New Sr and Nd isotopic data are presented and integrated with previous data for the Shirahama Gro... more New Sr and Nd isotopic data are presented and integrated with previous data for the Shirahama Group Mio-Pliocene medium-K volcanic arc suite of south-central Honshu, Japan-Main results are: (1) The Shirahama lavas range in Sr/^Sr from 0-70315 to 0-70337 and in m Nd/ 144 Nd from 0-51298 to 0-51306; the Sr and Nd isotopic data cluster tightly within the mantle array, and all lie within an overlapping field of midocean ridge basalt and ocean island basalt; (2) small differences exist among the Shirahama tholeiitic series, calc-alkaline series and mixed lavas. The present isotopic data are consistent with a previously published model, which proposes that chemical variations in magmas of coexisting tholeiitic and calc-alkaline series are produced through crystal fractionation from mantlederived magmas of basalt and magnesian andesite, respectively. Moreover, the tholeiitic series and the calc-alkaline series are isotopically identical Thus, both magma series can be derived from a source mantle with the same isotopic composition, supporting the hypothesis of simultaneous generation of basalt and magnesian andesite magmas from a single diapir rising through the mantle wedge above the subduction zone. The differences of water content and temperature within the diapir are again thought to have been produced through dehydration and heating of an isotopically homogeneous hydrous diapir. The isotopic data show that the high-SiO? lavas have the same isotopic compositions as more mafic lavas. These data and liquid lines of descent of the Shirahama magmas suggest that even rhyolites can be produced by differentiation from mantle-derived magmas without crustal contamination. Analyses from 38 other arc volcanoes have been compiled to investigate the intravolcano variability of Sr/^Sr. Twelve of these display no intravolcano strontium isotopic variability, as is the case with the Shirahama Group, but others show greater variation of ^Sr/ 86 Sr from individual volcanic centers, presumably reflecting crustal contamination. Most of the latter volcanoes are underlain by thick continental crust. It is noteworthy, however, that the greater variations of Sr/^Sr correlate with SiO 2 content; andesites or dacites, not basalts, from the same volcano have the lowest ^Sr/^Sr, and these rocks are calc-alkaline in terms of FeO*/MgO and SiO?. Theoretically, assimilation of continental crust by the isotopically uniform Shirahama magmas could produce these relationships. Given that mantle-derived basalt and magnesian andesite both encounter continental crust on their ascent to the surface, the hotter basalt magma would assimilate more crustal wallrocks than the cooler andesite, resulting in the basalt being more radiogenic. Fractional crystallization, magma mixing, and/or assimilation-fractional crystallization of these magmas in crustal magma chambers could produce large compositional variations, but the derivatives of the hotter basaltic magmas (tholeiitic series in the broad sense) would display greater contamination than those derived from the cooler andesitic magmas (calc-alkaline series).
We measured the N concentrations and isotopic compositions of 44 samples of terrestrial potassic ... more We measured the N concentrations and isotopic compositions of 44 samples of terrestrial potassic and micro-and meso-porous minerals and a small number of whole-rocks to determine the extent to which N is incorporated and stored during weathering and low-temperature hydrothermal alteration in Mars surface/near-surface environments. The selection of these minerals and other materials was partly guided by the study of altered volcanic glass from Antarctica and Iceland, in which the incorporation of N as NH 4 + in phyllosilicates is indicated by correlated concentrations of N and the LILEs (i.e., K, Ba, Rb, Cs), with scatter likely related to the presence of exchanged, occluded/trapped, or encapsulated organic/inorganic N occurring within structural cavities (e.g., in zeolites). The phyllosilicates, zeolites, and sulfates analyzed in this study contain between 0 and 99,120 ppm N and have d 15 N air values of-34& to +65&. Most of these minerals, and the few siliceous hydrothermal deposits that were analyzed, have d 15 N consistent with the incorporation of biologically processed N during low-temperature hydrothermal or weathering processes. Secondary ion mass spectrometry on altered hyaloclastites demonstrates the residency of N in smectites and zeolites, and silica. We suggest that geological materials known on Earth to incorporate and store N and known to be abundant at, or near, the surface of Mars should be considered targets for upcoming Mars sample return with the intent to identify any signs of ancient or modern life.
Presented here are the observations and interpretations from a comprehensive analysis of 16 repre... more Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher ' 18 O, " 17 O, and C 54 Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10's of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation.
A comprehensive geochemical study of the Chelyabinsk meteorite reveals further details regarding ... more A comprehensive geochemical study of the Chelyabinsk meteorite reveals further details regarding its history of impact-related fragmentation and melting, and later aqueous alteration, during its transit toward Earth. We support an 930 Ma age obtained by Ar-Ar method (Beard et al., 2014) for the impact-related melting, based on Rb-Sr isotope analyses of a melt domain. An irregularly shaped olivine with a distinct O isotope composition in a melt domain appears to be a fragment of a silicate-rich impactor. Hydrogen and Li concentrations and isotopic compositions, textures of Fe oxyhydroxides, and the presence of organic materials located in fractures, are together consistent with aqueous alteration, and this alteration could have pre-dated interaction with the Earth's atmosphere. As one model, we suggest that hypervelocity capture of the impact-related debris by a comet nucleus could have led to shock-wave-induced supercritical aqueous fluids dissolving the silicate, metallic, and organic matter, with later ice sublimation yielding a rocky rubble pile sampled by the meteorite.
We have devoted the past 25 years to the development of the Comprehensive Analytical System for T... more We have devoted the past 25 years to the development of the Comprehensive Analytical System for Terrestrial and Extraterrestrial Materials (CASTEM), an exclusive laboratory for materials science. CASTEM facilities allow for the determination of elemental and isotopic abundances of geochemically significant elements in multi-scale ranges. CASTEM research targets are not limited to lithic rocks. We have successfully analyzed a variety of materials including human tissue. Utilizing CASTEM, we conducted the "initial analysis" of grains collected from the outermost surface of the asteroid Itokawa that were subsequently returned to Earth by the Hayabusa spacecraft. These analyses involved processing the grains, describing surface morphology, and the determination of elemental and isotopic abundances. The history of the asteroid was unveiled through comprehensive geochemical examinations of the microscopic grains suggesting a physically hostile environment at the asteroid's surface. Our results reveal that impact processes play a central role in the long-term evolution of planetary bodies in the solar system.
While exposure to bers and particles has been proposed to be associated with several dierent lung... more While exposure to bers and particles has been proposed to be associated with several dierent lung malignancies including mesothelioma, the mechanism for the carcinogenesis is not fully understood. Along with mineralogical observation, we have analyzed forty-four major and trace elements in extracted asbestos bodies (bers and proteins attached to them) with coexisting ber-free ferruginous protein bodies from extirpative lungs of individuals with malignant mesothelioma. These observations together with patients' characteristics suggest that inhaled iron-rich asbestos bers and dust particles, and excess iron deposited by continuous cigarette smoking would induce ferruginous protein body formation resulting in ferritin aggregates in lung tissue. Chemical analysis of ferruginous protein bodies extracted from lung tissues reveals anomalously high concentrations of radioactive radium, reaching millions of times higher concentration than that of seawater. Continuous and prolonged internal exposure to hotspot ionizing radiation from radium and its daughter nuclides could cause strong and frequent DNA damage in lung tissue, initiate dierent types of tumour cells, including malignant mesothelioma cells, and may cause cancers.
Saline groundwaters are common to inland Australia, but their hydrochemical evolution and origin ... more Saline groundwaters are common to inland Australia, but their hydrochemical evolution and origin remain largely unknown. The saline groundwaters in the alluvial aquifers of the Darling River have previously been found to exhibit broad similarity in traditional hydrochemical and isotopic tracers. By contrast, in this study the trace element isotopes (d 7 Li, d 11 B and 87 Sr/ 86 Sr) have illuminated more complex hydrogeochemical processes in the same aquifer system. This paper reports the first ever set of d 7 Li values in any groundwater system in Australia. They varied from +5.8 to +16.2 with an average value of +9.7& (n = 19) in the alluvial aquifers of the Darling River catchment. The d 11 B values were all higher than seawater and close to some of the highest d 11 B values ever reported in the literature for a groundwater system (+44.4 to +53.9; average: +48.8, n = 17). The 87 Sr/ 86 Sr ratios ranged from 0.708 to 0.713, with an average value of 0.709 (n = 19). The differing signatures in these trace element isotope values, highlighted by discovery of the deeper older groundwater system with heavier Li isotope values and higher 87 Sr/ 86 Sr, is an important finding of this research. Simple mixing models between river water and saline groundwater cannot explain the observed variation in trace element isotopes. Hydrochemical evolution was found to be dependent on proximity to the Darling River and depth. Varying degrees of Li and B isotopic fractionation during watersediment interaction were interpreted to account for the evolution of the saline groundwaters. The measurement of these trace element isotopes has permitted delineation of groundwater end-members that would have otherwise not been identified; in their absence an inaccurate interpretation of the hydrochemical evolution of these saline groundwaters would have been made. This study highlights the importance of a multi-tracer approach, which includes trace element isotopes, in resolving complex geochemical processes in groundwater in semi-arid to arid zone environments.
A new preconcentration technique of Zr, Nb, Mo, Hf, Ta and W has been invented employing coprecip... more A new preconcentration technique of Zr, Nb, Mo, Hf, Ta and W has been invented employing coprecipiation with Ti compounds. Silicate samples were digested by HF with addition of Ti. Subsequent drying with HClO 4 resulting in complete elimination of fluorine produces Ti compounds (oxide/hydroxides). The sample was then dissolved with dilute nitric acid and centrifuged, and the residual Ti compounds were collected. The Ti compounds forming from 2 mg of Ti without matrix elements concentrate 84-98% of Zr, Nb, Mo, Hf, Ta and W. In 20 mg basaltic and 50 mg peridotitic matrices, the addition of 1 mg of Ti was appropriate and gave yields of 46-69 and 54-79%, respectively, for Zr, Nb, Mo, Hf, Ta and W. Exploiting this preconcentration, sequential separation protocols of Hf, Pb, Sr, Lu, Nd and Sm for isotope analysis are developed with total blanks of 16, 11, 60, 2.4, 3 and 0.4 pg, respectively. The method is suitable for Lu-Hf system studies with capability of simultaneous separation of Pb, Sr, Nd and Sm from the same sample digest as well as isotopic anomaly studies of Zr, Mo and W. As application examples, accurate Lu-Hf data and Pb isotope ratios were obtained for basalt (JB-3) and peridotite (JP-1) by MC-ICP-MS.
A new 3-step sequential separation chemistry for Sr, Nd and Pb from silicate samples, which is su... more A new 3-step sequential separation chemistry for Sr, Nd and Pb from silicate samples, which is suitable for isotope analysis by MC-ICP-MS as well as TIMS, has been developed. The chemistry is designed to minimize the number of evaporation steps, enabling high throughput especially when MC-ICP-MS is employed. The sample solution in 0.5 mol l-1 HNO 3 after digestion with HF-HClO 4 , which is prepared for trace element analysis, can be directly used in the new chemistry. In the first column using Sr resin, Sr and Pb are collected. The recovered solution for Sr can be directly aspirated into MC-ICP-MS. The Pb solution is dried, re-dissolved, separated into two aliquots and measured by double spike MC-ICP-MS. Subsequently, LREEs are collected by the second column packed with cation exchange resin. Finally, Nd was purified from Sm using Ln resin in the third column. The recovered Nd solution can also be directly nebulized into MC-ICP-MS. The Sr and Nd isotope ratios for the standard material JB-3 (basalt) from the Geological Survey of Japan by MC-ICP-MS and TIMS were reported to verify the chemistry and mass spectrometry developed in this study.
In view of the requirement of a well-characterized and easily available aquatic sediment referenc... more In view of the requirement of a well-characterized and easily available aquatic sediment reference material, a comprehensive analysis comprising of fifty major, minor and trace elements as well as Sr-Nd-Pb-Hf isotopes were carried out in the stream sediment reference material, JSd-1, issued by the Geological Survey of Japan. The data for marine sediment reference material, MAG-1, issued by U.S. Geological Survey is also obtained for comparison. The elements were divided into two groups: Group I and Group II. Elements in Group I form stable soluble ions in HNO 3 ; and those in Group II form soluble oxo-and fluoro-complexes in HF, such as Zr, Nb, Hf, Ta, etc. For Group I, the sample was decomposed with HF in a tetra fluoro ethylene (TFE) bomb at 245°C for 96 hrs with Mg addition. The elemental concentration was measured by quadrupole type inductively coupled plasma source mass spectrometry (ICP-QMS) and sector field type ICP-MS (ICP-SFMS) using isotope dilution-internal standardization (ID-IS) methods. The aliquot of the sample solution was passed through 3-step column chemistry for isotope ratio determination of Pb by multiple collector (MC) ICP-MS and thermal ionization mass spectrometry (TIMS), and Sr and Nd by TIMS. For Group II elements, the sample was decomposed with HF in a TFE bomb with the same time and temperature settings. Zr, Mo, Sn, Sb and Hf were determined by ID, and Nb and Ta by ID-IS using ICP-QMS. The original JSd-1 powder showed heterogeneity for Group II elements, indicating insufficient pulverization and distribution. Thus, we further pulverized the powder and measured the concentration, which showed improved homogeneity. The aliquot for the re-pulverized powder was passed through 2-step column chemistry, and the Hf isotope ratio was determined by MC-ICP-MS. Thus a new data on the trace elements as well as Sr-Nd-Pb-Hf isotope ratios is provided for JSd-1 and MAG-1 in this paper.
Includes the geographic coordinates for the Lago di Cignana locality, images and geochemical data... more Includes the geographic coordinates for the Lago di Cignana locality, images and geochemical data for the garnets that were studied, and a description of the analytical methods.
Observed enrichments of N (and the d 15 N of this N) in volcanic glasses altered on Earth's moder... more Observed enrichments of N (and the d 15 N of this N) in volcanic glasses altered on Earth's modern and ancient seafloor are relevant in considerations of modern global N subduction fluxes and ancient life on Earth, and similarly altered glasses on Mars and other extraterrestrial bodies could serve as valuable tracers of biogeochemical processes. Palagonitized glasses and whole-rock samples of volcanic rocks on the modern seafloor (ODP Site 1256D) contain 3-18 ppm N with d 15 N air values of up to +4.5&. Variably altered glasses from Mesozoic ophiolites (Troodos, Cyprus; Stonyford volcanics, USA) contain 2-53 ppm N with d 15 N of-6.3 to +7&. All of the more altered glasses have N concentrations higher than those of fresh volcanic glass (for MORB, <2 ppm N), reflecting significant N enrichment, and most of the altered glasses have d 15 N considerably higher than that of their unaltered glass equivalents (for MORB,-5-2&). Circulation of hydrothermal fluids, in part induced by nearby spreadingcenter magmatism, could have leached NH 4 + from sediments then fixed this NH 4 + in altering volcanic glasses. Glasses from each site contain possible textural evidence for microbial activity in the form of microtubules, but any role of microbes in producing the N enrichments and elevated d 15 N remains uncertain. Petrographic analysis, and imaging and chemical analyses by scanning electron microscopy and scanning transmission electron microscopy, indicate the presence of phyllosilicates (smectite, illite) in both the palagonitized cracks and the microtubules. These phyllosilicates (particularly illite), and possibly also zeolites, are the likely hosts for N in these glasses.
Journal of Mineralogical and Petrological Sciences, 2017
Omphacite replacing after relic edenitic pargasite has been found in an omphacite-bearing jadeiti... more Omphacite replacing after relic edenitic pargasite has been found in an omphacite-bearing jadeitite block of the Itoigawa-Omi area in the Hida-Gaien belt. Omphacite occurs sporadically as fine-grained aggregate reaching a few cm in length in a jadeite-albite matrix, and sometimes contains edenitic pargasite as a core. The edenitic pargasite is chemically and optically homogeneous and does not show direct contact with jadeite and albite. An irregular shaped omphacite-diopside mixed area occurs near edenitic pargasite in a coarse omphacite aggregate. The texture suggests that the breakdown of edenitic pargasite was triggered by the addition of a hydrothermal fluid, from which jadeite and albite were precipitated later, passing through diopside and omphacite by the reaction:
The geochemical variabilities in intraplate basalts (IB) from the West African passive margin (WA... more The geochemical variabilities in intraplate basalts (IB) from the West African passive margin (WAPM) region, have generally been employed to indicate the presence of recycled materials in an associated upwelling mantle plume. However, the absence of time-progressive linear hotspot tracks in WAPM-IB make it difficult to explain their genesis solely by the mantle plume hypothesis. Here, we show that the Sr–Nd–Hf–Pb isotopic variations in basalts from most of the WAPM-IB could have mainly attributed to the derivation from two types of fusible regions of the refertilized subcontinental lithospheric mantle (SCLM) and the sub-lithospheric mantle. The locations and magma genesis of WAPM-IB are strongly related to the distance from the Mesozoic rift axis and the structure of the rifted SCLM. The melting of the source region can possibly be attributed to small-scale mantle convection at the base of the SCLM without the involvement of a mantle plume.
Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Cariu... more Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high pressure asher) is the most common method used to extract highly siderophile elements (HSEs: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) from geological samples. Recently, it has been recognised that additional HF-desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion-exchange purification procedures are applied to desilicified samples. In this study, we developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable Accepted Article This article is protected by copyright. All rights reserved. to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd, and Cr for Ru, is circumvented for the desilicified samples.
Journal of Geophysical Research: Solid Earth, 2018
We present K‐Ar ages, major and trace element concentrations, and Sr‐Nd‐Pb isotope data for late ... more We present K‐Ar ages, major and trace element concentrations, and Sr‐Nd‐Pb isotope data for late Cenozoic volcanic rocks from the Chugoku district, southwest Japan arc. Andesite and dacite lavas in this region are enriched in Sr (mostly >800 μg g−1) and show geochemical characteristics of volcanic rocks commonly referred to as “adakite.” K‐Ar dating of these lavas revealed that the eruption of high‐Sr andesitic to dacitic magmas occurred during the last 2 Myr, following or concurrent with the eruption of basalt in adjacent regions. Trace‐element characteristics of high‐Sr andesites and dacites are consistent with the formation of their parent magmas by partial melting of the basaltic layer of the subducting Shikoku Basin Plate. Mass balance modeling of trace element concentrations and isotopic compositions suggests that the parental magmas of high‐Sr andesites and dacites are best explained by mixing of partial melts from oceanic crust (F = 5–15%) and sediment (F = 30%) at 80:20 ...
New Sr and Nd isotopic data are presented and integrated with previous data for the Shirahama Gro... more New Sr and Nd isotopic data are presented and integrated with previous data for the Shirahama Group Mio-Pliocene medium-K volcanic arc suite of south-central Honshu, Japan-Main results are: (1) The Shirahama lavas range in Sr/^Sr from 0-70315 to 0-70337 and in m Nd/ 144 Nd from 0-51298 to 0-51306; the Sr and Nd isotopic data cluster tightly within the mantle array, and all lie within an overlapping field of midocean ridge basalt and ocean island basalt; (2) small differences exist among the Shirahama tholeiitic series, calc-alkaline series and mixed lavas. The present isotopic data are consistent with a previously published model, which proposes that chemical variations in magmas of coexisting tholeiitic and calc-alkaline series are produced through crystal fractionation from mantlederived magmas of basalt and magnesian andesite, respectively. Moreover, the tholeiitic series and the calc-alkaline series are isotopically identical Thus, both magma series can be derived from a source mantle with the same isotopic composition, supporting the hypothesis of simultaneous generation of basalt and magnesian andesite magmas from a single diapir rising through the mantle wedge above the subduction zone. The differences of water content and temperature within the diapir are again thought to have been produced through dehydration and heating of an isotopically homogeneous hydrous diapir. The isotopic data show that the high-SiO? lavas have the same isotopic compositions as more mafic lavas. These data and liquid lines of descent of the Shirahama magmas suggest that even rhyolites can be produced by differentiation from mantle-derived magmas without crustal contamination. Analyses from 38 other arc volcanoes have been compiled to investigate the intravolcano variability of Sr/^Sr. Twelve of these display no intravolcano strontium isotopic variability, as is the case with the Shirahama Group, but others show greater variation of ^Sr/ 86 Sr from individual volcanic centers, presumably reflecting crustal contamination. Most of the latter volcanoes are underlain by thick continental crust. It is noteworthy, however, that the greater variations of Sr/^Sr correlate with SiO 2 content; andesites or dacites, not basalts, from the same volcano have the lowest ^Sr/^Sr, and these rocks are calc-alkaline in terms of FeO*/MgO and SiO?. Theoretically, assimilation of continental crust by the isotopically uniform Shirahama magmas could produce these relationships. Given that mantle-derived basalt and magnesian andesite both encounter continental crust on their ascent to the surface, the hotter basalt magma would assimilate more crustal wallrocks than the cooler andesite, resulting in the basalt being more radiogenic. Fractional crystallization, magma mixing, and/or assimilation-fractional crystallization of these magmas in crustal magma chambers could produce large compositional variations, but the derivatives of the hotter basaltic magmas (tholeiitic series in the broad sense) would display greater contamination than those derived from the cooler andesitic magmas (calc-alkaline series).
We measured the N concentrations and isotopic compositions of 44 samples of terrestrial potassic ... more We measured the N concentrations and isotopic compositions of 44 samples of terrestrial potassic and micro-and meso-porous minerals and a small number of whole-rocks to determine the extent to which N is incorporated and stored during weathering and low-temperature hydrothermal alteration in Mars surface/near-surface environments. The selection of these minerals and other materials was partly guided by the study of altered volcanic glass from Antarctica and Iceland, in which the incorporation of N as NH 4 + in phyllosilicates is indicated by correlated concentrations of N and the LILEs (i.e., K, Ba, Rb, Cs), with scatter likely related to the presence of exchanged, occluded/trapped, or encapsulated organic/inorganic N occurring within structural cavities (e.g., in zeolites). The phyllosilicates, zeolites, and sulfates analyzed in this study contain between 0 and 99,120 ppm N and have d 15 N air values of-34& to +65&. Most of these minerals, and the few siliceous hydrothermal deposits that were analyzed, have d 15 N consistent with the incorporation of biologically processed N during low-temperature hydrothermal or weathering processes. Secondary ion mass spectrometry on altered hyaloclastites demonstrates the residency of N in smectites and zeolites, and silica. We suggest that geological materials known on Earth to incorporate and store N and known to be abundant at, or near, the surface of Mars should be considered targets for upcoming Mars sample return with the intent to identify any signs of ancient or modern life.
Presented here are the observations and interpretations from a comprehensive analysis of 16 repre... more Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher ' 18 O, " 17 O, and C 54 Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10's of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation.
A comprehensive geochemical study of the Chelyabinsk meteorite reveals further details regarding ... more A comprehensive geochemical study of the Chelyabinsk meteorite reveals further details regarding its history of impact-related fragmentation and melting, and later aqueous alteration, during its transit toward Earth. We support an 930 Ma age obtained by Ar-Ar method (Beard et al., 2014) for the impact-related melting, based on Rb-Sr isotope analyses of a melt domain. An irregularly shaped olivine with a distinct O isotope composition in a melt domain appears to be a fragment of a silicate-rich impactor. Hydrogen and Li concentrations and isotopic compositions, textures of Fe oxyhydroxides, and the presence of organic materials located in fractures, are together consistent with aqueous alteration, and this alteration could have pre-dated interaction with the Earth's atmosphere. As one model, we suggest that hypervelocity capture of the impact-related debris by a comet nucleus could have led to shock-wave-induced supercritical aqueous fluids dissolving the silicate, metallic, and organic matter, with later ice sublimation yielding a rocky rubble pile sampled by the meteorite.
We have devoted the past 25 years to the development of the Comprehensive Analytical System for T... more We have devoted the past 25 years to the development of the Comprehensive Analytical System for Terrestrial and Extraterrestrial Materials (CASTEM), an exclusive laboratory for materials science. CASTEM facilities allow for the determination of elemental and isotopic abundances of geochemically significant elements in multi-scale ranges. CASTEM research targets are not limited to lithic rocks. We have successfully analyzed a variety of materials including human tissue. Utilizing CASTEM, we conducted the "initial analysis" of grains collected from the outermost surface of the asteroid Itokawa that were subsequently returned to Earth by the Hayabusa spacecraft. These analyses involved processing the grains, describing surface morphology, and the determination of elemental and isotopic abundances. The history of the asteroid was unveiled through comprehensive geochemical examinations of the microscopic grains suggesting a physically hostile environment at the asteroid's surface. Our results reveal that impact processes play a central role in the long-term evolution of planetary bodies in the solar system.
While exposure to bers and particles has been proposed to be associated with several dierent lung... more While exposure to bers and particles has been proposed to be associated with several dierent lung malignancies including mesothelioma, the mechanism for the carcinogenesis is not fully understood. Along with mineralogical observation, we have analyzed forty-four major and trace elements in extracted asbestos bodies (bers and proteins attached to them) with coexisting ber-free ferruginous protein bodies from extirpative lungs of individuals with malignant mesothelioma. These observations together with patients' characteristics suggest that inhaled iron-rich asbestos bers and dust particles, and excess iron deposited by continuous cigarette smoking would induce ferruginous protein body formation resulting in ferritin aggregates in lung tissue. Chemical analysis of ferruginous protein bodies extracted from lung tissues reveals anomalously high concentrations of radioactive radium, reaching millions of times higher concentration than that of seawater. Continuous and prolonged internal exposure to hotspot ionizing radiation from radium and its daughter nuclides could cause strong and frequent DNA damage in lung tissue, initiate dierent types of tumour cells, including malignant mesothelioma cells, and may cause cancers.
Saline groundwaters are common to inland Australia, but their hydrochemical evolution and origin ... more Saline groundwaters are common to inland Australia, but their hydrochemical evolution and origin remain largely unknown. The saline groundwaters in the alluvial aquifers of the Darling River have previously been found to exhibit broad similarity in traditional hydrochemical and isotopic tracers. By contrast, in this study the trace element isotopes (d 7 Li, d 11 B and 87 Sr/ 86 Sr) have illuminated more complex hydrogeochemical processes in the same aquifer system. This paper reports the first ever set of d 7 Li values in any groundwater system in Australia. They varied from +5.8 to +16.2 with an average value of +9.7& (n = 19) in the alluvial aquifers of the Darling River catchment. The d 11 B values were all higher than seawater and close to some of the highest d 11 B values ever reported in the literature for a groundwater system (+44.4 to +53.9; average: +48.8, n = 17). The 87 Sr/ 86 Sr ratios ranged from 0.708 to 0.713, with an average value of 0.709 (n = 19). The differing signatures in these trace element isotope values, highlighted by discovery of the deeper older groundwater system with heavier Li isotope values and higher 87 Sr/ 86 Sr, is an important finding of this research. Simple mixing models between river water and saline groundwater cannot explain the observed variation in trace element isotopes. Hydrochemical evolution was found to be dependent on proximity to the Darling River and depth. Varying degrees of Li and B isotopic fractionation during watersediment interaction were interpreted to account for the evolution of the saline groundwaters. The measurement of these trace element isotopes has permitted delineation of groundwater end-members that would have otherwise not been identified; in their absence an inaccurate interpretation of the hydrochemical evolution of these saline groundwaters would have been made. This study highlights the importance of a multi-tracer approach, which includes trace element isotopes, in resolving complex geochemical processes in groundwater in semi-arid to arid zone environments.
A new preconcentration technique of Zr, Nb, Mo, Hf, Ta and W has been invented employing coprecip... more A new preconcentration technique of Zr, Nb, Mo, Hf, Ta and W has been invented employing coprecipiation with Ti compounds. Silicate samples were digested by HF with addition of Ti. Subsequent drying with HClO 4 resulting in complete elimination of fluorine produces Ti compounds (oxide/hydroxides). The sample was then dissolved with dilute nitric acid and centrifuged, and the residual Ti compounds were collected. The Ti compounds forming from 2 mg of Ti without matrix elements concentrate 84-98% of Zr, Nb, Mo, Hf, Ta and W. In 20 mg basaltic and 50 mg peridotitic matrices, the addition of 1 mg of Ti was appropriate and gave yields of 46-69 and 54-79%, respectively, for Zr, Nb, Mo, Hf, Ta and W. Exploiting this preconcentration, sequential separation protocols of Hf, Pb, Sr, Lu, Nd and Sm for isotope analysis are developed with total blanks of 16, 11, 60, 2.4, 3 and 0.4 pg, respectively. The method is suitable for Lu-Hf system studies with capability of simultaneous separation of Pb, Sr, Nd and Sm from the same sample digest as well as isotopic anomaly studies of Zr, Mo and W. As application examples, accurate Lu-Hf data and Pb isotope ratios were obtained for basalt (JB-3) and peridotite (JP-1) by MC-ICP-MS.
A new 3-step sequential separation chemistry for Sr, Nd and Pb from silicate samples, which is su... more A new 3-step sequential separation chemistry for Sr, Nd and Pb from silicate samples, which is suitable for isotope analysis by MC-ICP-MS as well as TIMS, has been developed. The chemistry is designed to minimize the number of evaporation steps, enabling high throughput especially when MC-ICP-MS is employed. The sample solution in 0.5 mol l-1 HNO 3 after digestion with HF-HClO 4 , which is prepared for trace element analysis, can be directly used in the new chemistry. In the first column using Sr resin, Sr and Pb are collected. The recovered solution for Sr can be directly aspirated into MC-ICP-MS. The Pb solution is dried, re-dissolved, separated into two aliquots and measured by double spike MC-ICP-MS. Subsequently, LREEs are collected by the second column packed with cation exchange resin. Finally, Nd was purified from Sm using Ln resin in the third column. The recovered Nd solution can also be directly nebulized into MC-ICP-MS. The Sr and Nd isotope ratios for the standard material JB-3 (basalt) from the Geological Survey of Japan by MC-ICP-MS and TIMS were reported to verify the chemistry and mass spectrometry developed in this study.
In view of the requirement of a well-characterized and easily available aquatic sediment referenc... more In view of the requirement of a well-characterized and easily available aquatic sediment reference material, a comprehensive analysis comprising of fifty major, minor and trace elements as well as Sr-Nd-Pb-Hf isotopes were carried out in the stream sediment reference material, JSd-1, issued by the Geological Survey of Japan. The data for marine sediment reference material, MAG-1, issued by U.S. Geological Survey is also obtained for comparison. The elements were divided into two groups: Group I and Group II. Elements in Group I form stable soluble ions in HNO 3 ; and those in Group II form soluble oxo-and fluoro-complexes in HF, such as Zr, Nb, Hf, Ta, etc. For Group I, the sample was decomposed with HF in a tetra fluoro ethylene (TFE) bomb at 245°C for 96 hrs with Mg addition. The elemental concentration was measured by quadrupole type inductively coupled plasma source mass spectrometry (ICP-QMS) and sector field type ICP-MS (ICP-SFMS) using isotope dilution-internal standardization (ID-IS) methods. The aliquot of the sample solution was passed through 3-step column chemistry for isotope ratio determination of Pb by multiple collector (MC) ICP-MS and thermal ionization mass spectrometry (TIMS), and Sr and Nd by TIMS. For Group II elements, the sample was decomposed with HF in a TFE bomb with the same time and temperature settings. Zr, Mo, Sn, Sb and Hf were determined by ID, and Nb and Ta by ID-IS using ICP-QMS. The original JSd-1 powder showed heterogeneity for Group II elements, indicating insufficient pulverization and distribution. Thus, we further pulverized the powder and measured the concentration, which showed improved homogeneity. The aliquot for the re-pulverized powder was passed through 2-step column chemistry, and the Hf isotope ratio was determined by MC-ICP-MS. Thus a new data on the trace elements as well as Sr-Nd-Pb-Hf isotope ratios is provided for JSd-1 and MAG-1 in this paper.
Includes the geographic coordinates for the Lago di Cignana locality, images and geochemical data... more Includes the geographic coordinates for the Lago di Cignana locality, images and geochemical data for the garnets that were studied, and a description of the analytical methods.
Observed enrichments of N (and the d 15 N of this N) in volcanic glasses altered on Earth's moder... more Observed enrichments of N (and the d 15 N of this N) in volcanic glasses altered on Earth's modern and ancient seafloor are relevant in considerations of modern global N subduction fluxes and ancient life on Earth, and similarly altered glasses on Mars and other extraterrestrial bodies could serve as valuable tracers of biogeochemical processes. Palagonitized glasses and whole-rock samples of volcanic rocks on the modern seafloor (ODP Site 1256D) contain 3-18 ppm N with d 15 N air values of up to +4.5&. Variably altered glasses from Mesozoic ophiolites (Troodos, Cyprus; Stonyford volcanics, USA) contain 2-53 ppm N with d 15 N of-6.3 to +7&. All of the more altered glasses have N concentrations higher than those of fresh volcanic glass (for MORB, <2 ppm N), reflecting significant N enrichment, and most of the altered glasses have d 15 N considerably higher than that of their unaltered glass equivalents (for MORB,-5-2&). Circulation of hydrothermal fluids, in part induced by nearby spreadingcenter magmatism, could have leached NH 4 + from sediments then fixed this NH 4 + in altering volcanic glasses. Glasses from each site contain possible textural evidence for microbial activity in the form of microtubules, but any role of microbes in producing the N enrichments and elevated d 15 N remains uncertain. Petrographic analysis, and imaging and chemical analyses by scanning electron microscopy and scanning transmission electron microscopy, indicate the presence of phyllosilicates (smectite, illite) in both the palagonitized cracks and the microtubules. These phyllosilicates (particularly illite), and possibly also zeolites, are the likely hosts for N in these glasses.
Journal of Mineralogical and Petrological Sciences, 2017
Omphacite replacing after relic edenitic pargasite has been found in an omphacite-bearing jadeiti... more Omphacite replacing after relic edenitic pargasite has been found in an omphacite-bearing jadeitite block of the Itoigawa-Omi area in the Hida-Gaien belt. Omphacite occurs sporadically as fine-grained aggregate reaching a few cm in length in a jadeite-albite matrix, and sometimes contains edenitic pargasite as a core. The edenitic pargasite is chemically and optically homogeneous and does not show direct contact with jadeite and albite. An irregular shaped omphacite-diopside mixed area occurs near edenitic pargasite in a coarse omphacite aggregate. The texture suggests that the breakdown of edenitic pargasite was triggered by the addition of a hydrothermal fluid, from which jadeite and albite were precipitated later, passing through diopside and omphacite by the reaction:
The geochemical variabilities in intraplate basalts (IB) from the West African passive margin (WA... more The geochemical variabilities in intraplate basalts (IB) from the West African passive margin (WAPM) region, have generally been employed to indicate the presence of recycled materials in an associated upwelling mantle plume. However, the absence of time-progressive linear hotspot tracks in WAPM-IB make it difficult to explain their genesis solely by the mantle plume hypothesis. Here, we show that the Sr–Nd–Hf–Pb isotopic variations in basalts from most of the WAPM-IB could have mainly attributed to the derivation from two types of fusible regions of the refertilized subcontinental lithospheric mantle (SCLM) and the sub-lithospheric mantle. The locations and magma genesis of WAPM-IB are strongly related to the distance from the Mesozoic rift axis and the structure of the rifted SCLM. The melting of the source region can possibly be attributed to small-scale mantle convection at the base of the SCLM without the involvement of a mantle plume.
Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Cariu... more Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high pressure asher) is the most common method used to extract highly siderophile elements (HSEs: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) from geological samples. Recently, it has been recognised that additional HF-desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion-exchange purification procedures are applied to desilicified samples. In this study, we developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable Accepted Article This article is protected by copyright. All rights reserved. to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd, and Cr for Ru, is circumvented for the desilicified samples.
Journal of Geophysical Research: Solid Earth, 2018
We present K‐Ar ages, major and trace element concentrations, and Sr‐Nd‐Pb isotope data for late ... more We present K‐Ar ages, major and trace element concentrations, and Sr‐Nd‐Pb isotope data for late Cenozoic volcanic rocks from the Chugoku district, southwest Japan arc. Andesite and dacite lavas in this region are enriched in Sr (mostly >800 μg g−1) and show geochemical characteristics of volcanic rocks commonly referred to as “adakite.” K‐Ar dating of these lavas revealed that the eruption of high‐Sr andesitic to dacitic magmas occurred during the last 2 Myr, following or concurrent with the eruption of basalt in adjacent regions. Trace‐element characteristics of high‐Sr andesites and dacites are consistent with the formation of their parent magmas by partial melting of the basaltic layer of the subducting Shikoku Basin Plate. Mass balance modeling of trace element concentrations and isotopic compositions suggests that the parental magmas of high‐Sr andesites and dacites are best explained by mixing of partial melts from oceanic crust (F = 5–15%) and sediment (F = 30%) at 80:20 ...
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Papers by Eizo Nakamura