Chemical Geology最新文献

{"title":"In situ LaBa geochronology by LA-ICP-MS/MS: A new method to rapidly date LREE-rich minerals","authors":"Stijn Glorie ,&nbsp;Sarah E. Gilbert","doi":"10.1016/j.chemgeo.2025.123045","DOIUrl":"10.1016/j.chemgeo.2025.123045","url":null,"abstract":"<div><div>The La<img>Ba decay system has been demonstrated for dating LREE-rich minerals such as monazite, bastnaesite and allanite. However, due the laborious isotope dilution process and the limitations of a long half-life and low parent isotope abundance, the method is not used routinely. We present an analytical approach for <em>in situ</em> La<img>Ba geochronology using LA-ICP-MS/MS technology. Using a mixture of N₂O and H₂ in the reaction cell, Ba mostly reacts to BaOH, while La and Ce preferentially make oxide reaction products, enabling separate detection. Isobaric interferences of ¹³⁸⁺¹⁷LaO(H) and ¹³⁸⁺¹⁷CeO(H) on ¹³⁸⁺¹⁷BaOH are minimised by supplying a maximum of 18 ml.min⁻¹ H₂ gas via 2 mass-flow controllers (while reducing N₂O) in the reaction cell. NIST61X glasses are not suitable to calibrate La/Ba ratios for minerals with wt% LREE and ppm Ba concentrations. We developed a La(1000 ppm)-Ba(100 ppm) glass to correct La/Ba ratios for pulse/analog offsets. Using our most optimised analytical workflow, we report accurate La<img>Ba dates (within 1 % of reference values) for bastnaesite and allanite reference materials. The La<img>Ba dates for a range of monazites are offset by an average of 7.5 % from reference ages. Correcting for matrix-induced fractionation to the TS reference monazite, and considering fully propagated uncertainties, the monazite La<img>Ba dates are in good agreement with reference values. The main advantage of the <em>in situ</em> La<img>Ba method over the Lu<img>Hf method is that 1–3 % uncertainties can be achieved with laser beams as small as 20–30 μm, opening up new opportunities to accurately date LREE minerals at high spatial resolution.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123045"},"PeriodicalIF":3.6,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106469","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":"Can lithium dominantly occur in kaolinite with a high degree of crystallinity in the Carboniferous No. 11 coal from the Xinliangyou mine, Huozhou mining district, southern Shanxi Province, China?","authors":"Yan Wang ,&nbsp;Shifeng Dai ,&nbsp;Yu Liu ,&nbsp;David French ,&nbsp;Ian Graham ,&nbsp;Ning Wang ,&nbsp;Jiawei Feng ,&nbsp;Niande Shang ,&nbsp;Jintian Zheng ,&nbsp;Mengda Yao","doi":"10.1016/j.chemgeo.2025.123050","DOIUrl":"10.1016/j.chemgeo.2025.123050","url":null,"abstract":"<div><div>Lithium (Li) is a critical element for rechargeable batteries, and global demand is rapidly increasing due to the transition to clean energy. Coal-hosted clay minerals, particularly kaolinite, are important reservoirs of Li. While previous studies have emphasized the preferential enrichment of Li in poorly crystalline kaolinite, the mechanisms governing Li occurrence in highly crystalline kaolinite remain unclear. This study investigates the modes of occurrence and enrichment mechanisms of Li in highly crystalline kaolinite using inductively coupled plasma-mass spectrometry (ICP-MS), field emission-scanning electron microscopy (FE-SEM), time-of-flight-secondary ion mass spectrometry (TOF-SIMS), high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), and molecular simulation. Samples from the Carboniferous No. 11 coal seam in the Xinliangyou mine, Huozhou mining district, southern Shanxi Province, China, contain elevated Li concentrations, with average concentrations of 86.6 μg/g in raw coal and 505.5 μg/g in coal ash. These values are significantly higher than both the global average for hard coals (12 μg/g) and the national average for Chinese coals (31.8 μg/g), indicating a notable degree of Li enrichment. Correlation analyses and TOF-SIMS data indicate a strong association between Li and highly crystalline kaolinite. Molecular simulation results suggest that Li appears to reside within pseudo-hexagonal cavities formed by [SiO₄] tetrahedra or [AlO₆] octahedra, without disrupting the kaolinite structure or migrating between layers. Sequential chemical extraction confirmed the high structural stability of Li in kaolinite. These findings offer a new perspective on the structural incorporation mechanism of Li in kaolinite and provide a novel approach for investigating the occurrence of Li in coal.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123050"},"PeriodicalIF":3.6,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145093780","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":"Differential effects of Ca2+ and Mn2+ on cyanobacterial mineralization and organic matter preservation","authors":"Jie Li ,&nbsp;Yongjie Zhang ,&nbsp;Yanyang Zhao ,&nbsp;Chao Han ,&nbsp;Kaiming Hu ,&nbsp;Wenhui Chen ,&nbsp;Yangmei Fei ,&nbsp;Yongmei Liu ,&nbsp;Haoran Li ,&nbsp;Maurice E. Tucker ,&nbsp;Zuozhen Han","doi":"10.1016/j.chemgeo.2025.123049","DOIUrl":"10.1016/j.chemgeo.2025.123049","url":null,"abstract":"<div><div>Cyanobacteria serve as significant contributors to sedimentary organic matter, and their development and preservation play a role in the quality of hydrocarbon source rocks. While their role as primary producers and environmental impacts on productivity are well-documented, mechanistic effects of metal ions (Ca²⁺, Mn²⁺) on cyanobacterial growth, mineralization, and organic matter preservation remain poorly understood. This study used the filamentous cyanobacterium <em>Leptolyngbya boryana</em> to investigate these issues through controlled experiments in: Ca²⁺ systems (0.02–0.05 mol/L Ca²⁺), Mn²⁺ systems (0.002–0.005 mol/L Mn²⁺) and Ca²⁺-Mn²⁺ mixed systems. The results show that: exclusive calcite formation in Ca²⁺ systems, rhodochrosite in Mn²⁺ systems, Mn-calcite, rhodochrosite and kutnohorite in experimental mixed systems and Mn-calcite and kutnohorite in the control group. Specifically, biomass shows: stimulation at low concentrations but inhibition at high concentrations in Ca²⁺ systems, initial enhancement followed by suppression in Mn²⁺ systems, general inhibition in mixed systems. Batch 6 (Mn²⁺ system, 0.003 M) shows optimal growth with dry biomass of 88.9 mg, chlorophyll-<em>a</em> (13.37 mg/L), extracellular polymeric polysaccharide and protein contents increased by 2.41 and 3.19 times versus control. Organic matter in rhodochrosite aggregates exhibits maximal thermal decomposition loss (7.61 %), total organic carbon content (2.49 %) and hydrocarbon potential (S₂ = 9.16 mg/g). Effectively encapsulation of cyanobacterial organic matter in mineral aggregates, combined with initial productivity and sequestration patterns, enhances hydrocarbon potential. These findings elucidate critical roles of Mn²⁺ in cyanobacterial productivity, biomineralization, and organic matter preservation, advancing the efficiency of carbonate mineral coating in preserving labile organic matter.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123049"},"PeriodicalIF":3.6,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145046920","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":"Experimental determination of lithium partitioning between plagioclase and hydrous rhyolitic melt","authors":"Maylis Dupont de Dinechin ,&nbsp;Caroline Martel ,&nbsp;Hélène Balcone-Boissard ,&nbsp;Monika K. Rusiecka ,&nbsp;Rémi Champallier ,&nbsp;Etienne Deloule","doi":"10.1016/j.chemgeo.2025.123047","DOIUrl":"10.1016/j.chemgeo.2025.123047","url":null,"abstract":"<div><div>Lithium concentrations and partition coefficients were determined in plagioclase and Li-doped (300, 500, and 1500 ppm) H₂O-saturated rhyolitic melts experimentally produced at temperature of 800–875 °C and pressure of 50–150 MPa.</div><div>High bulk Li concentration of 1500 ppm have remarkable effects on the crystallization of rhyolitic melts, comparatively to lower concentrations: i) Ca-rich clinopyroxene crystallizes at the expense of plagioclase and Ca-poor clinopyroxene, ii) plagioclase anorthite content decreases, and iii) melt H₂O solubility increases significantly, resulting in lower crystallinities.</div><div>The Li content of plagioclase (70–900 ppm) and rhyolitic melt (300–1700 ppm) both increase with bulk Li content. The Li content in plagioclase increases with decreasing plagioclase anorthite content. The aqueous phase contains a negligible fraction of Li.</div><div>The plagioclase-rhyolitic melt partition coefficients (K_Li^plag/rhy) range from 0.2 to 0.6 and are mostly constant with bulk Li concentration. At 875 °C, the K_Li^plag/rhy increase from ∼0.3 to 0.6 with pressure decreasing from 150 to 50 MPa, while constant (0.2–0.4) with pressure at 800 °C. At 50–100 MPa, the K_Li^plag/rhy increase from 0.3 to 0.4 at 800 °C to 0.5–0.6 at 875 °C, while constant (0.3–0.4) with temperature at 150 MPa.</div><div>These results give information to interpret Li gradients in natural plagioclases with regard to processes such as magma degassing, decompression, and cooling. In particular, opposite Li gradients are expected in plagioclase during decompression-induced degassing (Li outward-gradients) and isobaric cooling (Li inward-gradients).</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123047"},"PeriodicalIF":3.6,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145046780","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 metasomatized lithospheric mantle in generating the Norilsk 1 Ni–Cu–platinum-group element sulfide deposit: Cu isotope evidence","authors":"Aleksandr Marfin ,&nbsp;Matthew Jacek Brzozowski ,&nbsp;Peter Lightfoot ,&nbsp;Xin Ding ,&nbsp;Michael Bizimis ,&nbsp;Shelby True Rader ,&nbsp;Molly Karnes ,&nbsp;Valeriya Brovchenko ,&nbsp;Tatyana Radomskaya ,&nbsp;Alexei Ivanov ,&nbsp;Olga Belozerova","doi":"10.1016/j.chemgeo.2025.123034","DOIUrl":"10.1016/j.chemgeo.2025.123034","url":null,"abstract":"<div><div>The mechanisms of formation of magmatic Ni–Cu–platinum-group element (PGE) sulfide ore deposits, such as those of the world-class Norilsk–Talnakh mineral system, have been extensively studied, but the source of metals in these systems remains unclear. Potential metal sources are a mantle plume (derived from the lower mantle), subcontinental lithospheric mantle, and crustal materials. To provide insights into the source of metals for the Norilsk–Talnakh system, we integrate new Cu isotope data of chalcopyrite with bulk-rock major-element, trace-element, and PGE–Au contents from the Norilsk 1 deposit in Polar Siberia.</div><div>The ⁶⁵Cu/⁶³Cu ratios (reported as δ⁶⁵Cu ratio relative to SRM NIST 976) of disseminated sulfides and massive sulfide samples vary from −0.3 to 0.42 ‰ and − 0.33 to 0.35 ‰, respectively. These values extend to both lower and higher values compared to unmodified upper mantle-derived rocks (δ⁶⁵Cu_mantle from −0.14 to 0.26 ‰). These isotopic signatures cannot be explained by post-magmatic alteration, metamorphic processes, or contamination by upper crustal rocks because they do not correlate with the abundance of secondary minerals, S/Se and Th/Nb ratios, or MgO contents. The variation of δ⁶⁵Cu in disseminated sulfides is consistent with progressive interaction of isotopically light sulfide liquid (δ⁶⁵Cu ≈ −0.5 ‰) with isotopically heavy silicate melt (δ⁶⁵Cu ≈ 0.63 ‰). This isotopic range reflects heterogeneity in the mantle source to the Norilsk 1 deposit. The heavy-δ⁶⁵Cu component may have been inherited from a pyroxenite source in the metasomatized lithospheric mantle beneath the Siberian Craton. After exhaustion of the pyroxenitic component in the source during melting, δ⁶⁵Cu values returned to mantle values, where subsequent magma pulses produced disseminated sulfides with δ⁶⁵Cu values less than 0, the variability of which can be explained by Rayleigh fractionation of the sulfide liquid. The δ⁶⁵Cu values of chalcopyrite in MS are positively correlated with bulk-rock Cu/(Cu + Ni) ratios, consistent with the fractionation of ∼40–60 % monosulfide solid solution from the original sulfide liquid. Our study demonstrates a potential contribution from metasomatized subcontinental lithospheric mantle and a pyroxenitic component to the formation of the Norilsk 1 Ni–Cu–PGE deposit, and highlights the important influence of previous subduction events in modifying and re-enriching the subcontinental lithospheric mantle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123034"},"PeriodicalIF":3.6,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145046919","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":"Holocene climate driving spatially variable mercury input to an Arctic fjord environment","authors":"Eun Jin Son ,&nbsp;Ju Hyeon Lee ,&nbsp;Kwangchul Jang ,&nbsp;Youngkyu Ahn ,&nbsp;Jochen Knies ,&nbsp;Matthias Forwick ,&nbsp;Jung-Hyun Kim ,&nbsp;Seung-Il Nam ,&nbsp;Sae Yun Kwon","doi":"10.1016/j.chemgeo.2025.123043","DOIUrl":"10.1016/j.chemgeo.2025.123043","url":null,"abstract":"<div><div>Mercury (Hg) is a globally distributed pollutant, affecting the Arctic through ocean and atmospheric circulation, coastal erosion, and riverine export from continents. We employ Hg stable isotopes and geochemical proxies to evaluate how climatic variation over the Holocene has influenced Hg sources in Arctic fjord environments. Hg isotopes measured in four sediment cores from western Svalbard are compared to gather insights into spatiotemporal variability of Hg sources and depositional history. Compared to other pre-industrial marine sediments, which are primarily influenced by wet deposition (precipitation) and terrestrial runoff, Hg sourced from bedrock erosion and Hg bound to particulate organic matter (pHg) transported by Atlantic Ocean currents are the dominant Hg sources to the Svalbard fjords. The temporal profiles of these two Hg sources vary spatially, with Kongsfjorden showing greater bedrock-Hg around 12.6 ka BP, while Woodfjorden and Dicksonfjorden exhibit higher influences at 8 ka and 4 ka BP, respectively. Despite these temporal differences, colder periods are generally dominated by Hg sourced from bedrock, whereas warmer periods are characterized by the contribution of pHg. In modern times, global anthropogenic activities have widespread Hg influences, whereas regional activities such as coal mining have little Hg influence. Our study highlights the importance of regional environmental setting and the global rise in anthropogenic activities in determining the spatiotemporal variation in Hg sources in Arctic over the Holocene. The findings provide insights into complex interactions between climate change and the Hg cycle in an Arctic fjord ecosystem.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123043"},"PeriodicalIF":3.6,"publicationDate":"2025-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145020538","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":"Regional variations in elemental and radiogenic isotope compositions of recent intraplate basaltic volcanics: Novel perspectives from longitudinal provinces","authors":"David A. Wood","doi":"10.1016/j.chemgeo.2025.123032","DOIUrl":"10.1016/j.chemgeo.2025.123032","url":null,"abstract":"<div><div>A compiled dataset of 5980 recent (&lt;10 Ma) intraplate basaltic rock samples from 85 widespread regions is evaluated in a novel way to provide high-level insight into worldwide major, minor, and trace element, and radiogenic Nd, Sr and Pb isotope ratio distributions and trends. The term “high-level” is used to refer to provincial rather than detailed regional or local interpretations. The studied regions are divided into six longitudinal provinces Pacific (PAC); Atlantic (ATL); Europe/ Middle East Africa (EMA); Indian Ocean (IND), East Asia (ESA), and Australasia (AUS). Average compositional values are computed for these provinces and the arithmetic average composition of the considered regions is used as a worldwide reference point (WLD). The region averages are distributed systematically along trends extending from normal mid-ocean ridge basalt (N-MORB) to incompatible element and Sr-isotope enriched compositions with the six provinces plotting in distinct positions. PAC, ATL and IND dominated, by ocean islands and oceanic crust, plot between WLD and N-MORB, whereas EMA, ESA and AUS, dominated by large landmasses composed of continental crust plot towards the incompatible-element enriched side of WLD. The provinces are positioned somewhat differently for Pb-isotope ratios. For ESA, these ratios are depleted in similar ways to N-MORB and plot on the opposite side of WLD compared to the other provinces. Normalizing elemental and isotope-ratio values to WLD compositions results in distinctive normalized profiles for the six provinces defined by 15 trace elements, Pb-, Nd- and Sr-isotope ratios. Ternary diagrams, specifically Th-Hf-Ta and K₂O/TiO₂-Hf/Th-²⁰⁷Pb/²⁰⁶Pb, the latter introduced in this study, provide useful characterization displays for high-level benchmarking of intraplate basalt compositions. The observed trends imply substantial but systematic upper mantle heterogeneity that are indicative of complex petrogenetic processes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123032"},"PeriodicalIF":3.6,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145011025","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":"Dating of marine authigenic minerals via in situ RbSr, UPb, and Lu–Hf: A case study from the Georgina Basin, Australia","authors":"Zhufu Shao ,&nbsp;Juraj Farkaš ,&nbsp;Stijn Glorie ,&nbsp;Alan S. Collins ,&nbsp;Sarah E. Gilbert ,&nbsp;Darwinaji Subarkah","doi":"10.1016/j.chemgeo.2025.123042","DOIUrl":"10.1016/j.chemgeo.2025.123042","url":null,"abstract":"<div><div>The <em>in situ</em> laser ablation–inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) technique enables rapid, high-resolution isotopic analysis with minimal contamination, ideal for dating authigenic minerals. This study employs LA-ICP-MS/MS triple dating (Rb<img>Sr, U<img>Pb, Lu<img>Hf) on key authigenic minerals from the mid-Cambrian (∼505 ± 3 Ma) marine sequence of Australia's Georgina Basin. Glauconite, micrite, dolomite, and apatite were analyzed to constrain depositional ages and diagenetic overprints. Glauconite exhibits high porosity, extensive illitization, and secondary minerals, reflecting post-depositional alteration. <em>In situ</em> Rb<img>Sr dating of glauconite yielded systematically younger ages (452 ± 13 Ma to 351 ± 8 Ma) coeval with two episodes of the Alice Springs Orogeny. Well-preserved micrite and fine dolomite yielded U<img>Pb ages of 500 ± 17 Ma and 513 ± 19 Ma, consistent with the depositional age, whereas a coarser dolomite yielded a younger age of 478 ± 23 Ma with lower initial Pb. <em>In situ</em> Lu<img>Hf dating of apatite from three dolostone samples yielded ages of 497 ± 69 Ma, 495 ± 79 Ma, and 493 ± 74 Ma, overlapping with the depositional window despite notable uncertainties. A phosphorite sample yielded a Lu<img>Hf age of 425 ± 49 Ma, coeval with the Rodingan event. <em>In situ</em> U<img>Pb apatite ages yielded dispersed and unrealistic ages demonstrating that the Lu<img>Hf system provides more robust ages than U<img>Pb for authigenic apatite, whereas Rb<img>Sr ages reflect diagenetic resetting during orogeny. The integration of three radiometric systems provides a refined framework for reconstructing the basin's depositional and diagenetic history.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123042"},"PeriodicalIF":3.6,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145020446","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":"Constraining the high-temperature viscoelastic behavior of basaltic melts through oscillatory rheometry","authors":"V. Haag ,&nbsp;Á. Höskuldsson ,&nbsp;A. Soldati","doi":"10.1016/j.chemgeo.2025.123030","DOIUrl":"10.1016/j.chemgeo.2025.123030","url":null,"abstract":"<div><div>The rheological behavior of magma impacts the eruption style and related hazards during a volcanic eruption. For example, the range of viscoelastic behavior of volcanic melts affects whether magma undergoes brittle fragmentation prior to eruption or not. Previous research has shown that solid-state (elastic) behavior is promoted by high strain rates, high viscosities, and high crystal fractions. However, few studies have been carried out to constrain the viscoelastic behavior of natural samples. This study is the first to investigate the Newtonian behavior of a natural sample at superliquidus temperature using oscillatory rheology. We selected a basaltic sample from the 2023 Litli-Hrútur eruption in Iceland. During experiments, the sample was first fully remelted and then cooled in a concentric cylinder rheometer from 1550 °C to superliquidus and subliquidus target temperatures between 1500 °C and 1151 °C. At each temperature step, oscillation measurements were performed to constrain the viscoelastic properties of the melt. The results show that the rheology of the melt is Newtonian at superliquidus temperatures, but becomes frequency-dependent at subliquidus temperatures, displaying shear thinning and an increase in the elastic component at high frequencies. This suggests that in silicate melts viscoelastic behavior is mainly promoted by processes other than viscosity increase alone (e.g. crystallization and particle interaction). Although current method limitations in sample retrieval prevent the explicit correlation of these results to crystal fraction and sample texture, this study shows that high-temperature oscillatory measurements yield valuable information about processes in volcanic systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123030"},"PeriodicalIF":3.6,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145020537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paired megacrystic zircon (U-Th)/He and U/Pb dating reveals kimberlite eruption ages, protracted emplacement histories, and insights into megacryst genesis","authors":"Spencer D. Zeigler ,&nbsp;Rebecca M. Flowers ,&nbsp;D. Graham Pearson ,&nbsp;Liam Courtney-Davies ,&nbsp;Bruce A. Kjarsgaard ,&nbsp;Stephen H. Richardson ,&nbsp;Kaden Berkhahn ,&nbsp;James R. Metcalf ,&nbsp;Izaac Cabral-Neto","doi":"10.1016/j.chemgeo.2025.123033","DOIUrl":"10.1016/j.chemgeo.2025.123033","url":null,"abstract":"<div><div>The timing of the processes occurring in the lithosphere during the ascent and eruption of kimberlites has been challenging to ascertain. Here, we present a novel application of paired (U-Th)/He and U/Pb geochronology on megacrystic zircon to date both the crystallization of the megacryst suite and the host kimberlite eruption. Unlike Pb, He is not retained in the crystal at temperatures &gt;250 °C. For megacrystic zircon that crystallizes in the mantle, He retention begins upon kimberlite eruption such that the zircon (U-Th)/He (ZHe) dates should record kimberlite emplacement. We collected cathodoluminescence, trace element, U/Pb, and (U-Th)/He data for nine megacrystic zircon from five kimberlites: Diavik and Panda (Canada), Juína and Batovi-9 (Brazil), and Monastery (South Africa). For all zircon except from Diavik, ZHe and U/Pb dates overlap within uncertainty, indicating megacryst crystallization during or shortly before kimberlite eruption, and suggesting a genetic link between the kimberlite magma and megacryst suite. For Diavik zircon, the ZHe dates are ∼2.5 Gyr younger than the U/Pb dates, documenting that the megacrysts and the host kimberlite magma are genetically unrelated. ZHe dates from three of the kimberlites overlap with eruption ages interpreted from other methods. However, for Panda and Monastery, our paired ZHe-U/Pb dates differ from previous results, consistent with multiple eruptions over ∼5 Myr and implying that protracted eruptive phases may be more common than previously thought. Our work shows that (U-Th)/He dating of megacrystic zircon accurately dates kimberlite emplacement, and when coupled with U/Pb dating can yield insights into megacryst-kimberlite relationships.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123033"},"PeriodicalIF":3.6,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145046921","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}