Chemical Geology最新文献

{"title":"Isotopically heavy sulfur in nephelinite from Etinde, Cameroon Volcanic Line: Implications for the origin of intraplate magmatism","authors":"Sophie L. Baldwin ,&nbsp;Linda A. Kirstein ,&nbsp;J. Godfrey Fitton ,&nbsp;Adrian J. Boyce ,&nbsp;William Hutchison ,&nbsp;Michael A.W. Marks ,&nbsp;Eva E. Stüeken ,&nbsp;Chris Hayward","doi":"10.1016/j.chemgeo.2025.122748","DOIUrl":"10.1016/j.chemgeo.2025.122748","url":null,"abstract":"<div><div>Intraplate magmatism has traditionally been linked to anomalously hot mantle (hotspots) transported upwards from deep-sourced mantle plumes. However, many intraplate magmatic provinces lack convincing evidence for a mantle-plume origin, and the Cameroon Volcanic Line (CVL) located on the West African continental margin is one such province. Despite being active for ca. 65 million years, it lacks the time-progressive volcanic activity that would suggest the presence of a fixed mantle hotspot or plume; instead CVL magmatism has been linked to a shallow, enriched asthenospheric source. Etinde, a relatively young (&lt;1 Ma) volcano located at the centre of the CVL on the continent-ocean boundary, is the most silica-undersaturated and incompatible element-enriched volcano in the region and forms the focus of this study. It is constructed almost entirely of feldspar-free nephelinite lava flows, with compositions ranging from olivine nephelinite to felsic leucite nephelinite. We report new sulfide-, sulfate- and bulk-δ³⁴S data for a suite of Etinde rock samples; the first sulfur-isotope data for the CVL. Strong (∼8 ‰) S-isotope fractionation between sulfide and sulfate (haüyne, nosean) phases suggest equilibration temperatures of ∼600 °C, well below the magma solidus temperature and likely due to sub-solidus exsolution of nanoscale sulfide particles from the sulfate phenocryst phases. The most mafic samples from Etinde have been extensively degassed, containing less than 60 ppm sulfur, and therefore cannot be used to constrain the primary δ³⁴S. Instead, we use the intermediate and felsic volcanic rocks, where sulfur is locked in phenocrysts of haüyne and nosean, respectively. Bulk δ³⁴S of these rocks, which best represents the primary magmatic values, ranges from +3.7 ‰ to +6.3 ‰, a heavier signature than previously reported in alkaline igneous rocks. We propose that the heavy sulfur isotope values, together with the extreme silica undersaturation and incompatible element concentrations, reflect enrichment of the mantle source and fingerprint carbonate metasomatism in the mantle beneath the CVL. The heavy sulfur isotopic signature requires low-temperature fractionation and therefore implies the addition of sulfur through subduction processes. Our study has broad geochemical significance in contributing to a growing understanding of sulfur-isotope compositional variability in geochemically enriched mantle globally.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122748"},"PeriodicalIF":3.6,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143696012","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":"Precise discrimination of basalt tectonic settings via dual-stream model with geochemical element matrix and series learning","authors":"Shuzhao Wu ,&nbsp;Changfeng Jing ,&nbsp;Sheng Yao ,&nbsp;Tianyi Zhang ,&nbsp;Gaoran Xu ,&nbsp;Shuhui Gong ,&nbsp;Sensen Wu ,&nbsp;Zhenhong Du ,&nbsp;KunFeng Qiu","doi":"10.1016/j.chemgeo.2025.122746","DOIUrl":"10.1016/j.chemgeo.2025.122746","url":null,"abstract":"<div><div>Precise discrimination of basalt tectonic settings serves as a crucial methodological approach for providing insights into Earth's history. To address the limitations of traditional discrimination methods, which include high subjectivity due to reliance on expert experience and restricted precision resulting from simplistic comparative analysis of geochemical elements, we developed an innovative discrimination model-the Element Matrix and Series Parallel Network (EMSPN). The model enhances the capacity of tectonic setting discrimination by integrating the correlation characteristics between geochemical elements and the sequential features of element reactivity, thereby obtaining more comprehensive lithogenetic information. Based on &gt;39,000 geochemical analyses of basalts from 9 typical tectonic settings after the Archaean period, we conducted application demonstrations through preprocessing operations, including feature engineering, missing value imputation, and category balancing. The proposed model demonstrated superior performance across multiple evaluation methods, achieving an overall discrimination accuracy of 88 %. This study compared the proposed model with four traditional machine learning models as baseline methods, and the results showed that the model outperformed other traditional machine learning models in overall discrimination accuracy across 9 tectonic settings. Additionally, in ablation experiments, by systematically removing key components of the EMSPN, the results validated the model design's rationality and confirmed each module's importance in information extraction and feature learning. Using the SHapley Additive exPlanations (SHAP) method, we analyzed and discussed the importance of different elements in discrimination results and the geochemical characteristics across various tectonic settings. When applied to controversial Archaean basalt samples, the results confirm the conclusions from traditional geochemical analysis methods, demonstrating the model's geological reliability and practical significance. This research provides a reliable technical approach for the field of lithogeochemistry and retrieves geodynamic information through tectonic setting discrimination, contributing to more accurate reconstruction of Earth's tectonic history.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122746"},"PeriodicalIF":3.6,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679203","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":"Assessing the hydrothermal influence on natural waters in the Kirishima Volcanic Complex: Insights from rivers, springs and groundwater with varying residence time","authors":"Gibran Romero-Mujalli ,&nbsp;Jens Hartmann ,&nbsp;Takahiro Hosono ,&nbsp;Kiyoshi Ide ,&nbsp;Thorben Amann ,&nbsp;Pascale Louvat","doi":"10.1016/j.chemgeo.2025.122716","DOIUrl":"10.1016/j.chemgeo.2025.122716","url":null,"abstract":"<div><div>Rivers and groundwaters that drain active volcanic areas are characterized by relatively high nutrient concentrations and dissolved loads. The high dissolved load generally results from the fluid–rock interactions with high temperature fluids containing voclanic gases. In this study, the chemistry of spring and river waters from the Kirishima volcanic region (Kyushu, Japan) is analysed to determine the hydrothermal influence and how their chemical composition varies with respect to the groundwater transit time (residence time). The hydrothermal component is distinguished by combining spring water residence times with stable isotopic composition of <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>13</mn></mrow></msup><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi><mi>I</mi><mi>C</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>34</mn></mrow></msup><msub><mrow><mi>S</mi></mrow><mrow><mi>s</mi><mi>u</mi><mi>l</mi><mi>p</mi><mi>h</mi><mi>a</mi><mi>t</mi><mi>e</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>18</mn></mrow></msup><msub><mrow><mi>O</mi></mrow><mrow><mi>s</mi><mi>u</mi><mi>l</mi><mi>p</mi><mi>h</mi><mi>a</mi><mi>t</mi><mi>e</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>18</mn></mrow></msup><msub><mrow><mi>O</mi></mrow><mrow><mi>w</mi><mi>a</mi><mi>t</mi><mi>e</mi><mi>r</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>H</mi></mrow><mrow><mi>w</mi><mi>a</mi><mi>t</mi><mi>e</mi><mi>r</mi></mrow></msub></mrow></math></span> and the selenium to sulphate molar ratio. We found that the DIC and SO₄^2- in the waters draining the Kirishima volcanic complex arose for more than 50 % from volcanic CO₂ and SO₂. Consistently, the groundwaters flowing through longer and deeper flow paths accumulate more volcanic CO_2(g) and SO_2(g). The results from this study highlight the relevance of regional studies of active volcanic settings in understanding the chemical evolution of groundwaters and its implication for the carbon and sulphur budgets in a volcanic edifice.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122716"},"PeriodicalIF":3.6,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643628","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":"Numerical study of the land-sourced iron precipitation and its effects on porewater flow at subterranean estuaries","authors":"Yajuan Yin ,&nbsp;Tao Wang ,&nbsp;Chenming Zhang","doi":"10.1016/j.chemgeo.2025.122744","DOIUrl":"10.1016/j.chemgeo.2025.122744","url":null,"abstract":"<div><div>During terrestrial freshwater discharge to the ocean, the freshwater containing high concentrations of dissolved ferrous iron (<em>Fe</em>²⁺) come into contact with the saltwater enriched in dissolved oxygen (<em>O</em>₂(<em>aq</em>)) within the coastal aquifer, resulting in the oxidation and precipitation of iron (Fe) as Fe oxy(hydr)oxides. The accumulated Fe precipitate forms a low-permeability zone, known as the “iron curtain” at subterranean estuaries (STEs), which influences the porewater flow. However, this process is not quantitatively well understood, and the underlying mechanisms remain unclear. Given the processes of variable density flow, Fe oxidation and oxidative precipitation, and the effects of Fe precipitation on porosity and permeability, the process of land-sourced Fe precipitation and its interactions with porewater flow at STEs have been numerically studied using the TOUGHREACT simulation program, which facilitates multiphase flow and reactive transport processes. Results indicate that Fe precipitates correspondingly reduce the porosity and permeability (by approximately 20 %–40 %) of the aquifer. These reductions subsequently decrease the porewater velocity (by approximately 6 % to 18 % seaward and 8 % to 32 % upward) over Fe-precipitated areas and increase the porewater velocity (by approximately 6 % to 12 % seaward and 4 % to 8 % upward) above and below Fe-precipitated areas. In turn, the porewater velocity changes decline the accumulation of Fe precipitates by approximately 0.001 to 0.003 in volume fraction or 3 % to 18 %. These findings highlight the interaction between groundwater-derived Fe and porewater flow at STEs, providing insights that enhance the understanding of the hydrochemical processes in coastal zones.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122744"},"PeriodicalIF":3.6,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666528","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":"Controls over cesium and rubidium contents of sedimentary rocks","authors":"Jan Środoń,&nbsp;Karol Jewuła","doi":"10.1016/j.chemgeo.2025.122745","DOIUrl":"10.1016/j.chemgeo.2025.122745","url":null,"abstract":"<div><div>In nature, Cs and Rb follow K, which is a much more abundant but chemically similar element. Data for these elements and their mineral carriers were acquired by the combined ICP-OES/ICP-MS (Inductively Coupled Plasma Optical Emission Spectroscopy/Inductively Coupled Plasma Mass Spectrometry) techniques and quantitative XRD (X-ray diffraction), supplemented by multivariate regression analysis, in order to detect controls over cesium and rubidium contents of clastic sedimentary rocks. The sample material comprised clay fractions of bentonites and paleosols, dominated by illite-smectite, and bulk mudstones, sandstones, paleosols, bentonites, basalts, and tuffs from several European basins, ranging from the Proterozoic to Miocene. Results indicate that Rb and Cs contents of clastic sedimentary rocks, and of mudstones in particular, are controlled by the relative concentrations of K-feldspar, micas, and illite-smectite, thus detrital and late diagenetic components of these rocks, and concentrations of Rb and Cs in these minerals. The concentrations of Cs in some illite-smectites, significantly higher than upper continental crust (UCC) averages, indicate hydrothermal alteration or, in case of paleosols and bentonites, can be inherited from anomalous parent rocks. K, Cs, and Rb contents of normal mudstones (unaffected by the hydrothermal fluids or anomalous parent rocks), whether marine or freshwater, are close to the UCC values. In normal mudstones of our collection, feldspars contain 0 to 22 % of Cs and 0 to 41 % Rb, micas 0 to 57 % Cs and 0 to 48 % Rb, and illite-smectite 32 to 100 % Cs and 17 to 100 % Rb, both mostly non-exchangeable and ‘fixed’ in the illite structure. The collected data do not support the use of Rb/K as a paleosalinity proxy and call for careful use of Rb and Cs in chemostratigraphy. The presented relationships indicate that Cs/K and Rb/K ratios in illite-smectite are controlled by the chemistry of fluids, which promote crystallization of illite during burial. Normal diagenetic fluids precipitate illite with, on average, 2.4 times more Cs and 70 % more Rb than the UCC values. In “abnormal” illites, the average Cs and Rb values are 18 and 2.5 times higher than the UCC, respectively. It is confirmed that thin illite crystals have higher Rb/K and Cs/K ratios, tentatively explained by the “supply and demand” mechanism: high ratio between the concentrations of Rb and Cs in pore fluids and the volume of neoformed illite at the beginning of illite crystallization. Major sources of Cs in diagenetic pore fluids in sedimentary basins are detrital micas or hydrothermal fluids invading those basins. The impact of Cs and Rb sorption at illite and mica wedges and/or frayed edges on the total budgets of these elements cannot be evaluated from our data.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122745"},"PeriodicalIF":3.6,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143735307","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":"Subducted sediment recycling and fractional crystallization of the Toba volcanic system constrained by plagioclase geochemistry","authors":"Meng-Hao Gao ,&nbsp;Ping-Ping Liu ,&nbsp;Dian-Bing Wang ,&nbsp;Xi-Jun Liu ,&nbsp;Gui-Bin Zhang ,&nbsp;Cheng Xu","doi":"10.1016/j.chemgeo.2025.122740","DOIUrl":"10.1016/j.chemgeo.2025.122740","url":null,"abstract":"<div><div>Understanding the processes and contributions of various sources to arc magmas, originating from the mantle wedge, is crucial for unraveling the complex interactions between crust and mantle in subduction zones. Plagioclase with a prolonged crystallization history serves as a key mineral in studying sources of magma and its evolution history. This study presents in-situ trace elements and Pb isotopes of plagioclase in basalts and rhyolites, and in-situ trace elements of clinopyroxene in basalts of the Toba volcanic system on the Sunda arc, Sumatra. The rhyolites from the ∼75 ka Youngest Toba tuff (YTT) and the basalts from the post-YTT Sipisupisu lave dome are cogenetic and share the same lower crustal magma reservoir. Some of the plagioclase crystals in rhyolites contain a sieved core with high Ca (An = 78 to 85 %) and high Fe contents (∼4800 ppm) that are not in equilibrium with the rhyolitic melts, but are compositionally similar to plagioclase in the cogenetic basalts. Since clinopyroxene in the basalts has negative Eu anomalies and crystallized at lower crustal depth (∼13 to 25 km deep), it can be inferred that plagioclase with positive Eu anomaly could have crystallized simultaneously with clinopyroxene at similar depth. Therefore, we infer that the high-Ca plagioclase cores were antecrysts crystallized from more primitive melts at lower crustal depth and then transported to the upper crust by more evolved melts. Lead isotopic compositions of the plagioclase cores are relatively homogeneous (²⁰⁶Pb/²⁰⁴Pb = 18.94–19.02, ²⁰⁷Pb/²⁰⁴Pb = 15.81–15.84, ²⁰⁸Pb/²⁰⁴Pb = 39.61–39.74) and plot between those of the depleted MORB mantle (DMM) and the upper crust/subducted sediments. The fact that plagioclase cores crystallized at lower crustal depth were endowed with an upper crustal Pb isotopic signature indicates that upper crustal materials were probably added to the mantle source of the Toba volcanic system via subduction. Considering that all the plagioclase crystals of the Toba volcanic system have similarly high ²⁰⁷Pb/²⁰⁴Pb ratios close to and slightly beyond that of the subducted Nicobar Fan sediments, the primary basaltic melts of the Toba volcanic system may have been enriched in radiogenic Pb isotopes by addition of the subducted sediments to the mantle wedge. The mantle-derived basaltic melts with highly radiogenic Sr and Pb isotopic compositions further evolve through assimilation and fractional crystallization (AFC) in the crust to form andesitic-rhyolitic melts. Using in-situ Pb isotopes of plagioclase, this study exemplifies a credible means to discern processes of sediment addition to the mantle wedge and crustal assimilation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122740"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666527","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":"Stratified distribution of recycled components in the mantle of the South China Sea unveiled through magnesium isotopes","authors":"Zhen-Min Ge ,&nbsp;Xiao-Long Huang ,&nbsp;Fan Yang ,&nbsp;Yang Yu ,&nbsp;Guan-Hong Zhu ,&nbsp;Le Zhang ,&nbsp;Yu-Xin Cai ,&nbsp;Guo-Hong Sun","doi":"10.1016/j.chemgeo.2025.122742","DOIUrl":"10.1016/j.chemgeo.2025.122742","url":null,"abstract":"<div><div>Plate subduction is pivotal in creating mantle heterogeneity and facilitating deep material recycling. However, the precise origins, input processes, and distribution of recycled components in the upper mantle remain poorly constrained by natural observations. Compared to large ocean basins, marginal sea basins are more likely to preserve detailed information about recycled components due to their close spatial relationship with subduction processes, relatively smaller size, and shorter evolutionary timescales. In this study, we present new Mg–Sr–Pb isotope data, in conjunction with previously published major and trace element analyses, as well as Nd–Hf isotope data for mid-ocean ridge basalt (MORB) samples from Holes U1431E, U1433B, and U1434A of the International Ocean Discovery Program (IODP) Expedition 349 in the South China Sea (SCS), a marginal sea basin in the Western Pacific with a complex subduction history. MORBs from the SCS exhibit a wide range of Mg isotope ratios (δ²⁶Mg = −0.32‰ to 0.05‰, with an average of −0.16‰), with some samples displaying lower or higher values compared to the average mantle (δ²⁶Mg = −0.25 ± 0.04‰). These variable Mg isotope compositions likely originate from mantle sources affected by subduction-related metasomatism at varying depths, given the limited impact of post-eruptive alteration, diffusion, and high-temperature magmatic processes. The heavy Mg isotopes in the SCS basalts can be attributed to metasomatism by serpentinite components related to surrounding subduction restricted to the shallow mantle (&lt;200 km). Conversely, MORBs with lighter Mg isotopes also show high Hf/Hf* (&gt;1) and low CaO/Al₂O₃ values, which were derived from recycled carbonated eclogites formed after decarbonization of residual subducted carbonate-bearing sediments in the upper mantle at depths exceeding 200 km or within the mantle transition zone (410–660 km). The southwestern subbasin records more information about serpentinite components due to its low expansion rate, insufficient magma supply, and weak mantle mixing, as well as recycled carbonated eclogites carried by subduction-induced mantle-return flows. In contrast, in the eastern subbasin, a greater proportion of recycled carbonated eclogites from the mantle transition zone was incorporated into the mantle source by an upwelling mantle plume. The data show that MORBs from the SCS preserve a record of derivation from various depths of the convecting mantle having a distinct geochemical and isotopic imprint, including evidence for a carbon-rich reservoir in the deep upper mantle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122742"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643345","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":"Iron isotope fractionation during silicate‑carbonatite liquid immiscibility processes","authors":"Xiao-Bao Zhang ,&nbsp;Jian-Qiang Liu ,&nbsp;Lukáš Krmíček ,&nbsp;Valentin R. Troll ,&nbsp;Tomáš Magna ,&nbsp;Adam Maťo ,&nbsp;Gang Zeng ,&nbsp;Xiao-Jun Wang ,&nbsp;Li-Hui Chen","doi":"10.1016/j.chemgeo.2025.122732","DOIUrl":"10.1016/j.chemgeo.2025.122732","url":null,"abstract":"<div><div>Liquid immiscibility is one of the viable genetic models to generate carbonatites. Experimental studies have demonstrated that lighter Fe isotopes are enriched in carbonatite melts, whereas heavier Fe isotopes preferentially enter silicate melts during liquid immiscibility. However, this observation has not been substantiated by natural samples, and the mechanism behind Fe isotope fractionation during silicate–carbonatite immiscibility remains unclear. Here, we present high-precision Fe isotope data, combined with petrography, whole-rock elemental and Sr–Nd isotopic compositions, for ultramafic lamprophyres (UML) and carbonatites from the Alnö complex in central Sweden, to elucidate the Fe isotope fractionation during silicate–carbonatite immiscibility processes. The presence of various carbonate spherules in UML, coupled with enrichments in Sr and Ba and depletion in high field strength elements in carbonatites, as well as their overlapping Sr–Nd isotope compositions, supports a petrogenetic relationship involving liquid immiscibility between the UML and carbonatites. The mean δ⁵⁷Fe of UML (0.16 ± 0.08 ‰) is higher than that of carbonatites (0.03 ± 0.04 ‰), with ∆⁵⁷Fe_sil−carb of 0.13 ‰ (± 0.05, 2SD). By excluding the effects of low temperature alteration and magmatic processes, we conclude that silicate–carbonatite immiscibility imparts significant Fe isotope fractionation. This fractionation may be influenced by different Fe bond strengths provided by the distinct polymer networks of silicate and carbonatite melts, as well as the varying degrees of Fe enrichment in minerals and melts. This leads to light Fe isotopes being preferentially enriched in the carbonate melt, while heavy Fe isotopes become enriched in the coexisting silicate melt.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122732"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643346","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":"Geochemistry of the sheeted dyke complex, Troodos Ophiolite (Cyprus): Evidence for the magmatic evolution during subduction initiation","authors":"Wiebke Lehmann ,&nbsp;Marcel Regelous ,&nbsp;Karsten Haase ,&nbsp;Manuel Keith ,&nbsp;Dominic Woelki","doi":"10.1016/j.chemgeo.2025.122743","DOIUrl":"10.1016/j.chemgeo.2025.122743","url":null,"abstract":"<div><div>Supra-subduction zone (SSZ) ophiolites, including the Troodos Ophiolite of Cyprus contain magmatic rocks with geochemical compositions indicating that they formed close to a subduction zone. However, the exact tectonic setting in which SSZ ophiolites were formed is debated, although it has been proposed that they represent fragments of fore-arc crust formed during subduction initiation. The sheeted dyke complex of an ophiolite provides information about the orientation and distance of the spreading axis relative to the slab. This study combines new and published geochemical data for the Troodos sheeted dyke complex with published data for volcanic glasses from the overlying lavas. We show that the sheeted dykes are generally tholeiitic compared to the tholeiitic to boninitic lavas, and most are less depleted (higher Zr/Yb) and contain less slab component (higher Ce/Pb) than the abundant boninitic Troodos lavas. This implies that the crust of the Troodos Ophiolite formed more distant from the trench than the off-axis boninites that mainly occur in the south of the ophiolite. Many of the Troodos dykes have compositions similar to fore-arc basalts from the Izu-Bonin-Mariana island arc, which were erupted during subduction initiation. Lavas equivalent to the sheeted dykes may exist in the lowermost lava pile of the Troodos Ophiolite. The observed geochemical evolution of Troodos from fore-arc basalt to boninite and tholeiite with a strong slab input resembles the stratigraphy of the Izu-Bonin-Mariana fore-arc. We suggest that the Troodos Ophiolite formed at a laterally propagating trench-ridge ‘double junction’ during subduction initiation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122743"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643428","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":"Probing chemical transport through a rock using a porphyroblast population: Insights from the distributions of major, minor, and trace elements in garnet from the Danba dome (SW China)","authors":"Zhen M.G. Li ,&nbsp;Fred Gaidies ,&nbsp;Yi-Chao Chen ,&nbsp;Chun-Ming Wu","doi":"10.1016/j.chemgeo.2025.122741","DOIUrl":"10.1016/j.chemgeo.2025.122741","url":null,"abstract":"<div><div>A population of garnet porphyroblasts, spaced apart between c. 6 mm and 40 mm, in a metapelite of the kyanite zone from the Danba dome was investigated to assess the equilibration length scales of major and trace elements in the intergranular medium during garnet crystallization. Garnet crystallization occurred from ∼525 °C / ∼6.2 kbar to peak conditions of ∼635 °C / ∼6.2–7.7 kbar. Enrichments in the concentrations of Fe, Nb, Cr, and V, as well as depletions in the contents of Ca, Li, Na, Y, and heavy rare earth elements (HREE) in the early-grown garnet portions indicate that garnet initially pseudomorphed biotite. Results of the statistical analysis of the garnet 3D distribution suggest clustering nucleation mechanisms, providing textural evidence of spatial variations in the distributions of energetically favourable nucleation sites early in the garnet crystallization history. With the exception of the core domains of two early-grown crystals (SC1 and SC8), the distributions of Mg, Ca, Mn, and Fe reflect growth zoning of a garnet population, overprinted by intracrystalline diffusion. The concentrations of Li, Na, Sc, Y, Dy, and Ho in simultaneously grown segments of all garnet crystals are quantitatively comparable, suggesting that the intergranular medium can be considered compositionally homogeneous with regards to these elements, indicative of rapid intergranular chemical transport over a distance of at least c. 40 mm. Differences in the concentrations of Er, Tm, Yb, and Lu are only observed in crystals more than c. 12 mm apart, with the concentrations of these elements decreasing as their atomic masses increase. This systematic trend is interpreted to reflect the possible influence of the relative atomic masses of these elements on the length scales of their diffusion through the intergranular medium during garnet growth. Elements that were heterogeneously distributed across the intergranular medium at the mm-scale during garnet growth include Cr and Zr, reflecting the compositional heterogeneity of the protolith, preserved due to the negligible transport of these elements during the metamorphism. This study emphasizes that the equilibration length scales of trace elements during metamorphism may be larger than previously assumed, presumably depending on the duration of the metamorphism.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122741"},"PeriodicalIF":3.6,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666339","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}