Chemical Geology最新文献

{"title":"Thallium isotope data suggest minimal recycled material within the proto-Iceland mantle plume source","authors":"J. Kaare-Rasmussen ,&nbsp;F. Horton ,&nbsp;C.M. Ostrander ,&nbsp;S.G. Nielsen","doi":"10.1016/j.chemgeo.2025.122798","DOIUrl":"10.1016/j.chemgeo.2025.122798","url":null,"abstract":"<div><div>Mantle plume isotopic compositions are useful for understanding the processes that produce heterogeneity within the mantle. Thallium (Tl) isotopic compositions are uniquely well suited for tracing pelagic sediments and low-temperature altered oceanic crust in the mantle. We measured the Tl isotopic composition of Paleocene lavas on Baffin Island, the earliest lavas associated with the Iceland mantle plume, to constrain the geochemical evolution of the mantle plume. After correcting for assimilation and degassing, these lavas have ²⁰⁵Tl/²⁰³Tl ratios indistinguishable from the inferred ratio of the upper mantle and from modern Iceland lavas. Therefore, the amount of subducted pelagic sediments or low temperature altered oceanic crust potentially within the head of the Iceland mantle plume is vanishingly small. These components cannot account for the well-documented evolution in other isotopic systems over time in the Iceland mantle plume. Thus, we evaluate other processes that could account for this evolution, including other subducted components and core-mantle interactions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122798"},"PeriodicalIF":3.6,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143855309","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":"Paleoenvironmental changes and nitrogen cycling of the lacustrine systems following the Toarcian Oceanic Anoxic Event in the Sichuan Basin (China): Insights from nitrogen isotopes","authors":"Yang Bai ,&nbsp;Jianfa Chen ,&nbsp;Jin Wu ,&nbsp;Wenzhe Gang ,&nbsp;Václav Suchý ,&nbsp;Cong Chen ,&nbsp;Xuemin Xu ,&nbsp;Rao Fu ,&nbsp;Jiaqi Zhang ,&nbsp;Shuaiqi Tang","doi":"10.1016/j.chemgeo.2025.122797","DOIUrl":"10.1016/j.chemgeo.2025.122797","url":null,"abstract":"<div><div>The Toarcian Oceanic Anoxic Event (T-OAE) represents a significant disturbance of the Earth's atmosphere-ocean system in the Early Jurassic, and its response in lacustrine systems has been widely studied in recent years. However, the impact of T-OAE on the subsequent environmental changes and nitrogen cycling patterns in lacustrine systems are poorly understood. This study investigated the paleoenvironmental changes following the T-OAE based on elemental geochemistry analyses of organic-rich shales from the Early Jurassic Da'anzhai Member and the Middle Jurassic Lianggaoshan Formation in the Sichuan Basin. The nitrogen cycling during this period was reconstructed drawing on nitrogen isotopes (δ¹⁵N) and their correlations with water column conditions. The results indicated that during the deposition of Da'anzhai shale (i.e., T-OAE period), the lacustrine system was dominated by a temperate-humid climate, with frequent oxic-suboxic variations in the water column. The sedimentary environment of the Lianggaoshan shale was similar to that of the Da'anzhai shale, even though there was a brief arid-cold climate during the sedimentary period at the bottom of Lianggaoshan Formation. The nitrogen isotopes of kerogen (δ¹⁵N_ker) were primarily controlled by the redox conditions of water column, and the silicate-bound inorganic nitrogen isotopes (δ¹⁵N_sil) were influenced by combined factors including climate, input of terrestrial clay minerals, and the redox conditions of the bottom water column. These variations in δ¹⁵N provided foundations for reconstructing nitrogen cycling under diverse lacustrine environmental conditions. Under the suboxic water column, the occurrence of denitrification and anaerobic ammonium oxidation (anammox) in the chemocline resulted in enrichment of ¹⁵N in kerogen. The positive excursion in δ¹⁵N_sil was a cumulative effect attributed to the enhanced influx of exogenous illite under temperate-humid climatic conditions, as well as the combined influence of anammox on NH₄⁺ concentrations. In water column with elevated oxygen concentrations, biogeochemical processes, predominantly driven by nitrification, resulted in lighter δ¹⁵N_ker values, and δ¹⁵N_sil, influenced by the low concentration of NH₄⁺ in the bottom water, also exhibited a lighter isotopic signature. The similar geochemical signatures in the Da'anzhai and Lianggaoshan shales implied that the lacustrine system might be susceptible to variations in localized paleoenvironment, and was not completely consistent with the marine system.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122797"},"PeriodicalIF":3.6,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143848291","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":"Archean deep melting and post-Archean metasomatism of the cratonic mantle: A garnet Lu-Hf isotope record","authors":"Kira A. Musiyachenko ,&nbsp;Matthijs A. Smit ,&nbsp;Maya G. Kopylova ,&nbsp;Andrey V. Korsakov","doi":"10.1016/j.chemgeo.2025.122796","DOIUrl":"10.1016/j.chemgeo.2025.122796","url":null,"abstract":"<div><div>Mantle xenoliths provide a direct window into the subcontinental lithospheric mantle (SCLM) beneath Archean cratons. Age constraints on the melting, metasomatism and deformation that have affected the SCLM are crucial for developing insight into continental dynamics and craton development. Obtaining constraints is nevertheless difficult. Garnet geochronology – and Lu-Hf geochronology in particular – has good prospects in this regard, because it uniquely allows dating of a rock forming mineral and petrogenetic indicator in the mantle. However, the behavior of the Lu-Hf system at mantle conditions is not yet well-understood, and stringent sample size requirements and issues relating to melt infiltration typically impede obtaining reliable garnet ages for single xenoliths. In this study, we tested the capabilities of modern Lu-Hf methods to date garnet in kimberlite-hosted mantle xenoliths that record mantle melting, metasomatism and shearing. The samples are from the Siberian, Kaapvaal and Slave cratons, and include garnet-bearing olivine pyroxenites, lherzolites and websterites, as well as orthopyroxenite with exsolved garnet, and include both sheared and granular lithologies. The analyses yielded low-dispersion Lu-Hf isochrons for single xenoliths with age uncertainties down to 0.3 % and ages up to 3.0 Ga. Garnet in equilibrium with clinopyroxene in coarse lherzolite and websterite samples records Proterozoic ages, whereas high-Cr garnet from coarse harzburgite and orthopyroxenite samples lacking clinopyroxene yields Archean ages. The age data do not reflect ‘normal’ volume diffusion-controlled chronometric closure but instead indicate strong age retention barring events of fluid or melt infiltration. Only sheared samples yielded Lu-Hf ages close to the age of kimberlite eruption. These ages highlight that deformation and metasomatism are ongoing within otherwise stable cratonic roots. Initial Hf isotope compositions obtained from the Lu-Hf isochrons approximate chondritic values in the Archean and become gradually more superchondritic with time. These results indicate that the cratonic mantle, as well as the melts that metasomatized it since the Archean, derive from a moderately depleted mantle reservoir that has existed since at least 3 Ga. Together, the new Lu-Hf data provide a new temporal framework for the petrological development of the SCLM and establish Lu-Hf garnet geochronology as prime geochronometer for dating mantle processes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122796"},"PeriodicalIF":3.6,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143848292","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 stable U-Mo-Fe isotope records of Middle Jurassic hydrogenetic ferromanganese deposits","authors":"Viona Klamt ,&nbsp;Dennis Kraemer ,&nbsp;Oscar Fernandez ,&nbsp;Ingo Horn ,&nbsp;Simon V. Hohl ,&nbsp;Stefan Weyer ,&nbsp;Sebastian Viehmann","doi":"10.1016/j.chemgeo.2025.122795","DOIUrl":"10.1016/j.chemgeo.2025.122795","url":null,"abstract":"<div><div>Ferromanganese (Fe-Mn) nodules are marine chemical sediments that represent unique archives for the reconstruction of ambient seawater conditions. This record is limited from modern to Cenozoic times due to the instability of Fe-Mn oxides during burial and subduction of the oceanic crust and overlying sediments. However, almost uncharacterized Fe-Mn nodules exist in Jurassic sedimentary strata throughout the ancient Tethyan region approximately 100 Ma older than the oldest yet-investigated Cenozoic nodules. Their reliability as geochemical archives for the reconstruction of ancient seawater is, however, poorly understood. In this study, Fe-Mn nodules from the Pyhrntal area (Austria) are geochemically and mineralogically characterized and subdivided into four types with variable amounts of carbonates (calcite, rhodochrosite), todorokite, and hematite as major phases. Shale-normalized rare earth element and yttrium systematics of all types indicate a hydrogenetic origin with characteristic positive Ce anomalies and negative Y anomalies. In-situ Fe isotope measurements of the Fe-Mn nodules display a <em>δ</em>^56/54Fe range between −0.32 and −0.02 ‰ for the Jurassic Tethyan Ocean, similar to values from modern Atlantic nodules. Stable Mo (<em>δ</em>^98/95Mo = −0.97 to −0.56 ‰) and U (<em>δ</em>^238/235U = −0.75 to −0.47 ‰) isotope compositions resemble those of modern and Cenozoic Fe-Mn nodules, suggesting that Middle Jurassic oceans were similarly well‑oxygenated as modern oceans. Our results demonstrate the reliability of fossil Fe-Mn nodules in the Pyhrntal as geochemical archives for the composition of paleo-seawater, encouraging the investigation of other ancient Fe-Mn deposits which may significantly improve and complement the picture of the redox evolution of Phanerozoic oceans.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122795"},"PeriodicalIF":3.6,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838718","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":"Modeling the impact of evaporites on burial fluid-rock interactions in carbonate reservoirs","authors":"Ying Xiong ,&nbsp;Xiucheng Tan ,&nbsp;Bo Liu ,&nbsp;Michael Z. Hou ,&nbsp;Kaibo Shi ,&nbsp;Shoukang Zhong ,&nbsp;Di Xiao","doi":"10.1016/j.chemgeo.2025.122793","DOIUrl":"10.1016/j.chemgeo.2025.122793","url":null,"abstract":"<div><div>Carbonate-evaporite successions can serve as important hydrocarbon reservoirs. However, the unique petrophysical properties of evaporites and various carbonate-evaporite lithological associations have impeded understanding of the complex fluid-rock interactions and diagenetic evolution of these reservoirs. Here we present numerical modeling of the diagenetic mineral-porosity evolution in various fluid‑carbonate-evaporite systems and compare them with those in carbonate only strata. The high thermal conductivity and low permeability of thick evaporites (e.g., salt and anhydrite) could result in elevated temperature in supra-salt environment and decreased temperature and overpressure in pre-salt environment. These conditions promote carbonate precipitation from in situ pore fluids in supra-salt formations and dissolution in pre-salt formations. Besides, evaporite interlayers can function as pressure and fluid seals, limiting the influence of diagenetic geochemical reactions. Mineral dissolution-precipitation primarily occurs near the first set of dense evaporite layer in the direction of fluid transport. From the perspective of porosity preservation, the cementation pattern (type and intensity) and porosity distribution are jointly controlled by carbonate-evaporite lithological associations, fluid properties, and flow paths. High-quality reservoirs may form in all three burial environments: pre-salt, inter-salt, and supra-salt strata. The results contribute to a better understanding of burial fluid-rock interactions and the mechanisms behind reservoir formation and preservation in carbonate-evaporite systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122793"},"PeriodicalIF":3.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143825677","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 sediment precipitated during acid mine drainage-seawater interaction. Implications for metal mining impacts on estuarine systems","authors":"K.L. Lecomte ,&nbsp;P.A. Yaciuk ,&nbsp;A.M. Sarmiento ,&nbsp;J. Borrego ,&nbsp;J.M. Nieto","doi":"10.1016/j.chemgeo.2025.122794","DOIUrl":"10.1016/j.chemgeo.2025.122794","url":null,"abstract":"<div><div>Metal-mining pollution impacts estuarine systems, where sediments with high available toxic metal concentrations precipitate. In the Ría de Huelva estuary (SW Spain), the metal-rich acidic water of the Tinto River (headwater pH = 2.2 and electrical conductivity -EC- = 25.8 mS cm⁻¹) interacts with saline-alkaline seawater of the Atlantic Ocean (pH = 7.87, EC = 55.2 mS cm⁻¹). This study analyses the geochemical characteristics of the dissolved and particulate fractions formed when mixing both systems. A pH-controlled test showed that about 2000 L of seawater are necessary to neutralise 1 L of Tinto River headwater. A six-step sequential extraction performed on the precipitated sediments indicated that: a) Fe, Al, Zn, Cu, ∑REE, Co, Pb, and As are highly available in soluble and adsorbed fractions; b) Fe, Al, Cu, Zn, ∑REE, Mo, and Co mostly concentrate in iron oxy-hydroxides and oxyhydroxysulfates; and c) As, V, Mo, U and Pb desorb at pH ≥ 5. Furthermore, Fe and Al precipitates play significant hydrochemical and environmental roles in the studied environment by attenuating pH changes, as sediment precipitation decreases pH and captures chemical elements. The results of this study are useful to better understand natural processes (e.g., disruption of buffers, instability of dissolved elements, sorption/desorption, co-precipitation) taking place in estuaries affected by AMD and to predict geochemical variations in the environment due to climate change (e.g., floods, extreme precipitations, sea level rise).</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122794"},"PeriodicalIF":3.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143828153","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":"Laser ablation K-Ar dating of illite on oriented aggregate mounts","authors":"Cynthia Bermúdez-Chávez ,&nbsp;Teresa Pi-Puig ,&nbsp;Jesús Solé","doi":"10.1016/j.chemgeo.2025.122792","DOIUrl":"10.1016/j.chemgeo.2025.122792","url":null,"abstract":"<div><div>Illite, a clay mineral formed during diagenesis and low-grade metamorphism, can be dated using the K-Ar method to reconstruct the chronological history of sedimentary basins, fault and fold formation, and hydrothermal alterations. However, conventional K-Ar and Ar-Ar dating of illite faces challenges due to the clay's small grain size, hygroscopicity, limited availability in finer fractions, and other analytical issues. This study proposes a modified K-Ar dating approach that uses a laser ablation technique to date small amounts of oriented clay aggregate mounts separated by grain size fractions and prepared on glass discs.</div><div>Four groups of illite-bearing samples from various geological settings were analyzed, ranging in age from 350 Ma to 40 Ma. X-ray diffraction of the aggregate mounts revealed different mineral compositions, with illite proportions between 20 % and 90 %, along with kaolinite, chlorite, quartz, and feldspars in some samples. The K-Ar dating setup includes ultrahigh vacuum laser ablation of oriented clay mounts combined with LIBS spectroscopy for potassium measurement and noble gas mass spectrometry for argon quantification within the same experiment. Ages were obtained through various methods (single craters, lines, and multiple craters), making the isochron method utilizing multiple craters the most precise and accurate.</div><div>This innovative K-Ar method simplifies the dating of clay fractions by avoiding problematic issues such as drying, weighing, homogeneity, and Ar recoil during irradiation while enabling mineralogical characterization through X-ray diffraction on the same sample preparation. This approach offers new insights into the geological history recorded by clay minerals. During this work, we identified unknown issues concerning sample preparation and geochronological data, including differential clay sedimentation during drying and the associated age dispersion in clays from detrital samples.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122792"},"PeriodicalIF":3.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143843575","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":"Insights into mantle metasomatism during oceanic subduction from late Paleozoic (∼260 Ma) high-Mg diorites in the northeastern Tibetan Plateau","authors":"Feng-Hui Zou ,&nbsp;Jian-Ping Zheng ,&nbsp;Cai-Lai Wu ,&nbsp;Chang-Qian Ma ,&nbsp;Li-Huan Deng","doi":"10.1016/j.chemgeo.2025.122782","DOIUrl":"10.1016/j.chemgeo.2025.122782","url":null,"abstract":"<div><div>Subduction recycled components can be incorporated into the mantle through aqueous solution/melt metasomatism; however, tracing the source and nature of metasomatic agents, as well as reconstructing the melting reactions of metasomatic mantles, has consistently posed significant challenges. In this work, we performed an extensive study involving petrology, geochronology, mineral chemistry, geochemistry including Sr-Nd-Pb-Hf isotopes, and numerical modeling on the newly discovered high-Mg diorites in the northeastern Tibetan Plateau to unravel their source reactions between subducting components and the mantle wedge. Zircon U<img>Pb data reveals that three diorites crystallized at ∼260 Ma, synchronous with the subduction of the Paleo-Zongwulong oceanic slab. These rocks show magnesian characteristics of amphibole and biotite, and most of plagioclase cores produce intermediate anorthite contents (An₃₆_–₄₉). The variable ⁸⁷Sr/⁸⁶Sr_(i) ratios ranging from 0.70656 to 0.7094 and most ε_Hf(t) values between −4.1 and + 4.7, but homogeneous ε_Nd(t) values from −5.4 to −2.3 indicate the diorites are derived from an enriched mantle source. The observed enrichment in large ion lithophile elements and depletion in high field strength elements further indicate the characteristics typical of arc igneous rocks. High Th/Nb ratios (0.54–1.37) and Th/Yb ratios (2.42–4.7), alongside low Sr/Th ratios (24.51–59.83) and narrow Pb isotopic variations (²⁰⁶Pb/²⁰⁴Pb_(i) of 18.09–18.34, ²⁰⁷Pb/²⁰⁴Pb_(i) of 15.59–15.63 and ²⁰⁸Pb/²⁰⁴Pb_(i) of 38.14–38.37), imply the presence of sediment components in the mantle source. Pyroxenites have been identified as their potential source, as indicated by whole-rock chemistry (e.g., high 10000*Zn/Fe ratios). Numerical modeling suggests that these diorites formed through the addition of ∼1 % aqueous solutions and 6 %–20 % hydrous melts into the mantle wedge. Therefore, the high-Mg diorites discovered in the northeastern Tibetan Plateau provide valuable insights into the interactions between the crust and mantle, which are associated with slab subduction during the late Paleozoic era.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122782"},"PeriodicalIF":3.6,"publicationDate":"2025-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838719","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":"Characterizing deposition and diagenesis history of post-Marinoan Snowball Earth carbonates from sedimentary pyrites","authors":"Yung-Hsin Liu ,&nbsp;Der-Chuen Lee ,&nbsp;Mao-Chang Liang ,&nbsp;Yoshiyuki Iizuka ,&nbsp;Mark H. Thiemens ,&nbsp;Yanan Shen ,&nbsp;Hsien Shang","doi":"10.1016/j.chemgeo.2025.122764","DOIUrl":"10.1016/j.chemgeo.2025.122764","url":null,"abstract":"<div><div>This study presents a comprehensive investigation of petrography, clumped isotope thermometry (T-∆₄₇), and NanoSIMS sulfur isotopic analysis of pyrites for the basal Doushantuo cap carbonates from the Jiulongwan (JLW) section. The majority of the analyzed pyrites originate from reduction of marine sulfates, primarily through thermochemical sulfate reduction (TSR), with minor contributions from microbial sulfate reduction (MSR) during dolomitization. Overall, the occurrence of pyrites and their δ³⁴S populations are controlled by H₂S generation, transportation, and storage. MSR- and TSR-derived H₂S are recorded by different pyrite generations, each exhibiting distinctive δ³⁴S_py values within a cm-sized specimen. In the case of TSR-derived pyrites, fluid pulses stored and mixed in cavities produce pyrites with variable occurrences but limited isotopic variation. In contrast, prolonged fluid alteration involves gradual pyrite precipitation during fluid transportation along the grain boundaries. This results in a broad δ³⁴S variation, even under high temperature conditions. The ∆³⁴S_CAS-py values of MSR-derived pyrites collected from two depths indicate a slight increase in seawater sulfate concentration during two transgression stages in the aftermath of the Marinoan Snowball glaciation. This study highlights the significance of employing multiple approaches at microscopic scales to elucidate sedimentation processes during post-glacial periods.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122764"},"PeriodicalIF":3.6,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838716","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 role of sulfur on the liquidus temperature and olivine-orthopyroxene equilibria in highly reduced magmas","authors":"Fabrizio Saracino ,&nbsp;Bernard Charlier ,&nbsp;Yishen Zhang ,&nbsp;Manon Lécaille ,&nbsp;Yanhao Lin ,&nbsp;Olivier Namur","doi":"10.1016/j.chemgeo.2025.122777","DOIUrl":"10.1016/j.chemgeo.2025.122777","url":null,"abstract":"<div><div>The geochemical data provided by the NASA MESSENGER spacecraft unveiled the geochemical heterogeneity of the volcanic crust of Mercury. Surprisingly, a high amount of sulfur was detected which combined with a low iron content, imply highly reduced conditions of parental magmas. Several variables (temperature, pressure, oxygen fugacity <em>f</em>O₂, and to a lesser extent, melt composition) affect the solubility of sulfur in silicate melts. In reduced silicate melts, sulfur has an oxidation state of S²⁻ and replaces anionic oxygen to form MgS and CaS complexes. Experimental studies have shown the high S solubility in silicate melts at low <em>f</em>O₂. As observed with other volatile elements, high S contents in silicate melts can deeply affect their properties such as (1) lowering the liquidus as compared to S-free compositions and (2) changing solid-liquid phase equilibria. In this study, we performed high temperature (1500–1950 °C) and high pressure (1.5–3 GPa) piston-cylinder experiments on Fe-poor compositions relevant to the petrogenesis of Mercury's volcanic crust with the aim of quantifying the effect of sulfur on depressing their liquidus temperature and understanding its role on phase equilibria. Several compositions were prepared to track the stability fields of olivine (high melt Mg/Si ratio) and orthopyroxene (low melt Mg/Si ratio) in both S-saturated melts and S-free melts. A range of reduced conditions were obtained by using different Si/SiO₂ ratios in the mixes. S-saturated experiments show increasing S abundances in the silicate melts (∼ 1–9 wt%) as <em>f</em>O₂ decreases (from IW -2.9 to IW -6.2, IW representing the iron-wüstite thermodynamic equilibrium). Parameterizing our experimental results gives the liquidus depression as a function of the sulfur content in the melt (mol. fraction):<span><span><span><math><mo>∆</mo><msub><mi>T</mi><mi>liq</mi></msub><mfenced><mrow><mo>°</mo><mi>C</mi></mrow></mfenced><mo>=</mo><mo>−</mo><mn>65208.22</mn><mspace></mspace><msubsup><mfenced><mi>S</mi></mfenced><mi>melt</mi><mn>3</mn></msubsup><mo>+</mo><mn>16595.32</mn><mspace></mspace><msubsup><mfenced><mi>S</mi></mfenced><mi>melt</mi><mn>2</mn></msubsup><mo>+</mo><mn>532.31</mn><mspace></mspace><msub><mfenced><mi>S</mi></mfenced><mi>melt</mi></msub></math></span></span></span></div><div>(MSWD = 3.24; SEE = 35 °C)</div><div>The range of sulfur concentration in our experimental melts would cause a liquidus depression of ca. 20–190 °C. Moreover, our experiments illustrate the role of sulfur in promoting the stability field of orthopyroxene over that of olivine which has major implications for the crystallization of the Mercurian magma ocean and the primordial mineralogical stratification of the mantle. In addition, the presence of sulfur lowers the pressure and temperature conditions of the olivine-orthopyroxene cotectic.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122777"},"PeriodicalIF":3.6,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143814984","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}