Chemical Geology最新文献

{"title":"Trace-metal hyper-enrichment in Tremadocian black shales of the Baltic Palaeobasin linked to transgression and ultra-slow sedimentation rates","authors":"Mawo Ndiaye ,&nbsp;Sophie Graul ,&nbsp;Merlin Liiv ,&nbsp;Toivo Kallaste ,&nbsp;Thomas J. Algeo ,&nbsp;Rutt Hints","doi":"10.1016/j.chemgeo.2025.122910","DOIUrl":"10.1016/j.chemgeo.2025.122910","url":null,"abstract":"<div><div>Determining the local versus global influence on the metallogeny of redox-sensitive trace-metal-enriched black shales remains challenging despite extensive geochemical research in related topics. A set of local triggers or modifiers of syngenetic metal enrichment, still poorly understood, impedes the ability to adequately predict the potential distribution of metal resources. This study of the Lower Ordovician Türisalu Formation examines the stratigraphic trends of Mo and U isotopes in Mo-U-V hyper-enriched thin transgressive black shales and associated beds from the inner shelf of the Baltic Palaeobasin (Aseri PH012B drillcore, NE Estonia) to reveal underlying connections between isotopic fractionation, palaeoenvironmental changes, and metal enrichment processes. Twenty samples from the basal 28-cm-thick Unit I and overlying 66-cm-thick Unit II were analysed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and interpreted within a recently developed high-resolution chemostratigraphic framework. The tested samples yielded variable δ⁹⁸Mo (from −0.89 to +2.03 ‰) and δ²³⁸U values (from −0.27 to +0.52 ‰). Unit I, which is Mo-enriched, yielded the highest δ²³⁸U and lowest δ⁹⁸Mo values, whereas Unit II, which is U-enriched, is marked by sharply lower δ²³⁸U values. This black shale succession was deposited under a prolonged sea-level transgression. Variations in δ⁹⁸Mo and δ²³⁸U suggest that the mechanism of Mo and U sequestration changed depending on facies during the transgression. Metal enrichment was influenced by a combination of ultra-slow sedimentation rates (0.6–1.0 mm kyr⁻¹), relative sea-level changes, and shallow redox stratification maintained in part by surface heating under a super-greenhouse climate. Extremely slow sedimentation prolonged seawater-sediment interactions, facilitating diffusion-controlled uptake of U and Mo under euxinic conditions. Landward expansion of the subpycnoclinal oxygen-depleted watermass and related redox shifts from suboxic to euxinic conditions near the seafloor drove the selective hyper-enrichment of Mo, and U. Isotopic trends highlight efficient Mo sequestration in euxinic settings likely aided by recycling of Fe<img>Mn near redoxcline and U hyper-enrichment under Mo-depleted watermasses.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122910"},"PeriodicalIF":3.6,"publicationDate":"2025-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144230874","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":"Solving the sulfur isotope discrepancy in Central America","authors":"Ally Peccia ,&nbsp;Terry Plank ,&nbsp;Shuo Ding ,&nbsp;Louise Bolge ,&nbsp;Alessandro Aiuppa ,&nbsp;Salvatrice Vizzini ,&nbsp;Cecilia Tramati ,&nbsp;Zoltán Taracsák ,&nbsp;David M. Pyle ,&nbsp;Tamsin A. Mather","doi":"10.1016/j.chemgeo.2025.122901","DOIUrl":"10.1016/j.chemgeo.2025.122901","url":null,"abstract":"<div><div>Sulfur has considerable leverage on the redox budget of subducted materials due to its presence as both sulfide (S²⁻) and sulfate (S⁶⁺). Recent work has revealed a discrepancy: arc magmas have positive δ³⁴S values, while much of the S entering subduction zones should be hosted in pyrite, which is likely to have negative sulfur isotopic values. To address this discrepancy, we focus on the Central American subduction zone, where previous work has revealed positive δ³⁴S values in parental arc magmas. We report the first comprehensive study of the sedimentary S input to any subduction zone with S concentration and sulfur-isotopic measurements of ODP Site 1040 sediments. Sedimentary S input for Central America is greater than previously thought (1.71 ± 0.38 × 10⁸ mol S/yr/100 km), although insufficient to supply the S output from the arc without contributions from subducting oceanic crust. Furthermore, ~90 % of the sedimentary S input is hosted in pyrite, leading to a bulk sedimentary δ³⁴S of −19.5 ‰. In assessing the mass balance for Central America, we find that selective removal of sulfate does not provide enough S to support arc output and thus, additional S must be mobilized by the oxidation of pyrite with several per mil rock-fluid δ³⁴S fractionation to positive values. Our results agree with existing evidence that subduction zones act as efficient redox reactors, with oxidized portions of the slab (e.g., altered oceanic crust) providing the oxidizing power to supply sulfate to the arc, while a reduced and ³²S-enriched complement sinks into the deeper mantle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122901"},"PeriodicalIF":3.6,"publicationDate":"2025-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144254910","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 effects of experimental heating and alteration on melt inclusions in magmatic zircon","authors":"Joseph P. Gonzalez ,&nbsp;Kouki Kitajima ,&nbsp;Tyler B. Blum ,&nbsp;Kei Shimizu ,&nbsp;Renat R. Almeev ,&nbsp;William O. Nachlas ,&nbsp;Sandra L. Kamo ,&nbsp;Alexander V. Sobolev ,&nbsp;Francois Holtz ,&nbsp;Michael J. Spicuzza ,&nbsp;Chloe Bonamici ,&nbsp;John W. Valley","doi":"10.1016/j.chemgeo.2025.122900","DOIUrl":"10.1016/j.chemgeo.2025.122900","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Melt inclusions (MIs) in zircon can preserve information on the evolution of magmas. However, MIs in plutonic zircons are typically devitrified, consisting of multiple phases that must be remelted to obtain a homogeneous glass for reconstruction of melt composition and magma processes. We undertake a systematic investigation of melt inclusions in zircons from a ∼ 3300 Ma xenolith of tonalite gneiss from the Barberton Greenstone belt, a well-studied section of cratonic lithosphere with components dating back to 3500 Ma. To better understand the influence of experimental heating on zircon and MI chemistry, multiple aliquots of zircons were heated in an internally heated pressure vessel at 0.4 GPa and temperatures ranging from 900 to 1200 °C (T&lt;sub&gt;step&lt;/sub&gt; = 100 °C). Homogeneous MIs in domains with low degrees of radiation damage and isolated from cracks in the zircon were found by examination of &gt;5000 zircons by SEM (CL, BSE). Oxygen isotopes (δ&lt;sup&gt;18&lt;/sup&gt;O), OH/O ratios, U-Pb isotopes, trace and rare earth element (TREE) concentrations in zircon, along with δ&lt;sup&gt;18&lt;/sup&gt;O, H&lt;sub&gt;2&lt;/sub&gt;O contents, and major element compositions in glassy MIs were measured by SIMS and EPMA. Investigated MIs have granitic compositions with 67 to 81 wt% SiO&lt;sub&gt;2&lt;/sub&gt;. Both heated and unheated host zircon possess statistically identical and uniform δ&lt;sup&gt;18&lt;/sup&gt;O values of 6.02 ± 0.45 ‰ (2SD), while OH/O ratios systematically decrease with increasing temperature of laboratory heating. Inclusion textures (BSE contrast homogeneity) and composition (H&lt;sub&gt;2&lt;/sub&gt;O, δ&lt;sup&gt;18&lt;/sup&gt;O) suggest that experimental heating at 1100 °C was the most successful in recovering initial MI compositions. Inclusions in lower temperature experiments either did not homogenize (900 °C) or are rarely homogenized (1000 °C), while those at higher temperature (1200 °C) are systematically dehydrated. Twenty-two hydrous MIs from the 1100 °C experiment have 3.1–11.5 wt% H&lt;sub&gt;2&lt;/sub&gt;O and an average δ&lt;sup&gt;18&lt;/sup&gt;O of 7.5 ± 0.9 ‰. Four zircons have a Δ&lt;sup&gt;18&lt;/sup&gt;O(MI-Zrn) fractionation inconsistent with equilibration at magmatic temperatures. In general, δ&lt;sup&gt;18&lt;/sup&gt;O values and TREE concentrations measured in the zircons heated at 1100 °C show consistent behavior with unannealed zircons, indicating these systems are not significantly disturbed on the μm-scale during heating experiments, and support the use of anomalous TREE concentrations/patterns as indicators of alteration. These measurements combined with Δ&lt;sup&gt;18&lt;/sup&gt;O(MI-Zrn) identify the MI-zircon pairs that are unlikely to represent the melt composition at the time of entrapment. Ti-in-zircon temperatures (αSiO&lt;sub&gt;2&lt;/sub&gt; = 1, αTiO&lt;sub&gt;2&lt;/sub&gt; = 0.3) and rhyoliteMELTS thermometry of the unaltered MI-zircon pairs return similar temperature ranges of 762–833 °C and 750–865 °C respectively, and combined with the granitic major element compositions, suggest that zircons crystallized relatively late during melt fracti","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122900"},"PeriodicalIF":3.6,"publicationDate":"2025-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144220821","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":"Promises and pitfalls of source terrane prediction from inclusions in detrital zircon","authors":"Elizabeth A. Bell ,&nbsp;Heather M. Kirkpatrick ,&nbsp;T. Mark Harrison","doi":"10.1016/j.chemgeo.2025.122899","DOIUrl":"10.1016/j.chemgeo.2025.122899","url":null,"abstract":"<div><div>Understanding the relationship between the assemblage of mineral inclusions trapped by an igneous zircon suite and the composition of the host magma is complicated by processes that preclude simple relationships between, for example, the relative proportions of modal mineral inclusions (e.g., quartz, alkali feldspar, and plagioclase; QAP) and the degree of magma differentiation. However, apatite and ferromagnesian inclusion abundances can be approximately related to the SiO₂ content in some magmas, potentially allowing for broad inferences of source rock composition from detrital zircon mineral inclusion suites. This study presents mineral inclusion assemblages in igneous zircon from a wide range of magma compositions, tectono-magmatic settings, and geographic locations to better determine the correlation between major inclusion phases and source rock chemistry. We find that the relationship between apatite and whole rock SiO₂ is strongly dependent on the aluminosity (as shown by A/CNK) of the source rock, with peraluminous and metaluminous rocks showing opposite trends. For inclusion assemblages containing less than about 30–40 % apatite, discrimination of highly silicic peraluminous from mafic-intermediate metaluminous granitoid sources is possible. Metaluminous samples display a broad increase in whole rock phosphate content with increasing apatite inclusion abundance, potentially allowing estimation of lower limits on protolith phosphate abundance. The ratio of ferromagnesian to late-crystallizing inclusions exceeds 0.5 mostly for mafic-intermediate samples, with some exceptions. Inclusion phases concentrating highly incompatible trace elements exceed 5 % of the inclusion suite only in highly silicic (&gt;70 % SiO₂) granites. However, there is no discernable relationship between QAP and whole rock chemistry, with inclusion QAP from compositionally diverse magmas clustering in a similar region of the QAP diagram. Application of these observations to several first-generation sediments derived from granitoid terranes suggests that apatite abundance, the ratio of ferromagnesian to late-crystallizing silicate inclusions, and trace elements can help select between peraluminous vs. metaluminous sources and help to distinguish mafic-intermediate from highly silicic source rocks. This could have wide applicability to using the detrital zircon record to infer petrogenetic provenance.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122899"},"PeriodicalIF":3.6,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144212742","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":"Boron isotope evidence for Ordovician-Silurian Transition postglacial marginal marine salinity with implications for redox conditions and biotic recovery","authors":"Jingyu Zhang ,&nbsp;Wei Wei ,&nbsp;Jun Shen ,&nbsp;Jingbo Nan ,&nbsp;Yi Zhong ,&nbsp;Xiaojie Fan ,&nbsp;Yanan Zhang ,&nbsp;Qingsong Liu ,&nbsp;Lin Chen ,&nbsp;Leslie J. Robbins ,&nbsp;Kurt O. Konhauser","doi":"10.1016/j.chemgeo.2025.122891","DOIUrl":"10.1016/j.chemgeo.2025.122891","url":null,"abstract":"<div><div>Anoxic conditions in marginal marine settings play a critical role in paleoceanographic and paleoecological studies. Understanding the mechanisms underpinning anoxia requires insights into watermass conditions in the study area. While salinity is a fundamental property of water, proxies for reconstructing paleosalinity and its influence on redox conditions in ancient systems are often overlooked. To illustrate this, we focus on the Yangtze Marginal Sea during the Ordovician-Silurian Transition (OST), specifically the Early Silurian postglacial anoxia. We utilized proxy records for salinity and redox conditions archived in organic-rich cherts and black shales deposited in the Yangtze Block, South China, between ca. 447.62–438.49 million years ago. Our study is the first to report the variation in bulk boron (B) isotopic (δ¹¹B) values during the OST. Analyzing paleosalinity data, such as δ¹¹B and B/gallium (Ga) along with redox indicators, such as molybdenum (Mo), uranium (U), and vanadium (V), provides constraints on the continuous vertical hydrological variability across the central Yangtze Marginal Sea. Our analysis suggests that the watermass in the study area was close in salinity to seawater during the Late Ordovician due to a well-established connection with the ocean. This was followed by a decline in salinity in the Early Silurian resulting from an influx of glacial melt water. Postglacial warming-induced freshwater input and sea-level change subsequently contributed to strong seawater stratification and elevated primary productivity. This disruption in the exchange between shallow and deep waters led to the development of anoxia in the Early Silurian Yangtze Sea, a phenomenon that has significantly impacted Earth's evolutionary history. Our study provides fresh insights into the Late Ordovician Mass Extinction event and the subsequent biotic recovery. In addition, we underscore the importance of integrating redox analyses with salinity reconstructions in explaining the mechanisms of anoxic environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122891"},"PeriodicalIF":3.6,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144204609","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":"Variable sampling of distinct ancient mantle domains by the Iceland mantle plume over its 62 Ma eruption history","authors":"Bradley J. Peters ,&nbsp;Andrea Mundl-Petermeier ,&nbsp;Lotte M. Larsen","doi":"10.1016/j.chemgeo.2025.122882","DOIUrl":"10.1016/j.chemgeo.2025.122882","url":null,"abstract":"<div><div>Mantle plumes produce geochemically diverse lavas over their lifetime, some of which preserve compositions derived from Earth's earliest events. Most studies of plume-related lavas in this context have focused on modern ocean island basalts (OIB), primarily because these are relatively free of geochemical influences from crustal assimilation that may obscure the compositions of their mantle sources. Notwithstanding, there is no a priori reason why a mantle plume should consistently tap the same mantle domain over geological time, which means that early plume-related magmas may preserve a perspective on the early Earth that complements that of modern OIB. This study expands a previous investigation of picrites with high ³He/⁴He ratios, a likely indicator for ancient, less degassed mantle domains, with new ¹⁴²Nd/¹⁴⁴Nd (<em>n</em> = 7) and ¹⁸²W/¹⁸⁴W (<em>n</em> = 2) data that, together with literature data, comprise a detailed short-lived radiogenic isotope database for the Iceland hotspot. Heterogeneous ¹⁴²Nd/¹⁴⁴Nd ratios in lavas from different stages of the Iceland plume imply that it has tapped a variety of early-formed mantle domains, in particular that the head of the Iceland plume rapidly shifted between tapping domains with distinct histories. This behavior may reflect both the higher buoyancy flux of plume heads as well as the petrological and physical properties of these domains. Together, these data highlight the importance of developing comprehensive, high-precision short-lived radiogenic isotope datasets for all stages of plume magmatism, since the geochemical compositions of modern OIB reflect only one set of mantle domains that can be potentially tapped by mantle plumes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122882"},"PeriodicalIF":3.6,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144261960","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":"Increased oxygenation during the peak Cambrian Explosion: Evidence from global carbon isotope records","authors":"Dongping Hu ,&nbsp;Lilin Sun ,&nbsp;Yilun Xu ,&nbsp;Xingliang Zhang ,&nbsp;Xiaolin Zhang ,&nbsp;Yanan Shen","doi":"10.1016/j.chemgeo.2025.122890","DOIUrl":"10.1016/j.chemgeo.2025.122890","url":null,"abstract":"<div><div>The early Cambrian is characterized by the rapid emergence of diverse animal lineages within a relatively short time interval, known as the “Cambrian Explosion”. During this period, ecosystems dominated by metazoans were established, with an increase in morphological and ecological complexity of metazoan phyla. While enhanced oxygenation of subsurface environments has often been suggested as a primary driver of this unprecedented evolutionary event, the relative magnitude and underlying mechanisms of changes in O₂ levels remain elusive. Here, we integrate high-resolution carbonate and organic carbon isotope records (δ¹³C_carb and δ¹³C_org) compiled from 17 globally distributed successions to elucidate carbon‑oxygen cycle dynamics during the Cambrian late Stage 2 to Stage 3, corresponding with the apex of Cambrian Explosion. Our dataset reveals a synchronous positive Δ¹³C (δ¹³C_carb–δ¹³C_org) excursion in phase with the CARE (historically termed as the Cambrian Arthropod Radiation Isotope Excursion), a significant excursion in both δ¹³C_carb and δ¹³C_org records, which is interpreted as indicative of increased organic carbon burial in marine sediments. Numerical modelling based on the O₂-dependent fractionation of C-isotopes during oxygenic photosynthesis suggests that this carbon isotope shift corresponds to a substantial increase in atmospheric O₂ levels. Independent O₂ estimates derived from traditional C-isotope mass balance models and the total organic carbon (TOC) contents of various sedimentary facies further corroborate a rise in atmospheric O₂ caused by enhanced organic matter burial. Our findings reveal a broad temporal correspondence between inferred rising O₂ levels and the acme of Cambrian Explosion, suggesting that increased oxygen availability may have provided a permissive environmental backdrop for the diversification of marine metazoans and the establishment of modern-like marine ecosystems during the early Cambrian.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122890"},"PeriodicalIF":3.6,"publicationDate":"2025-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144189821","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":"Contrasting PGM assemblages in the Verkh-Neivinsk and Alapaevsk chromite deposits: Implications for the source of the HSE in the Urals ophiolite-type massifs","authors":"Kreshimir N. Malitch ,&nbsp;Igor S. Puchtel ,&nbsp;Inna Yu. Badanina ,&nbsp;Valery V. Murzin","doi":"10.1016/j.chemgeo.2025.122881","DOIUrl":"10.1016/j.chemgeo.2025.122881","url":null,"abstract":"<div><div>In order to gain further insights into the origin of platinum-group minerals (PGM) and the source of the highly siderophile elements (HSE: Os, Ir, Ru, Pt, Pd, Re) in the chromite deposits associated with the Urals ophiolite-type massifs, we carried out a mineralogical, HSE abundance, and Pt-<em>Re</em>-Os isotope study of chromitites and PGM from the Verkh-Neivinsk and Alapaevsk dunite-harzburgite massifs in the Middle Urals. The chromitites are characterized by negatively-sloped Bulk Silicate Earth (BSE)-normalized HSE patterns, consistent with the predominance of PGM of the Ir-group platinum-group elements (PGE), i.e., Os-Ru-Ir alloys and Ru<img>Os sulfides, over the PGM of the Pd-group PGE, i.e., stibiopalladinite and geversite. These two groups of PGM are interpreted to represent the primary and secondary mineral assemblages, respectively. The observed HSE patterns in the studied chromitites are typical of those formed in supra-subduction zone (SSZ) settings. The near-chondritic average initial γ¹⁸⁷Os and μ¹⁸⁶Os values in the chromitites and PGM of the Verkh-Neivinsk massif indicate that its HSE budget was derived from the convecting upper mantle source that evolved with time-integrated near-chondritic Re/Os and Pt/Os ratios. These features are also typical of the sources of most Archean and Proterozoic mafic-ultramafic rocks worldwide. In contrast to the Verkh-Neivinsk massif rocks, the Alapaevsk massif chromitites show radiogenic initial γ¹⁸⁷Os values indicating evolution of the mantle source of these rocks with a supra-chondritic time-integrated Re/Os ratio. This long-term enrichment in Re relative to Os could be the result of interaction of the source peridotites with ¹⁸⁷Os-enriched melts derived from ancient recycled oceanic crust.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122881"},"PeriodicalIF":3.6,"publicationDate":"2025-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144204610","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":"Spatial heterogeneity in salinity and redox dynamics during the Ordovician-Silurian transition: Multi-proxy constraints on the Late Ordovician Mass Extinction mechanisms","authors":"Yangbo Lu ,&nbsp;Fang Hao ,&nbsp;Yiquan Ma ,&nbsp;Wei Wei ,&nbsp;Shen Jun ,&nbsp;Yuxuan Wang ,&nbsp;Qiyang Gou","doi":"10.1016/j.chemgeo.2025.122860","DOIUrl":"10.1016/j.chemgeo.2025.122860","url":null,"abstract":"<div><div>The Ordovician-Silurian transition (OST; ∼448–443 Ma) was marked by the Hirnantian glaciation, rapid climatic shifts, and the Late Ordovician Mass Extinction (LOME). While redox changes and ice-sheet dynamics have been widely studied, the role of salinity-pH-redox feedbacks in modulating extinction mechanisms remains poorly constrained. Here, we present a high-resolution multi-proxy dataset (δ¹¹B, Sr/Ba, B/Ga, redox-sensitive trace metals, and iron speciation) from middle- and outer-shelf successions of the Upper Yangtze Sea, South China, to unravel spatial-temporal feedbacks between glacial meltwater, ocean connectivity, and biogeochemical cycles. Our results reveal pronounced salinity stratification in the middle-shelf (brackish to freshwater conditions, B/Ga &lt;4, δ¹¹B &lt; −13 ‰) driven by pulsed meltwater inputs during glacial retreat, which amplified euxinic wedges (Mo &gt; 64 ppm, Fe_Py/Fe_HR &gt; 0.8) through sulfate limitation and pH-driven boron adsorption. In contrast, the outer shelf maintained stable marine salinity (B/Ga ∼6.2, δ¹¹B ∼ −8 ‰) and suboxic conditions (Mo &lt; 25 ppm, Fe_Py/Fe_HR &lt; 0.35), acting as refugia for benthic fauna. Crucially, boron isotopes unveil pH-salinity coupling during icehouse collapse−freshwater dilution of the middle-shelf amplified H₂S toxicity by reducing carbonate buffering capacity, while open-marine connectivity stabilized outer-shelf pH. The first LOME pulse was initiated by glacial expansion-driven cooling and habitat contraction, with its severity amplified by pulsed meltwater-induced mid-shelf euxinia, whereas the second pulse was linked to post-glacial transgressive euxinia amplified by sulfate influx. This study establishes paleosalinity as a critical amplifier of climate-biogeochemical feedbacks, demonstrating how spatial ocean connectivity regulated extinction selectivity through salinity stratification. Our findings provide a novel mechanistic framework linking icehouse dynamics to marine ecosystem collapse, with implications for understanding hypoxia expansion in modern warming oceans.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122860"},"PeriodicalIF":3.6,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144148100","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":"Formation of early continental crust by remelting of hydrothermally altered oceanic crust: Evidence from potassium and oxygen isotopes","authors":"Shao-Bing Zhang ,&nbsp;Liang Zhang ,&nbsp;Xing-Yu Yao ,&nbsp;Zhen-Xin Li ,&nbsp;Xiaoqiang Li ,&nbsp;Guilin Han ,&nbsp;Yong-Fei Zheng","doi":"10.1016/j.chemgeo.2025.122888","DOIUrl":"10.1016/j.chemgeo.2025.122888","url":null,"abstract":"<div><div>Early continental crust mainly consists of tonalite, trondhjemite, and granodiorite (TTG), yet the origin of TTG rocks has been controversial with respect to the operation of plate tectonics. It is of critical importance, therefore, to resolve whether Archean TTG rocks formed from thick oceanic crust generated at spreading ridges or from oceanic plateaus in intraplate settings. Here, we use K and O isotopes to trace the source of Archean TTG rocks. The rationale is that the hydrothermal alteration of oceanic crust during its growth at mid-ocean ridges would result in correlated changes in their δ⁴¹K and δ¹⁸O values. A series of Archean TTG rocks with zircon U<img>Pb ages of 3.45–2.85 Ga and zircon δ¹⁸O values ranging from 5.3 ‰ to 7.4 ‰ from the Kaapvaal Craton of South Africa and the Yangtze Craton of South China were analyzed for K isotope compositions. These TTG rocks show variable δ⁴¹K values from −0.58 ‰ to −0.19 ‰. The δ⁴¹K values show weakly positive correlations with Na/K, Eu/Eu* and Sr/Y ratios, suggesting that accumulation of plagioclase may lead to the increase of K isotope ratios because plagioclase is enriched in heavier K isotopes. After correcting for the effect of plagioclase accumulation on samples with high Eu/Eu* and Sr/Y ratios, a negative correlation is obtained between whole-rock δ⁴¹K and zircon δ¹⁸O values. This suggests that the source of Archean TTG rocks should be the oceanic crust that had experienced hydrothermal alteration. Given that hydrothermal alteration is pervasive near mid-ocean ridges but minimal in oceanic plateaus, we propose that the source of Archean TTG rocks was thick oceanic crust generated at spreading mid-ocean ridges rather than oceanic plateau basalts in intraplate settings. The most plausible geodynamic setting for the formation of early continental crust, therefore, is at convergent plate margins, where thick seawater-altered oceanic crust would be subducted or stacked and partially melted to produce TTGs.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122888"},"PeriodicalIF":3.6,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144204608","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}