Chemical Geology最新文献

{"title":"Sublacustrine faults discharge as an important source of nutrients into a tectonic lake","authors":"Weigang Su ,&nbsp;Qiugui Wang ,&nbsp;Yujun Ma ,&nbsp;Xiuzhen Ma ,&nbsp;Chengcheng Tian ,&nbsp;Jinlong Wang","doi":"10.1016/j.chemgeo.2025.123010","DOIUrl":"10.1016/j.chemgeo.2025.123010","url":null,"abstract":"<div><div>In tectonic lake systems, fault-driven lacustrine groundwater discharge (F-LGD) plays a critical role in regulating lacustrine water and nutrient budgets. This study quantifies F-LGD fluxes in Lake Qinghai by analyzing the spatial distribution of radium isotopes (²²³Ra, ²²⁴Ra) and stable isotopes (δ¹⁸O, δD) across horizontal and vertical gradients during July 25–August 19, 2021. Results demonstrate that mean radium activity in bottom layers exceeds pelagic zones (attributable to sediment diffusion and an additional Ra source), with significantly elevated activities and δ¹⁸O enrichment in bottom waters proximal to sublacustrine faults. These findings confirm that sublacustrine faults act as conduits for groundwater influx. The estimated F-LGD flux ranges from 9.56 × 10⁸ to 13.24 × 10⁸ m³ yr⁻¹, equivalent to 60–80 % of combined precipitation and surface runoff inputs. Critically, fault-derived fluxes of dissolved inorganic phosphorus (DIP), dissolved inorganic nitrogen (DIN), and dissolved silica (DSi) surpass those from atmospheric wet deposition and riverine sources. To our knowledge, this work provides the first quantitative assessment of sublacustrine fault-driven water transport in a tectonic lake, demonstrating that F-LGD is a dominant controller of hydrological and biogeochemical cycling in such systems. Further investigation of fault-mediated material exchange is essential to refine lake-scale circulation models.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123010"},"PeriodicalIF":3.6,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144894886","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 evaporites in Kiruna-type iron oxide-apatite deposits in the Northern Norrbotten region, Sweden: Evidence from in situ halogen analyses of scapolite","authors":"Li-Ping Zeng ,&nbsp;Carl Spandler ,&nbsp;Ying-Ying Liu ,&nbsp;Johannes Hammerli ,&nbsp;Wang Liao ,&nbsp;Hao Hu ,&nbsp;Sanna Olsson ,&nbsp;De-Xian Zhang ,&nbsp;Tao He ,&nbsp;Jian-Wei Li ,&nbsp;Xin-Fu Zhao","doi":"10.1016/j.chemgeo.2025.123009","DOIUrl":"10.1016/j.chemgeo.2025.123009","url":null,"abstract":"<div><div>Hydrosaline liquids or salt melts have recently been suggested to play a key role in forming Kiruna-type iron oxide-apatite (IOA) deposits, with sedimentary evaporites proposed as contributors to ore-forming processes. However, the timing and role of evaporites in ore formation are poorly understood. Scapolite minerals, typical products of sodic alteration resulting from the interaction between hydrosaline liquids (also called highly saline fluids) and country rocks, may provide key insights into ore genesis. Here, we measured in situ Cl/Br ratios of scapolite from two representative IOA deposits (Mertainen and Gruvberget-Fe) and the Aitik porphyry Cu system from the Northern Norrbotten region of Sweden to trace the sources and evolution of ore-related liquids. Based on mineral assemblages, scapolite grains are classified into Scp I and Scp II. Scp I, formed during pre-ore or <em>syn</em>-ore alteration, exhibits distinct molar Cl/Br ratios (510–2000) across domains and grains. This variation implies multiple, though dominantly magmatic, sources for the associated liquids. Zoned Scp I crystals show relatively low molar Cl/Br ratios of 510–790 in their cores, increasing to 730–1640 in the mantles and/or rims. This trend suggests that the grains initially equilibrated with dominantly pore waters (bittern brines and/or seawater) but were later primarily buffered by liquids of magmatic origin. Scp II, associated with hematitization, have much higher molar Cl/Br ratios (2300–3500) and likely precipitated from halite-bearing evaporite-dissolution fluids derived from the Kiruna Greenstone Group. Our findings suggest that evaporite components were introduced into the studied IOA systems primarily through fluid circulation triggered by magmatic intrusion. However, later-stage evaporite dissolution fluids overprinting the ore system may create the misleading impression that evaporite-derived fluids played a key role in ore genesis.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123009"},"PeriodicalIF":3.6,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144865835","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":"Fe(II)-induced phase transformation of La-substituted ferrihydrite significantly influences the reduction and immobilization of Cr(VI) in soils","authors":"Changjin Liang ,&nbsp;Honghai Wu ,&nbsp;Yaowei Li ,&nbsp;Yufeng Guan","doi":"10.1016/j.chemgeo.2025.123005","DOIUrl":"10.1016/j.chemgeo.2025.123005","url":null,"abstract":"<div><div>Ferrihydrite (Fh) can usually transform into phases with higher crystallinities. This may greatly alter Fh adsorption capacity for chromium ions, thereby affecting their immobilizations and fates. Foreign elements [e.g., lanthanum (La)] as impurities can become incorporated into Fh. Herein, the effect of La-substitution into Fh and the influence of the presence of Cr(VI) on Fh phase transformation and fate of Cr(VI) were investigated. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Electro-chemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) and other test methods were employed to probe phase changes after the Fe(II)-induced La-substituted Fh (La-Fh) transformations. At pH 5.5, no neoformed phase was observed until 7 d for La-Fh or pure Fh at 1 mM Fe(II) aq, but all La-Fh systems underwent transformations at 5 mM Fe(II)aq. A low pH and Fe(II)aq level favored lepidocrocite (Lp) to form, whereas goethite (Gt) was the predominant phase rather than Lp as pH increased to 7.2 with higher level Fe(II)aq. However, the La-substitution inhibits the La-Fh transformation rate and path. This made 5 % La-Fh transformed to Lp after 30 d at pH 7.2 and 1 mM Fe(II)aq. The La-release was present to some extent during the transformation process. Either the inhibition to La-Fh transformation or the La-slow release favors the retention of early-adsorbed Cr(VI) on iron-mineral surface. The added Cr(VI) might promote the La-Fh transformation even under a lower-level Fe(II), primarily attributed to the rapid reduction of Cr(VI) to Cr(III) by Fe(II), which produced more liable Fe(III) in addition to the Cr(III) that can improve the mineral conductivity, thereby enhancing the La-Fh transformation. Mechanisms responsible for the Fe(II)-induced La-Fh transformation companying the La slow-release are proposed to provide insights into the reduction and immobilization of Cr(VI) under anaerobic conditions, thus demonstrating that La-Fh is a promising material for application in Cr-contaminated site remediation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123005"},"PeriodicalIF":3.6,"publicationDate":"2025-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144829706","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 critical role of matrix effect correction in oxygen isotope analysis of clinopyroxene by SIMS","authors":"Andrey Gurenko ,&nbsp;Lydéric France ,&nbsp;Elena Dubinina ,&nbsp;Benita Putlitz ,&nbsp;Ilya Bindeman ,&nbsp;Etienne Deloule ,&nbsp;Anna Avdeenko ,&nbsp;Valentin Casola","doi":"10.1016/j.chemgeo.2025.122997","DOIUrl":"10.1016/j.chemgeo.2025.122997","url":null,"abstract":"<div><div>Raw stable isotope ratios measured by secondary ion mass spectrometry (SIMS) can deviate from their true values due to instrumental mass fractionation (IMF), a phenomenon known as the matrix effect. Accurate determination and prompt correction of IMF during SIMS measurements are essential for obtaining reliable stable isotope data. In minerals and glasses, relationships between IMF values and element concentrations, along with associated endmember components, are commonly used to account for matrix effects that can reach a few tens of permille. Although this approach is relatively universal, it can introduce significant bias in IMF determinations, especially when the chemical compositions of reference materials differ from those of the analyzed samples. The primary objective of this study is to evaluate the impact of diversities in clinopyroxene chemical composition in assessing matrix effects during oxygen isotope analysis. Our results demonstrate that clinopyroxene Mg-number is usually not a reliable proxy for determining matrix-related IMF. Instead, Ca content or the amount of wollastonite component provide reasonably accurate means of accounting for matrix effects. However, multivariable linear regression models can markedly improve matrix-dependent IMF prediction compared to single-variable approaches, particularly when the composition of unknown clinopyroxene samples deviates from that of the reference materials. We evaluate the strengths and limitations of the aforementioned IMF correction methods by examining oxygen isotopic compositions of coexisting olivine and clinopyroxene from the Midfell gabbro nodules, SW Iceland.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 122997"},"PeriodicalIF":3.6,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144829705","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":"Grain-scale δ34S zonation in pyrite from the Chilpi Basin, India: Evidence for closed-system microbial sulfate reduction in the Proterozoic","authors":"Susobhan Neogi,&nbsp;Trisrota Chaudhuri","doi":"10.1016/j.chemgeo.2025.123004","DOIUrl":"10.1016/j.chemgeo.2025.123004","url":null,"abstract":"<div><div>This study presents the first documentation of stromatolitic carbonates from the Chilpi Basin, a Proterozoic volcano-sedimentary succession within the Bastar Craton of central India. The succession records a transition from shallow clastic to chemogenic sedimentation, with micritic limestone interbedded with <em>syn</em>-sedimentary barite and hosting domal stromatolites, overlain by phyllite. Euhedral diagenetic pyrite, disseminated within these microbialites, preserves a high-resolution archive of microbial and geochemical processes in a dynamic shallow marine environment. A total of 107 in situ sulfur isotope (³⁴S/³²S) analyses were conducted on pyrite grains using large-geometry Secondary Ion Mass Spectrometry (SIMS; CAMECA IMS-1300 HR³), yielding δ³⁴S_V-CDT values from +22.9 ‰ to +33.5 ‰. Larger grains exhibit clear intra-crystal zonation, with ³⁴S-enriched rims relative to lighter cores (+25.5 ‰ to +33.5 ‰), consistent with Rayleigh distillation by microbial sulfate reduction (MSR) under semi-closed diagenetic conditions. Smaller grains show minimal internal variation, reflecting grain-specific histories within localized redox microenvironments. Rayleigh modeling indicates ∼41 % depletion of the original sulfate reservoir during pyrite growth. Petrographic and BSE imaging reveal features such as calcite–quartz overgrowths and magnetite rims, supporting a two-stage diagenetic growth of pyrite, followed by partial oxidation and replacement by magnetite. Stratiform barite within stromatolitic laminae records pulses of barium and sulfate availability under oxic to sub-oxic conditions, likely linked to episodic volcanic or hydrothermal input, while subsequent pyrite and magnetite document a progression through reducing to re-oxidizing conditions. This mineralogical sequence—from barite to pyrite to magnetite—captures a complete redox cycle at the grain scale. The Chilpi Basin thus provides a rare Proterozoic archive, resolved by SIMS, that links environmental transitions, microbial activity, and diagenetic mineralization in a low-sulfate shallow marine setting, filling a critical geographic and temporal gap in global δ³⁴S datasets and offering new insight into early Earth redox evolution.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123004"},"PeriodicalIF":3.6,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144810010","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":"Occurrence of tungsten-rich shallow groundwaters linked to underlying hydrothermal activities and thiotungstates formation in deep geothermal fluids","authors":"Qinghai Guo,&nbsp;Junbiao Qian,&nbsp;Hao Luo,&nbsp;Li Luo","doi":"10.1016/j.chemgeo.2025.122996","DOIUrl":"10.1016/j.chemgeo.2025.122996","url":null,"abstract":"<div><div>Tungsten (W) geochemistry in natural aquatic systems has garnered significant scientific interest in recent years. While non-mineralized shallow groundwaters typically exhibit low W concentrations, the coexistence of both elevated (over 500 μg/L) and depleted (&lt;1 μg/L) W levels in shallow groundwaters within the non-mining Tianyang basin (China) presents a compelling case for investigating novel mechanisms of natural W enrichment. High-W shallow groundwaters—both thermal and nonthermal—are spatially clustered above deep boreholes-discovered Archaean geothermal fluids with exceptional W concentrations (up to 614.1 μg/L). Hydrogeochemical analyses reveal that these high-W Quaternary groundwaters (also enriched in Cl, Si, B, F, Li, Rb, and Cs), ‌in line with our predictions, originate from Archaean geothermal fluids through processes including adiabatic cooling, conductive heat loss, mixing with infiltrating meteoric waters at shallow depths, or hybrid ones. The W enrichment in Archaean geothermal fluids arises primarily from two synergistic mechanisms: (1) extensive leaching of W-rich Archaean reservoir rocks, and (2) sulfide-driven conversion of aqueous tungstate to thiotungstates, which circumvents solubility limitations imposed by common W-bearing minerals (e.g., wolframite). Specifically, thiotungstates formation in sulfidic geothermal fluids inhibits W sequestration into mineral phases, sustaining anomalously high dissolved W concentrations. This study provides the definitive evidence linking thiotungstate speciation in deep geothermal fluids to W enrichment in shallow groundwaters, advancing our understanding of W geochemistry in interfaces between geothermal and non-thermal aquifers.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 122996"},"PeriodicalIF":3.6,"publicationDate":"2025-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144809633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Zircon U-Pb ages, geochemical and Sr-Nd-Hf-O isotopic data of newly discovered ultrapotassic and adakitic rocks in the Kohistan Island Arc, North Pakistan: Constraints on petrogenesis and post-collisional alkaline magmatism","authors":"Amjad Hussain ,&nbsp;Kui-Dong Zhao ,&nbsp;Mohammad Arif ,&nbsp;Bin Fu ,&nbsp;Martin R. Palmer ,&nbsp;Wei Chen ,&nbsp;Shao-Yong Jiang ,&nbsp;Delores M. Robinson ,&nbsp;Hafiz U. Rehman","doi":"10.1016/j.chemgeo.2025.122989","DOIUrl":"10.1016/j.chemgeo.2025.122989","url":null,"abstract":"<div><div>The succession from adakitic granite to peralkaline ultrapotassic rocks within collisional orogens provides valuable insights into the regional tectonic evolution. This study presents detailed petrography, zircon U-Pb ages, whole-rock geochemical data, and isotopic data from newly discovered adakitic granite and peralkaline ultrapotassic syenite rocks from the Kohistan Batholith in the Kohistan Island Arc (KIA), northern Pakistan. Zircon U-Pb dating indicates that the adakitic granite was emplaced at ∼33.6 Ma, slightly earlier than the syenite at ∼31.2 Ma. The adakitic granite is characterized by high contents of SiO_2, K₂O, Na₂O, Al₂O_3, Sr, and Sr/Y ratios, as well as low MgO, Ni, and Cr, which likely reflects partial melting of water-fluxed mafic rocks in the thickened lower crust. The positive ε_Hf(t) (avg. +3.6) and mantle-like δ¹⁸O_zir (avg. +5.3 ‰) values of the adakitic granite suggest that the magma was derived from a thickened lower crustal mafic source, with no significant contribution from subducted sediments or upper crustal materials. The syenite is potassic to ultrapotassic/shoshonitic, characterized by high K₂O contents (8.7–10.3 wt%) and K₂O/Na₂O ratios (2.2–3.2), and exhibits enrichment in LILE and LREE while being depleted in HFSE. Geochemical and Sr–Nd–Hf–O isotopic data indicate that the syenite likely derived from partial melting of the metasomatized lithospheric mantle beneath the thickened lower crust. The low Ba/La (avg. 7.4) and Hf/Sm (avg. 0.06) ratios, combined with isotopic modeling, reveal a 10–20 % contribution of subducted pelagic marine sediments to the mantle source of ultrapotassic peralkaline rocks in the KIA, which is linked to subduction of the earlier Tethyan Ocean crust. These geochemical results provide evidence that slab break-off occurred in the western Himalaya ∼10 Ma after the India–KIA collision at ∼45 Ma, and resulted in the emplacement of the adakitic and ultrapotassic rocks, similar to post-collisional alkaline magmatism observed elsewhere in the Tethys Orogenic Belt. These coeval but petrogenetically distinct magmas highlight the interplay of crustal and mantle heterogeneity during post-collisional evolution across the Tethyan Orogen. In addition, this study refines our understanding of the post-collisional alkaline magmatism in the KIA and provides a broader geodynamic model applicable to other similar convergent orogenic belts worldwide.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122989"},"PeriodicalIF":3.6,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144773083","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":"Euphotic iodate production along an Atlantic Meridional Transect","authors":"Kirsten P. Fentzke, Andrew P. Rees, Glen A. Tarran, Sarah A. Breimann, Jerzy Blusztajn, Sune G. Nielsen, Dalton S. Hardisty","doi":"10.1016/j.chemgeo.2025.122988","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2025.122988","url":null,"abstract":"The oxidized iodine species, iodate, is abundant in well‑oxygenated marine waters and can be tracked in sediments to reconstruct ancient oxygen availability. Despite known modern marine spatial variations in both iodate and reduced iodide, the rates, pathways, and locations of iodate formation remain poorly understood for temporal gradients across Earth history. To quantify rates and pathways of iodate formation across an ocean basin, we performed ship-board tracer experiments in euphotic waters with known gradients in iodine speciation on an Atlantic Meridional Transect (45°S and 37°N). We performed incubations at depths corresponding to 7 % and 1 % of ambient surface light levels, thus tracking the boundaries of the deep chlorophyl maximum (DCM), from 11 stations along the transect. All incubations were spiked with a <ce:sup loc=\"post\">129</ce:sup>I (t<ce:inf loc=\"post\">1/2</ce:inf>≈15.7 My) tracer and mimicked ambient conditions. We observed iodate production via multiple pathways. The most common observation was a lack of significant iodate production, with iodate production limited to 7 of the 22 locations and nearly exclusively observed at the DCM and outside the nitrogen and iron limited South Atlantic Gyre. Iodate formation from direct iodide oxidation is inferred in only two locations based on increases in iodate <ce:sup loc=\"post\">129</ce:sup>I/<ce:sup loc=\"post\">127</ce:sup>I ratios. At the other locations, decreases in iodate <ce:sup loc=\"post\">129</ce:sup>I/<ce:sup loc=\"post\">127</ce:sup>I ratios imply that rapid reactions with and overturning of alternative natural iodine pools, likely iodine intermediates, are an important factor for iodate production. Our work emphasizes that the rates and pathways of iodate production are spatially heterogenous in the Atlantic Ocean. Future work is needed to determine the drivers, temporal variations, and trends within global ocean basins.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"23 1","pages":"122988"},"PeriodicalIF":3.9,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144901764","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":"Recycling of sub-continental lithosphere during early ocean spreading revealed by Triassic trachytes in the central Tibetan Plateau","authors":"Zong-Yong Yang, Qiang Wang, Jun Wang, Lin Ma, Derek Wyman, Andrew C. Kerr, Xian-Wu Bi, Peng Sun, Xiu-Zheng Zhang, Lu-Lu Hao, Xiao Liu, Chuan-Bing Xu, Jin-Heng Liu, Tong-Yu Huang","doi":"10.1016/j.chemgeo.2025.122985","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2025.122985","url":null,"abstract":"Delamination of sub-continental lithosphere fragments and their descent into the asthenospheric mantle should be a common process following the rupture of continental lithosphere and the initiation of an oceanic basin. However, evidence for sub-continental lithospheric mantle recycling in the source of oceanic intra-plate non-plume volcanism remains unclear. This study reports newly identified ca. 240 Ma trachytes in the Duoma ophiolite complex within the Bangong-Nujiang suture zone, central Tibet, which shed new light on sub-continental lithospheric mantle recycling. These trachytes have high and variable SiO<ce:inf loc=\"post\">2</ce:inf> (59.5–67.3 wt%) along with low MgO, and Cr contents and this combined with significant depletions in Eu, Ba, Sr, and Ti, suggests extensive fractional crystallization. Furthermore, they display positive Nb-Ta anomalies, along with moderately depleted Nd (εNd(t) from +3.3 to +4.5) and Hf isotopes (εHf(t) from +6.1 to +8.0), along with high <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">204</ce:sup>Pb values (15.50 to 15.59), and zircon δ<ce:sup loc=\"post\">18</ce:sup>O values (5.3 ± 0.3 ‰). These data indicate that an enriched mantle endmember, possibly sub-continental lithosphere along with asthenosphere played a role in the generation of these trachytic magmas. We propose that fragments of sub-continental lithospheric mantle were trapped by upwelling asthenosphere during the initiation of oceanic spreading. This resulted in the generation of alkaline magmas in an oceanic intraplate setting. This study provides the first evidence for recycling of continental lithosphere in extinct ocean basins, and the process may be more widespread in the geological record than previously recognized.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"153 1","pages":"122985"},"PeriodicalIF":3.9,"publicationDate":"2025-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900910","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":"Vapor-liquid and liquid-liquid phase equilibria in the CO2-CH4-N2 system: A Gibbs ensemble Monte Carlo simulation","authors":"Zhenhao Duan,&nbsp;Nanfei Cheng","doi":"10.1016/j.chemgeo.2025.122983","DOIUrl":"10.1016/j.chemgeo.2025.122983","url":null,"abstract":"<div><div>CO₂, CH₄, and N₂ are the most common gaseous species in geological fluids, originating from diverse sedimentary, metamorphic, igneous, and hydrothermal processes. Analyzing relic paleo-geofluids trapped in minerals as fluid inclusions is crucial for understanding their roles in these geological processes, which depends on the established phase and volumetric behavior of the fluids as a function of pressure (<em>P</em>), temperature (<em>T</em>), and composition (<em>x</em>). However, collecting comprehensive data for such a ternary system across all potential <em>PTx</em> variables is a significant experimental challenge. Therefore, this study simulated the fluid-phase equilibrium in the unary, binary, and ternary systems of CO₂-CH₄-N₂ using the Gibbs Ensemble Monte Carlo (GEMC) method, a powerful molecular simulation technique for studying systems with multiple fluid phases. The considered <em>PT</em> range encompasses liquid/liquid, liquid/vapor, and liquid/liquid/vapor equilibrium regions. Molecular interactions in the system are described using two-body Lennard-Jones potentials, requiring only two temperature-independent parameters for similar molecules. The Berthelot-Lorentz rules are applied to define the Lennard-Jones interactions for dissimilar molecules, with an additional temperature-independent mixing parameter. The equilibrium compositions and molar volumes of the coexisting phases in all mixtures are predicted with an accuracy comparable to that of the experimental data. The <em>PT</em> dependence of liquid-liquid-vapor coexistence at very low temperatures and the potential for gas-gas coexistence at high temperatures are discussed for the binary subsystems. It can be concluded that the GEMC simulation is an important “computational experiment” to investigate thermodynamic properties of natural fluids if molecular interaction potential is well described, providing appreciable supplementation to experimental findings.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122983"},"PeriodicalIF":3.6,"publicationDate":"2025-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144749025","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}