Pub Date : 2025-11-25DOI: 10.1016/j.gca.2025.11.043
Katharine G.D. Rose-Hull , Artaches Migdisov , Haylea Nisbet , Margaret E. Reece , Hakim Boukhalfa , Alexander Gysi , Nicole Hurtig , Chen Zhu , Alexandra Navrotsky , Hongwu Xu
The transport and enrichment of rare earth element (REE) ore bodies are dependent on the stability of aqueous metal ligand complexes and the solubility of REE bearing minerals. REE ores are commonly associated with igneous systems having aqueous fluids with high carbonate concentrations and REE solubilities have been shown to be dependent on temperature and associate anion aqueous ligands present in solution. This work presents solubility experiments of hydroxybastnäsite-(La) at elevated temperatures in aqueous solutions of varying carbonate concentrations. At lower temperatures, hydroxybastnäsite-(La) solubility is controlled by neutral mono-carbonate LaCO3OH° but at higher temperatures and activities of carbonate species, charged di-carbonate La(CO3)2- increases and predominates. This divergence, and the difference in solubility products of other hydroxybastnäsite-(REE) phases, provides a potential mechanism for REE fractionation in carbonate dominated aqueous solutions. To illustrate one such mechanism the solubility data of hydroxybastnäsite-(La) is compared with previously reported data of hydroxybastnäsite-(Nd) at elevated temperatures.
{"title":"An experimental study of synthetic Hydroxybastnäsite-(La) solubility and speciation in carbonate bearing aqueous solutions at 175–250 °C","authors":"Katharine G.D. Rose-Hull , Artaches Migdisov , Haylea Nisbet , Margaret E. Reece , Hakim Boukhalfa , Alexander Gysi , Nicole Hurtig , Chen Zhu , Alexandra Navrotsky , Hongwu Xu","doi":"10.1016/j.gca.2025.11.043","DOIUrl":"10.1016/j.gca.2025.11.043","url":null,"abstract":"<div><div>The transport and enrichment of rare earth element (REE) ore bodies are dependent on the stability of aqueous metal ligand complexes and the solubility of REE bearing minerals. REE ores are commonly associated with igneous systems having aqueous fluids with high carbonate concentrations and REE solubilities have been shown to be dependent on temperature and associate anion aqueous ligands present in solution. This work presents solubility experiments of hydroxybastnäsite-(La) at elevated temperatures in aqueous solutions of varying carbonate concentrations. At lower temperatures, hydroxybastnäsite-(La) solubility is controlled by neutral mono-carbonate LaCO<sub>3</sub>OH° but at higher temperatures and activities of carbonate species, charged di-carbonate La(CO<sub>3</sub>)<sub>2</sub><sup>-</sup> increases and predominates. This divergence, and the difference in solubility products of other hydroxybastnäsite-(REE) phases, provides a potential mechanism for REE fractionation in carbonate dominated aqueous solutions. To illustrate one such mechanism the solubility data of hydroxybastnäsite-(La) is compared with previously reported data of hydroxybastnäsite-(Nd) at elevated temperatures.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"413 ","pages":"Pages 138-146"},"PeriodicalIF":5.0,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145598961","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}
Pub Date : 2025-11-25DOI: 10.1016/j.gca.2025.11.042
Ricardo D. Monedero-Contreras , Francisca Martínez-Ruiz , Martin Frank , Ed C. Hathorne , Adina Paytan
The stable isotopic composition of barium in marine barite (δ138/134Babarite) has been proposed as a proxy for reconstructing past Ba cycling in the oceanic water column. However, whether δ138/134Babarite can also be a proxy for export productivity remains uncertain, particularly in semi-enclosed basins such as the Eastern Mediterranean (EMed). Here we present the first record of δ138/134Babarite extracted from EMed Pliocene to Holocene sapropels from six Ocean Drilling Program (ODP) Sites. Despite strong variability in Ba concentrations (∼400–4000 ppm) and organic carbon content (∼3–25 %)—reflecting varying export productivity levels—the δ138/134Babarite values show limited variation (ranging between 0.02 to −0.16 ‰), even during periods of exceptionally high inferred export productivity (e.g., during late Pleistocene sapropel S5). Consistent δ138/134Babarite values are also observed in sapropel S1 sites located at a wide range of water depths (∼900–3600 m). Well-preserved pelagic barite crystal textures (observed under scanning electron microscopy) and barite sulphur isotope composition similar to seawater (∼21 ‰; Paytan et al., 2004) in the sapropels, suggest that neither partial dissolution in bottom waters nor postdepositional Ba ion-exchange significantly altered the δ138/134Babarite signal. These results suggest that fluctuations in marine productivity had a limited impact on the dissolved Ba pool and its isotopic composition in the EMed upper water column during sapropel deposition. Instead, the EMed δ138/134Ba was likely controlled primarily by the Ba isotope composition of Atlantic Water inflow and local dissolved Ba sources, such as riverine and groundwater inputs, rather than by productivity-driven barite fluxes. This finding highlights that δ138/134Babarite in sedimentary records should not be interpreted as a straightforward proxy for export productivity, particularly in semi-restricted basins.
{"title":"Constraining the drivers of barium isotope composition in marine barite: Insights from Pliocene-Holocene Eastern Mediterranean sapropels","authors":"Ricardo D. Monedero-Contreras , Francisca Martínez-Ruiz , Martin Frank , Ed C. Hathorne , Adina Paytan","doi":"10.1016/j.gca.2025.11.042","DOIUrl":"10.1016/j.gca.2025.11.042","url":null,"abstract":"<div><div>The stable isotopic composition of barium in marine barite (<em>δ</em><sup>138/134</sup>Ba<sub>barite</sub>) has been proposed as a proxy for reconstructing past Ba cycling in the oceanic water column. However, whether <em>δ</em><sup>138/134</sup>Ba<sub>barite</sub> can also be a proxy for export productivity remains uncertain, particularly in semi-enclosed basins such as the Eastern Mediterranean (EMed). Here we present the first record of <em>δ</em><sup>138/134</sup>Ba<sub>barite</sub> extracted from EMed Pliocene to Holocene sapropels from six Ocean Drilling Program (ODP) Sites. Despite strong variability in Ba concentrations (∼400–4000 ppm) and organic carbon content (∼3–25 %)—reflecting varying export productivity levels—the <em>δ</em><sup>138/134</sup>Ba<sub>barite</sub> values show limited variation (ranging between 0.02 to −0.16 ‰), even during periods of exceptionally high inferred export productivity (e.g., during late Pleistocene sapropel S5). Consistent <em>δ</em><sup>138/134</sup>Ba<sub>barite</sub> values are also observed in sapropel S1 sites located at a wide range of water depths (∼900–3600 m). Well-preserved pelagic barite crystal textures (observed under scanning electron microscopy) and barite sulphur isotope composition similar to seawater (∼21 ‰; Paytan et al., 2004) in the sapropels, suggest that neither partial dissolution in bottom waters nor postdepositional Ba ion-exchange significantly altered the <em>δ</em><sup>138/134</sup>Ba<sub>barite</sub> signal. These results suggest that fluctuations in marine productivity had a limited impact on the dissolved Ba pool and its isotopic composition in the EMed upper water column during sapropel deposition. Instead, the EMed <em>δ</em><sup>138/134</sup>Ba was likely controlled primarily by the Ba isotope composition of Atlantic Water inflow and local dissolved Ba sources, such as riverine and groundwater inputs, rather than by productivity-driven barite fluxes. This finding highlights that <em>δ</em><sup>138/134</sup>Ba<sub>barite</sub> in sedimentary records should not be interpreted as a straightforward proxy for export productivity, particularly in semi-restricted basins.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"412 ","pages":"Pages 75-89"},"PeriodicalIF":5.0,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145593659","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}
Pub Date : 2025-11-24DOI: 10.1016/j.gca.2025.11.034
Peng-Yuan Han, Kang Chen, Roberta L. Rudnick, Zhao-Chu Hu
{"title":"Average major element composition of the upper continental crust derived from an integrated study of sedimentary and igneous rocks","authors":"Peng-Yuan Han, Kang Chen, Roberta L. Rudnick, Zhao-Chu Hu","doi":"10.1016/j.gca.2025.11.034","DOIUrl":"https://doi.org/10.1016/j.gca.2025.11.034","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"137 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145593660","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}
Pub Date : 2025-11-23DOI: 10.1016/j.gca.2025.11.040
Yifan Li , Li Zhang , Zhen-Xin Li , Hejiu Hui , Liping Qin , Yunguo Li , Huaiwei Ni
Isotope fractionation between mineral and a parental melt often deviates from the prediction by equilibrium fractionation factor (Δeq). This nonequilibrium phenomenon could be caused by two kinetic mechanisms: (1) diffusive isotope fractionation, by which light isotope diffuses faster than heavy isotope in the melt; and (2) reactive isotope fractionation, by which light isotope is associated with higher zero-point energy and tends to preferentially participate in chemical reaction. Crystal growth in silicate melt involves both element diffusion inside the melt and chemical reaction at the crystal-melt interface, but no model has dealt with the two kinetic isotope fractionation effects together. This study fills this gap by realizing that interface reaction can be modeled as short-range diffusion (as opposed to long-range diffusion inside the melt) and using a numerical approach to couple these two diffusion processes. Modeling results on the isotopic composition of the principal equilibrium-determining element for crystal growth (e.g., Ca for plagioclase growth and Zr for zircon growth) indicate that the regime of kinetic isotope fractionation is governed by a dimensionless parameter f = (DL/t)0.5/(/λ), where DL is the diffusivity of light isotope (major isotope) in the melt, is the short-range (melt-to-crystal) diffusivity of light isotope, t is the time, and λ is the jump distance. At f ≥ 10, reactive kinetic fractionation predominates, and the formed crystal is significantly depleted in heavy isotope. At f ≤ 0.1, diffusive kinetic fractionation predominates, and the formed crystal is in equilibrium fractionation with interface melt that tends to be modestly depleted in heavy isotope relative to far-field melt. In the range of 0.1 < f < 10, both diffusive and reactive kinetic isotope fractionation are effective. With the decrease of f over time, the reactive kinetic effect plays a less important role, leading to heavier isotopic composition of crystal and smaller overall kinetic isotope fractionation. The magnitude of kinetic isotope fractionation is also demonstrated to increase with increasing degree of supersaturation of the principal element in the melt. The combination of diffusive and reactive kinetic isotope fractionation can successfully explain Ca and Zr isotope fractionations observed in experimental and natural samples.
{"title":"Kinetic isotope fractionation during crystal growth","authors":"Yifan Li , Li Zhang , Zhen-Xin Li , Hejiu Hui , Liping Qin , Yunguo Li , Huaiwei Ni","doi":"10.1016/j.gca.2025.11.040","DOIUrl":"10.1016/j.gca.2025.11.040","url":null,"abstract":"<div><div>Isotope fractionation between mineral and a parental melt often deviates from the prediction by equilibrium fractionation factor (Δ<sub>eq</sub>). This nonequilibrium phenomenon could be caused by two kinetic mechanisms: (1) diffusive isotope fractionation, by which light isotope diffuses faster than heavy isotope in the melt; and (2) reactive isotope fractionation, by which light isotope is associated with higher zero-point energy and tends to preferentially participate in chemical reaction. Crystal growth in silicate melt involves both element diffusion inside the melt and chemical reaction at the crystal-melt interface, but no model has dealt with the two kinetic isotope fractionation effects together. This study fills this gap by realizing that interface reaction can be modeled as short-range diffusion (as opposed to long-range diffusion inside the melt) and using a numerical approach to couple these two diffusion processes. Modeling results on the isotopic composition of the principal equilibrium-determining element for crystal growth (e.g., Ca for plagioclase growth and Zr for zircon growth) indicate that the regime of kinetic isotope fractionation is governed by a dimensionless parameter <em>f</em> = (<em>D</em><sub>L</sub>/<em>t</em>)<sup>0.5</sup>/(<span><math><mrow><msubsup><mrow><mi>D</mi></mrow><mrow><mtext>L</mtext></mrow><mrow><mo>∗</mo><mtext>m-c</mtext></mrow></msubsup></mrow></math></span>/λ), where <em>D</em><sub>L</sub> is the diffusivity of light isotope (major isotope) in the melt, <span><math><mrow><msubsup><mrow><mi>D</mi></mrow><mrow><mtext>L</mtext></mrow><mrow><mo>∗</mo><mtext>m-c</mtext></mrow></msubsup></mrow></math></span> is the short-range (melt-to-crystal) diffusivity of light isotope, <em>t</em> is the time, and λ is the jump distance. At <em>f</em> ≥ 10, reactive kinetic fractionation predominates, and the formed crystal is significantly depleted in heavy isotope. At <em>f</em> ≤ 0.1, diffusive kinetic fractionation predominates, and the formed crystal is in equilibrium fractionation with interface melt that tends to be modestly depleted in heavy isotope relative to far-field melt. In the range of 0.1 < <em>f</em> < 10, both diffusive and reactive kinetic isotope fractionation are effective. With the decrease of <em>f</em> over time, the reactive kinetic effect plays a less important role, leading to heavier isotopic composition of crystal and smaller overall kinetic isotope fractionation. The magnitude of kinetic isotope fractionation is also demonstrated to increase with increasing degree of supersaturation of the principal element in the melt. The combination of diffusive and reactive kinetic isotope fractionation can successfully explain Ca and Zr isotope fractionations observed in experimental and natural samples.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"412 ","pages":"Pages 51-63"},"PeriodicalIF":5.0,"publicationDate":"2025-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145583844","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}
Pub Date : 2025-11-22DOI: 10.1016/j.gca.2025.11.041
Mohd Amir Husain , Andreas C. Scheinost , Ashis Biswas
<div><div>Studies have highlighted that natural organic matter (NOM) can bind arsenic (As) species by ternary complexation via a polyvalent metal cation (M<sup>n+</sup>) bridging (As-M−NOM) and, therefore, regulate As mobility at the soil/sediment–water interface. Ferric iron (Fe(III)) has been identified as a key bridging metal ion for such complexation. However, high As in natural waters often coexist with high concentrations of ferrous iron (Fe(II)) instead of Fe(III), together with dissolved organic matter (DOM). Therefore, it is important to assess whether Fe(II) can induce a similar complexation of As species with DOM to understand the complete role of As-DOM interactions in As mobility. Despite its importance, the possible role of Fe(II) in the As-DOM interactions has not been thoroughly investigated. Therefore, we incubated arsenite (As(III)) with the original and hydrogenated Leonardite Humic Acid (LHA) and Suwannee River aquatic DOM (SRNOM) in the presence of varying concentrations of Fe(II) to determine the extent of binding onto DOM under anoxic conditions. The role played by Fe(II) in the As binding was determined by the As and Fe K-edge X-ray absorption spectroscopic (XAS) analysis of the As-Fe-DOM complexes. Results show that the co-occurrence of arsenite, Fe(II), and DOM in water induces considerable As bindings onto DOM; the extent of As bindings positively correlates with the amount of Fe bound with the DOM. The XAS analysis demonstrated that As is bound with DOM due to As-Fe-DOM ternary complexation, specifically, via bidentate mononuclear (<em><sup>1</sup>E</em>) (R<sub>As···Fe</sub>: 2.93 Å) and bidentate binuclear (<em><sup>2</sup>C</em>) (R<sub>As···Fe</sub>: 3.35 ± 0.08 Å) complexation of As with the organically bound monomeric Fe(O,OH)<sub>6</sub> octahedra, in addition to direct binary complexation of As with the O-containing functional moieties (e.g., –COOH and –OH) (R<sub>As···C</sub>: 2.76 ± 0.01 Å) of the DOM. Although arsenite mostly maintains its oxidation state in such complexations, the possibility of its oxidation to arsenate by the DOM cannot be neglected. Interestingly, although incubations were performed with Fe(II), the redox speciation of Fe in the As-Fe-DOM complexes was dominated by Fe(III), suggesting that Fe(II) was oxidized to Fe(III) by the DOM, even by the hydrogenated DOMs, during incubations under anoxic conditions. We attribute the oxidation of Fe(II) to Fe(III) to gain a higher stability of the As-Fe-DOM complexes because Fe(III) forms stronger complexes than Fe(II) with the O-containing groups of the DOM. The tendency to gain extra stability can also explain the occasionally observed oxidation of arsenite to arsenate during direct complexation with the O-containing functional groups of the DOM. The formed As-Fe-DOM complexes are mostly of colloidal size. Overall, the present study implicates that the co-occurrences of arsenite, Fe(II), and DOM can induce Fe(III)-bridged ternary complexation of A
{"title":"Dissolved organic matter oxidizes ferrous iron and forms colloidal ternary complexes with arsenic via ferric iron bridging in water under anoxic conditions","authors":"Mohd Amir Husain , Andreas C. Scheinost , Ashis Biswas","doi":"10.1016/j.gca.2025.11.041","DOIUrl":"10.1016/j.gca.2025.11.041","url":null,"abstract":"<div><div>Studies have highlighted that natural organic matter (NOM) can bind arsenic (As) species by ternary complexation via a polyvalent metal cation (M<sup>n+</sup>) bridging (As-M−NOM) and, therefore, regulate As mobility at the soil/sediment–water interface. Ferric iron (Fe(III)) has been identified as a key bridging metal ion for such complexation. However, high As in natural waters often coexist with high concentrations of ferrous iron (Fe(II)) instead of Fe(III), together with dissolved organic matter (DOM). Therefore, it is important to assess whether Fe(II) can induce a similar complexation of As species with DOM to understand the complete role of As-DOM interactions in As mobility. Despite its importance, the possible role of Fe(II) in the As-DOM interactions has not been thoroughly investigated. Therefore, we incubated arsenite (As(III)) with the original and hydrogenated Leonardite Humic Acid (LHA) and Suwannee River aquatic DOM (SRNOM) in the presence of varying concentrations of Fe(II) to determine the extent of binding onto DOM under anoxic conditions. The role played by Fe(II) in the As binding was determined by the As and Fe K-edge X-ray absorption spectroscopic (XAS) analysis of the As-Fe-DOM complexes. Results show that the co-occurrence of arsenite, Fe(II), and DOM in water induces considerable As bindings onto DOM; the extent of As bindings positively correlates with the amount of Fe bound with the DOM. The XAS analysis demonstrated that As is bound with DOM due to As-Fe-DOM ternary complexation, specifically, via bidentate mononuclear (<em><sup>1</sup>E</em>) (R<sub>As···Fe</sub>: 2.93 Å) and bidentate binuclear (<em><sup>2</sup>C</em>) (R<sub>As···Fe</sub>: 3.35 ± 0.08 Å) complexation of As with the organically bound monomeric Fe(O,OH)<sub>6</sub> octahedra, in addition to direct binary complexation of As with the O-containing functional moieties (e.g., –COOH and –OH) (R<sub>As···C</sub>: 2.76 ± 0.01 Å) of the DOM. Although arsenite mostly maintains its oxidation state in such complexations, the possibility of its oxidation to arsenate by the DOM cannot be neglected. Interestingly, although incubations were performed with Fe(II), the redox speciation of Fe in the As-Fe-DOM complexes was dominated by Fe(III), suggesting that Fe(II) was oxidized to Fe(III) by the DOM, even by the hydrogenated DOMs, during incubations under anoxic conditions. We attribute the oxidation of Fe(II) to Fe(III) to gain a higher stability of the As-Fe-DOM complexes because Fe(III) forms stronger complexes than Fe(II) with the O-containing groups of the DOM. The tendency to gain extra stability can also explain the occasionally observed oxidation of arsenite to arsenate during direct complexation with the O-containing functional groups of the DOM. The formed As-Fe-DOM complexes are mostly of colloidal size. Overall, the present study implicates that the co-occurrences of arsenite, Fe(II), and DOM can induce Fe(III)-bridged ternary complexation of A","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"413 ","pages":"Pages 122-137"},"PeriodicalIF":5.0,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575279","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}
<div><div>In arc settings, substantial amounts of S are released during volcanic eruptions or sequestered in magmatic–hydrothermal ore deposits, yet the associated silicic melts generally appear S poor. Although mafic magma recharge is considered a major additional S source, the mechanisms by which S is efficiently transferred from recharging mafic magmas into overlying silicic systems remain poorly understood. To address this mechanistic gap, we conducted a detailed petrographic study of anhydrite-bearing mafic microgranular enclaves (MMEs) from the subduction-related Yangxin pluton in the Middle-Lower Yangtze River Metallogenic Belt, China. Two types of plagioclase and amphibole crystals in the MMEs are identified based on textural and compositional characteristics, respectively. Pl<sub>A</sub> and Amp<sub>A</sub> exhibit reverse core–mantle–rim zonings (An = 24–50 to 61–81 to 20–46 and Al<sub>2</sub>O<sub>3</sub> = 6.8–7.4 wt% to 8.7–9.6 wt% to 6.7–7.8 wt%, respectively) with patchy cores in both crystals and sieve textures in Pl<sub>A</sub>, whereas Pl<sub>B</sub> and Amp<sub>B</sub> display normal core–rim zonings (An = 60–79 to 28–43 and Al<sub>2</sub>O<sub>3</sub> = 9.3–12.0 wt% to 6.0–8.7 wt%, respectively). Integrating mineral disequilibrium textures, geochemical data, and inferred amphibole equilibrium melt compositions, we propose that the MMEs originated through mingling between the host Yangxin granodioritic magma (characterized by sodic Pl<sub>A</sub> cores and low-Al Amp<sub>A</sub> cores) and a recharging, oxidized mafic magma (entraining high-Al Amp<sub>B</sub> cores). This mingling occurred within a hybrid boundary layer along the mafic–silicic interface and proceeded in two stages: (1) in the early-stage, mixed melts with more affinity to the recharging magma crystallized calcic Pl<sub>A</sub> mantles, calcic Pl<sub>B</sub> cores, and medium-Al Amp<sub>A</sub> mantles; (2) in the late-stage, progressive mingling with the overlying granodioritic magma increased the silicic affinity of the mixed melt, resulting in the development of sodic rims of Pl<sub>A</sub> and Pl<sub>B</sub>, and low-Al rims of Amp<sub>A</sub> and Amp<sub>B</sub>.</div><div>Apatite inclusion S–F–Cl and inferred OH variations in the early‐stage assemblage probably record crystallization‐induced melt S enrichment under fluid‐undersaturated conditions. The exclusive occurrence of primary anhydrite inclusions in the late-stage assemblage indicates that anhydrite saturation was achieved during this interval. Late-stage apatite inclusions likely document a transition from fluid-undersaturated to fluid-saturated conditions, with anhydrite saturation preceding fluid saturation. During aqueous fluid exsolution, crystallized anhydrite would decompose to buffer melt S at anhydrite solubility value for the given melt composition and temperature. Accordingly, the S would continuously be transferred from crystallized anhydrite into the exsolving aqueous fluids without alt
{"title":"Petrologic reconstruction of sulfur transfer processes during mafic magma recharge: Insight from anhydrite-bearing mafic microgranular enclaves","authors":"Yilun Jin , Guiqing Xie , Madeleine C.S. Humphreys , Nian Chen , Xuyang Meng , Zhaochong Zhang , Jingwen Mao","doi":"10.1016/j.gca.2025.11.037","DOIUrl":"10.1016/j.gca.2025.11.037","url":null,"abstract":"<div><div>In arc settings, substantial amounts of S are released during volcanic eruptions or sequestered in magmatic–hydrothermal ore deposits, yet the associated silicic melts generally appear S poor. Although mafic magma recharge is considered a major additional S source, the mechanisms by which S is efficiently transferred from recharging mafic magmas into overlying silicic systems remain poorly understood. To address this mechanistic gap, we conducted a detailed petrographic study of anhydrite-bearing mafic microgranular enclaves (MMEs) from the subduction-related Yangxin pluton in the Middle-Lower Yangtze River Metallogenic Belt, China. Two types of plagioclase and amphibole crystals in the MMEs are identified based on textural and compositional characteristics, respectively. Pl<sub>A</sub> and Amp<sub>A</sub> exhibit reverse core–mantle–rim zonings (An = 24–50 to 61–81 to 20–46 and Al<sub>2</sub>O<sub>3</sub> = 6.8–7.4 wt% to 8.7–9.6 wt% to 6.7–7.8 wt%, respectively) with patchy cores in both crystals and sieve textures in Pl<sub>A</sub>, whereas Pl<sub>B</sub> and Amp<sub>B</sub> display normal core–rim zonings (An = 60–79 to 28–43 and Al<sub>2</sub>O<sub>3</sub> = 9.3–12.0 wt% to 6.0–8.7 wt%, respectively). Integrating mineral disequilibrium textures, geochemical data, and inferred amphibole equilibrium melt compositions, we propose that the MMEs originated through mingling between the host Yangxin granodioritic magma (characterized by sodic Pl<sub>A</sub> cores and low-Al Amp<sub>A</sub> cores) and a recharging, oxidized mafic magma (entraining high-Al Amp<sub>B</sub> cores). This mingling occurred within a hybrid boundary layer along the mafic–silicic interface and proceeded in two stages: (1) in the early-stage, mixed melts with more affinity to the recharging magma crystallized calcic Pl<sub>A</sub> mantles, calcic Pl<sub>B</sub> cores, and medium-Al Amp<sub>A</sub> mantles; (2) in the late-stage, progressive mingling with the overlying granodioritic magma increased the silicic affinity of the mixed melt, resulting in the development of sodic rims of Pl<sub>A</sub> and Pl<sub>B</sub>, and low-Al rims of Amp<sub>A</sub> and Amp<sub>B</sub>.</div><div>Apatite inclusion S–F–Cl and inferred OH variations in the early‐stage assemblage probably record crystallization‐induced melt S enrichment under fluid‐undersaturated conditions. The exclusive occurrence of primary anhydrite inclusions in the late-stage assemblage indicates that anhydrite saturation was achieved during this interval. Late-stage apatite inclusions likely document a transition from fluid-undersaturated to fluid-saturated conditions, with anhydrite saturation preceding fluid saturation. During aqueous fluid exsolution, crystallized anhydrite would decompose to buffer melt S at anhydrite solubility value for the given melt composition and temperature. Accordingly, the S would continuously be transferred from crystallized anhydrite into the exsolving aqueous fluids without alt","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"412 ","pages":"Pages 32-50"},"PeriodicalIF":5.0,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575280","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}
Pub Date : 2025-11-22DOI: 10.1016/j.gca.2025.11.036
Yuqian Peng, Shanyu Han, Xiaobin Cao
Sulfate produced during the oxidative weathering of reduced sulfur can preserve the triple oxygen isotope signature of atmospheric O2 (Δ’17O) through the intermediate step of sulfite oxidation by O2. Because Δ’17O in O2 varies as a function of atmospheric pO2 and pCO2 and, arguably, gross primary productivity, large negative Δ’17O values in sulfate have been used to reconstruct past atmospheric composition and biospheric activity. More recently, this framework has been extended to interpret small Δ’17O variations in sulfate. For such applications, accurate constraints on both equilibrium and kinetic triple oxygen isotope fractionation during sulfite oxidation by O2 are essential. While equilibrium fractionation factors have been relatively well constrained, kinetic fractionation factors remain poorly quantified.
In this study, we employed density functional theory (DFT) to evaluate kinetic triple oxygen isotope fractionation during sulfite oxidation by O2, using classical transition state theory. We focused on the elementary reaction SO3− + O2 → SO5−, which represents a key O2 consuming step in the proposed chain reaction mechanism for sulfite oxidation in aqueous solution. Vibrational frequencies of reactants and transition states were calculated at the ωB97XD/6-311G+(2df,2p) level of theory. Our results indicate a substantial normal kinetic 18O fractionation for O2 consumption (−21.6 ± 0.6 ‰) at 25 °C, significantly different from experimental estimates (−9.8 ‰ to 23.3 ‰). This discrepancy likely arises from variations in O2 reaction reversibility under different experimental conditions, such as sulfite concentration and O2 partial pressure. If full isotopic equilibrium is achieved between O2 corresponding sites in SO5− and ambient O2, the equilibrium 18O fractionation is predicted to be −3.5 ± 0.8 ‰ at 25 °C, partially reconciling the difference between theoretical and experimental observations. The corresponding θ values for the kinetic and equilibrium scenarios (θ≡ln17KIE/ln18KIE or ln17αeq/ln18αeq) are 0.5145 ± 0.0009 and 0.5199 ± 0.0021, respectively. These results imply that the Δ’17O of O2 incorporated into sulfate could be higher by up to ∼ 0.35 ‰ relative to ambient O2, depending on reaction reversibility. Our findings highlight the importance of accounting for O2 reaction reversibility when interpreting both laboratory and geological Δ’17O signatures in sulfate.
{"title":"Theoretical evaluation of kinetic triple oxygen isotope fractionation during sulfite oxidation by atmospheric oxygen","authors":"Yuqian Peng, Shanyu Han, Xiaobin Cao","doi":"10.1016/j.gca.2025.11.036","DOIUrl":"10.1016/j.gca.2025.11.036","url":null,"abstract":"<div><div>Sulfate produced during the oxidative weathering of reduced sulfur can preserve the triple oxygen isotope signature of atmospheric O<sub>2</sub> (Δ<sup>’17</sup>O) through the intermediate step of sulfite oxidation by O<sub>2</sub>. Because Δ<sup>’17</sup>O in O<sub>2</sub> varies as a function of atmospheric pO<sub>2</sub> and pCO<sub>2</sub> and, arguably, gross primary productivity, large negative Δ<sup>’17</sup>O values in sulfate have been used to reconstruct past atmospheric composition and biospheric activity. More recently, this framework has been extended to interpret small Δ<sup>’17</sup>O variations in sulfate. For such applications, accurate constraints on both equilibrium and kinetic triple oxygen isotope fractionation during sulfite oxidation by O<sub>2</sub> are essential. While equilibrium fractionation factors have been relatively well constrained, kinetic fractionation factors remain poorly quantified.</div><div>In this study, we employed density functional theory (DFT) to evaluate kinetic triple oxygen isotope fractionation during sulfite oxidation by O<sub>2</sub>, using classical transition state theory. We focused on the elementary reaction SO<sub>3</sub><sup><img>−</sup> + O<sub>2</sub> → SO<sub>5</sub><sup><img>−</sup>, which represents a key O<sub>2</sub> consuming step in the proposed chain reaction mechanism for sulfite oxidation in aqueous solution. Vibrational frequencies of reactants and transition states were calculated at the ωB97XD/6-311G+(2df,2p) level of theory. Our results indicate a substantial normal kinetic <sup>18</sup>O fractionation for O<sub>2</sub> consumption (−21.6 ± 0.6 ‰) at 25 °C, significantly different from experimental estimates (−9.8 ‰ to 23.3 ‰). This discrepancy likely arises from variations in O<sub>2</sub> reaction reversibility under different experimental conditions, such as sulfite concentration and O<sub>2</sub> partial pressure. If full isotopic equilibrium is achieved between O<sub>2</sub> corresponding sites in SO<sub>5</sub><sup><img>−</sup> and ambient O<sub>2</sub>, the equilibrium <sup>18</sup>O fractionation is predicted to be −3.5 ± 0.8 ‰ at 25 °C, partially reconciling the difference between theoretical and experimental observations. The corresponding θ values for the kinetic and equilibrium scenarios (θ≡ln<sup>17</sup>KIE/ln<sup>18</sup>KIE or ln<sup>17</sup>α<sub>eq</sub>/ln<sup>18</sup>α<sub>eq</sub>) are 0.5145 ± 0.0009 and 0.5199 ± 0.0021, respectively. These results imply that the Δ<sup>’17</sup>O of O<sub>2</sub> incorporated into sulfate could be higher by up to ∼ 0.35 ‰ relative to ambient O<sub>2</sub><strong>,</strong> depending on reaction reversibility. Our findings highlight the importance of accounting for O<sub>2</sub> reaction reversibility when interpreting both laboratory and geological Δ<sup>’17</sup>O signatures in sulfate.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"412 ","pages":"Pages 64-74"},"PeriodicalIF":5.0,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145567821","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}
Pub Date : 2025-11-22DOI: 10.1016/j.gca.2025.11.032
Giuseppe D. Saldi , Pascale Louvat , Frank Heberling , Vasileios Mavromatis , Jacques Schott
<div><div>Adsorption of dissolved species on mineral surfaces is a key elementary process, which controls crystal growth and incorporation of trace elements into mineral structures, affecting the isotopic composition of geological archives. Changes of chemical composition of aqueous solution can induce significant variations in the type, concentration and isotopic composition of boron surface species incorporated by CaCO<sub>3</sub>. To better understand and quantify these effects, the boron isotope fractionation associated with B adsorption on calcite and aragonite was investigated in artificial seawater and equimolar solutions of NaCl (0.5 M) at room temperature and 7.5 ≤ pH<sub>NBS</sub> ≤ 11.9. Boron adsorption on aragonite was 2–4 times stronger than on calcite, in agreement with the higher affinity of aragonite for borate ions reported by previous studies. In seawater solutions at pH > 8.5, B removal from the solution increased due to increasing adsorption on both CaCO<sub>3</sub> polymorphs and coprecipitation with brucite, which was observed to form at more alkaline conditions. Boron sorption reactions on calcite and aragonite surfaces were described using the calcite three-plane model (TPM) assuming the presence of a borate inner-sphere complex (<span><math><mrow><mo>></mo><mi>B</mi><msub><mi>O</mi><mn>3</mn></msub><msubsup><mi>H</mi><mrow><mn>2</mn></mrow><mrow><mo>+</mo><mn>0.5</mn></mrow></msubsup></mrow></math></span>), formed by the replacement of B(OH)<sub>4</sub><sup>−</sup> for surface carbonate groups, and the adsorption of B(OH)<sub>4</sub><sup>−</sup> at calcium protonated sites (><span><math><mrow><msup><mrow><mo>[</mo><mi>C</mi><mi>a</mi><msubsup><mrow><mi>OH</mi></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo><mn>0.5</mn></mrow></msubsup><mo>⋯</mo><mi>B</mi><msubsup><mrow><mfenced><mrow><mi>O</mi><mi>H</mi></mrow></mfenced></mrow><mrow><mn>4</mn></mrow><mrow><mo>-</mo><mn>1</mn></mrow></msubsup><mo>]</mo></mrow><mrow><mo>-</mo><mn>0.5</mn></mrow></msup></mrow></math></span>). The relative distribution of the two species and the associated isotope fractionation factors were different for calcite and aragonite and changed between artificial seawater and NaCl solutions. On calcite the two surface complexes were heavier than aqueous borate, showing an overall fractionation of +5.5 to +6.4 ‰ in NaCl solutions (7.8 ≤ pH<sub>NBS</sub> ≤ 10.3), the inner-sphere complex being ∼3 ‰ heavier than the outer-sphere complex and 7.7 ‰ heavier than B(OH)<sub>4</sub><sup>−</sup>. The isotope fractionation decreased to +4.7 ‰ in seawater (7.9 ≤ pH<sub>NBS</sub> ≤ 8.9), where the inner-sphere complex accounted for >99 % of adsorbed boron. On aragonite the inner-sphere complex formed in NaCl 0.5 M resulted heavier than aqueous borate by 4.2 ‰, whereas the outer-sphere complex, accounting for 9 to 52 % of adsorbed boron between pH 8 and 11, exhibited the same isotopic composition as the aqueous anion. The overall isotopic fractionation
{"title":"Boron isotope fractionation during adsorption on aragonite and calcite in artificial seawater and NaCl aqueous solutions","authors":"Giuseppe D. Saldi , Pascale Louvat , Frank Heberling , Vasileios Mavromatis , Jacques Schott","doi":"10.1016/j.gca.2025.11.032","DOIUrl":"10.1016/j.gca.2025.11.032","url":null,"abstract":"<div><div>Adsorption of dissolved species on mineral surfaces is a key elementary process, which controls crystal growth and incorporation of trace elements into mineral structures, affecting the isotopic composition of geological archives. Changes of chemical composition of aqueous solution can induce significant variations in the type, concentration and isotopic composition of boron surface species incorporated by CaCO<sub>3</sub>. To better understand and quantify these effects, the boron isotope fractionation associated with B adsorption on calcite and aragonite was investigated in artificial seawater and equimolar solutions of NaCl (0.5 M) at room temperature and 7.5 ≤ pH<sub>NBS</sub> ≤ 11.9. Boron adsorption on aragonite was 2–4 times stronger than on calcite, in agreement with the higher affinity of aragonite for borate ions reported by previous studies. In seawater solutions at pH > 8.5, B removal from the solution increased due to increasing adsorption on both CaCO<sub>3</sub> polymorphs and coprecipitation with brucite, which was observed to form at more alkaline conditions. Boron sorption reactions on calcite and aragonite surfaces were described using the calcite three-plane model (TPM) assuming the presence of a borate inner-sphere complex (<span><math><mrow><mo>></mo><mi>B</mi><msub><mi>O</mi><mn>3</mn></msub><msubsup><mi>H</mi><mrow><mn>2</mn></mrow><mrow><mo>+</mo><mn>0.5</mn></mrow></msubsup></mrow></math></span>), formed by the replacement of B(OH)<sub>4</sub><sup>−</sup> for surface carbonate groups, and the adsorption of B(OH)<sub>4</sub><sup>−</sup> at calcium protonated sites (><span><math><mrow><msup><mrow><mo>[</mo><mi>C</mi><mi>a</mi><msubsup><mrow><mi>OH</mi></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo><mn>0.5</mn></mrow></msubsup><mo>⋯</mo><mi>B</mi><msubsup><mrow><mfenced><mrow><mi>O</mi><mi>H</mi></mrow></mfenced></mrow><mrow><mn>4</mn></mrow><mrow><mo>-</mo><mn>1</mn></mrow></msubsup><mo>]</mo></mrow><mrow><mo>-</mo><mn>0.5</mn></mrow></msup></mrow></math></span>). The relative distribution of the two species and the associated isotope fractionation factors were different for calcite and aragonite and changed between artificial seawater and NaCl solutions. On calcite the two surface complexes were heavier than aqueous borate, showing an overall fractionation of +5.5 to +6.4 ‰ in NaCl solutions (7.8 ≤ pH<sub>NBS</sub> ≤ 10.3), the inner-sphere complex being ∼3 ‰ heavier than the outer-sphere complex and 7.7 ‰ heavier than B(OH)<sub>4</sub><sup>−</sup>. The isotope fractionation decreased to +4.7 ‰ in seawater (7.9 ≤ pH<sub>NBS</sub> ≤ 8.9), where the inner-sphere complex accounted for >99 % of adsorbed boron. On aragonite the inner-sphere complex formed in NaCl 0.5 M resulted heavier than aqueous borate by 4.2 ‰, whereas the outer-sphere complex, accounting for 9 to 52 % of adsorbed boron between pH 8 and 11, exhibited the same isotopic composition as the aqueous anion. The overall isotopic fractionation","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"413 ","pages":"Pages 104-121"},"PeriodicalIF":5.0,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575282","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}
Pub Date : 2025-11-22DOI: 10.1016/j.gca.2025.11.038
Baptiste Le Bellego, Célia Dalou, Béatrice Luais, Pierre Condamine, Vincent Motto-Ros, Laurent Tissandier
{"title":"Experimental constraints on germanium diffusivity in metal and silicate phases during core formation of planetesimals and terrestrial planets","authors":"Baptiste Le Bellego, Célia Dalou, Béatrice Luais, Pierre Condamine, Vincent Motto-Ros, Laurent Tissandier","doi":"10.1016/j.gca.2025.11.038","DOIUrl":"https://doi.org/10.1016/j.gca.2025.11.038","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"143 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145567550","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":"Zinc isotopic fractionation during magmatic differentiation and hydrothermal processes: implications for Li mineralization in the Jiajika granitic pegmatites, Sichuan, China","authors":"Jia-Wen Liu, Shi-Hong Tian, Xian-Lei Geng, Ying-Li Gong, Lu Chen, Shi-Qi Huang","doi":"10.1016/j.gca.2025.11.031","DOIUrl":"https://doi.org/10.1016/j.gca.2025.11.031","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"68 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145553680","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}
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