Geochimica et Cosmochimica Acta最新文献

{"title":"Mn(II)-induced phase transformation of Mn(IV) oxide in seawater","authors":"Peng Yang , Ke Wen , Kevin A. Beyer , Wenqian Xu , Mengqiang Zhu","doi":"10.1016/j.gca.2025.01.014","DOIUrl":"10.1016/j.gca.2025.01.014","url":null,"abstract":"<div><div>Manganese (Mn) oxides are key components of oceanic and lacustrine Mn nodules and influence metal cycling through oxidation and adsorption processes. Layered Mn oxides (LMOs) are the most common minerals in these nodules and the immediate products of microbially mediated Mn(II) oxidation by O<sub>2</sub>. LMOs can transform into tunneled Mn oxides (TMOs), Mn oxyhydroxides (MnOOH), or Mn(II,III) phase (Mn<sub>3</sub>O<sub>4</sub>). LMOs often concur with Mn(II) in the environment and the adsorption and oxidation of Mn(II) by LMOs can greatly promote the transformation of LMOs to those phases. However, the Mn(II)-promoted transformation of LMOs in seawater—rich in various cations (300 mM Na<sup>+</sup>, 10 mM K<sup>+</sup>, 50 mM Ca<sup>2+</sup>, and 10 mM Mg<sup>2+</sup>) remains poorly understood. We examined the transformation of δ-MnO<sub>2</sub> in artificial seawater (pH 8.2) under anoxic conditions with the Mn(II)/MnO<sub>2</sub> ratio (r) ranging from 0.08 to 3.83. To assess the effect of ionic strength (IS), parallel experiments were conducted in a mixed 530 mM NaCl and 10 mM KCl solution (having seawater ionic strength but without Ca<sup>2+</sup> and Mg<sup>2+</sup>) and in 100 mM NaCl solution as a control. At low r (0.08), δ-MnO<sub>2</sub> transformed into triclinic birnessite and a 4 × 4 TMO in 100 mM NaCl solution, which, however, was suppressed in seawater due to strong interactions of Ca<sup>2+</sup>/Mg<sup>2+</sup> with δ-MnO<sub>2</sub>. In the mixed 530 mM NaCl and 10 mM KCl solution (the same ionic strength as of seawater), the transformation occurred extensively but the products had lower crystallinity compared to in 100 mM NaCl solution. At the high Mn(II)/MnO<sub>2</sub> ratios (0.5 ≤ r ≤ 3.83), δ-MnO<sub>2</sub> transformed extensively into MnOOH phases and hausmannite (Mn<sub>3</sub>O<sub>4</sub>) in 100 mM NaCl solution. The seawater suppressed the transformation, but the suppression became weaker with increasing Mn(II)/MnO<sub>2</sub> ratio. For example, the transformation was completely suppressed at r = 0.5 but essentially negligible at r = 3.83. The suppression at these high Mn(II)/MnO<sub>2</sub> ratios was mainly ascribed to the influence of Ca<sup>2+</sup> and Mg<sup>2+</sup> rather than of the high IS, and the weaker suppression at the higher Mn(II)/MnO<sub>2</sub> ratio suggests stronger competition of Mn(II) with Ca<sup>2+</sup>/Mg<sup>2+</sup> for interacting with δ-MnO<sub>2</sub>. Moreover, the composition and crystallinity of the transformation products (i.e., the relative abundance of MnOOH (α, β, and γ) and Mn<sub>3</sub>O<sub>4</sub>) were influenced by both the high ionic strength and the presence of Ca<sup>2+</sup> and Mg<sup>2+</sup>. Therefore, even though Ca<sup>2+</sup> and Mg<sup>2+</sup> concentrations are much lower than Na<sup>+</sup> in seawater, their impacts on the transformation are dominant. Our study explains why MnOOH phases, hausmannite, and TMOs are less common than LMOs in oc","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 155-169"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055251","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":"Experimental metasomatic incorporation of sulfur into fluorapatite as a function of coupled substitutions involving sodium, silicon, iron, and cerium","authors":"Daniel E. Harlov ,&nbsp;Justin Casaus ,&nbsp;Brian A. Konecke ,&nbsp;Adam C. Simon","doi":"10.1016/j.gca.2025.01.024","DOIUrl":"10.1016/j.gca.2025.01.024","url":null,"abstract":"<div><div>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 S⁶⁺ + Na⁺ = P⁵⁺ + Ca²⁺ and S⁶⁺ + Si⁴⁺ = 2P⁵⁺. 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 S⁶⁺ + Na⁺ = P⁵⁺ + Sr²⁺. 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 Ca²⁺ + P⁵⁺ = Fe³⁺ + S⁴⁺ and Ca²⁺ + P⁵⁺ = Ce³⁺ + S⁴⁺, 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.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 268-289"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","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":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Discovery of Ge2+ in quartz: Evidence from EPR/XAS experiments and DFT calculations, and implications for Ge/Si systematics","authors":"Rudolf I. Mashkovtsev ,&nbsp;Sanda M. Botis ,&nbsp;Jinru Lin ,&nbsp;Reza Deevsalar ,&nbsp;Leo Ka Long Cheung ,&nbsp;Eli Wiens ,&nbsp;Ayetullah Tunc ,&nbsp;Ning Chen ,&nbsp;Roman Chernikov ,&nbsp;Yuanming Pan","doi":"10.1016/j.gca.2025.01.025","DOIUrl":"10.1016/j.gca.2025.01.025","url":null,"abstract":"<div><div>The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and <em>ab initio</em> theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi₂]⁰ and [GeHH₂]⁰ centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge²⁺ state. Ge <em>K</em>-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge²⁺. Theoretical calculations reproduce the experimental ¹H and ⁷Li hyperfine constants of the [GeHLi₂]⁰ center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant <em>c</em>-axis channel, again supporting the Ge²⁺ state. The presence of Ge²⁺ in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge⁴⁺ is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge²⁺ in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 290-303"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055426","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":"The I/Ca paleo-oxygenation proxy in planktonic foraminifera: A multispecies core-top calibration","authors":"Anya V. Hess ,&nbsp;Yair Rosenthal ,&nbsp;Xiaoli Zhou ,&nbsp;Kaixuan Bu","doi":"10.1016/j.gca.2025.01.018","DOIUrl":"10.1016/j.gca.2025.01.018","url":null,"abstract":"<div><div>Iodine-to-calcium ratios (I/Ca) in planktonic foraminifera have been used for the reconstruction of upper ocean oxygenation in the geologic past, particularly for detecting oxygen-deficient zones (ODZs). We examine the response of I/Ca in various planktonic foraminifera species from core-top sediment samples to changes in iodate and the minimum oxygen concentration in the uppermost 500 m of the water column ([O₂]_min). Published data are concentrated in the Atlantic Ocean and in areas with either very high or very low oxygen concentrations. Our study supplements those studies using samples from the GEOTRACES GP16 transect through the southern lobe of the eastern tropical Pacific oxygen deficient zone and areas in the western equatorial Pacific and Atlantic Ocean characterized by intermediate oxygen concentrations ([O₂]_min of 100–170 µmol/kg). We use Mg/Ca values measured alongside I/Ca to determine apparent calcification depth for foraminifera in the tropical Pacific. We find that I/Ca values in foraminifera species from different water depth habitats vary predictably based on patterns in iodate concentration spatially and with depth in the upper water column. In well-oxygenated areas of the ocean, I/Ca values are relatively high, with the highest values in deep subsurface foraminifera species that lived furthest from the mixed layer where primary productivity converts iodate to iodide and organic iodine. In ODZs, I/Ca values are relatively low and this pattern reverses, with the lowest I/Ca values in deep subsurface species living near or within the ODZ where iodate is used as an electron acceptor during oxidation of sinking organic matter. The difference between deep subsurface and surface I/Ca values can therefore provide another line of evidence for identifying the core of an ODZ in paleoceanographic records. This study suggests that the large scatter in the I/Ca data reflects the complexity of the relationship between the distribution of iodate and dissolved oxygen through the water column and spatially, and the depths at which foraminifera calcify with respect to that distribution. We employ a linear correlation between I/Ca and [O₂]_min as the most parsimonious explanation for this complex system. Across the eastern tropical Pacific transect, I/Ca responds to small oxygenation changes on the order of 10s of µmol/kg, suggesting that I/Ca may be able to detect small relative changes in oxygenation of this magnitude in consecutive downcore samples. We note, however, that interpretation of such changes is strengthened by the use of additional paleo-oxygenation proxies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 182-195"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684048","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":"Chlorine and NaCl in hydrous basaltic melts","authors":"Monika K. Rusiecka,&nbsp;Bernard J. Wood","doi":"10.1016/j.gca.2025.01.020","DOIUrl":"10.1016/j.gca.2025.01.020","url":null,"abstract":"&lt;div&gt;&lt;div&gt;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&lt;sub&gt;2&lt;/sub&gt;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&lt;sub&gt;Cl&lt;/sub&gt; for each experiment as:&lt;/div&gt;&lt;div&gt;&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;Cl&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mi&gt;Cl&lt;/mi&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;w&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mo&gt;%&lt;/mo&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;msqrt&gt;&lt;mrow&gt;&lt;mi&gt;f&lt;/mi&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;Cl&lt;/mi&gt;&lt;/mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/msqrt&gt;&lt;/mfrac&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mroot&gt;&lt;mrow&gt;&lt;mi&gt;f&lt;/mi&gt;&lt;msub&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;/mroot&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;&lt;/div&gt;&lt;div&gt;The 70 results were then fitted by stepwise linear regression to an equation containing pressure, temperature and compositional terms. Terms which did not pass the F-test (α = 0.05) were excluded. This approach led to the following fit-equation, with P in GPa and X&lt;sub&gt;Si&lt;/sub&gt; X&lt;sub&gt;Ca&lt;/sub&gt; referring to mole fractions of the oxides on a single cation basis:&lt;/div&gt;&lt;div&gt;&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;log&lt;/mi&gt;&lt;msub&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;Cl&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;1.492&lt;/mn&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mn&gt;4331&lt;/mn&gt;&lt;msub&gt;&lt;mi&gt;X&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;Ca&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;mn&gt;3508&lt;/mn&gt;&lt;msub&gt;&lt;mi&gt;X&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;Si&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mn&gt;2440&lt;/mn&gt;&lt;msub&gt;&lt;mi&gt;X&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;Fe&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;mn&gt;3921&lt;/mn&gt;&lt;msub&gt;&lt;mi&gt;X&lt;/mi&gt;&lt;mi&gt;K&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;mn&gt;741&lt;/mn&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;/mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;/mfrac&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;&lt;/div&gt;&lt;div&gt;The standard error of the fit is 0.083 and R&lt;sup&gt;2&lt;/sup&gt; is 0.963. This equation closely approximates that obtained from the results on anhydrous compositions by Thomas and Wood (2023). Surprisingly the term in HO&lt;sub&gt;0.5&lt;/sub&gt; was found not to be significant, implying that water behaves as an ideal diluent with respect to chlorine.&lt;/div&gt;&lt;div&gt;We used our chloride capacity equation to calculate the activity of NaCl in experimentally-produced hydrous basalts of known chlorine content. The method involved combining chloride capacities with Na&lt;sub&gt;2&lt;/sub&gt;SiO&lt;sub&gt;3&lt;/sub&gt; and SiO&lt;sub&gt;2&lt;/sub&gt; activities derived from the Rhyolite-MELTS program. The results for NaCl activity were found to be in reasonably good agreement with values obtained from the Thomas and Wood (2023) equation which had been based predominantly on data from silica-rich compositions. Finally, measurements of the compositions of melt inclusions from Etna were used to calculate the activities of NaCl in the inclusions and the salinities of fluids with which the inclusions would be in equilibrium. F","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 208-218"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","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":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Equilibrium indium isotope fractionation in chloride-rich aqueous solutions using first-principles calculations","authors":"Haochen Duan ,&nbsp;Fang Huang","doi":"10.1016/j.gca.2025.01.026","DOIUrl":"10.1016/j.gca.2025.01.026","url":null,"abstract":"<div><div>Aqueous indium (In) speciation and isotope fractionation factors are important to understand the origin and transport of indium during magmatic-hydrothermal and atmosphere-hydrosphere processes. Here, we investigate indium speciation in chloride-rich aqueous solutions and explore their reduced partition function ratios (10³<em>lnβ</em>) using first-principles calculations. The simulations with initial configurations of InCl(H₂O)₅²⁺, InCl₂(H₂O)₄⁺, InCl₃(H₂O)₃, InCl₄(H₂O)₂⁻ and InCl₅(H₂O)²⁻ were performed at 400 and 600 K, respectively. The results show that InCl(H₂O)₅²⁺, InCl₂(H₂O)₄⁺, InCl₃(H₂O)_2.4, InCl₄⁻ and InCl₅²⁻ are the stable In³⁺ species at 400 K, and their 10³<em>lnβ</em> decreases from 1.00 ‰, 0.89 ‰, 0.83 ‰, 0.75 ‰ to 0.66 ‰. At 600 K, the stable In³⁺ species are composed of InCl(H₂O)₅²⁺, InCl₂(H₂O)_3.7⁺, InCl₃(H₂O)_1.7, InCl₄⁻ and InCl₅²⁻ with their 10³<em>lnβ</em> decreasing from 0.46 ‰, 0.42 ‰, 0.39 ‰, 0.35 ‰ to 0.31 ‰. These results indicate that 10³<em>lnβ</em> is negatively correlated with the coordination number and bond length of chlorine ligands in aqueous In³⁺ species. Meanwhile, water molecules are gradually removed from the first hydration shell gradually with increasing temperature, such as InCl₂(H₂O)₄⁺ and InCl₄(H₂O)₂⁻ to InCl₂(H₂O)_3.7⁺ and InCl₄⁻, indicating that stable In³⁺ species changes with temperature. Hence, estimating the 10³<em>lnβ</em> of aqueous liquids at different temperatures should consider the potential structure transition of cation species. The calculations of equilibrium indium isotope fractionation factors provide important insights into the mechanism of isotope fractionation in aqueous liquids, and show the potential application of indium isotopes in the geological and supergene processes of indium.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 304-317"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055370","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":"Bulk silicate Earth-like 142Nd and 182W mantle component sampled by 2.0 Ga Onega Basin picrites, Fennoscandia","authors":"I.S. Puchtel ,&nbsp;J.L. Hellmann ,&nbsp;H. Rizo ,&nbsp;J. Blichert-Toft ,&nbsp;A.V. Stepanova ,&nbsp;A.V. Samsonov ,&nbsp;R.J. Walker","doi":"10.1016/j.gca.2025.01.013","DOIUrl":"10.1016/j.gca.2025.01.013","url":null,"abstract":"&lt;div&gt;&lt;div&gt;In order to further evaluate the timing and possible mechanisms responsible for the transition from both positive and negative to no &lt;sup&gt;142&lt;/sup&gt;Nd and &lt;sup&gt;182&lt;/sup&gt;W anomalies in the Archean mantle, we obtained &lt;sup&gt;142,143&lt;/sup&gt;Nd, &lt;sup&gt;176&lt;/sup&gt;Hf, &lt;sup&gt;186,187&lt;/sup&gt;Os, &lt;sup&gt;182&lt;/sup&gt;W isotope and lithophile trace and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data for mantle plume-derived ∼2.0 Ga picrites and an associated differentiated mafic–ultramafic sill from the Onega Basin on the Fennoscandian Shield. The Onega Basin picrites share striking chemical similarities with the modern Kilauea picrites, featuring enrichments in light rare earth elements (LREE; La/Sm&lt;sub&gt;N&lt;/sub&gt; = 1.5 ± 0.2), depletions in heavy rare earth elements (HREE; Gd/Yb&lt;sub&gt;N&lt;/sub&gt; = 2.2 ± 0.1), positive high field strength element (HFSE) anomalies (Hf/Hf* = 1.2 ± 0.1, Nb/Nb* = 1.6 ± 0.1), and modern bulk silicate Earth (BSE)-like average W/Th = 0.20 ± 0.08 (2SD). Model calculations indicate that the parental picritic magmas were likely derived from 3 % equilibrium batch melting of a LREE-depleted garnet lherzolite PREMA-type mantle source containing a component of recycled oceanic crust.&lt;/div&gt;&lt;div&gt;The &lt;sup&gt;147&lt;/sup&gt;Sm-&lt;sup&gt;143&lt;/sup&gt;Nd, &lt;sup&gt;176&lt;/sup&gt;Lu-&lt;sup&gt;176&lt;/sup&gt;Hf, and &lt;sup&gt;187&lt;/sup&gt;Re-&lt;sup&gt;187&lt;/sup&gt;Os mineral-whole-rock isochron ages constrain precisely the timing of the Onega Basin lava emplacement at ∼1974 Ma. The corresponding initial ε&lt;sup&gt;143&lt;/sup&gt;Nd = +3.0 ± 0.5 and ε&lt;sup&gt;176&lt;/sup&gt;Hf = +2.8 ± 1.2 values indicate evolution of the Onega mantle source with time-integrated suprachondritic Sm/Nd and Lu/Hf ratios. The lower ε&lt;sup&gt;176&lt;/sup&gt;Hf relative to ε&lt;sup&gt;143&lt;/sup&gt;Nd further implies decoupling of the two lithophile element isotope systems in the source. The initial μ&lt;sup&gt;186&lt;/sup&gt;Os and γ&lt;sup&gt;187&lt;/sup&gt;Os values are suprachondritic at +4.9 ± 2.1 and +2.9 ± 0.4, respectively, indicating evolution of the Onega mantle plume source with time-integrated slightly suprachondritic Pt/Os and Re/Os ratios. The μ&lt;sup&gt;142&lt;/sup&gt;Nd = –1.1 ± 3.3 (2SD) and μ&lt;sup&gt;182&lt;/sup&gt;W = 0.0 ± 4.8 (2SD) obtained for the Onega picritic magmas are unresolvable from the modern BSE values, implying that their mantle source had &lt;sup&gt;142&lt;/sup&gt;Nd and &lt;sup&gt;182&lt;/sup&gt;W compositions similar to those of the BSE. When considered together, the trace element systematics, suprachondritic Pt/Os and Re/Os ratios, and Hf-Nd isotopic decoupling are best explained in terms of incorporation into the Onega mantle plume source of 10–20 % recycled komatiite-basalt crust aged in the mantle for 1 to 2 Ga. These results provide new evidence that &lt;sup&gt;142&lt;/sup&gt;Nd and &lt;sup&gt;182&lt;/sup&gt;W anomalies that were common in the Archean mantle were effectively homogenized by 2.0 Ga ago on the scale of the mantle domains sampled by the Onega Basin magmas. This may have occurred due to the enhanced convective whole-mantle mass and heat transfer facilitated by processes of oceanic crust recyc","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 133-154"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055371","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 effect of burning on the dissolution behaviour and silicon and oxygen isotope composition of phytolith silica","authors":"Andrea J. Prentice ,&nbsp;Elizabeth A. Webb","doi":"10.1016/j.gca.2024.11.007","DOIUrl":"10.1016/j.gca.2024.11.007","url":null,"abstract":"<div><div>The <em>δ</em>³⁰Si and <em>δ</em>¹⁸O values of opal-A precipitated in plants (silica phytoliths) have been shown to be useful for paleoenvironmental reconstructions. Here, the effects of burning and partial dissolution of phytoliths on their isotopic compositions and dissolution behaviour were examined. Phytoliths were heated to 700 °C and then dissolution experiments were conducted in batch reactors under a range of pH (4–8) and temperature (4–19 °C) conditions. Heating caused a −2.6 ‰ shift in phytolith <em>δ</em>¹⁸O values. NMR results suggest that heating reduces the number of surface vicinal silanols, which likely results in the formation of strained Si<img>O<img>Si bonds which incorporate oxygen from ¹⁸O-depleted hydroxyl groups. During dissolution, the <em>δ</em>¹⁸O of burned phytoliths increased by up to 3.5 ‰ (average 1.8 ‰) until 15–45 % saturation was reached, and then adsorption of silica on the surface of the solid began to reduce the <em>δ</em>¹⁸O value of solid silica despite a net dissolution. The maximum increase in <em>δ</em>¹⁸O during dissolution of burned phytoliths is 1.8 ‰ smaller than previously observed for unburned silica subjected to partial dissolution under the same conditions. Heating did not cause a significant change in <em>δ</em>³⁰Si values, and partial dissolution of burned phytoliths caused a slight increase in <em>δ</em>³⁰Si values that was smaller in magnitude than for unburned phytoliths. Dissolution of burned phytoliths progressed more slowly than dissolution of fresh phytoliths in low pH and temperature conditions, but was faster than the dissolution of fresh phytoliths when pH &gt; 6 and temperature = 19 °C. We propose that because fewer hydrolysis sites exist on the surface of burned phytoliths that the isolated silanols that remain after heating are difficult to deprotonate at low pH resulting in slower dissolution. However, at higher pH the breakage of strained Si<img>O<img>Si bonds in burned phytoliths may explain their higher dissolution rate relative to fresh phytoliths. We recommend caution in using the <em>δ</em>¹⁸O values of soil phytoliths in paleoclimate reconstructions as they can be altered during both heating and partial dissolution. For phytolith assemblages collected from archaeological hearths or grasslands prone to wildfires, the shift towards lower <em>δ</em>¹⁸O values caused by heating would result in overestimations of temperature using paleothermometer equations. Care must be taken to identify alteration by dissolution or burning, which may not always be visually evident.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 98-106"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673613","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":"Tardi-magmatic iddingsite in the Martian Nakhlite NWA 817","authors":"V. Megevand ,&nbsp;J.-C. Viennet ,&nbsp;C. Le Guillou ,&nbsp;F. Guyot ,&nbsp;S. Bernard","doi":"10.1016/j.gca.2025.01.028","DOIUrl":"10.1016/j.gca.2025.01.028","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 318-333"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","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":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Supply of phospholipid precursors and evolution sites on the early Earth by impact","authors":"Jiawen Zhao,&nbsp;Koichi Mimura","doi":"10.1016/j.gca.2025.01.003","DOIUrl":"10.1016/j.gca.2025.01.003","url":null,"abstract":"<div><div>The abiotic supply of phospholipid precursors on the early Earth constitutes a critical stage in cellular evolution. Glycerophosphate (GP) and acylglycerol (AG) are potential precursors to the bonding of polar heads and lipidic chains attached to the glycerol backbone in phospholipids. A deeper understanding of the synthesis of GP and AG on early Earth is essential for unraveling the origin of life. In this study, we performed shock experiments to simulate the impact of extraterrestrial bodies on both wet and dry surfaces of early Earth to investigate the synthesis of GP and AG. These experiments were conducted in the temperature transition zone between negligible alteration and complete decomposition of organic materials. Despite GP and AG synthesis involving dehydration, our experiments revealed they can synthesize under both wet and dry conditions by impact shock. This suggests that the process occurs universally in both wet and dry environments and presents a feasible pathway for phosphorylation and acylation on the early Earth. Moreover, the crater created by the impact may evolve into “warm little ponds” that collect the synthesized GP and AG for further evolution. The dry-wet cycles in the ponds not only facilitate the assembly of vesicles but also provide opportunities for further evolution. Our findings indicate that impacts from extraterrestrial bodies may have contributed to cellular evolution by supplying phospholipid precursors on the early Earth.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 122-132"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683557","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}