Geochimica et Cosmochimica Acta最新文献

{"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":"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":"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":"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":"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":"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}

{"title":"Sedimentary vanadium depletion under sulfidic conditions: Implications for (paleo)redox proxy applications","authors":"Niels A.G.M. van Helmond ,&nbsp;Olga M. Żygadłowska ,&nbsp;Wytze K. Lenstra ,&nbsp;Robin Klomp ,&nbsp;Christoph Humborg ,&nbsp;Daniel J. Conley ,&nbsp;Mike S.M. Jetten ,&nbsp;Caroline P. Slomp","doi":"10.1016/j.gca.2025.01.022","DOIUrl":"10.1016/j.gca.2025.01.022","url":null,"abstract":"<div><div>Sedimentary concentrations of redox-sensitive trace metals are widely used to reconstruct past ocean redox conditions. Vanadium (V) has great potential as a (paleo)redox proxy, due to its strong redox-dependent speciation (+III, +IV, +V) and the increased sedimentary sequestration of its more reduced species. The geochemistry of V in sulfide-rich marine environments is not yet well understood, however, hampering the use of V as a (paleo)redox proxy. Here, we present V data for two coastal systems, with bottom water redox conditions ranging from oxic to euxinic, to further constrain V geochemistry. Our sedimentary record from a eutrophic coastal marine basin (Scharendijke basin, Lake Grevelingen, the Netherlands), covering the last decade, shows distinct enrichments in molybdenum (Mo) and organic carbon (C_org) but depletions in V during seasonal bottom water euxinia, which can be discerned due to the exceptionally high sedimentation rate at our study site (up to 20 cm yr⁻¹). A seasonal study for the same coastal basin confirms this trend and reveals the accumulation of V, iron (Fe) and manganese (Mn) in the water column during summer euxinia. We conclude that the slow kinetics of V reduction to V(III) and subsequent precipitation as (oxy)hydroxide V(OH)_3(s) likely provide the opportunity for V to escape sedimentary sequestration during summer euxinia, resulting in the observed sedimentary V depletion. Sediments from three sites with contrasting bottom water redox conditions (oxic, seasonally hypoxic, euxinic) in the eutrophic Stockholm Archipelago, show a similar trend as that of Lake Grevelingen, with decreasing V concentrations and increasing Mo and C_org concentrations as bottom water conditions become more reducing. This confirms that our findings for Lake Grevelingen are not site-specific and are likely a generic feature of euxinic coastal systems with high sulfide concentrations (&gt; 0.5 mmol L⁻¹) near the sediment surface and high rates of anaerobic degradation of organic matter. Our results show that co-occurring sedimentary Mo and C_org enrichments and V depletion (or absence or suppression of an enrichment) are indicators of strongly sulfidic conditions in such settings. Finally, we show that maxima in sedimentary molar V/Mn ratios correlate with strongly reducing conditions. This finding contrasts with prior work on V/Mn ratios as a (paleo)redox proxy, implying that further research is necessary.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 238-253"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of microbial alteration of oceanic crust on sulfur cycling in hydrothermal systems","authors":"Sarah N. Moriarty ,&nbsp;Emma Bertran ,&nbsp;James W. Dottin III ,&nbsp;James Farquhar ,&nbsp;David T. Johnston ,&nbsp;Stephen J. Piercey ,&nbsp;Dennis Sánchez-Mora ,&nbsp;Michael G. Babechuk ,&nbsp;Jason B. Sylvan ,&nbsp;John W. Jamieson","doi":"10.1016/j.gca.2024.11.031","DOIUrl":"10.1016/j.gca.2024.11.031","url":null,"abstract":"<div><div>The accumulation of continental-derived sediment along mid-ocean ridges can influence sub-seafloor hydrothermal fluid circulation, including fluid composition, and the composition of associated mineral accumulations at the seafloor. The intermediate spreading-rate Juan de Fuca Ridge, off the west coast of North America, hosts both sedimented and sediment-free hydrothermal systems (Middle Valley and Axial Volcano, respectively), as well a hydrothermal system which occurs at the outer extent of continental-derived turbiditic sediment accumulation (Endeavour Hydrothermal Vent Field). The seafloor at Endeavour is mostly sediment-free and consists of basaltic lava flows. However, previously reported hydrothermal vent fluid compositions suggest the presence of buried sediment. Here, we compare S isotope ratios (³³S/³²S and ³⁴S/³²S) of hydrothermal chimney and talus samples, as well as sediments, from these three varyingly sedimented hydrothermal sites on the Juan de Fuca Ridge to S isotope ratios from hydrothermal deposits along the fast spreading archetypical East Pacific Rise in order to investigate the geological controls and microbial influence on hydrothermal S cycling. Using a combined isotopic mixing and fractionation model in Δ³³S and δ³⁴S space, we demonstrate that reduced S within sediments does not provide a significant contribution to the S budget of hydrothermal systems in sedimented environments on the Juan de Fuca Ridge. Instead, our data indicate that variations in S isotope compositions within and between vent fields reflects different degrees of sub-seafloor microbial crustal alteration and kinetic fractionations associated with reduction of seawater sulfate. The degree of microbially induced S isotope fractionation can be linked to intensity of crustal alteration and therefore age of the hydrothermal system. Our results illustrate the added value of a multiple S isotope approach to investigating S cycling in hydrothermal systems, and that the influence of microbial activity on hydrothermal systems extends well below the seafloor.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 107-121"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683558","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":"Element Redistribution and Age Resetting in Shock-Deformed Zircon from the Chicxulub Impact Structure","authors":"Jiawei Zhao ,&nbsp;Long Xiao ,&nbsp;Zhiyong Xiao ,&nbsp;Xiang Wu ,&nbsp;Qi He ,&nbsp;Jialong Hao ,&nbsp;Ruiying Li ,&nbsp;Yangting Lin","doi":"10.1016/j.gca.2025.01.021","DOIUrl":"10.1016/j.gca.2025.01.021","url":null,"abstract":"<div><div>Zircon has been used to chronicle the geological evolution of the Earth and other planetary bodies. In some circumstances the U-Pb radioisotopic system in zircon can be completely reset by shock metamorphism (e.g. high-pressure phase formation and reversion, and recrystallization), erasing the initial crystallization record and instead recording the impact age. These behaviors of element redistribution accompanied with structure variation in shocked zircon provide pivotal evidence to unravel the extreme impact processes. However, the contributions from a variety of shock effects to element redistribution within shocked zircons are not clear due to the complicated and protracted metamorphic processes associated with an impact event. Here we use high-resolution Nano secondary ion mass spectrometry (NanoSIMS) to show that zircon grains from the Chicxulub impact structure that contain microstructural features such as planar/irregular fractures, zircon twins, reidite and zircon granules, record three main types of element redistribution processes related to shock metamorphism and post-impact modification. The first is the preferential yttrium (Y) enrichments at the zircon-reidite boundaries that is closely related to the formation of the high-pressure polymorph reidite, but the primary zoning is preserved in reidite-bearing zircon. The second process involves shock-related heating, resulting in the solid-state transformation from reidite-bearing zircon to granular zircon, and the growth of neo-formed zircon granules. This process facilitates the loss of radiogenic lead (Pb) and allows the retain of primary zoning of uranium (U) in granular zircon due to the different element diffusion properties, thus providing the chance to date the impact event. Thirdly, the studied zircon grains within the Chicxulub impact structure experienced post-impact hydrothermal alteration to varying degrees by localized element incorporation of additional yttrium (Y), titanium (Ti), uranium (U), lead (Pb) and phosphorus (P). The U-Pb systematics altered by post-impact hydrothermal processes reveal a generally discordant line affected by the external input of U and common Pb, which could be an alternative mechanism of localized age resetting happened in shocked zircon grains. Particularly, this study demonstrates the systematic characteristics of element redistribution in shocked zircons that experienced the sequential metamorphic processes from reidite formation to growth of zircon granules, and subsequent hydrothermal alteration within the Chicxulub impact structure. These findings provide the effective constraints for behaviors and mechanisms of element redistribution and age resetting in zircon under extreme shock and post-impact metamorphic conditions in terrestrial impact craters.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 219-237"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684049","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":"Mechanism of mineral adsorption enhancing the reduction of hexavalent chromium by natural organic matter","authors":"Peng Zhang ,&nbsp;Yiran Liu ,&nbsp;Yingxiao Tian ,&nbsp;Chenglong Yu ,&nbsp;Songhu Yuan","doi":"10.1016/j.gca.2025.03.011","DOIUrl":"10.1016/j.gca.2025.03.011","url":null,"abstract":"<div><div>Natural organic matter (NOM) serves a crucial electron reservoir for the reduction of hexavalent chromium (Cr(VI)) in subsurface environments. However, the influence of mineral adsorption on Cr(VI) reduction by NOM remains poorly understood, despite the widespread interaction among NOM, mineral matrices and Cr(VI) in natural environments. In this study, aluminum oxides (Al₂O₃) and Fe oxyhydroxides (such as ferrihydrite) were chosen as representative minerals to investigate how mineral adsorption influences on the reduction of Cr(VI) by both native and reduced NOM across a pH range of 5–9. Results of this study showed that the extent of Cr(VI) reduction (10 μM) was 1.5–11.1 % in the native NOM (12 mg/L) system, while it increased to 10.6–19.4 % in the native NOM-Al₂O₃ systems and to 19.4–25.4 % in the native NOM-ferrihydrite systems. Similarly, the extent of Cr(VI) reduction was 16.7–23.1 % in the reduced NOM system, while it increased to 17.5–38.3 % in the reduced NOM-Al₂O₃ systems and to 30–54.9 % in the reduced NOM-ferrihydrite systems. This enhancement effect increased with higher amounts of Al₂O₃ and ferrihydrite but diminished as the solution pH increased from 5 to 9. The enhancement of Cr(VI) reduction by Fe oxyhydroxides at the same dosage followed by the sequence: ferrihydrite &gt; lepidocrocite &gt; goethite &gt; hematite. In NOM system alone, phenolic moieties in NOM mainly contributed to Cr(VI) reduction. In NOM-Al₂O₃/Fe oxyhydroxide systems, mineral adsorption shifted the reaction site from solution phase to mineral surface, subsequently inducing oxidative polymerization of polyphenolic compounds in NOM, which generated more phenolic moieties that further facilitated the reduction of Cr(VI). Additionally, Fe oxyhydroxides served as electron shuttles, facilitating electron transfer from NOM to Cr(VI). This study highlights a previously unrecognized catalytic role of mineral adsorption in enhancing Cr(VI) reduction by NOM in subsurface environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 32-43"},"PeriodicalIF":4.5,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643488","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}