Chemical Geology最新文献

{"title":"Introduction of isotopically heavy barium from back-arc basin hydrothermal systems into the ocean","authors":"Xia Zhang ,&nbsp;Zhilei Sun ,&nbsp;Tao Li ,&nbsp;Nengyou Wu ,&nbsp;Hong Cao ,&nbsp;Yaoling Niu","doi":"10.1016/j.chemgeo.2025.123079","DOIUrl":"10.1016/j.chemgeo.2025.123079","url":null,"abstract":"<div><div>The concentrations of Ba in high-temperature hydrothermal fluids are several orders of magnitude higher than those in seawater and therefore may play an important role in marine Ba cycle. However, the ultimate hydrothermal inputs of Ba (isotopically light or heavy) into the oceans remain debated, and the Ba inputs from back-arc hydrothermal vents are poorly constrained. To address this issue, we have analyzed the Ba isotope compositions of hydrothermal barites from the Okinawa Tough. The δ¹³⁸Ba values of the studied barites show a limited variation (δ¹³⁸Ba = −0.16 to −0.05 ‰) compared to the natural range and is primarily controlled by the Rayleigh Ba isotope fractionation from the parental hydrothermal fluids during precipitation. About 33 to 51 % removal of Ba from the hydrothermal fluid will account for the observed δ¹³⁸Ba values. The δ¹³⁸Ba values of hydrothermal fluids after barite precipitation would be 0.19 to 0.30 ‰, which are isotopically heavier than the Ba sinks in the ocean. The new data thus suggest that back-arc hydrothermal systems may introduce isotopically heavy Ba into the oceans due to the non-conservative behavior of Ba during the fluid-seawater mixing in these systems. The marine Ba budget has been evaluated and the calculated Ba inputs to the ocean are isotopically heavier than sediment outputs, implying either isotopically light sources or isotopically heavy sinks of Ba are missing. One possibility is that the light Ba released from MORB during low-temperature alteration may play an important role in maintaining marine Ba isotope budget balance.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123079"},"PeriodicalIF":3.6,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217522","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":"Siderite transformation pathways in early diagenesis: Effects of phosphate, silicate, humic acid and sulfide","authors":"Zhe Zhou ,&nbsp;Heng Xiao ,&nbsp;Baorong Huang ,&nbsp;Jiangtao Li ,&nbsp;Shouye Yang","doi":"10.1016/j.chemgeo.2025.123075","DOIUrl":"10.1016/j.chemgeo.2025.123075","url":null,"abstract":"<div><div>Siderite (FeCO₃) is a widely distributed authigenic mineral found in marine and terrestrial sediments, playing a crucial role in benthic biogeochemical cycling and preserving key paleoenvironmental information. Despite its importance, the transformation pathways of siderite under complex sedimentary environments remain poorly understood. Here batch experiments were conducted to investigate the transformation of siderite (containing 10 mM Fe(II)) in the presence of phosphate (P/Fe ratios of 0.2, 0.5, and 1), sulfide (S/Fe ratios of 0.5, and 1), silicate (Si/Fe ratios of 0.5, and 1), and humic acid (C/Fe ratios of 0.5, and 1) over hours to 6 days under strictly anoxic conditions. Our results show that phosphate induced a rapid dissolution-reprecipitation process of siderite at pH 7.8, forming nanocrystalline vivianite first and gradually integrating into the lath-like structure, effectively sequestering phosphate. However, after transition into sulfidic conditions, vivianite rapidly converts into mackinawite, releasing nearly all immobilized phosphate, underscoring its transient role as a phosphate reservoir. Silicate and humic acid, though inert in directly transforming siderite under anoxic conditions, significantly influence sulfide-induced siderite transformation. Sulfide can rapidly transform siderite into FeS (e.g., mackinawite) while preserving the pseudomorph of siderite and generating a highly porous ultrastructure on the surface. The presence of silicate promotes mackinawite crystallization, while humic acid suppresses secondary iron mineral formation, resulting in smoother, less porous FeS structures. These findings highlight the dynamic interplay between siderite and environmental factors, offering new insights into phosphorus cycling mediated by siderite. Importantly, this study provides a refined understanding of the mineralogical and morphological evolution of siderite, enhancing the accuracy of applying this redox proxy for sedimentary history reconstructions, and informing biogeochemical models of the coupled Fe-P-S cycling in early diagenesis.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123075"},"PeriodicalIF":3.6,"publicationDate":"2025-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217520","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":"Origin of rodingites in the Xigaze ophiolite, SW Tibet: Constraints from Ca and Sr isotopes","authors":"Yu-Wei She ,&nbsp;Jian Sun ,&nbsp;Zhi-Yong Zhu ,&nbsp;Qiu-Hong Xie ,&nbsp;Chen-Xu Pan","doi":"10.1016/j.chemgeo.2025.123071","DOIUrl":"10.1016/j.chemgeo.2025.123071","url":null,"abstract":"<div><div>Rodingites, extremely calcium-rich but sodium- and silicon-poor rocks forming through fluid-rock reactions, are crucial for understanding the oceanic cycling of materials. However, the source of calcium in rodingites remains debated. Here, we investigate whole rock Ca and Sr isotopic compositions of samples collected across a continuous section of a rodingite dyke from the Xigaze ophiolite, SW Tibet. The rodingite dyke exhibits progressive metasomatism from core to margin, defining central, transitional, and marginal zones. The dyke displays a wide range of δ^44/40Ca values from 0.28 ‰ to 1.63 ‰ but limited variation in Sr isotope (⁸⁷Sr/⁸⁶Sr_(<em>i</em>) = 0.70308–0.70438). The slightly metasomatized central rodingites exhibit lower δ^44/40Ca values (0.53 ‰ to 0.68 ‰) than MORB, whereas the moderately metasomatized transitional rodingites display significantly lighter Ca isotope compositions (δ^44/40Ca = 0.28 ‰ to 0.61 ‰). The intensively metasomatized marginal rodingites show the highest δ^44/40Ca values (0.64 ‰ to 1.63 ‰). The transverse profile of δ^44/40Ca values across the rodingite dyke reveals clear oscillatory zoning, suggesting multiple fluid sources for Ca during rodingitization. In the early-stage, the mafic dyke was metasomatized by a carbonate-bearing fluid characterized by low δ^44/40Ca values, which originated from the mixing of deserpentinization-related fluids with marine carbonates during subduction. Subsequently, the dyke experienced more intense metasomatism by a high-δ^44/40Ca serpentinizing fluid, leading to additional Ca input and an elevation of δ^44/40Ca values. The gradual increase in ⁸⁷Sr/⁸⁶Sr_(<em>i</em>) ratios from the central zone to the marginal zone indicates that the primary fluids were derived from seawater-triggered serpentinization. This study proposes that during the initial stages of subduction fluids released by serpentinite dehydration dissolved sedimentary carbonates on the subducted oceanic slab. As subduction progressed, extensive dehydration of the surrounding serpentinites produced high-δ^44/40Ca serpentinizing fluids, which further elevated both δ^44/40Ca and ⁸⁷Sr/⁸⁶Sr_(<em>i</em>) values of the dyke. The highly variable δ^44/40Ca values of rodingites from diverse tectonic settings support the model involving multiple fluid contributions with distinct Ca isotopic compositions during rodingitization.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123071"},"PeriodicalIF":3.6,"publicationDate":"2025-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217586","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":"Chemical features of sediment-derived supercritical fluid-melt at subduction zone conditions","authors":"Alexander G. Sokol,&nbsp;Olga A. Kozmenko,&nbsp;Alexey N. Kruk","doi":"10.1016/j.chemgeo.2025.123073","DOIUrl":"10.1016/j.chemgeo.2025.123073","url":null,"abstract":"<div><div>Phase relations and partitioning of major and some trace elements are studied in samples of metasediment (natural schist) poor in H₂O (2.2 wt%) and CO₂ (0.9 wt%) in diamond trap experiments at pressures of 3.0 GPa, 5.5, and 7.8 GPa and temperatures from 750 to 1090 °C. At the applied <em>P-T</em> parameters simulating the conditions of warm and hot subduction, the run products comprise a mobile phase and a residue composed of garnet, phengite, clinopyroxene, coesite, kyanite, as well as accessory monazite, rutile, and zircon. The mobile phase is a hydrous melt of a granitic composition till 3.0 GPa and 750–900 °C but transforms into a supercritical fluid-melt (SCFM) with SiO₂ &gt; Al₂O₃ ≈ K₂O &gt; Na₂O ≈ CaO ≈ MgO ≈ FeO at 5.5 GPa and 850–1030 °C. The transformation is accompanied by increase in the contents of H₂O + CO₂ from 17–24 wt% to &gt;40 wt%, at the weight ratio H₂O/(H₂O + CO₂) ∼0.75. SCFM remains almost invariable in its fraction and amounts of H₂O + CO₂ and solutes within the 5.5–7.8 GPa and 850–1090 °C intervals. At higher pressures and temperatures, the coefficients of Al and Na partitioning between the mobile phase and the residue (<em>D</em> = C_SCFM/C_Residue) become lower and that of K increases, whereby the K₂O/Na₂O ratio in SCFM becomes an order of magnitude greater than in hydrous melt. The revealed trend can be used as a criterion for discriminating between hydrous melt and SCFM proceeding from the bulk composition of multiphase inclusions in mantle minerals. The K₂O/H₂O ratio in metasediment-derived SCFM increases with pressure but does not vary much with temperature. This provides experimental evidence for the potash-depth relationship inferred earlier for primitive arc lavas. The partition coefficients of Sr, K, Rb and P become progressively higher with pressure and temperature to make these elements least compatible at 7.8 GPa and 940–1090 °C in the presence of SCFM. The partition coefficient of Li is &gt;1 at moderate temperatures only. Thus, SCFM can originate in pre-devolatilized metasediment poor in H₂O and CO₂ subducting to depths of 150 to 240 km. The low contents of volatiles in the metasediment ensure stability of the residue monazite and phengite which are main carriers of LREE and LILE recycled by slabs into the mantle wedge. K-rich silicic SCFM penetrating into the mantle can be an important agent in the generation of arc and back-arc magmas, as well as in metasomatism of lithospheric mantle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123073"},"PeriodicalIF":3.6,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217584","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":"Elemental signatures of metamorphic, diagenetic, and pedogenic magnesites from Central Queensland, Australia","authors":"Carl Swindle ,&nbsp;Paulo Vasconcelos ,&nbsp;Zoe Dimarco ,&nbsp;Nathan Dalleska ,&nbsp;Ai Nguyen ,&nbsp;Emily Cardarelli ,&nbsp;Surjyendu Bhattacharjee ,&nbsp;Kenneth Farley ,&nbsp;Theodore Present","doi":"10.1016/j.chemgeo.2025.123068","DOIUrl":"10.1016/j.chemgeo.2025.123068","url":null,"abstract":"<div><div>Magnesium carbonates record information on water-rock interactions during and after mineral precipitation. The Marlborough Terrane in central Queensland, Australia, contains magnesite-bearing serpentinite highlands surrounded by low-lying sedimentary basins that host authigenic magnesite (MgCO₃). Open pit mines in both settings provide exposures of serpentinites (Gumigil) and Cenozoic sediments and overlying black soils (Yaamba) that host the magnesite and other authigenic phases. The Gumigil mine contains deeply weathered serpentinite hosting metamorphic magnesite veins that formed <em>syn</em>-tectonically; both serpentinite and magnesite are now partially dissolving, silicifying, and ferruginizing. Aqueous Mg²⁺ is being exported into the basins surrounding the serpentinite ridges. The Yaamba magnesite mine in the surrounding plains exposes diagenetic magnesite formation within unlithified alluvial sediments, where ascending magnesium-rich groundwaters replace arkosic sands and silts by magnesite cements, nodules, and pinnacles. Late-stage pedogenic processes at Gumigil and Yaamba drive retrograde transformation of magnesite into geochemically distinct exterior regions of second-generation cryptocrystalline magnesite recording interactions with Fe/Mn-oxides/hydroxides via cerium anomalies, yttrium anomalies and manganese concentrations in zoned magnesites from Yaamba. The complex history of mineral precipitation, dissolution, diagenetic replacement, and supergene alteration is recorded in the major, minor and trace element compositions of magnesites at each site. Serpentinite ridges and magnesite-bearing valley floors in Central Queensland provide a useful analog to the processes that might occur in the ultramafic highlands and carbonated lowlands at Jezero crater, Mars.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123068"},"PeriodicalIF":3.6,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217585","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 seawater-basalt interaction at 10–100 °C: Controlling parameters and effects on the composition of the oceanic crust and seawater","authors":"Simon Prause ,&nbsp;Barbara I. Kleine-Marshall ,&nbsp;Tobias B. Weisenberger ,&nbsp;Andri Stefánsson","doi":"10.1016/j.chemgeo.2025.123074","DOIUrl":"10.1016/j.chemgeo.2025.123074","url":null,"abstract":"<div><div>Chemical reactions and element mobilization during seawater-basalt interaction play a central role in regulating global element fluxes between seawater and the oceanic crust. This study uses kinetic reaction path modeling to investigate basalt alteration by seawater at 10–100 °C, assessing the influence of reaction time, temperature, pH, rock crystallinity and CO₂ concentration on alteration mineral formation and seawater composition during crustal aging and cooling. Early alteration involves dissolution of basaltic glass and primary minerals, releasing Si, Al, Fe, Ca, Mg, Na and K, followed by the formation of oxides, hydroxides, pyrite, Fe(III)- and Fe(II)-bearing clays, carbonates, celadonite and zeolites. At elevated CO₂ concentrations, for example due to deep magmatic degassing, water pH remains buffered at slightly acidic to circumneutral values. In contrast, at lower CO₂ concentrations, corresponding to standard seawater, H⁺ consumption during basalt dissolution increases pH and drives the system towards more reducing conditions, thereby favoring the formation of zeolites, Ca-silicates and Mg-rich clays. Reaction progress, redox conditions, pH and CO₂ concentration are the primary controls on alteration mineralogy and seawater chemistry. Basalt crystallinity mainly influenced reaction rates and timescales while having minor effects on the mineralogical and chemical outcome of alteration. Temperature likewise mostly affected kinetics but also had an additional effect on K fluxes during seawater-basalt interaction, with K being removed from seawater below ∼50 °C, but added to seawater at higher temperatures. The model predicts significant long-term sinks of both K and Mg due to the formation of clay minerals and celadonite over the course of crustal aging and cooling. Calcium behaved variably, being mostly removed from seawater by early carbonate formation but becoming increasingly released over the cause of crustal aging due to basalt leaching. These results emphasize the need to constrain key parameters controlling seawater-basalt interaction when evaluating its role in low-temperature hydrothermal alteration and seafloor weathering.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123074"},"PeriodicalIF":3.6,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155692","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":"New He-O-Sr-Nd isotopes and chronology of Quaternary lavas from the Kula volcanic field (western Türkiye): Implications for temporal changes in the magma source","authors":"Duru Cesur ,&nbsp;Halim Mutlu ,&nbsp;Ercan Aldanmaz ,&nbsp;Finlay M. Stuart ,&nbsp;Ana Carracedo ,&nbsp;Robert M. Ellam ,&nbsp;Nilgün Güleç","doi":"10.1016/j.chemgeo.2025.123070","DOIUrl":"10.1016/j.chemgeo.2025.123070","url":null,"abstract":"<div><div>The Quaternary Kula volcanic field in western Turkey comprises predominantly sodium-rich alkaline basaltic products from several eruption periods. We report new bulk-rock major-trace element, Sr<img>Nd isotopes, helium and oxygen isotope determinations of olivine phenocrysts and Ar/Ar and cosmogenic He ages to investigate the mantle source characteristics and the temporal change in melt source isotope compositions. The volcanic activity in the Kula field continued episodically from 1.28 Ma to around 8 ka and can be divided into three main eruption phases characterized by distinct eruption type and lava morphology. The lava compositions from these phases evolve from basanite to phonolitic tephrite. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd range from 0.703012 to 0.703407 and 0.512968 to 0.513032, respectively, becoming less enriched in time. The earliest basalts display a small degree of crustal contamination that reduces with time that may be the result of rapid ascent of magmas in the volcanic conduit, likely resulting from gradually increasing rate of extensional deformation and enhanced lithospheric fracturing. ³He/⁴He ratios vary from 3.50 to 8.04 Ra, while δ¹⁸O values vary from 4.7 to 5.2 ‰. The less differentiated samples are characterized by higher ³He/⁴He with &gt;7 Ra, indicating melt derivation from a low-³He/⁴He OIB-type sub-lithospheric mantle source. The relatively large range in ³He/⁴He and δ¹⁸O values with insignificant change in ⁸⁷Sr/⁸⁶Sr for the entire suite further indicates mixing of melts from a multi-component mantle source.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123070"},"PeriodicalIF":3.6,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155129","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":"All-optical measurements of MORB-glass density at high pressure hint at a stiffness-composition relation in silicate glasses","authors":"Sergey S. Lobanov ,&nbsp;Sergio Speziale ,&nbsp;Ilya Kupenko ,&nbsp;Vladimir Roddatis ,&nbsp;Louis Hennet ,&nbsp;Séverine Brassamin ,&nbsp;Konstantin Solovev ,&nbsp;Lukas Schifferle","doi":"10.1016/j.chemgeo.2025.123066","DOIUrl":"10.1016/j.chemgeo.2025.123066","url":null,"abstract":"<div><div>The density of silicate melts at high pressure determined the efficiency of gravitational differentiation in the solidifying magma ocean and thus the starting conditions for the Earth's evolution. The denisty also controls the migration of melts in the lithosphere and their stabilization in the transition zone and near the core mantle boundary. Yet, no density systematic exists for melts across the pressure range of the mantle. This is primarily because of severe experimental difficulties associated with measuring the density of silicate liquids at mantle pressures and temperatures (tiny sample size, melt chemical reactivity, lack of crystalline structure). The use of glasses as proxies of melts at high pressure lifts some but not all of these challenges, and may prove important in developing theoretical models of melts physical behavior at high pressures. Here we report on the density of MORB glass up to 32.3 GPa at room temperature measured by the recently developed all-optical method in a diamond anvil cell. The comparison of the MORB glass density to that for other basaltic glasses reported in the literature reveals contradictions, similarly to those existing between data available for MORB-like melts, which underscore the need for consistent, systematic melt and glass density measurements at high pressure across a broad compositional space. More broadly, the compression behavior of MORB and other basaltic glasses, SiO₂, MgSiO₃, and Mg₂SiO₄ glasses suggests that the incorporation of SiO₂ and/or large network-modifiers (larger than Mg) softens the glass (smaller isothermal bulk modulus and its pressure derivative). Future all-optical measurements of glass density may provide fundamental, critical input to develop models of complex glasses and melts physical properties, and help assessing the solidification of the primordial magma ocean, the initiation and development of physical and chemical heterogeneity in the mantle, and the migration or stabilization of melts at different levels in the deep Earth.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123066"},"PeriodicalIF":3.6,"publicationDate":"2025-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155695","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":"Deep carbon cycling due to mélange diapir melting","authors":"Junfu Zhang ,&nbsp;Feng Wang ,&nbsp;Jie Tang ,&nbsp;Wenliang Xu","doi":"10.1016/j.chemgeo.2025.123065","DOIUrl":"10.1016/j.chemgeo.2025.123065","url":null,"abstract":"<div><div>The melting of a mélange diapir is a new petrogenetic model for the origins of alkaline arc igneous rocks. However, the deep carbon (C) cycle related to mélange diapir melting is poorly understood. Here, we investigate the decarbonation related to mélange diapir melting based on major and trace elements, and Sr–Nd–Pb–Zn–Mg isotopic data for the Oligocene alkaline rocks in northeast China. These rocks consist of plagioclase-bearing and plagioclase-free trachyandesite, and aegirine–augite syenite. From trachyandesites to syenites, the REE and trace element abundances increase, and the high-field-strength element contents change from depleted to enriched. These characteristics are indicative of interactions between carbonated mantle and a mélange. Their Sr-Nd isotopic compositions and variations in Hf/Nd ratios indicate the alkaline rocks formed by partial melting of a mélange diapir. The heavy Zn isotopic compositions (+0.35 ‰ to +0.44 ‰) of the alkaline rocks, combined with the Nb-Ta enrichment of the syenites, reflects the contribution of carbonate components during melting of the mélange diapir. However, the alkaline rocks have heavy Mg isotopic compositions (−0.30 ‰ to −0.03 ‰), implying that dehydration of the subducted mélange occurred before it melting. The correlations between major and trace elements and δ⁶⁶Zn values show that altered oceanic crust contributed most of the carbonate during decarbonation, which means previous studies have overestimated the contribution of subducted sediments during the decarbonation of a diapir. Mélange diapir melting had an important role in driving the deep C cycle in northeast Asia during the Cenozoic.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123065"},"PeriodicalIF":3.6,"publicationDate":"2025-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155694","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":"Seawater intrusion and mud volcanism impact the groundwater geochemistry of small Bornean islands","authors":"Chin Yik Lin ,&nbsp;Baba Musta ,&nbsp;Mohd. Harun Abdullah ,&nbsp;Fera Cleophas ,&nbsp;Feona Isidore ,&nbsp;Muhammad Hatta Roselee ,&nbsp;Alfonso O. Mucci","doi":"10.1016/j.chemgeo.2025.123064","DOIUrl":"10.1016/j.chemgeo.2025.123064","url":null,"abstract":"<div><div>Mud-volcanic environments represent a striking departure from typical shallow aquifer settings, exhibiting geochemical processes and elemental mobilities rarely encountered in non-volcanic coastal systems. In this study, we compare the chemical composition of groundwater and solid-phase samples from mud-volcanic islands and a nearby non-volcanic control island in Northern Borneo to characterize how mud-volcanism alters the ionic composition, trace-element fluxes, and seawater intrusion dynamics through the fossil reef terrains. Although expelled muds introduce elevated concentrations of trace elements (e.g., Al., Mn, Sr) and gases into the shallow subsurface, posing potential contamination risks, the abundant siliciclastic clays derived from mud-volcanism also infill pore spaces and reduce aquifer permeability. As a result, mud-volcanic islands exhibit less seawater intrusion than a lithologically similar non-volcanic island, despite active anthropogenic pumping and tidal forcing. Geochemical mass-balance and PHREEQC-based mixing models reveal that, in mud-volcanic settings, cation-exchange reactions and localized carbonate dissolution/precipitation dominate over conservative seawater mixing, whereas on the non-volcanic island, seawater intrusion and carbonate dissolution are the primary controls on groundwater chemistry. These findings demonstrate that mud-volcanism not only mobilize pollutants but also reshapes local aquifer hydrodynamics, uncovering a dual role as both a source of trace-element contamination and a natural barrier against seawater intrusion.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123064"},"PeriodicalIF":3.6,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155693","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}