Chemical Geology最新文献

{"title":"Predominant biogenic contribution of dissolved inorganic carbon in karst rivers, Southwest China","authors":"Yue Zheng ,&nbsp;Hu Ding ,&nbsp;Jun Zhong ,&nbsp;Yunchao Lang ,&nbsp;Si-Liang Li ,&nbsp;Sheng Xu ,&nbsp;Cong-Qiang Liu","doi":"10.1016/j.chemgeo.2024.122404","DOIUrl":"10.1016/j.chemgeo.2024.122404","url":null,"abstract":"<div><p>Dissolved inorganic carbon (DIC) holds significant importance within river systems, particularly in karst regions. The concentration of DIC is intricately linked to both biological processes, such as the respiration of organic matter, and geological processes, notably the strength of carbonate weathering. This dual influence exerts a profound impact on regional and global carbon cycles. However, the precise biological and geological origins of DIC in karst rivers remain a subject of debate. In this study, we delineate the sources of DIC in a typical karst catchment (Houzhai catchment) through isotopic analysis coupled with water chemistry examination. The results showed that δ¹³C_DIC and Δ¹⁴C_DIC variations range from −14.0 ‰ to −7.3 ‰ and − 426 ‰ to −31 ‰, respectively, with average values of −10.5 ‰ and − 180 ‰. Results derived from the isotopic mixing model suggest that approximately 83 % of DIC emanates from the soil CO₂, while 17 % originates from carbonate sources. This indicates that biological processes exert a greater influence on DIC within the study area compared to geological processes. Seasonal variation, exemplified by higher DOC concentrations and Δ¹⁴C_DIC values, alongside with lower DIC concentrations and δ¹³C_DIC values during the wet season indicate increased input from biogenic sources, closely related to temperature and moisture conditions. Our study underscores an unbalanced contribution from biogenic and geogenic sources in karst rivers, highlighting potential inaccuracies in past carbon sink flux calculations. The roles of biogenic and geogenic sources in the carbon cycling of karst rivers, as well as their responses to future climate change, warrant a reevaluation.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122404"},"PeriodicalIF":3.6,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142271547","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 effect of carbonate assimilation and nanoheterogeneities on the viscosity of phonotephritic melt from Vesuvius","authors":"Gabriele Giuliani ,&nbsp;Danilo Di Genova ,&nbsp;Fabrizio Di Fiore ,&nbsp;Pedro Valdivia ,&nbsp;Silvio Mollo ,&nbsp;Claudia Romano ,&nbsp;Tiziana Boffa Ballaran ,&nbsp;Alexander Kurnosov ,&nbsp;Alessandro Vona","doi":"10.1016/j.chemgeo.2024.122408","DOIUrl":"10.1016/j.chemgeo.2024.122408","url":null,"abstract":"<div><p>Interaction between magma and carbonate plays a pivotal role in volcanic systems, yet its impact on magma transport properties remains inadequately explored. This study presents novel viscosity data on a leucite-bearing phonotephritic melt from the 472 CE Pollena eruption (Vesuvius, Italy), doped with varying amounts of CaO and CaO + MgO. The compositions match the chemistry of melt inclusions and interstitial glasses from skarns at Vesuvius, which have been interpreted as related to mixing of magma with different amounts of CaO and MgO derived from the host carbonates (limestone and dolostone). Viscosity measurements were conducted at both high (1150–1400 °C) and low temperatures (640–760 °C) by concentric cylinder viscometry, differential scanning calorimetry, and micropenetration methods. Through an integrated approach which combines Brillouin and Raman spectroscopy with the aforementioned techniques, we accurately predict the viscosity changes induced by magma‑carbonate interaction and identify the formation of nanoheterogeneities during low-temperature viscosity measurements. Notably, viscosity models from the literature fail to accurately reproduce our experimental data set at both high and low temperature. In the high-temperature regime, the addition of CaO induces a remarkable viscosity decrease, surpassing that produced by CaO + MgO addition. Furthermore, our findings reveal a significant viscosity/temperature crossover resulting from the addition of CaO and CaO + MgO to the melt phase. Undoped melt exhibits a higher viscosity compared to doped melts above 750 °C, with an inverse trend observed below this temperature threshold. Such rheological constraints may affect the mobility and mixing capability of melts exposed to different levels of carbonate assimilation.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122408"},"PeriodicalIF":3.6,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124004881/pdfft?md5=97efd1abd044d8867f10484031398438&pid=1-s2.0-S0009254124004881-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142238739","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":"Ghost age components in detrital thermochronology","authors":"B. Härtel ,&nbsp;Pieter Vermeesch ,&nbsp;Eva Enkelmann ,&nbsp;Stijn Glorie","doi":"10.1016/j.chemgeo.2024.122406","DOIUrl":"10.1016/j.chemgeo.2024.122406","url":null,"abstract":"<div><p>Thermochronological dating of detrital samples is an important tool for understanding the thermal history of basins and their source regions. Detrital thermochronology data are often complex with apparent ages ranging over hundreds of million years due to variations in source-rock cooling age and rate, and the influence of post-depositional burial. A common strategy to interpret such data is to split a dataset into several age components by finite-mixture modeling. Herein, we describe for the first time a remarkable pattern of age components in some thermochronological datasets: two or more components showing ages that are approximately multiples of each other. We apply finite-mixture modeling to a log-normal age distribution (a random effects model) and show that these “<em>ghost age components”</em> are artifacts of inappropriately fitting discrete components to continuous age ranges. The striking pattern of the age components is a direct consequence of the underlying age distribution. For a continuous log-normal age distribution, the ghost components have approximately similar age ratios that depend on the overdispersion and the number of components. Due to their artifactual nature, ghost components appear in a range of dating methods, including fission-track, U<img>Pb and (U<img>Th)/He dating, and in equivalent doses of luminescence dating. As they are not geologically meaningful, their occurrence hampers the geological interpretation of thermochronological data. We thus propose to carefully decide for the number of fitted components based on grain properties and additional geological information and to screen modeling results for the constant age ratios that are characteristic of ghost components.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122406"},"PeriodicalIF":3.6,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124004868/pdfft?md5=650280a31a63e6abad99206c08f019ad&pid=1-s2.0-S0009254124004868-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142238724","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":"Oxygen and silicon isotopic compositions of Archean silicified lava and cherts of the Onverwacht Group: Implication for seafloor hydrothermalism and the nature of recycled components in the source of granitoids","authors":"L.S. Kitoga ,&nbsp;D. Zakharov ,&nbsp;J. Marin-Carbonne ,&nbsp;M. Boyet ,&nbsp;J.-F. Moyen ,&nbsp;T. Di Rocco ,&nbsp;A. Pack ,&nbsp;N. Olivier ,&nbsp;G. Stevens","doi":"10.1016/j.chemgeo.2024.122407","DOIUrl":"10.1016/j.chemgeo.2024.122407","url":null,"abstract":"<div><div>Cherts are commonly used as proxies for Archean environmental conditions such as oceanic temperature. However, because cherts encompass a wide variety of silica-rich rocks, including post-depositional silicified of clastic sediments or chemical precipitates from seawater, reconstructions of the Archean environment based on their O and Si isotopic compositions remain controversial. In this study, we present triple O isotope analyses associated with SIMS O and Si isotope measurements of Palaeoarchean pervasively silicified lavas and clastic sediments, which have been less studied than the associated cherts within the Onverwacht Group (Barberton Greenstone Belt, South Africa). We also provide triple O isotopic compositions of seawater-precipitated cherts. The O and Si isotope composition of silicified clastic sediments and lavas is not considerably variable through the Onverwacht succession. These lithologies display relatively low δ¹⁸O (11.3–14.9 ‰) and high Δ’¹⁷O values (−0.05 to - 0.07 ‰) attributed to precipitation of silica from hydrothermal fluids at lower temperatures than 200 °C. Using these results, we reconstruct the approximate O isotope composition of the hydrothermal fluids. Water-rock interaction models suggest that this fluid composition is consistent with the existence of low δ¹⁸O oceans, but the exact δ¹⁸O value of the Palaeoarchean ocean remains elusive. Seawater-precipitated cherts show a mixture of hydrothermal and seawater-like triple O isotope signatures, confirming that cherts are not a straightforward proxy for constraining Archean seawater composition or temperature. The average δ³⁰Si value of the pervasively silicified lavas and clastic sediments is positive (&gt; +0.19 ‰) and compositionally similar to published values of the seawater-precipitated cherts. This suggests comparable δ³⁰Si values between Archean hydrothermal fluids and seawater. A gradual increase of δ¹⁸O values of silicified lavas and cherts from 10 to 13 ‰ to 15–20 ‰ observed along the Onverwacht succession is ascribed to local lithospheric cooling occurring between 3.47 Ga and 3.3 Ga, while Si isotope compositions remained mostly unchanged in the silica-rich rocks. As silicified lavas are likely part of materials that melted to generate Palaeoarchean granitoids, the evolutional difference between O and Si isotopes may have characterised the silicified rocks that were recycled in different generations of granitoid sources. This may explain the variation in O isotopic compositions measured in different granitoid generations in the Barberton area.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122407"},"PeriodicalIF":3.6,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424004","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":"Heavy halogen compositions of peridotite massifs in the Ivrea-Verbano Zone and implications for strong modification of mantle rocks","authors":"Yixin Zheng ,&nbsp;Zaicong Wang ,&nbsp;Ray Burgess ,&nbsp;Xiang Wang ,&nbsp;Zhaoxian Zhu ,&nbsp;Zongqi Zou ,&nbsp;Tao He ,&nbsp;Zhaochu Hu ,&nbsp;Yongsheng Liu","doi":"10.1016/j.chemgeo.2024.122405","DOIUrl":"10.1016/j.chemgeo.2024.122405","url":null,"abstract":"<div><p>The lithospheric mantle affected by metasomatism is an important reservoir for halogens and often preserves significant heterogeneity in halogen abundances. However, the halogen compositions of the non-metasomatized mantle rocks with depleted geochemical features have not been well studied, impeding a comprehensive understanding of the halogen distribution in the mantle. The Balmuccia (BM) and Baldissero (BD) peridotite massifs in the Ivrea-Verbano Zone, Italian Alps, represent fragments of the sub-continental lithospheric mantle (SCLM) that are fresh and devoid of subduction-related mantle metasomatism. Here we examine the heavy halogen contents of well-characterized spinel-facies mantle peridotites (<em>n</em> = 20) and pyroxenites (<em>n</em> = 16) from the BM and BD massifs. The results indicate significant variation in whole rock halogen contents of peridotites and pyroxenites, with chlorine (Cl) ranging from &lt;30 to 244 μg/g, bromine (Br) from &lt;0.10 to 0.94 μg/g, and iodine (I) from &lt;0.015 to 0.12 μg/g. Some peridotites and pyroxenites show rather low halogen contents (below the detection limit), consistent with their depleted features. However, a large number of samples display halogen contents far higher than the depleted MORB mantle (i.e., Cl: 3–10 μg/g) and peridotite xenoliths from the strongly metasomatized mantle, although ∼30 % of the halogens were leached out by ultrapure water or dilute nitric acid. The data suggest variable halogen enrichment in many mantle rocks. The halogen contents of different types of mantle rocks do not vary with major elements and incompatible trace elements (e.g., Nb), indicating that halogen compositions are not controlled by magmatic processes such as melting and melt-peridotite reaction. Instead, secondary fluid inclusions are abundant and mainly distributed as trails within olivine and pyroxene in both peridotites and pyroxenites, which were likely trapped during the exhumation of these mantle rocks. Their elevated halogen/Nb ratios compared with MORB mantle and strong correlations with Ba/Nb support the effect of fluids. Micro-Raman analyses identify hydrous serpentines within fluid inclusions. Moreover, mass balance calculation indicates that halogen enrichment is mainly caused by secondary fluids (&gt; 90 %). Together, our findings highlight that the fluid percolation in the mantle rocks during exhumation can intensely modify the halogens, to a similar degree as mantle metasomatism, suggesting the sensitivity of halogens to secondary modification.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122405"},"PeriodicalIF":3.6,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142238718","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":"Silicon isotopes reveal the impact of fjordic processes on the transport of reactive silicon from glaciers to coastal regions","authors":"Tong Wang ,&nbsp;Hong Chin Ng ,&nbsp;Jade E. Hatton ,&nbsp;Samantha J. Hammond ,&nbsp;E. Malcolm S. Woodward ,&nbsp;Lorenz Meire ,&nbsp;Katharine R. Hendry","doi":"10.1016/j.chemgeo.2024.122403","DOIUrl":"10.1016/j.chemgeo.2024.122403","url":null,"abstract":"<div><p>Accelerated mass loss from the Greenland Ice Sheet leads to retreating glaciers and enhanced freshwater runoff to adjacent coastal regions, potentially providing additional essential nutrients, such as silicon, to downstream primary producers. However, the role of fjordic sediments in modulating the supply of silicon from glacial environments to marine ecosystems remains poorly constrained, particularly for the quantification of silicon fluxes from the sediments into overlying waters in high-latitude fjordic systems. In this study, we use the concentration and stable isotopic composition of dissolved silicon in pore waters and core-top waters, and amorphous silica phases (such as glacially-derived amorphous silica) in sediments and suspended particulate matter, collected from two fjords in the southwest Greenland margin to address this knowledge gap. We combine downcore observations with core incubations and isotope mass balance approaches to assess the benthic flux of dissolved silicon and deconvolve potential contributors to this flux during early diagenesis. Our results suggest that molecular diffusion only accounts for a portion of benthic dissolved silicon transport. Relative to surrounding continental shelves and highly-productive open ocean waters, the estimated benthic dissolved silicon flux at our sites is smaller in magnitude, supporting the role of fjords as a ‘trap’ for reactive silicon in high-latitude systems.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122403"},"PeriodicalIF":3.6,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124004832/pdfft?md5=7689a3f2ccbcaaae00778344c8922dda&pid=1-s2.0-S0009254124004832-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142238849","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":"Unravelling the magmatic and hydrothermal evolution of rare-metal granites through apatite geochemistry and geochronology: The Variscan Beauvoir granite (French Massif Central)","authors":"Océane Rocher ,&nbsp;Christophe Ballouard ,&nbsp;Antonin Richard ,&nbsp;Loïs Monnier ,&nbsp;Patrick Carr ,&nbsp;Oscar Laurent ,&nbsp;Yanis Khebabza ,&nbsp;Andreï Lecomte ,&nbsp;Nordine Bouden ,&nbsp;Johan Villeneuve ,&nbsp;Benjamin Barré ,&nbsp;Patrick Fullenwarth ,&nbsp;Mathieu Leisen ,&nbsp;Julien Mercadier","doi":"10.1016/j.chemgeo.2024.122400","DOIUrl":"10.1016/j.chemgeo.2024.122400","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Peraluminous rare-metal granites (PRMGs) represent highly differentiated crustal granites characterised by extreme enrichment in metals, such as Li, Sn, Nb, Ta, W, and Be. This geochemical specificity is considered to be the result of a succession of magmatic and hydrothermal processes, the importance and individual impact of which are still debated. In this study, we investigate the magmatic and hydrothermal evolution of the Beauvoir leucogranite, a world-class PRMG from the French Paleozoic Variscan belt, through extensive characterisation of suprasolidus to subsolidus apatite. We employ a multi-tracing approach, combining &lt;em&gt;in-situ&lt;/em&gt; elemental compositions (major, trace, and halogen elements), oxygen isotopic systematics, and U-Pb geochronology.&lt;/div&gt;&lt;div&gt;Four major magmatic and hydrothermal stages were identified through apatite petrography and U-Pb geochronology. Magmatic apatite crystallised at 314.6 ± 4.7 (2s) Ma. Decrease in the amplitude of the Eu anomaly in magmatic apatite from the deeper to shallower granitic units record an increase in the oxygen fugacity (&lt;em&gt;fO&lt;/em&gt;&lt;sub&gt;&lt;em&gt;2&lt;/em&gt;&lt;/sub&gt;) of the magma with differentiation, likely contributing to the crystallisation of a first and predominant cassiterite generation. Magmatic apatite REE patterns show significant tetrad effects; they reflect the exsolution of magmatic fluids involved in the precipitation of early hydrothermal apatite replacing igneous minerals or precipitating within veins during greisenisation episode dated at 314.3 ± 5.5 Ma and 311.7 ± 8.1 Ma. Early hydrothermal apatite, characterised by enrichment in Sr or S and Mn-REE depletion along with variable Br/I ratios and δ&lt;sup&gt;18&lt;/sup&gt;O compositions down to negative values, record mixing dynamics between two fluid end-members: (i) magmatic fluids, and (ii) oxidising meteoric fluids partially reequilibrated with country rocks. Meteoric fluids progressively invaded the Beauvoir PRMG at temperatures ≥ 450 °C and triggered precipitation of a second generation of cassiterite during mixing with magmatic fluids. Two late, non-magmatic, hydrothermal events are dated at 268.3 ± 20.4 Ma and 148.5 ± 26.6 Ma. Related apatite is marked by specific mineralogical and geochemical features such as high As contents and heavy oxygen isotope signatures. They are proposed to be linked to extension-related regional hydrothermal fluid circulation that contributed to metal endowment (U, F-Ba-Pb-Zn) in the crystalline basement and overlying sedimentary cover of Western Europe following the Variscan Orogeny.&lt;/div&gt;&lt;div&gt;Our results demonstrate that apatite is a key mineral to decipher the role of magmatic and hydrothermal processes leading to ore deposition and remobilisation in PRMGs, in relation with geodynamic evolution. Apatite records of external fluid incursions at near-solidus conditions highlight the open system nature of the Beauvoir PRMG, which is crucial for developing fully integrated metallogenic models applicable to simi","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122400"},"PeriodicalIF":3.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142538223","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":"Robust methods, tricky materials: Challenges in dating high common-Pb perovskite from Cretaceous Brazilian kimberlites","authors":"R.G. Azzone ,&nbsp;D.G. Pearson ,&nbsp;C. Sarkar ,&nbsp;L.M.T. Cetina ,&nbsp;L. Chmyz ,&nbsp;Y. Luo ,&nbsp;E. Ruberti ,&nbsp;V. Guarino ,&nbsp;I. Cabral-Neto","doi":"10.1016/j.chemgeo.2024.122392","DOIUrl":"10.1016/j.chemgeo.2024.122392","url":null,"abstract":"<div><p>Kimberlites and related rocks are the focus of research and exploration in the Alto Paranaiba Igneous Province (APIP; Brazil) due to their potential correlation with adjacent diamond fields. New U-Pb perovskite ages were obtained using recommended protocols for error propagation and data interpretation. Despite the utility of perovskites for dating, their incorporation of significant common-Pb (common-Pb of new APIP data: 52–84 % for <em>in situ</em> analyses, 75–95 % for TIMS concentrate analyses) limits the age resolution of this dating approach. Consequently, the APIP U-Pb ages neither confirm nor discredit previously proposed geodynamic models that invoke age progression or distinct magmatic episodes. Comparing the new ID-TIMS and LA-ICP-MS ages of the same intrusions, the LA-ICP-MS data have lower uncertainties, largely due to accessing a greater spread in common-Pb, improving regressions, and tend to yield older ages. For perovskite grains collected from weathering profiles, we found evidence of Pb-loss. This process leads to higher uncertainties in individual analyses, increased data scatter, and consequently higher uncertainties in age estimates. For fresh samples with different degrees of crustal contamination from a single intrusion, we found an indication of some variability in ²⁰⁷Pb/²⁰⁶Pb and ²³⁸U/²⁰⁶Pb ratios of the perovskite data, with a tendency towards older ages for more contaminated sample. For almost fresh intrusions with geochemically and isotopically similar mantle sources, related to the same event and in a close geographic area, we prefer to use a unique local ²⁰⁷Pb/²⁰⁶Pb ratio as anchoring for each Tera-Wasserburg plot. This approach is particularly preferred when perovskite data of an intrusion are too clustered and the ²⁰⁷Pb/²⁰⁶Pb ratio from the unanchored T-W differs from that predicted from theoretical Pb-isotope evolution model. Despite the high-common Pb in APIP perovskite crystals, our new data using these strategies clearly indicate that APIP magmatism is restricted to the Cretaceous, with most cases crystallized in Upper Cretaceous, but some from Early Cretaceous, such as the diamondiferous occurrence of Catalão-1b (120.6 ± 6.7 Ma). Different triggers of APIP magmatism are related to both episodes, mainly attributed to supercontinent break-up stages.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122392"},"PeriodicalIF":3.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142230662","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":"LA-ICP-Q-MS/MS ReOs geochronology: A comparison of N2O and CH4 reaction gases","authors":"Alexander Simpson ,&nbsp;Stijn Glorie ,&nbsp;Sarah Gilbert ,&nbsp;Renée Tamblyn ,&nbsp;Michael G. Gadd","doi":"10.1016/j.chemgeo.2024.122384","DOIUrl":"10.1016/j.chemgeo.2024.122384","url":null,"abstract":"<div><p>The <em>Re</em><img>Os isotope system can directly date sulphide formation, making it useful for ore deposit studies. Recent work has demonstrated that laser ablation inductively coupled tandem mass spectrometry (LA-ICP-MS/MS) can be used to effectively separate ¹⁸⁷Re from ¹⁸⁷Os during analysis by reacting Os with CH₄ gas, allowing for in situ <em>Re</em><img>Os age determination of molybdenite. However, the age calculation often requires a significant interference correction of ¹⁸⁷ReCH₂⁺ on ¹⁸⁷OsCH₂⁺. Here, we demonstrate that N₂O gas is a viable alternative reaction gas for in situ <em>Re</em><img>Os geochronology. In this new method, Os forms a tetra-oxide complex, while Re shows very low reactivity with the N₂O reaction gas (∼0.15 %), reducing the isobaric interference correction requirement relative to the CH₄ method. We compare results from both reaction gases across a range of molybdenite samples of different ages (spanning ca. 1700–300 Ma), demonstrating that the N₂O method achieves greater precision and accuracy for young molybdenite samples (ca. 300 Ma) compared to CH₄. In addition, we demonstrate that in situ <em>Re</em><img>Os is capable of dating high-Re pyrite (i.e., &gt;10 ppm).</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122384"},"PeriodicalIF":3.6,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142238848","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":"Organic matter the major sink of redox-sensitive trace elements in Upper Devonian black shale","authors":"Omid H. Ardakani ,&nbsp;Michael G. Gadd ,&nbsp;Makram Hedhli ,&nbsp;Duane Petts ,&nbsp;Gavin Jensen","doi":"10.1016/j.chemgeo.2024.122385","DOIUrl":"10.1016/j.chemgeo.2024.122385","url":null,"abstract":"<div><p>The Bakken Formation is a hydrocarbon-rich, metalliferous shale with subordinate sandstone and limestone that was deposited in the Williston Basin in Canada and the USA. Deposition of the Bakken Formation spanned the Devonian-Carboniferous boundary – a key interval in Earth's history representing profound biotic and geochemical changes in the terrestrial and marine realms, leading to deposition of metal-rich shales in the lower part of the sequence. Most studies of metal enrichment in the Bakken Formation have focused solely on the bulk rock litho-geochemistry, with little attention given to the organic matter, mineralogical, and diagenetic controls on metal sequestration and distribution.</p><p>The current study combined bulk sulfur isotope and litho-geochemistry, along with reflected light and scanning electron microscopy (SEM) petrography to elucidate organic matter and mineralogical controls on trace element geochemistry. We have also used laser ablation-inductively couple plasma-mass spectrometry (LA-ICP-MS) to quantitatively assess the distribution of trace elements among different mineral phases, shale matrix, and organic matter.</p><p>We show that sphalerite is the main zinc host, and that sphalerite sequesters Cu, Ga, Ge, and Cd within its crystal structure. Pyrite is the main Fe mineral and has typical abundances for sedimentary pyrite, however, the total bulk rock abundances of Ni, Mo, and Cu cannot be accounted for in pyrite alone, and indeed, are present within early mature organic matter in the shale matrix. Vanadium (V) is associated with organic carbon but is also high in aluminosilicates within the matrix. Collectively, this study demonstrates the need for detailed petrographic analyses even in seemingly monotonous black shales.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122385"},"PeriodicalIF":3.6,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167668","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}