Chemical Geology最新文献

{"title":"The effect of cation ordering in omphacite on the phonon compressibility: A step towards Raman elastic geothermobarometry","authors":"Lisa Baratelli ,&nbsp;Mara Murri ,&nbsp;Matteo Alvaro ,&nbsp;Boriana Mihailova ,&nbsp;Tiziana Boffa Ballaran ,&nbsp;Maria Chiara Domeneghetti ,&nbsp;Fernando Cámara","doi":"10.1016/j.chemgeo.2025.122650","DOIUrl":"10.1016/j.chemgeo.2025.122650","url":null,"abstract":"<div><div>Omphacite-in-garnet is a common host-inclusion system that has the potential to be used in Raman elastic geobarometry. However, the application of omphacite for this purpose requires the study of the effect of cation order on the phonon compressibility <span><math><msub><mi>β</mi><mi>ω</mi></msub><mo>=</mo><mfenced><mrow><mn>1</mn><mo>/</mo><msub><mi>ω</mi><mn>0</mn></msub></mrow></mfenced><mfenced><mrow><mi>dω</mi><mo>/</mo><mi>dP</mi></mrow></mfenced></math></span>, i.e. on the pressure dependency of the relative changes of phonon wavenumbers. Here, we report high-pressure Raman spectra of six omphacite crystals with the same composition (∼Jd₅₂Di₄₈) but having a different state of cation occupancy at the six- and eight-coordinated (<em>M</em>) cation sites and compare results with those derived for ordered and disordered omphacite with composition ∼Jd₄₃Di₅₇. We demonstrate that the position of the well-resolved Raman peak near 688 cm⁻¹, which originates from Si-O-Si bond bending, is strongly influenced by pressure but its phonon compressibility remains unaffected by both the chemical composition and state of <em>M</em>-site cationic order. Thus, the Si-O-Si bond-bending wavenumber can be used as a marker of the residual pressure in omphacite-garnet systems. However, the omphacite grain has to be subsequently disclosed to determine the peak position at atmospheric pressure because the phonon wavenumber also varies with the omphacite chemical composition. On the other hand, the width of the peak near 688 cm⁻¹ varies with chemical order, but not with pressure, making it a valuable indicator for determining the temperature of inclusion entrapment or the closure temperature of the system, as the cationic order in omphacite provides insights into the closure temperature of the cation-exchange reaction.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122650"},"PeriodicalIF":3.6,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143207234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The control of oceanic crustal age and redox conditions on seafloor alteration: Examples from a quantitative comparison of elemental mass transport in the South and Northwest Pacific","authors":"Satoshi Matsuno,&nbsp;Masaoki Uno,&nbsp;Atsushi Okamoto","doi":"10.1016/j.chemgeo.2025.122651","DOIUrl":"10.1016/j.chemgeo.2025.122651","url":null,"abstract":"<div><div>Oceanic crust interacts with infiltrating seawater, resulting in the formation of secondary minerals. Sediment cover on oceanic plates can potentially change the redox conditions of the underlying basaltic crust, which may influence which secondary minerals form and what elemental mass transport occurs during alteration. However, quantitative estimates of the variations in seafloor alteration using altered samples from different sites have not previously been carried out, and the factors controlling seafloor alteration remain unclear. We present a novel approach for the quantitative analysis of element mobility during seafloor alteration, based on a regional dataset of whole-rock compositions of altered basalts sourced from different drilling sites and alteration systems. Protolith reconstruction models (machine-learning-based element mobility analyses) were applied to the compositions of samples of basaltic crust from the South and Northwest Pacific. Our analyses show that older altered basalt has higher element mobility. In particular, Rb and K are enriched relative to their estimated contents in the protolith by a factor of 100 and 10, respectively, due to the formation of secondary minerals under oxidizing conditions. In the oxidizing settings of the South Pacific, enrichment in Ba and U was observed in samples with intense oxidation. In contrast, under relatively reducing conditions in the Northwest Pacific, alteration was associated with the formation of carbonate veins and U enrichment. The differences in quantitative element mobility and secondary mineralization demonstrate that sediment thickness and crustal age control redox conditions and the duration of seafloor alteration.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122651"},"PeriodicalIF":3.6,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377006","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Volcanism-induced generation of high-silica A-type granite: A snapshot from Yandangshan caldera, southeastern China","authors":"Jing-Yuan Chen ,&nbsp;Jin-Hui Yang ,&nbsp;Ji-Heng Zhang ,&nbsp;Yu-Sheng Zhu","doi":"10.1016/j.chemgeo.2025.122641","DOIUrl":"10.1016/j.chemgeo.2025.122641","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Silicic magmatism was extensively developed in the coastal regions of southeast China. The abundant volcanic fields and granitic plutons in this region provide exceptional opportunities to investigate upper crustal magmatic processes and their evolution. We investigate the petrogenetic connections among alkali feldspar granites (AFGs), porphyritic enclaves, porphyritic rocks (including porphyritic monzonites and porphyritic syenites), and rhyolites from the Yandangshan caldera and surrounding area using zircon U&lt;img&gt;Pb dating, trace elements, Hf isotopic ratios, and bulk-rock geochemistry. Zircon U&lt;img&gt;Pb dating reveals that the plutonic and volcanic rocks of the Yandangshan caldera crystallized concurrently (98–102 Ma), with consistent Hf isotopic compositions and trace element trends in low-U zircons further supporting that lithological variations within the caldera result from crystal-melt segregation. The porphyritic rocks and enclaves are rich in Sr and Ba, display high Zr/Hf ratios, and show positive to weakly negative Eu anomalies, suggesting they represent cumulate residues from crystal-melt segregation. The AFGs and rhyolites are enriched in Rb but exhibit depletions in Sr, Ba, and Eu, characterized by low Eu/Eu&lt;sup&gt;⁎&lt;/sup&gt; and high Rb/Sr ratios. Both units are interpreted as evolved silicic melts extracted from a crystal-rich magma reservoir. Compared to the erupted rhyolites, the AFGs display higher silica content and Rb/Sr ratios, along with lower Eu/Eu&lt;sup&gt;⁎&lt;/sup&gt; ratios. Moreover, high-U zircons are exclusively found in the AFGs and exhibit the most evolved trace element signatures within the entire suite, characterized by elevated Hf and U concentrations, as well as low Eu/Eu&lt;sup&gt;⁎&lt;/sup&gt; ratios. These characteristics indicate that the AFGs, which exhibit A-type features, are more evolved than the rhyolites, reflecting extended in-situ crystallization and differentiation following the eruption of the rhyolitic magmas. We propose that the magma responsible for the AFGs originated from the underlying feldspar-rich mush, following the rhyolite eruption. These melts then underwent in-situ crystallization and melt differentiation, leading to the formation of A-type granites that are more evolved than the rhyolites. By comparing the geochemical characteristics of contemporaneous silicic plutonic and volcanic rocks from southeastern China, we demonstrate that large volumes of high-silica granitic magma accumulated after silicic melt eruptions. Our study further reveals that the compositional diversity of A-type granites primarily results from crystal-melt segregation processes rather than distinct magma sources, emphasizing the importance of shallow crustal differentiation in granite formation. Recognizing these processes enhances our understanding of how similar geological mechanisms generate diverse granite compositions across various tectonic environments, ultimately deepening our insight into the evolution of silicic magmas w","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122641"},"PeriodicalIF":3.6,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143061996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seawater temperatures during the early to middle Ediacaran: Phosphate oxygen isotope records","authors":"Haifeng Fan ,&nbsp;Zhigang Chen ,&nbsp;Fang Zhang ,&nbsp;Chuanwei Zhu ,&nbsp;Shengjiang Du ,&nbsp;Yuxu Zhang ,&nbsp;Hanjie Wen ,&nbsp;Danish Khan ,&nbsp;Thomas J. Algeo","doi":"10.1016/j.chemgeo.2025.122642","DOIUrl":"10.1016/j.chemgeo.2025.122642","url":null,"abstract":"<div><div>Early multicellular eukaryotes are hypothesized to have first evolved in deep-water (i.e., subphotic) environments with a narrow temperature range and low oxygen levels (pO₂). However, seawater paleotemperature estimates for the Ediacaran Period remain poorly known. To address this issue, we measured the oxygen isotopic compositions of phosphate (δ¹⁸O_P) in fine-grained marine siliciclastic sedimentary rocks from two slope sections of the Doushantuo Formation (∼635–551 Ma) in the Nanhua Basin, South China. The bulk δ¹⁸O_P values (∼19–26 ‰) found in early-middle Ediacaran phosphatic marine shales represent the oldest known records of modern seawater-like δ¹⁸O_P values. These values are inferred to record original seawater signatures and suggest that subtropical surface temperatures had a modern-like range of 15–30 °C. Based on these estimates, we propose that the extreme greenhouse conditions of the earliest Ediacaran following the Marinoan Ice Age were of quite short duration (&lt;∼0.1 Myr). Subsequently, the oldest known metazoan fossil assemblage, the Lantian Biota (∼602 Ma), thrived in a deep-water environment characterized by low oxygen levels and a relatively cold, narrow temperature range (∼7–8 ± 2 °C). In contrast, the slightly younger Weng'an Biota (∼587 Ma) inhabited shallower waters with higher oxygen levels and a broader temperature range (16–30 °C). Finally, our evidence shows that the oxygen isotopic composition of phosphate in fine-grained siliciclastic marine sedimentary rocks can serve as a valuable proxy for reconstructing the temperature of ancient seawater. Such paleotemperature information, combined with oxygen concentration data, is crucial for understanding the origin and evolution of early animal life.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122642"},"PeriodicalIF":3.6,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143103286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Constraining sulfate sources and its implications on atmospheric pCO2 in Arid Regions: Evidence from the Tarim Basin","authors":"Guo-Dong Jia ,&nbsp;Jun Zhong ,&nbsp;Si-Liang Li ,&nbsp;Sen Xu ,&nbsp;Han Luo ,&nbsp;Cong-Qiang Liu","doi":"10.1016/j.chemgeo.2025.122644","DOIUrl":"10.1016/j.chemgeo.2025.122644","url":null,"abstract":"<div><div>The pyrite oxidation-driven weathering has important implications for carbon cycle over geological timescales. Despite extensive researche using SO₄²⁻ as information carriers across diverse climatic zones, studies in arid regions remain limited, underscoring the urgency for research in these areas. This study collected and analyzed water samples from rivers and lakes in the Tarim Basin, one of the driest regions worldwide and China's largest endorheic basin. The samples were analyzed for physical, chemical and isotopic parameters e.g., water temperature, pH, electrical conductivity, concentrations of major anions and cations, and isotopic compositions of SO₄²⁻ (δ³⁴S_SO4 and δ¹⁸O_SO4). The results reveal pronounced spatial variations in δ³⁴S_SO4 and δ¹⁸O_SO4 values, which ranged from −2.4 to +14.8 ‰ and + 0.6 to +16.8 ‰, respectively. Post-simulation with a Monte Carlo inversion model suggests that carbonates (i.e., calcite and dolomite) weathering, evaporites (i.e., gypsum and halite) dissolution and pyrite (i.e., FeS₂) oxidation predominantly control water chemical compositions, contributing ∼72.9 % to 97.7 % (median 91.8 %) to dissolved solutes. The findings indicate that pyrite oxidation and gypsum dissolution are the primary sources of SO₄²⁻, accounting for 32.7 % to 80.9 % (median 55.9 %) and 13.4 % to 66.5 % (median 39.7 %), respectively. The estimated SO₄²⁻ fluxes in the study area amount to 0.108 Tmol/year, representing ∼3.2 % of the global SO₄²⁻ flux, underscoring the significance of SO₄²⁻ in arid regions for global sulfur cycle. Furthermore, the saturation indices of calcite, aragonite and dolomite are all greater than 0, indicating carbonate precipitation occurring in current environment. The high evaporation under arid conditions and wide distribution of evaporites (e.g., gypsum) in the study area can promote carbonate precipitation, enhancing the carbon sink capacity of rock weathering. This research provides critical data for elucidating the role of pyrite oxidation-driven weathering and evaporite dissolution on carbonate budget in arid regions influenced by the Westerlies, offering novel empirical evidence on continental weathering.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122644"},"PeriodicalIF":3.6,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143061995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Could rear-arc volcanism be driven by mantle instability?","authors":"Alex C. Davidson ,&nbsp;Chris W. Firth ,&nbsp;Simon P. Turner ,&nbsp;Shane J. Cronin","doi":"10.1016/j.chemgeo.2025.122647","DOIUrl":"10.1016/j.chemgeo.2025.122647","url":null,"abstract":"<div><div>The drivers of rear-arc volcanism remain poorly understood. Taranaki volcano, in the North Island of New Zealand, offers an ideal location to investigate the causes of such volcanism. Taranaki erupts hydrous, amphibole-bearing, high-K calc-alkaline magmas with trace element and Sr-Nd-O isotope compositions characteristic of arc-like fluid-flux melting regimes. Its location 150 km behind the arc front and &gt;250 km above the subducting slab, however, has led some geodynamic models to consider convective removal of lithosphere as an alternative driver of magmatic activity. Unlike typical arc magmas, late Pleistocene-Holocene eruptives from Taranaki preserve up to 40 % excesses of ²³⁰Th over ²³⁸U. These cannot be explained by crystal fractionation or assimilation processes and are unlikely to be imparted by sediment melting at the slab interface. We present a geochemical case to hypothesise that Taranaki magmas result from mantle instability associated with convective removal of lithosphere. In this model magmas represent variable mixtures of asthenospheric melts resulting from decompression melting with melts from downwelling lithosphere that have arc-like trace element signatures inherited from past (Miocene) metasomatism. Calculated upwelling rates for the asthenospheric component are similar to surface uplift and the timescales from melting to eruption must be less than 5 kyr, similar to eruptive periodicity. High-K rear-arc magmas with ²³⁰Th-excesses are common globally (e.g., Stromboli, Sangeang Api, Rishiri) suggesting mantle instability could be a more common scenario to explain rear-arc volcanism.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122647"},"PeriodicalIF":3.6,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143103218","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Carbonate metasomatism at mantle wedge conditions, evidence from trace element and stable isotope (Fe, Zn) signatures of orogenic peridotites","authors":"B. Debret ,&nbsp;P.A. Sossi ,&nbsp;N. Malaspina ,&nbsp;A. Gautier ,&nbsp;N. Mattielli ,&nbsp;H. O'Neill ,&nbsp;J. Villalobos-Orchard ,&nbsp;F. Moynier","doi":"10.1016/j.chemgeo.2025.122649","DOIUrl":"10.1016/j.chemgeo.2025.122649","url":null,"abstract":"<div><div>The composition and redox state of the mantle wedge over geological time can be impacted by fluid transfer from the slab during subduction. Although arc magmas are oxidised and enriched in fluid-mobile elements relative to mid-ocean ridge basalts (MORB), the nature of the fluid phase (aqueous or melts) produced by the slab in mantle wedge remains debated. Here we compare the elemental and isotopic (Fe and Zn isotopes) composition of both unmetasomatised and metasomatized ultramafic rocks from the Western Alps, respectively the Balmuccia and Finero massifs, to identify and characterise the relative effects of subduction-related processes on mantle peridotite composition. The metasomatism of Finero massif is evidenced by Light Rare Earth Element (LREE), U and Th enrichment coupled with isotopically light Zn and Fe signatures and an increase in oxygen fugacity relative to the MORB mantle-like peridotites of the Balmuccia massif. Negative correlations between LREE/HREE and U/Th ratios in metasomatized samples suggest preferential transport of Th relative to U in the infiltrating phase. Based on experimental constraints on fluid/melt partitioning, these observations are most consistent with Th dissolution in slab-derived melts. On the other hand, the light Zn isotope signatures in the Finero peridotites relative to those of Balmuccia peridotites are inconsistent with metasomatism by silicate melts and melt extraction processes. Trace elements and Zn isotopes results can be reconciled through the metasomatism of the mantle wedge by carbonate bearing fluids or melts in an open system. This process favours the formation of isotopically light metasomatic minerals in the Finero peridotite and the subsequent release of isotopically heavy CO₂-rich fluids or melts, probably during massif exhumation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122649"},"PeriodicalIF":3.6,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143529452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interaction between dissolution and precipitation during olivine carbonation: Implications for CO2 mineralization","authors":"U.C. Iyare ,&nbsp;L.O. Boampong ,&nbsp;W. Li ,&nbsp;C.W. Neil ,&nbsp;L.P. Frash ,&nbsp;J.W. Carey ,&nbsp;R. Feng ,&nbsp;Emmanuel Detournay ,&nbsp;H.S. Viswanathan","doi":"10.1016/j.chemgeo.2025.122645","DOIUrl":"10.1016/j.chemgeo.2025.122645","url":null,"abstract":"<div><div>Large-scale carbonation of olivine is considered a promising approach for in situ mineral carbonation, offering a permanent and stable method for CO₂ storage. A critical aspect of this process is understanding how dissolution and precipitation interact, as this could drive fracturing and enhance further reactions. In this study, we conducted carbonation experiments on olivine using CO₂-saturated aqueous solutions of NaHCO₃ and NaCl. Two experimental setups were used: one representing an open geochemical system and the other a closed system, corresponding to reaction-limited and flow-limited scenarios, respectively. Post-reaction textural analysis using scanning electron microscopy (SEM) revealed surface coatings of reaction products in the closed system, while etch pits and etch channels were prevalent in the open system. Although no direct evidence of reaction-driven fracturing was observed, etch pits and etch channels may serve as initiation points for subcritical crack formation and growth, potentially maintaining permeability and exposing new unreacted surfaces. Using linear elastic fracture mechanics (LEFM) model, we estimate that microcracks could propagate under a pressure of 0.1 GPa if reaction products accumulate within the etch pits. Our findings offer new insights into the mechanisms governing olivine carbonation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122645"},"PeriodicalIF":3.6,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143103285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"U-Pb and Lu-Hf isotopic evolution of ∼3.6 Ga remnants in NE Brazil – Implications on Eo-Paleoarchean global crustal evolution","authors":"Manuela Botero ,&nbsp;Jeffrey D. Vervoort ,&nbsp;Vinicius T. Meira ,&nbsp;Daniel F. Martins de Sousa ,&nbsp;Ticiano J.S. Santos","doi":"10.1016/j.chemgeo.2025.122646","DOIUrl":"10.1016/j.chemgeo.2025.122646","url":null,"abstract":"<div><div>Precambrian terrains preserving rocks older than 3.5 Ga contain an essential record of the crustal evolution of the primitive Earth. In this study, we investigated Eo-Paleoarchean rocks from the northern São Francisco Craton (NSFC) and the Borborema Province in northeastern Brazil to contribute to a more complete global isotopic record of this pivotal time in Earth's history. Zircon U-Pb ages along with zircon Hf isotope compositions were obtained for migmatitic gneiss complexes in both terrains. Zircon U-Pb data from the NSFC yield well-defined populations with ²⁰⁷Pb/²⁰⁶Pb ages from 3.61 to 3.59 Ga and younger components at ∼3.5 and ∼3.4 Ga. Similarly, the Borborema Province gneiss yields a main zircon age population of 3.58 Ga and a younger ∼3.5 Ga age component. The ∼3.6 Ga zircon components yield consistently sub-chondritic Hf isotopic compositions with initial ε_Hf between −1.9 and −3.1 for the NSFC and of ε_Hf −0.5 for the Borborema Province. Gneisses from northeastern Brazil record a main crust forming period at 3.65–3.60 Ga with sub-chondritic Hf isotope compositions that indicate derivation from melting of a ∼3.8 Ga source of broadly chondritic isotope composition, similar to that of many Eo-Paleoarchean gneisses worldwide. This Hf isotope record supports the existence of broadly chondritic mantle reservoir in the Eoarchean with development of depleted mantle and the appearance of evolved crust later in the Paleoarchean.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122646"},"PeriodicalIF":3.6,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143427921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Triple oxygen isotopic fractionation in CO2-CaCO3-H2O system during CO2-H2O exchange, carbonate precipitation, and acid digestion","authors":"Pallab Roy ,&nbsp;Amzad H. Laskar ,&nbsp;Sangbaran Ghoshmaulik ,&nbsp;S.K. Bhattacharya ,&nbsp;Ravi Rangarajan ,&nbsp;Mao-Chang Liang","doi":"10.1016/j.chemgeo.2025.122634","DOIUrl":"10.1016/j.chemgeo.2025.122634","url":null,"abstract":"<div><div>The triple oxygen isotope composition of carbonate deposits provides a proxy for understanding changes in the past hydrological cycle. The reconstruction relies on knowing the temperature dependence of ¹⁷O and ¹⁸O fractionation factors, ¹⁷α and ¹⁸α, and θ = ln¹⁷α/ln¹⁸α, associated with the carbonate precipitation which can take place at various temperatures in nature. To determine these parameters, we synthesized carbonates at temperatures ranging from 10 °C to ∼50 °C from various substrate waters. The oxygen isotope composition of the waters was obtained using the CO₂-H₂O exchange method at 25 °C and the composition of the carbonate was derived from that of CO₂ generated by reacting the carbonate with phosphoric acid at 25 °C. In both cases, the δ¹⁷O and δ¹⁸O values of the CO₂ were measured. To convert the δ¹⁷O and δ¹⁸O values of the water equilibrated CO₂ to the corresponding values of the water phase, a prior knowledge of the ¹⁷O and ¹⁸O fractionations during the CO₂-H₂O exchange is necessary. Liang et al. (2023) previously determined these fractionations by equilibrating CO₂ with VSMOW2 (δ¹⁷O and δ¹⁸O = 0 ‰) at 25 °C and measuring the resulting isotope values. Building on this work, we present rescaled and refined fractionation values: ¹⁷α = 1.02135 ± 0.00001, ¹⁸α = 1.04122 ± 0.00002, and θ = 0.5230 ± 0.0001. With this knowledge, we calculated the values of θ relating the CO₂ derived from acid–reacted carbonates (precipitated at different temperatures) and the parent water (θ_CO2(carb)-w). The θ_CO2(carb)-w (mean ± SE) at 10 °C, 25 °C, and 35 °C are 0.5232 ± 0.0001, 0.5233 ± 0.0003, and 0.5229 ± 0.0002, respectively. We also did these experiments at 50 °C. However, the θ_CO2(carb)-w (0.5129 ± 0.0004) at 50 °C was likely affected by kinetic isotope fractionation. We also determined the acid digestion fractionations at various temperatures ranging from 0 °C to 110 °C. We did not observe significant temperature dependence in Δ′¹⁷O values of the acid digested CO₂ across the above temperature range, the triple oxygen isotope slope (relating δ’¹⁷O and δ’¹⁸O) is 0.5220 ± 0.0002.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122634"},"PeriodicalIF":3.6,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143103217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}