Chemical Geology最新文献

{"title":"Thermo-temporal constraints on CM parent body via spectroscopic study of insoluble organic matter","authors":"S. Natrajan ,&nbsp;K.K. Marhas ,&nbsp;V.J. Rajesh ,&nbsp;A. Mitra","doi":"10.1016/j.chemgeo.2025.122880","DOIUrl":"10.1016/j.chemgeo.2025.122880","url":null,"abstract":"<div><div>A comprehensive study was conducted using Fourier Transform Infra-Red spectroscopy and Raman spectroscopy on chemically isolated insoluble organic matter from sixteen different carbonaceous chondrites (CI, CM) to understand the alteration duration and temperature relationships within CM- CI like bodies. The average temperatures based on disordered components of Raman spectra (T_IOM), range from ~35 °C to 90 °C which are consistent with previously reported estimates. Using the established kinetic parameters based on insoluble organic matter, this study presents a novel approach to estimate duration of alteration in the CM parent body. An attempt is made to link the origin of the CM suite of samples from this study using the correlation between duration of alteration and parent body size as suggested by previous hydrothermal models. The majority of our samples fall into the category of multiple cloned small planetesimals or were part of an aggregate of these bodies (rubble pile). Infrared and Raman characteristics of Ryugu studies supports the correlation between parent body size, temperature, and the duration of alteration identified in our research. Additionally, we observe that the alteration of organic matter is regulated by the temperature of alteration rather than the duration itself. However further analysis is required to constrain the influence of other parameters that influence these spectral trends such as variations in water-rock ratios and the degree of system openness (open/close system based on local morphology).</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122880"},"PeriodicalIF":3.6,"publicationDate":"2025-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144185207","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":"A modified Rock-Eval approach to track organics in (bio)carbonates","authors":"A. Perron ,&nbsp;B. Ménez ,&nbsp;F. Baudin ,&nbsp;F. Stalport","doi":"10.1016/j.chemgeo.2025.122815","DOIUrl":"10.1016/j.chemgeo.2025.122815","url":null,"abstract":"<div><div>Biominerals, notably carbonates, serve as valuable biosignatures for identifying past or present life in terrestrial environments. However, distinguishing between biogenic and abiotic minerals usually required multiple high-resolution techniques, challenging their application for the <em>in situ</em> search for extraterrestrial life in space missions with limited analytical capabilities. This study investigated the potential of gas profiles (<em>i.e.</em>, carbon dioxide CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>, carbon monoxide CO, and sulfur dioxide SO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>) generated by Rock-Eval purified air combustion (in the range 50–700 °C) and dinitrogen pyrolysis (in the range 700–1000 °C) of 66 natural and laboratory carbonates to detect organics associated with these carbonate minerals that could hold clues to their origin (either abiotic or biogenic) and formation process. For bio-related and organo-carbonates containing Ca and Ca/Mg, CO and SO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> emissions detected below 700 °C were the product of combustion and associated thermal cracking of organic compounds initially coating mineral grain surfaces, while those detected above 700 °C, during and after the thermal decomposition of Ca- and Ca/Mg-carbonates, were derived from the thermal cracking of organic compounds trapped within carbonate crystals, suggesting the carbonates formed in the presence of organic compounds of biological or abiotic origin. For hydrated Mg-carbonates, the interpretation is more challenging due to multiple phase transitions that overlap with the combustion and thermal cracking of surface and trapped organic compounds in the same temperature range. Overall, this study highlights the potential of our modified Rock-Eval approach as a valuable technique for rapidly identifying and characterizing potential biosignatures in Ca- and Ca/Mg-carbonate at the bulk sample scale, an approach that can be reasonably implemented on <em>in situ</em> space instruments for the search for present or past extraterrestrial life.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122815"},"PeriodicalIF":3.6,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144185209","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":"Platinum-group elements geochemistry of chromite from Kondyor ultramafic intrusion, Siberia: Re-evaluation of factors controlling PGE content of intrusive chromite","authors":"Irina A. Zhukova ,&nbsp;Aleksandr S. Stepanov ,&nbsp;Shao-Yong Jiang ,&nbsp;Fedor I. Zhimulev ,&nbsp;Dmitry V. Gurevich ,&nbsp;Alexander A. Polonyankin ,&nbsp;Andrey V. Lavrenchuk ,&nbsp;Alexey Kotlyarov","doi":"10.1016/j.chemgeo.2025.122871","DOIUrl":"10.1016/j.chemgeo.2025.122871","url":null,"abstract":"<div><div>Platinum-group elements (PGE) concentrations in chromite could be sensitive to crystallisation conditions and potentially are a useful petrologic and exploration indicator. Chromite from certain volcanic rocks is enriched in PGE, occurring as lattice-hosted forms and microinclusions of platinum group minerals (PGM), whereas chromite from many intrusive complexes has insignificant PGE content. We report new in situ data on PGE concentrations in chromite from platiniferous Kondyor intrusion in Siberia obtained by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Investigated samples included dunites and chromitites from unmetasomatised and metasomatised domains. Kondyor chromite is enriched in IPGE (iridium-group PGE: 2–51 ppb Ir, 29–147 ppb Ru and 2–23 ppb Os), Rh (36–96 ppb) and has less than detection levels Pt and Pd. Chromite from two petrological domains was compared: relatively unmetasomatised dunite core (Verhniy) and metasomatized dunite (Anomalniy). Chromite from the metasomatic domain is enriched in Fe, Al, Ti, Mn and Zn, relative to dunite core, however, IPGE and Rh content remains similar. The presence of IPGE and Rh in Kondyor chromite shows that IPGE could have significant concentrations in chromite from some intrusions. We discuss various factors affecting PGE content in chromite and conclude that a relatively high cooling rate, high <em>f</em>O₂, the low abundance of sulfides in dunite and chromitites and the low activity of Al in Kondyor rocks, all favored concentration and preservation of IPGE and Rh in chromite. Our results suggest that in some intrusions, chromite could be a significant host for PGE and represent a useful tool for understanding of mafic-ultramafic intrusions and exploration for PGE deposits.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122871"},"PeriodicalIF":3.6,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144261961","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 thermal state controls the formation of post-collisional Cu-fertile magmas in the eastern Gangdese belt","authors":"Yuanzhi Zhou ,&nbsp;Zhenjie Zhang ,&nbsp;Jie Yang ,&nbsp;Hanyi Wang ,&nbsp;Molei Zhao ,&nbsp;Qiuming Cheng","doi":"10.1016/j.chemgeo.2025.122870","DOIUrl":"10.1016/j.chemgeo.2025.122870","url":null,"abstract":"<div><div>The genesis of post-collisional porphyry copper deposits (PCDs) remains debated. The post-collisional magmas in the eastern Gangdese belt exhibit significant variability in copper enrichment. There is broad consensus that all these magmas originated from lower crustal partial melting, yet the mechanisms driving their Cu fertility are unclear. Quantifying the thermal state and residual mineral proportion in magma sources may provide insight into geodynamic processes and the formation conditions of Cu-fertile magmas. Here, we compiled geochemical data for Eocene and Miocene magmatic rocks and simulated the <em>P–T–</em>X(H₂O) conditions and mineral proportions of magma sources by using thermodynamic and trace element modeling. Our results indicate that the Miocene magma source exhibits higher pressure and H₂O content compared to the Eocene magma source. The corresponding residual mineral assemblage also shows a transition from plagioclase to garnet and from pyroxene to amphibole. This implies the deepening of crustal melting zone and extra H₂O addition during the Miocene. The high-pressure and high-water conditions favored the formation of highly Cu-fertile post-collisional magmas. However, the high fertility might not be solely attributed to the effects of residual minerals (e.g., garnet and amphibole) in the lower crust but might also be partially inherited from the parent materials, which have been modified by prior subduction. These factors could be crucial for the occurrence of strong copper mineralization during the Miocene in the eastern Gangdese belt. Our findings provide quantitative constraints for formation conditions of porphyry copper deposits in post-collision settings.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122870"},"PeriodicalIF":3.6,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144134319","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":"Nitrate addition in different anoxic stages of acid paddy soil and the impacts on cadmium immobilization","authors":"Hanbing Meng ,&nbsp;Shan Wang ,&nbsp;Yang Yang ,&nbsp;Zebin Hong ,&nbsp;Shiwen Hu ,&nbsp;Guojun Chen ,&nbsp;Kuan Cheng ,&nbsp;Tongxu Liu","doi":"10.1016/j.chemgeo.2025.122867","DOIUrl":"10.1016/j.chemgeo.2025.122867","url":null,"abstract":"<div><div>Nitrate-reducing Fe(II) oxidation (NRFO) has emerged as a significant process in soil systems. However, few studies have examined the effects of coupled Fe and N cycling on cadmium (Cd) availability, especially in alternating flooding-drainage paddy soil. In this study, nitrate (NO₃⁻) was added to Cd-contaminated acidic paddy soil at different stages of flooding incubation. Results demonstrated that NO₃⁻ addition to the microcosm system at 0, 10, and 30 days reduced bioavailable Cd proportions by 21.53 %, 21.02 %, and 15.07 %, respectively, compared to the treatment without addition of NO₃⁻. The NO₃⁻ addition in the early stage proved to be more conductive to NRFO. As the NO₃⁻ addition stimulated the formation of secondary iron minerals, which immobilized Cd through adsorption and co-precipitation, thus reducing its mobility and bioavailability. Furthermore, NO₃⁻ addition increased soil pH, promoting the adsorption of Cd onto soil particles and further reducing its bioavailability. This study demonstrated that NRFO plays a crucial role in reducing Cd availability in acidic paddy soil and provides a novel insight into the mechanisms of NO₃⁻ remediation in Cd-contaminated paddy soils.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122867"},"PeriodicalIF":3.6,"publicationDate":"2025-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144134318","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":"Stable strontium isotope fractionation by fluid-melt interaction recorded in the Himalayan leucogranites","authors":"Xuqi Chen ,&nbsp;Yikang Quan ,&nbsp;Xiao-Chi Liu ,&nbsp;Gengxin Deng ,&nbsp;Xiaoyun Nan ,&nbsp;Fang Huang","doi":"10.1016/j.chemgeo.2025.122869","DOIUrl":"10.1016/j.chemgeo.2025.122869","url":null,"abstract":"<div><div>The evolution of granitic magmas represents a crucial process in the compositional differentiation of the continental crust. Stable Sr isotopic composition (δ⁸⁸Sr), which may undergo significant fractionation during fractional crystallization, has been recognized as an effective geochemical tracer for investigating granitic magma evolution. However, the behavior of stable Sr isotopes during fluid-melt interaction remains poorly understood. In this study, we present Sr isotope data for the fluid-interacted Kampa leucogranite from the Tethyan Himalaya Sequence in the Himalayan orogenic belt. Our results reveal distinct δ⁸⁸Sr variations (−1.51 ‰ to 0.31 ‰). The extremely low δ⁸⁸Sr values of the leucogranites cannot be attributed to partial melting, inheritance from the sedimentary source, or fractional crystallization. Petrographic evidence such as metasomatic textures demonstrates that the Kampa leucogranite experienced significant fluid interaction. The relationships between δ⁸⁸Sr and multiple fluid activity indicators (i.e., Nb/Ta, Y/Ho, and TE_1,3) suggest that lighter stable Sr isotopic compositions are associated with intense fluid activity. The interaction between deep-derived Cl-rich fluids with light Sr isotopic signatures and evolved granitic melts is likely the primary cause of the low δ⁸⁸Sr values. Therefore, stable Sr isotopes can provide key constraints on late-stage evolution processes and fluid-melt interaction in granitic systems. Furthermore, the correlations observed among stable Sr, Ba, and Rb isotopes indicate that combined isotopic tracing of fluid-mobile elements may provide further insight into fluid activity.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122869"},"PeriodicalIF":3.6,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144167136","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":"Structural and transport properties of supercritical NaAlSi3O8-H2O fluids: Insight from ReaxFF molecular dynamics simulations","authors":"Huifang Ke ,&nbsp;Yingchun Zhang ,&nbsp;Xiandong Liu ,&nbsp;Tianhua Wang ,&nbsp;Xiancai Lu","doi":"10.1016/j.chemgeo.2025.122863","DOIUrl":"10.1016/j.chemgeo.2025.122863","url":null,"abstract":"<div><div>With intermediate compositions between hydrous fluids and silicate melts, supercritical fluids are ideal agents for mass transfer from the subducting slab into the mantle wedge with fluid-like viscosity and melt-like elemental carrying capacity. However, the structure and transport properties of supercritical fluid have not been well understood. In this study, we investigated the structure and transport properties of supercritical NaAlSi₃O₈-H₂O systems by using the ReaxFF reactive molecular dynamics technique at 1000–3000 K and ∼ 2 GPa. The effect of water content and temperature on speciation, structure, diffusivity, and viscosity of supercritical fluids was explored. Si is primarily 4-coordinated, while Al exhibits coordination numbers of 3 to 6. As water content increases, Q⁴ and Q⁵ species decrease and Q⁰ species increase continuously, while the dominant species progressively transition from Q⁴ to Q³, followed by Q², Q¹, Q⁰. The elemental diffusivity and viscosity were both modeled as a function of water content and temperature. These models can be useful for the prediction of transport properties of hydrous silicate melts/fluids. Overall, the findings presented in this study formed a molecular level understanding of a typical supercritical fluid.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122863"},"PeriodicalIF":3.6,"publicationDate":"2025-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137868","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":"Warm magma storage in a continental rift: Insights from U/Th zircon dating and geochemistry of the Salton Buttes","authors":"Mélanie Barboni ,&nbsp;Juan Pablo Bernal","doi":"10.1016/j.chemgeo.2025.122866","DOIUrl":"10.1016/j.chemgeo.2025.122866","url":null,"abstract":"<div><div>The Salton Rhyolite Buttes, situated within the actively extending Salton Trough, offer a unique opportunity to investigate magma storage conditions in continental rift settings. We present new LA-MC-ICP-MS U<img>Th ages, trace element geochemistry, and Ti-in-zircon thermometry for zircons from all five Salton domes to constrain the timing and nature of past eruptive episodes and magmatic rejuvenation events. Our results reveal a complex history of multiple magmatic and eruptive episodes over the past ∼12,000 years. At Mullet Island, we identify major zircon crystallization events at 11.6 ± 0.6 kyr and 9.8 ± 1.9 kyr, followed by confirmed eruptions between 6 and 8 ka and at 2.3 ka. Obsidian Butte experienced two confirmed eruptions at 1.92 ± 0.06 ka and 5.2 ± 1.2 ka, with significant crystallization periods evidenced by ages of 3.4 ± 0.9 kyr. Rock Hill shows a crystallization event at 4.0 ± 0.9 kyr and a confirmed eruption at 1.8 ± 0.1 ka. The Red Hill domes demonstrate distinct histories: South Red Hill records eruptions at 0.8 ka and 2.5 ± 0.5 ka, with a major crystallization period at 4.7 ± 0.7 kyr, while North Red Hill shows an eruption at 0.8 ka and significant crystallization at 3.1 ± 1.1 kyr. Evidence suggests the presence of a long-lived, interconnected magmatic reservoir that has remained in a warm storage state for over 12,000 years. This finding extends the concept of warm storage, previously documented mainly in arc settings, to continental rift environments. The thin crust, high heat flow, and active extension in the Salton Trough likely facilitate the maintenance of a near-eruptible state over extended periods, even with relatively low magma flux. This has important implications for volcanic hazard assessment and geothermal energy exploration in rift settings. Our study demonstrates that LA-MC-ICP-MS U<img>Th dating can provide high-resolution chronology for young volcanic systems, offering insights into the complex thermal and magmatic evolution of warm storage reservoirs in diverse tectonic environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122866"},"PeriodicalIF":3.6,"publicationDate":"2025-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144117093","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":"Evaluating the impact of methane flux on the trace element geochemistry of sedimentary pyrite: Insights from the South China Sea","authors":"Shanggui Gong ,&nbsp;Haini Mao ,&nbsp;Xinyu Jiang ,&nbsp;Tao Sun ,&nbsp;Qianyong Liang ,&nbsp;Jörn Peckmann ,&nbsp;Dong Feng","doi":"10.1016/j.chemgeo.2025.122868","DOIUrl":"10.1016/j.chemgeo.2025.122868","url":null,"abstract":"<div><div>The trace element (TE) content of pyrite has been used as an archive of ocean and sediment pore fluid chemistry, depending on the respective formation conditions and potentially providing valuable insight into past atmospheric and oceanic conditions and sedimentary environments. The formation of authigenic pyrite is predominantly governed by organoclastic sulfate reduction (OSR) and sulfate-driven anaerobic oxidation of methane (SD-AOM). While methane flux significantly influences TE enrichment of marine sediments, its impact on the TE geochemistry of pyrite remains poorly understood. This study investigates the geochemistry of pore water, sediment, and handpicked pyrite from a gravity-piston core collected at the Haima seeps on the South China Sea continental slope. The current sulfate-methane transition zone (SMTZ) is located at approximately 200 cm below the seafloor (cmbsf), as indicated by sulfate penetration depth and the extremely negative δ¹³C values of dissolved inorganic carbon. The presence of a paleo-SMTZ in shallower sediment layers (above 200 cmbsf) is inferred from consistently low δ¹³C values (&lt; −40 ‰) of carbonate nodules, suggesting higher methane flux during past seepage episodes. Relatively higher δ³⁴S values of pyrite (−35.5 ‰ to −6.4 ‰) relative to background OSR-derived pyrite and elevated TS/TOC ratios (0.36 to 1.94) relative to typical marine sediments throughout the core suggest that pyrite formation was predominantly driven by SD-AOM. While TE enrichment (e.g., Mo, U, As) in bulk sediment is confined to the upper 20 cmbsf, reflecting seawater-derived TE input under high methane flux conditions, pyrite TE content remains largely invariant across the current and the paleo-SMTZ. Such lack of variability probably results from a dilution effect of the locally enhanced pyrite formation and/or competing TE sequestration by organic phases. The absence of a correlation between seawater TE concentrations and pyrite TE contents challenges the use of SD-AOM-derived pyrite as a seawater chemistry proxy. However, consistently elevated Mo/Cd ratios in pyrite, independent of methane flux variations, serve as a robust discriminator between SD-AOM- versus OSR-derived pyrite. Our findings improve the understanding of TE dynamics in methane-rich sediments, refining the role of pyrite geochemistry as a paleoenvironmental proxy.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122868"},"PeriodicalIF":3.6,"publicationDate":"2025-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144105858","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":"Potential pathways for lithium and Cr-isotopes during biogeochemical redox processes: Insights from karst-type laterites of Greece","authors":"Maria Economou-Eliopoulos,&nbsp;Sofia Kalatha","doi":"10.1016/j.chemgeo.2025.122865","DOIUrl":"10.1016/j.chemgeo.2025.122865","url":null,"abstract":"<div><div>The present study is focused on the distribution of unexplored critical and strategic element lithium (Li) in ophiolitic peridotites and weathered products (laterites, altered ultramafic rocks), affected soil and groundwater from Central Greece. The provided Li and other trace elements data are combined with available Cr-isotope compositions as tracers for redox reactions and their geochemical cycling from the magmatic source to these weathered products, aiming to define favorable conditions and potential pathways. All samples contain organic matter, but it is higher in bauxite laterites. The activity of the associated reducing microorganisms, catalyzing redox reactions, on Al-Fe-oxides may result in the reduction of the Fe(III) to soluble Fe(II), providing pathways for the iron leaching and the increase of Al and Li, as is exemplified by a good positive correlation between Al and Li (<em>r</em> = 0.85). However, partly re-deposition of iron is obvious by the occurrence of nanoparticulate spheroidal and/or bacterio-morphic pyrite. Given that the Cr occurs mainly as Cr(III) in chromite, olivine, serpentine, it may be released and oxidized to Cr(VI), under oxidizing conditions. The variations in the δ⁵³Cr values in chromitites from Greece are small but detectable, ranging from the most negative slightly negative to positive, due probably to differences in the mantle processes or metasomatism, during post-magmatic stages. The variations of the δ⁵³Cr values recorded in Fe-Ni-laterites, weathered rocks and groundwater from C. Greece are much wider compared to a very small variation in chromitites and show a negative correlation versus Cr(VI), supporting the post-mobilization reduction of Cr(VI) back to Cr(III) by Fe(II), organic matter, sulfides or microorganisms. However, δ⁵³Cr values in the leachates are lower compared to these in groundwater, due probably to the reduction of Cr(VI) and its precipitation as Cr(OH)₃, and/or the adsorption and bio-accumulation processes. Elevated Li concentrations in groundwater from coastal areas contaminated by Cr(VI) may reflect the intrusion of seawater, suggesting that the reduction of Cr(VI) to Cr(III) is inhibited, due to the potential stability of Cr(VI). This may be applied to the soil-groundwater-plant/crops system, using appropriate techniques to facilitate the reduction of Cr(VI) and protect food chain.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"687 ","pages":"Article 122865"},"PeriodicalIF":3.6,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144106021","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}