Geochimica et Cosmochimica Acta最新文献

{"title":"Ureilite parent body evolution from the perspective of noble gases and oxygen in samples from the Almahata Sitta strewn field","authors":"M.E.I. Riebe, A.A. Plant, M.M.M. Meier, T. Di Rocco, M. Anguelova, P. Morino, P. Will, A.-K. Krämer, A. Bischoff, A. Pack, C. Maden, M. Schönbächler, H. Busemann","doi":"10.1016/j.gca.2025.01.034","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.034","url":null,"abstract":"Most ureilites are melt residues from the partially melted Ureilite Parent Body. The Ureilite Parent Body was catastrophically disrupted at ∼ 5 Ma after Calcium-Aluminum rich Inclusions (CAI) while it was still hot and the ureilites provide a unique window into early solar system magmatic processing. One ureilitic trachyandesite, one cumulate, and 16 melt residue ureilites, all from the Almahata Sitta meteorite strewn field, were analyzed for their noble gas compositions and, when such data was unavailable, for oxygen isotopes and petrology. Additionally, ureilite noble gas data from the literature was compiled together with petrology and oxygen isotope data of the same samples, this data is available in the supplementary materials. The compositions of noble gases and oxygen, as well as petrological characteristics, are similar to previously analyzed ureilites. This includes variable <ce:sup loc=\"post\">36</ce:sup>Ar<ce:inf loc=\"post\">tr</ce:inf>/<ce:sup loc=\"post\">132</ce:sup>Xe ratios of ∼ 20–1000 correlated with variable <ce:sup loc=\"post\">84</ce:sup>Kr/<ce:sup loc=\"post\">132</ce:sup>Xe ratios of ∼ 0.15–2.5 and Xe isotopic compositions similar to the Q gases but with somewhat lower <ce:sup loc=\"post\">134,136</ce:sup>Xe/<ce:sup loc=\"post\">132</ce:sup>Xe ratios. The well-established correlation between Mg-Fe olivine core composition and Δ’<ce:sup loc=\"post\">17</ce:sup>O, interpreted as material mixing, is corroborated. There is no correlation between noble gas compositions and petrology or Δ’<ce:sup loc=\"post\">17</ce:sup>O. Therefore, it is unlikely that the variable noble gas elemental ratios are due to mixing of noble gases from different sources, as previously suggested. We suggest that compositional variability was established during implantation of noble gases into disordered carbon prior to accretion and possibly during later processing. We discuss that partial graphitization resulted in noble gas loss, with noble gases remaining in un-graphitized organics, which were converted to diamond during the catastrophic disruption. Noble gases released during graphitization may have entered the melt. Isotopic compositions of trapped noble gases in the cumulate and trachyandesitic rocks, which crystallized from the melt are similar to those in the melt residue ureilites. The elemental noble gas composition of the cumulate shows evidence of a degassing stage and that the concentrations of noble gases in the ureilites were higher before melting. The noble gases in the trachyandesite contains radiogenic noble gases from decay of K, I, Th, and U, which were not enriched in the cumulate, showing that the trachyandesite crystallized from a more evolved melt. The cosmic-ray exposure ages of 15–22 Ma, with mostly overlapping uncertainties, are similar to those previously determined for ureilites from the Almahata Sitta strewn field and display a limited spread in contrast to ages previously detected in Almahata Sitta chondrites.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"13 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ultra-fast metamorphic reaction during regional metamorphism","authors":"Jia-Hui Liu, Pierre Lanari, Renée Tamblyn, Hugo Dominguez, Jörg Hermann, Daniela Rubatto, Jacob B. Forshaw, Francesca Piccoli, Qian W.L. Zhang, Thorsten A. Markmann, Julien Reynes, Zhen M.G. Li, Shujuan Jiao, Jinghui Guo","doi":"10.1016/j.gca.2025.01.036","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.036","url":null,"abstract":"Constraining the timescales of metamorphic processes is critical to understanding geodynamics on Earth. It is generally accepted that the rates of metamorphic reactions in regional metamorphism, where fluids are limited or transient, are several orders of magnitude slower than in laboratory experiments. This discrepancy is attributed to several rate-limiting mechanisms affecting metamorphic reactions in natural settings, such as differences in the reactive surface area of the reactants, the magnitude of the driving force for reaction, rates of inter-granular transport and possible fluid content. Here we report an ultra-fast metamorphic reaction within a year, constrained by diffusion modeling on frozen-in chemical gradients of trace elements preserved in metamorphic garnet across a partially melted corona texture. The growth of peritectic garnet occurred in the presence of a melt phase, which distributed along the grain boundaries. The observed chemical gradient of HREE+Y in garnets is interpreted to have formed due to trace element diffusion in the inter-granular melt, recorded by the simultaneous growth of multiple garnet grains across the corona texture. A diffusion model using a fixed boundary condition suggests a timescale of 8.4 (+5.4/-3.3) days for the formation of this corona texture, whereas a moving boundary model provides a slightly longer timescale of less than a year. These timescales are much shorter than those previously obtained from regional metamorphism in nature, but are similar to contact metamorphism in nature and laboratory-based results. Based on these findings, we propose that ultra-fast pulses of metamorphic reactions occur in nature under fluid/melt-present conditions, as elemental diffusion and mass transport in an aqueous fluid or melt are significantly faster than those in mineral lattices and anhydrous grain boundaries. However, rapid metamorphic reactions are difficult to identify due to the insufficient temporal resolution of radioisotope dating and the poor preservation of chemical gradients during subsequent metamorphic reactions.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"28 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The multicomponent exchange of metals between magmatic fluids and silicate melts","authors":"Austin M. Gion, Fabrice Gaillard","doi":"10.1016/j.gca.2025.01.033","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.033","url":null,"abstract":"Magmatic fluids are an integral part of volcanic eruptions and the transport of metals through the crust. In order to understand this transport and the evolution of magmatic fluids, we performed experiments on rhyolitic melts saturated with an aqueous fluid at 800 °C and 200 MPa and measured the major and trace element composition, as well as the chlorine and fluorine content of coexisting fluids and melts. We find that most trace elements are largely fluid immobile, i.e. partition coefficients of &lt; 1, with the exception of some transition metals, such as Cr, Ni, Cu, and Zn. Fluid mobility is primarily affected by the chlorine concentration of the fluid where increasing chlorine concentration in the fluid increases metal mobility. Such experimental observations have been previously parameterized using empirical relationships between partition coefficients and fluid salinity; however, such relationships do not consider metal speciation or fully capture the fluid-melt exchanges in which cations (major and trace elements) compete for available ligands (Cl, F, OH, etc.). In order to better characterize the behavior of metal in magmatic fluids we utilize existing thermodynamic databases and experimental fluid compositions to calculate the equilibrium concentration of aqueous hydroxide, chloride, and fluoride species in the fluid phase. The equilibrium concentrations of each species were then used to calculate apparent equilibrium constants and characterize the exchange of 42 cations between the fluid and silicate melts for 129 aqueous species. We find that these apparent equilibrium constants vary as a function of the HCl and HF content of the experimental fluid. We further present a model based on these experimentally determined apparent equilibrium constants that is capable of calculating fluid-melt equilibria. This model can subsequently be used to predict fluid-melt partition coefficients for metals, as well as chlorine and fluorine, over a wide range of P-T-X conditions.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"80 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462868","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Carbonation processes in Oman peridotite: temperature-dependent reactions and Mg isotope composition of reacting fluids","authors":"Giuseppe D. Saldi, Thierry Decrausaz, Vasileios Mavromatis, Pascale Bénézeth","doi":"10.1016/j.gca.2025.01.029","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.029","url":null,"abstract":"The study of natural analogues of CO<ce:inf loc=\"post\">2</ce:inf> mineral sequestration combined with the experimental quantification of carbonation reactions constitutes a fundamental approach to understand the spatial and structural distribution of carbonated bodies and the time scales by which large amounts of CO<ce:inf loc=\"post\">2</ce:inf> can be stored in solid form into geologic formations. To better quantify the carbonation rates of ultramafic rocks and study the evolution of dissolved Mg isotope composition during their interaction with CO<ce:inf loc=\"post\">2</ce:inf>-rich fluids, a series of batch carbonation experiments using a partially serpentinized harzburgite from the Semail ophiolite (Oman) was conducted at 90–180 °C and at constant CO<ce:inf loc=\"post\">2</ce:inf> partial pressures (∼ 15–20 bar). The yield of the carbonation reaction increased from ∼ 0 at 90 °C to a maximum of 31 mol % at 150 °C, decreasing to 12 mol % at 180 °C over a period of one month. Magnesites containing 3–9 wt% of Fe and silica polymorphs (SiO<ce:inf loc=\"post\">2(am)</ce:inf> and chalcedony) were the main reaction products, with a fraction of secondary Mg-silicates that increased with increasing temperature, significantly reducing the carbonation extent at 180 °C. The aqueous fluid became progressively enriched in heavy isotopes with the progress of the carbonation reaction. The apparent Mg isotope fractionations between the rock and bulk fluid (Δ<ce:sup loc=\"post\">26</ce:sup>Mg = δ<ce:sup loc=\"post\">26</ce:sup>Mg<ce:inf loc=\"post\">solid</ce:inf> − δ<ce:sup loc=\"post\">26</ce:sup>Mg<ce:inf loc=\"post\">fluid</ce:inf>) varied from −1.6 ‰ at 120 °C to −0.9 ‰ at 180 °C, consistent with the preferential uptake of <ce:sup loc=\"post\">24</ce:sup>Mg by carbonate minerals and the decrease of isotope fractionation with increasing temperature. The average magnesite isotope compositions (−1.6 ‰ ≤ δ<ce:sup loc=\"post\">26</ce:sup>Mg ≤ -0.3 ‰) derived from mass-balance calculations were found to be within the range of δ<ce:sup loc=\"post\">26</ce:sup>Mg values reported for Oman listvenites, suggesting that the carbonation processes in this geological unit took place within the temperature range considered in this study (∼120–180 °C).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"41 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Earth’s early differentiation recorded by halogen abundance ratios in Hawaiian lavas","authors":"Mark A. Kendrick, Oliver Nebel, Takeshi Hanyu, Bryden L. Maunder, Roland Maas","doi":"10.1016/j.gca.2025.01.019","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.019","url":null,"abstract":"Halogens (F, Cl, Br, I) and radiogenic isotopes were investigated in a suite of submarine basalt glasses from across the Hawaiian archipelago in order to better understand the origin of xenon isotope anomalies related to extinct <ce:sup loc=\"post\">129</ce:sup>I and the nature of metasomatic agents involved in peripheral Arch magmatism. We found that Lō’ihi tholeiites with high <ce:sup loc=\"post\">3</ce:sup>He/<ce:sup loc=\"post\">4</ce:sup>He of up to 26 Ra (where Ra denotes the atmospheric <ce:sup loc=\"post\">3</ce:sup>He/<ce:sup loc=\"post\">4</ce:sup>He) are characterised by unusually low I/Cl of (27 ± 3) × 10<ce:sup loc=\"post\">−6</ce:sup>, whereas peripheral alkaline lavas from the South Arch that have <ce:sup loc=\"post\">3</ce:sup>He/<ce:sup loc=\"post\">4</ce:sup>He of up to 18 Ra are characterised by unusually high I/Cl of (120 ± 20) × 10<ce:sup loc=\"post\">−6</ce:sup>. In comparison, rejuvenated lavas with <ce:sup loc=\"post\">3</ce:sup>He/<ce:sup loc=\"post\">4</ce:sup>He of ∼ 8 Ra have I/Cl in the range of (60 ± 30) × 10<ce:sup loc=\"post\">−6</ce:sup> that is typical of mid-ocean ridge and ocean island basalt lavas elsewhere. The variations in I/Cl, <ce:sup loc=\"post\">3</ce:sup>He/<ce:sup loc=\"post\">4</ce:sup>He and radiogenic isotopes are consistent with mixing between three mantle end-members. The most primitive end-member with high <ce:sup loc=\"post\">3</ce:sup>He/<ce:sup loc=\"post\">4</ce:sup>He and low <ce:sup loc=\"post\">129</ce:sup>Xe<ce:inf loc=\"post\">I</ce:inf>/<ce:sup loc=\"post\">136</ce:sup>Xe<ce:inf loc=\"post\">Pu</ce:inf> has low I/Cl but normal Br/Cl, H<ce:inf loc=\"post\">2</ce:inf>O/Cl and F/Cl ratios. Compared to the primitive mantle it is strongly depleted in I and weakly depleted in the other volatiles F, Cl, Br and H<ce:inf loc=\"post\">2</ce:inf>O. The depletion of I (and <ce:sup loc=\"post\">129</ce:sup>Xe derived from extinct <ce:sup loc=\"post\">129</ce:sup>I) probably results from a combination of Earth’s heterogenous accretion and preferential partitioning of I into the Earth’s core. The high I/Cl of the South Arch lavas can be explained by input of low degree carbonatitic melts derived from carbonated eclogite in the plume source. This is implied because carbonated ocean crust is uniquely enriched in I. The involvement of carbonatitic melts is consistent with previously reported H<ce:inf loc=\"post\">2</ce:inf>O, Ba and light rare earth element enrichments of South Arch lavas. Taken together the halogen abundance ratios in lavas sourced from around Hawaii record Earth’s early accretion and differentiation, the subsequent subduction of carbonated ocean crust into the mantle and its mobilisation in minor carbonatitic components enriching the periphery of the plume.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"25 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gold(I)-bisulfite complexation in hydrothermal nanodroplets: A molecular dynamics study","authors":"Wallace C.H. Hui, Kono H. Lemke","doi":"10.1016/j.gca.2025.01.015","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.015","url":null,"abstract":"Water nanodroplets present a unique environment for gold hydrothermal transport, with fluid properties in aqueous nanodroplets distinct from bulk liquid and vapor phases. By performing classical and <ce:italic>ab initio</ce:italic> molecular dynamics simulations, we have probed the stability of water nanodroplets (H<ce:inf loc=\"post\">2</ce:inf>O)<ce:italic><ce:inf loc=\"post\">n</ce:inf></ce:italic> (<ce:italic>n</ce:italic> = 100, 1000) at 25 °C and 100 °C. The solvation and complexation of gold(I)-bisulfite AuHSO<ce:inf loc=\"post\">3</ce:inf> in nanodroplet environments were also examined, with a particular focus on surface and interior solvation. Classical TIP4P/2005 molecular dynamics simulations reveal extreme densities in the interior of (H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">100</ce:inf> and (H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">1000</ce:inf> nanodroplets compared to droplet surface regions. At 25 °C, the interior region of (H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">100</ce:inf> exhibits fluctuating densities at 1.016–1.079 g/cm<ce:sup loc=\"post\">3</ce:sup>, with two maxima at 1.079 g/cm<ce:sup loc=\"post\">3</ce:sup> and 1.074 g/cm<ce:sup loc=\"post\">3</ce:sup>, corresponding to pressures of ∼ 2.23 kbar and 2.07 kbar, respectively; Reduced densities are predicted for the larger (H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">1000</ce:inf> systems, these being 1.013 g/cm<ce:sup loc=\"post\">3</ce:sup> (25 °C, 370 bar) and 0.968 g/cm<ce:sup loc=\"post\">3</ce:sup> (100 °C, 220 bar). The outer regions, on the other hand, featured densities intermediate between saturated liquid and vapor conditions, as part of a transition from liquid to vapor-like densities at the edge of the droplet. Born-Oppenheimer molecular dynamics simulations at 100 °C show that the gold(I)-bisulfite complex H<ce:inf loc=\"post\">2</ce:inf>O-AuHSO<ce:inf loc=\"post\">3</ce:inf> maintains a near linear solvation structure (θ<ce:inf loc=\"post\">O-Au-S</ce:inf> = 172°-174°) in bulk aqueous fluids and at surface and interior sites of (H<ce:inf loc=\"post\">2</ce:inf>O)<ce:inf loc=\"post\">100</ce:inf> nanodroplets. Distance constrained simulations reveal that, upon extension of the gold(I)-bisulfite Au-S contact (equilibrium <ce:italic>r</ce:italic><ce:inf loc=\"post\">Au-S</ce:inf> = 2.3 Å), HSO<ce:inf loc=\"post\">3</ce:inf><ce:sup loc=\"post\">−</ce:sup> is displaced by a water molecule, forming a two-water solvation shell around Au<ce:sup loc=\"post\">+</ce:sup>. Thermodynamic integration gives gold(I)-bisulfite dissociation energies (ΔG) of 17.65 ± 0.37 kcal/mol (bulk), 20.22 ± 0.38 kcal/mol (nanodroplet surface), and 18.31 ± 0.31 kcal/mol (nanodroplet interior). Our <ce:italic>ab initio</ce:italic> molecular dynamics results demonstrate that water nanodroplets are stable at hydrothermal conditions and would play an important role in the speciation and transport of gold in volcanic and hydrothermal vapors.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"31 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental metasomatic incorporation of sulfur into fluorapatite as a function of coupled substitutions involving sodium, silicon, iron, and cerium","authors":"Daniel E. Harlov, Justin Casaus, Brian A. Konecke, Adam C. Simon","doi":"10.1016/j.gca.2025.01.024","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.024","url":null,"abstract":"Here, we report results from hydrothermal alteration and crystallization experiments at 800 °C and 1 GPa that constrain the partitioning of S, Fe, Sr, and Ce (as a proxy for the REE) between fluorapatite and hydrothermal fluids of variable compositions. The data from these experiments demonstrate that S can be incorporated in apatite by the two known coupled substitutions S<ce:sup loc=\"post\">6+</ce:sup> + Na<ce:sup loc=\"post\">+</ce:sup> = P<ce:sup loc=\"post\">5+</ce:sup> + Ca<ce:sup loc=\"post\">2+</ce:sup> and S<ce:sup loc=\"post\">6+</ce:sup> + Si<ce:sup loc=\"post\">4+</ce:sup> = 2P<ce:sup loc=\"post\">5+</ce:sup>. The data also demonstrate that the presence of Sr in hydrothermal fluids promotes the incorporation of Na and S in apatite via the coupled substitution S<ce:sup loc=\"post\">6+</ce:sup> + Na<ce:sup loc=\"post\">+</ce:sup> = P<ce:sup loc=\"post\">5+</ce:sup> + Sr<ce:sup loc=\"post\">2+</ce:sup>. Our data also reveal a previously unknown intrinsic relationship between Fe and S, and Ce and S in metasomatized fluorapatite that can be explained by the coupled substitutions Ca<ce:sup loc=\"post\">2+</ce:sup> + P<ce:sup loc=\"post\">5+</ce:sup> = Fe<ce:sup loc=\"post\">3+</ce:sup> + S<ce:sup loc=\"post\">4+</ce:sup> and Ca<ce:sup loc=\"post\">2+</ce:sup> + P<ce:sup loc=\"post\">5+</ce:sup> = Ce<ce:sup loc=\"post\">3+</ce:sup> + S<ce:sup loc=\"post\">4+</ce:sup>, respectively. The concentrations of Cl, OH, and S in run-product apatite are positively correlated with each other, which indicates that the presence of Cl and OH can play a determinative role in the incorporation of S in apatite. Overall, the data from these metasomatism experiments, involving S and apatite, demonstrate that incorporation of sulfate and sulfite into apatite during metasomatism depends on the abundance of charge-balancing cations in the fluid.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"25 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chlorine and NaCl in hydrous basaltic melts","authors":"Monika K. Rusiecka, Bernard J. Wood","doi":"10.1016/j.gca.2025.01.020","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.020","url":null,"abstract":"We have determined the solubility and behavior of chlorine in hydrous basaltic melts at high pressures (0.5–1.5 GPa) and temperatures (1200–1300 °C) using the chlorine fugacity control method of Thomas and Wood (2021). By systematically increasing the water content of the melt from 0 to 4 wt% at fixed chlorine and oxygen fugacities we find that addition of H<ce:inf loc=\"post\">2</ce:inf>O leads to an increase in chlorine concentration under all conditions studied. In order to develop a comprehensive equation for chlorine solubility we combined our data with 60 results on anhydrous compositions from Thomas and Wood (2021,2023). We define chloride capacity C<ce:inf loc=\"post\">Cl</ce:inf> for each experiment as:","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"8 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tardi-magmatic iddingsite in the Martian Nakhlite NWA 817","authors":"V. Megevand, J.-C. Viennet, C. Le Guillou, F. Guyot, S. Bernard","doi":"10.1016/j.gca.2025.01.028","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.028","url":null,"abstract":"The mineral assemblage referred to as “iddingsite” has been described in Martian meteorites. In Nakhlites, this assemblage is mainly composed of Fe/Mg-rich phyllosilicates (such as serpentine and smectites) associated in some cases with Fe-oxides (such as ferrihydrite, goethite or (titano)magnetite) and carbonates, and occurs either as patches and veinlets in the mesostasis or as veins infiltrating olivines and clinopyroxenes. So far, iddingsite has usually been interpreted as a product of low-temperature (&lt;150 °C) alteration of pre-existing silicates by (sub)surface water. Here, we report results of the petrographic study of a section of NWA 817 revealing that the olivine-hosted iddingsite veins are symmetrically structured with an internal part exhibiting a mica-celadonite composition and an external part displaying a nontronite-saponite composition. These features are consistent with a progressive differentiation of a residual magmatic fluid having infiltrated decompression-induced cracks of olivines at the end of the cooling sequence. We propose that this residual liquid directly produced the ferric mica-celadonite phyllosilicates while triggering the deuteric alteration of the hosting olivine (i.e. oxidative alteration during magma cooling), thereby producing an alteration front made of Fe-nontronite-saponite at the contact with olivine. Altogether, without excluding the possibility that other Nakhlites (such as Lafayette) may have experienced secondary alteration by (sub)surface Martian water, the observations reported in the present study rather point to the tardi-magmatic production of iddingsite in NWA 817.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sedimentary vanadium depletion under sulfidic conditions: Implications for (paleo)redox proxy applications","authors":"Niels A.G.M. van Helmond, Olga M. Żygadłowska, Wytze K. Lenstra, Robin Klomp, Christoph Humborg, Daniel J. Conley, Mike S.M. Jetten, Caroline P. Slomp","doi":"10.1016/j.gca.2025.01.022","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.022","url":null,"abstract":"Sedimentary concentrations of redox-sensitive trace metals are widely used to reconstruct past ocean redox conditions. Vanadium (V) has great potential as a (paleo)redox proxy, due to its strong redox-dependent speciation (+III, +IV, +V) and the increased sedimentary sequestration of its more reduced species. The geochemistry of V in sulfide-rich marine environments is not yet well understood, however, hampering the use of V as a (paleo)redox proxy. Here, we present V data for two coastal systems, with bottom water redox conditions ranging from oxic to euxinic, to further constrain V geochemistry. Our sedimentary record from a eutrophic coastal marine basin (Scharendijke basin, Lake Grevelingen, the Netherlands), covering the last decade, shows distinct enrichments in molybdenum (Mo) and organic carbon (C<ce:inf loc=\"post\">org</ce:inf>) but depletions in V during seasonal bottom water euxinia, which can be discerned due to the exceptionally high sedimentation rate at our study site (up to 20 cm yr<ce:sup loc=\"post\">−1</ce:sup>). A seasonal study for the same coastal basin confirms this trend and reveals the accumulation of V, iron (Fe) and manganese (Mn) in the water column during summer euxinia. We conclude that the slow kinetics of V reduction to V(III) and subsequent precipitation as (oxy)hydroxide V(OH)<ce:inf loc=\"post\">3(s)</ce:inf> likely provide the opportunity for V to escape sedimentary sequestration during summer euxinia, resulting in the observed sedimentary V depletion. Sediments from three sites with contrasting bottom water redox conditions (oxic, seasonally hypoxic, euxinic) in the eutrophic Stockholm Archipelago, show a similar trend as that of Lake Grevelingen, with decreasing V concentrations and increasing Mo and C<ce:inf loc=\"post\">org</ce:inf> concentrations as bottom water conditions become more reducing. This confirms that our findings for Lake Grevelingen are not site-specific and are likely a generic feature of euxinic coastal systems with high sulfide concentrations (&gt; 0.5 mmol L<ce:sup loc=\"post\">−1</ce:sup>) near the sediment surface and high rates of anaerobic degradation of organic matter. Our results show that co-occurring sedimentary Mo and C<ce:inf loc=\"post\">org</ce:inf> enrichments and V depletion (or absence or suppression of an enrichment) are indicators of strongly sulfidic conditions in such settings. Finally, we show that maxima in sedimentary molar V/Mn ratios correlate with strongly reducing conditions. This finding contrasts with prior work on V/Mn ratios as a (paleo)redox proxy, implying that further research is necessary.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"50 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}