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In this study, we explored the impacts of radiation damage and chemical composition on the etching time of monazite fission-track (MFT). Despite the potential of MFT as an ultra-low-temperature thermochronology, the comprehensive effects of radiation damage and non-formula elements, especially on the etching rate of MFT, remain unexplored, and established analytical procedures are lacking. We quantified the degree of radiation damage (ΔFHWM) of Cretaceous to Quaternary monazites distributed in the Japan arc through Raman spectroscopy and chemical composition analyses. Subsequently, MFT etching was performed to examine the correlation between these parameters and the etching time. Estimation of the degree of radiation damage showed an increase in radiation damage corresponding to the cooling age of each geological unit. For example, Monazites from Quaternary geological units, the Toya ignimbrite (ca. 0.1 Ma) and the Kurobegawa granodiorite (ca. 0.8 Ma), have ΔFHWM of 0.48 and 0.70 cm-1, respectively. In contrast, the Muro ignimbrite (ca. 15 Ma) has a ΔFHWM of 4.11 cm⁻¹, while Cretaceous granitoids, including the Kibe granite and the Sagawa granite, yielded 7.42 and 6.40 cm⁻¹, respectively. MFT etching of these samples according to the existing recipe (6M HCl at 90 °C for 60–90 minutes) was completed at 1200, 860, 210, 120, and 90 minutes for Toya ignimbrite, Kurobegawa granodiorite, Muro ignimbrite, Sagawa granite, and Kibe granite respectively. These outcomes highlight an inverse relationship between MFT etching time and the degree of radiation damage in monazite, while the correlation between MFT etching time and chemical composition was unclear. The results affirm earlier considerations that the etching rate of MFT is strongly influenced by radiation damage. Conversely, young samples with lower levels of radiation damage exhibit higher chemical resistance, suggesting that existing etching recipes may not adequately etch MFT. [ABSTRACT FROM AUTHOR]

Thermochronological methods were applied to the Higher Himalayan Crystalline (HHC) nappe and the underlying Lesser Himalayan Sequences (LHS) to elucidate the denudation process for the middle‐ and upper‐crust of eastern Nepal over millions of years. Thermochronological inverse modeling was undertaken for new results of fission‐track (FT) age and FT length data of zircon and apatite in order to reconstruct the time‐temperature (t‐T) paths in the temperature range of 60–350°C. Eight t‐T paths calculated along the across‐strike section show that the cooling process of the HHC nappe in this study area is characterized by the following three aspects: (a) gradual cooling followed by rapid cooling and subsequent gradual cooling, (b) northward‐younging of the timing of the rapid cooling, and (c) gradual cooling followed by <2 Myr rapid cooling in the frontmost part of the HHC nappe. The observed FT ages and t‐T paths were then compared with those predicted by forwarding thermokinematic modeling. The results of the thermokinematic modeling for the "Flat‐Ramp‐Flat MHT model", in which the HHC and the underlying LHS are denudated in direct proportion to the uplift of rocks transported along the Main Himalayan Thrust (MHT), reproduced the observed t‐T paths and FT ages in eastern Nepal. This indicates that the observed FT ages and t‐T paths reflect a denudation process driven by the movement of the MHT with a flat‐ramp‐flat geometry and that the denudation rate and its spatial distribution have roughly been constant in eastern Nepal since ca. 9 Ma. Plain Language Summary: Motion of the deep‐seated rocks toward earth's surface (exhumation/denudation) in continental collision zones is a key phenomenon to understanding the mechanism of mountain building associated with a continental collision. Thermochronological method enables us to reconstruct the cooling history of the rock samples and address their denudation history of them. In this study, we collected metamorphic rocks from eastern Nepal and succeeded in reconstructing a detailed cooling history. The observed cooling history was compared with the predicted cooling history derived from numerical modeling of three different denudation processes. As a result, the observed cooling history in eastern Nepal was explained well by denudation associated with the movement of a stable, single plate‐boundary fault. This indicates that the denudation style of the deep‐seated rocks in eastern Nepal was established about 9 million years ago and remained unchanged since then. This finding contributes to understanding mountain building process that affects shallow crustal levels. Key Points: Inversion of fission‐track data and forward thermokinematic modeling were applied to reconstruct the denudation history of eastern NepalObserved gradual‐rapid‐gradual cooling time‐temperature paths were reproduced by the model assuming the flat‐ramp‐flat structure of the MHTOur result indicates that the denudation pattern has roughly been constant in southeastern Nepal since ca. 9 Ma [ABSTRACT FROM AUTHOR]

In this contribution, we present the petrological characteristics and pressure–temperature–deformation (P–T–D) history of the Dalrymple Amphibolite in Palawan Island, Philippines. This unit occurs below the residual mantle peridotites of the Palawan Ophiolite composed of interlayered dunite and harzburgite. The Dalrymple Amphibolite is predominantly composed of high‐grade metamafic blocks with minor metasedimentary units surrounded by a highly sheared hybridized matrix (kyanite + Ca‐amphibole + biotite + ilmenite ± garnet). Zr‐in‐rutile geothermometry and quartz‐in‐garnet geobarometry of the garnet amphibolite block reveal the P–T conditions of the prograde metamorphism from ~625°C, 11.5 kbar to ~700°C, 13 kbar. Zr‐in‐rutile geothermometer and the TZARS geobarometer (clinozoisite + rutile + quartz = anorthite + titanite + H2O) further indicate comparable peak metamorphic conditions for the amphibolite and epidote amphibolite (~605–710°C, 10–13 kbar) blocks. Geothermobarometry of the matrix surrounding the blocks reveals similar peak metamorphic conditions of ~700°C and 13 kbar to the garnet amphibolite blocks. The paleogeothermal gradient preserved in the Dalrymple Amphibolite (~16°C/km) and its block‐in‐matrix structure are atypical of metamorphic soles and are more akin to high‐T mélange complexes interpreted to have formed during incipient subduction. These P–T estimates and its block‐in‐matrix structure suggest that the Dalrymple Amphibolite likely represents the slab–mantle wedge interface of a young arc complex already transitioning from the much warmer paleogeothermal gradients of the slab–mantle wedge interface when subduction was first initiated. The similar peak metamorphic conditions constrained in the matrix and the metamafic blocks in the Dalrymple Amphibolite indicate that the matrix‐forming deformation started before the sequence reached peak metamorphic conditions at depths of around 45 km. Furthermore, the petrological and geochemical characteristics of this block‐in‐matrix sequence and the multiple generation of cross‐cutting veins reveal the complex processes that occur in the slab–mantle wedge interface of an arc in its infancy. Our results highlight the prevalence of Ca‐amphibole and kyanite over phyllosilicates (e.g., chlorite and serpentine) in the mélange matrix, mixing of crustal components along the slab–mantle wedge interface promoted by multiple deformation events and the ubiquity of fluids throughout its history. Subduction zones with similar geothermal gradients (e.g., warm subduction zones) possibly share these petrological characteristics. [ABSTRACT FROM AUTHOR]

Solidification pressures and ages of mafic microgranular enclaves (MMEs) and their host granite were determined and compared based on Al‐in‐hornblende geobarometry and U–Pb zircon dating in two sample localities in the Kurobegawa Granite. In sample KRG19‐A03 from the middle unit of the pluton, the MME and the host granite yielded 0.18 ± 0.03 to 0.24 ± 0.04 GPa and 0.16 ± 0.03 to 0.23 ± 0.04 GPa, respectively. The MME and the host granite of sample KRG19‐B08b from the lower unit, respectively, yielded 0.12 ± 0.02 to 0.21 ± 0.03 GPa and 0.13 ± 0.02 to 0.18 ± 0.03 GPa. In each sample locality, the estimated solidification pressures of the MME and its host granite overlap. The weighted mean ages were calculated as 0.775 ± 0.045 Ma and 0.831 ± 0.055 Ma for the MME and the host granite of KRG19‐A03, respectively. The MME and the host granite of KRG19‐B08b, respectively, yielded 0.672 ± 0.033 Ma and 0.735 ± 0.042 Ma. The ages for MMEs tend to be younger than the host granites, although they overlap within uncertainty. Zircon commonly occurs as the matrix minerals in both lithologies, meanwhile, zircon also occurs as early phases in plagioclase cores only in the host granites. Such differences in mode of occurrence of zircon suggest that the age variation reflects the differences in timing of zircon crystallization between the lithologies. Therefore, the MMEs record the same solidification pressures as the host granites and better represent the final solidification timing of the pluton. From these data of the MMEs, an average exhumation rate of each sample locality was estimated as 7.1–14.5 mm/year (KRG19‐A03) and 5.5–14.4 mm/year (KRG19‐B08b). These exhumation rates are much larger than that of the ca. 5.6–5.2 Ma Shiaidani Granodiorite (0.93–2.5 mm/year), implying that drastic change of the exhumation rate took place between ca. 5.2 Ma and ca. 0.83 Ma. [ABSTRACT FROM AUTHOR]

We report contrasting pressure–temperature–time (P–T–t) paths of migmatites developed in the highest‐grade metamorphic zone (Grt–Crd zone) and the contact metamorphic zone (Crd–Kfs zone) of the Mikawa area, Ryoke belt, southwest Japan to discuss the complex P–T–D–t evolution of the middle crust that experienced pulsed granitoid intrusions. In the Grt–Crd zone, sillimanite‐grade high‐T metamorphic condition prevailed from ca. 97 to 87 Ma, followed by cooling to ~500 °C, ~4 kbar. The intrusion of gneissose granitoids below the Grt–Crd zone isobarically reheated the Grt–Crd zone rocks again to the sillimanite‐grade high‐T condition at ca. 84 Ma. This was followed by ca. 71–70 Ma contact metamorphism. Ductile deformation that formed and folded the foliation of migmatites started before ca. 89 Ma and continued at least until ca. 84 Ma in the Grt–Crd zone. On the other hand, ca. 74 Ma age of the Crd–Kfs zone migmatite developed around the Inagawa Granodiorite in addition to ca. 70 Ma age of a syn‐tectonic pegmatite vein revealed that the intrusion of "75–69 Ma granitoids" caused partial melting and locally triggered low‐strain ductile deformation in their contact aureoles. Comparison with other areas of the Ryoke belt suggests that plutono‐metamorphic evolution of the Mikawa and Aoyama areas are similar with each other in that ca. 80 Ma reheating events (i.e., contact metamorphism) are observed, while absence of separate reheating event postdating peak metamorphism in the Yanai area is a rather uncommon feature in the Ryoke belt. [ABSTRACT FROM AUTHOR]

Solidification pressure and crystallization age of the ~5 Ma Shiaidani Granodiorite (Hida Mountain Range, central Japan) are determined based on Al‐in‐hornblende geobarometry and U–Pb zircon dating. Al‐poor patchy replacements developed in amphiboles are common in this granite and petrographic study revealed that the replacements include chloritized biotite and albitic plagioclase. These are probably the hydrothermally recrystallized domains, and should not be used for solidification pressure estimates. Magmatic rim of amphibole is characterized by Si < 7.3 a.p.f.u. (AlIV > 0.7 a.p.f.u.), and utilized in solidification pressure estimate that yielded 0.17–0.29 GPa. The solidification age of the granite is estimated as ~5.6–5.2 Ma using U–Pb zircon dating. From these data, the lower limit of an average denudation rate after ~5.6–5.2 Ma for the area where Shiaidani Granodiorite is exposed is estimated as 0.93–2.5 mm/year. [ABSTRACT FROM AUTHOR]

A geological survey and morphological analysis of quartz grains were performed to investigate the distribution of ductile deformation caused by the Himalayan Main Central Thrust (MCT) around Dhankuta, southeastern Nepal. The MCT was mapped as the lithological boundary between the gneiss of the Higher Himalayan Crystalline (HHC) as the hanging wall and the inverted metamorphic sequence of the Lesser Himalayan Sediments (LHS) as the footwall. The MCT was found to truncate various stratigraphic levels of LHS and cuts a map‐scale gentle fold developed in the LHS. Ductile deformation was quantified by fractal dimension between size and perimeter of dynamically recrystallized quartz grains in bedded metaquartzite intercalated in both HHC and LHS. Serrate and polygonal shapes of quartz indicate large and small strain rates, respectively, when the temperature during ductile deformation was assumed to be uniform. A peak of strain rate was found at the lithological boundary with the peak width of ca. 500 m. Such a thin shear zone is favorable for producing frictional heat to promote the inverted metamorphism in LHS. [ABSTRACT FROM AUTHOR]

In situ analysis of a garnet porphyroblast from a granulite facies gneiss from Sør Rondane Mountains, East Antarctica, reveals discontinuous step‐wise zoning in phosphorus and large δ18O variations from the phosphorus‐rich core to the phosphorus‐poor rim. The gradually decreasing profile of oxygen isotope from the core (δ18O = ~15‰) to the rim (δ18O = ~11‰) suggests that the 18O/16O zoning was originally step‐wise, and modified by diffusion after the garnet rim formation at ~800°C and 0.8 GPa. Fitting of the 18O/16O data to the diffusion equation constrains a duration of the high‐T event (~800°C) to c. 0.5–40 Ma after the garnet rim formation. The low δ18O value of the garnet rim, together with the previously reported low δ18O values in metacarbonates, indicates regional infiltration, probably along a detachment fault, of low δ18O fluid/melt possibly derived from meta‐mafic to ultramafic rocks. [ABSTRACT FROM AUTHOR]

Brine-induced microtexture formation in upper amphibolite to granulite facies lower crust is investigated using a garnet–hornblende (Grt-Hbl) selvage developed along a planar crack discordantly cutting the gneissic structure of an orthopyroxene-bearing gneiss (central Sør Rondane Mountains, East Antarctica). The Cl contents of hornblende and biotite, K contents of hornblende and the thickness of relatively Na-rich rims of plagioclase decrease with distance from the center of the Grt–Hbl selvage (inferred position of the crack). Biotite and hornblende arrangement defining the gneissic structure can be traced into the selvage, suggesting that the wall-rock was overprinted by the selvage formation. Addition and loss of elements to the wall-rock was examined using Zr as an immobile element. Trace elements that tend to be mobile in brines rather than in melts are added to the wall-rock, indicating that the Grt–Hbl selvage was formed by the advection of NaCl–KCl brine into a thin crack. Plagioclase in the wall-rock shows a discontinuous drop of anorthite content at the rim, indicating that coupled dissolution–reprecipitation took place and the grain boundaries were once wet. Trace element concentrations in the wall-rock minerals decrease with distance from the crack, and, in most cases show exponentially decreasing/increasing profiles depending on the elements. These profiles are best modelled by a diffusion equation, suggesting that the wet grain–boundary diffusion in the wall-rock minerals controlled the observed mass transfer and resulted in dissolution–reprecipitation of mineral rims. [ABSTRACT FROM AUTHOR]

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The alkali-feldspar and biotite in the sillimanite-biotite-garnet gneiss from East Antarctica preserves characteristic microstructural evidence of multi-stage HO supplement during the retrograde metamorphism. The first microstructural evidence is the 'zoned feldspar,' in which the mesoperthitic zone, the anti-perthitic zone, and lamella-free plagioclase zone coexist within a single crystal. They are occasionally found next to biotite, and are always depleted in orthoclase (Or) component toward the biotite. The formation process of this microstructure could be explained by the diffusion that oversteps the solvus. The second microstructural evidence is the serrate boundary between alkali-feldspar and biotite. The projections of biotite are selectively developed next to Or lamellae of alkali-feldspar every 3-5 μm. These two microstructures would have formed as the biotite grew by consuming potash in alkali-feldspar when HO-bearing fluid locally passed through the grain boundaries. The former microstructure was formed at 825-900 °C before lamella formation, and the latter microstructure was formed after the lamella formation. These microstructures are the indicators of fluid pathways formed under two different temperature conditions. The common coexistence of these microstructures implies that the fluid used similar pathways during the retrograde metamorphism. [ABSTRACT FROM AUTHOR]

Behavior of zircon at the schist/migmatite transition is investigated. Syn-metamorphic overgrowth is rare in zircon in schists, whereas zircon in migmatites has rims with low Th/U that give 90.3 ± 2.2 Ma U-Pb concordia age. Between inherited core and the metamorphic rim, a thin, dark-CL annulus containing melt inclusion is commonly developed, suggesting that it formed contemporaneous with the rim in the presence of melt. In diatexites, the annulus is further truncated by the brighter-CL overgrowth, suggesting the resorption and regrowth of the zircon after near-peak metamorphism. Part of the zircon rim crystallized during the solidification of the melt in migmatites. Preservation of angular-shaped inherited core of 5-10 μm in zircon included in garnet suggests that zircon of this size did not experience resorption but developed overgrowths during near-peak metamorphism. The Ostwald ripening process consuming zircon less than 5-10 μm is required to form new overgrowths. Curved crystal size distribution pattern for fine-grained zircons in a diatexite sample may indicate the contribution of this process. Zircon less than 20 μm is confirmed to be an important sink of Zr in metatexites, and ca. 35-μm zircon without detrital core are common in diatexites, supporting new nucleation of zircon in migmatites. In the Ryoke metamorphic belt at the Aoyama area, monazite from migmatites records the prograde growth age of 96.5 ± 1.9 Ma. Using the difference of growth timing of monazite and zircon, the duration of metamorphism higher than the amphibolite facies grade is estimated to be ca. 6 Myr. [ABSTRACT FROM AUTHOR]

The possibility of scanning electron microscope (SEM) observation and energy dispersive X-ray (EDX) spectrometry analysis in microscale regions of insulating samples using diluted ionic liquid was investigated. It is possible to obtain clear secondary electron images of insulating samples such as a rock and mineral at 5,000 times magnification by dropping 10 μL of 1 wt% of 1-ethyl-3-methylimidazolium acetate (EMI-CH3COO) diluted with ethanol onto the samples. We also obtained EDX spectra of the samples in microscale regions (∼5 μm2) without overlapping EDX spectra of other minerals with different composition. It might be possible to perform quantitative analysis of the samples if a method that does not need standard samples is applied or an X-ray detector sensitive for light elements was attached. The method of dropping 1 wt% EMI-CH3COO diluted with ethanol onto insulating samples is useful for SEM observation, EDX analysis in microscale regions, and the preservation of scarce rock and mineral samples because ionic liquid can be easily removed with acetone. [ABSTRACT FROM PUBLISHER]

Chemical Th-U-total Pb isochron method (CHIME) monazite dating was carried out for pelitic-psammitic migmatites and the Ao granite (one of the Younger Ryoke granites) from the Aoyama area, Ryoke metamorphic belt, Southwest Japan. The Ao granite gives an unequivocal age of 79.8 ± 3.9 Ma. The monazite grains in migmatites yield an age of 96.5 ± 1.9 Ma with rims and patchy domains of 83.5 ± 2.4 Ma. The 83.5 ± 2.4-Ma overprinting on migmatites over the garnet-cordierite zone suggests a wide and combined effect of thermal input and fluid activity on the monazite grains caused by the contact metamorphism by the Younger Ryoke granites including the Ao granite. This contact metamorphism has not been detected from the major metamorphic mineral assemblage previously, possibly because the migmatites already possessed the high-temperature mineral assemblage before the granite intrusions and were immune from contact metamorphism in terms of major metamorphic minerals. However, monazite records contact metamorphism clearly. Therefore, the field mapping of the CHIME monazite age is a powerful tool for recognition of polymetamorphism in high-temperature metamorphic terrains where later thermal effects can not be easily detected by the growth of new major metamorphic minerals. [ABSTRACT FROM AUTHOR]

Laser step heating 40Ar/39Ar analysis of biotite and muscovite single crystals from a Barrovian type metamorphic belt in the eastern Tibetan plateau yielded consistent cooling ages of ca. 40 Ma in the sillimanite zone with peak metamorphic temperatures higher than 600°C and discordant ages from 46 to 197 Ma in the zones with lower peak temperatures. Chemical Th-U-Total Pb Isochron Method (CHIME) monazite (65 Ma) and sensitive high mass-resolution ion microprobe (SHRIMP) apatite (67 Ma) dating give the age of peak metamorphism in the sillimanite zone. Moderate amounts of excess Ar shown by biotite grains with ages of 46 to 94 Ma at metamorphic grades up to the high-grade part of the kyanite zone probably represent incomplete degassing during metamorphism. In contrast, the high-grade part of the kyanite zone yields biotite ages of 130 to 197 Ma. The spatial distribution of these older ages in the kyanite zone along the sillimanite zone boundary suggests they reflect trapped excess argon that migrated from higher-grade regions. The most likely source is muscovite that decomposed to form sillimanite. The zone with extreme amounts of excess argon preserves trapped remnants of an ‘excess argon wave’. We suggest this corresponds to the area where biotite cooled below its closure temperature in the presence of an elevated Ar wave. Extreme excess Ar is not recognized in muscovite suggesting that the entrapment of the argon wave by biotite took place when the rocks had cooled down to temperatures lower than the closure temperature of muscovite. The breakdown of phengite during ultrahigh-pressure (UHP) metamorphism may be a key factor in accounting for the very old apparent ages seen in many UHP metamorphic regions. This is the first documentation of a regional Ar-wave spatially associated with regional metamorphism. This study also implies that resetting of the Ar isotopic systems in micas can require temperatures up to 600°C; much higher than generally thought. [ABSTRACT FROM AUTHOR]

The mode of occurrence of borosilicates and the breakdown fronts of prograde tourmaline (tourmaline-out isograd) in three anatectic migmatite regions of the Ryoke metamorphic belt, SW Japan, are reported. The breakdown of tourmaline in the migmatite zones and release of boron into the melts, followed by the extraction of the boron-bearing melts from the migmatite zones occurred throughout the Ryoke metamorphic belt. Retrograde, magmatic tourmaline in interboudin partitions filled with leucosome is useful for calculating the degree of partial melting in the migmatites. Using boron contents in the leucosomes and pelitic schists, the degree of partial melting at the migmatite front of the Aoyama area is estimated to be 12 wt.%. Extraction of the boron-bearing melt is suggested by the boron-depleted nature of the migmatites. Connection of boudinage structures probably supplied the vertical pathways of the segregated melts, and major transport of the melts was accomplished by dyking. Irregularly shaped, amoeboid tourmaline locally occurs on the high-temperature side of the tourmaline-out isograds in the Yanai and Komagane areas, implying incomplete extraction of boron-bearing melts from those areas. Discriminating retrograde from prograde tourmaline enables correct recognition of the tourmaline-out isograd. The amount of retrograde tourmaline in migmatites can potentially be used as an indicator of the degree of melt extraction from them. [ABSTRACT FROM PUBLISHER]

Tourmaline-out isograd formed by the breakdown of tourmaline is defined in the upper amphibolite-facies metapelites in the Yanai area, Ryoke metamorphic belt, SW Japan. The rim composition of tourmaline progressively becomes aluminous with ascending metamorphic grade, and the chemical zoning of tourmaline is controlled by X□AlNa–1Mg–1 and MgTiYAl–2 vectors in low- to medium-grade zones where muscovite is stable, whereas it is controlled by Mg(OH)YAl–1O–1, CaMgOX□–1YAl–1(OH)–1 and MgTiYAl–2 vectors in further higher–grade, muscovite-unstable zones. The size of tourmaline increases drastically where breakdown of muscovite+quartz takes place, probably due to the growth of tourmaline during breakdown of muscovite. On the high-temperature side of the tourmaline-out isograd, depletion of whole-rock boron is observed. Escape of boron-bearing melt or the fluid evolved from the melt during its crystallization probably caused this depletion, although locally trapped, boron-bearing melt or fluid formed irregularly shaped tourmaline and dumortierite during retrograde metamorphism. [ABSTRACT FROM AUTHOR]

Investigates the residual disease in children with acute lymphoblastic leukemia (ALL) in Japan. Clonal rearrangement of immunoglobulin genes; Effects of chemotherapy on the disease; Prognosis of childhood ALL.

Evaluates the clinical implications of CD45 expression in acute childhood lymphoblastic leukemia (ALL). Measurement of CD45 expression of blast cells; CD45 expression in patients with hyperdiploidy versus normal karyotype; Correlation of degree of antigen expression with treatment outcome of B-precursor ALL children.