Geochimica et Cosmochimica Acta最新文献

{"title":"Spectrophotometric determination of bicarbonate dissociation constants (K2) for freshwater, estuarine, and marine waters over a wide range of temperatures","authors":"Macarena Martin-Mayor ,&nbsp;Robert H. Byrne ,&nbsp;Katelyn M. Schockman ,&nbsp;Xuewu Liu","doi":"10.1016/j.gca.2025.06.001","DOIUrl":"10.1016/j.gca.2025.06.001","url":null,"abstract":"<div><div>This study presents the first spectrophotometric determination of <em>K</em>₂ at estuarine conditions (0 ≤ <em>S</em>_P ≤ 20; where <em>S</em>_P is practical salinity) and over a broad range of temperatures (275.15 ≤ <em>T</em> ≤ 308.15 K; where <em>T</em> is temperature in Kelvin). Spectrophotometric data from <span><span>Schockman and Byrne (2021)</span></span> and <span><span>Schockman et al. (2024)</span></span> were combined with data obtained in the present study to produce a set of p<em>K</em>₂ (i.e., p<em>K</em>₂ = – log <em>K</em>₂) values for the salinity range 0 ≤ <em>S</em>_P ≤ 41 and temperature range 275.15 ≤ <em>T</em> ≤ 308.15 K. The resulting set of p<em>K</em>₂ values was fitted as a function of <em>S</em>_P and <em>T</em> to obtain a new p<em>K</em>₂ parameterization on the total pH scale:</div><div>p<em>K</em>₂ = 5.1703 + 2136.77 <em>T</em>⁻¹ – 177788 <em>T</em>⁻² – 0.4457 <em>S_P</em>^0.5/(1 + 1.11 <em>S_P</em>^0.5) + 0.0674 <em>S_P</em>/ln<em>T</em> – 0.0008238 <em>S_P</em>^0.5 <em>T.</em></div><div>The random uncertainty in this work is 0.0071 based on the standard deviation of the best-fit p<em>K</em>₂ parameterization. Residuals in the fit (i.e., measured minus parameterized p<em>K</em>₂ values) are approximately two times smaller in magnitude than the residuals obtained in past studies for similar <em>S_P</em> and <em>T</em> ranges. The total combined standard uncertainty of p<em>K</em>₂ in this work is 0.0145. Assessments of high-quality total dissolved inorganic carbon (<em>C</em>_T), total alkalinity (<em>A</em>_T), and pH data obtained on oceanic research cruises indicate that internal consistency of CO₂ system calculations (comparing measured and calculated values; e.g., comparing measured pH with pH calculated from <em>C</em>_T and <em>A</em>_T) is improved when calculations use this <em>K</em>₂ parameterization, especially for the Coastal Ocean Data Analysis Product in North America (CODAP-NA) data set (0.117 ≤ <em>S_P</em> ≤ 36.980). As such, this new p<em>K</em>₂ parameterization provides an improved characterization of bicarbonate dissociation constant behavior that encompasses freshwater, estuarine, and open ocean conditions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"401 ","pages":"Pages 149-159"},"PeriodicalIF":4.5,"publicationDate":"2025-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144321865","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":"Precambrian mantle metasomatism preserved by the Nd-Hf isotopic compositions of modern HIMU-type intraplate basalts","authors":"Leonie Sieger ,&nbsp;Bradley J. Peters ,&nbsp;Andrea Giuliani ,&nbsp;Maria Schönbächler","doi":"10.1016/j.gca.2025.05.040","DOIUrl":"10.1016/j.gca.2025.05.040","url":null,"abstract":"<div><div>The presence of HIMU (high-²³⁸U/²⁰⁴Pb) signatures in ocean island basalts has long been used to argue that ancient oceanic crust has been tectonically recycled into the mantle sources of plume-derived volcanic hotspots such as St. Helena or Mangaia. However, alternative hypotheses regarding the origins of HIMU signatures have also been put forward. This study addresses the origins of HIMU-like Pb isotopic signatures in Isla Isabel, a small (∼1 km²) intraplate volcanic island located off the western coast of México, southeast of the southern tip of Baja California. The Nd-Hf isotopic signatures of Isla Isabel are nearly identical to the classical HIMU-type hotspots St. Helena and Mangaia; however, the physical and geochemical characteristics of Isla Isabel are inconsistent with the derivation of its lavas from deeply recycled oceanic crust. We argue that Isla Isabel lavas were instead produced by mixing of local depleted mantle and continental lithospheric mantle that experienced a prior enrichment event, likely in a ≥ 600 Ma-old paleo-subduction setting. Such preservation of ancient tectonic events is remarkable, since the exposed geological record in continental México preserves only a limited record of geological events older than the Mexican Cordillera (&lt;165 Ma). Isla Isabel, therefore, illustrates that the origins of HIMU-type intraplate lavas are not limited to ancient recycled oceanic crust. Rather, they can also preserve information about the evolution of the upper mantle through large-scale tectonic cycles, even when these events have been otherwise erased from the surficial rock record.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"401 ","pages":"Pages 77-88"},"PeriodicalIF":4.5,"publicationDate":"2025-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144270980","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":"Co-evolution of organics and water in experimentally shocked Murchison and EET 90628 chondrites","authors":"E. Quirico, H. Yabuta, P. Beck, L. Bonal, A. Bardyn, L.R. Nittler, C.M.O’D. Alexander","doi":"10.1016/j.gca.2025.05.046","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.046","url":null,"abstract":"A significant population of primitive carbonaceous chondrites experienced short-duration heating, which is usually attributed to either impact or solar heating. Shock recovery experiments performed on carbonaceous chondrites have successfully reproduce the typical evolution in the petrographies and mineralogical compositions of natural samples. However, only few studies focused on the chemical and structural transformations of insoluble organic matter (IOM). We report here on shock recovery experiments conducted on two chondrites: Murchison (CM2) and Elephant Moraine EET 90628 (L3.0). Experiments on Murchison show carbonization and oxidation of IOM at all shock intensities (5–50 GPa) and a pronounced structural evolution at 40 GPa associated with complete dehydroxylation of serpentines, as well as formation of olivine and amorphous silicates. The δD value of Murchison IOM (initial δD = 1636 ± 529 ‰) evolves significantly, with the rapid disappearance of isotopic hot spots and a bulk δD of −79 ‰ at 40 GPa. At 40 GPa, the extent of dehydroxylation of serpentines is consistent with stage III heated chondrites, but the structural characteristics of the IOM resembles material from stage II meteorites, i.e. a slight modification of the IOM in a matrix dominated by serpentines.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"46 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144237334","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":"Across-arc variations of potassium isotope compositions in a fluid-dominated subduction zone and implications for global potassium recycling","authors":"Ying-Yu Xue, Haiyang Liu, He Sun, Haiou Gu, Shichao An, Gerhard Wörner, Guozhi Xie, Maoqiang Yan, Dapeng Li, Yuxin Xiong, Fanfan Tian, Weidong Sun","doi":"10.1016/j.gca.2025.05.047","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.047","url":null,"abstract":"To reveal the fluid variations in the mantle sources of arc lavas from a fluid-dominated subduction zone and to further constrain its implications for global potassium (K) recycling, we present the K isotope compositions of thirty-two arc lavas from a 220 km arc-front to back arc transect across the Kamchatka Peninsula. Our results show that arc lavas from Eastern Volcanic Front (EVF, −0.48 ± 0.02 ‰ to −0.19 ± 0.03 ‰, average at −0.37 ± 0.08 ‰, n = 15) and Central Kamchatka Depression (CKD, −0.39 ± 0.03 ‰ to −0.25 ± 0.05 ‰, average at −0.32 ± 0.05 ‰, n = 9) display slightly higher δ<ce:sup loc=\"post\">41</ce:sup>K than those from Sredinny Range (SR, −0.44 ± 0.03 ‰ to −0.37 ± 0.02 ‰, average at −0.41 ± 0.03 ‰, n = 5) and the mantle value (−0.42 ± 0.08 ‰), which indicate the incorporation of slab-derived fluids within their mantle sources. Notably, the δ<ce:sup loc=\"post\">41</ce:sup>K values of CKD arc lavas show positive correlations with δ<ce:sup loc=\"post\">18</ce:sup>O, and fluid indices (e.g., K/Nb, Sb/Ce, Pb/Ce and As/Ce ratios), suggesting the contributions of fluids derived from the subducted Hawaii-Emperor Seamount Chain. In addition, this study reveals that arc lavas from North Central Kamchatka Depression (NCKD) have higher δ<ce:sup loc=\"post\">41</ce:sup>K values (−0.32 ± 0.03 ‰ to −0.31 ± 0.02 ‰, average at −0.32 ± 0.01 ‰, n = 3) than the mantle value. Their high δ<ce:sup loc=\"post\">41</ce:sup>K values were accompanied with high Sr/Y ratios, indicating that the K isotope data of NCKD arc lavas may reflect the influence of slab-derived melts. This study demonstrates that recycling of a slab-derived fluid components can modify the K isotope compositions in the mantle source of the arc magmas. Consequently, when combined with other indicators (e.g., Sb/Ce, As/Ce ratios and Pb-O isotopes), the K isotope system helps to constrain recycling of fluid-mobile elements in subduction settings and to reveal how crustal materials recycle back via dehydration fluids from the subducted slab to the Earth’s surface.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"10 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144237636","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":"Accretion of the anomalous CR2 chondrite Northwest Africa 14674: Implications for the complexities of the CR parent bodies","authors":"R.H. Hewins, P.-M. Zanetta, H. Leroux, S. Laforet, C. Le Guillou, M. Marinova, S. Pont, B. Zanda, R. Brunetto, J. Gattacceca, C. Sonzogni, L. Piani, Y. Marrocchi","doi":"10.1016/j.gca.2025.05.037","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.037","url":null,"abstract":"An understanding of the differences between ungrouped, or anomalous, and normal carbonaceous chondrites could provide information on the population of parent bodies required to explain a chondrite group and on first solid accretion and evolution in the outer protoplanetary disk. The CR chondrites are key in this respect, as they display a unique formation history that distinguishes them from other groups. They are known to have formed between 4.1 and 4.6 Myr after CAI, with two generations of chondrules. Northwest Africa (NWA) 14674 is a CR2 anomalous (CR2-an) chondrite with very similar oxygen isotope composition, dark inclusion (DI) content, and serpentine-magnetite matrix to Al Rais (CR2-an). Both are petrologic subtype 2.3 with fresh magnesian olivine, and partly altered ferroan olivine, pyroxene, and metal. Additionally, NWA 14674 contains residual GEMS-like material at the nanoscale within preserved moderately altered areas. DI and matrix in NWA 14674 are mineralogically similar but they have different fabrics, and matrix is more porous than both DI and fine-grained rims (FGR). Matrix has aligned framboidal magnetite aggregates swathing the chondrules, suggesting slight compaction of the chondrite. Some DI have inner chondrule fragments and concentric layers richer and poorer in magnetite, indicating formation as accretionary pellets and lapilli: they are pebbles rather than clasts. The framboidal magnetite abundance is consistent with an alkaline alteration fluid potentially due to NH<ce:inf loc=\"post\">3</ce:inf> ice mixed with the more common water ice, which implies late distal accretion. Comparison with the CR chondrites Bells (regolith-like) and NWA 801 (with high-pressure clasts) indicates that a complex history involving inward drift, disruption of the grandparent body, and reaccretion of debris along with chondrules, DI pebbles, and dust is required to explain CR chondrite formation. The diverse facies observed in CR chondrites may be explained by the formation of relatively large parent bodies, comprising distinct layers (core to regolith). Some material has been inherited from a chondritic protoplanet that formed during the oligarchic growth phase of planetary formation. Subsequently, this initial body underwent disruption and partial reaccretion into the CR parent body.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"6 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144304932","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":"Whole-rock Mg isotopes distinguishing high- and low-temperature S-type granites","authors":"Yan Wang, Peng Gao, Zi-Fu Zhao, Hai-Ou Gu, Guo-Chao Sun, Hui-Chan Huang, Zhang-Jian Wu, Changqing Yin","doi":"10.1016/j.gca.2025.05.048","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.048","url":null,"abstract":"Determining the temperature of crustal anatexis associated with granitic magmatism is vital for understanding the petrogenesis of granites and the processes underlying crustal anatexis. During the partial melting of metasedimentary rocks, the breakdown of biotite at elevated temperatures can lead to the formation of peritectic garnet, which is typically rare or absent at lower temperatures when melting is predominantly driven by muscovite breakdown. This distinction makes magnesium (Mg) isotopes a valuable tool for tracing relative variations in crustal melting temperatures, as garnet exhibits the lowest δ<ce:sup loc=\"post\">26</ce:sup>Mg values compared to other Mg-bearing phases under equilibrium fractionation. However, the extent to which temperature variations influence melt Mg isotope compositions remains inadequately understood. In this study, we present Mg and oxygen isotope data for high- and low-temperature leucogranites from the Himalayan orogen, alongside whole-rock major and trace element data, and zircon Ti content from previous studies. Low-temperature leucogranites, with maximum Ti-in-zircon temperatures ranging from 739 to 801 °C, display negative δ<ce:sup loc=\"post\">26</ce:sup>Mg values between −0.70 and −0.14 ‰, aligning with most global S-type granites. Conversely, high-temperature leucogranites, exhibiting maximum Ti-in-zircon temperatures of 800 to 855 °C, possess positive δ<ce:sup loc=\"post\">26</ce:sup>Mg values ranging from 0.46 to 0.53 ‰, significantly exceeding those of Himalayan metasedimentary rocks and most global S-type granites. The high-temperature leucogranites also demonstrate relatively elevated Nb/Ta and Eu/Eu* ratios, while their whole-rock δ<ce:sup loc=\"post\">18</ce:sup>O and CIA values are comparable to those of low-temperature leucogranites. These findings suggest that fluid alteration, fractional crystallization, and crustal assimilation have a minimal impact on the Mg isotope discrepancies between the two granite groups. We propose that the positive δ<ce:sup loc=\"post\">26</ce:sup>Mg values of the high-temperature leucogranites result from a greater fraction of peritectic garnet in the melting residue, attributable to higher anatectic temperatures. Phase equilibrium modeling indicates that the peritectic reaction involving muscovite breakdown is swiftly replaced by biotite breakdown as temperatures rise, leading to a steady increase in the corresponding fraction of garnet. Equilibrium fractionation calculations further corroborate that melt δ<ce:sup loc=\"post\">26</ce:sup>Mg values rise with an increasing fraction of peritectic garnet, with values at high temperatures significantly surpassing those at lower temperatures. Consequently, this study elucidates a causal relationship between Mg isotope composition and anatectic temperature, highlighting that whole-rock Mg isotopes can serve as a reliable indicator for distinguishing between high- and low-temperature S-type granites.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"36 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144304950","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 deformation and U-Pb isotope systematics in zircon from impactites of the Rochechouart impact structure: Impact age and zircon provenance","authors":"Daniela Guerrero, Wolf Uwe Reimold, Natalia Hauser, Gavin Kenny, Martin Whitehouse, Philippe Lambert","doi":"10.1016/j.gca.2025.05.049","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.049","url":null,"abstract":"The &gt;23 km diameter, ∼207 Ma old Rochechouart impact structure is located in the NW part of the Paleozoic basement of the French Massif Central. Despite significant erosion, this impact structure preserves a heterogeneous suite of impactites, and the transition between the crater floor and the basement. Recent textural and geochronologic studies of U-Pb on zircon from impactites and basement lithologies of this structure have shown a wide variety of shock deformation textures and age distributions. In this study, we present a comprehensive analysis combining detailed textural characterization (CL, BSE, EBSD) and U-Pb geochronological analyses at different spatial resolutions (SIMS and LA-ICP-MS) of zircon from two melt-bearing breccias (suevites) from Chassenon and Videix, and one impact melt rock (IMR) from Babaudus. The analyzed crystals display a variety of shock deformation textures. Identification of FRIGN zircon and grains with high proportions of reidite in the Videix suevite indicates that these types of shock deformation are more widespread than previously reported. In the Chassenon suevite, U-Pb age resetting increases with shock intensity, whereas in the Videix suevite, higher U and/or Th contents also appear to control resetting. In the Babaudus IMR, the similar ages for shocked granular zircons and some unshocked grains suggest that additional factors, beyond shock deformation and zircon composition, influence age resetting. The SIMS analyses yielded more reliable results after common Pb correction. The best estimate of the impact age obtained from this study is 203 ± 4 Ma (2σ, MSWD = 3.4, probability = 0.065) for SIMS analyses of two granular grains from the Babaudus IMR and one granular crystal from the Videix suevite. Zircons with younger (191 ± 4 Ma, post-impact) ages show similar characteristics to those close to the widely accepted age for the impact at 207 Ma, highlighting the challenge of distinguishing between grains and separating ages related to the impact from possible post-impact events (e.g., hydrothermal alteration). Finally, the geochronological results for the Videix and the Chassenon suevites show a clear correlation with provenance results for granitic and gneissic target lithologies, respectively. In contrast, the Babaudus IMR has an age distribution comparable with other impact melt rocks from Montoume and Recoudert but cannot be related to an identified target lithology.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"26 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144304931","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":"Germanium isotope fractionation during evaporation from metal and sulfide melts: Implications for volatile element loss from planetary materials","authors":"Elias Wölfer ,&nbsp;Christian J. Renggli ,&nbsp;Christoph Burkhardt ,&nbsp;Thorsten Kleine","doi":"10.1016/j.gca.2025.05.044","DOIUrl":"10.1016/j.gca.2025.05.044","url":null,"abstract":"<div><div>The Ge elemental and isotopic composition of planetary materials holds essential clues on volatile element fractionation processes in nebular and planetary environments. To facilitate the interpretation of natural sample data we report the results of an experimental campaign that quantitatively assesses the elemental and isotopic fractionation of Ge during evaporation from graphite saturated Fe metal and FeS sulfide melts. The experiments were run under reducing conditions both at atmospheric and low vacuum (∼0.001 bar) pressure and at temperatures between 1200–1600 °C. In general, evaporation of Ge increases with increasing temperatures, decreasing pressure, and in the presence of S. The residual run products become isotopically heavier with ongoing evaporation of Ge, yielding kinetic fractionation factors α_k between 0.9940 and 0.9971 for the Fe melt degassing series performed under low vacuum and atmospheric pressure, respectively.</div><div>The experimental data are applied to investigate the role of planetary degassing processes for setting the moderately volatile element budget of non-magmatic iron meteorites. For this, new Ge concentration and isotope data for ungrouped iron meteorites of non-magmatic origin are combined with literature data for group IAB and IIE irons. We find that the large Ge isotopic variations (∼4‰) among variably Ge-depleted, non-magmatic iron meteorites are well explained by evaporative Ge loss from Fe metal or FeS sulfide melts at pressure conditions ≤ 1 bar. This supports models proposing an origin of non-magmatic iron meteorites by near-surface impact processes.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"401 ","pages":"Pages 17-30"},"PeriodicalIF":4.5,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144212277","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":"Contrasting Zn isotope fractionation effect during adsorption on micro- and nano-goethite","authors":"Zhao Wang ,&nbsp;Michael F. Hochella Jr ,&nbsp;Yiren Duan ,&nbsp;Ganlin Zhang ,&nbsp;Xiancai Lu ,&nbsp;Wei Li","doi":"10.1016/j.gca.2025.05.031","DOIUrl":"10.1016/j.gca.2025.05.031","url":null,"abstract":"<div><div>Goethite is essential in controlling Zn mobility and behavior in surface environments and can strongly influence Zn isotope fractionation through adsorption processes. However, the influence of particle size of goethite on stable isotopic fractionation remains poorly understood. This research investigates the fractionation of Zn stable isotopes during adsorption onto nano- and micro-goethite, focusing on factors such as reaction duration, Zn concentrations, and pH. The findings reveal that equilibrium in Zn isotope fractionation is achieved after roughly 48 h at pH 6 in both nano- and micro-goethite systems. For nano-goethite, the isotopic fractionation between adsorbed and aqueous Zn (Δ⁶⁶Zn_{adsorbed–aqueous}) remains around −0.1 ± 0.04 ‰, regardless of pH and initial Zn concentrations. During Zn adsorption on micro-goethite, a significantly more negative fractionation of Δ⁶⁶Zn_{adsorbed–aqueous} =  − 0.40 ± 0.04 ‰ is observed. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows that Zn binds to the surface of nano-goethite as a combination of inner-sphere octahedral and tetrahedral surface complexes, with average Zn<img>O bond lengths ranging from 2.00 to 2.02 Å. In contrast, on micro-goethite, Zn predominantly exists as a distorted octahedral structure, exhibiting an average Zn<img>O interatomic distance of 2.09 Å. Our findings suggest that the size-dependent Zn isotope fractionation in goethite is driven by the structural differences in the Zn surface complexes formed on nano- and micro-goethite. These results provide valuable insights into Zn isotope signatures in natural iron-rich soils, supporting the use of Zn isotopes as tracers for understanding the fate of Zn influenced by iron minerals in soil environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"401 ","pages":"Pages 47-61"},"PeriodicalIF":4.5,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144220482","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":"Incorporation of fluoride in calcite: Insights from solid-state NMR, NanoSIMS, APT, HRSTEM and DFT calculations","authors":"Wei Li ,&nbsp;Chao Ren ,&nbsp;Kideok D. Kwon ,&nbsp;Xiaolei Feng ,&nbsp;Gang Sha ,&nbsp;Jinhui Li ,&nbsp;Sijia Dong ,&nbsp;Xiancai Lu","doi":"10.1016/j.gca.2025.05.045","DOIUrl":"10.1016/j.gca.2025.05.045","url":null,"abstract":"<div><div>Despite the abundant occurrence and large variation in fluorine (F) in calcium carbonate minerals in geological settings, it remains poorly understood to what degree F can be incorporated into calcium carbonate minerals. Particularly, molecular-scale evidence for F incorporation modes in the calcite structure is lacking. In this study, we conducted coprecipitation experiments for F with calcium carbonate to reveal the nature of F partitioning in calcite minerals. The ¹⁹F solid-state NMR spectra yield four peaks at −82, −97, −107 and −108 ppm, suggesting that F can be taken up by calcite via at least four mechanisms. The −108 ppm peak occurs at F⁻ concentrations above 2 mM and is consistent with fluorite (CaF₂), suggesting that fluorite precipitation predominates at high [F]. Combined with ¹⁹F chemical shifts, ¹⁹F{¹³C} rotational echo double resonance (REDOR) techniques, and DFT-based quantum computations, the ¹⁹F NMR signals at −82, −97 and −107 ppm are assigned to surface adsorbed species, surface incorporated “CaF₂” defects and incorporated “CaF₂” defects within the bulk of calcite, respectively. Visualization via three-dimensional atomic probe topography (3D APT), high-resolution scanning transmission microscopy (HRSTEM) and nanoscale secondary ion mass spectrometry (NanoSIMS) analysis further supported that F can be incorporated into the bulk structure of calcite. These findings provide atomic and molecular insight into F incorporation in carbonate minerals and are helpful for the application of carbonate materials as potential geochemical proxies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"401 ","pages":"Pages 31-46"},"PeriodicalIF":4.5,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144212278","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}