Chemical Geology最新文献

{"title":"A multi-isotopic study to constrain groundwater geochemistry - case study of a quaternary sand and gravel aquifer in Cardiff, UK","authors":"Zhe Dong, Katharine Hendry, David Boon, Ashley Patton, Jamie Lewis, Hong Chin Ng, Fiona Whitaker, Tong Wang, Xiaoning Liu, Tom Kibblewhite","doi":"10.1016/j.chemgeo.2026.123812","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123812","url":null,"abstract":"Chemical alteration of groundwaters has implications for elemental fluxes into rivers, estuaries and coastal oceans. Individual isotope systems offer strong process constraints, while integrating multiple isotopes adds complementary insight that reveals the complexity of coupled geochemical processes. Here, we use multiple stable isotopic systems to investigate the physical and chemical controls on groundwater composition in a Quaternary sand and gravel coastal aquifer from Cardiff, UK. Stable isotopic compositions of silicon (Si), magnesium (Mg), and strontium (Sr), along with radiogenic Sr isotopes reveal significant impacts of anthropogenic interventions on the groundwater system, particularly the construction of a barrage and groundwater extraction. The saltier coastal groundwaters likely reflect contributions from saline estuarine/seawater-derived water and/or localized seepage from the underlying Triassic bedrock. This influx of saline water, combined with reducing conditions, has facilitated calcite precipitation that has removed substantial amounts of dissolved calcium (Ca) from the groundwater. The mechanisms controlling dissolved silicon (DSi) dynamics in the groundwater are complex. In coastal regions, silica precipitation predominantly influences DSi concentrations and isotopic composition, whereas vegetation uptake is the primary control on DSi concentrations and isotopic signatures in inland groundwaters. These findings are crucial for understanding the intricate interplay between natural processes and human interventions in shaping groundwater geochemistry, offering valuable insights for managing coastal water resources and mitigating anthropogenic impacts. By providing a multi-isotopic framework for investigating groundwater systems, this study provides a clearer perspective on the factors controlling modern and palaeo groundwater chemistry and can aid in predicting solute fluxes from groundwater to the ocean.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"10 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149358716","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 diagenetic transformation of biogenic aragonite to calcite in sulfate and/or phosphate-bearing fluids","authors":"Amalia Jiménez, Joel Marcelo Coronel, José Manuel Astilleros","doi":"10.1016/j.chemgeo.2026.123795","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123795","url":null,"abstract":"The transformation of biogenic aragonite to calcite in phosphate or phosphate-sulfate bearing fluids was investigated through hydrothermal experiments at 60–80 °C up to 90 days. A phosphate-only system (BF) and a phosphate-sulfate system (BFS) were characterized by XRD, FTIR, and aqueous geochemical analyses supported by PHREEQC modelling.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"287 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149358720","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":"Rodingites as archives of Ca-Mg-Fe metasomatism and trace element mobility: constraints from Mount Orliakas (Pindos Ophiolite, Greece)","authors":"L. Tsiarsioti, C. Karkalis, A. Sideridis, H. Tsikos, P. Mason, P. Petrounias, P. Pomonis, A. Rogkala, P. Koutsovitis","doi":"10.1016/j.chemgeo.2026.123799","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123799","url":null,"abstract":"Rodingites serve as critical archives of fluid-rock interaction in mafic-ultramafic complexes. In the Mount Orliakas massif (Pindos Ophiolite, Greece), rodingitization of gabbronoritic protoliths occurred through distinct multi-stage Ca-metasomatism within serpentinized ultramafics. Notably, the dykes preserve nearly unaltered gabbroic cores, providing a direct reference for quantifying metasomatic fluxes without relying on extrapolated protolith compositions. Stage-1 (~370 °C, 3–5 kbar) formed prehnite and grossular, while Stage-2 (~300 °C, final exhumation) developed (hydro)andradite, Ti-rich garnet, and vesuvianite. Geochemical trends reveal a two-stage fluid evolution: initial Ca-enrichment coupled with Si, Mg, and Fe depletion (Stage-1), followed by distinct Mg and Fe enrichment in advanced Stage-2 rodingites. This reversal marks a shift to Mg-Fe-rich fluids driven by extensive interaction with surrounding serpentinizing ultramafics. Alkali depletion reflects plagioclase replacement by garnet. Trace elements show early REE depletion and late re-enrichment; Th, Ta, Nb, Cr, and Ni were depleted, while Zr was enriched. Highly mobile elements (Ba, Pb, Cs, U, As) were largely removed. Notably, Ti was immobile in shallow Group-A but mobilized at depth in Group-B rodingites, while Nb and Y showed inverse enrichment, reflecting pressure-dependent fluid mobility. Thermodynamic modeling results (PERPLE_X) validate the P-T path, constraining the Stage-1 to Stage-2 transition as a shift towards oxidizing, low-CO₂, Fe-Mg-rich fluids. These findings highlight rodingitization as a key process in element mobility within mafic-ultramafic complexes, controlled by protolith depth, redox conditions, and evolving fluid composition.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"43 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149358718","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 geochemistry of uraniferous hyalite from Zacatecas, Mexico: Implications for the origin, timing, and deposition of Electric Opal","authors":"Bozana Pasic, John Mavrogenes, Ian S. Williams, Dominique Tanner, Peter K.M. Megaw","doi":"10.1016/j.chemgeo.2026.123796","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123796","url":null,"abstract":"Green, daylight-luminescent hyalite from Zacatecas is a rare form of opal containing elevated concentrations of uranium. Through combined in situ isotopic and trace element analyses we investigated the process of uranium sequestration by opal to determine hyalite depositional conditions. Trace element analyses revealed a near perfect 1:1 correlation between uranium and calcium, which we attribute to “trapping” of calcium-uranyl carbonate complexes. Oxygen isotopic analyses and modelling estimate depositional temperatures of between ~23 °C and ~ 64 °C, respectively. Uranium‑lead dating of zoned hyalite indicates three principal generations of growth at 14.2 ± 0.69 Ma, 11.7 ± 0.8 Ma and 9.2 ± 0.7 Ma. Electric Opal was probably deposited from silica supersaturated, alkaline, groundwater-dominated fluids under confined lateral flow, making formation of Electric Opal a product of late volcanic or post-volcanic processes.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"15 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149358857","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":"Trace element composition of cold-water corals from coastal antarctic surface sediments: Implications for biomineralization mechanisms and paleoceanographic reconstructions","authors":"Derong Zhao ,&nbsp;Sang Chen ,&nbsp;Junru Guan ,&nbsp;Haihong Wu ,&nbsp;Xin Chen ,&nbsp;Cong Zeng ,&nbsp;Zhekai Tang ,&nbsp;Maojun Yan ,&nbsp;Ning Zhao ,&nbsp;Liqiang Xu ,&nbsp;Meng Zhou","doi":"10.1016/j.chemgeo.2026.123525","DOIUrl":"10.1016/j.chemgeo.2026.123525","url":null,"abstract":"<div><div>The Southern Ocean is one of the most sensitive regions to ongoing climate change, and plays an important role in the global ocean circulation and carbon cycle through a range of physical, chemical and biological processes. Understanding long-term environmental changes in the Southern Ocean can help us better resolve the key processes influencing its impact on global climate. Paleoceanographic reconstructions in the Southern Ocean, however, are often challenging due to a lack of feasible archives and well-calibrated environmental proxies. Cold-water corals are a type of benthic organism of relatively high abundance in the Southern Ocean, with their calcium carbonate skeletons that can potentially record environmental changes at relatively high temporal resolution. Here we report measurements of the trace element composition of cold-water corals and a tubeworm collected from surface sediments in the Ross Sea and west of the Amundsen Sea. We find that spatial distribution of calcitic and aragonitic corals in the Southern Ocean is likely controlled by the bottom water carbonate saturation state. Trace element composition of the biogenic carbonates is mainly determined by their respective mineralogy and displays significant vital effects. Different element-to‑calcium ratios show strong correlations in individual organisms that are similar to cold-water corals found in other regions, and can generally be explained with existing biomineralization models. Several elemental ratio proxies show relations with environmental conditions that are consistent with global calibrations, most notably the Li/Mg-temperature relation in both biogenic aragonite and high-Mg calcite, yet large uncertainties remain in terms of their use in paleoceanographic reconstructions. Understanding the biomineralization mechanisms underlying the vital effects in different types of cold-water corals with in-situ analytical techniques and numerical models is a key step in improving the proxies that are suitable for the extreme environmental conditions in the Southern Ocean.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"719 ","pages":"Article 123525"},"PeriodicalIF":3.6,"publicationDate":"2026-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148011288","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":"Arsenopyrite-driven oxidative dissolution of stibnite: pH-dependent ROS effect and antimony transformation","authors":"Kequn Li, Jingkang Zhang, Hao Liu, Liyuan Ma, Jianwei Zhou, Xingjie Wang","doi":"10.1016/j.chemgeo.2026.123493","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123493","url":null,"abstract":"The fate of antimony (Sb) in mining environment is markedly influenced by the coexisting arsenic and iron sulfide minerals. However, the mechanism underlying the effect of arsenopyrite (FeAsS) on the oxidative dissolution of stibnite (Sb<ce:inf loc=\"post\">2</ce:inf>S<ce:inf loc=\"post\">3</ce:inf>) under ambient pH conditions remains unclear. This study investigated the release of antimony from stibnite associated with arsenopyrite under acidic and neutral conditions. Arsenopyrite promoted stibnite dissolution at both pH values, with total Sb released at pH 3.0 (10.03 mg·L<ce:sup loc=\"post\">−1</ce:sup>) being 3.65 times that at pH 7.0 (2.75 mg·L<ce:sup loc=\"post\">−1</ce:sup>), and Sb(V) predominated in solution. Under neutral conditions, Fe (oxyhydr)oxides accumulated on the surfaces of arsenopyrite, diminishing its promoting effect on stibnite dissolution. The Sb(III)-arsenopyrite interaction experiments demonstrated that the arsenopyrite significantly facilitated the Sb(III) oxidation with 95.04% conversion at pH 3.0. In contrast, only 4.85% Sb(V) formed at pH 7.0, far lower than that in the neutral stibnite-arsenopyrite system (96.98%). The suppressed oxidation is likely attribute to the higher Sb(III) loading, which enhanced the adsorption and passivation effects of arsenopyrite. Quenching experiments further confirmed that the ROS generated through Fe(II)/Fe(III) redox cycling on arsenopyrite surfaces serve as the predominant oxidants responsible for stibnite dissolution and Sb(III) oxidation. Notably, hydroxyl radicals (•OH) were identified as the predominant ROS under acidic conditions, while the ROS generation was inhibited under neutral conditions, where non-radical pathways or surface-contact oxidation may prevail. Overall, this study reveals a pH-dependent oxidative dissolution mechanism in the stibnite-arsenopyrite co-existing system, advancing understanding of Sb geochemical behavior in sulfide-rich environments.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"21 1","pages":"123493"},"PeriodicalIF":3.9,"publicationDate":"2026-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148291647","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":"Geochemical characterisation of the Ellsworth-Whitmore Mountains crustal block: a critical piece in the puzzle to unravel ice retreat in West Antarctica","authors":"Emily J. Archibald ,&nbsp;James W. Marschalek ,&nbsp;Adrian R. Muxworthy ,&nbsp;Teal R. Riley ,&nbsp;Claus-Dieter Hillenbrand ,&nbsp;Tom A. Jordan ,&nbsp;Pieter Vermeesch ,&nbsp;Michael J. Flowerdew ,&nbsp;Martin Siegert ,&nbsp;Dominic A. Hodgson ,&nbsp;Tina van de Flierdt","doi":"10.1016/j.chemgeo.2026.123290","DOIUrl":"10.1016/j.chemgeo.2026.123290","url":null,"abstract":"<div><div>The West Antarctic Ice Sheet (WAIS) is prone to major retreat. Identifying when previous WAIS retreats occurred could improve sea level rise projections, but detection of these events in marine sediments is limited by knowledge of the geochemical signature of key sediment source regions located further inland - primarily the Ellsworth-Whitmore Mountains (EWM). This is because a smaller WAIS would likely result in enhanced erosion of the EWM and permit more widespread transport of EWM detritus offshore. We here characterise the provenance signature of the EWM, showing that different stratigraphic units exhibit distinct geochemical characteristics based on unique combinations of zircon U-Pb ages and Nd and Sr isotope ratios. The oldest Heritage Group displays dominant Grenville Orogeny (1000–1250 Ma) ages, with mean ε_Nd values of ∼ − 8 and ⁸⁷Sr/⁸⁶Sr ratios of ∼0.719. The overlying Crashsite Group and Whiteout Conglomerate exhibit dominant Ross Orogeny ages (490–580 Ma), with mean ε_Nd values of ∼ − 12 and − 18 and ⁸⁷Sr/⁸⁶Sr ratios of ∼0.740 and ∼ 0.725, respectively. The youngest Polarstar Formation has common Permian zircon U-Pb ages and ε_Nd values of ∼ − 4 and ⁸⁷Sr/⁸⁶Sr ratios of ∼0.711. Outlying nunataks are assigned to the Heritage and Crashsite groups, extending our geological knowledge of the Ellsworth Subglacial Highlands. Together, our data suggest that the Ellsworth Mountains crustal block is characterised by a mean ε_Nd value of ∼ − 10, ⁸⁷Sr/ ⁸⁶Sr ratio of ∼0.728, and bimodal Ross and Grenville orogeny zircon U-Pb ages. This “provenance fingerprint” should be identifiable in offshore sediments recording times of major WAIS retreat.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"706 ","pages":"Article 123290"},"PeriodicalIF":3.6,"publicationDate":"2026-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146138458","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":"Strontium isotopes tracing of weathering processes and tidal mixing in a mountainous river system","authors":"Ni Su ,&nbsp;Junjie Guo ,&nbsp;Xiaolei Xie ,&nbsp;Zhouyang Wu ,&nbsp;Yalong Li ,&nbsp;Shouye Yang","doi":"10.1016/j.chemgeo.2026.123289","DOIUrl":"10.1016/j.chemgeo.2026.123289","url":null,"abstract":"<div><div>Radiogenic and stable Sr isotope ratios are effective tracers of source mixing and isotopic fractionation at the land-ocean interface, yet their behavior in rivers under tidal influence remains insufficiently constrained. This study presents major element compositions together with ⁸⁷Sr/⁸⁶Sr and δ^88/86Sr data for river water, groundwater, and sediments from the Mulanxi River, a small mountainous catchment in southeast China. Major ion chemistry indicates that river water is primarily controlled by carbonate weathering, while ⁸⁷Sr/⁸⁶Sr ratios of river water and sediment leachates suggest that dissolved Sr is mainly sourced from trace carbonate phases. Sediment leaching results indicate that labile phases contribute less radiogenic but heavier Sr to river water compared to the sediment residues (means 0.70969 vs. 0.71570; 0.21‰ vs. 0.11‰). In contrast, δ^88/86Sr values of bulk and clay fractions of sediments (0.08 ± 0.08‰ and 0.07 ± 0.08‰) are indistinguishable, indicating limited isotopic fractionation during clay formation. The combined ⁸⁷Sr/⁸⁶Sr and δ^88/86Sr signatures reveal that Sr cycling in river water is primarily governed by mixing between surface water and groundwater Sr sources, while mass-dependent isotope fractionation, largely driven by calcite precipitation, alters the δ^88/86Sr composition of the dissolved Sr pool. In addition, differences in major ion chemistry between tidal and non-tidal reaches are attributed to cation exchange during freshwater-seawater mixing. Riverine ⁸⁷Sr/⁸⁶Sr ratios show no clear mixing trend due to similar compositions of freshwater and seawater end-members, whereas δ^88/86Sr values behave conservatively without measurable isotopic fractionation. Further analysis of Sr–Nd isotope variations in river sediments reflect a shift in sediment provenance. Sediments in the non-tidal reach mainly originate from local bedrock weathering, whereas those in the tidal reach mostly consist of Changjiang-derived fine sediments. These results demonstrate that integrating multi-phase analysis with dual Sr isotope tracers (⁸⁷Sr/⁸⁶Sr and δ^88/86Sr) establishes a comprehensive framework for resolving geochemical processes in tidal river systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"706 ","pages":"Article 123289"},"PeriodicalIF":3.6,"publicationDate":"2026-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146138459","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":"Rapid hydration of rhyolitic glass at atmospheric conditions: Evidence from Diffuse Reflectance Infrared Fourier Transform spectroscopy and Temperature Conversion Elemental Analysis","authors":"Thomas Giachetti ,&nbsp;Erwan Martin ,&nbsp;Etienne Balan","doi":"10.1016/j.chemgeo.2026.123291","DOIUrl":"10.1016/j.chemgeo.2026.123291","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The molar abundance ratio of H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH of rhyolitic porous pyroclasts, obsidian pyroclasts, and flow obsidians from the 1060CE Glass Mountain eruption at Medicine Lake Volcano (USA) were obtained by Diffuse Reflectance Infrared Fourier Transform spectroscopy. Samples were also analyzed for their total water content, [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;], and isotopic composition, &lt;span&gt;&lt;math&gt;&lt;mi&gt;δ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;D, via Temperature Conversion Elemental Analysis (TC/EA). Porous clasts exhibit a H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH ratio of 0–4.63 (and a [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;] measured by Giachetti et al. (2020) of 0.34–1.2 wt%) that is positively correlated with their porosity and [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;], contrary to the low [H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;] and low H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH ratios of both obsidian pyroclasts (0.32–0.72 wt.&lt;span&gt;&lt;math&gt;&lt;mtext&gt;%&lt;/mtext&gt;&lt;/math&gt;&lt;/span&gt;, 0.14–0.63) and flow obsidians (0.04–0.07 wt.&lt;span&gt;&lt;math&gt;&lt;mtext&gt;%&lt;/mtext&gt;&lt;/math&gt;&lt;/span&gt;, 0.24–0.28). These results confirm the interpretations of Giachetti et al. (2020) that porous clasts were rehydrated for about 1000 years after the eruption via diffusion of overwhelmingly molecular, meteoric water in the matrix-glass, whereas obsidian pyroclasts and flow obsidians are essentially dense and thus rehydrate poorly. Analyses were also conducted on two size fractions of flow obsidian (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;mn&gt;63&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; and 63–&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;250&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) that were ground either (1) immediately before analysis or, (2) about nine years prior to analysis and kept in closed containers ever since. Results show that the &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;mn&gt;63&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; ground samples gained 0.06–0.24 wt% of meteoric water in just nine years, with a H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/OH ratio increasing","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"706 ","pages":"Article 123291"},"PeriodicalIF":3.6,"publicationDate":"2026-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146173000","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":"Prolonged cooling of andesitic-dacitic lava flows produces optimal groundmass material for 40Ar/39Ar dating","authors":"Chris E. Conway ,&nbsp;Andrew T. Calvert ,&nbsp;Osamu Ishizuka ,&nbsp;Seiko Yamasaki ,&nbsp;Isoji Miyagi ,&nbsp;Yumiko Harigane ,&nbsp;Graham S. Leonard","doi":"10.1016/j.chemgeo.2026.123268","DOIUrl":"10.1016/j.chemgeo.2026.123268","url":null,"abstract":"<div><div>Organizing the eruptive histories and petrogenetic models that underpin hazard assessments at active volcanoes typically requires high-precision ages for late Pleistocene to Holocene lava flows. In this study, features of an existing ⁴⁰Ar/³⁹Ar dataset for andesitic-dacitic rocks from Ruapehu volcano, Aotearoa New Zealand, were interrogated with new microanalytical data to identify the optimal groundmass material for age determination. To understand the behavior of K and Ar within the cooling melt of lavas during their emplacement, we examined and compared the petrological features of samples from the ice-chilled margin and interior of a lava flow. The groundmass of the rapidly cooled sample comprises non-vesicular rhyolitic glass and microlites of plagioclase, orthopyroxene, and magnetite. The sample from the flow interior has minimal amounts of groundmass glass, and interstices are instead occupied by sanidine and tridymite. Thermodynamic modelling supports the interpretation that sanidine crystallized as a stable groundmass phase during slow cooling of degassed melt in the interior zones of lavas that were insulated behind their glassy margins. Our evaluation of the age data shows that sanidine contributed high yields of radiogenic argon during step-heating experiments for samples collected from lava interiors, which enabled high-precision ⁴⁰Ar/³⁹Ar ages to be determined. Using Ruapehu as an example of an arc volcano affected by lava-ice interaction, we provide a basic field guide for identifying lava flows that contain groundmass sanidine at the expense of glass. Target outcrops also offer opportunities for reconstructing geomagnetic dynamics and volcano–climate relationships during the Pleistocene and Holocene.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"705 ","pages":"Article 123268"},"PeriodicalIF":3.6,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072698","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}