Molybdenum isotope evidence for subduction-modified mantle beneath mid-ocean ridges

"Ghost" arc geochemical signatures persistently occur in mid-oceanic ridge basalts (MORBs), yet their origin remains elusive. Here, we identified arc-like heavy Mo isotopic compositions in basalts from the St. Helena plume-influenced southern Mid-Atlantic Ridge. Their heavy Mo isotopic signature (delta 98/95Mo = -0.21 %o to +0.11 %o), along with relatively low (La/Sm)N, Nb/Zr, Ce/Pb, and Sr-Nd isotope ratios, cannot be explained by interactions of the depleted mantle with recycled crustal or lithospheric mantle materials or the influence of the St. Helena plume on their mantle source. By integrating seismic tomographic images and plate reconstruction models, we interpret these unique geochemical and heavy Mo isotopic signatures to reflect the inputs of fluidmodified mantle produced during the Mesozoic subduction beneath the southwestern Gondwana convergent margin. Our discovery provides crucial evidence for the role of the paleo-subduction-modified mantle in shaping present-day MORB-mantle heterogeneity and sheds light on the formation of ghost-arc signatures in global MORBs

Identification of Hydroxylated Chlorinated Paraffins in Human Serum and Their Potential Metabolic Pathways

Short- and medium-chain chlorinated paraffins (SCCPs and MCCPs) are frequently detected in humans. However, information regarding their metabolites is still very limited. Herein, target analysis and halogenation-guided nontarget and suspect screening were conducted on serum samples using UHPLC-Orbitrap-HRMS. The median concentrations of SCCPs and MCCPs were 7.76 and 4.31 ng/mL, respectively. A series of hydroxylated chlorinated paraffins (OH-CPs) were tentatively identified with an estimated average concentration of 1.80 ng/mL, which was approximately 9.9% of the total SCCPs and MCCPs. A chlorine distribution shift was observed from chlorinated paraffins (CPs) dominated by Cl6 and Cl7 to OH-CPs dominated by Cl5, Cl6, and Cl4. In human liver cytochrome P450 (CYP) enzyme incubation assays, the CPs in commercial mixtures were mainly metabolized into OH-CPs with various carbon lengths and chlorine substituents. The results obtained from human serum and in vitro experiments suggested the oxidative metabolism of SCCPs and MCCPs in humans. The metabolic pathways were then comprehensively explored using a CP monomer (1,1,1,3,10,11-hexachloroundecane) incubated with the same CYP enzymes, demonstrating that CPs can be metabolized through successive oxidative dechlorination and direct hydroxylation, with subsequent oxidation to carboxylic acids. Further studies should focus on the long-term toxicity of OH-CPs

Compositions and Distributions of Secondary Organic Aerosols and Their Tracers over the Pearl River Estuary Region Influenced by Continental and Marine Air Masses

The compositions and distributions of monoterpenes, isoprene, aromatics and sesquiterpene SOA tracers (SOAM, SOAI, SOAA and SOAS, respectively) at an island site (Da Wan Shan Island, DWS) were investigated in the context of the influence of continental and marine air masses over the Pearl River Estuary (PRE) region in winter 2021. The sum concentration of SOA tracers was 6.2-132.8 ng m-3, with SOAM and SOAI as the main components in both continental (scenarios A1 and A2) and marine air masses (scenario A3), as well as their combination (scenario A4). The highest and lowest levels of SOAM were observed in A1 and A3, respectively, which were mainly related to the variations in meteorological conditions, precursor concentrations, and the degree of photochemical processes. Higher MBTCA/HGA (3-methyl-1,2,3-butanetricarboxylic acid/3-hydroxyglutaric acid) ratios suggested a less significant contribution from alpha-pinene to SOAM. The variations of SOAI in the different scenarios were associated with differences in relative humidity, particle acidity, and isoprene/NOx ratios. The respective highest and lowest concentrations of aromatics SOA tracers in A1 and A3 revealed the influence of anthropogenic precursors from upwind continental areas, which was confirmed by the correlation among biogenic and anthropogenic precursors. The results of the tracer-based-method suggested dominant contributions of SOAs from aromatics and monoterpenes, with the highest concentrations in A1. A WRF-Chem simulation revealed that the SOAs from the above precursors only contributed 12%-25% to the total SOA at DWS, while the spatial distributions of SOAs further highlighted that the abundance of SOAs over the PRE region in winter is highly associated with air masses transported from upwind continental areas

Enrichment and fractionation of rare earth elements (REEs) in ion-adsorption-type REE deposits: Constraints of an iron (hydr)oxide-clay mineral composite

Ion-adsorption-type rare earth element (REE) deposits are the source of more than 90% of global heavy REEs (HREEs). Thus, understanding the ore genesis of REEs, particularly the distribution characteristics and enrichment mechanisms of HREEs, is vital for efficient exploration and mining of ion-adsorption-type REE deposits worldwide. The characteristics and petrogenesis of bedrock and the aqueous mobility of REEs are known to be important factors controlling REE accumulation and fractionation in the weathering crust of REE deposits. However, the effect of REE adsorption on secondary minerals, a crucial step in deposit formation, remains poorly understood. This problem was addressed by the study described herein, which involved a systematic analysis of the complete weathering profile (78 m) of the Renju ion-adsorption-type REE deposit in South China and a simulated adsorption experiment. Clay minerals and iron (Fe) (hydr)oxides are the dominant REE adsorbents in the weathering crust and most are micro-to-nanosizedparticles. Thus, the fine-particle fraction (<2 mu m) was separated from field samples to disclose better their effects on the concentration and redistribution of REEs. Phase compositions and morphologies were characterized by X-ray diffraction, M & ouml;ssbauer spectrometry, and scanning/transmission electron microscopy (SEM/TEM), which revealed that various clay minerals and Fe (hydr)oxides form composites along the profile of the deposit. Composites of ferrihydrite-kaolinite, goethite-kaolinite/halloysite, and hematite-kaolinite/halloysite were found to be distributed in the semi-weathered, completely weathered, and topsoil layers, respectively, with different sizes and shapes. The concentrations and partition patterns of REEs in different occurrence states were distinguished after sequential extraction. Ion-exchangeable-REEs were the major state and enriched in the upper completely weathered layer. These species were found to be adsorbed onto kaolinite and halloysite via electrostatic attraction without obvious fractionation. Fe (hydr) oxides were determined to comprise ca. 20% of REEs at most depths and over 50% of REEs in the topsoil and semi-weathered layer. It was found that Fe (hydr)oxides scavenge REEs through complexation and oxidation, resulting in HREE enrichment and a positive cerium (Ce) anomaly, respectively. In addition, compared with crystalline Fe (hydr)oxides, amorphous Fe (hydr)oxides immobilize more REEs but exhibit weaker preferential adsorption of HREEs. The above-described findings are consistent with the results of simulated experiments for REE adsorption onto a clay mineral-Fe (hydr)oxide composite (Bt-60d), which was obtained from hydrothermal processing of biotite. Furthermore, the distributions and stabilities of LREEs and HREEs were distinguished by TEM-energy-dispersive spectroscopy (EDS) of Bt-60d before and after REE extraction by ammonium sulfate. The phase transformation pathways of clay minerals and Fe (hydr)oxides and their different enrichment and fractionation characteristics in REEs were also discussed in terms of the structure and surface properties of minerals, adsorption mechanisms, and variations in chemical properties across the REE group. The results shed new light on how clay minerals and Fe (hydr)oxides affect the enrichment and fractionation of REEs in ion-adsorption-type deposits

A continental record of Early Cretaceous (Aptian) vegetation and climate change based on palynology and clay mineralogy from the North China Craton

The Early Cretaceous Aptian Stage (121.4-113.0 Ma) witnessed significant climate changes and environmental perturbations including Ocean Anoxic Event 1a; however, reconstructions of paleoclimate have predominantly relied on marine records. In this paper, we report palynological and clay mineralogical data from a continuous core (YSDP-4) in the Kazuo Basin of Northeast China to produce a high-resolution terrestrial Aptian record that is correlated with the marine record. In the lowermost part of the Aptian succession (similar to 121 to similar to 120 Ma), vegetation types were dominated by bisaccate conifers (>75%), while smectite and illite clay minerals were co- dominant (each similar to 40-50%), indicating cool and semi-humid to semi-arid conditions with a tendency towards aridity. This was followed by an exceptionally dry and hot climatic event, from similar to 120 Ma to similar to 117.5 Ma, marked by a rapid increase in drought-resistant plants including members of the Cheirolepidiaceae (>60%). During the transition from the early Aptian to the late Aptian (similar to 117.5 to similar to 114 Ma), the clay mineral composition exhibited a complex pattern containing chlorite and kaolinite, and the proportion of vegetation representing relatively cool and moist conditions increased, indicating a gradual transition to a humid climate. By the end of the late Aptian (similar to 114 to similar to 112 Ma), climate became cooler and more humid, as indicated by a sharp increase in Taxodiaceae pollen (similar to 50%). Based on the similar patterns of vegetation and sedimentary records observed in the Kazuo Basin and across the Tethyan Realm, we propose that the early Aptian hot/dry climatic event was synchronous with Oceanic Anoxia Event 1a. The findings of our study provide an important terrestrial sedimentary reference section for future integration of Cretaceous climatic events and biological evolution across the marine-terrestrial spectrum

Transitional chromitites within the Maqsad crust-mantle transition zone of the Semail ophiolite formed above the nascent forearc setting

The Semail ophiolite is a classic example of a well-preserved ophiolite, hosting over 450 documented podiform chromite deposits. This study investigates a transitional chromitite occurrence in the crust-mantle transition zone (CMTZ) of the Maqsad area within the Sumail massif of the Semail ophiolite. The chromitites, enveloped by dunites, exhibit massive and disseminated textures. Host harzburgites, representing upper mantle residues, underwent similar to 20-35 % partial melting followed by metasomatism from subducting slab-derived melts/fluids. These peridotites show geochemical affinities with Izu-Bonin-Mariana (IBM) forearc peridotites, indicating a forearc tectonic setting. The Maqsad chromitites, with Cr# values of 54.3-66.2, are classified as transitional chromitites. Their geochemical features resemble chromites crystallized from mid-ocean ridge basalt (MORB) melts. Elevated oxygen fugacity (f(O2)) values compared to abyssal peridotites further support their formation in a supra-subduction zone (SSZ)environment. Based on the petrogeological and geochemical characteristics of the host rocks, we propose that the parental magma of the Maqsad transitional chromitites derived from a nascent forearc mantle above an SSZ setting, with MORB-like affinity

Iron isotopic fractionation during seafloor hydrothermal alteration of oceanic upper crust, as recorded in Geotimes lavas of Semail ophiolite, Oman

The Semail ophiolite in Oman features a crustal stratigraphy akin to a fast-spreading modern oceanic lithosphere. Its Geotimes pillow lavas, the stratigraphically oldest extrusive sequence at the bottom, share geochemical traits with contemporary mid-ocean ridge basalts, offering a unique opportunity to examine iron (Fe) isotopic fractionation during hydrothermal alteration under varied redox conditions. Significant alteration transformed primary minerals, evidenced by the dissolution of clinopyroxene, plagioclase, and ilmenite, alongside the precipitation of chlorite, albite, and magnetite-hematite. The 87Sr/88Sr ratios of 18 basalt subsamples from altered pillow lava range from 0.705110 to 0.705680, indicating extensive seawater interaction. The delta 56Fe values show systematic variations at a centimeter scale (0.037-0.291 parts per thousand), primarily resulting from hydrothermal processes rather than source inheritance. Notably, the pillow lava's core displays higher delta 56Fe values, suggesting the initial dissolution of Fe-bearing minerals under reduced conditions. In contrast, the edges show lower delta 56Fe values akin to mean mid-ocean ridge basalt, indicating that strong oxidation conditions minimally affected these isotopic values. In conclusion, this study reveals the complex variations of the Fe concentrations and Fe isotopic compositions of altered basalt that suffered hydrothermal alteration during the various redox conditions

A comprehensive characterization biotransformation of chlorinated paraffin by human and carp liver microsomes via liquid chromatography-high-resolution mass spectrometry and screening algorithm

The chlorinated paraffin (CP) monomer 1,2,5,6,9,10-Hexachlorodecane (CP-4) was subjected to in vitro biotransformation using human and carp liver microsomes. Five types of CP-4 metabolites (OH-, keto-, enol-, aldehyde- and carboxy-CP-4) were identified in human liver microsomer while only mono-OH-CP-4 was found in the carp liver microsomes. Kinetic studies revealed that the formation of mono-, di-, tri-hydroxylated CP-4, keto-, enol-, and aldehyde-CP-4 in human liver microsomes was best described by substrate inhibition models, whereas the formation of carboxylated CP-4 metabolites best fit the Michaelis-Menten model. Notably, keto-CP-4, enolCP-4 and aldehyde-CP-4 were the predominant metabolites. The estimated Vmax values for these metabolites were significantly higher in the human liver microsomes than in the carp liver microsomes. The intrinsic hepatic clearance (CLint) of CP-4 was higher in humans than in carp, indicating species-specific differences in its metabolism. This study also highlighted potential toxicity concerns, with computational predictions showing varying degrees of acute oral toxicity for CP-4 and its metabolites. These findings indicate significant speciesspecific differences in the biotransformation of CP-4, emphasizing the potential health and environmental risks associated with chlorinated paraffins and their metabolites, and underscore the need for further research to address these concerns

Unravelling the mechanisms underlying marine redox shifts during sedimentary manganese metallogenesis: insights from the Carboniferous Muhu deposit, China

Sedimentary manganese (Mn) mineralization requires a switch between anoxic and oxic water column conditions, which is commonly explained by the "bathtub ring" model and more recently interpreted by the emerging "episodic ventilation" model. To date, however, it remains unclear regarding how to distinguish between these two mechanisms, profoundly influencing Mn ore prospecting. Here, we conducted a comprehensive investigation on the Muhu Mn deposit in northwestern China. The upward lithological variations from breccia-dominated to fine-grained siliciclastic units (e.g., black shales) are typical of sequence characteristics of rifted basins. Black shales were deposited in deep waters due to continued tectonic subsidence that resulted in hydrographic restriction and bottom water euxinia, as indicated by their high ratios of FeHR/FeT and FePy/FeHR, as well as relatively low Mo/TOC ratios. The Mn ore beds are interbedded with black shales and consist of divalent Mn minerals (e.g., rhodochrosite). They display shale-normalized positive cerium anomalies and negative inorganic carbon isotopes and Mo isotopes, suggesting that these Mn carbonate minerals originated from the diagenetic conversion of primary buried Mn oxides deposited under oxic benthic conditions. Taken together, the intimate spatial association between Mn ore beds and black shales records a dynamic temporal redox change. Such a redox shift is consistent with the "episodic ventilation" scenario, where incursions of oxygenated seawater triggered the deposition of initial Mn oxides. In contrast with the "bathtub ring" model, the ventilation scenario represents distinct spatial-temporal configurations of redox-hydrological conditions. Therefore, deciphering the detailed redox variations of Mn-hosting sedimentary successions, in conjunction with paleogeographic reconstruction, is the key to distinguishing between these two mechanisms

Attribute Reduction in a Hybrid Decision Information System Based on Fuzzy Conditional Information Entropy Using Iterative Model and Matrix Operation

Attribute reduction of hybrid decision information systems (HDISs) is a significant research area within the field of machine learning. Due to the presence of nominal attributes, it is difficult to accurately measure the distance between objects in HDISs, which often results in poor attribute reduction for these systems. Rough set theory (RST) is a crucial tool for attribute reduction, but it requires computation of upper and lower approximations, which often leads to computational difficulties. In response to the aforementioned issues, this paper proposes a fast attribute reduction algorithm for HDISs based on fuzzy conditional information entropy that utilizes an iterative model and matrix operations. Firstly, a novel measurement of the distance between nominal attribute values is defined using decision attributes. Subsequently, fuzzy conditional information entropy is calculated from the perspective of "the attribute values is fed back to the attribute set" and its properties are provided. Additionally, an iterative attribute reduction model and difference matrix are established, and two new matrix operations are introduced. Finally, an iterative attribute reduction algorithm is provided. The results of experiments and statistical tests on fifteen UCI datasets, including three large datasets, demonstrate that the proposed algorithm is more effective and efficient than nine state-of-the-art algorithms. This paper not only addresses the issue of difficulty in measuring the distance between nominal attribute values but also significantly improves the computational efficiency of attribute reduction algorithms based on RST, making it possible for them to be applied to large datasets