Geochimica et Cosmochimica Acta最新文献

{"title":"Interaction of metal oxyions and phosphate with carbonate green rust: Insights into Earth’s modern and ancient environments","authors":"Ichiko Sugiyama, Itay Halevy","doi":"10.1016/j.gca.2025.03.018","DOIUrl":"10.1016/j.gca.2025.03.018","url":null,"abstract":"<div><div>Carbonate green rust (GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>) is often found in suboxic and anoxic environments, and is known to be highly reactive towards dissolved metals and other aqueous compounds. Though the reactivity of GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> towards a variety of aqueous compounds has been determined in previous studies, its reactivity under conditions relevant to modern and ancient marine environments has not been systematically explored. Furthermore, the fate of the aqueous compounds upon aging of the GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> remains almost completely unknown.</div><div>To inform the interaction of GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> with oxyion-forming metals during the mineral’s precipitation and aging, we conducted a series of co-precipitation experiments of Cr<span><math><msup><mrow></mrow><mrow><mi>VI</mi></mrow></msup></math></span>, Mo<span><math><msup><mrow></mrow><mrow><mi>VI</mi></mrow></msup></math></span>, V<span><math><msup><mrow></mrow><mrow><mi>V</mi></mrow></msup></math></span>, U<span><math><msup><mrow></mrow><mrow><mi>VI</mi></mrow></msup></math></span>, and PO<span><math><msubsup><mrow></mrow><mrow><mn>4</mn></mrow><mrow><mn>3</mn><mo>−</mo></mrow></msubsup></math></span> with GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> in seawater-analog solutions, at pH 8.0, 25 °C, and under anoxic conditions. The experimental results are provided as uptake percentages at different metal:Fe ratios and as a series of partition coefficients of the studied oxycation and oxyanions between aqueous solution and GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>. Additionally, aging experiments up to 13 months in duration were conducted at metal concentrations of 1 <span><math><mi>μ</mi></math></span>M and under the same experimental conditions, to quantify the retention or release of the metals associated with GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> transformation to thermodynamically stable phases. Uptake of both V<span><math><msup><mrow></mrow><mrow><mi>V</mi></mrow></msup></math></span> and Cr<span><math><msup><mrow></mrow><mrow><mi>VI</mi></mrow></msup></math></span> was near-quantitative, and these metals were retained during aging. We identify reduction by the Fe<span><math><msup><mrow></mrow><mrow><mi>II</mi></mrow></msup></math></span> in GRCO<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> as the predominant mechanism of Cr<span><math><msup><mrow></mrow><mrow><mi>VI</mi></mrow></msup></math></span> uptake, whereas in V<span><math><msup><mrow></mrow><mrow><mi>V</mi></mrow></msup></math></span> both reduction and adsorption are implied by our results. Up to <span><math><mo>∼</mo></math></span>20% of ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 96-112"},"PeriodicalIF":4.5,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824982","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":"Changes in calcium ion concentration as the common driver for Na, K, S, and B incorporation during inorganic calcite precipitation in Mg-free artificial seawater","authors":"Joji Uchikawa ,&nbsp;Szabina Karancz ,&nbsp;Mariëtte Wolthers ,&nbsp;Laura Pacho ,&nbsp;Dustin T. Harper ,&nbsp;Donald E. Penman ,&nbsp;Lennart J. de Nooijer ,&nbsp;Gert-Jan Reichart ,&nbsp;Richard E. Zeebe","doi":"10.1016/j.gca.2025.03.022","DOIUrl":"10.1016/j.gca.2025.03.022","url":null,"abstract":"<div><div>Calcite is known to incorporate a range of non-constituent ions during its precipitation from aqueous solutions. Their concentrations (measured as <em>E</em>/Ca ratios, where <em>E</em> denotes the elemental forms of non-constituent ions) in calcite formed in seawater can serve as useful tools for paleoceanographic studies. But this requires concrete understanding of the incorporation patterns and their dependence to environmental factors at the time of mineral precipitation. Here, we present Na/Ca, K/Ca, S/Ca, and B/Ca ratios of inorganic calcite samples generated in laboratory experiments using Mg-free artificial seawater with systematic manipulations of pH, [DIC], and [Ca²⁺]. The three parameters were varied both individually (the pH, DIC, and Ca experimental series) and in tandem (the pH-Ca and DIC-Ca series) to form calcites under variable versus near-constant precipitation rates (denoted as <em>R</em>). All measured <em>E</em>/Ca ratios showed a robust positive linear dependence to changes in [Ca²⁺] in the Ca, pH-Ca, and DIC-Ca series, irrespective of changes in <em>R</em>. While K/Ca and S/Ca ratios changed almost exclusively with [Ca²⁺], Na/Ca and B/Ca ratios showed an additionally strong increase with increasing pH and a more moderate increase with rising [DIC], when <em>R</em> changed accordingly in the pH and DIC series. While <em>R</em>-driven kinetic effects and/or formation of certain cation–anion pairs may be important for the elemental uptake in calcite under some circumstances, these mechanisms or processes cannot fully account for the observed trends in every experimental series for all <em>E</em>/Ca ratios considered here. We propose that the observed <em>E</em>/Ca trends can be comprehensively explained by simultaneously considering the nonequivalent influence of changes in solution [Ca²⁺] and [CO₃²⁻] on step-specific kink formation dynamics and the size difference between the respective non-constituent ions (K⁺, Na⁺, SO₄²⁻, and B(OH)₄⁻ and B(OH)₃) relative to Ca²⁺ and CO₃²⁻ that constitute the calcite lattice.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Pages 67-82"},"PeriodicalIF":4.5,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824993","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":"Towards building a unified adsorption model for goethite based on variable crystal face contributions: II. Pb(II), Zn(II) and phosphate adsorption","authors":"Mario Villalobos,&nbsp;América Xitlalli Cruz-Valladares,&nbsp;Alan U. Loredo-Jasso,&nbsp;Paola Villar-Nava,&nbsp;Fernanda López-Castilla,&nbsp;Luis Fernando Huerta-Hernández","doi":"10.1016/j.gca.2025.03.023","DOIUrl":"10.1016/j.gca.2025.03.023","url":null,"abstract":"<div><div>Following the first series of this work, where the acidity constants of the two surface proton-reactive sites of goethite were found, as well as the capacitance values for each of the four previously well-characterized goethites, in this second part we report the successful simulation of the adsorption of two heavy metal cations [Pb(II) and Zn(II)] and an oxyanion (phosphate) of high affinity for the goethite surface. All experimental data were freshly generated with the same four previously characterized goethites with independent crystal surface composition determinations and calculations of the corresponding surface site densities, to maintain complete self-consistency and avoid unwanted interfering variables. Three experimental pH adsorption edges at different total concentrations were constructed for each cation on each goethite, and four adsorption isotherms at different pH values for phosphate. Two surface complexes bound to singly-coordinated surface oxygens were found for both types of ions to optimally describe the experimental data: In the case of the cations, a bidentate complex with the unhydrolized cation and a monodentate complex with the hydroxylated cation. For phosphate a bidentate complex with the deprotonated phosphate moiety and a monodentate complex with a mono-protonated phosphate yielded the optimal results (a small contribution of a protonated bidentate complex was also found necessary to describe the data at pH 4). The values of the optimized goethite affinity constants for Pb(II) were <em>ca</em>. two orders of magnitude higher than those of Zn(II), and the optimized values of Charge Distributions were different for each metal cation, but most of the charge for the bidentate complexes occurred at the 1-plane, while that for the monodentate hydroxylated complexes occurred mostly at the 0-plane. In the case of phosphate, the same three stoichiometries as those found previously for arsenate described all adsorption isotherm data, but their affinity constants were found to be higher (less than one order of magnitude) than those for arsenate; and their charge distributions were slightly different as well.</div><div>The results of this work contribute to progressively build a unified model that describes the geochemical behavior of goethite towards adsorption of species of environmental interest. This endeavor may eventually be of aide to describe more complex systems and the interactions occurring among different component species as related to the presence of goethite.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 1-12"},"PeriodicalIF":4.5,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143739901","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":"Localized versus distributed dissolution in carbonate rocks: The key role of microstructure","authors":"Theo Briolet ,&nbsp;Elisabeth Bemer ,&nbsp;Olivier Sissmann ,&nbsp;Jerome Fortin","doi":"10.1016/j.gca.2025.03.019","DOIUrl":"10.1016/j.gca.2025.03.019","url":null,"abstract":"<div><div>Carbonate rocks are widespread and highly reactive, making their study a key topic for various environmental and anthropogenic issues. Dissolution of carbonate rocks is controlled by different factors, related to the fluid (chemical composition, pH, flow velocity) or the rock (mineral content, porosity, permeability, microstructure), and results in different dissolution patterns. To investigate the specific impact of microstructure on dissolution pattern, we perform controlled dissolution experiments under identical experimental conditions on two nearly pure calcite limestones (Euville and Lavoux) characterized by different grain and pore structures. Two distinct dissolution patterns are evidenced by the integration of CT-scanner and thin section observations, implying significant microstructural control. For Euville samples, dissolution is distributed across the entire width of the sample, whereas for Lavoux samples, dissolution is localized in wormhole-type channels. These contrasting responses are explained by differences in pore connectivity, reactivity and accessible specific surface areas. Conventional expressions of Péclet and Damköhler dimensionless numbers fail to differentiate the two studied limestones in a <em>Pe</em>-<em>Da</em> diagram despite their different behavior. Specific expressions are then defined to account for the specific accessibility to the intragranular microporosity and the associated specific surface area. The proposed approach allows a clear positioning of both limestones in areas of <em>Pe</em>-<em>Da</em> diagram consistent with the observed dissolution patterns.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 113-133"},"PeriodicalIF":4.5,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824983","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":"Nickel hydroxide–nickel carbonate competitive growth on carbonate surfaces","authors":"Winnie Liu ,&nbsp;Nabajit Lahiri ,&nbsp;Sebastian T. Mergelsberg ,&nbsp;Shawn L. Riechers ,&nbsp;John S. Loring ,&nbsp;Mark E. Bowden ,&nbsp;Sebastien N. Kerisit","doi":"10.1016/j.gca.2025.03.020","DOIUrl":"10.1016/j.gca.2025.03.020","url":null,"abstract":"<div><div>The thermodynamic and kinetic factors controlling the competitive heterogeneous nucleation and growth of ubiquitous metal carbonate and hydroxide phases are poorly understood. In this work, calcite (CaCO₃) and magnesite (MgCO₃) powders were reacted with NiCl₂ (0–600 μM) for 7 days at 22 °C and 5 °C. The reacted powders were analyzed with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and energy-dispersive X-ray spectroscopy to characterize the Ni surface precipitates formed. Evidence from these techniques pointed to the formation of mixed Ni carbonate-Ni hydroxide amorphous surface precipitates. On calcite, XPS detected primarily Ni(OH)₂ despite the initial solutions being more supersaturated with respect to gaspéite (NiCO₃) than to theophrastite (Ni(OH)₂) by a factor of 17–18. In contrast, NiCO₃ was the dominant component detected by XPS on magnesite in the same conditions. Decreasing the temperature had the effect of increasing the proportion of NiCO₃ to the detriment of Ni(OH)₂. The experimental observations were consistent with low lattice/cation size mismatch favoring NiCO₃ nucleation and temperature most influencing Ni(OH)₂ nucleation. Comparison to previous work on Co-reacted powders indicated the differences in lattice/cation size mismatch and/or water exchange rate impacted the composition of the surface precipitates more than the relative thermodynamic stabilities of the competing minerals. This work explored the heterogeneous growth regime of Ni carbonate and hydroxide phases on carbonate surfaces and shed light on the factors that control the competition between surface precipitates when mineral surfaces are in contact with aqueous solutions supersaturated with respect to multiple mineral phases. These results contribute to geochemists’ efforts toward interpreting data from geochemical systems with elevated Ni concentrations, improving Ni environmental remediation and recovery strategies, and predicting the fate and transport of Ni in geochemical systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 182-194"},"PeriodicalIF":4.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821320","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":"Bayesian calibration of the 40K decay scheme with implications for 40K-based geochronology","authors":"Jack N. Carter ,&nbsp;Caroline E.J. Hasler ,&nbsp;Anthony J. Fuentes ,&nbsp;Andrew J. Tholt ,&nbsp;Leah E. Morgan ,&nbsp;Paul R. Renne","doi":"10.1016/j.gca.2025.03.024","DOIUrl":"10.1016/j.gca.2025.03.024","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The K/Ar and &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar geochronometers are based on the naturally occurring radionuclide &lt;sup&gt;40&lt;/sup&gt;K. Their precision and accuracy are limited by uncertainties on the &lt;sup&gt;40&lt;/sup&gt;K decay constants and, in the case of the &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar geochronometer, the isotopic composition of neutron fluence monitors. To address these limitations, we introduce a Bayesian calibration of the &lt;sup&gt;40&lt;/sup&gt;K decay scheme. We formulate robust priors for all model parameters including partial &lt;sup&gt;40&lt;/sup&gt;K decay constants, &lt;sup&gt;238&lt;/sup&gt;U and &lt;sup&gt;235&lt;/sup&gt;U decay constants, and age offset parameters to account for phenomena that can perturb apparent U-Pb and &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar ages. We then harness a set of complementary &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar, &lt;sup&gt;238&lt;/sup&gt;U/&lt;sup&gt;206&lt;/sup&gt;Pb, and &lt;sup&gt;235&lt;/sup&gt;U/&lt;sup&gt;207&lt;/sup&gt;Pb data from well- characterized geological samples with ages from 1.919 ka to 2000 Ma to derive Bayesian estimates of the &lt;sup&gt;40&lt;/sup&gt;K decay constants. Posterior values for the partial &lt;sup&gt;40&lt;/sup&gt;K decay constants are &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;β&lt;/mi&gt;&lt;/mrow&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;/msup&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;= (4.9252 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.0054) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−10&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;β&lt;/mi&gt;&lt;/mrow&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;/msup&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; = (5.6658 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.1543) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−15&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;EC&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;∗&lt;/mo&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; = (5.7404 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.0053) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−11&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;, and &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;EC&lt;/mi&gt;&lt;/mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/msub&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;= (4.9060 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.2942) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−13&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt; (uncertainties reported at the 68 % (1&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) credible interval). These combine to a total &lt;sup&gt;40&lt;/sup&gt;K decay constant &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;tot&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;= (5.5042 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.0054) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−10&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;. Model estimates of the &lt;sup&gt;238&lt;/sup&gt;U and &lt;sup&gt;235&lt;/sup&gt;U decay constants are statistically indistinguishable from those reported by &lt;span&gt;&lt;span&gt;Jaffey et al. (1971)&lt;/span&gt;&lt;/span&gt;. Posterior values of the &lt;sup&gt;40&lt;/sup&gt;K decay constants and the &lt;sup&gt;40&lt;/sup&gt;Ar*/&lt;sup&gt;40&lt;/sup&gt;K isotopic composition of Fish Canyon sanidine (FCs) define a K/Ar FCs age of 28.183 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.017 Ma (1&lt;span&gt;&lt;math&gt;&lt;","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 149-163"},"PeriodicalIF":4.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824994","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":"Comparison of the earliest NC and CC planetesimals: Evidence from ungrouped iron meteorites","authors":"Fridolin Spitzer ,&nbsp;Christoph Burkhardt ,&nbsp;Thomas S. Kruijer ,&nbsp;Thorsten Kleine","doi":"10.1016/j.gca.2025.03.021","DOIUrl":"10.1016/j.gca.2025.03.021","url":null,"abstract":"<div><div>Isotope anomalies in meteorites reveal a fundamental dichotomy between <em>Non-Carbonaceous-</em> (NC) and <em>Carbonaceous-type</em> (CC) planetary bodies. Until now, this dichotomy is established for the major meteorite groups, representing about 36 distinct parent bodies. Ungrouped meteorites represent an even larger number of additional parent bodies, but whether they conform to the overall NC-CC dichotomy is unknown. Here, the genetics and chronology of 26 ungrouped iron meteorites are considered through nucleosynthetic Mo and radiogenic W isotopic compositions. Secondary cosmic ray-induced modifications of these isotope compositions are corrected using Pt isotope measurements on the same samples. We find that all of the ungrouped irons have Mo isotope anomalies within the range of the major meteorite groups and confirm the NC-CC dichotomy for Mo, where NC and CC meteorites define two distinct, subparallel <em>s</em>-process mixing lines. All ungrouped NC irons fall on the NC-line, which is now precisely defined for 41 distinct parent bodies. The ungrouped CC irons show scatter around the CC-line indicative of small <em>r</em>-process Mo heterogeneities among these samples. These <em>r</em>-process Mo isotope variations correlate with O isotope anomalies, most likely reflecting mixing of CI chondrite-like matrix, chondrule precursors, and Ca-Al-rich inclusions. This implies that CC iron meteorite parent bodies accreted the same nebular components as the later-formed carbonaceous chondrites. The Hf-W model ages of core formation for the ungrouped irons overlap with those of the iron meteorite groups from each reservoir and reveal a narrow age peak at ∼3.3 Ma after Ca-Al-rich inclusions for the CC irons. By contrast, the NC irons display more variable ages, including younger ages indicative of impact-induced melting events, which seem absent among the CC irons. This is attributed to the more fragile and porous nature of the CC bodies, making impact-induced melting on their surfaces difficult. The chemical characteristics of all iron meteorites together reveal slightly more oxidizing conditions during core formation for CC compared to NC irons. More strikingly, strong depletions in moderately volatile elements, typical of many iron meteorite parent bodies, predominantly occur among CC irons, for reasons that remain unclear at present.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 134-148"},"PeriodicalIF":4.5,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824995","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":"Corrigendum to “Carbonate dissolution fluxes in deep-sea sediments as determined from in situ porewater profiles in a transect across the saturation horizon” [Geochim. Cosmochim. Acta. 390 (2025) 145–159]","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;William Gray ,&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.2025.03.014","DOIUrl":"10.1016/j.gca.2025.03.014","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Page 193"},"PeriodicalIF":4.5,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144089557","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":"Site-specific D-H exchange of amino acids under asteroidal hydrothermal conditions","authors":"Yuanyuan He ,&nbsp;Flavio Siro Brigiano ,&nbsp;Michel Sablier ,&nbsp;Nadezda Khodorova ,&nbsp;David Boulesteix ,&nbsp;Arnaud Buch ,&nbsp;Peter Reinhardt ,&nbsp;Sylvain Bernard ,&nbsp;Laurent Remusat","doi":"10.1016/j.gca.2025.03.017","DOIUrl":"10.1016/j.gca.2025.03.017","url":null,"abstract":"<div><div>Amino acids detected in carbonaceous chondrites are commonly enriched in heavy isotopes of hydrogen compared to terrestrial counterparts. This is interpreted as the consequence of synthesis processes happening in cold extraterrestrial environments. However, the magnitude of this enrichment is variable among classes of chondrites and among individual amino acid in a given chondrite. In this study, we investigated the evolution of the D/H isotope ratio of amino acids experimentally exposed to pure D₂O at 150 °C. We observed that not all the hydrogen-specific sites are prone to deuterium-hydrogen exchange under hydrothermal conditions. Ab-initio modeling pinpoints the higher acidity of the carbon in α position (C_α) leading to a site-specific preferential D-H exchange, affecting the hydrogen atoms bonded to C_α (α-H). This explains the low exchange rate of 2-aminoisobutyric acid and isovaline, these branched amino acids lacking α-H, and the rather high exchange rate of glycine, α-alanine and β-alanine, their α-H exchanging faster. By extrapolating these results, it can be assumed that chondritic amino acids lacking α-H and containing only primary hydrogen (i.e., –CH₃ group) have better retained their pre-accretional D/H values despite hydrothermal alteration on the parent body.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 170-181"},"PeriodicalIF":4.5,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821318","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":"Heterogeneous enriched geochemical compositions in Hawaiian lavas: Contributions from recycled continental materials in the Loa source of the Hawaiian plume","authors":"Nicole M.B. Williamson ,&nbsp;Dominique Weis ,&nbsp;Elly Thistlethwaite ,&nbsp;Lauren N. Harrison ,&nbsp;Catherine Armstrong ,&nbsp;James S. Scoates ,&nbsp;Michael O. Garcia","doi":"10.1016/j.gca.2025.03.012","DOIUrl":"10.1016/j.gca.2025.03.012","url":null,"abstract":"<div><div>Several mantle plumes (Hawai‘i, Kerguelen, Pitcairn) produce ocean island basalt with enriched mantle I (EM-I) geochemical compositions. Hawai‘i is the most vigorous of these plumes, with the highest buoyancy flux. The isotopically enriched, EM-I-like compositions measured along the Hawaiian Island chain are limited to the Ko‘olau, Lāna‘i, and Kaho‘olawe volcanoes, which form the Enriched Loa geochemical group. A total of 37 new samples from seven locations across the Wai‘anae and Ko‘olau volcanoes (O‘ahu, Hawai‘i) were analysed for major element oxides, trace element concentrations, and Pb-Sr-Nd-Hf isotopic compositions to determine the composition and spatial distribution of Enriched Loa compositions along the Hawaiian chain. Combined with data from Lāna‘i and Kaho‘olawe, and a compilation of shield stage Hawaiian data spanning ∼6 Ma, this study shows that Enriched Loa compositions are chemically heterogeneous and that the Enriched Loa component was present intermittently along the Hawaiian chain over approximately 130 km and 1.4 Ma. The statistically distinct Pb-Sr-Nd-Hf isotopic means between the Makapu‘u stage of Ko‘olau, Lāna‘i, and Kaho‘olawe suggest that the Enriched Loa geochemical group consists of two different heterogeneities and implies that enriched components in the deep mantle source of the Hawaiian plume exist at multiple physical scales. The geochemical features of the Enriched Loa volcanoes require a distinct mantle component, with a source that likely contains recycled surface materials, possibly of continental origin, stored in the Pacific large low shear velocity province (LLSVP). Enriched Loa isotopic compositions share similarities with other EM-I ocean island basalt; however, they are not as radiogenic in ⁸⁷Sr/⁸⁶Sr as compositions from Kerguelen and Pitcairn. This suggests that the materials stored in the Pacific and African LLSVPs have slightly different sources and ages. Specifically, this work supports the hypothesis that the recycled surface materials from the Pacific LLSVP are younger than those from the African LLSVP.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 75-95"},"PeriodicalIF":4.5,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824996","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}