Chemical Geology最新文献

{"title":"Extremely heavy Ca isotope compositions of rodingites in the oceanic lithosphere formed by fluid-rock interaction: Implications for the discrimination of light Mg isotope components","authors":"Mei-Shan Zhao ,&nbsp;Jia-Le Xu ,&nbsp;Yi-Xiang Chen ,&nbsp;Jia-Wei Xiong ,&nbsp;Xin-Yue Qiao ,&nbsp;Tatsuki Tsujimori ,&nbsp;Marco Scambelluri","doi":"10.1016/j.chemgeo.2025.122697","DOIUrl":"10.1016/j.chemgeo.2025.122697","url":null,"abstract":"<div><div>Rodingite is a crucial component of the altered oceanic lithosphere and is an extremely Ca-rich rock (CaO content reaching ca. 30 wt%). However, its Ca isotope composition remains unclear. Furthermore, rodingite and carbonate represent two common Ca-rich reservoirs in the oceanic lithosphere characterized by light Mg isotope compositions. Currently, it remains unclear how these two rock reservoirs contribute to the light Mg isotope composition of some igneous rocks. In this study, we present the Ca isotope compositions of rodingites and their protolith gabbros from the Xigaze ophiolites in southern Tibet. The gabbros exhibit relatively homogeneous δ^44/40Ca values ranging from 0.70 to 0.87 ‰, which are comparable to the MORB composition, while rodingites display significantly higher δ^44/40Ca values ranging from 0.92 to 1.89 ‰. Based on formation temperature conditions and mineral assemblages, rodingites can be categorized into two groups that exhibit contrasting correlations with respect to the ⁸⁷Sr/⁸⁶Sr isotope ratios, bulk Sr contents and Sr/Ca ratios. Group I δ^44/40Ca values show a positive correlation with (⁸⁷Sr/⁸⁶Sr)_i but negative correlations with Sr/Ca ratios and Sr contents. Group II δ^44/40Ca values exhibit a negative correlation with (⁸⁷Sr/⁸⁶Sr)_i but positive correlations with Sr/Ca ratios and Sr contents. The opposing relationships between δ^44/40Ca values and geochemical compositions for Group I and II rodingites suggest Ca additions from different fluid sources and fluid compositions during rodingitization. Initially, seawater predominates the metasomatic fluids during the early stages of rodingitization, however, serpentinizing fluid that dissolves clinopyroxene and orthopyroxene becomes dominating as the fluid-rock reaction progresses. The results indicate that fluid-rock reactions occurring during rodingitization control the Ca isotope composition of the resulting rodingites. Rodingite represents a previously unrecognized reservoir of high Ca contents and δ^44/40Ca values in the altered oceanic lithosphere, which could significantly influence mantle Ca isotope compositions through oceanic slab subduction. In addition, due to the distinct δ^44/40Ca values between rodingite and carbonate-related components, Ca isotopes may serve as an effective tool for distinguishing these light Mg isotope components in the oceanic lithosphere, which is critical for utilizing Ca<img>Mg isotopes as powerful tracers in crust-mantle interaction and carbonate recycling processes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122697"},"PeriodicalIF":3.6,"publicationDate":"2025-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143474610","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 contribution of Good's buffers to laboratory experiments on Fe(II)aq-induced ferrihydrite transformation","authors":"Chao Li ,&nbsp;Peng Liu ,&nbsp;James Jamieson ,&nbsp;Henning Prommer ,&nbsp;Adam J. Siade ,&nbsp;Jiafeng Wang ,&nbsp;Ling Shi ,&nbsp;Jie Yan ,&nbsp;Shirong Liu ,&nbsp;Wen Yu ,&nbsp;Chengshuai Liu ,&nbsp;Jing Sun","doi":"10.1016/j.chemgeo.2025.122700","DOIUrl":"10.1016/j.chemgeo.2025.122700","url":null,"abstract":"<div><div>Numerous previous experiments on Fe(<em>II</em>)_aq-induced Fe(III) oxide transformation used Good's buffers to maintain pH. However, Good's buffer has previously been found to directly complex with the mineral surface and the metals in solution, and indirectly influence the interactions between Fe(<em>II</em>)_aq and Fe(III) oxides by changing the mineral surface properties. So far, to what extent the presence of buffer unintentionally affects the experimental results remains unclear. Herein, this study evaluated the potential contribution of three typical Good's buffers, MES, MOPS and HEPES, to Fe(<em>II</em>)_aq-induced ferrihydrite transformation using batch experiments with 10 mM ferrihydrite, 1 mM Fe(<em>II</em>)_aq, 0–50 mM buffer and 0–0.1 M NaCl at pH 6.0–7.5. The results showed none of the tested buffers could adsorb on ferrihydrite. The extents and products of ferrihydrite transformation in the presence of 0–50 mM buffer were similar at any given pH within 24 h. However, the extents of ferrihydrite transformation with 10–50 mM buffer were significantly (<em>p</em> &lt; <em>0.05</em>) higher than those with 0–1 mM buffer after 72 h. The enhanced transformation with higher buffer concentrations can be attributed to the elevated ionic strength, which raised initial surface loading of Fe(II) on ferrihydrite. The comparison between experiments with and without background electrolyte (NaCl) further confirmed that high ionic strength could promote ferrihydrite transformation with the effect becoming more and more evident over time. Our data systematically assessed the contribution of Good's buffers to laboratory experiments on Fe(<em>II</em>)_aq-induced Fe(III) oxide transformation and provide important reference for similar experiments in the future.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122700"},"PeriodicalIF":3.6,"publicationDate":"2025-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143463776","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":"Burial of seawater–rock interaction-derived pyrites in altered oceanic crust: Implication for Phanerozoic oceanic sulfur cycle","authors":"Xiuquan Miao ,&nbsp;Yunying Zhang ,&nbsp;Zhen Sun ,&nbsp;Liheng Sun ,&nbsp;Ruifang Huang","doi":"10.1016/j.chemgeo.2025.122701","DOIUrl":"10.1016/j.chemgeo.2025.122701","url":null,"abstract":"<div><div>The oceanic sulfur cycle is intimately linked to the cycles of organic matters and oxygen on the Earth's surface. However, controversy exists on the dominant pathway (pyrite vs. evaporite burial) of Phanerozoic oceanic sulfur cycle and its influence on atmospheric oxygen concentrations. This controversy arises from controversial pyrite burial flux (<em>F</em>_py = 2.40 vs. 31.5 × 10¹¹ mol yr⁻¹), sparked by only counting sedimentary pyrites without seawater–rock interaction (SRI)-derived ones and by underestimating evaporite burial flux. To address these issues, we present in-situ sulfur isotopic data for SRI-derived pyrites from Hole U1502B in the South China Sea and calculate the burial flux (<em>F_SRI</em>_-py) of SRI-derived pyrites by employing a new equation without using evaporite burial flux. The studied pyrites exhibit positive <em>δ</em>³⁴S values (1.93–5.96 ‰), high contents of fluid-mobile elements (Pb of 5,810–8,870 ppm and Mo of 8,260–10,240 ppm) and temperature-sensitive elements (Co up to 1,761 ppm and Cu up to 798 ppm), indicating a hydrothermal origin. The values of <em>F_SRI</em>_-py (7.23–14.9 × 10¹¹ mol yr⁻¹), estimated from the S isotopic data of this study and compiled data for SRI-derived pyrites, are similar to the burial flux of sedimentary pyrite, highlighting the essential role of SRI in shaping the Phanerozoic oceanic sulfur cycle. The calculated high total <em>F</em>_py (1.40–2.91 × 10¹² mol yr⁻¹) and pyrite burial fraction (<em>ƒ</em>_py = 47–97 %), incorporating both sedimentary and SRI-derived pyrites, suggest that pyrite burial was the dominant pathway of Phanerozoic oceanic sulfur cycle, and actively regulated atmospheric oxygen concentrations. Moreover, the abrupt increases in Phanerozoic <em>F</em>_py and atmospheric oxygen concentrations were potentially associated with supercontinent assembly.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122701"},"PeriodicalIF":3.6,"publicationDate":"2025-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510654","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":"Widespread melt percolation in the subcontinental mantle: Perspectives from chromium stable isotopes","authors":"Qiuxia Wang ,&nbsp;Jianping Zheng ,&nbsp;Xianquan Ping ,&nbsp;Xiangli Wang","doi":"10.1016/j.chemgeo.2025.122699","DOIUrl":"10.1016/j.chemgeo.2025.122699","url":null,"abstract":"<div><div>Peridotites xenoliths from the subcontinental mantle exhibit a notably broad range of chromium isotope compositions in the literature, with refractory harzburgites demonstrating slightly higher δ⁵³Cr values (mean = −0.04 ± 0.06 ‰, 2SE, <em>N</em> = 49) compared to fertile lherzolites (mean = −0.12 ± 0.03 ‰, 2SE, <em>N</em> = 80). Such discrepancy cannot be explained by the partial melting of lherzolite. To better understand the observation, we analyzed the Cr isotope compositions of twenty-two lherzolites and fifteen harzburgites in Cenozoic basalts from eastern China. Taking the literature data together, the lherzolites yield an average δ⁵³Cr of −0.12 ± 0.05 ‰ (2SE, <em>N</em> = 99), similar to that estimated for the BSE (−0.12 ± 0.04 ‰, 2SD). Moreover, their δ⁵³Cr show no correlations with indicators of melt extraction (such as Al₂O₃ and CaO in whole-rock) or metasomatism (such as (La/Yb)_N in whole-rock and Ca/Al ratios in clinopyroxene), suggesting negligible effects of partial melting or metasomatism. Therefore, the Cr isotopic composition of the studied lherzolites may represent the original mantle signal. In contrast, the harzburgite display significantly higher δ⁵³Cr values (average − 0.04 ± 0.05 ‰, 2SE, <em>N</em> = 60) compared to the lherzolites. They also show no correlation between δ⁵³Cr values and melt extraction indices (such as Al₂O₃ and CaO concentrations of in whole-rocks) or metasomatism indicators (such as (La/Yb)_N in whole-rock and Ca/Al ratios in clinopyroxene). Chromium isotope fractionation during batch or fractional melting can only induce &lt;0.01 ‰ Cr isotope variation, and thus cannot explain the elevated δ⁵³Cr values observed in harzburgites. Instead, kinetic isotope fractionation during melt percolation is more likely responsible for causing such Cr isotope offset between lherzolites and harzburgites in the subcontinental mantle. The isotopically heavy Cr pool harzburgites completements the isotopically light Cr pool in pyroxenite recognized previously.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122699"},"PeriodicalIF":3.6,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143509900","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":"Intragranular to xenolith-scale water heterogeneity in mantle olivine: Insights into cratonic processes","authors":"Wenzhao Dong ,&nbsp;Yui Kouketsu ,&nbsp;Katsuyoshi Michibayashi","doi":"10.1016/j.chemgeo.2025.122694","DOIUrl":"10.1016/j.chemgeo.2025.122694","url":null,"abstract":"<div><div>This study presents Fourier Transform Infrared (FT-IR) mapping of olivine in mantle xenoliths from the Kaapvaal Craton, introducing methodological innovations for quantifying olivine water content. Our advancements include enabling direct Electron Backscatter Diffraction (EBSD) analysis of FT-IR-measured grains, and developing an automated calculation method to minimize serpentinization effects. This approach enables the calculation of the water content of olivine with high reliability and facilitates a point-to-point correlation between water content and crystallographic orientation. Analysis of garnet lherzolites (100–150 km depth) and spinel peridotites (∼60 km depth) revealed our method's effectiveness for olivine water contents above 40 ppm. Olivine in garnet lherzolites contained 40–210 ppm water, while olivine in spinel lherzolites exhibited contents below the detection limit, indicating heterogeneous water distribution in the Kaapvaal Craton mantle. We observed significant water content heterogeneity across multiple scales: intragranular, inter-grain, and xenolithic. Intragranular water content gradients up to 50 ppm were observed, with high-water olivine (&gt;120 ppm) tending to show gradients aligned with crystallographic axes, suggesting anisotropic water incorporation and diffusion processes. Variations in water content between olivine grains within xenoliths and across different microstructures in garnet lherzolites were also noted. This heterogeneity likely results from complex lithospheric mantle processes, including localized metasomatism and deformation. These findings have important implications for understanding cratonic stability, mantle dynamics, and water-related processes in the Earth's mantle, potentially facilitating small-scale metasomatism or deformation without compromising overall cratonic stability.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122694"},"PeriodicalIF":3.6,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143478741","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 ophicarbonates as source for B-bearing diamond formation","authors":"E. Cannaò","doi":"10.1016/j.chemgeo.2025.122693","DOIUrl":"10.1016/j.chemgeo.2025.122693","url":null,"abstract":"<div><div>This study presents <em>in-situ</em> B isotope compositions (δ¹¹B) of antigorite from well-characterized ophicarbonates that underwent prograde to high-pressure (high-<em>P</em>) metamorphic evolution during the Alpine orogeny (300–500 °C and 0.6–2.3 GPa). The δ¹¹B values in antigorite are highly variable, ranging from <em>ca.</em> -8 to +7 ‰. Coupled with <em>in-situ</em> ⁸⁷Sr/⁸⁶Sr ratios of carbonates (ranging from 0.7065 to 0.7085), this B isotope variability may reflect either inherited oceanic imprints or re-equilibration with metamorphic fluids during subduction processes. These interpretations are further corroborated by <em>in-situ</em> REE and incompatible trace element data on antigorite. The devolatilization and densification of slab lithologies during subduction drive the recycling of slab and wedge materials into the Earth's mantle, contributing to its chemical heterogeneity. Remarkably, the δ¹¹B signatures of antigorite reported here overlap with the variability observed in B-bearing diamonds formed at transition zone/lower mantle depths, as well as in carbonatites and ocean island basalts (OIBs), suggesting a geochemical connection. Together with literature data, this study proposes that deeply subducted ophicarbonates may transform into carbonate-bearing secondary peridotites with geochemical features compatible with B-bearing diamonds. Deeply subducted ophicarbonates, with enriched trace element and isotopic signatures, may also act as reservoirs influencing mantle dynamics and the geochemical diversity of OIB and carbonatite mantle sources. These findings provide new constraints into the recycling of B and volatiles at convergent margins, extending to depths compatible with the lower mantle region.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122693"},"PeriodicalIF":3.6,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143454687","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":"Corrigendum to “Study of olivine-hosted melt and spinel inclusions from the Song Da ultramafic volcanic suite, northern Vietnam: Compositions, crystallization temperatures, and origin of the low-Ti komatiite-like and high-Ti primary melts” [Chemical Geology 662 (2024) 122219]","authors":"Charbel Kazzy ,&nbsp;Alexander V. Sobolev ,&nbsp;Valentina G. Batanova ,&nbsp;Evgeny V. Asafov ,&nbsp;Eero Hanski ,&nbsp;Igor S. Puchtel ,&nbsp;Andrey E. Izokh ,&nbsp;Leonid V. Danyushevsky ,&nbsp;Vũ Hoàng Ly ,&nbsp;Can Pham-Ngoc ,&nbsp;Tran Tuan Anh","doi":"10.1016/j.chemgeo.2025.122678","DOIUrl":"10.1016/j.chemgeo.2025.122678","url":null,"abstract":"","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"679 ","pages":"Article 122678"},"PeriodicalIF":3.6,"publicationDate":"2025-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143420730","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":"Overcoming analytical limitations with 5-line multi-dynamic Nd isotope measurements by thermal ionisation mass spectrometry","authors":"C. Israel ,&nbsp;C. Chauvel ,&nbsp;T.-H. Luu ,&nbsp;E.C. Inglis ,&nbsp;D. Roberts","doi":"10.1016/j.chemgeo.2025.122686","DOIUrl":"10.1016/j.chemgeo.2025.122686","url":null,"abstract":"<div><div>The extinct ¹⁴⁶Sm<img>¹⁴²Nd radio-isotope chronometer is a valuable tool to study the first 500 Myr of Earth's history, although the entire range of variations of the ¹⁴²Nd/¹⁴⁴Nd ratio in terrestrial materials is on the order of 20 ppm only. The challenge is that measuring small isotope variations needs very high precision measurements (better than 5 ppm), which are difficult to obtain.</div><div>Here we present high-precision measurements of Nd isotope ratios performed over a period of three years using the latest generation Thermal Ionisation Mass Spectrometer (TIMS) developed by Nu Instruments – Nu TIMS. The Nu TIMS comprises 16 fixed Faraday cups and a zoom optics system that allow 5-line multi-dynamic analyses with the acquisition of three dynamic ratios for all Nd isotopes. This new method, coupled with an enhanced Nd⁺ signal provides precise measurements with internal errors lower than 2 ppm on ¹⁴²Nd/¹⁴⁴Nd.</div><div>We assess the performance of the method using multiple measurements of JNdi-1 and AMES Rennes Nd pure standards, together with rock reference materials. For example, typical JNdi-1 measurements performed over a period of 19 months average at ¹⁴²Nd/¹⁴⁴Nd = 1.1418299 ± 36 (2sd – 3.2 ppm), ¹⁴³Nd/¹⁴⁴Nd = 0.5121007 ± 10 (2.0 ppm), ¹⁴⁵Nd/¹⁴⁴Nd = 0.3484046 ± 6 (1.8 ppm), ¹⁴⁸Nd/¹⁴⁴Nd = 0.2415790 ± 10 (4.1 ppm) and ¹⁵⁰Nd/¹⁴⁴Nd = 0.2364481 ± 27 (11.3 ppm). With such precision and accuracy, subtle variations of ¹⁴²Nd/¹⁴⁴Nd ratios, as low as 3 ppm, can now be detected in natural samples.</div><div>Minute differences in ¹⁴⁵Nd/¹⁴⁴Nd, ¹⁴⁸Nd/¹⁴⁴Nd and ¹⁵⁰Nd/¹⁴⁴Nd ratios can now also be detected in natural samples, allowing better identification of nucleosynthetic anomalies in extra-terrestrial samples. For terrestrial samples, it allows detection of traces of samarium, and of nuclear field shift effect due to analytical issues. In particular, we demonstrate that some Sm is present in the JNdi-1 standard and affects both its ¹⁴⁸Nd/¹⁴⁴Nd and ¹⁵⁰Nd/¹⁴⁴Nd ratios, making a systematic interference correction necessary. By detecting the existence of nuclear field shift effect on Nd isotopes, we can now prevent mis-interpretations of ¹⁴²Nd/¹⁴⁴Nd deviations that could be wrongly attributed to radiogenic signatures acquired during the Hadean.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122686"},"PeriodicalIF":3.6,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143463775","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":"Dynamic redox evolution in the middle-late Mesoproterozoic oceans","authors":"Wei Wei ,&nbsp;Huajian Wang ,&nbsp;Shuichang Zhang ,&nbsp;Lin-Hui Dong ,&nbsp;Dongdong Li ,&nbsp;Fang Huang","doi":"10.1016/j.chemgeo.2025.122685","DOIUrl":"10.1016/j.chemgeo.2025.122685","url":null,"abstract":"<div><div>The middle Proterozoic (ca. 1.8–0.8 Ga) was thought to be persistently static in eukaryotic biodiversity and oxygenation at the Earth's surface, until the Neoproterozoic Oxygenation Event (NOE). The conventional view of Boring Billion is being challenged by increasing evidence of frequently disturbed oxygenation events in the atmosphere and ocean at ca. 1.6–1.4 Ga, namely the Mesoproterozoic Oxygenation Event (MOE). However, marine redox information during the intermediate period between the MOE and NOE (the middle-late Mesoproterozoic) remains elusive. Here, we report V isotope compositions (δ⁵¹V) of black shales from the middle and upper Shennongjia subgroups in the Shennongjia micro-block, in order to reconstruct the evolution in global marine oxygenation extent during this poorly studied period. The δ⁵¹V values exhibit a large variability, which should have been caused by changes in local depositional environment and global marine oxygenation extent. Based on the sedimentary δ⁵¹V records and local redox information, we reconstruct temporary open-ocean seawater δ⁵¹V variation during the middle-late Mesoproterozoic. The result suggests several episodes of widespread marine oxygenation interspersed with extensive euxinia. It sheds new light into dynamic environmental and eukaryotic evolutions in the middle-late Mesoproterozoic oceans.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"679 ","pages":"Article 122685"},"PeriodicalIF":3.6,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143437201","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":"Zircon solubility in silicate melts: New empirical models and thermodynamics","authors":"Alexander Borisov ,&nbsp;Leonid Aranovich ,&nbsp;Paula Antoshechkina","doi":"10.1016/j.chemgeo.2025.122682","DOIUrl":"10.1016/j.chemgeo.2025.122682","url":null,"abstract":"<div><div>Published experimental data on zircon (<em>Zrn</em>) solubility in silicate melts are critically evaluated to conclude that H₂O dissolved in the melts has no to minor effect on the <em>Zrn</em> solubility. The effect of pressure is small but resolvable. A new empirical equation describing zircon solubility in silicate melts as a function of temperature, pressure and melt composition, is derived based on the published experimental data. The new equation predicts log Zr (ppm) in the melts with a standard error of 0.087, which is equivalent to ca. 22 % error in the range from 178 to 61,370 ppm Zr, 750-1500 °C, and 0.001–25 kbar covered by the experiments. A new equation describing the relatively low-temperature range 750-1200 °C, more appropriate for application to natural magmatic rocks, is also suggested.</div><div>The new equation for temperature dependence of the standard Gibbs free energy of zircon melting reaction is derived for the first time. The equation is consistent with the high temperature phase diagram of the ZrO₂-SiO₂ system and predicts metastable zircon fusion temperature at T_fus = 2232 K. This equation is silicate melt model independent. Thermodynamic mixing properties of the zircon species in silicate melts consistent with the MELTS thermodynamic model retrieved by fitting 186 experimental data points, agree qualitatively with the empirical formulation and simple equations suggested by Bruce Watson and co-workers.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"679 ","pages":"Article 122682"},"PeriodicalIF":3.6,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143429253","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}