American Geophysical Union (AGU) Acta Medica Okayama 1525-2027 27 5 2026 Chemical Geodynamics of Granitoid Magmatism During a Pacific�]Philippine Sea Plate Transition in Southwest Japan e2026GC012945 EN Nghiem V. Dao The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University at Misasa Tsegereda A. Yemer The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University at Misasa Tulibako T. Mwaisuba The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University at Misasa Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University at Misasa Hiroshi Kitagawa The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University at Misasa Katsura Kobayashi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University at Misasa Teruyoshi Imaoka Division of Earth Science, Graduate School of Sciences and Technology for Innovation, Yamaguchi University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University at Misasa Granitoid magmatism along the western Pacific margin records interactions between subduction dynamics and crust–mantle processes; however, the links between plate reorganization and magma-source evolution remain debated. Here we integrate U–Pb zircon geochronology with Pb–Sr–Nd–Hf isotope systematics to investigate Cretaceous–Paleogene granitoids in Southwest Japan. Zircon U–Pb ages define two discrete magmatic episodes at 110–60 Ma and 45–30 Ma, separated by a magmatic hiatus of ∼10–15 Myr. These granitoid groups exhibit distinct isotopic signatures, indicating derivation from isotopically distinct magma sources linked to the paleo-Pacific (Izanagi) plate and the Philippine Sea plate, respectively. Isotope-based mass-balance modeling indicates higher sediment contributions to the older granitoids, with decreasing sediment input both landward and through time. The magmatic lull at ca. 52–40 Ma coincides with an abrupt isotopic shift and is interpreted to reflect plate reorganization, during which subduction of the paleo-Pacific plate was replaced by a transform or highly oblique plate boundary associated with the northward migration of the proto–Philippine Sea plate. Independent constraints from convergence rates, sediment flux, and accretionary complex development support this interpretation. These results demonstrate that granitoid magmatism in Southwest Japan was fundamentally controlled by temporal changes in subducted lithosphere and sediment flux driven by plate reorganization, highlighting the sensitivity of arc magmatism to transient tectonic regimes. No potential conflict of interest relevant to this article was reported.

American Astronomical Society Acta Medica Okayama 0004-637X 965 1 2024 Unraveling the Cr Isotopes of Ryugu: An Accurate Aqueous Alteration Age and the Least Thermally Processed Solar System Material 52 EN Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Dilan M. Ratnayake The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Tsutomu Ota The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Noah Miklusicak The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Tak Kunihiro The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Christian Potiszil The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Katsura Kobayashi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hiroshi Kitagawa The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masanao Abe Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Akiko Miyazaki Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Aiko Nakato Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Satoru Nakazawa Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Masahiro Nishimura Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Tatsuaki Okada Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Takanao Saiki Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Satoshi Tanaka Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Fuyuto Terui Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Yuichi Tsuda Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Tomohiro Usui Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Sei-ichiro Watanabe Department of Earth and Planetary Sciences, Nagoya University Toru Yada Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Kasumi Yogata Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Makoto Yoshikawa Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University The analysis of samples returned from the C-type asteroid Ryugu has drastically advanced our knowledge of the evolution of early solar system materials. However, no consensus has been obtained on the chronological data, which is important for understanding the evolution of the asteroid Ryugu. Here, the aqueous alteration age of Ryugu particles was determined by the Mn–Cr method using bulk samples, yielding an age of 4.13 + 0.62/�|0.55 Myr after the formation of Ca–Al-rich inclusions (CAI). The age corresponds to 4563.17 + 0.60/�|0.67 Myr ago. The higher 55Mn/52Cr, ��54Cr, and initial ��53Cr values of the Ryugu samples relative to any carbonaceous chondrite samples implies that its progenitor body formed from the least thermally processed precursors in the outermost region of the protoplanetary disk. Despite accreting at different distances from the Sun, the hydrous asteroids (Ryugu and the parent bodies of CI, CM, CR, and ungrouped C2 meteorites) underwent aqueous alteration during a period of limited duration (3.8 �} 1.8 Myr after CAI). These ages are identical to the crystallization age of the carbonaceous achondirtes NWA 6704/6693 within the error. The ��54Cr and initial ��53Cr values of Ryugu and NWA 6704/6693 are also identical, while they show distinct ��'17O values. This suggests that the precursors that formed the progenitor bodies of Ryugu and NWA 6703/6693 were formed in close proximity and experienced a similar degree of thermal processing in the protosolar nebula. However, the progenitor body of Ryugu was formed by a higher ice/dust ratio, than NWA6703/6693, in the outer region of the protoplanetary disk. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 0386-2208 95 4 2019 Hypervelocity collision and water-rock interaction in space preserved in the Chelyabinsk ordinary chondrite 165 177 EN Eizo Nakamura The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Tak Kunihiro The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Tsutomu Ota The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hiroshi Kitagawa Okayama Univ, Inst Planetary Mat, Pheast Mem Lab Geochem & Cosmochem Katsura Kobayashi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Yuri Shimaki The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Gray E. Bebout The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hitoshi Miura Graduate School of Natural Sciences, Nagoya City University Tetsuo Yamamoto Institute of Low Temperature Science, Hokkaido University Vladimir Malkovets The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Victor Grokhovsky Institute of Physics and Technology, Ural Federal University Olga Koroleva Institute of Mineralogy, Ural Branch of the Russian Academy of Sciences South-Ural State University Konstantin Litasov V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences 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 similar to 30 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 0 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. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 1639-4488 43 1 2018 Determination of Abundances of Fifty-Two Elements in Natural Waters by ICP-MS with Freeze-Drying Pre-concentration 147 161 EN Que D. Hoang The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Tak Kunihiro The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hiroshi Kitagawa The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University To precisely determine the abundances of fifty-two elements found within natural water samples, with mass fractions down to fg g(-1) level, we have developed a method which combines freeze-drying pre-concentration (FDC) and isotope dilution internal standardisation (ID-IS). By sublimation of H2O, the sample solution was reduced to < 1/50 of the original volume. To determine element abundance with accuracy better than 10%, we found that for solutions being analysed by mass spectrometry the HNO3 concentration should be > 0.3 mol l(-1) to avoid hydrolysis. Matrix-affected signal suppression was not significant for the solutions with NaCl concentrations lower than 0.2 and 0.1 cg g(-1) for quadrupole ICP-MS and sector field ICP-MS, respectively. The recovery yields of elements after FDC were 97-105%. The detection limits for the sample solutions prepared by FDC were <= 10 pg g(-1), except for Na, K and Ca. Blanks prepared using FDC were at pg-levels, except for eleven elements (Na, Mg, Al, P, Ca, Mn, Fe, Co, Ni, Cu and Zn). The abundances of fifty-two elements in bottled drinking water were determined from five different geological sources with mass fractions ranging from the fg g(-1) to mu g g(-1) level with high accuracy. No potential conflict of interest relevant to this article was reported.

John Wiley Acta Medica Okayama 16394488 43 4 2019 Method to Suppress Isobaric and Polyatomic Interferences for Measurements of Highly Siderophile Elements in Desilicified Geological Samples 611 633 EN Xiaoyu Zhou The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University 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 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. No potential conflict of interest relevant to this article was reported.