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Publications (54)
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 spec...
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...
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 ∼40 km depth and ∼450°C unde...
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 µm along the long axis and are typically oriented along three directions, each intersecting at 120°. This indicates that the needle-shaped rutile is a lamella exsolved from the garnet. Garnet w...
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, wer...
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 ∼100 Ma, which corresponds to the protolith...
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 carbon...
In sedimentary rocks rich in Fe-oxide, such as red beds, white bleached spots that are free of Fe-oxide minerals are often observed. The spot formation has been explained by localized reduction reactions in relation to organic substances, such as fluids including hydrocarbon and organic debris as a precursor, and the recent major prevalent approach...
Aluminum-rich and Si-poor calcium amphibole [~3.9 Al atoms per formula unit (apfu) and ~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...
The Yuli belt is a high-pressure (HP) metamorphic terrane located at the convergent boundary between the Eurasia plate and the Philippine Sea plate. It is mainly composed of metapelites with minor serpentinites and metaigneous rocks. In the northern part of the belt, HP metamorphism is by far only reported on the omphacite-bearing metagabbro in ser...
Raman spectroscopy of carbonaceous material (RSCM) thermometry is an effective method to determine the thermal structure of metasedimentary domains with high spatial resolution. The mean value of numerous measurements in a single sample is used for temperature estimation. A potential complicating factor is the presence of detrital carbonaceous mate...
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, w...
The Mado Megamullion is an oceanic core complex (OCC) in the Shikoku back‐arc basin within the Philippine Sea Plate. Mantle peridotites (serpentinized) recovered by six dredge and submersible cruises exhibit signatures of extensive deformation. Amorphous pseudomorphs after plagioclase in many of the samples, as well as plagioclase‐spinel intergrowt...
The pattern and timing of tectonic discontinuity and partial melting in the Garhwal Himalaya, resulting from the India-Asia collision, are crucial factors for understanding the evolution of the Himalayan orogen, but these parameters remain poorly constrained. Middle-to high-grade metamorphic rocks from the Main Central Thrust (MCT) zone and the Hig...
In the 1950s, the aim of the original mantle drilling projects was to obtain oceanic mantle samples in order to address the unanswered question of what constitutes the Earth's mantle. However, in the 21st century, it is widely accepted that the uppermost mantle is mainly composed of peridotite. Now, the challenge of mantle drilling is to understand...
We determined the mineralogical and petrological characteristics of ultramafic rocks dredged from two oceanic core complexes: the Mado Megamullion and 23°30′N Non‐Transform Offset massif, which are located within the Shikoku back‐arc basin in the Philippine Sea. The ultramafic rocks are strongly serpentinized, but can be classified as harzburgite/l...
Olivine is a major mineral in ultramafic and mafic rocks. Due to the higher Mg/Fe partition coefficient of olivine than the coexisting phases, the occurrences of Mg–poorer olivine grains, especially with Mg#[= Mg/(Mg + Fe²⁺)] = 0.2–0.6, are rarely reported, and thus, their spectroscopic data are limited. Fe–rich olivine phenocrysts showing composit...
Structural analyses based on field survey and peak-temperature estimations using Raman spectra of carbonaceous-material thermometry were conducted for the Cretaceous subduction complexes on the central Kii Peninsula, southwest Japan, where there is a direct contact region between the Sanbagawa high-P/low-T Metamorphic Complex (MC) and the Shimanto...
The stabilization of coesite is a diagnostic indicator of ultrahigh-pressure metamorphism and in many cases it implies that a rock has been subducted to a minimum depth of 80 km. Coesite typically occurs as rare relicts in rigid host minerals, but most commonly transforms into α-quartz pseudomorphs during exhumation. The abundance of coesite-bearin...
Raman spectral analyses were conducted of carbonaceous materials (CM) in meta-sedimentary rocks to estimate the metamorphic thermal structure of the Outer Zone of Southwest Japan in the Akaishi Mountains area, central Japan. Twenty samples of pelitic and psammitic rocks were collected along the Koshibu River and by traversing the Sanbagawa, Chichib...
The Shibukawa region of the Sanbagawa belt, central Japan, is one of the historic jadeite localities in Japan. Although its petrological and mineralogical characteristics of the locality were briefly reported over 35 years ago, no further studies have been conducted since the disappearance of the jadeite-bearing outcrop. Recently, jadeite was disco...
Raman CM geothermometry applied to 126 samples of pelitic schists collected over an area of 11 km × 7 km reveals the thermal structure of the Asemigawa region of the Sanbagawa metamorphic belt, southwest Japan in unprecedented detail. In general, the estimated temperatures gradually increase from south to north in the range of 288 to 553°C. However...
Serpentinization of the mantle wedge immediately above a subducting slab is a key process controlling the strength contrast between the slab and the overriding nominally anhydrous (i.e., olivine-rich) mantle. To assess the influence of serpentinite rheology on the degree of decoupling between the slab and mantle wedge, we conducted axial compressio...
Attenuated total reflection infrared (ATR–IR) spectroscopy allows measurements to be made directly from the surface of one–sided, diamond polished thin sections of geological samples. This method greatly reduces the sample preparation time when compared to other IR spectroscopy methods and opens the possibility of using infrared spectroscopy to stu...
The microtexture of graphite exposed on the polished surface was studied using confocal laser scanning microscopy, laser Raman spectroscopy, and focused ion beam–transmission electron microscopy (FIB–TEM) to elucidate the effect on surface condition and crystallinity of graphite by polishing process. The polished surface of the graphite was divided...
The Yuli belt is considered a high-pressure (HP) metamorphic belt because glaucophane and omphacite occur in metabasite-serpentinite-dominated tectonic blocks embedded in metasedimentary rocks. Peak pressure-temperature (P-T) conditions of the HP rocks imply a type of subduction metamorphism. However, P-T conditions of the serpentinites are still u...
The Yuli belt is considered a high-pressure (HP) metamorphic belt because glaucophane and omphacite occur in metabasite-serpentinite-dominated tectonic blocks embedded in metasedimentary rocks. Peak pressure-temperature (P-T) conditions of the HP rocks imply a type of subduction metamorphism. However, P-T conditions of the serpentinites are still u...
The Sanbagawa belt is one of the famous subduction‐related high‐pressure (HP) metamorphic belts in the world. However, spatial distributions of eclogite units in the belt have not yet satisfactorily established, except within the Besshi region, central Shikoku, southwest Japan because most eclogitic rocks were affected by lower‐pressure overprintin...
en Garnet grains in Sanbagawa quartz eclogites from the Besshi region, central Shikoku commonly show a zoning pattern consisting of core and mantle/rim that formed during two prograde stages of eclogite and subsequent epidote–amphibolite facies metamorphism, respectively. Garnet grains in the quartz eclogites are grouped into four types (I, II, III...
Extremely negative δ¹³C values (as low as –48‰) of blocky calcite cements filling cavities, sheet-cracks, and fractures in the basal Ediacaran cap dolostone of the Doushantuo Formation in South China have been considered as evidence for methane release possibly associated with gas hydrate destabilization in the aftermath of the terminal Cryogenian...
We analyzed micro-Raman spectra of carbonaceous materials (CM) in natural and experimentally deformed fault rocks from Longmenshan fault zone that caused the 2008 Wenchuan earthquake, to characterize degree of disordering of CM in a fault zone. Raman spectral parameters for 12 samples from a fault zone in Shenxigou, Sichuan, China, all show low-gra...
The prograde metamorphic history of the Sulu ultrahigh-pressure metamorphic terrane has been revealed using Raman-based barometry of the SiO2 phases and other mineral inclusions in garnet porphyroblasts of a coesite eclogite from Yangzhuang, Junan region, eastern China. Garnet porphyroblasts have inner and outer segments with the boundary being mar...
This paper reports the major, minor and trace element abundances and Nd isotope compositions of bulk rock samples of eclogites from the Stak Valley in northwestern Himalaya and discusses their protolith. Major element compositions confirm the basaltic nature of the protolith. Trace element abundances normalized to the primitive mantle show almost f...
Research on the Sulu terrane of eastern China has provided abundant geological data on ultrahigh-pressure (UHP) rocks, which facilitates understanding of the geodynamic processes occurring in continental collision zones. Although the peak UHP conditions and subsequent decompression path are well constrained in the Sulu terrane, information on the p...
Raman spectra of carbonaceous materials were observed for 20 chondrite samples (one R, four CV, four CO, two CM, one CR, one CB, one C–ung, three LL, one L, and two H chondrites). The observed specimens were chips (fifteen samples) and thin sections (five samples). The obtained spectra were decomposed into four components: GL, D1, D3, and D4 bands...
Highly retrogressed eclogite is present in the Stak massif located on the northern edge of the Indian continental margin in northern Pakistan. Garnet in foliated samples contains omphacite inclusions (Xjd=0.33-0.40) and quartz inclusions and latter retain Raman spectroscopic evidence for high residual pressures up to 0.52GPa. These garnet grains do...
Vitrinite reflectance (Ro) and Raman spectra of carbonaceous material (RSCM) are both widely used as indicators of the maximum attained temperatures in sedimentary and metamorphic rocks. However, the potential of these methods to estimate temperature increases associated with fault slip has not been closely studied. To examine this issue, friction...
This report describes an investigation of the composite metamorphic history recorded in garnet porphyroblasts of Sambagawa metasediments, and presents discussions of the possible distribution of eclogite facies lithologies in the Besshi region, central Shikoku, southwest Japan. Garnet grains usually show chemically composite zoning with resolved in...
We have examined the mineralogy and deformation of black shear zones containing abundant carbonaceous materials (CM) and clay minerals in bedded ribbon cherts in a Jurassic accretionary complex, central Japan. Microtextural observations indicate that pressure solution and cataclastic deformation were the primary deformation mechanisms in the cherts...
Raman spectra of quartz inclusions in garnet hosts of low-pressure/temperature metamorphic rocks from the Yanai district in the Ryoke belt (around 0.1-0.3 GPa/500-600 degrees C), Southwest Japan, exhibit frequency (peak position) shifts toward lower wavenumbers as compared to those of a quartz standard measured at ambient conditions. The observed n...
The Raman spectra of carbonaceous material (CM) from 19 metasediment samples collected from six widely separated areas of Southwest Japan and metamorphosed at temperatures from 165 to 655°C show systematic changes with metamorphic temperature that can be classified into four types: low-grade CM (c. 150–280°C), medium-grade CM (c. 280–400°C), high-g...
Abstract Pressure (P)–temperature (T) pseudosection analyses were carried out on metapelites from Sambagawa belt by using Perple_X 07 so as to determine mineral equilibria and the stability of sodic phases, in the model system MnO–Na2O–K2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–(CO2) under high-pressure (HP) conditions (0.5–2.5 GPa/400–600 °C). A pressure–XNA...
P-T pseudosection analyses of high-pressure metapelites from several subduction related regions were carried out by using the computer program Perple_X 07 in order to determine the mineral equilibrium, particularly the stability of sodic phases, in the model system MnO-Na2O-K2O-CaO-FeO-MgO-Al2O3-SiO2-H2O. Metapelites from Sambagawa, Western Alps, N...
The degree of graphitization of carbonaceous material (CM) has been widely used as an indicator of metamorphic grade. Previous work has demonstrated that peak metamorphic temperature (T) of regional metamorphic rocks can be estimated by an area ratio (R2) of peaks recognized in Raman spectra of CM. The applicability of this method to low-pressure (...
Aragonite and omphacite-bearing metapelite occurs in the albite–biotite zone of the Togu (Tohgu) area, Besshi region, Sambagawa metamorphic belt, central Shikoku, Japan. This metapelite consists of alternating graphite-rich and graphite-poor layers that contain garnet, phengite, chlorite, epidote, titanite, calcite, albite, and quartz. A graphite-p...
Omphacite-bearing metapelite was found from the Seba area of the Besshi region, Sambagawa metamorphic belt, central Shikoku, Japan. Omphacite occurs as inclusions in garnet together with quartz, sodic amphibole, phengite, and paragonite. The major matrix phases are quartz, albite, phengite, chlorite, subcalcic amphibole, calcite, dolomite, and grap...
Omphacite and aragonite-bearing metapelites occur in the epidote-amphibolite facies grade area of the Besshi region, Sambagawa metamorphic belt, central Shikoku, Japan. Omphacite in the Sambagawa metapelite is very rare and aragonite is the first report from the high-grade region of the Sambagawa belt. Omphacite (Xjd = 0.37-0.62) and aragonite (SrC...
