Chemical Geology最新文献

{"title":"Comprehensive modification of cratonic lithospheric mantle beneath the central North China Craton: Insights from Li isotope systematics of olivine xenocrysts in Cenozoic basalts","authors":"Yao Xu ,&nbsp;Hong-Fu Zhang ,&nbsp;Yan-Jie Tang ,&nbsp;A-Bing Lin ,&nbsp;Juan Zhang ,&nbsp;Ming-Jie Zhang","doi":"10.1016/j.chemgeo.2025.122721","DOIUrl":"10.1016/j.chemgeo.2025.122721","url":null,"abstract":"<div><div>The flat subduction and subsequent rollback of the Paleo-Pacific plate played a critical role in the destruction of the eastern North China Craton (NCC), manifested by a drastic transformation of the subcontinental lithospheric mantle (SCLM) in physico-chemical properties. However, the nature of the SCLM beneath the central NCC remains poorly defined. This study presents in situ major element compositions and Li systematics (concentrations and δ⁷Li) of olivine xenocrysts from Cenozoic Xiyang–Pingding basalts to investigate the impacts of circum-craton plate subduction on the SCLM. Olivine grains from the basalts are classified into four types based on core forsterite (Fo) contents and mineralogical traits. Types 1–3 xenocrysts show sub-rounded shapes, kink bands, and geochemical affinities with xenolithic olivines, distinct from Type 4 phenocrysts. Xenocrystic zoned textures resulted from re-equilibration with host magma, while large xenocrystic cores retain the SCLM composition. Type 1 cores (Fo = 92.1–93.5) exhibit Li contents (1.0–1.7 ppm) comparable to mantle olivines and δ⁷Li values within or slightly above the normal mantle range (2–6 ‰), representing relicts of ancient refractory SCLM enriched by Paleo-Pacific slab-derived silicate melts. Type 2 (Fo = 90.0–92.0) and high-Fo (88.6–89.9) Type 3 xenocrysts display Li enrichment (1.3–3.5 ppm) and δ⁷Li depletion (down to −20 ‰). Positive relationships between δ⁷Li and both Fo and 1/Li indicate their formation through interaction between Archean refractory SCLM and asthenospheric carbonated silicate melts. Low-Fo (84.7–88.2) Type 3 cores record the highest Li (1.7–4.9 ppm) and δ⁷Li (9 ‰ to 14 ‰), marking the recent refertilization by asthenospheric silicate melts. Combined with previous studies, these Li-δ⁷Li variations reflect the most comprehensive record of SCLM modification beneath the NCC, offering crucial insights into the dynamics of cratonic evolution.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122721"},"PeriodicalIF":3.6,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143563280","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":"Paired mass-dependent and mass-independent Hg isotope excursions through non-euxinic intervals: Signals of post-depositional Hg isotope fractionation?","authors":"Guanyu Zhao ,&nbsp;Qian Deng ,&nbsp;Bin Cheng ,&nbsp;Yunpeng Wang ,&nbsp;Zewen Liao","doi":"10.1016/j.chemgeo.2025.122718","DOIUrl":"10.1016/j.chemgeo.2025.122718","url":null,"abstract":"<div><div>Mercury (Hg) in sedimentary deposits has become a widely used proxy for reconstructing paleo-volcanic activity. However, a comprehensive understanding of Hg accumulation pattern and the isotope variation during early diagenesis is still lacking. A thorough diagenetic evaluation of sedimentary rocks is crucial prior to the interpretation of geochemical data, as diagenetic changes can lead to considerable differences between the original seawater signatures and the sedimentological records. We observed a Hg isotopic pattern characterized by a negative trend in δ²⁰²Hg with a concurrent gradual positive shift in Δ¹⁹⁹Hg throughout non-euxinic intervals in multiple marine sedimentary successions. We propose that the synchronous Hg mass dependent fractionation (MDF) and mass independent fractionation (MIF) were driven by diagenetic events. The release of organic-bound Hg and its subsequent diffusion downward to sites where it complexed with pyrite in early diagenetic stages may induce δ²⁰²Hg shift towards more negative values in the Hg precipitate, and in turn, contribute to the concurrent positive shift of Δ¹⁹⁹Hg observed in these sections.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122718"},"PeriodicalIF":3.6,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143552598","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 rheological evolution of a phonotephritic melt upon variable degrees of carbonate assimilation and deformation regimes","authors":"Gabriele Giuliani ,&nbsp;Danilo Di Genova ,&nbsp;Fabrizio Di Fiore ,&nbsp;Silvio Mollo ,&nbsp;Serena Dominijanni ,&nbsp;Chiara Maria Petrone ,&nbsp;Claudia Romano ,&nbsp;Alessandro Vona","doi":"10.1016/j.chemgeo.2025.122711","DOIUrl":"10.1016/j.chemgeo.2025.122711","url":null,"abstract":"<div><div>The dynamic interplay between magmas and carbonate wall rocks within volcanic plumbing systems heavily influences the chemical and physical properties of erupted magmas. In this study we present results from isothermal static experiments (ISEs) and isothermal deformation experiments (IDEs) aimed at investigating the rheological evolution of a phonotephritic melt from Somma-Vesuvius (Italy) under variable shear rates and CaO and CaO + MgO doping levels. Flash differential scanning calorimetry is also used to determine the viscosity of interstitial melt, allowing for the first direct assessment of how crystallization affects melt rheology without relying on empirical viscosity models. Two distinct rheological scenarios emerge from IDEs: 1) a viscous deformation, characterized by uniform flow, and 2) a non-homogeneous deformation, featuring shear localization and viscous/brittle rupture of the magma. As both shear rate and doping level increase, a non-Newtonian melt behavior is observed due to stress localization and rupture, facilitated by the development of the crystal network. The narrower viscosity range measured from IDEs, compared to models of pure viscous behavior, suggests that shear localization and fracturing reduce the resistance to flow in doped, crystal-rich samples. The complex rheology of doped melts reflects the disaggregation of skarn shells at the margins of magma chambers, thereby facilitating skarn recycling and enhancing magma contamination.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122711"},"PeriodicalIF":3.6,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143550161","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":"Twice the global average carbon burial efficiency in the Helgoland Mud Area of the North Sea: Insights into carbon sequestration in small-size depocenters on sand-dominated shelves","authors":"Bingbing Wei ,&nbsp;Daniel Müller ,&nbsp;Stephanie Kusch ,&nbsp;Lu Niu ,&nbsp;Jens Hefter ,&nbsp;Lasse Sander ,&nbsp;Ulrike Hanz ,&nbsp;Gesine Mollenhauer ,&nbsp;Guodong Jia ,&nbsp;Sabine Kasten ,&nbsp;Moritz Holtappels","doi":"10.1016/j.chemgeo.2025.122712","DOIUrl":"10.1016/j.chemgeo.2025.122712","url":null,"abstract":"<div><div>Continental shelves are integral to the global carbon cycle, yet uncertainties persist about the nature and extent of carbon burial, particularly in sand-dominated areas. In the sand-dominated North Sea, the Helgoland Mud Area (HMA) emerges as a small-size mud depocenter, surrounded by sandy sediments that do not accumulate organic carbon (OC) and are separated from adjacent rivers. Such small-size depocenters, common on high-energy shelves, have underexplored OC degradation and burial efficiencies due to their limited individual size. Since sandy sediments with interspersed small-size depocenter cover ∼50 % of global shelves, these depocenters may collectively offer greater OC burial capacity than previously recognized.</div><div>This study investigated the composition, degradation, and sequestration of OC from terrestrial (OC_terr) and marine (OC_mar) sources in surface sediments of the HMA and adjacent sandy areas using bulk (mean grain size, OC content, loading and ¹³C isotope composition) and molecular (fatty acids and alkanes) analyses. Our results, derived from a two end-member mixing model based on δ¹³C values of bulk OC, revealed that OC_terr dominates (∼74 %) the sedimentary OC in both areas, with OC_mar contributing ∼26 %. The HMA exhibited OC_terr and OC_mar contents ∼5 times higher than in the sandy areas. Both OC_terr and OC_mar loadings negatively correlated with mean grain size, indicating reduced OC degradation in muddy sediments. Molecular analysis further revealed that OC_terr in the HMA is less refractory compared to adjacent sandy regions. These differences are attributed to differences in porewater transport, oxygen penetration depths and exposure times, all of which influence OC preservation, despite the important role of mineral protection. OC_terr and OC_mar accumulation fluxes in the HMA were calculated at (6.75 ± 0.61) × 10⁻³ and (2.54 ± 0.68) × 10⁻³ Tg C/yr, respectively, representing 34.3 % of OC_terr export from adjacent rivers and 2.8 % of net OC_mar production in the HMA. These values are twice the global average for shelf areas, highlighting the exceptional efficiency of the HMA as a carbon sink and hinting at the significance of small-size depocenters within sandy areas in the global carbon cycle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122712"},"PeriodicalIF":3.6,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143552597","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":"Contrasting variations in solid acidity of smectite and kaolinite in acid-base environments and implications for organic matter sequestration","authors":"Jiazong Du ,&nbsp;Jingong Cai ,&nbsp;Xiang Zeng ,&nbsp;Tianzhu Lei ,&nbsp;Qian Chao ,&nbsp;Kuihua Zhang ,&nbsp;Xuejun Wang","doi":"10.1016/j.chemgeo.2025.122714","DOIUrl":"10.1016/j.chemgeo.2025.122714","url":null,"abstract":"<div><div>The nanoscale interactions between clay mineral active sites and organic matter (OM) determine OM sequestration and transformation. Smectite and kaolinite, prominent OM adsorbing minerals, are sensitive to acid-base fluctuations, but dynamics of their active sites remain unexplored, limiting our knowledge of the mineral matrix-related fate of OM. Solid acidity (Brønsted and Lewis acid sites) is a tangible indicator to quantify the active sites. This study examined the dynamics of solid acidity in smectite and kaolinite subjected to acid-base environmental variability, exploring implications for OM sequestration. Results revealed that both acid and alkaline environments increased the number of total acid sites (Q_T) for both smectite and kaolinite, with higher Brønsted acid site fraction (<em>f</em>_B) as pH decreased, but smectite and kaolinite exhibited contrasting behaviors. Smectite underwent more prominent structural rearrangements under acid environments, with interlayer cations substitution and preferential dissolution of octahedron. This process exposed Al³⁺ and/or facilitated re-adsorption of Al³⁺/Fe³⁺, contributing to Lewis acid sites, while exposed silanols and enhanced interlayer water polarization contributed more to Brønsted acid sites, yielding substantial Q_T and <em>f</em>_B increases. Acid environments exposed silanols in kaolinite, but it responded more strongly to alkaline environments, where disrupted Si-O-Al bonds at edges exposed incompletely coordinated Al³⁺, contributing to Q_T increase and <em>f</em>_B decrease. Increased Q_T enhanced the adsorbed lysine content; therefore, the mineral- and environment-specific dynamics of solid acidity have the potential to shape OM sequestration capacity of clay minerals, and their catalytic efficiency and mechanisms in driving the diagenetic fate of OM.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122714"},"PeriodicalIF":3.6,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143550908","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":"Extracellular metabolites relieve the inhibitory effect of ferrous ions on microbial reduction of schwertmannite","authors":"Changdong Ke ,&nbsp;Qian Yao ,&nbsp;Yanping Deng ,&nbsp;Siyu Zhang ,&nbsp;Zhiliang Li ,&nbsp;Renren Wu ,&nbsp;Chuling Guo ,&nbsp;Zhi Dang","doi":"10.1016/j.chemgeo.2025.122709","DOIUrl":"10.1016/j.chemgeo.2025.122709","url":null,"abstract":"<div><div>In the environment, microbe-mineral-metabolites are tightly linked. Currently, the microbe-mineral interactions have been studied, but the effect of microbial metabolites on the microbe-mineral interactions is unclear. This study investigated the effect of metabolites of <em>Shewanella oneidensis</em> (an iron-reducing bacterium, FeRB) (or <em>Desulfosporosinus meridiei</em> [a sulfate-reducing bacterium, SRB]) on SRB (or FeRB) mediated transformation of schwertmannite (Sch), a mineral in acidic soils rich in sulfate (SO₄²⁻). The results showed that microbial metabolites relieved the inhibition of FeRB and SRB by complexing ferrous ions (Fe²⁺), thus promoting the microbial reduction of Sch. Besides, metabolites altered the pathways of microbial reduction and mineral transformation. In the absence of metabolites, FeRB mediated Fe(III) reduction mainly by increasing the cell abundance, while in the presence of metabolites, FeRB upregulated gene expression (<em>mtrC</em> and <em>omcA</em>) to enhance the Fe(III) reduction, and the Sch transformation pathway was Sch → goethite → siderite. For SRB, metabolites upregulated the <em>dsr</em> gene expression to accelerate SRB reducing SO₄²⁻, and the Sch transformation pathway was Sch → goethite and mackinawite → siderite, mackinawite and pyrite. Metabolomics and high-performance liquid chromatography analysis revealed a large amount of phenylalanine (∼1.5 mM) and citric acid (∼0.2 mM) were present in the metabolites of FeRB and SRB, respectively, which complexed Fe²⁺ and promoted the microbial reduction of Sch. This study highlighted the important role of metabolites in maintaining soil biological activity and provided new insights into the microbe-mineral-metabolite interactions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122709"},"PeriodicalIF":3.6,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510655","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":"Precise 40Ar/39Ar dating of multiple potassic minerals constrain the age and rapid cooling history of the Walgidee Hills lamproite pipe, Kimberley Region, Western Australia, at 17.49 Ma","authors":"Simon A. Wilde ,&nbsp;Fred Jourdan ,&nbsp;Lynda Frewer ,&nbsp;Monika A. Kusiak","doi":"10.1016/j.chemgeo.2025.122698","DOIUrl":"10.1016/j.chemgeo.2025.122698","url":null,"abstract":"<div><div>To determine the emplacement age of the initial eruptive phase of the Walgidee Hills lamproite pipe in the Kimberley region of Western Australia, the veracity of utilizing multi-mineral dating of the non-standard potassium-bearing minerals potassic richterite, wadeite, jeppeite, and priderite and was tested by ⁴⁰Ar/³⁹Ar dating, along with the more traditionally-utilized potassium-rich mineral phlogopite. All minerals give excellent single-crystal plateau ages ranging from 17.82 ± 0.53 to 17.0 ± 1.6 Ma (2σ), and with age uncertainties ranging from ±0.14 Ma to ±1.6 Ma. The variation in precision is dependent on both the volume and K₂O content of the crystal analyzed. The mean age of the combined data set is 17.487 ± 0.083 Ma [± 0.086; inclusive of all sources of uncertainties] (<em>n</em> = 10; MSWD = 0.50; <em>P</em> = 0.87) and represents the initial crystallization age of the Walgidee Hills diatreme, the largest known and youngest diamondiferous lamproite in the world. The lack of age difference, despite the probable variation in mineral closure temperatures, confirms rapid cooling. Although most of the minerals analyzed are rare to absent in common magmatic rocks, some are widely distributed in alkaline complexes and in lamproite, kamapugite and kimberlite intrusions. Our results show these K-rich minerals are excellent for ⁴⁰Ar/³⁹Ar dating and can be used singly or in combination to obtain precise magmatic crystallization ages, and possible cooling rates, of ultrapotassic rocks. For a suite of potassic rocks generated in a plume setting, they can track the rate of plate motion.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122698"},"PeriodicalIF":3.6,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143519350","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":"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}