Chemical Geology最新文献

{"title":"Controls over cesium and rubidium contents of sedimentary rocks","authors":"Jan Środoń,&nbsp;Karol Jewuła","doi":"10.1016/j.chemgeo.2025.122745","DOIUrl":"10.1016/j.chemgeo.2025.122745","url":null,"abstract":"<div><div>In nature, Cs and Rb follow K, which is a much more abundant but chemically similar element. Data for these elements and their mineral carriers were acquired by the combined ICP-OES/ICP-MS (Inductively Coupled Plasma Optical Emission Spectroscopy/Inductively Coupled Plasma Mass Spectrometry) techniques and quantitative XRD (X-ray diffraction), supplemented by multivariate regression analysis, in order to detect controls over cesium and rubidium contents of clastic sedimentary rocks. The sample material comprised clay fractions of bentonites and paleosols, dominated by illite-smectite, and bulk mudstones, sandstones, paleosols, bentonites, basalts, and tuffs from several European basins, ranging from the Proterozoic to Miocene. Results indicate that Rb and Cs contents of clastic sedimentary rocks, and of mudstones in particular, are controlled by the relative concentrations of K-feldspar, micas, and illite-smectite, thus detrital and late diagenetic components of these rocks, and concentrations of Rb and Cs in these minerals. The concentrations of Cs in some illite-smectites, significantly higher than upper continental crust (UCC) averages, indicate hydrothermal alteration or, in case of paleosols and bentonites, can be inherited from anomalous parent rocks. K, Cs, and Rb contents of normal mudstones (unaffected by the hydrothermal fluids or anomalous parent rocks), whether marine or freshwater, are close to the UCC values. In normal mudstones of our collection, feldspars contain 0 to 22 % of Cs and 0 to 41 % Rb, micas 0 to 57 % Cs and 0 to 48 % Rb, and illite-smectite 32 to 100 % Cs and 17 to 100 % Rb, both mostly non-exchangeable and ‘fixed’ in the illite structure. The collected data do not support the use of Rb/K as a paleosalinity proxy and call for careful use of Rb and Cs in chemostratigraphy. The presented relationships indicate that Cs/K and Rb/K ratios in illite-smectite are controlled by the chemistry of fluids, which promote crystallization of illite during burial. Normal diagenetic fluids precipitate illite with, on average, 2.4 times more Cs and 70 % more Rb than the UCC values. In “abnormal” illites, the average Cs and Rb values are 18 and 2.5 times higher than the UCC, respectively. It is confirmed that thin illite crystals have higher Rb/K and Cs/K ratios, tentatively explained by the “supply and demand” mechanism: high ratio between the concentrations of Rb and Cs in pore fluids and the volume of neoformed illite at the beginning of illite crystallization. Major sources of Cs in diagenetic pore fluids in sedimentary basins are detrital micas or hydrothermal fluids invading those basins. The impact of Cs and Rb sorption at illite and mica wedges and/or frayed edges on the total budgets of these elements cannot be evaluated from our data.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122745"},"PeriodicalIF":3.6,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143735307","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":"Subducted sediment recycling and fractional crystallization of the Toba volcanic system constrained by plagioclase geochemistry","authors":"Meng-Hao Gao ,&nbsp;Ping-Ping Liu ,&nbsp;Dian-Bing Wang ,&nbsp;Xi-Jun Liu ,&nbsp;Gui-Bin Zhang ,&nbsp;Cheng Xu","doi":"10.1016/j.chemgeo.2025.122740","DOIUrl":"10.1016/j.chemgeo.2025.122740","url":null,"abstract":"<div><div>Understanding the processes and contributions of various sources to arc magmas, originating from the mantle wedge, is crucial for unraveling the complex interactions between crust and mantle in subduction zones. Plagioclase with a prolonged crystallization history serves as a key mineral in studying sources of magma and its evolution history. This study presents in-situ trace elements and Pb isotopes of plagioclase in basalts and rhyolites, and in-situ trace elements of clinopyroxene in basalts of the Toba volcanic system on the Sunda arc, Sumatra. The rhyolites from the ∼75 ka Youngest Toba tuff (YTT) and the basalts from the post-YTT Sipisupisu lave dome are cogenetic and share the same lower crustal magma reservoir. Some of the plagioclase crystals in rhyolites contain a sieved core with high Ca (An = 78 to 85 %) and high Fe contents (∼4800 ppm) that are not in equilibrium with the rhyolitic melts, but are compositionally similar to plagioclase in the cogenetic basalts. Since clinopyroxene in the basalts has negative Eu anomalies and crystallized at lower crustal depth (∼13 to 25 km deep), it can be inferred that plagioclase with positive Eu anomaly could have crystallized simultaneously with clinopyroxene at similar depth. Therefore, we infer that the high-Ca plagioclase cores were antecrysts crystallized from more primitive melts at lower crustal depth and then transported to the upper crust by more evolved melts. Lead isotopic compositions of the plagioclase cores are relatively homogeneous (²⁰⁶Pb/²⁰⁴Pb = 18.94–19.02, ²⁰⁷Pb/²⁰⁴Pb = 15.81–15.84, ²⁰⁸Pb/²⁰⁴Pb = 39.61–39.74) and plot between those of the depleted MORB mantle (DMM) and the upper crust/subducted sediments. The fact that plagioclase cores crystallized at lower crustal depth were endowed with an upper crustal Pb isotopic signature indicates that upper crustal materials were probably added to the mantle source of the Toba volcanic system via subduction. Considering that all the plagioclase crystals of the Toba volcanic system have similarly high ²⁰⁷Pb/²⁰⁴Pb ratios close to and slightly beyond that of the subducted Nicobar Fan sediments, the primary basaltic melts of the Toba volcanic system may have been enriched in radiogenic Pb isotopes by addition of the subducted sediments to the mantle wedge. The mantle-derived basaltic melts with highly radiogenic Sr and Pb isotopic compositions further evolve through assimilation and fractional crystallization (AFC) in the crust to form andesitic-rhyolitic melts. Using in-situ Pb isotopes of plagioclase, this study exemplifies a credible means to discern processes of sediment addition to the mantle wedge and crustal assimilation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122740"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666527","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":"Stratified distribution of recycled components in the mantle of the South China Sea unveiled through magnesium isotopes","authors":"Zhen-Min Ge ,&nbsp;Xiao-Long Huang ,&nbsp;Fan Yang ,&nbsp;Yang Yu ,&nbsp;Guan-Hong Zhu ,&nbsp;Le Zhang ,&nbsp;Yu-Xin Cai ,&nbsp;Guo-Hong Sun","doi":"10.1016/j.chemgeo.2025.122742","DOIUrl":"10.1016/j.chemgeo.2025.122742","url":null,"abstract":"<div><div>Plate subduction is pivotal in creating mantle heterogeneity and facilitating deep material recycling. However, the precise origins, input processes, and distribution of recycled components in the upper mantle remain poorly constrained by natural observations. Compared to large ocean basins, marginal sea basins are more likely to preserve detailed information about recycled components due to their close spatial relationship with subduction processes, relatively smaller size, and shorter evolutionary timescales. In this study, we present new Mg–Sr–Pb isotope data, in conjunction with previously published major and trace element analyses, as well as Nd–Hf isotope data for mid-ocean ridge basalt (MORB) samples from Holes U1431E, U1433B, and U1434A of the International Ocean Discovery Program (IODP) Expedition 349 in the South China Sea (SCS), a marginal sea basin in the Western Pacific with a complex subduction history. MORBs from the SCS exhibit a wide range of Mg isotope ratios (δ²⁶Mg = −0.32‰ to 0.05‰, with an average of −0.16‰), with some samples displaying lower or higher values compared to the average mantle (δ²⁶Mg = −0.25 ± 0.04‰). These variable Mg isotope compositions likely originate from mantle sources affected by subduction-related metasomatism at varying depths, given the limited impact of post-eruptive alteration, diffusion, and high-temperature magmatic processes. The heavy Mg isotopes in the SCS basalts can be attributed to metasomatism by serpentinite components related to surrounding subduction restricted to the shallow mantle (&lt;200 km). Conversely, MORBs with lighter Mg isotopes also show high Hf/Hf* (&gt;1) and low CaO/Al₂O₃ values, which were derived from recycled carbonated eclogites formed after decarbonization of residual subducted carbonate-bearing sediments in the upper mantle at depths exceeding 200 km or within the mantle transition zone (410–660 km). The southwestern subbasin records more information about serpentinite components due to its low expansion rate, insufficient magma supply, and weak mantle mixing, as well as recycled carbonated eclogites carried by subduction-induced mantle-return flows. In contrast, in the eastern subbasin, a greater proportion of recycled carbonated eclogites from the mantle transition zone was incorporated into the mantle source by an upwelling mantle plume. The data show that MORBs from the SCS preserve a record of derivation from various depths of the convecting mantle having a distinct geochemical and isotopic imprint, including evidence for a carbon-rich reservoir in the deep upper mantle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122742"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643345","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":"Iron isotope fractionation during silicate‑carbonatite liquid immiscibility processes","authors":"Xiao-Bao Zhang ,&nbsp;Jian-Qiang Liu ,&nbsp;Lukáš Krmíček ,&nbsp;Valentin R. Troll ,&nbsp;Tomáš Magna ,&nbsp;Adam Maťo ,&nbsp;Gang Zeng ,&nbsp;Xiao-Jun Wang ,&nbsp;Li-Hui Chen","doi":"10.1016/j.chemgeo.2025.122732","DOIUrl":"10.1016/j.chemgeo.2025.122732","url":null,"abstract":"<div><div>Liquid immiscibility is one of the viable genetic models to generate carbonatites. Experimental studies have demonstrated that lighter Fe isotopes are enriched in carbonatite melts, whereas heavier Fe isotopes preferentially enter silicate melts during liquid immiscibility. However, this observation has not been substantiated by natural samples, and the mechanism behind Fe isotope fractionation during silicate–carbonatite immiscibility remains unclear. Here, we present high-precision Fe isotope data, combined with petrography, whole-rock elemental and Sr–Nd isotopic compositions, for ultramafic lamprophyres (UML) and carbonatites from the Alnö complex in central Sweden, to elucidate the Fe isotope fractionation during silicate–carbonatite immiscibility processes. The presence of various carbonate spherules in UML, coupled with enrichments in Sr and Ba and depletion in high field strength elements in carbonatites, as well as their overlapping Sr–Nd isotope compositions, supports a petrogenetic relationship involving liquid immiscibility between the UML and carbonatites. The mean δ⁵⁷Fe of UML (0.16 ± 0.08 ‰) is higher than that of carbonatites (0.03 ± 0.04 ‰), with ∆⁵⁷Fe_sil−carb of 0.13 ‰ (± 0.05, 2SD). By excluding the effects of low temperature alteration and magmatic processes, we conclude that silicate–carbonatite immiscibility imparts significant Fe isotope fractionation. This fractionation may be influenced by different Fe bond strengths provided by the distinct polymer networks of silicate and carbonatite melts, as well as the varying degrees of Fe enrichment in minerals and melts. This leads to light Fe isotopes being preferentially enriched in the carbonate melt, while heavy Fe isotopes become enriched in the coexisting silicate melt.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122732"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643346","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":"Geochemistry of the sheeted dyke complex, Troodos Ophiolite (Cyprus): Evidence for the magmatic evolution during subduction initiation","authors":"Wiebke Lehmann ,&nbsp;Marcel Regelous ,&nbsp;Karsten Haase ,&nbsp;Manuel Keith ,&nbsp;Dominic Woelki","doi":"10.1016/j.chemgeo.2025.122743","DOIUrl":"10.1016/j.chemgeo.2025.122743","url":null,"abstract":"<div><div>Supra-subduction zone (SSZ) ophiolites, including the Troodos Ophiolite of Cyprus contain magmatic rocks with geochemical compositions indicating that they formed close to a subduction zone. However, the exact tectonic setting in which SSZ ophiolites were formed is debated, although it has been proposed that they represent fragments of fore-arc crust formed during subduction initiation. The sheeted dyke complex of an ophiolite provides information about the orientation and distance of the spreading axis relative to the slab. This study combines new and published geochemical data for the Troodos sheeted dyke complex with published data for volcanic glasses from the overlying lavas. We show that the sheeted dykes are generally tholeiitic compared to the tholeiitic to boninitic lavas, and most are less depleted (higher Zr/Yb) and contain less slab component (higher Ce/Pb) than the abundant boninitic Troodos lavas. This implies that the crust of the Troodos Ophiolite formed more distant from the trench than the off-axis boninites that mainly occur in the south of the ophiolite. Many of the Troodos dykes have compositions similar to fore-arc basalts from the Izu-Bonin-Mariana island arc, which were erupted during subduction initiation. Lavas equivalent to the sheeted dykes may exist in the lowermost lava pile of the Troodos Ophiolite. The observed geochemical evolution of Troodos from fore-arc basalt to boninite and tholeiite with a strong slab input resembles the stratigraphy of the Izu-Bonin-Mariana fore-arc. We suggest that the Troodos Ophiolite formed at a laterally propagating trench-ridge ‘double junction’ during subduction initiation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122743"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643428","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":"Probing chemical transport through a rock using a porphyroblast population: Insights from the distributions of major, minor, and trace elements in garnet from the Danba dome (SW China)","authors":"Zhen M.G. Li ,&nbsp;Fred Gaidies ,&nbsp;Yi-Chao Chen ,&nbsp;Chun-Ming Wu","doi":"10.1016/j.chemgeo.2025.122741","DOIUrl":"10.1016/j.chemgeo.2025.122741","url":null,"abstract":"<div><div>A population of garnet porphyroblasts, spaced apart between c. 6 mm and 40 mm, in a metapelite of the kyanite zone from the Danba dome was investigated to assess the equilibration length scales of major and trace elements in the intergranular medium during garnet crystallization. Garnet crystallization occurred from ∼525 °C / ∼6.2 kbar to peak conditions of ∼635 °C / ∼6.2–7.7 kbar. Enrichments in the concentrations of Fe, Nb, Cr, and V, as well as depletions in the contents of Ca, Li, Na, Y, and heavy rare earth elements (HREE) in the early-grown garnet portions indicate that garnet initially pseudomorphed biotite. Results of the statistical analysis of the garnet 3D distribution suggest clustering nucleation mechanisms, providing textural evidence of spatial variations in the distributions of energetically favourable nucleation sites early in the garnet crystallization history. With the exception of the core domains of two early-grown crystals (SC1 and SC8), the distributions of Mg, Ca, Mn, and Fe reflect growth zoning of a garnet population, overprinted by intracrystalline diffusion. The concentrations of Li, Na, Sc, Y, Dy, and Ho in simultaneously grown segments of all garnet crystals are quantitatively comparable, suggesting that the intergranular medium can be considered compositionally homogeneous with regards to these elements, indicative of rapid intergranular chemical transport over a distance of at least c. 40 mm. Differences in the concentrations of Er, Tm, Yb, and Lu are only observed in crystals more than c. 12 mm apart, with the concentrations of these elements decreasing as their atomic masses increase. This systematic trend is interpreted to reflect the possible influence of the relative atomic masses of these elements on the length scales of their diffusion through the intergranular medium during garnet growth. Elements that were heterogeneously distributed across the intergranular medium at the mm-scale during garnet growth include Cr and Zr, reflecting the compositional heterogeneity of the protolith, preserved due to the negligible transport of these elements during the metamorphism. This study emphasizes that the equilibration length scales of trace elements during metamorphism may be larger than previously assumed, presumably depending on the duration of the metamorphism.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122741"},"PeriodicalIF":3.6,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666339","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":"Quantitative nanoscale mapping of the Mn redox states in silicates by scanning transmission X-ray microscopy at the Mn L2,3-edges","authors":"Franck Bourdelle ,&nbsp;Cyril Durand ,&nbsp;Erwan Paineau ,&nbsp;Emily Lloret ,&nbsp;Laura Airaghi","doi":"10.1016/j.chemgeo.2025.122739","DOIUrl":"10.1016/j.chemgeo.2025.122739","url":null,"abstract":"<div><div>We present a novel analytical protocol for quantifying and mapping Mn oxidation states in silicates at the nanoscale. Based on X-ray Absorption Near Edge Structure spectra of the Mn L_2,3-edges (630–660 eV) acquired thanks to a Scanning transmission X-ray microscope available at various Synchrotron facilities, we calibrate two equations using reference Mn-bearing samples to precisely determine the Mn mean valence. We detail the spectra processing and the methodology for deriving quantitative Mn redox maps from the proposed calibrations, with a high spatial resolution (20–30 nm). Furthermore, we explore the potential for coupling Mn and Fe L_2,3-edge redox calibrations over the 630–730 eV energy range. The effectiveness of these calibrations, the coupling of Mn<img>Fe results, and the subsequent redox mapping are evaluated through two case studies, showcasing the benefits of this non-destructive approach.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122739"},"PeriodicalIF":3.6,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666340","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":"Characterisation of deep intra-continental magma reservoirs – Insights from noble gases and p-T estimates into the western Eger Rift (Czech Republic)","authors":"Kyriaki Daskalopoulou ,&nbsp;Samuel Niedermann ,&nbsp;Franziska D.H. Wilke ,&nbsp;Martin Zimmer ,&nbsp;Heiko Woith ,&nbsp;Johannes Glodny ,&nbsp;Wolfram H. Geissler ,&nbsp;Horst Kämpf","doi":"10.1016/j.chemgeo.2025.122722","DOIUrl":"10.1016/j.chemgeo.2025.122722","url":null,"abstract":"<div><div>The western Eger Rift (Czech Republic) is a currently inactive volcanic rift that is characterised by earthquake swarm activity and degassing of mantle-derived fluids. Free gases and (ultra-) mafic phenocrysts and xenoliths are used to determine the origin and evolution of volatiles in the system and to define the magma reservoir p-T conditions. Isotope compositions of helium in both fluids and minerals are up to 6.79 R_A. ²⁰Ne/²²Ne ratios range up to ∼11.0 and ²¹Ne/²²Ne ratios up to ∼0.048. Correction for isotopic mass fractionation of Ne suggests a source of mixed atmospheric and mantle type components with a significant crustal input. The slightly lower-than-mantle ³He/⁴He ratios and the Ne isotopic compositions indicate that these gases may have been impacted by a subduction-related crustal component during the Variscan (or Hercynian) Orogeny. ⁴⁰Ar/³⁶Ar ratios range up to 4680. Such higher-than-atmospheric values in most mineral and free gas samples indicate that Ar likely derives from the mixing of atmospheric and mantle sources as well. Thermobarometry of ortho- and clinopyroxene rim pairs of matrix grains yields predominantly p-T conditions of 1.1 ± 0.5 GPa and 700 ± 100 °C, respectively, indicating a lithospheric depth of 40–45 km for 1.5 GPa and 20–25 km for 0.5 GPa. Conversely, pairing cores of mm-sized pyroxenes points to p-T conditions of 2.5 ± 0.5 GPa and 1100 ± 100 °C, corresponding to a lithospheric depth of ∼75 km. The diverse chemistry and the wide range of p-T conditions characterising the crystals indicate magma ascent.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122722"},"PeriodicalIF":3.6,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643347","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":"Molecular indicators of microbial community change linked to salinity variation and terrestrial inputs during the Ordovician-Silurian transition (East-Central USA)","authors":"Yi Song ,&nbsp;Thomas J. Algeo ,&nbsp;Carlton Brett ,&nbsp;Zhanhong Liu ,&nbsp;Shucheng Xie","doi":"10.1016/j.chemgeo.2025.122724","DOIUrl":"10.1016/j.chemgeo.2025.122724","url":null,"abstract":"<div><div>The end-Ordovician mass extinction (LOME), one of the largest biocrises of the Phanerozoic, was linked to a major climatic cooling event, continental glaciation, and oceanic environmental changes. To date, the effect of this biocrisis on marine microbial communities has received scant attention. Here, we generate biomarker records for Upper Ordovician to lower Silurian strata in eastern North America, along with geochemical proxies for watermass salinity and terrestrial fluxes, to investigate contemporaneous microbial community changes and possible controls thereon. Hopane-to-sterane ratios (H/S) exhibit reduced values related to enhanced eukaryotic inputs during the Hirnantian Ice Age. A decrease in the proportion of long-chain <em>n</em>-alkanes and an increase in moretane-to-hopane ratios reflect increased contributions from land plants to the organic fraction of marine sediments during the Ordovician-Silurian transition (OST). The high relative abundances of C₁₉-C₂₀ long-chain tricyclic terpenes in the lower Silurian imply increased inputs from marine algae, possibly in response to enhanced nutrient fluxes from terrestrial sources to the ocean. The salinity proxies B/Ga and S/TOC indicate a shift in watermass conditions from marine to slightly brackish in the pre-Hirnantian to marine to slightly hypersaline in the Hirnantian and early Silurian, probably linked to shallowing of the Lexington Platform and climate aridification resulting from Gondwanan continental glaciation. This increase in salinity is consistent with rapid variation in hopane/sterane ratios, showing the influence of watermass salinity on microbial community composition. Thus, marine environmental changes (i.e., in salinity, redox, and nutrient fluxes) were the immediate cause of microbial community evolution during the OST, although the ultimate driver may have been expansion and diversification of terrestrial floras.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122724"},"PeriodicalIF":3.6,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143610418","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Trace element partitioning coefficients between orthopyroxene and melt: Parameterizations of D variations and an improved Lattice Strain Model for rare Earth elements","authors":"Jean H. Bédard","doi":"10.1016/j.chemgeo.2025.122710","DOIUrl":"10.1016/j.chemgeo.2025.122710","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Nernst partition coefficient data (&lt;em&gt;D&lt;/em&gt;) between orthopyroxenes with &lt;5.5 mol% &lt;em&gt;Wollastonite&lt;/em&gt; component and melts are compiled and interpreted to generate simple linear equations allowing &lt;sup&gt;orthopyroxene/melt&lt;/sup&gt;&lt;em&gt;D&lt;/em&gt; values to be calculated for 48 trace elements. The regression coefficients apply to melts ranging in composition from carbonatite to granite, and use commonly measured and petrologically significant variables as inputs. 2561 crystal/liquid pairs yielding 8219 individual &lt;em&gt;D&lt;/em&gt; measurements were considered. Results from extra-terrestrial melts and synthetic (non-natural) melts often yield trends distinct from those of terrestrial melts, and were excluded from many regressions so as to tailor the parameterizations to terrestrial melts. With few exceptions &lt;sup&gt;orthopyroxene/melt&lt;/sup&gt;&lt;em&gt;D&lt;/em&gt; increases with decreasing temperature, orthopyroxene molar &lt;em&gt;mg/(mg&lt;/em&gt; &lt;em&gt;+&lt;/em&gt; &lt;em&gt;fe&lt;/em&gt;&lt;sup&gt;&lt;em&gt;total&lt;/em&gt;&lt;/sup&gt;&lt;em&gt;)&lt;/em&gt;, weight % melt MgO and MgO/(MgO + FeO&lt;sup&gt;&lt;em&gt;⁎&lt;/em&gt;&lt;/sup&gt;); and with increasing wt% melt SiO&lt;sub&gt;2&lt;/sub&gt; and Na&lt;sub&gt;2&lt;/sub&gt;O + K&lt;sub&gt;2&lt;/sub&gt;O contents. No strong correlations of &lt;em&gt;D&lt;/em&gt; with melt water content were observed. Changes in oxygen fugacity affect partitioning of V, Mo, W, Re, and to a lesser extent Eu, and several of these regressions can be used as oxygen barometers. &lt;sup&gt;orthopyroxene/melt&lt;/sup&gt;&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;REE&lt;/em&gt;&lt;/sub&gt; yield well-constrained linear functions for ratios of Ln&lt;em&gt;D&lt;/em&gt; (&lt;em&gt;e.g.&lt;/em&gt; Ln&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;La&lt;/em&gt;&lt;/sub&gt;/Ln&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;Ce&lt;/em&gt;&lt;/sub&gt;) of elements with similar ionic radii. Model Nearest-Neighbour &lt;sup&gt;orthopyroxene/melt&lt;/sup&gt;&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;REE&lt;/em&gt;&lt;/sub&gt; profiles (NN-&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;REE&lt;/em&gt;&lt;/sub&gt;) were constructed from these Ln&lt;em&gt;D&lt;/em&gt;/Ln&lt;em&gt;D&lt;/em&gt; ratios from a starting point at &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;Yb&lt;/em&gt;&lt;/sub&gt;. As &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;Yb&lt;/em&gt;&lt;/sub&gt; increases, the LREE-depleted NN-&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;REE&lt;/em&gt;&lt;/sub&gt; model profiles rise and flatten. Model NN-&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;REE&lt;/em&gt;&lt;/sub&gt; profiles computed at a given melt MgO or SiO&lt;sub&gt;2&lt;/sub&gt; content resemble published partitioning data for chemically comparable melts. A series of model NN-&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;&lt;em&gt;REE&lt;/em&gt;&lt;/sub&gt; profiles for a wide range of corresponding melt MgO and SiO&lt;sub&gt;2&lt;/sub&gt; were fit with a Lattice Strain Model (LSM) to constrain variations of &lt;em&gt;D&lt;/em&gt;&lt;sup&gt;3+&lt;/sup&gt;&lt;sub&gt;0&lt;/sub&gt; (the strain compensated partition coefficient), r&lt;sup&gt;3+&lt;/sup&gt;&lt;sub&gt;0&lt;/sub&gt; (the strain-free radius of the site into which REE substitute), and E&lt;sup&gt;3+&lt;/sup&gt;&lt;sub&gt;M&lt;/sub&gt; (the elastic response of the M-site hosting REE as measured by Young's Modulus). Excellent LSM fits were obtained assuming a constant value of r&lt;sup&gt;3+&lt;/sup&gt;&lt;sub&gt;0&lt;/sub&gt; = 0.81 Å. Regression of experimental temperature against wt% melt LnMgO applied to the global data set was used to parameterize an internal temperature-composition function, required for application of the LSM. Values of r&lt;sup&gt;","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"681 ","pages":"Article 122710"},"PeriodicalIF":3.6,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143686554","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}