Carbonaceous chondrites contain organic matter, but the majority consists of complex macromolecular organic matter collected after acid demineralization. The N contents in carbonaceous chondrites are much lower than C, limiting our understanding of N-bearing functional groups. However, such N-containing compounds could be precursors for life's raw materials, making detailed chemical analysis essential. This study investigates Ncontaining organic matter such as N-heterocycles and amines, in various carbonaceous chondrites and xenolithic C-rich clasts using high-sensitivity N K-edge X-ray absorption near-edge structure (XANES) spectroscopy at SPring-8. We compared intact chondrites and insoluble organic matter (IOM) from Orgueil, Murchison, and Tagish Lake meteorites. Most chondrites exhibit three distinct N-XANES peaks: (A) pyridinic N (398.7 eV), (B) pyridinic N and/or nitriles (399.7 eV), and (C) pyrrolic N, amines, amides, and/or ammonium salts (400.8 eV). The Zag meteorite clast and ungrouped type 2 chondrites, such as Tagish Lake and Tarda, show an intense peak at 400.8 eV, indicating enrichment in non-conjugated N-compounds such as amines, amides, and/or ammonium salts. This suggests that their parent bodies contained more abundant ammonia and water. Comparing intact chondrites and IOM reveals significant differences in N-XANES features, suggesting acid-labile N-bearing moieties, like amides and ammonium salts, in addition to solvent extractable compounds such as amines and amino acids, are lost or altered during IOM extraction. This implies that extraterrestrial N compounds may be more diverse and abundant than previously recognized. These findings provide new insights into the N chemistry of meteorites and their potential contribution to the prebiotic inventory of early Earth.
This paper provides the first wide-ranging data for iodine concentrations of natural CaCO3 samples (50 in total) from various geologic and marine-biogenic sources. The geologic samples are (i) calcite and aragonite crystals grown in underground or cave environments and (ii) calcite-aragonite coexisting travertines deposited from mountain spring water. The marine-biogenic samples are shells/skeletons/spicules of bivalves, gastropods, anthozoans, hydrozoans, bryozoans and foraminifera (36 extant and 3 extinct species), each consisting of either calcite, aragonite, or both, and including two geochemical reference materials GSJ CRM JCt-1 (giant clam) and JCp-1 (scleractinian coral). The iodine concentration data show distinct differences depending on the sample source and taxonomic group, probably indicating effects of (i) environmental conditions (e.g., redox conditions) and (ii) inter-taxonomic differences in the iodine-incorporation mechanism. Some samples with lowest iodine concentrations suggest that iodine (probably iodate) is incorporated more preferentially into calcite than into aragonite, as previously demonstrated in a laboratory experiment and a crystal-structure simulation. Measurements of Ca, Mg, Sr and Na were also made for all the samples, which revealed that some calcite samples (e.g., bryozoan skeletons) were composed of magnesian calcite with Mg and Ca concentrations of similar to 12,000-42,000 ppm and similar to 370,000-340,000 ppm, respectively (i.e., the higher the Mg concentration, the lower the Ca concentration). For more accurate expression of the iodine concentration in various natural CaCO3 samples, including magnesian calcite, we propose the I/(Ca + Mg + Sr + Na) ratio instead of the I/Ca and I/(Ca + Mg) ratios; in future studies, it may be desirable to investigate, for some specific marine CaCO3 materials, whether the I/(Ca + Mg + Sr + Na) ratio can practically be a more accurate paleo-redox proxy in comparison with the I/Ca and I/(Ca + Mg) ratios. Our dataset and detailed discussion will make a significant contribution to iodine-based geochemistry and marine biology.
Volcanic eruptions that formed Ontong Java Nui (OJN) during the Aptian (similar to 120 Ma), Early Cretaceous, triggered substantial environmental perturbations, including global warming and Oceanic Anoxic Event (OAEs) 1a. However, the precise transition of OJN eruption styles and the influence of each volcanic phase on Earth's environment remains poorly understood. Here, we present Pb isotopic evidence for the OJN as the source of tuffaceous sedimentary sequence deposited on nearby Magellan Rise. Furthermore, we reviewed geochemical and lithological data around OAE1a, and updated the discussion on how the OJN emplacement influenced the earth environment. Our results point to explosive OJN eruption during the earliest phase of OAE1a based on compiled geochemical and lithological data. Stratigraphic variations in Pb isotopic compositions during this volcanic phase indicate a transition in OJN volcanism, from Kwaimbaita/Kroenke-like magma eruptions that formed the lower part of OJN to Singgalo-like magma eruptions that formed the upper part. Based on previously reported isotopic (Os and C), mineralogical, and geochemical data, this short (similar to 250 kyr) explosive volcanic phase, indicated by the Pb isotopic signal, was accompanied by extensive volatile emissions and corresponds to the onset of the previously documented early to mid-Aptian environmental perturbations (global warming, OAE1a, and the nannoconid crisis).
Soluble organic matter (SOM) in carbonaceous chondrites is an important aspect of understanding the origin and evolution of extraterrestrial organic matter. Interactions with minerals and water on planetesimals are essential for the formation and evolution of SOM, yet the detailed processes remain poorly understood. To elucidate these processes, it is necessary to establish relationships between SOM and minerals, particularly secondary minerals. In this study, nitrogen (N)-heterocyclic compounds (CHN compounds) in the methanol extracts of powdered Murchison meteorite fragments were characterized by high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC/HRMS). Their abundance patterns and chemical characteristics were examined in direct relation to mineral compositions determined by X-ray diffraction (XRD) from the same samples. Five homologous series of CHN compounds (alkylpyridines: CnH2n-4N+ or CnH2n-6N+, alkylpiperidines: CnH2n+2N+, and alkylimidazoles: CnH2n-1N2+ or CnH2n-3N2+, which were identified as positive ions) were identified from all of the samples. XRD analyses revealed inter-sample variability in the abundance of phyllosilicate, anhydrous silicates, sulfides, and carbonates. Several CHN homologous series exhibited systematic relationships with alteration minerals, particularly phyllosilicates and magnetite, whereas correlations with minor phases were generally weak. These relationships are consistent with water-mineral-organic interactions on the Murchison parent body, such as mineral-surface/interlayer interactions, fluid-driven chromatographic effects during aqueous alteration, redox-dependent alteration, and the potential heterogeneity of precursor organic molecules. Although this present approach is not universally applicable to all classes of SOM and requires careful evaluation of potential mineral alteration during extraction, it enables direct comparisons between SOM and minerals, thereby providing new insights into water-mineral-organic interactions on planetesimals.
The compositions of planetary atmospheres provide key constraints on the origin and evolution of the planets. Mars has a thin atmosphere dominated by CO2, with Ne detected by the Viking mission, although its abundance and isotopic composition is not well defined. A major technical challenge for in situ Ne measurements on Mars is to separate Ne from Ar before mass spectrometry, because Ar-40(2+) interferes with Ne-20(+). Previous studies have demonstrated that Ne-Ar separation can be achieved using polyimide membranes. In order to characterize the temperature dependence of permeation relevant to Martian mission, we investigated gas permeation through a 100-mu m-thick polyimide sheet at 6 degrees C, -18 degrees C, and -38 degrees C, and measured the permeated He, Ne, and Ar amounts, as well as Ne-20/Ne-22 ratio. The amounts of permeated He and Ne decrease with decreasing temperature. At -38 degrees C, the permeated He-4 and Ne-20 amounts are lower than the room temperature values by factors of similar to 6 and similar to 7, respectively. No permeated Ar-40 above background level was detected. The Ne-20/Ne-22 ratios corrected for mass-dependent fractionation agree with the terrestrial atmospheric ratio within analytical uncertainty, except during initial non-steady-state permeation at -38 degrees C. Temperature dependency of permeated amounts indicates that the permeation fluxes through a 100-mu m-thick polyimide at 20 degrees C give 2.2 x 10(-11) and 2.7 x 10(-12) cm(3)STP/sec/cm(2)/Pa for He-4 and Ne-20, respectively. Under Martian atmospheric pressure, permeation through a 100-mu m-thick polyimide for 40-60 min at temperature between similar to 10 degrees C and room temperature provides a Ne amount of 1-2 x 10(-9) cm(3)STP/100 cm(2) with effective Ne-Ar separation.
The rare earth element (REE) europium (Eu) exists in Eu2+ and Eu3+ states. The Eu2+ can be substituted for Ca2+ during plagioclase feldspar crystallization in reducing magmas to create an observable Eu anomaly in REE distribution patterns. Europium has two stable isotopes, 151Eu and 153Eu. Recent reports for Eu isotope ratios in igneous rocks indicate that Eu anomalies and isotope fractionation show good correlation, suggesting that Eu isotope fractionation appears due to feldspar crystallization during magma differentiation. Here, we report Eu isotope ratio and REE concentrations for five feldspar standard reference materials (SRMs) such as JF-1, JF-2, SRM 70a, SRM 70b, and SRM 99a prepared by the Geological Survey of Japan (GSJ) and National Institute of Standards and Technology (NIST) of USA. This study is the first investigation of the Eu isotope variation in feldspars to test several hypotheses for the origin of Eu isotope fractionation in igneous rocks. The chemical compositions of four feldspar SRMs except SRM 99a indicate that they are close to the KAlSi3O8 end-member within the feldspar series. The SRM 99a meanwhile indicated oligoclase composition. Most feldspar SRMs showed chondrite-normalized patterns of light REE (LREE)-enrichment and heavy REE (HREE)-depletion or flat REE patterns with large positive Eu anomalies. This did not hold true for NIST SRM 70b, which contains small amounts of impurities. Results showed that potassium feldspar SRMs were enriched in the lighter Eu isotope (i.e., had negative delta 153Eu values), whereas the sodium feldspar SRM (NIST SRM 99a) was enriched in the heavier Eu isotope (i.e., had positive delta 153Eu values). Interpretation of Eu isotope ratios in igneous rocks should thus consider feldspar crystallization during magma differentiation.
This study deconvolves natural subseafloor alteration processes and post-sampling modification recorded in submarine pumices recovered from active hydrothermal fields at Iheya North Knoll and Izena Hole in the middle Okinawa Trough. Major-element geochemistry, isocon analysis, mineralogical observations, and sulfur isotopes of associated pore fluids were integrated to reconstruct the alteration history of the pumices. Although some pumice samples exhibit intense alteration characterized by Fe and Mg enrichment, K depletion, and high Chemical Index of Alteration (CIA) values, all samples show evidence of seawater-rock interaction associated with subseafloor seawater recharge prior to recovery. Isocon slope values and element mass-transfer coefficients indicate systematic loss of Si, Na, and Ca and net gain of Mg and/or Fe, constraining alteration to low-temperature conditions (<50-60 degrees C) rather than high-temperature hydrothermal alteration. The pore fluids display extremely high sulfate concentrations (similar to 722 mmol/L) and negative delta S-34 values generally close to those of authigenic pyrite within the pumices, indicating that most sulfate was generated by oxidation of the pyrite during long-term freezer storage after sampling. delta S-34 values nevertheless preserve information on sulfur sources, showing that the pyrite originally formed predominantly via bacterial sulfate reduction within permeable pumice layers acting as seawater recharge conduits. REE patterns of the fluids resemble those of the host pumices, reflecting low-temperature fluid-rock interaction prior to recovery, whereas weak Ce anomalies are attributed to minor seawater contamination during sampling. Overall, the pumice-hosted geochemical record represents a multi-stage palimpsest involving low-temperature subseafloor alteration, pyritization under active seawater recharge, and superimposed post-sampling oxidative overprinting.
Theoretical estimates of equilibrium platinum-isotope (Pt-198/Pt-194) fractionation including both the nuclear volume component of the field shift effect and mass dependent fractionation are reported. Field shift (nuclear volume) fractionations in the related elements iridium, osmium, and ruthenium are also reported. For Os, Ir, and Pt, field shift fractionation is predicted to be no more than similar to 0.1-0.2 parts per thousand per amu at geochemically relevant temperatures, with mass-dependent fractionation in Pt-bearing species having a larger range at 25 degrees C (up to 0.6 parts per thousand per amu for Pt-IV-oxides relative to Pt-0 and Pt-II). However, the mass-dependent component decreases more rapidly at higher temperatures, scaling in proportion to 1/T-2 while the field shift component scales as 1/T. Field shift fractionations in the other platinum group elements are qualitatively similar, but typically smaller on a per amu basis. Field shift fractionation for all elements studied show a pattern of isotopes with larger charge volumes (more massive isotopes, for these elements) being most concentrated in species with the smallest positive oxidation states studied (Pt-II, Ir-III, Ru-IV, and Os-IV), and less concentrated in species with higher oxidation states (Pt-IV, Ir-IV, Ru-VI (to) (VIII), and Os-VI (to) (VIII)). Field shift fractionations of platinum, osmium, and iridium isotopes in metals are dependent on alloy composition, favoring smaller (less massive) isotopes in iron-rich compositions. In contrast, mass dependent fractionation tends to concentrate massive isotopes in species with high oxidation states, and shows little sensitivity to alloy composition. A hypothetical Pt-substituted olivine is predicted to show total equilibrium Pt-198/Pt-194 fractionation of approximately +0.1 parts per thousand relative to the iron-rich alloy Fe7Pt at core-mantle differentiation temperatures near 2000 K, and +0.06 parts per thousand near 3000 K. While it is unclear which modeled species (if any) is the best analog for platinum in a silicate melt, Pt-substituted olivine, native platinum, and solid PtS are all capable of producing an isotopically heavy pre-late-veneer mantle. Only a Rayleigh-type Pt-olivine vs. Fe7Pt model is able to approach the previously observed 0.4-0.6 parts per thousand fractionation between chondrites and the early Archean mantle.
Spacecraft-returned samples from the C-type asteroid (162173) Ryugu and the B-type asteroid (101955) Bennu record various processes from presolar chemistry and early-stage aqueous alteration processes on their parent planetesimals to ongoing geological processes on their surfaces. Hydrous magnesium phosphate is a common phosphate in Bennu, whereas it is present but rare in Ryugu. Because phosphates in both asteroids formed during aqueous alteration on their parent planetesimals, the difference in the abundance of hydrous magnesium phosphate indicates that the two asteroids experienced different aqueous chemistries. Hydrous magnesium phosphate grains in both asteroid samples show varying degrees of dehydration, which may have been resulted from heating at later evolutionary stages, such as solar heating in their Earth-crossing orbits. This study aims to elucidate the dehydration behavior of hydrous magnesium phosphate on near-Earth asteroids, we conducted kinetic dehydration experiments on MgHPO4 center dot 3H(2)O (newberyite), a likely precursor mineral phase before dehydration, under low-pressure conditions (similar to 200 and similar to 10(-4) Pa). Dehydration of MgHPO4 center dot 3H(2)O occurs efficiently at lower temperatures under pressures lower than at 1 atm, likely due to the more effective escape of H2O molecules from the sample. The dehydration reaction stalled at different extents of dehydration depending on temperature, suggesting that the reaction rate decreases significantly as dehydration progresses. We demonstrate that this reaction stall in the experiments reflects an increase in the activation energy for dehydration caused by a decrease in the coordination number of Mg atoms as H2O molecules detach. The kinetic dehydration model developed in this study successfully reproduces the temporal evolution of the degree of dehydration at each temperature ranging from 50 to 300 degrees C. The dehydration model suggests that hydrous magnesium phosphates on the surfaces of Ryugu and Bennu would experience only partial dehydration under their current orbits over their dynamical lifetimes as near-Earth asteroids. The model also suggests that the samples from Ryugu and Bennu have never been heated above 190 degrees C-the radiation equilibrium temperature in a Venus-crossing orbit-which could place a constraint on their orbital evolution after migration from the main asteroid belt.
We analyzed the chemical composition of porewater extracted from sediment samples collected at shallow methane hydrate fields off Joetsu, in the Japan Sea, during Expedition CK22-03 of the drilling vessel Chikyu in 2022. At Joetsu Knoll, where massive methane hydrates were observed, the Cl- concentrations of porewaters were high (879-1282 mM) at the depth interval between 12 and 60 meters below the seafloor and roughly twice the concentration in the sediment at the top of the core (545 mM). These elevated Cl- concentrations were observed at greater depths and were higher than those reported in previous studies of this field. We analyzed the delta D and delta 18O of the porewaters and quantitatively confirmed that the hypersaline waters represent residual waters accumulated by rapid formation of methane hydrates. Based on Cl- concentration, amount of methane incorporated into hydrates in the sediments was estimated to be 51-81 m3/m3 at standard temperature and pressure.
Iron exhibits variable redox states between Fe2+ and Fe3+, governing key processes from Earth's deep interior to surface environments. Quantitative evaluation of Fe valence is therefore essential in geoscience; however, partial fluorescence yield XANES (PFY-XANES), a widely used nondestructive technique, often suffers from thickness or self-absorption effect in samples with high Fe concentrations. In this study, we applied the inverse PFY (IPFY) method, to geological samples to assess its reliability in Fe valence determination. Iron LIII-edge IPFY-XANES and conventional PFY-XANES analyses were performed on olivine, wadsleyite, bridgmanite, and two biotite samples with FeO contents of 6.6-37.7 wt.%. Conventional PFY-XANES overestimated Fe3+/Sigma Fe by approximately 10% relative to M & ouml;ssbauer spectroscopy, whereas IPFY-XANES yielded values differing by less than 3%, showing excellent agreement. The inverse spectra also exhibited reduced pre-and post-edge tailing, confirming suppression of thickness effects. These results demonstrate that IPFY-XANES provides more accurate determination of the valence state of Fe, particularly for Fe-rich or thick samples. Because many geoscientific specimens such as asteroidal return samples, meteorites, or recovered high-pressure samples cannot be destructively prepared, the IPFY approach offers a powerful and reliable method for nondestructive Fe valence analysis across a wide range of natural materials.
Drifting pumices provide important clues for determining the activity of submarine volcanoes. On October 8, 2023, a tsunami hypothetically caused by a submarine eruption occurred near Izu-Torishima in the Izu-Bonin Arc. Later that month, two types of drifting pumice, white and gray, were found floating on the sea surface west of IzuTorishima. The white pumices were also found on the coast of Izu-Torishima. The textural and geochemical characteristics of the gray pumice clasts indicate they were derived from the 2021 eruption of Fukutoku-Oka-noBa. The white pumice clasts have angular to subangular shapes with little evidence of abrasion. They contain plagioclase, pyroxenes, and Fe-Ti oxides as phenocrysts, and typically include dark enclaves. The composition of the white pumices is rhyolite to dacite, and their trace element characteristics resemble those of volcanic products from the back-arc rift zone of the Izu-Bonin Arc. These pumices are potentially associated with a recent submarine eruption in the back-arc region of the Izu-Bonin Arc.
We report the occurrence of glimmerite and melteigite xenoliths from a hybrid Early Cretaceous camptonitetinguaite dyke from the Nongchram Fault Zone, East Garo Hills, Shillong Plateau, North East India. Glimmerite xenolith contains predominantly biotite with subordinate to minor amounts of pyroxene, ferro-dolomite, rutile, and ilmenite. The melteigite xenolith is dominated by pyroxene and contain pseudo-nepheline (altered to analcime) and rutile. The host campto-tinguaite dyke features a distinctive porphyritic-panidiomorphic and a tinguaitic texture with clinopyroxenes as macrocrysts, microcrysts and clots and amphibole as phenocrysts with accessory minerals such as apatite, magnetite, rutile, and ilmenite. In-situ trace element geochemistry of pyroxenes from the xenoliths and the host rock reveals significant enrichment in LILEs such as Ba and Sr, as well as LREEs like La and Ce, suggesting an enriched mantle source. The geothermobarometric data for pyroxenes from the (i) glimmerite and melteigite xenoliths and macrocrysts and (ii) microcrysts and clots from the camptotinguaite suggest varying crystallization pressures and temperatures, indicating different depths of origin ranging from 23-96 km. The mineral composition, in-situ trace element data of pyroxenes as well as the geothermobarometric study of clinopyroxenes from both the host and the xenoliths, suggest involvement of multiple shallower magma chambers composed of the camptonitic and tinguaitic magmas generated during distinct pulses, thereby forming a complex magmatic plumbing system. The presence of orogenic geochemical signatures in the minerals of xenoliths and anorogenic geochemical signatures in the host campto-tinguaite pyroxenes imply a complex tectono-magmatic setting, with contributions from both the plume and subductionmodified mantle sources.
Detecting seawater-derived elements in terrestrial sediments as evidence of tsunami inundation is challenging due to dilution by freshwater over time. This study provides data useful for evaluating the potential of the strontium (Sr) isotope ratios (Sr-87/Sr-86) as indicators of seawater intrusion. We analyzed Sr-87/Sr-86 ratios in water leachates and acetic acid (AcOH) leachates from a sedimentary sequence sampled in November 2015 from a coastal lowland in Tohoku, Japan, which includes deposits from the March 2011 Tohoku earthquake tsunami. The Sr-87/Sr-86 values of water leachates were low (similar to 0.7082) in the pre-tsunami muddy layer, close to local freshwater values (0.7069), but higher (similar to 0.7085) in the upper muddy part of the tsunami deposit, approaching seawater values (0.7092). This suggests that the muddy part retained seawater-derived Sr due to its low permeability and high cation adsorption capacity of clay minerals. However, alternative sources of high Sr isotope ratios, such as rainwater, atmospheric deposition, and acid-leachable materials, must be considered. If the high values reflect seawater intrusion, Sr isotope ratios provide a distinct advantage over element concentrations as tsunami indicators due to their longer retention, detectable even four years after the event. In contrast, AcOH leachates exhibited significantly higher Sr isotope ratios (>0.7095) throughout the sequence, perhaps reflecting contributions from less-soluble components, such as oxides and clay minerals, in addition to marine carbonates. This finding suggests that AcOH leaching is unsuitable for isolating seawater-derived Sr.
The elemental composition of vegetation is poorly known so we report on the minor and trace element concentrations (similar to 50 elements) in leaves and needles from the dominant species of woody vegetation at locations across Canada. Data are combined with estimates for elements near analytical detection limits, to yield an average composition for temperate climate vegetation, mostly grown on post-Pleistocene glacial soils approximating average continental crust (total 71 elements). Lithophile K, Mg, Ca, Sr, chalcophile Hg, Cu, Zn, Mo and Cd and siderophile Ag, Pd, Ir, and Os with low ionic charges and intermediate effective ionic radii show average vegetation/average continental crust ratios (hereafter vegetation/crust) above 0.1. Environmentally-sensitive, 2+, Cd and Hg are highly water-soluble and enriched in vegetation (2.4 and 1.0 * continental crust, respectively). Other high vegetation/crust ratios (1.0 to similar to 10) are shown by life-essential, 3+ B, 5+ P and 6+ S which have small ionic radii and thus, high effective ionic potentials. Elements with low ratios (similar to 0.001) include the lithophile 3+ rare earth elements (REE, La to Yb), Al, Sc and Ga, 4+ Ti, U, and Th and 5+ V. However, 4+ Zr and Hf and 5+ Nb and Ta form a low concentration trough (similar to 0.0001 * continental crust) in charge-radius space. These concentration patterns reflect charge and radius control on the solubility of elements in soil water. Assuming the immature soils approach average continental crust, the vegetation/crust ratios reflect the partitioning of elements between soil minerals and water taken up by plants. Organizing the elements from highest (S = 13) to lowest (Hf = 0.00004) ratios, allows normalizing other vegetation-based materials with average vegetation to decipher processes impacting the materials. Two published agrifood data sets for Canadian wines and maple syrups illustrate utility of the average vegetation data set for inferring processes.
The concentrations and isotope ratios of molybdenum (Mo) and tungsten (W) are expected to serve as proxies for paleoceanography. Although submarine hydrothermal activities are potentially major sources and sinks of Mo and W, data on these elements in hydrothermal fluids are scarce. In this study, we present the concentrations and isotope ratios of dissolved Mo and W in hydrothermal fluid samples collected from nine active sites-Higashi Ensei, Iheya North, JADE, Hakurei, Higashi Izena, Daisan Kume, Yokosuka, Futagoyama, and Hatoma Knoll- within the Okinawa Trough, which is a back-arc basin. The Mo concentrations ranged from 4.2-411 nmol/kg, S98/95Mo values ranged from -0.17 to 3.92%o, W concentrations ranged from 1.7-238 nmol/kg, and S186/184W values ranged from -0.03 to 1.08%o. We found that both S98/95Mo and S186/184W were close to 0%o when Mo and W were dissolved from rocks and sediments during hydrothermal circulation. The phase separation of the hydrothermal fluids concentrates Mo and W in the liquid phase. Sediments can be a significant source of W at high temperatures and Mo even at low temperatures. The scavenging of Mo by Fe sulfides reduces its concentrations and elevates S98/95Mo values during the emission of high-temperature hydrothermal fluids, while having an insignificant effect on W. The scavenging of W by Fe hydroxides reduces its concentrations and elevates S186/184W values during mixing of hydrothermal fluids and seawater, while having an insignificant effect on Mo. Therefore, the data on Mo and W are useful for investigating the processes that occur during hydrothermal circulation.
The whole-rock composition of peridotites is essential for understanding geological processes related to the Earth's mantle. X-ray fluorescence (XRF) analysis employing glass beads is the most common method to determine the chemical composition of igneous rocks because of its simplicity and efficient decomposition of refractory minerals. The accuracy of the XRF analysis using a multipoint calibration curve depends on the matrix effects and the reference values in the reference materials (RMs) used. In the quantitative analysis of peridotites, the limited availability of certified ultramafic RMs necessitates the incorporation of other igneous rocks into the calibration curve (along with a small number of ultramafic RMs), leading to potential systematic biases. In this study, we propose a robust approach to obtain accurate major element concentrations in ultramafic rocks. Specifically, we examine (1) the difference in the X-ray fluorescence intensity of total iron (T-Fe2O3) relative to the concentration between peridotite and other igneous rocks, and (2) the selection of the reference values in RMs for the quantification of Cr2O3. We found that the matrix correction using Ca and Mg improves the T-Fe2O3 calibration curve, and the quantified T-Fe2O3 concentrations of peridotite and basalt using the corrected calibration curve are consistent with the certified values in RMs. T-Fe2O3 concentration in peridotite could be overestimated by similar to 0.5-0.6 wt% without matrix correction. In contrast, NiO and other major elements exhibit minimal matrix effects; the accuracy of their calibration curve depends on the variation of reference values in RMs. For Cr2O3, peridotite RM JP-1 is the most critical because of its highest Cr concentration among the calibration standards, and its recent analyzed value provided by the Geological Survey of Japan (GSJ) was used to optimize the accuracy of the calibration curve. The proposed correction of matrix effect and reference values in RMs in the analysis of peridotite enhances quantification accuracy and improves our understanding of the Earth's mantle geochemistry.
We report five new igneous rock reference materials: andesite JA-2a, granite JG-2a, granodiorite JG-3a, gabbro JGb-1a, and peridotite JP-2. JA-2a, JG-2a, JG-3a, and JGb-1a are new reference materials prepared from the same parent rocks as JA-2, JG-2, JG-3, and JGb-1, respectively; the ultramafic JP-2 was newly prepared from plagioclase lherzolite. These certified reference materials were prepared according to the ISO 17034-certified procedures. The certified values of these new reference materials were determined for SiO2, TiO2, Al2O3, T-Fe2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, and H2O(-) (moisture content) based on the collaborative analysis. The chemical compositions of the new reference materials, JA-2a, JG-2a, JG-3a, and JGb-1a, are consistent with those of JA-2, JG-2, JG-3, and JGb-1, respectively. JP-2 exhibits higher Al2O3, CaO, TiO2, Na2O, and SiO2 and a lower MgO mass fractions than those of dunite JP-1. This can expand the petrological and chemical diversity of ultramafic rock reference materials, which are a very rare variety worldwide.
