle section of the Mersin ophiolite is a residual peridotite after high degree of melting (~ 35%) induced by LREE and H₂O-rich influx.

View full abstract

Black-colored dunites have been found from the Horoman peridotite complex and others. They are mainly composed of olivines with minute rod-like exsolutions of magnetite and diopside through a process of dehydrogenation/internal oxidation of primary hydrous olivines. More generally, hydrous mantle olivines formed through various processes converted to anhydrous olivine, pyroxene phases and a spinel phase with a progress of dehydrogenation. This process contributes to recycling of water or hydrogen of Earth.

View full abstract

There is little researched about plutonic rock in Chikuzen Oshima, Munakata City, Fukuoka Prefecture, Japan. Exposure of equigranular textured rock is found about 100m east of the Miyazaki area of the island. The exposed rock is about 20m in width, adjacent to the Cretaceous Shimonoseki subgroup and is comprised of K-feldspar, plagioclase (sericited), quartz, hornblende, clinopyroxene, and orthopyroxene with a size of ca.1mm.

View full abstract

Cordierite hornfels formed by contact metamorphism by granitic masses around Lake Biwa was obtained from Mt. Daimonji, Ohishishi area, Akebihara area, north part of Mt. Dake, Mt, Kanakuso.and Shiraishi area. Cordierite sector trilling was observed except the sample from north part of Mt. Dake, in which all cordierite change to pinite. Cordierite sector trilling in cordierite hornfels was general around Lake Biwa.

View full abstract

Youngest ophiolitic rocks in Japan produce in the Mineoka Tectonic Belt. But outcrops are scares in the Belt by reason of landslide based on tectonic deformation. In gravels in conglomerate of younger strata in and around the Belt and floats at riverbed and beach in the Belt, various kind of ophiolitic rocks are find out than those in outcrops, and they become the key of investigation of origin and development of the Belt.

View full abstract

Togi gold mine is located in the middle part of Noto peninsula. However, the occurrence of gold and silver minerals in Togi mine has not been revealed. Therefore, we investigated to reveal the occurrence of these minerals in Togi mine. The pyroxene andesites of mother rock of have been caught on hydrothermal alteration. The main ore minerals in quartz vein including gold and silver minerals are pyrite, chalcopyrite and sphalerite. Electrum with 47 mol.% Ag, aguilarite, native silver and aggregate of unidentified minerals occurs as interstitial minerals in reddish brown quartz vein.

View full abstract

Obiro deposit is located in the Tagawa Acidic Rocks (AR), Uetsu region, NE Japan. Drill core and ore samples have been collected from the deposit and examined by XRD, EPMA and microthermometry. The main reasons of the mineralization at the Obiro deposit are as follows; the oxidized magma intruded at a shallower level, and thereafter hydrothermal fluids were boiled, resulting to be saline. The saline fluid dissolved the metals such as Pb, Zn, Cu and Bi, and these metals precipitated by cooling accompanied by dilution of meteoric water and increasing pH, resulting in decreasing solubility.

View full abstract

The Kurihashi granitic pluton is one of the plutonic complexes located in Kitakami mountains, and has a golden skarn deposit in the southern part. Rocks constituting the pluton were mainly classified as granodiorite or tonalite. This study is intended to clarify the relationship between the cooling environment of the pluton and the formation of the deposit on the basis of the results of the observation and the analysis of minerals in the rocks.

View full abstract

Tourmalines collected from several pegmatites are analyzed by EPMA. The tourmalines from the Teshirogi (TSG) and Miyamori (MYM) regions show characteristic composition. The TSG tourmalines would be affected by host rock, ultrabasic rocks, whereas the MYM tourmalines are indicated other than granitic origin. Zoned tourmalines in the MYM sample exhibit significant compositional variation from the core to rim. This trend suggests the pegmatite melt were effected by some kind of factor.

View full abstract

Targets of this study are to reveal the REE mineralization, and geochemical and geochronological characteristics of REE occurrences in north-west Mongolia; Ar gol, Alag erdene, Khujirtiin Davaa REE and alkali plutonic rocks in Bulgiin uvur and Suul tolgoi areas are also investigated. REE minerals of eudialyte, britholite, bastnasite, synchisite are found in Ar gol occurrence, only eudialyte mineral found from other two REE occurrences. Ar gol and Alag erdene REE occurrences reveal good potential for REE prospect criteria.

View full abstract

New petrological data and hornblende Ar-Ar ages for metabasites from the Buhwa Greenstone Belt located along the southern margin of an Archean TTG-greenstone terrane of the Zimbabwe Craton adjacent to the Neoarchean granulite terrane of the Limpopo Complex, suggest increase of metamorphic grade toward the contact with the Limpopo Complex. 2.0 Ga Ar-Ar ages suggest that the final collision of the Kaapvaal and Zimbabwe Cratons and the formation of the Kalahari Craton might have taken place at ca. 2.0 Ga

View full abstract

Slickenside is the microstructure formed during faulting. Understanding the formation process of slickenside is important in order to clarify the behavior and the condition of the faulting. In this study, we report the detailed formation process of slickenside, considered through the microstructural observation of natural and experimentally formed slickenside.

View full abstract

This study shows Silicate inclusions (SIs) observed in a chromitite in northeastern part of Botswana. The chromitite is mainly composed of chromite and chlorite. Texture relationship shows that the chromite aggregate is altered by later hydrothermal fluid which led to form chlorite. Chemical compositions of chromite have chemical zoning. SIs are mainly amphibole and talc. Compared with previous researches, these minerals are typical for inclusions in chromitite.

View full abstract

This study reports the U-Pb age and rare earth elements characteristics of zircon from pelitic gneisses in the Higo metamorphic Belt to constrain its timing of high-temperature metamorphism. The results indicate ca. 125 Ma age may be corresponding to the timing of prograde metamorphism, while ca. 110 ma age might be indicative of post-date of peak metamorphic condition. The retrograde metamorphism happened before ca. 105 Ma one obtained from zircon of discordant granite intrusion.

View full abstract

Determination Hf isotopic compositions of inherited zircons from metaigneous rocks in Highland and Wanni Complexes, Sri lanka was carried out in this study. As a result, the former showed mature compositions, while the latter showed relatively immature compositions. It suggests the differences of thier original sources.

View full abstract

The Lanzo peridotite massif could have recorded ancient thermal/chemical structures near the lithosphere-asthenosphere boundary (LAB). Careful analyses of grain-scale chemical zonings show that the massif underwent monotonous cooling with decreasing rate from the south to the north and that the initial temperatures decrease from the south to the north. The original thermal structure indicates a thermal gradient of 6K/km near LAB, which suggests an asthenospheric thermal perturbation.

View full abstract

We discussed evolution of sillimanite-, andalusite-, and kyanite-bearing metapelites from tha Altai Mountains, Mongolia.

View full abstract

Newly discovered eclogite from the Zakhan block in the Western Mongolia show a primary mineral assemblage of omphacite (Jd. up to 43 mol.%) + quartz + white mica + garnet + rutile, and its bulk chemical compositions is similar to "oceanic island basalt". U-Pb age dating of zircon by EPMA gave ca. 1,200 Ma, indicating this eclogite was formed prior to the formation of Rodinia supercontinent.

View full abstract

We report the U-Pb zircon ages from augen gneiss and associated granite and leucogranites from Higher Himalayan Crystalline rocks, Bhagirathi Valley, Garhwal Himalaya, India. The age data reveals a Cambro-Ordovician high-grade metamorphic event and coeval felsic magmatism indicating the pre-Himalayan history. The garnet-bearing leucogranite veins intruding the augen gneiss shows a possible melting of source rock and subsequent garnet overgrowth and concomitant zircon growth at early Miocene age.

View full abstract

Tourmaline-bearing nanogranite inclusions (NIs) are found from the pelitic gneiss collected from the Marsyangdi river area, Nepal Himalayas. Garnet has a rim defined by the discontinuous zoning in Ca and P. The NIs are included throughout the garnet core. ~100μm-sized NIs are composed of Bt+Tur+Chl+Pl+Qtz and Bt+Pl+Qtz, whereas several 10μm-sized NIs are composed of Bt+Ms+Qtz±Chl, etc. Tur-bearing NI is a direct evidence of the presence of B-bearing melt, segregation and ascent of which probably formed the High Himalayan leucogranite bodies.

View full abstract

Prograde, peak and retrograde stages are distinguished in the Gotsu blueschists.The prograde (<325 ℃, <4-5 kbar) and the peak (475-500 ℃, 14-16 kbar) metamorphic conditions are determined using pseudosection modeling in the NCKFMASHO system.

View full abstract

A barroisite (Brs)-bearing metabasite is newly found from the Mikabu belt in the Kii Peninsula, where the pumpellyite-actinolite facies rocks are predominant. The Brs is closely associated with epidote and chlorite and is rimmed by sodic amphibole and/or winchite with a distinct gap, which are identical with a Brs-bg metabasite found from the Kebara Formation, ca. 2km east from the new locality (Kato & Hirajima, 2017). In this lecture, we will introduce the significance of this new finding.

View full abstract

Reaction and exsolution textures in the Nomo rodhingites, Nagasaki Metamorphic Rocks, are examined in detail, which gives a host of information on the genesis of the rodingite.
1. Perovskite - ilmenite
Ilmenite occurs rimmed by perovskite, occasionally accompanied with magnetite at the outermost part. This indicates the following reaction:
3FeTiO₃ + 3Ca²⁺ + 2O₂ = 3CaTiO₃ + FeOFe₂O₃.
Magnetite lammelae occrus in ilmenite and magnetite blobs occur in perovskite. Because ilmenite dose not make a solid solution with magnetite, this relation is enigmatic.

View full abstract

Retrograde pumpellyite formed during blueschist-facies overprinting was newly found in the late Paleozoic garnet blueschist in the Yunotani Valley (Omi area, Hida-Gaien Belt). The petrological and mineralogical features are comparable with retrograde pumpellyite-bearing garnet blueschist in the Osayama area (Chugoku Mountains). This finding provides a strong evidence that the deeply subducted (eclogite-facies) metabasaltic rocks both in the Hida-Gaien Belt and the Chugoku Mountains were subjected a very similar blueschist-facies overprinting.

View full abstract

This is an attempt to estimate the rate of kelyphitization from the zoning width of garnet adjacent to the kelphite rim assuming a steady state diffusion. When a garnet is being kelyphitized, its composition is locally re-adjusted by an exchange reaction with product minerals and accompanying diffusion in garnet. The width of zoning is defined by the rate of diffusion and the rate of advancing of the reaction front. We use garnet peridotite, garnet pyroxenite from Ronda peridotite, Spain, garnet peridotite from Czech Bohemian massif and a garnet peridotite from western Norway.

View full abstract

(1) Distribution of eclogite and non-eclogite units in the Kokuryo-gawa area and (2) prograde increase of X(CO₂) value of metamorphic fluid at lithologic boundary will be discussed.

View full abstract

Kashio mylonite zone is exposed in the Oshika villege, Nagano, and widely extends along the Meadiean Tectonic Line (MTL) from Aoki to Kashio Rivers. The pelite origin mylonite shows a white thin layer within granitic mylonite. Based on the chemical analyses of recrystallized minerals, the P-T conditions of weakly and highly deformed pelite-origin mylonites ranged from 590~600 ℃ / 0.3-0.45 GPa, and 400~540 ℃ / 0.9 GPa, respectively. Our P-T estimations imply that Kashio mylonite zone was formed by two different mylonites related to HT-LP type and LT-HP type metamorphism.

View full abstract

Trace elements distributions of hydrothermal zircons (523 ± 1.8 Ma) from Osayama jadeitite were determined using a LA-ICPQMS. Zircon with ossilatory growth texture contains up to 30-70 μ/μg [Li], showing systematic element coupling with Y, Nb, U, Pb,Th, Ce and HREEs. [Li] doesn't correlate to Ti. Considering trace elements partitioning coefficients between zircon and hydrothermal fluid, a jadeitite-forming fluid in equilibrium with the hydrothermal zircon had very high [Li], which was at least one magnitude order higher than inferred subduction zone fluids in the literature.

View full abstract

So-called `high-grade' blocks of `non-eclogitic' metabasaltic rocks from the Franciscan Complex were petrologically investigated. High Ti content in brown clinoamphibole and the presence of clinopyroxene-rich veins with possibly pseudomorph after orthopyroxene suggest the block underwent nearly granulite-facies metamorphism with migmatitic partial melting. Those rocks might represent fragments of `metamorphic sole' formed during infant stage subduction with a `hot' geothermal gradient, following intra-oceanic subduction initiation.

View full abstract

The low-pressure type metamorphic rocks occur in the eastern foot of Mt. Sangun-san. The metamorphic rocks consist mainly of fine amphibolite and biotite gneiss with small amounts of metamorphosed chert and crystalline limestone. The inferred peak conditions show 620-720 degree-C and 0.4-0.5 GPa, and the metamorphic process could suggest a hairpin-shaped clockwise trajectory. The lithology and metamorphic process are similar to those of metamorphic rocks from the Sefuri Mountains in northwest Kyushu.

View full abstract

Sangun metamorphic rocks have diversity from region to region, but they have not been thoroughly studied and necessary constraints for discussing the tectonics of the metamorphic belt are not obtained. In this study, U-Pb dating of psammitic schist from Wakasa area in Tottori was tried. Three samples were analyzed and values of 168 Ma, 152 Ma, and 203 Ma were obtained. These values are considerably younger than the isotope ages of the conventionally reported Suo belt.

View full abstract

The Iratsu body in Sanbagawa belt experienced eclogite facies metamorphism. Impure marbles, as a minor lithology in the eastern Iratsu body, contain various mineral assemblages and reaction textures depending on the local bulk. These textures can be formed by the decompression more than 10 kbar at 600℃ and/or the decrease of XCO₂. The estimated XCO₂ for the reactant stability ranges from 0.018-0.027 at 600℃ & 2GPa, and it for the product ranges from 0.001-0.004 at same PT conditions.

View full abstract

The purpose of the present study is to clarify the deformation characteristics of the antigorite serpentinite from Sasaguri, Fukuoka Prefecture. We focus especially on the deformed antigorite serpentinite which are newly found. The important phenomena that proceed with deformation are creation of defect-induced undulose extinction, followed by the grain size reduction and creation of LPO.

View full abstract

This study reports new findings of nanogranites from Balchenfjella, Sor Rondane Mountains, East Antarctica. Nanogranites are included in garnet in two garnet-biotite gneisses and a garnet-clinopyroxene-orthopyroxene gneiss. Mineral assemblage of the nanogranites is biotite + quartz +/- plagioclase +/- andalusite +/- sillimanite. In this study, we will discuss the field distribution of Cl-rich fluid and melt and the timing when the fluid and melt were present in these samples, using biotite compositions in nanogranites and in the matrix.

View full abstract

Phase equilibrium modeling was applied to garnet-bearing mafic granulites from the Lutzow-Holm Complex, East Antarctica. Water content of the rocks in mole was inferred using T-M(H₂O) pseudosections at 8 kbar. Constructed P-T pseudosections suggest regional granulite-facies metamorphism, whereas continuous increase of the metamorphic grade has not been confirmed. Zircon U-Pb dating was also performed for meta-igneous rocks from the central LHC. Magmatic units of ca. 700 Ma and 900 Ma were newly obtained, suggesting that this region corresponds to a Neoproterozoic suture zone.

View full abstract

Serpentine mineralogy controls fault rheology in ocean and continental rift settings to subduction settings and can be used to discern the paleo-deformational conditions. Thus, deformed serpentinites of the Rakhabdev lineament from Rajasthan India, provides unique opportunity to understand its tectonic evolution in relation with the deformation inferred from deformation mechanisms of the antigorite and calcite that coexisted as veins.

View full abstract

This study conducted geochronological study of metapelites from the Zavkhan, Tarvagatay, Baydrag and Ereendavaa areas. The research focused on field investigations with U-Th-Pb monazite age dating by FE-EPMA and U-Pb zircon age dating by LA-ICP-MS to understand following timing of metamorphism and detrital zircon provenance from all terranes. These results allow us to realize the similarity and differences of the origin of the metamorphic rocks and to compare with other neighboring terranes such Tuva-Mongolia terrane and Siberia, Tarim and North China cratons.

View full abstract

Chimwadzulu sapphire and ruby mine is located in Chimwadzulu Hill, Ncheu District from 150 km south of Lilongwe, Malawi. It is one of the oldest gemstone deposits on the African continent. The corundum is found in the amphibolite. The mechanism of corundum crystallization is unclear. In this study, we examine the mineralogical and chemical characteristics of corundum. Chemical compositions of corundum grains were determined using EPMA and LA-ICP-MS. The results show that the corundum is the metamorphic origin on the discrimination diagram utilizing trace element compositions.

View full abstract

We propose a method to estimate probability of crustal thinning during exhumation of a metamorphic complex. We firstly assume that the maximum horizontal displacement was same as the vertical distance, ΔD. The probability of thinning is expressed as a function ofΔD/L. We secondly treat the maximum horizontal displacement as a variable x to express the probability as a function ofΔD/L and x/L. The probability at constant ΔD/L decreases when x/L approaches ΔD/L. The former evaluation provides approximately minimum estimation of the probability of the crustal thinning.

View full abstract

To analyze the chemical composition of tiny inclusions, which are commonly found in metamorphic rocks, we established an analytical procedure including FIB-based micro sampling and cryogenic observation. The analysed "ice" inclusion shows an inhomogeneous freezing, possibly because of its freezing rate. To obtain calibration curve for the quantitative analysis, we also performed analyses of standard ice.

View full abstract

This is the experimental report of the FeAlO₃ phase found at 9 kbar and 1050 °C under the moisture conditions. FeAlO₃ phase coexists with corundum, sillimanite, SiO2-rich melt and vapour without hematite from a mixture of sillimanite and hematite (weight ratio of 95 : 5) within the Pt capsule. In contrast, the assemblage of FeAlO₃ phase, magnetite-hercynite spinel, sillimanite, SiO₂-rich melt and vapour was found in the sillimanite-magnetite system (weight ratio of 86 : 14) within the AuPd capsule.

View full abstract