Chemical Geology最新文献

{"title":"Carbonate metasomatism of the lithospheric mantle and its implication to formation of PGE-bearing intrusions along the northern margin of the North China Craton: Insights from mantle xenoliths at Dongbaxiang, Inner Mongolia","authors":"Yonghua Cao, Zhongyu Zhang, Youming Liu, Manye Xu, Luqing Zhou, Lingling Yuan","doi":"10.1016/j.chemgeo.2025.123198","DOIUrl":"10.1016/j.chemgeo.2025.123198","url":null,"abstract":"<div><div>Metasomatism in the lithospheric mantle not only modifies its properties but also exerts a control on the initiation and evolution of magmatic events, some of which are associated with mineralization. However, direct petrological evidence linking mantle metasomatism with subsequent magmatic processes remains limited. The northern margin of the North China Craton (NCC) contains abundant mantle xenolith-bearing Cenozoic-Mesozoic basalts, and some PGE-bearing intrusions. Here, we present a detailed petrological and geochemical investigation of mantle xenoliths from the Dongbaxiang area on the northern margin of the NCC, with the aim of unraveling the types of metasomatism occurring in the lithospheric mantle and evaluating its potential link to the formation of PGE-bearing intrusions. The Dongbaxiang xenoliths are composed mainly of harzburgite, lherzolite, and olivine websterite. In harzburgite xenoliths, some orthopyroxene grains show sieve-textured reaction rims composed of clinopyroxene and olivine. Compared to the clinopyroxene primocrysts in this xenolith type, the clinopyroxene rims have significantly higher (La/Yb)<sub>N</sub> (>2), Zr/Hf (>60), and <sup>87</sup>Sr/<sup>86</sup>Sr (0.7044 to 0.7046) ratios, indicating reaction of orthopyroxene with carbonate melts. Clinopyroxene grains in lherzolite xenoliths commonly show core-to-rim textures, with spongy rims characterized by markedly higher Ca contents, (La/Yb)<sub>N</sub> ratios (>2), and <sup>87</sup>Sr/<sup>86</sup>Sr values (0.7056 to 0.7080), and much lower Ti/Eu ratios (<2500), compared to their cores, suggesting that the spongy rims were likely formed in relation to carbonate metasomatic processes. The olivine websterite xenoliths contain abundant carbonate veins, which have sedimentary carbonate-like Yb/Ca and Yb/La ratios and show trace-element patterns resembling those of carbonate melts derived from partial melting of sedimentary carbonate, indicating that the carbonate veins represent crystallization products of carbonate melts in the mantle. The mantle <em>f</em>O<sub>2</sub> values, calculated using the olivine-spinel-orthopyroxene oxybarometer, indicate that all three types of xenoliths record elevated mantle <em>f</em>O<sub>2</sub> levels (FMQ +0.52 to +1.73) relative to typical Mid-Ocean Ridge Basalt (MORB) mantle (≤FMQ +0.5), providing further support for infiltration of oxidizing, carbonate melts in the lithospheric mantle. Model ages for carbonate metasomatism (515 to 380 Ma) estimated from the <sup>87</sup>Sr/<sup>86</sup>Sr ratios of clinopyroxene reaction rims broadly overlap with the timeframe for the subduction of the Paleo-Asian Ocean, suggesting that the metasomatic agent was likely derived from partial melting of sedimentary carbonates on the subducting Paleo-Asian oceanic crust. Notably, the timing of carbonate metasomatism recorded in the Dongbaxiang xenoliths also coincides with the emplacement of nearby Wengeqi (ca. 399 Ma) and Chaqin ","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123198"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145732114","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":"The glass transition and non-Arrhenian viscosity of extremely depolymerized silicate melts","authors":"Thilo Bissbort ,&nbsp;Kai-Uwe Hess ,&nbsp;Elena Sturm ,&nbsp;Sebastian Sturm ,&nbsp;Detlef Rogalla ,&nbsp;Ralf Dohmen ,&nbsp;Knut Müller-Caspary ,&nbsp;Donald B. Dingwell","doi":"10.1016/j.chemgeo.2025.123193","DOIUrl":"10.1016/j.chemgeo.2025.123193","url":null,"abstract":"<div><div>Properties of extremely depolymerized melts and glasses have always been elusive due to their inaccessibility in experiments. Information on viscosity, for example, was previously restricted to very high temperatures. Yet, theory and experimental details about peridotites suggest that highly depolymerized melts exhibit exceptional properties, such as extremely non-Arrhenian viscosity-temperature relationships. Studies at low temperatures, i.e., just above the glass transition temperature, required for investigating such phenomena have been impossible for many compositions due to their rapid crystallization and thus extremely poor glass-forming ability. Here, we have developed a novel method combining synthesis by pulsed laser deposition with characterization by fast differential scanning calorimetry (FDSC) to deposit glassy thin films, from a plasma directly onto FDSC sensors, combined with calorimetric analysis at very high heating-cooling rates (3500–9500 °C s⁻¹). In this way we have been able to explore the glass transition of the glasses (at or near olivine stoichiometry): Mg_1.30SiO_3.3, Fe_0.34Mg_1.67SiO_4.0, Fe_0.49Mg_1.53SiO_4.0, Fe_1.21Mg_0.91SiO_4.1, and Fe_2.26SiO_4.3. The peak glass transition temperature at 5000 °C s⁻¹ increases from 550 °C for Fe_2.26SiO_4.3 with decreasing (Fe + Mg)/Si and with increasing Mg/(Fe + Mg) to 736 °C for Mg_1.30SiO_3.3. Viscosities derived through the shift factor approach range from 10^5.61 to 10^6.04 Pa∙s in that temperature range. These results thus extend the experimentally available viscosity range by ca. seven log units and were employed here, together with high-temperature superliquidus viscosity data to fit the Vogel-Fulcher-Tammann (VFT) equations for these melts. The viscosity-temperature relationships are all strongly non-Arrhenian (m = 82–123 ± 15). We provide a comparison with other experimental studies of ultrabasic melts and with predictions from viscosity models. The inability of the latter to predict the observed viscosities highlights the necessity of direct experimental studies such as that presented here.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123193"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145732117","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":"Reconstruction of oceanic paleosalinity during the Late Ordovician in the inner Yangtze Sea of South China","authors":"Qiang Gu ,&nbsp;Fengcun Xing ,&nbsp;Karem Azmy ,&nbsp;Gesheng Wang ,&nbsp;Xinying Liu ,&nbsp;Xi Wei ,&nbsp;Ziqi Liu ,&nbsp;Aishi Liang","doi":"10.1016/j.chemgeo.2025.123190","DOIUrl":"10.1016/j.chemgeo.2025.123190","url":null,"abstract":"<div><div>The Ordovician-Silurian Transition (OST) was a key geological period, which recorded the Late Ordovician Mass Extinction (LOME), volcanic eruption, oceanic anoxia, rapid sealevel fluctuations, glacial event and carbon isotope excursion. Recent studies also identify a late Katian extinction pulse as part of the LOME. During the OST, the inner Yangtze Sea (IYS) was tectonically restricted, but the controlling factors of salinity heterogeneity in the basin and their impact on LOME remain debated. Carbonate sedimentation dominated the IYS in the Late Ordovician, thus complicating continuous salinity reconstructions because most paleosalinity proxies are calibrated for shales and are less readily applied to carbonates. Based on carbon-isotope stratigraphy, we used geochemical proxies (e.g., elemental and the new proxy “excess B\") to assess the relative salinity variations in the IYS during the OST. The carbonate salinity proxies revealed a paleosalinity trend like that observed in shale (Decreases and then increases near the Hirnantian). Combining multiple paleoenvironmental proxies and previously published data, we evaluated the contribution of paleosalinity changes to LOME. Our δ¹³C_org and δ¹³C_carb records the Guttenberg positive isotope carbon excursion (GICE) and the Hirnantian Isotopic Carbon Excursion (HICE). The paleosalinity proxies, along with others, allowed the division of the OST into four Units where salinity was controlled by sealevel changes, the Kwangsian Orogeny, and climate-induced changes in terrestrial runoff. The reduction in species and abundance supports the occurrence of the Katian Extinction in the IYS. The expansion of anoxic seawater was not the only factor controlling the LOME, but salinity likely has played a crucial role.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123190"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145689922","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":"Mineralization of bacterial cells during proto-dolomite precipitation mediated by the halophilic bacteria Bacillus licheniformis","authors":"Ruirui Meng ,&nbsp;Zuozhen Han ,&nbsp;Wen Nie ,&nbsp;Chao Han ,&nbsp;Yu Han ,&nbsp;Maurice E. Tucker","doi":"10.1016/j.chemgeo.2025.123205","DOIUrl":"10.1016/j.chemgeo.2025.123205","url":null,"abstract":"<div><div>Previous studies have demonstrated that bacteria can induce proto-dolomite precipitation at ambient temperatures. Yet, the mineralization of the bacteria during this process has rarely been reported. Here we describe mineralized bacteria formed during proto-dolomite precipitation mediated by the moderate halophilic bacteria <em>Bacillus licheniformis</em> Y1. The XRD data and SEM images show that proto-dolomite precipitated mainly as aggregates in media with Mg/Ca ratios of 6, 8 and 10 cultured at temperatures of 30 °C and 40 °C, but this was not observed in solutions cultured at 20 °C. Solution chemistry analysis showed that all solutions maintained a higher CO₃²⁻ concentration and correspondingly higher saturation indices for proto-dolomite at 40 °C. The HRTEM results illustrate that the crystal structures and Mg/Ca atomic ratio of the proto-dolomite more closely match those of dolomite, and some superstructure reflections appear in the HRTEM and SAED images. These features indicate that a few crystal units of proto-dolomite may have been formed with some degree of cation ordering. The SED/EDS and HRTEM images also demonstrate that the bacteria are mineralized and form proto-dolomite crusts. The HTREM analyses of bacterial ultrathin slices show that the proto-dolomite crystals formed within cells, on the cell surface and within EPS. We assume that during biomineralization, Ca²⁺ and Mg²⁺ ions are trapped by the negatively charged EPS and transferred into the cells through diffusion, leading to the extracellular and intracellular precipitation of proto-dolomite; the bacteria themselves are mineralized during the constant formation of proto-dolomite crystals within and upon the surface of the cells. This study provides insights into our understanding of the formation of biotic proto-dolomite, and contributes to the origin of “microbial dolomite”.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123205"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145753515","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":"Internally consistent thermodynamic properties of Nd chloride aqueous species and Nd3+ derived from hydrothermal solution calorimetry at 25–150 °C","authors":"Yerko Figueroa Penarrieta ,&nbsp;Alexander P. Gysi","doi":"10.1016/j.chemgeo.2025.123192","DOIUrl":"10.1016/j.chemgeo.2025.123192","url":null,"abstract":"<div><div>Rare earth elements (REE) are important critical elements used in the high-technology and green energy industries. Hydrothermal fluid-rock interaction and the stability of aqueous chloride complexes play an important role in the mobilization and deposition of REE in geologic systems. Geochemical modeling can be used to interpret the mobility of REE in these hydrothermal fluids. However, the accuracy of modeling predictions strongly depends on the underlying thermodynamic properties for REE aqueous species. In this study, hydrothermal solution calorimetry was used to measure the standard partial molal enthalpy of solution (Δ_sol<em>H</em>°) of Nd chloride solid (NdCl₃·6H₂O) from 25 to 150 °C in order to determine the standard thermodynamic properties of Nd chloride aqueous species. The experiments were conducted in aqueous hydrochloric acid-based aqueous solutions with an initial pH of 2 and varying ionic strength (0.08–0.42 mol/kg), at which conditions the Nd³⁺ and Nd chloride species are both stable. In the studied temperature range, the measured Δ_sol<em>H</em>° values differ by 35 kJ/mol in comparison to thermodynamic predictions based on available literature data. These large discrepancies have important implications for geochemical modeling because the thermodynamic properties of REE aqueous species are derived from the properties of REE chloride solids. To address this problem, the standard enthalpy of formation (Δ_f<em>H</em>°) of NdCl₃·6H₂O(s) and aqueous NdCl²⁺ species were optimized to reproduce the experimentally derived Δ_sol<em>H</em>° values and keeping internal consistency with the recently updated thermodynamic properties of Nd³⁺. The outcome of this study permits deriving a set of recommended internally consistent thermodynamic properties for the Nd aqueous species which improve thermodynamic modeling of REE mobilization in acidic NaCl-bearing aqueous fluids.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123192"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145690055","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":"Closure temperature for the fission-track systems","authors":"Matheus Rufino,&nbsp;Arnaldo Luis Lixandrão-Filho,&nbsp;Sandro Guedes","doi":"10.1016/j.chemgeo.2025.123195","DOIUrl":"10.1016/j.chemgeo.2025.123195","url":null,"abstract":"<div><div>We introduce a novel analytical equation (AE) for computing closure temperature (<span><math><msub><mi>T</mi><mi>c</mi></msub></math></span>) in fission-track (FT) systems, grounded in a rigorous physicochemical framework. By extending Dodson's foundational concept to the complex, non-first-order kinetics characteristic of fission-track annealing, this work overcomes historical barriers to a direct analytical formulation in FT thermochronology. To date, most <span><math><msub><mi>T</mi><mi>c</mi></msub></math></span> estimates for fission track systems have relied on numerical simulations based on the Principle of Equivalent Time (PET). However, a recently developed physicochemical framework allows modeling variable thermal histories without relying on PET. In this study, we employ this framework to construct an analytical equation for computing closure temperature in the fission-track system. The resulting <span><math><msub><mi>T</mi><mi>c</mi></msub></math></span> values are then compared with previously published results to assess accuracy and consistency. The analytical formulation is simpler, faster to compute, and more easily automated. However, the practical accuracy of this analytical solution is intrinsically linked to the quality and advancements of the empirical annealing models and bias models (track length to density relationships) upon which it relies.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123195"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145731859","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":"Rapid recycling of sediment-derived granites in accretionary orogens: Implications from the Alataw Mountains, NW China","authors":"Jiyuan Yin ,&nbsp;He Huang ,&nbsp;Ilya Bindeman ,&nbsp;Chiara Maria Petrone ,&nbsp;Mike Fowler ,&nbsp;Andrew C. Kerr ,&nbsp;Zaili Tao ,&nbsp;Tao Wang ,&nbsp;Min Sun ,&nbsp;Guochun Zhao ,&nbsp;Wenjiao Xiao","doi":"10.1016/j.chemgeo.2025.123181","DOIUrl":"10.1016/j.chemgeo.2025.123181","url":null,"abstract":"<div><div>The origin of S- and I-type granites in accretionary orogens remains contentious due to complex geochemical and isotopic signatures, challenging traditional granite classifications. We present new zircon U-Pb-Hf-O, quartz O isotope and whole-rock geochemical data from two-mica (S-type) and biotite (nominally I-type) granites in the Alataw Mountains, northwest China, showing both are derived from sediment-dominated protoliths. Zircon U<img>Pb dating indicates emplacement at 303–298 Ma, with differing inherited ages of 443–397 Ma and 1404–811 Ma. The two-mica granites were derived from metapelitic sources and are strongly peraluminous, while the biotite granites are metaluminous to weakly peraluminous with many “I-type” characteristics. Both types exhibit high SiO₂, low MgO, elevated zircon δ¹⁸O, high quartz δ¹⁸O and high Δ^’17O values consistent with sedimentary sources, but depleted εNd(t) and εHf(t) values that require a juvenile origin. Phase equilibrium modelling indicates that these granites formed through water-fluxed partial melting of variable Carboniferous sedimentary rocks. Thus, crustal melts appear juvenile and S-type granites appear to be I-type. Our findings highlight the critical role of rapid crustal recycling via sediment melting during the reworking of juvenile crust within arc-related accretionary orogens and suggest the need for caution when considering granite origins based on traditional typological classifications.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123181"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145690052","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":"Effects of chemical weathering and grain size sorting on SrNd isotopic source rock signatures of river sediments in the lower Mekong River Basin: Implications for provenance studies","authors":"Pham Nhu Sang ,&nbsp;Zhifei Liu ,&nbsp;Yulong Zhao ,&nbsp;Pham Trung Hieu ,&nbsp;Sopheak Thav ,&nbsp;Sopheap Den","doi":"10.1016/j.chemgeo.2025.123199","DOIUrl":"10.1016/j.chemgeo.2025.123199","url":null,"abstract":"<div><div>Sr<img>Nd isotopic compositions are reliable proxies for tracing the provenance of riverine and marine sediments. However, these isotopic compositions can be influenced by processes such as chemical weathering in the source region and grain size sorting during transport, which can obscure the original provenance signals. In this study, Sr<img>Nd isotopic compositions of clay, silt, and sand fractions from river sediments in the Lower Mekong River Basin are analyzed to investigate the influence of chemical weathering and grain size sorting and their implications for provenance studies. Mainstream sediments exhibit higher ⁸⁷Sr/⁸⁶Sr (0.724) and lower ε_Nd (−9.72) values compared to tributary sediments (0.717 and − 5.61, respectively). The clay fractions in both mainstream and tributary sediments show more radiogenic ⁸⁷Sr/⁸⁶Sr (0.726) and higher ε_Nd (−7.29) values than the silt (0.721 and − 8.88, respectively) and sand (0.718 and − 9.27, respectively) fractions. Rb/Sr and ⁸⁷Sr/⁸⁶Sr in both mainstream and tributary sediments present moderate or strong correlations with K₂O/(CaO + Na₂O) and SiO₂/Al₂O₃, indicating that chemical weathering and grain size sorting moderately influence Sr isotopes. In contrast, Sm/Nd and ε_Nd display no or weak correlations with K₂O/(CaO + Na₂O) and SiO₂/Al₂O₃, suggesting that Nd isotopes are less affected by these factors. Despite these influences, significant differences in Sr<img>Nd isotopic compositions between mainstream and tributary sediments are evident, with moderate to strong negative correlations between ⁸⁷Sr/⁸⁶Sr and ε_Nd across clay, silt, and sand fractions. These differences effectively distinguish the mainstream from the tributary sediments, reflecting the control of source rock lithology and the preservation of source rock signatures in this region. To minimize the effects of chemical weathering and grain size sorting, this study recommends using Sr<img>Nd isotopic data from uniform grain size fractions for provenance investigations of riverine and marine sediments, with the silt fraction being the most suitable.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123199"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145731853","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":"Crustal growth and modification of the Muzidian Gneiss complex revealed by detrital zircon from modern river sediments","authors":"Xiao-Fei Qiu ,&nbsp;Xi-Run Tong ,&nbsp;Da Wang ,&nbsp;Xin Deng ,&nbsp;Shan-Song Lu","doi":"10.1016/j.chemgeo.2025.123171","DOIUrl":"10.1016/j.chemgeo.2025.123171","url":null,"abstract":"<div><div>The Muzidian Gneiss Complex located in the Yangtze Block, South China Craton was recently shown to contain &gt;4.0 Ga zircon grains and magmatic rocks as old as ∼3.8 Ga. Our understanding is limited regarding the crustal growth and modification history of this complex. In order to understand the crustal evolution history of the early Archean Muzidian Gneiss Complex and its relationship to the surrounding broader Yangtze Block, we focused on the sediments in five local streams and rivers across the Muzidian area where the Muzidian Gneiss Complex was located. Here we report 899 U-Pb dates and 620 Lu<img>Hf isotope measurements of detrital zircons in river sediments. The detrital zircon grains from these rivers show generally similar U<img>Pb age patterns, yielding two major age peaks at ∼2.5–2.4 Ga and ∼ 140–120 Ma, and a few minor groups at 3.8–3.2 Ga, 2.1–1.9 Ga, 780–650 Ma, and 450–400 Ma, respectively.</div><div>Zircon Lu<img>Hf isotopic data suggest dominant crustal reworking over most of the Archean from an ultimate Hadean or Eoarchean magmatic source, and the input of juvenile materials mixing with pre-existing ancient continental crust since the Neoarchean and Paleoproterozoic. The initial Hf isotopic compositions of the Mesozoic zircon grains in the studied river sediments can be projected to those of the Eoarchean and Mesoarchean zircon grains, suggesting a likely reworked origin for the young zircon grains. These observations collectively suggest that the proportion of continental crust formed in the early Archean is likely greater than what is shown in the U<img>Pb age distribution of detrital zircons. Based on our new data, we propose that the Hadean to Eoarchean rocks in the Muzidian Gneiss Complex likely represent a continental nuclei in the present-day South China Craton, which was long-lived and continuously re-melted to form younger rocks around it during the Archean. Significant input of depleted mantle derived, juvenile materials was not a component in the crustal growth and modification of the Muzidian Gneiss Complex until the Neoarchean, which may correspond to the accretion and cratonization of the broader north Yangtze Block of the South China Craton.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123171"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145613837","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":"Redox evolution of carbon- and sulphur-bearing clinopyroxenites as proxies of deeply recycled crustal material","authors":"Nadia Malaspina ,&nbsp;Falko Langenhorst ,&nbsp;Kilian Pollok ,&nbsp;Valerio Cerantola ,&nbsp;Mara Murri ,&nbsp;Carolina Longa ,&nbsp;Danilo Bersani ,&nbsp;Alessandra Montanini","doi":"10.1016/j.chemgeo.2025.123173","DOIUrl":"10.1016/j.chemgeo.2025.123173","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Fossil subduction zones are key to studying the deep geochemical cycles of C, O, and S. We analysed graphite-sulphide-bearing garnet clinopyroxenites from the External Ligurian (Northern Apennines, Italy), which serve as indicators of deep recycling of subducted crust. These rocks are among the only three known pyroxenite occurrences worldwide (along with Beni Bousera, Morocco, and Ronda, Spain) that formed through the crystallisation of eclogite-derived melts (&lt;em&gt;P&lt;/em&gt; ≥ 3 GPa and 1100 °C), following a prolonged recycling history in off-craton mantle. In particular, a MOR-type heterogeneous gabbroic sequence was recycled into the mantle as eclogite 1.5–1.0 Ga ago, then partially melted and crystallised in the convective mantle, followed by subsolidus re-equilibration and exhumation. We analysed the redox state of garnets and clinopyroxenes associated with graphite and sulphides in garnet clinopyroxenites, that crystallised from a liquid produced by partial melting of recycled eclogite. Electron Energy Loss Spectroscopy within a transmission electron microscope and Synchrotron micro-Mössbauer analyses revealed heterogeneities in Fe&lt;sup&gt;3+&lt;/sup&gt;/Fe&lt;sup&gt;2+&lt;/sup&gt; distribution and its partitioning among mineral phases (Fe&lt;sup&gt;3+&lt;/sup&gt;/ΣFe error is 0.03 for Electron Energy Loss Spectroscopy and 0.01–0.03 for Synchrotron micro-Mössbauer).&lt;/div&gt;&lt;div&gt;The analysed clinopyroxenites display three generations of clinopyroxenes: unexsolved crystals included in garnet cores with Fe&lt;sup&gt;3+&lt;/sup&gt;/ΣFe = 0.16–0.38 (representative of eclogite-derived melt crystallisation in the asthenosphere), clinoenstatite exsolution-bearing grains with Fe&lt;sup&gt;3+&lt;/sup&gt;/ΣFe = 0.03–0.10 (related to a first stage of exhumation in the lithospheric mantle), and Al-poorer rims without Fe&lt;sup&gt;3+&lt;/sup&gt; (related to the final stage of exhumation). In contrast, garnets have Fe&lt;sup&gt;3+&lt;/sup&gt;/ΣFe-poor cores (&lt;0.03) and slightly higher ratios in the rims (0.04–0.07). When considered together with the markedly higher Fe&lt;sup&gt;3+&lt;/sup&gt; contents in the earliest clinopyroxene generation, this pattern is consistent with a pressure–temperature–dependent partitioning of ferric iron from garnet to clinopyroxene during cooling from 1100 to 950 °C along the exhumation path. &lt;em&gt;f&lt;/em&gt;O&lt;sub&gt;2&lt;/sub&gt; calculations suggest a variation from more oxidised samples (ΔFMQ = −1.25 to 0) to more reduced ones (ΔFMQ = −4.2 to −1.6) at 3 GPa. At 1.5 GPa, ΔFMQ ranges from −1.2 to −0.6 down to &lt; −5, indicating that graphite may have formed through reduction of a previously oxidised carbon phase. The oxidation state variations are linked to sub-solidus decompression, and not to S-C-related redox reactions, describing a closed system with no fluid/melt-rock interaction. Our results show that sulphur plays no role in controlling the redox state of these graphite-bearing mantle rocks, even over prolonged geological histories, and that variations in the redox state of carbon and iron in garnet and clinopyroxen","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"700 ","pages":"Article 123173"},"PeriodicalIF":3.6,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145645562","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}