Chemical Geology最新文献

{"title":"In situ Lu–Hf dating of allanite by LA-ICP-MS/MS: Implications for geochronology","authors":"Shitou Wu ,&nbsp;Yueheng Yang ,&nbsp;Hao Wang ,&nbsp;Nick M.W. Roberts ,&nbsp;Junlong Niu ,&nbsp;Yijia Wang ,&nbsp;Jinhui Yang ,&nbsp;Fuyuan Wu","doi":"10.1016/j.chemgeo.2024.122383","DOIUrl":"10.1016/j.chemgeo.2024.122383","url":null,"abstract":"<div><p>Allanite is a common REE-rich accessory mineral found in various igneous and metamorphic rocks, and can record a variety of geological processes. Therefore, allanite geochronology has the potential to answer a range of important geological questions. Allanite U–Th–Pb geochronology is hampered by common open-system behavior in the system. In this study, we demonstrate the feasibility of <em>in situ</em> allanite Lu–Hf dating by LA–ICP–MS/MS. A total of nine allanite samples from different rock types (<em>e.g.</em>, granite, pegmatite) were investigated. These allanite samples have ages ranging from <em>ca.</em> 2650 to <em>ca.</em>100 Ma, and Lu contents ranging from several to hundreds of μg g⁻¹ levels and relatively high Lu/Hf ratios (&gt; 30). At a mass shift of +82, the isobaric interferences ¹⁷⁶Lu and ¹⁷⁶Yb have extremely low reaction rates of ∼0.003 % and ∼ 0.0003 %, respectively, indicating the isobaric interference corrections are insignificant for the allanite samples (mean ¹⁷⁵Lu/¹⁷⁷Hf = ∼814; mean ¹⁷²Yb/¹⁷⁷Hf = ∼719). A two-step calibration strategy was proposed for the ¹⁷⁶Lu/¹⁷⁶Hf and ¹⁷⁷Hf/¹⁷⁶Hf ratio corrections using NIST SRM 610 (for instrument drift) and LE2808 (for matrix effect). The nine allanite samples contain common Hf contents (<em>f</em>_176Hf) of ∼5 % to &gt;90 %, and the data are plotted in inverse isochron diagrams. Unanchored inverse isochron ages exhibit a large deviation in accuracy (5–10 %), whilst anchored isochron ages have a better accuracy of &lt;5 %. The uncertainty of anchor initial ¹⁷⁶Hf/¹⁷⁷Hf values was investigated and, in general, was insignificant (&lt; 2.8 %) for samples with <em>f</em>_176Hf &lt; 80 %. Our results demonstrate that <em>in situ</em> allanite Lu–Hf dating by LA-ICP-MS/MS is feasible and can yield precise and accurate ages (&lt; 5 %). Lu–Hf geochronometer captures the high-temperature process and may be more resistant during the late thermal event. Thus, it provides an alternative solution for those samples which are suffered by open-system behavior in U-Th-Pb system.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122383"},"PeriodicalIF":3.6,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142230661","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":"Carbonate clumped isotope values compromised by nitrate-derived NO2 interferent","authors":"Jens Fiebig ,&nbsp;Miguel Bernecker ,&nbsp;Niels Meijer ,&nbsp;Katharina Methner ,&nbsp;Philip Tauxe Staudigel ,&nbsp;Amelia Jane Davies ,&nbsp;Lkhamsuren Bayarjargal ,&nbsp;Dominik Spahr ,&nbsp;Björn Winkler ,&nbsp;Sven Hofmann ,&nbsp;Manuel Granzin ,&nbsp;Sierra V. Petersen","doi":"10.1016/j.chemgeo.2024.122382","DOIUrl":"10.1016/j.chemgeo.2024.122382","url":null,"abstract":"&lt;div&gt;&lt;p&gt;&lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; based clumped isotope thermometry has enabled reconstruction of Earth's surface temperatures independent of the source of oxygen within the carbonate. It has been postulated that carbonate samples can contain contaminants that cause isobaric interferences, compromising measured &lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; values and reconstructed temperatures. The exact nature of contaminants and isobaric interferents, however, largely remained unidentified.&lt;/p&gt;&lt;p&gt;Here, we compare theoretically predicted contamination vectors with measured &lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt;-&lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt; values and measured NO&lt;sub&gt;2&lt;/sub&gt; abundances in the CO&lt;sub&gt;2&lt;/sub&gt; evolved from phosphoric acid digestion of carbonates in a common acid bath at 90 °C. We show that nitrate-derived NO&lt;sub&gt;2&lt;/sub&gt; constitutes a serious isobaric interferent for the extracted CO&lt;sub&gt;2&lt;/sub&gt;. During acid digestion, nitrate decomposes to NO and NO&lt;sub&gt;2&lt;/sub&gt;. Both compounds are not effectively removed during subsequent purification of carbonate-derived CO&lt;sub&gt;2&lt;/sub&gt; using cryogenic traps (−80 °C) and gas chromatography (packed Porapak Q column at −15 °C), generating a bias in measured &lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; and &lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt; values. In dual clumped isotope space, biased samples plot along a slope of −0.3 that is characteristic for variable sub-ppm contributions of NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; to CO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; in the ion source. Measured NO&lt;sub&gt;2&lt;/sub&gt; concentrations in the analyte-grade CO&lt;sub&gt;2&lt;/sub&gt; correspond to observed biases in &lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; and &lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt; values if preferential ionization of CO&lt;sub&gt;2&lt;/sub&gt; over NO&lt;sub&gt;2&lt;/sub&gt; is taken into account.&lt;/p&gt;&lt;p&gt;Nitrate contamination occurs in a synthetic calcite precipitated using Ca(NO&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;, a pedogenic carbonate nodule, a plasma-ashed echinoid spine, a bioapatite (Greenland shark dentine), and in ETH-3 (a recently assigned anchor for &lt;em&gt;Δ&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; analysis of carbonates). Sequential bleaching tests reveal that nitrate contaminant and NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; bias can be effectively removed if carbonate samples are pre-treated overnight with 3 wt-% sodium hypochlorite (NaOCl). NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; bias in ETH-3-derived CO&lt;sub&gt;2&lt;/sub&gt; and its effective removal through bleaching is also indicated in a completely different analytical setup that makes use of individual reaction vessels, acid digestion at 70 °C, cryogenic traps at −60 °C and a static Porapak Q trap at −30 °C.&lt;/p&gt;&lt;p&gt;Considering that NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; bias is observed in two fairly conventional analytical setups, we strongly recommend that each laboratory tests to which extent their setup is affected. Unless independent evidence is given that NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; bias is irrelevant for a specific setup, ETH-3 should be bleached and further systematic sequential bleaching tests be carried out on unknown samples in order to avoid any isotopic bias. Our high-precision","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122382"},"PeriodicalIF":3.6,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124004625/pdfft?md5=4ffef9513537184b0c314fdd11145ceb&pid=1-s2.0-S0009254124004625-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142172490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Detrital K-feldspar as a novel archive of continental crustal evolution using coupled in situ RbSr dating and Pb isotope analysis","authors":"Dan Bevan ,&nbsp;Daniel Stubbs ,&nbsp;Christopher D. Coath ,&nbsp;Jamie Lewis ,&nbsp;Tim Elliott","doi":"10.1016/j.chemgeo.2024.122379","DOIUrl":"10.1016/j.chemgeo.2024.122379","url":null,"abstract":"<div><p>Here we present <em>in situ</em> Rb<img>Sr and Pb isotopic analysis of K-feldspar from the Shap Granite, (Cumbria, UK) and detrital K-feldspar from the associated Shap Wells Conglomerate Formation, to investigate the potential of the detrital K-feldspar record as an archive of crustal composition. We use a unique, collision cell – multi collector inductively coupled plasma tandem mass spectrometer to make the <em>in situ</em> isotope measurements, using ‘chemical resolution’ of ⁸⁷Rb⁺ and ²⁰⁴Hg⁺ isobaric interferences on ⁸⁷Sr⁺ and ²⁰⁴Pb⁺, achieved with SF₆ and NH₃ reaction gases, respectively. Using this technique, we successfully demonstrate that the majority of detrital K-feldspar Rb<img>Sr ages, as well as initial Sr and Pb isotope ratios, from the Shap Wells Conglomerate are within uncertainty of those for parental Shap Granite K-feldspar (398 ± 1 Ma, <em>n</em> = 6). Some detrital K-feldspar grains record perturbed Rb<img>Sr ages, reflecting post depositional alteration events. The majority of samples with disturbed Rb<img>Sr ages carry distinct petrographic features evident in SEM imaging, prior to <em>in situ</em> dating, which indicates a means to help screen for reliable ages.</p><p>We further illustrate the potential value of combined Rb<img>Sr and Pb isotopic information preserved in K-feldspar to estimate the timing and chemical composition of juvenile continental crust formed in the past. Where U<img>Pb has been fractionated during juvenile crust formation, the initial Pb isotope ratio provided by the K-feldspar yields model crustal U/Pb (diagnostic of tectonic setting) and extraction age. The contrast in the U/Pb composition of juvenile crust formed in intraplate or subduction settings allows the model U/Pb ratios of the detrital K-feldspars to be used to constrain the style of juvenile crust formation. Additionally, the initial ⁸⁷Sr/⁸⁶Sr isotope ratio measured in detrital K-feldspar can be combined with the calculated crustal extraction age and Rb<img>Sr K-feldspar age to model the Rb/Sr of the juvenile crustal protolith.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122379"},"PeriodicalIF":3.6,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124004595/pdfft?md5=5d1b47e55ded5443535f59f42c07a602&pid=1-s2.0-S0009254124004595-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seawater-oceanic crust interaction constrained by triple oxygen and hydrogen isotopes in rocks from the Saglek-Hebron complex, NE Canada: Implications for moderately low-δ18O Eoarchean Ocean","authors":"A. Kutyrev ,&nbsp;I.N. Bindeman ,&nbsp;J. O'Neil ,&nbsp;H. Rizo","doi":"10.1016/j.chemgeo.2024.122378","DOIUrl":"10.1016/j.chemgeo.2024.122378","url":null,"abstract":"<div><p>Estimations of Earth's earliest surface conditions assume a strong connection between the temperature and oxygen isotopic composition of oceans, balanced by surface weathering and submarine hydrothermal alteration. The oldest preserved supracrustal rocks provide rare opportunities to study and constrain the earliest surface conditions prevailing on the Earth. Here, we present a study of triple oxygen and hydrogen isotopes of hydrothermally altered Eoarchean metamorphosed basalts, ultramafic rocks, and detrital and chemical sediments, from the Saglek-Hebron Complex in northern Labrador, Canada. For the metavolcanic rocks, δ’¹⁸O values range from 4.83 ‰ to 8.56 ‰, while Δ’¹⁷O values vary from −0.076 ‰ to −0.023 ‰, both higher and lower than the mantle. Accounting for the effects of metamorphism on oxygen and hydrogen isotopic compositions, we demonstrate that triple oxygen isotopic values are preserved from the hydrothermal suboceanic stage, while none of the hydrogen isotope compositions (δD from −77.9 ‰ to −10.7 ‰) are interpreted as primary. Several metabasalt samples from the Saglek-Hebron Complex yielded Δ’¹⁷Ο values lower than modern mantle values, which cannot be explained by direct interaction with modern seawater and indicate complex upstream interactions. Our numerical models and Monte Carlo simulation considers one- and two-stage mechanisms of water-rock interaction, including the δ’¹⁸Ο and Δ’¹⁷Ο isotopic shift effects due to interaction between basalts and chemical sediment-derived fluids. The modelling favors Eoarchean seawater characterized by low δ’¹⁸Ο &lt; −8 ‰ at Δ’¹⁷Ο up to 0.01 ‰. This model also works for higher Δ’¹⁷Ο at lower δ’¹⁸Ο. Our results also suggest that without proper modelling of multi-stage water-rock interaction, involving isotopic shifts and input of sediment-derived fluids, exposed sections of altered oceanic crust present only remote evidence of the original seawater. Due to the modeled isotopic shifts and fluid mixing, we favor “weak” coupling of seawater-oceanic crust interaction globally. This potentially reduces the relative importance of submarine hydrothermal alteration in explaining the oxygen isotopic record in submarine basalts across the geologic history.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122378"},"PeriodicalIF":3.6,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124004583/pdfft?md5=f4eb698201950b75266e931f8a896d97&pid=1-s2.0-S0009254124004583-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142144018","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Uptake time and enrichment mechanism of rare earth elements in deep-sea bioapatite","authors":"Yonghang Xu ,&nbsp;Dongyi Li ,&nbsp;Yang Alexandra Yang ,&nbsp;Jian Chen ,&nbsp;Siyu Zhao ,&nbsp;Louwang Yan ,&nbsp;Xijie Yin ,&nbsp;Fanyu Lin ,&nbsp;Yunhai Li ,&nbsp;Feng Wang","doi":"10.1016/j.chemgeo.2024.122371","DOIUrl":"10.1016/j.chemgeo.2024.122371","url":null,"abstract":"<div><p>Bioapatite is widely recognized as the primary carrier for rare earth elements and yttrium (REY) in deep-sea REY-rich muds. The incorporation of REY into bioapatite occurs at the water-sediment interface, which has the potential to serve as a proxy for reconstructing paleoenvironmental conditions. The timing of REY uptake and the fractionation of rare earth elements (REEs) within bioapatite are crucial factors to understanding the application of these proxies. In this study, we present in-situ geochemical data for bioapatite obtained from surface sediments in the high sedimentation rate Somali Basin of the northwestern Indian Ocean (NWIO), as well as fish teeth within nodules from the low sedimentation rate in the northwestern Pacific Ocean (NWPO). Our findings indicate that the uptake time of REY occurred rapidly, with the ΣREY content reaching 7265 μg/g in bioapatite from the surface sediments in the NWIO within several thousand years. The bone fragments exhibited a high ΣREY content, which was primarily attributed to substitution processes. This led to a notably elevated proportion of middle rare earth elements (MREE) compared to fish teeth. In contrast, the adsorption and substitution mechanisms responsible for REY incorporation decreased from the root to the tip in fish teeth, resulting in a pronounced decline in ΣREY content. The adsorption mechanism was identified as the primary process responsible for REY uptake in the fish teeth within the studied nodules from the NWPO. The fractionation pattern of REEs in these teeth exhibited similarities to that of fish teeth from the NWIO. Therefore, we inferred that the fish teeth within the studied nodules may preserve the original information during late diagenesis. The variation of REY contents in the nodules was influenced by the redox environment, and there is no evidence to support the migration of REY from the nodules into the fish teeth.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"669 ","pages":"Article 122371"},"PeriodicalIF":3.6,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142144017","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":"Control of magmatic halogen composition and redox state on the zonation of metal mineralization across active continental margins: Perspectives from the world-class South China metallogenic province","authors":"Xinghua Ma ,&nbsp;Honghui Wang ,&nbsp;Bernd Lehmann ,&nbsp;Chunli Guo ,&nbsp;Jingwen Mao","doi":"10.1016/j.chemgeo.2024.122363","DOIUrl":"10.1016/j.chemgeo.2024.122363","url":null,"abstract":"<div><p>Active continental margins are the major sites of continental magmatism and associated hydrothermal ore deposits with a broad metal spectrum. Mineralization across active continental margins typically displays spatial zonation, with porphyry copper-(molybdenum‑gold) deposits in volcanic arcs and tin- and tungsten-dominated mineralization occurring further inland in a back-arc setting. Particularly, tin and tungsten commonly form separate deposits in back-arc regions, even though both metals exhibit similar lithophile behavior. The key factors governing this metallogenic zonation remain unclear. The world-class South China metallogenic province hosts over 50 % of the global tungsten resources, along with a significant amount of tin and copper resources distributed in different mineralization belts, making it an ideal location in which to study regional metal zonation. Here, we comprehensively integrate a very large dataset of the halogen volatile composition (F, Cl) and oxygen fugacity of granites related to tin, tungsten, and copper mineralization in the South China continental margin. Our compilation, derived from a substantial collection of zircon, apatite, mica, and whole-rock geochemistry data, suggests that lateral variations in granite magmatism (away from the trench), transitioning from chlorine-rich and oxic to fluorine-rich and reduced conditions, exert the primary control on copper versus tin‑tungsten mineralization in the arc and back-arc regions, respectively. Differences in oxygen fugacity have a minor impact on the decoupling of tin and tungsten mineralization despite tin granites being universally reduced (ΔFMQ = −1.8 to −0.1, where FMQ is the fayalite-magnetite-quartz redox buffer) and tungsten granites having a broader redox range (ΔFMQ = −1.5 to +1.2). Instead, the disparity in fluorine content plays a more crucial role in controlling the spatial separation of tin and tungsten mineralization observed in the back-arc setting. Nd-Hf and He-Ar isotopic modeling calculations suggest that magmas linked to tin mineralization have a more pronounced involvement of F-rich mantle components compared to those associated with tungsten. Elevated fluorine (ca. 650–8000 ppm) in tin-associated magmas allowed an extreme degree of magmatic differentiation and delayed fluid exsolution due to high H₂O solubility in F-rich silicate melts, ensuring Sn enrichment in highly evolved melts. In contrast, early fluid exsolution under less F-rich conditions (ca. 100–700 ppm) led to early tin loss from the melts, ultimately resulting in tungsten-dominant mineralization. This work emphasizes the combined influence of halogen composition and redox state on the regional mineralization zonation in world-class metallogenic provinces, providing vectors for global metal exploration in both past and currently active continental margins.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"669 ","pages":"Article 122363"},"PeriodicalIF":3.6,"publicationDate":"2024-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142242600","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":"Tracing the orogenic sulfur cycle in the Andes using stable isotope composition of dissolved sulfate in thermal springs","authors":"Tyler A. Grambling ,&nbsp;Dennis L. Newell ,&nbsp;Karen G. Lloyd ,&nbsp;Coleman D. Hiett ,&nbsp;Heather Upin ,&nbsp;Peter H. Barry ,&nbsp;Donato Giovannelli ,&nbsp;J. Maarten de Moor ,&nbsp;Agostina Chiodi ,&nbsp;Gerdhard L. Jessen ,&nbsp;Jenny M. Blamey ,&nbsp;Anna Szynkiewicz","doi":"10.1016/j.chemgeo.2024.122365","DOIUrl":"10.1016/j.chemgeo.2024.122365","url":null,"abstract":"<div><p>The cycling of sulfur (S) to the upper crust and surface via thermal springs at convergent margins has not been explored outside areas with active arc volcanism, even though subduction plays a key role in the Earth's long-term S cycle. To address this knowledge gap, we analyzed stable sulfur and oxygen isotope compositions (δ³⁴S and δ¹⁸O values) of dissolved sulfate (SO₄²⁻) in 55 thermal springs from five distinct settings in the Andean orogen. These regions are the Peruvian flat slab and backarc, transition between these two, Argentinian backarc, and Chilean forearc. Although the flat-slab settings had lower SO₄²⁻ concentrations (&lt;2000 mg/L) compared to the steep-slab settings (&lt;12,700 mg/L), there was no significant relationship between isotope composition of SO₄²⁻ and slab geometry. The δ³⁴S and δ¹⁸O values of SO₄²⁻ varied widely across the studied areas (+0.2 to +23.5 ‰ and − 3.3 to +16.0 ‰, respectively) and reflected the isotope compositions of local bedrock endmembers from dissolution of marine evaporites (+5 to +25 ‰ and + 10 to +20 ‰, respectively) and oxidation of magmatic and/or hydrothermal S and ore sulfide minerals with variable δ³⁴S (0 to +16 ‰). The δ¹⁸O and δ²H values of thermal spring water (−18.5 to −3.3 ‰ and − 141.1 to −23.7 ‰, respectively) were consistent with meteoric precipitation, and in most cases decreased with increasing altitude following precipitation in the Andes. Generally, our isotope results do not support the direct transfer of slab-derived S/SO₄²⁻ to thermal springs in the investigated settings. Rather, the δ³⁴S and δ¹⁸O of SO₄²⁻ in the thermal springs are a sensitive indicator of local water-rock interactions that remobilize bedrock S originating from a complex orogenic cycle reflecting tectonic uplift, erosion, weathering, and exhumation history across the duration of Andean Mountain building.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"669 ","pages":"Article 122365"},"PeriodicalIF":3.6,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142144036","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":"Intense intrusion of low-oxygen waters into mid-Cambrian surface ocean carbonate factories","authors":"Yang-fan Li ,&nbsp;Fei Li ,&nbsp;Gregory E. Webb ,&nbsp;Jitao Chen","doi":"10.1016/j.chemgeo.2024.122360","DOIUrl":"10.1016/j.chemgeo.2024.122360","url":null,"abstract":"<div><p>The Phanerozoic surface ocean is characterized by its high dissolved oxygen content owing to mixing with the atmosphere. However, atmospheric oxygen levels varied in the early Paleozoic and it remains unclear whether the surface ocean was susceptible to significant redox fluctuations in response to extreme environmental events. In this study, we probed the redox structures of shallow middle Cambrian marine depositional environments across the North China Platform, ranging from open tidal flats to relatively deep subtidal environments. We utilized a combination of least diagenetically altered carbonate materials (such as ooid cortices, calcimicrobes, and their fringing cements), as well as in situ element measurement and imaging techniques. By analyzing a set of redox-related elements (e.g., Ce anomaly, Zn/Fe molar ratio, Mn and Cr) and mineralogical proxies (hydrogenetic Fe oxides), we revealed a stratified redox structure in the Drumian surface oceans. Compared to earlier Drumian conditions, late Drumian surface oceans experienced significant intrusions of ferruginous waters, probably reaching into shallow subtidal environments with water depths less than 10 m. Furthermore, we identified shallow subtidal microbial O₂-producing factories, characterized by dendritic <em>Epiphyton</em> thalli. These calcimicrobes exhibited more oxygenated signatures (negative Ce anomalies and enrichment of hydrogenetic Fe oxides) relative to contemporaneous less oxic shallower and deeper environments. This finding indicates that they produced oxygen oases or refuges during periods of both normal and poor dissolved O₂ conditions. This study has the potential to broaden our understanding of redox conditions and microbial oxygen-producing mechanisms in the surface ocean, particularly during intervals characterized by low atmospheric oxygen levels or episodic anoxic events.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"669 ","pages":"Article 122360"},"PeriodicalIF":3.6,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142144019","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 regolith weathering controls δ30Si composition of groundwater under contrasting landuse in tropical watersheds","authors":"Sarath Pullyottum Kavil ,&nbsp;Jean Riotte ,&nbsp;Ramananda Chakrabarti ,&nbsp;Arnaud Dapoigny ,&nbsp;Véronique Vaury ,&nbsp;Laurent Ruiz ,&nbsp;Damien Cardinal","doi":"10.1016/j.chemgeo.2024.122370","DOIUrl":"10.1016/j.chemgeo.2024.122370","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Land use changes are known to alter terrestrial silicon cycling and the export of dissolved silicon from soil to fluvial systems, but the impact of such changes on groundwater systems remain unclear. In order to identify the processes responsible for groundwater geochemistry and to assess the impact of agricultural processes, we examined multiple isotopic tracers (δ&lt;sup&gt;30&lt;/sup&gt;Si, oxygen (δ&lt;sup&gt;18&lt;/sup&gt;O) and hydrogen (δ&lt;sup&gt;2&lt;/sup&gt;H) isotopes) in groundwater, soil porewater and surface water from two contrasted watersheds having the same gneissic lithology, one forested (Mule Hole) and one intensely cultivated (Berambadi) in the Kabini basin in South India. In the cultivated watershed, groundwater exhibits high Cl&lt;sup&gt;−&lt;/sup&gt; and NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; concentrations indicative of fertilizer inputs and solute enrichment from evapotranspiration due to multiple groundwater pumping/recharge cycles. The DSi concentration in groundwater is significantly higher in the cultivated watershed (980 ± 313 μM) than in the forested one (711 ± 154 μM), indicating more intense evapotranspiration due to irrigation cycles. The groundwater δ&lt;sup&gt;30&lt;/sup&gt;Si values ranged from 0.6 ‰ to 3.4 ‰ and exhibit no significant differences between cultivated (1.2 ± 0.5 ‰) and forested (1.0 ± 0.2 ‰) watersheds, indicating limited impact of land use and land cover. Groundwater also shows no significant seasonal differences in DSi and δ&lt;sup&gt;30&lt;/sup&gt;Si within watersheds, indicating a buffer to seasonal recharge during wet season. The δ&lt;sup&gt;30&lt;/sup&gt;Si of a majority of groundwater samples fits a steady-state open flow through system, with an isotopic fractionation factor (&lt;sup&gt;30&lt;/sup&gt;ε) between precipitating phase and groundwater ranging from −1.0 ‰ and − 2.0 ‰, consistent with precipitation of kaolinite-type clays, dominant in the study area. The steady-state flow through system in groundwater can be interpreted as a continuous DSi input from mineral weathering reactions with a dynamic equilibrium between Si supply and precipitation of secondary phases. We also observe, in both watersheds, similar DSi and δ&lt;sup&gt;30&lt;/sup&gt;Si values in local surface water that includes small streams and a river (406 ± 194 μM, 1.6 ± 0.3 ‰) and in soil porewater (514 ± 119 μM, 1.6 ± 0.2 ‰). Compared to soil porewater, groundwater exhibits significantly lower δ&lt;sup&gt;30&lt;/sup&gt;Si signatures and higher DSi, reflecting the contribution of an isotopically light silicon source, resulting from water-rock interaction during percolation through the unsaturated zone. We assign this steady input of DSi to the weathering of primary silicate minerals in the regolith, such as Na-plagioclase, biotite and chlorite, with formation of kaolinite and smectites type clays. A simple isotopic mass balance suggests that deep regolith weathering can contribute to almost half of the DSi in groundwater. We conclude that silicon cycling in soil porewaters, and surface waters are directly impacted by land use, while th","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122370"},"PeriodicalIF":3.6,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142328017","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A review of the major chemical and isotopic characteristics of groundwater in crystalline rocks of the Canadian Shield","authors":"Lamine Boumaiza,&nbsp;Randy Stotler,&nbsp;Shaun Frape","doi":"10.1016/j.chemgeo.2024.122366","DOIUrl":"10.1016/j.chemgeo.2024.122366","url":null,"abstract":"&lt;div&gt;&lt;p&gt;Canadian Shield groundwater characterization studies have been conducted over the last four decades through operating mines, underground research areas, and wells installed for a variety of purposes. A newly available database containing chemical and isotopic analytical results of groundwaters includes data from all of these sources and spans the Canadian Shield. The Precambrian Canadian Shield Groundwater and Gas Geochemistry (PCSG&lt;sup&gt;3&lt;/sup&gt;) database provides the most comprehensive data of groundwater chemistry in the Canadian Shield region to date. In this initial review of the PCSG&lt;sup&gt;3&lt;/sup&gt; database, major ion, Br, water type, δ&lt;sup&gt;18&lt;/sup&gt;O, δ&lt;sup&gt;2&lt;/sup&gt;H and &lt;sup&gt;3&lt;/sup&gt;H trends with depth and salinity are described. In future reviews, other aspects of the database will be examined, including minor and trace elements, other isotopes, and gases. The PCSG&lt;sup&gt;3&lt;/sup&gt; database is comprised of 69 % freshwaters, mostly found at depths &lt;1000 m, and dominated by Ca-HCO&lt;sub&gt;3&lt;/sub&gt; and Na-HCO&lt;sub&gt;3&lt;/sub&gt; water types; 17 % brackish waters, at depths &lt;2000 m, and dominated by Na&lt;img&gt;Cl, Ca&lt;img&gt;Cl, Ca-HCO&lt;sub&gt;3&lt;/sub&gt;, and Ca-SO&lt;sub&gt;4&lt;/sub&gt; water types; 9 % saline waters, mostly at depths &gt;1000 m, and dominated by Ca&lt;img&gt;Cl, Na&lt;img&gt;Cl, Ca-HCO&lt;sub&gt;3&lt;/sub&gt;, and Na-HCO&lt;sub&gt;3&lt;/sub&gt; water types; and 4 % brine samples, identified at depths up to 1800 m, composed entirely of Ca&lt;img&gt;Cl water types. An increase in all major ion and Br concentrations with depth is observed, except for HCO&lt;sub&gt;3&lt;/sub&gt;, with groundwaters typically becoming more saline with depth. Variability in salinities at specific depths and at individual sites across the Canadian Shield reflect the effect of (primarily) anthropogenically induced mixing, although heterogeneous geology and hydrogeologic flow paths are also important. When eliminating data that are likely affected by anthropogenically-induced mixing, saline waters are the most affected, with median depths of Na&lt;img&gt;Cl and Ca&lt;img&gt;Cl type waters shifting downward, and median concentrations of Na&lt;img&gt;Cl type waters increasing. The isotopic data indicate that groundwaters from across the Canadian Shield reflect a variety of water recharge sources, with many samples plotting along the Global Meteoric Water Line (GMWL). Deviations to the right of the GMWL are indicative of freezing and mixing with drill fluid, while deviations to the left are indicative of isotopic exchange between water and rock and/or silicate hydration over long time scales. Rock/silicate-water interactions over hundreds of million of years resulted in development and isolation of Ca&lt;img&gt;Cl brines at multiple locations. Cold climate processes, including glacial meltwater recharge and/or ionic concentration during permafrost formation, yielded a third end-member. A conceptual model of the expected groundwater chemistry variation with depth across the Canadian Shield is presented based on an evaluation of the variation of water type and salinit","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"669 ","pages":"Article 122366"},"PeriodicalIF":3.6,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124004467/pdfft?md5=ee5f3db7b80f13387683d0459334bd5f&pid=1-s2.0-S0009254124004467-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142136844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}