Geochimica et Cosmochimica Acta最新文献

{"title":"Carbonate dissolution fluxes in deep-sea sediments as determined from in situ porewater profiles in a transect across the saturation horizon","authors":"Jaclyn E.P. Cetiner ,&nbsp;William M. Berelson ,&nbsp;Nick E. Rollins ,&nbsp;Xuewu Liu ,&nbsp;Frank J. Pavia ,&nbsp;Anna R. Waldeck ,&nbsp;Sijia Dong ,&nbsp;Kalla Fleger ,&nbsp;Holly A. Barnhart ,&nbsp;Matthew Quinan ,&nbsp;Rucha P. Wani ,&nbsp;Patrick A. Rafter ,&nbsp;Andrew D. Jacobson ,&nbsp;Robert H. Byrne ,&nbsp;Jess F. Adkins","doi":"10.1016/j.gca.2024.11.027","DOIUrl":"10.1016/j.gca.2024.11.027","url":null,"abstract":"<div><div>Despite their importance for long-term climate regulation, the rates and mechanisms of seafloor carbonate dissolution are poorly understood, especially with respect to calcite saturation and the role of sedimentary metabolic CO₂ production. Here, we present results from an in situ porewater sampler deployed at the Cocos Ridge in the eastern equatorial Pacific, where we examine seafloor carbonate dissolution in locations with bottom water Ω_calcite ranging from 1.0 to 0.84 (1600–3200 m). With cm-scale resolution from the sediment–water interface to 35 cm, we present porewater profiles of total alkalinity, pH, dissolved inorganic carbon (DIC), δ¹³C of DIC, Ω_calcite, [Mn], [Ca], and [Sr], as well as solid phase porosity, % CaCO₃, and % organic C. These profiles provide evidence that deep-sea sedimentary carbonate dissolution occurs via sediment-side control, wherein dissolution is dominated by sedimentary processes rather than strictly bottom water saturation state. We estimate dissolution fluxes using three independent approaches: alkalinity fluxes, δ¹³C of DIC combined with DIC fluxes, and [Ca] fluxes. We report seafloor dissolution fluxes with uncertainties &lt; 38 %: 40 ± 15, 98 ± 20, 100 ± 32, and 89 ± 27 μmol CaCO₃/m²/day at sites 3200, 2900, 2700, and 1600 m deep, respectively. The magnitude of dissolution fluxes is a function of bottom water saturation state (Ω_calcite), bottom water dissolved oxygen, and sedimentary CaCO₃ content, but not correlated with any of these parameters independently. We observe dissolution occurring at all stations, including where bottom water is saturated with respect to calcite, and present evidence that this occurs through respiration-driven dissolution within the sediment. At all sites, porewater Ω_calcite decreases below bottom water values before increasing toward saturation deeper in the sediment. Using the δ¹³C of DIC, we partition the DIC fluxes across the sediment–water interface and find 21–48 % of DIC is sourced from CaCO₃ dissolution, with the remainder sourced from organic matter respiration. We present a sedimentary mass balance, assembled with dissolution rates and mass accumulation rates obtained through Δ¹⁴C of foraminiferal calcite, and calculate CaCO₃ burial efficiencies between 2 and 67 %, inversely correlating with water depth. Our results also provide evidence that net chemical erosion of 5,000––10,000 year old carbonate is occurring at the deepest site. Aerobic organic C respiration coupled with sedimentary CaCO₃ dissolution, as documented here, will provide more alkalinity to bottom waters than from undersaturation-driven dissolution alone. This process can neutralize anthropogenic CO₂ at the seafloor in a larger range of saturation states than previously estimated.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 145-159"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143095064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coupled feldspar dissolution and secondary mineral precipitation in batch systems: 6. Labradorite dissolution, calcite growth, and clay precipitation at 60 °C and pH 8.2–8.4","authors":"Mingkun Chen ,&nbsp;Lei Gong ,&nbsp;Jacques Schott ,&nbsp;Peng Lu ,&nbsp;Kaiyun Chen ,&nbsp;Honglin Yuan ,&nbsp;Jian Sun ,&nbsp;Si Athena Chen ,&nbsp;John Apps ,&nbsp;Chen Zhu","doi":"10.1016/j.gca.2024.11.030","DOIUrl":"10.1016/j.gca.2024.11.030","url":null,"abstract":"<div><div>We conducted experiments on concurrent labradorite dissolution, calcite precipitation, and clay precipitation in batch reactor systems and tracked reaction processes using multiple isotope tracers. Labradorite was chosen for its role as a major and reactive component in basalt; the experiments thus directly impact our understanding of CO₂ storage in basalt aquifers and enhanced rock weathering. We doped initial solutions with ²⁹Si, ⁴³Ca, and Ca¹³CO₃(s). Experiments were conducted at 60 °C and pH ∼ 8.3 for up to 840 h, with isotope ratios in the experimental aqueous solutions measured using MC-ICP-MS. Unidirectional rates of labradorite dissolution near equilibrium were approximately two orders of magnitude slower than far-from-equilibrium rates reported in the literature. Calcite growth occurred near equilibrium and the rates were limited by the labradorite dissolution rates.</div><div>In the steady state phase, the interplay of these three heterogeneous reactions—labradorite dissolution, calcite growth, and clay precipitation—results in a coupled system that approaches a near-equilibrium state. The system does not reach true equilibrium because labradorite continues to dissolve, albeit at a much slower rate near equilibrium. The overall reaction can be approximated as,</div><div>Na_0.4Ca_0.6Al_1.6Si_2.4O₈ + 0.6HCO₃^- + 1·.7H₂O + 0.4H⁺ → 0.4Na⁺ + 0.6CaCO_3(s) + 0.5Al₂Si₂O₅(OH)_4(s) + 0.6Al(OH)₄^- + 1.4SiO₂^o_(aq)</div><div>The experimental results show that using short-term far-from-equilibrium rate constants would lead to an overestimation of feldspar weathering rates at the Earth’s surface (e.g., basalt weathering and enhanced rock weathering) and CO₂ mineralization in basalt aquifers.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 181-198"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143095063","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":"Are scandium sulfate complexes effective in mobilizing scandium?","authors":"Jia-Xin Wang, A.E. Williams-Jones, Xue-Ni Zhang, Shun-Da Yuan","doi":"10.1016/j.gca.2025.01.038","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.038","url":null,"abstract":"Sulfate has been increasingly acknowledged as a key ligand for the mobilization and enrichment of rare earth elements (REEs). Here, we report the results of an investigation of the solubility of Sc<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf>(s), scandium speciation, and the coordination geometry of scandium species in sulfate-bearing solutions using solubility experiments and <ce:italic>ab initio</ce:italic> molecular dynamics (AIMD) simulations. The investigation was conducted for temperatures of 175 to 250 °C at vapor-saturated water pressure. From the results of our experiments, we conclude that Sc(SO<ce:inf loc=\"post\">4</ce:inf>)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">−</ce:sup> is the dominant scandium species, and that its formation constant (log <ce:italic>β<ce:inf loc=\"post\">1</ce:inf></ce:italic>) varies from 11.20 ± 0.08 at 175 °C to 14.21 ± 0.12 at 250 °C. The AIMD simulations show that the Sc(SO<ce:inf loc=\"post\">4</ce:inf>)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">−</ce:sup> complex is either doubly monodentate or has a mixed monodentate-bidentate configuration, and is coordinated with four water molecules. The species ScSO<ce:inf loc=\"post\">4</ce:inf> + was also identified in our experiments, but has a relatively low formation constant (log <ce:italic>β<ce:inf loc=\"post\">2</ce:inf></ce:italic>) varying from 7.24 ± 0.46 at 175 °C to 9.51 ± 3.50 at 250 °C. Modeling of the transport and deposition of scandium provides convincing evidence that sulfate scandium complexes can transport scandium efficiently in acidic fluids (pH below 4). Our simulations emphasize the critical roles played by fluid-rock interaction and fluid–fluid mixing in the genesis of scandium ores. This study presents the key thermodynamic data needed to evaluate scandium mobilization in sulfate-rich hydrothermal systems.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"4 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401584","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":"Behaviour of bromine in Cl- and F-bearing alkali-rich felsic magmas at crustal depth: An experimental study at 800–1100 °C, 10–200 MPa","authors":"Carmela Federica Faranda,&nbsp;Gaëlle Prouteau,&nbsp;Bruno Scaillet,&nbsp;Joan Andújar","doi":"10.1016/j.gca.2024.11.024","DOIUrl":"10.1016/j.gca.2024.11.024","url":null,"abstract":"<div><div>Bromine, although a minor component in volcanic gases, has received increasing interest in recent studies due to its high atmospheric ozone depletion potential, but its behaviour in alkali-rich felsic hydrous magmas remains unexplored. In this study, fluid-melt partitioning experiments were carried out using natural, Cl- and F-bearing silicate glasses with phonolitic, comenditic and pantelleritic compositions. For each composition, experiments were performed with a range of Br concentrations, at <em>P-T</em> conditions simulating isothermal decompression degassing or isobaric equilibrium cooling at shallow crustal depth (800–1000 °C, 10–200 MPa, oxidising and reducing conditions). The major element, Cl and F concentrations of the run-product glasses were determined by electron microprobe and the Br concentrations by LA-ICPMS. Volatile concentrations in the fluid were determined by mass balance calculations. The experimental results show that more Br partitions into the fluid phase with increasing bulk halogen concentration. The most Br-doped experiments are typically saturated with a vapor phase and a hydrosaline liquid. Experiments at the lowest Br concentrations, closest to natural systems, show that the pressure dependence of vapor-melt Br partitioning is complex, with a minimum vapor-melt partition coefficient observed at 50 MPa in the phonolitic composition (1.8 ± 0.9 at 1000 °C and oxidising conditions). Our results indicate that the eruptive degassing of Br from peralkaline felsic magmas is restricted to the shallowest levels of the magmatic plumbing system and is likely to occur at much lower pressures than in metaluminous magmas. This observation is consistent with the composition of melt inclusions preserved in alkaline silicic magmas. An important finding is that the vapor-melt partitioning of Br and Cl decreases with increasing temperature. In phonolite, at 200 MPa and oxidising conditions, the Br vapor-melt partition coefficient decreases from 18.5 ± 3.6 at 900 °C to 3.8 ± 1.5 at 1000 °C. As the ratio between the Br and Cl vapor-melt partition coefficients is not conservative, the Br/Cl ratio in the vapor phase is likely to increase during isobaric cooling and degassing. The vapor-melt partition coefficients of Br and, to a lesser extent Cl also increase with decreasing <em>fO₂</em> in the phonolitic system, and the Br vapor-melt partition coefficient for a reduced alkaline magma is close to that for an oxidised calc-alkaline magma. Our results also show that during protracted storage at shallow levels, oxidised alkali- and F-rich rhyolites coexist with vapor and brine. This suggests that high F concentration promotes unmixing of the halogen-bearing phase coexisting with such melts. The exsolution of immiscible vapor and brine efficiently removes Br from peralkaline magmas and probably limits the flux of Br to the atmosphere from such magmas.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 117-144"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142884588","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":"Source composition or melting effect: New evidence from Archean komatiites concerning the origin of low highly siderophile element abundances in Earth’s mantle","authors":"Xiaoyu Zhou ,&nbsp;Ratul Banerjee ,&nbsp;Laurie Reisberg ,&nbsp;Sisir K. Mondal","doi":"10.1016/j.gca.2024.12.004","DOIUrl":"10.1016/j.gca.2024.12.004","url":null,"abstract":"<div><div>Highly siderophile element (HSE) contents of komatiites have been widely used to estimate the HSE composition of Earth’s mantle. However, the interpretation of existing komatiite data is controversial, with some authors arguing that the Archean deep mantle komatiite source was impoverished in HSE due to slow admixture of a late accretion component, while others invoke a melting process that would allow observed komatiite abundances to be obtained from a mantle source with present-day HSE abundances. To obtain insight into this issue, we present new HSE abundance data for komatiites from the Gorumahishani greenstone belt of the Singhbhum Craton, eastern India. Our Sm-Nd and Re-Os isotope data indicate a ∼3.5 Ga age for these little-studied rocks, which provide extreme examples of Al-depleted and Ti-depleted komatiite varieties, juxtaposed over a short-length scale. The calculated parental melt compositions for the Al-depleted komatiites have 2.7 ± 0.2 ppb Ru, 3.4 ± 0.2 ppb Pt, and 3.2 ± 0.6 ppb Pd, whereas, for the Ti-depleted type these values are 4.4 ± 0.3 ppb Ru, 3.2 ± 0.6 ppb Pt, 3.0 ± 0.5 ppb Pd. These concentrations are similar to those found in most Archean komatiites at &gt;3.4 Ga. For the Al-depleted samples, these values would correspond to mantle abundances equivalent to ∼38 % of modern Bulk Silicate Earth (BSE) Ru contents and ∼24 and ∼21 % of BSE Pt and Pd contents, respectively, if it is assumed that simple extrapolation of the measured values to the MgO content of fertile peridotite provides an adequate approximation of the HSE composition of the BSE. To examine the alternative model that the low contents of Ru, Pd and Pt in Gorumahishani komatiites could be obtained from a mantle source with BSE-like HSE contents, we apply a simple two-stage critical melting model using current experimental HSE partitioning coefficients. The Ru abundances of the Gorumahishani Al-depleted komatiitic magmas can be produced from the pooled melts of a fertile source with BSE-like Ru and S contents during the first melting stage. The Ru abundances of the Ti-depleted komatiitic magmas can then be produced from remelting the residue left by this first melting stage. On the other hand, Pt and Pd abundances cannot be successfully modelled for either the Al-depleted or the Ti-depleted komatiites using available partition coefficients, though our current understanding of Pt and Pd partitioning after sulfide exhaustion is limited. The use of komatiites to characterize the abundance and distribution of HSE in the early mantle critically depends on developing a better understanding of the partitioning behaviors of these elements between mantle sources and komatiitic magmas.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 211-231"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841535","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":"Constraining sulfur cycling in the Eastern Tibetan Plateau: Evidence for cryptic sulfur cycling and implications for the weathering budget","authors":"Jun Zhong, Albert Galy, Preston Cosslett Kemeny, Xuetao Zhu, Gilad Antler, Cong-Qiang Liu, Si-Liang Li","doi":"10.1016/j.gca.2025.01.041","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.041","url":null,"abstract":"The production of sulfuric acid (H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;) through the oxidation of reduced sulfur removes alkalinity from the ocean–atmosphere system and increases atmospheric carbon dioxide concentration (&lt;ce:italic&gt;p&lt;/ce:italic&gt;CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;) over geologic timescales. In practice, quantifying CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; changes due to H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;-driven weathering requires deciphering the sources of sulfate (SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;) in river water. However, river SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; concentrations ([SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;]) or SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; sulfur and oxygen isotopic ratios (δ&lt;ce:sup loc=\"post\"&gt;34&lt;/ce:sup&gt;S&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt; and δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt;) can potentially be modified after the initial weathering reactions, biasing the inversion calculations that underlie quantification for the impact of chemical weathering on &lt;ce:italic&gt;p&lt;/ce:italic&gt;CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;. Here, we identify such a non-conservative behavior with a new dataset of δ&lt;ce:sup loc=\"post\"&gt;34&lt;/ce:sup&gt;S&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt;, δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt; in the Jinsha River and Yalong River draining the Eastern Tibetan Plateau is best explained by cryptic sulfur cycling in the catchments. As a result, measurements in δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt; do not necessarily provide a simple tool for inferring SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; sources, especially in the dry season. The partition of major dissolved ions concentrations between their different sources by inversion suggests that the discharged-weighted mean [SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;]&lt;ce:inf loc=\"post\"&gt;sulfide oxidation&lt;/ce:inf&gt;/[SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;] ratio is 0.47 and 0.78, corresponding to a yield for the oxidation of sulfide of 4.55 × 10&lt;ce:sup loc=\"post\"&gt;4&lt;/ce:sup&gt; and 6.05 × 10&lt;ce:sup loc=\"post\"&gt;4&lt;/ce:sup&gt; mol/km&lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;/yr, for the Jinsha River and the Yalong River, respectively. The fraction of cations from carbonate weathering and the fraction of acid from sulfide oxidation obtained from river inversion show that chemical weathering for most samples is a CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; sink on short-term timescales but CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; source on long-term timescales. The year-long survey shows that sulfide weathering counteracts and surpasses all atmospheric CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; consumption by silicate weathering for the Yalong River and the Jinsha River, respectively. We attribute the enhanced role of H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;SO&lt;ce:inf loc=\"post\"&gt;4&lt;","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"225 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401585","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 pathways of clay formation and kinetics of basalt alteration in poor drainage systems: Implications for weathering","authors":"Piyush Sriwastava, Vijay Kumar Saini, George Mathew, Anil D. Shukla","doi":"10.1016/j.gca.2025.01.042","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.042","url":null,"abstract":"Basalt being the most dominant rock on the earth’s crust, contributes significantly to the global elemental cycle through weathering. In recent years, the potential of basalt weathering has been continuously scrutinized as a carbon dioxide removal (CDR) strategy. An accurate estimation of such large-scale processes requires a deeper insight into the mechanism controlling the basalt glass dissolution under field conditions. This contribution assesses the chemical evolution of fluid interacting with basalt glass in poorly drained regimes. Experiments showed a drop in kinetics of alteration (r<ce:inf loc=\"post\">0</ce:inf> = 1.7 × 10<ce:sup loc=\"post\">-9</ce:sup> mol.m<ce:sup loc=\"post\">−2</ce:sup>. s<ce:sup loc=\"post\">−1</ce:sup>) by two orders of magnitude in 24 days and emphasizes the onset of secondary mineral formation within 20 hr of the start of dissolution. At first, Mg starts fractionating from the solution due to brucite oversaturation and reaches undersaturation after 60th hour due to onset of other Mg-bearing minerals. From the 54th hour, montmorillonite remains oversaturated until Mg is entirely consumed by precipitation at the 164th hour. SEM-EDS investigation shows the presence of two major morphologies of secondary products: (a) honeycomb shape (smectite), with high Mg (&gt;3 wt%) and octahedral composition similar [(Si/Al + Fe + Mg) and Al/Si] to smectite, (b) aggregate of ellipsoid and/or equant granular phases. Compositionally, elliptical and granular aggregates show affinity towards low Mg and high Fe variety of smectite amorphous precursor. The absence of pure brucite grains indicates epitaxial growth of Mg-rich, honeycomb-shaped phyllosilicate precursor on the brucite template due to well-reported structural similarity between the brucite layer and 2:1 phyllosilicate octahedral sheet. Elliptical and equant-shaped grains with or without compositional similarity with smectite phases have high Fe and low Mg, indicating their formation under a low Mg concentration stage in solution. Precipitation of the secondary phases at various stages of reaction progress affects the total reaction affinity in a closed system. Coupled dissolution and precipitation at the fluid-rock interface are responsible for lowering the kinetics of dissolution reactions in a closed system, previously explaining the slow kinetics of natural weathering regimes. The damped kinetics of dissolution and cations fractionation in secondary products within a few hours of onset of dissolution reaction can result in an overestimation (ten times) of CDR potential estimation by enhanced rock weathering (ERW) if calculations do not involve the nature of closed system evolution during basalt glass alteration.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"15 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401586","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":"Land-ocean connections in organic carbon cycling amid the Early Triassic (Smithian-Spathian) revealed through compound specific isotope analysis","authors":"Franziska R. Blattmann, Torsten W. Vennemann, Elke Schneebeli-Hermann, Hugo F.R. Bucher, Clayton R. Magill","doi":"10.1016/j.gca.2025.01.037","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.037","url":null,"abstract":"Following the largest mass extinction of the Phanerozoic, the Early Triassic was characterized by a series of carbon cycle perturbations as revealed through multiple global carbon isotope excursions (CIEs). The mechanistic drivers behind these perturbations are a subject of debate due to limited records that differentiate terrestrial and marine carbon cycling processes. In this study, we focus on the Smithian-Spathian boundary, which is characterized by a global positive CIE approximately 2<ce:hsp sp=\"0.25\"></ce:hsp>million years after the onset of the carbon cycle perturbations. We present the results of biomarker molecular distributions (i.e., <ce:italic>n</ce:italic>-alkanes) and compound-specific carbon isotope analyses (<ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf>) for organic matter extracted from shales deposited at the Stensiöfjellet section in Spitsbergen, Norway. The measured middle Smithian <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf> values are among the lowest in the Phanerozoic and potentially indicate high atmospheric <ce:italic>p</ce:italic>CO<ce:inf loc=\"post\">2</ce:inf> and a low <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C value for CO<ce:inf loc=\"post\">2</ce:inf> as a result of the oxidation of organic carbon. Marine and terrestrial <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf> records show parallel CIEs reflecting that both systems were equally affected by carbon cycle perturbations. Our data suggest the onset of the CIE started in the late middle Smithian, suggesting an earlier perturbation of the carbon cycle than previously recognized. Spathian <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf> values remain elevated and diverge from bulk <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C trends, reflecting an intrinsic shift in both the marine and terrestrial carbon cycle. Considered together, our compound-specific carbon isotope analyses foster useful insights into the multiple carbon cycle perturbations during an interval of extreme environmental conditions marked by continuous biological radiation and extinction pulses, which might even be analogous to imminent future anthropogenic changes in climate. This study further shows that compound specific carbon isotope analyses can potentially also disentangle deep-time carbon cycle perturbations.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"161 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401622","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":"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}