Geochimica et Cosmochimica Acta最新文献

{"title":"Boron isotopic and mineral chemical composition in greisen-related Li-Fe micas: Pathways and mechanisms for hydrothermal lithium enrichment","authors":"Dino Leopardi , Axel Gerdes , Richard Albert , Joachim Krause , Jens Gutzmer , Bernd Lehmann , Mathias Burisch","doi":"10.1016/j.gca.2025.05.028","DOIUrl":"10.1016/j.gca.2025.05.028","url":null,"abstract":"<div><div>We present electron probe micro analyses (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mineral chemistry and B-isotope data for magmatic and hydrothermal Li-Fe micas of the granite-related Sn-W-Li Sadisdorf greisen system in the Erzgebirge, Germany. These mineral-specific data were combined with novel <em>in-situ</em> mica and whole-rock powder-pellet LA-ICP multi-collector mass spectrometry (MC-MS) B-isotope data to understand the magmatic and hydrothermal processes controlling the distribution and local enrichment of Li, Sn, and W. Igneous Li-Fe micas range from Li-bearing annite to zinnwaldite in composition. They are enriched in Li, as well as Rb, F, and Cs, with contents increasing with progressive magmatic fractionation. The concurrent decrease of concentrations of Nb, Ti, W, and Sn in Li-Fe micas is attributed to the efficient partitioning of these metals into coeval minor and trace minerals. Greisen- and vein-hosted hydrothermal micas of the main and waning hydrothermal stages have zinnwaldite and Li-phengite compositions, respectively. Hydrothermal zinnwaldite is enriched in fluid mobile elements such as Li, Zn and Mn, whereas Sn and W are slightly depleted relative to magmatic Li-Fe micas. Higher concentrations of Mg, Ba and V are observed in micas in a distal position, compared to those occurring in veins more proximally or within the Sadisdorf intrusion. Since the metasedimentary host rocks have higher concentrations of these elements as compared to the granites, their increased abundance is tentatively attributed to fluid-rock interaction processes. Similarly, estimated relative fluid activities of most elements systematically decrease towards paragenetically younger generations of hydrothermal micas, indicating that significant dilution or element depletion occurred during the waning stage of the magmatic-hydrothermal mineral system.</div><div>In addition to mica trace element data, decreasing average whole-rock δ<sup>11</sup>B from −12.4 ‰ in the older syenogranite to −15.0 ‰ in the younger microgranite at the Sadisdorf prospect suggest degassing occurred between consecutive magmatic stages, concomitantly to magmatic fractionation. The boron isotope composition of hydrothermal micas ranges from −27.0 to −9.5 ‰ δ<sup>11</sup>B in the proximal greisen to –23.6 and −14.6 ‰ δ<sup>11</sup>B in distal oxide-sulfide veins. Quantitative isotopic modelling indicates that the observed variations in mineral chemistry are mainly controlled by magmatic fractionation as well as cooling of the magmatic-hydrothermal fluid, whereas intra-sample variations are likely a result of local fluid-mineral equilibria and Rayleigh fractionation. Our results show that Li enrichment in metasomatic greisen systems is a result of magmatic and hydrothermal processes. During the early stages of greisenization, local changes between fluid- and rock-buffered conditions and cooling prevailed, whereas progressive mixing ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 72-93"},"PeriodicalIF":4.5,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144177594","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 role of the melt aluminum saturation index in controlling gold and molybdenum proportions in porphyry copper deposits: An experimental investigation","authors":"Jianping Li, A.E. Williams-Jones, Xing Ding, Ziqi Jiang, Huayong Chen","doi":"10.1016/j.gca.2025.05.025","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.025","url":null,"abstract":"Partition coefficients for Cu, Au and Mo between an aqueous fluid (∼ 4–16 wt% NaCl eq.) and felsic melts, were determined experimentally to better constrain the enrichment of these metals during magmatic fluid exsolution in porphyry copper systems. The experiments were conducted with a variety of melt and fluid compositions at 850 ℃, 200 MPa and an oxygen fugacity approximating that of the Ni-NiO buffer. The results show that at a total chlorinity of 1 mol/kg H<ce:inf loc=\"post\">2</ce:inf>O, the values of D<ce:sup loc=\"post\">fluid/melt</ce:sup><ce:inf loc=\"post\">Cu</ce:inf>, D<ce:sup loc=\"post\">fluid/melt</ce:sup><ce:inf loc=\"post\">Au</ce:inf> and D<ce:sup loc=\"post\">fluid/melt</ce:sup><ce:inf loc=\"post\">Mo</ce:inf> are ∼ 7.5–27.7, ∼ 1.2–41.2 and ∼ 0.5–2.7, respectively, and that these values vary as function of the melt aluminum saturation index (ASI). For a fixed starting glass composition with an ASI of 1.02 and a fluid with a total chlorinity that increases from 1 to 4 mol/kg H<ce:inf loc=\"post\">2</ce:inf>O, the D<ce:sup loc=\"post\">fluid/melt</ce:sup><ce:inf loc=\"post\">Cu</ce:inf> and D<ce:sup loc=\"post\">fluid/melt</ce:sup><ce:inf loc=\"post\">Au</ce:inf> values increase from 27.7 to 68.8 and from 26.1 to 45.6, respectively, whereas the D<ce:sup loc=\"post\">fluid/melt</ce:sup><ce:inf loc=\"post\">Mo</ce:inf> value increases from 0.6 to 2.6. Rayleigh fractionation modeling of fluid exsolution from an oxidized (<ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>＞∼ FMQ + 2) and sulfide-poor arc magma using these data shows that the ratios involving Cu, Au and Mo in porphyry copper deposits are controlled by the ASI of the melt. Exsolution of a low chlorinity magmatic fluid from a metaluminous to weakly peraluminous magma (ASI= ∼ 1–1.1) will produce a fluid with a high Au/Cu ratio fluid and a Cu-Au porphyry deposit, whereas a strongly peraluminous (ASI＞1.1) magma will produce a low Au/Cu ratio fluid and a Cu porphyry deposit. In contrast, both metaluminous and strongly peraluminous silicate magmas (ASI ∼ 1.0 or ASI＞1.2) will exsolve fluids with high Mo/Cu (or Mo/Au) ratios. Varying the initial chlorinity of the exsolved fluid from ∼ 1 to 4 mol/kg H<ce:inf loc=\"post\">2</ce:inf>O and the initial H<ce:inf loc=\"post\">2</ce:inf>O content of the magma have little effect on the selective partitioning of Cu, Au and Mo into the exsolved fluid, and also an insignificant effect on the bulk Au/Cu and Mo/Cu ratios of the hydrothermal ore systems.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"43 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144304934","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":"Reactive iron controls sulfur partitioning between pyrite and organic matter in sedimentary rocks","authors":"Hadar Cohen-Sadon ,&nbsp;Yoav Oved Rosenberg ,&nbsp;Simon Emmanuel ,&nbsp;Shimon Feinstein ,&nbsp;Alon Amrani","doi":"10.1016/j.gca.2025.05.027","DOIUrl":"10.1016/j.gca.2025.05.027","url":null,"abstract":"<div><div>Sulfur isotopic values (δ³⁴S) of pyrite and organic matter (OM) in sediments are widely used for the reconstruction of the sulfur and oxygen cycles as well as pathways of OM preservation. Currently, significant uncertainties persist regarding the mechanism by which sulfur is partitioned between pyrite and OM and its effect on the δ³⁴S record of rocks. Here, we present experimental analysis of iron, carbon, sulfur and δ³⁴S values in marine and lacustrine rock samples. The experimental data was compared with published data of rock samples from the Mesoproterozoic era (1.6 Ga) to the Paleogene period (23 Ma). We also developed a kinetic model to simulate the evolution of δ³⁴S of pyrite and OM under different environmental conditions. Our analysis reveals linear relationships between δ³⁴S value of pyrite and its isotopic difference from δ³⁴S value of organic sulfur (R² ranging from 0.43 to 0.96) for large δ³⁴S ranges of pyrite (110 ‰) and organic sulfur (93 ‰). These ranges and linear trends cannot be explained by variations in the δ³⁴S value of seawater sulfate or by the isotopic fractionation associated with microbial sulfate reduction. Rather, local conditions that change the ratio between reactive iron and sulfate are shown to control the δ³⁴S values of organic sulfur and pyrite and their isotopic gap. This is because reactive iron pyritization rapidly captures isotopically light H₂S generated by microbial sulfate reducers in the early stages of diagenesis, leaving behind heavy H₂S that reacts with OM. In some environments, the isotopic gap between organic sulfur and pyrite correlates with the OM content in the rock, reflecting the critical role of reactive iron in OM preservation via sulfurization. Hence, the role of iron on the partitioning of sulfur between OM and pyrite in sedimentary environments is essential for reconstructing the sulfur cycle and its interaction with the carbon cycle in geological sequences.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 18-31"},"PeriodicalIF":4.5,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144168324","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":"Shock metamorphic effects in phosphates from ordinary chondrites","authors":"E. Dobrică, V. Megevand, A.N. Krot, A.J. Brearley","doi":"10.1016/j.gca.2025.05.020","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.020","url":null,"abstract":"Studies of shock metamorphic effects in apatite and merrillite in nine ordinary chondrites (OCs) of petrologic types 3.5–6 and shock metamorphic stages S1–S5 using transmission electron microscopy (TEM) reveal a correlation between the extent of brittle deformation in phosphates and the shock metamorphic stage of six host meteorites. No correlation is observed in thermally annealed and partially melted phosphates in Kyushu (L6), Paragould (L5), and Hamlet (LL3.5 − 3.9). Apatites in several shocked equilibrated (petrologic type 6) OCs show micro- and nano-scale heterogeneities in volatile elements, suggesting they were locally mobilized during shock metamorphism rather than during thermal metamorphism. In Alfianello (L6, S5) and Kyushu (L6, S5), maskelynite associated with apatite shows clear evidence for melting. We suggest that maskelynite formed during melting processes rather than solid-state deformation, which has significant implications for geochronology and reflects the time of impact rather than the crystallization age of phosphates. Our study demonstrates the inadequacy of optical microscopy methods currently applied to determine shock metamorphic stages of chondrites; incorporation of micro and nanostructural observations will improve the accuracy of these determinations. We suggest that integration of detailed observations of shock and thermal metamorphism and fluid alteration is required for a comprehensive understanding of the secondary processes that modified most small Solar System bodies.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"6 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144188965","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":"Temperature-dependent modulation of the methylation degree of (tetra)ester-linked membrane-spanning lipids in an Acidobacterium","authors":"Yufei Chen, Huan Yang, Fengfeng Zheng, Ruijie Wu, Chuanlun Zhang, B. David A. Naafs, Richard D. Pancost, Zhirui Zeng","doi":"10.1016/j.gca.2025.05.019","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.019","url":null,"abstract":"Ester-linked membrane-spanning lipids, such as <ce:italic>iso</ce:italic>-diabolic acid (<ce:italic>iso</ce:italic>-DA), are known components of some bacterial cell membranes, e.g., several species of <ce:italic>Acidobacteria</ce:italic>. However, the underlying biosynthetic mechanism and the physiological function of <ce:italic>iso</ce:italic>-DA remain elusive. In this study, we identified ester-linked membrane-spanning lipids, <ce:italic>iso</ce:italic>-diabolic-based tetraesters (<ce:italic>iso</ce:italic>-DTs) and their derivatives including C-6 methylated homologues, synthesized by the <ce:italic>Acidobacterium Candidatus</ce:italic> Koribacter versatilis Ellin345. We demonstrate that in this bacterium <ce:italic>iso</ce:italic>-DA is derived as a hydrolyzed or degradation product of <ce:italic>iso</ce:italic>-DT rather than being a building block for membrane-spanning lipids, as previously proposed. Moreover, we observed a positive correlation between the growth temperature of <ce:italic>Ca.</ce:italic> Koribacter versatilis and the C-6 <ce:underline>M</ce:underline>ethylation index of <ce:italic>iso</ce:italic>-<ce:underline>D</ce:underline>iabolic <ce:underline>T</ce:underline>etraesters (MDT<ce:inf loc=\"post\">6ME</ce:inf>)/<ce:underline>A</ce:underline>cids (MDA<ce:inf loc=\"post\">6ME</ce:inf>) in our cultures (grown between 10 and 25 °C). These correlations were like those observed between temperature and the degree of methylation of branched glycerol dialkyl glycerol tetraethers (e.g., MBT′<ce:inf loc=\"post\">5ME</ce:inf>) observed in cultures of another <ce:italic>Acidobacterium</ce:italic> as well as environmental samples. These results suggest a similar temperature-dependent physiological characteristic between ester- and ether-linked membrane-spanning lipids. Overall, this study provides insight into the physiological modulation for the methylation of different types of bacterial membrane-spanning lipids and further suggests its potential as a temperature indicator in environmental investigations.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"2 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144237375","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":"Self-organizational origin of oscillatory zoning in pyrite: A coupled diffusion–reaction model and pH-dependent As adsorption feedback mechanism","authors":"Wenhong Johnson Qiu, Mei-Fu Zhou","doi":"10.1016/j.gca.2025.05.021","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.021","url":null,"abstract":"Pyrite from hydrothermal deposits often exhibits oscillatory zoning, controlling the distribution of trace elements, like As and Au. The origin of this zonal pattern has long been debated between episodic fluid changes and local chemical disequilibrium. Our study of an epithermal Pb-Zn deposit reveals arsenic oscillatory zonation in monocrystalline pyrite grains. Guided by the results of examination and the fact that As can be adsorbed onto pyrite under high pH conditions, inhibiting crystallization, we propose a quantitative diffusion–reaction model to numerically simulate the formation of oscillatory zoning in pyrite. The simulation reveals that in As-bearing supersaturated hydrothermal fluids, pyrite growth consumes HS&lt;ce:sup loc=\"post\"&gt;−&lt;/ce:sup&gt; and releases H&lt;ce:sup loc=\"post\"&gt;+&lt;/ce:sup&gt;, reducing As adsorption and accelerating crystallization. With Fe&lt;ce:sup loc=\"post\"&gt;2+&lt;/ce:sup&gt; on the crystal surface rapidly consumed, growth speed of pyrite is reduced to allow As to be adsorbed and thus to inhibit growth. This cycle restarts as Fe&lt;ce:sup loc=\"post\"&gt;2+&lt;/ce:sup&gt; is replenished from the enveloping bulk fluid via diffusion, leading to periodic growth and As adsorption. The formation of As-oscillatory zoning in pyrite is resultant from a fine balance between multiple parameters in environments, including diffusion coefficients (&lt;mml:math altimg=\"si10.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;D&lt;/mml:mi&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;Fe&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mrow&gt;&lt;mml:mn&gt;2&lt;/mml:mn&gt;&lt;mml:mo&gt;+&lt;/mml:mo&gt;&lt;/mml:mrow&gt;&lt;/mml:msup&gt;&lt;/mml:msub&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt; and &lt;mml:math altimg=\"si11.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;D&lt;/mml:mi&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi&gt;H&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mo&gt;+&lt;/mml:mo&gt;&lt;/mml:msup&gt;&lt;/mml:msub&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt;) and concentrations (&lt;mml:math altimg=\"si45.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;C&lt;/mml:mi&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;Fe&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mrow&gt;&lt;mml:mn&gt;2&lt;/mml:mn&gt;&lt;mml:mo&gt;+&lt;/mml:mo&gt;&lt;/mml:mrow&gt;&lt;/mml:msup&gt;&lt;/mml:msub&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt;, &lt;mml:math altimg=\"si62.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;C&lt;/mml:mi&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;HS&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mo&gt;-&lt;/mml:mo&gt;&lt;/mml:msup&gt;&lt;/mml:msub&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt;, &lt;mml:math altimg=\"si46.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;C&lt;/mml:mi&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi&gt;H&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mo&gt;+&lt;/mml:mo&gt;&lt;/mml:msup&gt;&lt;/mml:msub&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt;) of ions, pH, temperature and hydrodynamic conditions. The simulation reveals that slightly acidic (e.g., pH = ∼4) As-bearing supersaturated epithermal environments (&lt;∼180 °C) with &lt;mml:math altimg=\"si62.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;C&lt;/mml:mi&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;HS&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mo&gt;-&lt;/mml:mo&gt;&lt;/mml:msup&gt;&lt;/mml:msub&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt;(e.g., ∼30 mM) higher than &lt;mml:math altimg=\"si45.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;C&lt;/mml:mi&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;Fe&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mrow&gt;&lt;mml:mn&gt;2&lt;/mml:mn&gt;&lt;mml:mo&gt;+","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"37 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144188966","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 molecular weight-dependent redox capacity of soil dissolved organic matter: Roles of aromaticity and organic sulfur","authors":"Jiang Xiao, Zhenqing Shi, Fu Liu, Qianting Ye, Lanlan Zhu, Quan Gao, Xin Yang, Paul G. Tratnyek","doi":"10.1016/j.gca.2025.05.018","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.018","url":null,"abstract":"The redox capacities of soil DOM regulate the oxidation–reduction reactions by accepting or donating electrons, which influences a variety of critical redox processes such as greenhouse gas emissions and the (bio)geochemical cycle of contaminants. The composition and reactivity of DOM components vary with their molecular weight (MW), and, therefore, the redox capacities of soil DOM are expected to depend on the MW. However, the limited data that are available on how specific molecular compositions affect the MW-dependent soil DOM redox capacities are inconclusive. In this study, we investigated how soil DOM fractions, separated according to their MW, differed in redox capacity as quantified with electron accepting and donating capacity, and evaluated the relationships between redox capacity of DOM fractions and their optical indices and molecular compositions. As expected, with increasing MW, aromaticity of DOM fractions increased and aliphaticity and protein-like composition decreased, which were measured with Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS) and the optical methods. For the high MW fraction, electron-accepting capacity (EAC) as measured by mediated chronoamperometry was positively correlated with condensed aromatics and polyphenol content and negatively correlated with aliphatic content. More interestingly, our data show that electron-donating capacity (EDC) correlated with sulfur-containing components of the low MW fraction but did not show any correlations with other molecular compounds/properties of soil DOM. Our results highlight the importance of considering both aromaticity and organic sulfur and integrating the molecular information of soil DOM (e.g., MW) for predicting soil DOM redox capacities.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"23 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133756","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 link between seawater magnesium concentrations and anhydrite formation in the ocean crust","authors":"Angus Fotherby, Harold J. Bradbury, Benjamin Tutolo, Danielle Santiago Ramos, Eoin P. Walsh, Alexandra V. Turchyn","doi":"10.1016/j.gca.2025.05.016","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.016","url":null,"abstract":"Subseafloor hydrothermal systems exert a strong control on the chemical composition of the ocean. Likewise, the chemical composition of the ocean impacts the chemical and physical reactions that happen during hydrothermal circulation, although this has been less well considered. We present a 2D model of basalt alteration under hydrothermal conditions, exploring how changes in major seawater ion concentration over geologic time affect anhydrite (CaSO<ce:inf loc=\"post\">4</ce:inf>) formation in the oceanic crust. Anhydrite precipitation plays a key role in influencing the permeability structure of the ocean crust and acts as a sink for sulfur in the global biogeochemical sulfur cycle, one of the major biogeochemical cycles that regulates Earth’s redox state over geologic time. We develop a fully-coupled 2D reactive transport model to simulate the alteration of fresh mid-ocean ridge basalt by circulating seawater. We verify the model by comparing it to measured vent fluid chemistry and associated alteration mineralogy observed in modern drill cores. We then conduct a series of experiments, systematically changing the chemical composition of seawater to evaluate the impact these changes have on alteration and anhydrite formation. Model results support that the largest controls on the amount of anhydrite precipitation in the oceanic crust are sulfate and calcium concentrations in the ocean, and show that magnesium concentrations exert a strong control on the depth and distribution of anhydrite precipitation. The model results suggest that with the chemistry of certain oceans—in particular low magnesium-calcium ratios and higher magnesium and sulfate concentrations—there may have been significantly shallower anhydrite precipitation, with implications for the permeability structure of the crust and therefore extent of hydrothermal alteration. We suggest that the shallowing of the depth of anhydrite precipitation due to higher magnesium concentrations is via the impact of higher seawater magnesium concentrations on clay formation, which also modulates the pH of fluids during hydrothermal circulation. We speculate that, over Earth’s history, changes in the seawater magnesium, sulfate, and calcium concentrations may have influenced the amount and distribution of anhydrite in hydrothermally altered ocean crust, thus affecting crustal permeability structures, with consequences for key global biogeochemical cycles (e.g. sulfur, calcium).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"21 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144237377","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":"Transition from kinetic to equilibrium Zr isotope fractionations during magma crystallization","authors":"Zhen-Xin Li ,&nbsp;Shao-Bing Zhang ,&nbsp;Yong-Fei Zheng ,&nbsp;Michael A. Antonelli ,&nbsp;Wen Zhang ,&nbsp;Liang Zhang ,&nbsp;Fang-Yuan Sun ,&nbsp;Ting Liang","doi":"10.1016/j.gca.2025.05.017","DOIUrl":"10.1016/j.gca.2025.05.017","url":null,"abstract":"<div><div>Zirconium (Zr) isotopes are an emerging tool to study igneous processes. However, Zr isotope fractionation mechanisms are debated, especially regarding the relative roles of kinetic and equilibrium effects. Here, we report high-precision <em>in-situ</em> Zr isotope (δ⁹⁴Zr) measurements in zircons from granitoids with ages of 3.4 to 2.5 Ga. The δ⁹⁴Zr values in all magmatic zircons range from −0.63 to + 0.41 ‰. These zircons show negative correlations between δ⁹⁴Zr values and Zr/Hf ratios, indicating that the crystallization of zircon plays an important role in Zr isotope variations. However, our calculations suggest that neither fractional crystallization of zircon under equilibrium conditions nor that with a fixed kinetic effect cannot explain the δ⁹⁴Zr values observed in our zircons. Combined with theoretical models of crystal growth, we propose that the fractionation mechanisms evolve from diffusion-dominated situations in the early stage to equilibrium-controlled conditions in the later stage of a zircon population’s crystallization history. Our modelling results suggest that a gradual shift from diffusive-kinetic (growth-related) fractionation to near-equilibrium fractionation best explains our results. Zr isotopes, therefore, have the potential to probe the crystallization kinetics of high-temperature processes that are otherwise inaccessible to direct observation.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 1-17"},"PeriodicalIF":4.5,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144116927","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 dual origin of granites from fluid-absent and fluid-fluxed melting of the juvenile lower crust: New constraints from Mo isotopes and phase equilibrium modeling","authors":"You-Shan Xia, Guo-Chao Sun, Peng Gao, Zi-Fu Zhao, Yao Zhou, Zhen-Xin Li, Gang Wen, Lei Qin","doi":"10.1016/j.gca.2025.05.013","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.013","url":null,"abstract":"Water plays a pivotal role in the differentiation of continental crust and the formation of granitic magmas. However, it is still hotly debated how to identify fluid regimes during crustal anatexis. Molybdenum (Mo) isotopes have shown the potential to trace fluid activity during magmatic and metamorphic processes and thus are a valuable tool to identify the presence of free fluid during crustal anatexis. This is exemplified by our previous study on the Early Paleozoic sodic adakitic rocks from the Dabie orogen, eastern China, which were explained to originate from fluid-fluxed melting of juvenile crust based on their Mo isotope characteristics. However, the Early Paleozoic potassic granites (K&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O/Na&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O = 0.81–1.13) in the Dabie orogen—spatially and temporally associated with sodic granites—exhibit distinct geochemical signatures (e.g., higher K&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O/Na&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O ratios and lower Sr/Y, La/Yb ratios). Sr–Nd isotope results indicate that the potassic granites originate from the juvenile lower crust, consistent with the sodic granites. To evaluate the controlling factors behind the geochemical differences between the two groups of granites, we conducted whole-rock Mo isotope analyses of the potassic granites and compared them with the sodic granites and coeval mafic rocks. The results reveal that the potassic granites exhibit δ&lt;ce:sup loc=\"post\"&gt;98&lt;/ce:sup&gt;Mo values (–0.41 to 0.23 ‰, median = 0.02 ‰) similar to adjacent contemporaneous mafic rocks (–0.17 to 0.21 ‰, median = 0.02 ‰), whereas the sodic granites display systematically higher δ&lt;ce:sup loc=\"post\"&gt;98&lt;/ce:sup&gt;Mo values (–0.13 to 0.74 ‰, median = 0.22 ‰). Simulation calculations indicate that neither pure fractional crystallization (FC) nor AFC (assimilation-FC) process can account for the observed differences in K&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O/Na&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O ratios and Mo isotope compositions between the potassic and sodic granites. Instead, such differences can be well explained by partial melting of the same mafic source rocks at different fluid regimes. Further phase equilibrium modeling indicates that the addition of fluids can promote preferential plagioclase breakdown and amphibole retention in the source rocks, thereby generating or amplifying high Sr/Y and La/Yb ratios in melts. In contrast, pressure variations alone cannot account for the observed K&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O/Na&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O ratio differences. These results indicate that distinct fluid regimes in the source region exert the primary control on the geochemical disparities between the two groups of granites. The fluid-fluxed melting could be caused by fluids exsolved from crystallization of the underplated hydrous mafic arc magmas or released by the breakdown of hydrous minerals in the juvenile lower crust. As a comparison, the fluid-absent melting of the mafic crust is primarily dri","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"296 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083375","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}