Guangzhou Institute of Geochemistry
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Adsorption behaviors and atomistic mechanisms of iodate and iodide on hollow spherical allophane nanoparticles
No full textThe adsorption of radioactive iodate (IO3-) and iodide (I-) anions on natural minerals is critical for nuclear environmental safety. Allophane, a nanosized clay mineral, is considered to adsorb IO3- and I-, but the essential interactions between both anions and allophane remain unknown, due to the challenges of characterizing extremely small allophane nanoparticles in complex soils and obtaining high-purity natural allophane. In this work, neat allophane (Allo) nanoparticles were synthesized and used to study their adsorption for IO3- and Ianions. The adsorption kinetics, adsorption thermodynamics, pH -dependent adsorption-desorption, and competitive adsorption (Cl- and SO42-) were quantitatively investigated. Moreover, combined with advanced spectroscopic analyses of X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS), the atomistic adsorption mechanisms were illustrated. The adsorption capacities of Allo can be about 0.22 mmol/g for IO3- and 0.077 mmol/g for I-, which are at least one order of magnitude and 2.6 -fold higher than those of other clay minerals, respectively. The IO3- adsorption involved the ligand exchange and electrostatic attraction interactions, while the I- adsorption involved the Lewis acid-base and hydrogen -bond interactions. The innersphere adsorption mainly occurred in the wedge-shaped nanopores within Allo. The findings will improve the understanding of IO3- and I- adsorption on allophane, promote the practical applications of natural allophane in the management of nuclear wastes, and provide foundations for revealing the geochemical behaviors of iodine
Subducted serpentinite contributes to the formation of arc lavas with heavy Mo isotopic compositions
No full textThe petrogenesis of basaltic arc lavas with heavy Mo isotopic compositions is controversial. Given that oceanic crust preferentially loses isotopically heavy Mo during subduction at forearc depth and the remaining Mo is isotopically light and locked in rutile, fluids derived from such crust at subarc depth cannot account for the heavy Mo isotopic compositions of basaltic arc lavas. Serpentinites can contain substantial Mo and volatiles and are a potential source of isotopically heavy Mo in basaltic arc lavas. However, the Mo isotopic composition of serpentinites and the Mo isotope behavior during serpentinite dehydration are poorly constrained. Here, we present Mo contents and isotope data for serpentinites from the South Sandwich Trench-Fracture Zone intersection, and deserpentinized peridotites and high-pressure meta-serpentinite veins from the western-central Alps and Betic Cordillera, Spain. Most of these samples have heavy Mo isotopic compositions (delta 98/95MoNIST 3134, ranging from -0.26 %o to 1.84 %o) with low Ce/Mo (0.10-23.98) and Ce/Pb (0.17-3.59) ratios, which are distinct from the compositions of eclogite-facies metabasalts and metapelites. In addition, no systematic variations in Mo contents and Mo isotopic compositions occur for the studied samples, indicating limited Mo isotope fractionation during serpentinite dehydration. The above results suggest that serpentinites and their derived fluids at subarc depths can serve as the main isotopically heavy Mo sources for basaltic arc lavas. The Mo isotope data with Ce/Mo and Ce/Pb systematics suggest that serpentinite-derived fluids or melting of serpentinite diapirs at subarc depths can explain the heavy Mo isotopic compositions of basaltic arc lavas. Furthermore, recycled oceanic slab (oceanic crust + serpentinized mantle) would has limited influence on the Mo systematics of the mantle, which explains why the mantle has maintained a nearly constant Mo isotopic composition since 3.5 Ga
Subducted serpentinite contributes to the formation of arc lavas with heavy Mo isotopic compositions
No full textThe petrogenesis of basaltic arc lavas with heavy Mo isotopic compositions is controversial. Given that oceanic crust preferentially loses isotopically heavy Mo during subduction at forearc depth and the remaining Mo is isotopically light and locked in rutile, fluids derived from such crust at subarc depth cannot account for the heavy Mo isotopic compositions of basaltic arc lavas. Serpentinites can contain substantial Mo and volatiles and are a potential source of isotopically heavy Mo in basaltic arc lavas. However, the Mo isotopic composition of serpentinites and the Mo isotope behavior during serpentinite dehydration are poorly constrained. Here, we present Mo contents and isotope data for serpentinites from the South Sandwich Trench-Fracture Zone intersection, and deserpentinized peridotites and high-pressure meta-serpentinite veins from the western-central Alps and Betic Cordillera, Spain. Most of these samples have heavy Mo isotopic compositions (delta 98/95MoNIST 3134, ranging from -0.26 %o to 1.84 %o) with low Ce/Mo (0.10-23.98) and Ce/Pb (0.17-3.59) ratios, which are distinct from the compositions of eclogite-facies metabasalts and metapelites. In addition, no systematic variations in Mo contents and Mo isotopic compositions occur for the studied samples, indicating limited Mo isotope fractionation during serpentinite dehydration. The above results suggest that serpentinites and their derived fluids at subarc depths can serve as the main isotopically heavy Mo sources for basaltic arc lavas. The Mo isotope data with Ce/Mo and Ce/Pb systematics suggest that serpentinite-derived fluids or melting of serpentinite diapirs at subarc depths can explain the heavy Mo isotopic compositions of basaltic arc lavas. Furthermore, recycled oceanic slab (oceanic crust + serpentinized mantle) would has limited influence on the Mo systematics of the mantle, which explains why the mantle has maintained a nearly constant Mo isotopic composition since 3.5 Ga
δ142Ce minus δ146Nd value as a redox indicator in Earth's surface environments
No full textStable Ce isotope ratios are considered potential indicators for tracing the redox state of Earth's surface; however, their quantitative relationship remains undefined. Here, we investigated the influences of both redox and nonredox processes on stable Ce isotope fractionation in a terrestrial environment by analyzing the weathering products, selective soil chemical extracts, and parent materials of a typical basaltic profile formed in Hainan Island, South China. During redox processes, the preferential enrichment of the heavier 142Ce in the tetravalent Ce and/or the inheritance of the heavier isotope signature from the soluble led to the crystalline Fe-Mn (hydro) oxide phases having the highest delta 142/140Ce values (up to +0.184 +/- 0.040 parts per thousand). This phenomenon is likely governed by the oxidative adsorption of Mn oxides, while Fe -oxides appear to be less important. In addition, distinct Mn concentrations are important in the tau Th,Ce and delta 142/140Ce values but did not correlate with Ce anomalies, indicating that the Mn (hydro)oxides delta 142/140Ce values may be more reliable than Ce/Ce* in quantitatively tracing redox conditions. Regarding non-redox processes, we discussed the impact mechanisms, including external input, pH, organic matter complexation, adsorption/co-precipitation of the poorly crystalline Fe-Mn oxide, and the formation of clay minerals on stable Ce isotopic fractionation. Results indicated that Fe-Mn-Al oxides preferentially enriched the heavier 142Ce, while the formation of kaolinite preferentially incorporated the lighter 140Ce. However, the impact of external input, pH, organic matter complexation, and clay mineral adsorption on stable Ce isotopes appeared to be limited. Furthermore, delta 142/140Ce values displayed a positive correlation with delta 146/144Nd in both the 0.5 mol L-1 HCl leachates and residual phases, suggesting that stable Ce and Nd isotopes behave similarly during non-redox processes. To isolate the signal of stable Ce isotopes in response to redox conditions, we proposed that delta 142/140Ce minus delta 146/144Nd could serve as a quantitative proxy for tracing redox fluctuations in terrestrial environments
Speculations on the Paleozoic legacy of Gondwana amalgamation
No full textUsing Gondwana as an example, we show how the geological record can be interrogated to detect significant changes in mantle convection patterns at critical junctures in Earth's evolution. Evidence of major changes in mantle circulation in the aftermath of late Neoproterozoic-early Paleozoic Gondwana assembly is provided by widespread (i) plume-related magmatism around Gondwana's periphery, (ii) ironstone deposits related to mantle plume-ocean ridge interaction and enhanced hydrothermal activity, and (iii) super-mature clastic deposits that reflect epeirogenic uplift triggered by mantle upwelling beneath Gondwana combined with deep tropical weathering. In our model, Gondwana assembled above a region of mantle downwelling in which subducted slabs between the converging Gondwanan continents descended to the core-mantle boundary. Renewed subduction along Gondwana's periphery yielded early arc magmas. But as downwelling beneath Gondwana evolved into upwelling as a result of the ponding of subducted slabs at the base of the mantle, mantle plumes rose from the margins of the nascent upwelling to interact with the edges of Gondwana, where they penetrated the peripheral subduction zones via slab windows, tears and transform faults to generate voluminous calc-alkalic crustal melts in hydrated arc regions and A-type magmas in dry back-arc regions. The plumes also underplated oceanic lithosphere and interacted with adjacent ocean ridges, thereby enhancing hydrothermal activity and the flux of bioessential nutrients, leading to the recurrence of marine iron-rich sedimentary rocks in the geological record. At the same time, upwelling beneath a tropical to equatorial Gondwana led to epeirogenic uplift, deep weathering and erosion, resulting in the production of widespread super-mature clastic deposits. We contend that major changes in mantle convection patterns were encoded into the geological record of Gondwana assembly, influenced global-scale mantle convection patterns, and should be incorporated into geodynamic models for the assembly of Pangea. (c) 2023 Published by Elsevier B.V. on behalf of International Association for Gondwana Research
Magmatic fingerprints of subduction initiation and mature subduction: numerical modelling and observations from the Izu-Bonin-Mariana system
No full textUnderstanding the formation of new subduction zones is important because they have been proposed as the main driving mechanism for plate tectonics and they are crucial for geochemical cycles on Earth. However, the conditions needed to facilitate subduction zone initiation and the associated magmatic evolution are still poorly understood. Using a natural case study, we conducted a series of high-resolution 2D petrological-thermomechanical (i2VIS) subduction models assuming visco-plastic rheology. We aim to model the initiation and early stage of an intra-oceanic subduction zone connected to the gravitational collapse of a weak transform zone and compare it to the natural example of the Izu-Bonin-Mariana subduction zone. We also analysed the influence of low convergence rates on magmatic evolution. We propose a viable transition from initiation to mature subduction zone divided into distinct stages that include initiation by gravitational collapse of the subducting slab, development of a near-trench spreading centre, gradual build-up of asthenospheric mantle return flow, and maturation of a volcanic arc. We further show that mantle flow variations and shear instabilities, producing thermal perturbations and depleted interlayers, influence the temporal and spatial distribution of asthenospheric mantle composition and fertility in the mantle wedge. Our modelling results are in good agreement with geological and geochemical observations of the early stages of the Izu-Bonin-Mariana subduction zone
A study on the influence of inorganic ions, organic carbon and microstructure on the hygroscopic property of soot
No full textSoot is a crucial component of aerosols in the atmosphere. Understanding the hygroscopicity of soot particles is important for studying their role as cloud condensation nuclei (CCN) as well as their chemical behavior and atmospheric lifetime. However, there is still a lack of comprehensive understanding regarding the factors that determine the hygroscopic properties of soot. In this work, the hygroscopic behavior of soot particles generated from different types of fuel combustion and aged with SO 2 for varying durations was measured by a vapor sorption analyzer. Various characterizations of soot were conducted to understand the key factors that influence the hygroscopic properties of soot. It was found that water-soluble substances in soot facilitate the completion of monolayer water adsorption at low relative humidity and increase the number of water adsorption layers at high relative humidity. On the other hand, soot prepared from fuel burning typically lacks water-soluble inorganic ions, and their hygroscopicity is primarily influenced by organic carbon (OC) and microstructure. Furthermore, the hygroscopicity of soot can be enhanced by the formation of sulfate due to heterogeneous oxidation of SO 2 . These finding sheds light on the critical factors that affect soot hygroscopicity during water adsorption and allows for estimating the interaction between water molecules and soot particles in a humid atmosphere
In situ biomass burning enhanced the contribution of biogenic sources to sulfate aerosol in subtropical cities
No full textSulfurous gases released by biogenic sources play a key role in the global sulfur cycle. However, the contribution of biogenic sources to sulfate aerosol in the urban atmosphere has received little attention. Emission sources and formation process of sulfate in Guangzhou, a subtropical mega-city in China, were clarified using multiple methods, including isotope tracers and chemical markers. The delta 18O of sulfate suggested that secondary sulfate was the dominant component (84 %) of sulfate aerosol, which mainly formed by transition metal ion (TMI) catalyzed oxidation (31 %) and OH radical oxidation (30 %). The factors driving secondary sulfate formation were revealed using a tree boosting model, which suggested that NH3, temperature, and oxidants were the most important factors. The delta 34S of sulfate indicated that biogenic sources accounted for annual average of 26.0 % of the sulfate, which increased to 30.4 % in winter monsoon period. Rice straw burning enhanced sulfate formation by promoting the release of reduced sulfur from soil, which is rapidly converted into sulfate under a subtropical urban atmosphere with high concentration of NH3 and oxidants. This study revealed the important influence of rice straw burning on biogenic sulfur emission during the rice harvest, thereby providing insight into the sulfur cycle and regional air pollution
Sulfur isotopes of lamprophyres and implications for the control of metasomatized lithospheric mantle on the giant Jiaodong gold deposits, eastern China
No full textThe giant Jiaodong gold deposits represent one of the largest gold provinces (>5000 tons of Au) in the North China Craton of eastern China. They formed similar to 1.7 b.y. after high-grade metamorphism of the crust. The metasomatized subcontinental lithospheric mantle (SCLM) has been increasingly proposed as the main source of such gold mineralization, but the direct geochemical links remain scarce. Here, we present a comprehensive delta S-34 dataset of sulfides from fresh lamprophyres (130-121 Ma) that formed from the metasomatized SCLM that is spatially and temporally associated with the Jiaodong gold deposits (ca. 120 Ma). Due to the negligible effects of crustal contamination and magmatic degassing, the consistently high delta S-34 (4 parts per thousand-6 parts per thousand, n = 73) of lamprophyres from variable localities reveals delta S-34-enriched mantle sources relative to the asthenospheric mantle (-1.3 parts per thousand +/- 0.3 parts per thousand). Combined with the radiogenic Sr-Nd-Pb isotope signatures of these lamprophyres, we determined that such high delta S-34 signatures could have resulted from a period of mantle metasomatism related to subducted continental materials. The lamprophyres share delta S-34 (4.4 parts per thousand +/- 0.8 parts per thousand) and Sr-Nd-Pb isotopes with coeval gold-mineralized diorites (ca. 120 Ma) beneath the ore field (delta S-34: 5.4 parts per thousand +/- 2.5 parts per thousand), which were interpreted to have sampled the magma chamber underlying the auriferous fluid systems. The lamprophyres and diorites consistently indicate the key control of metasomatized SCLM, although these mantle-derived magmas followed different pathways from source to crust. These relatively primitive and evolved magmas all show S and Pb isotopes similar to ore-related sulfides from the Jiaodong gold deposits, particularly those formed in the deep parts and at the early stage of the Jiaodong auriferous fluid system (delta S-34: 5 parts per thousand-7 parts per thousand). Such results suggest that the primary auriferous fluids are genetically linked to the magmas derived from the metasomatized SCLM. Combined with radiogenic isotopes, our study on the sulfur isotopes of mantle-derived magmas identifies the metasomatized mantle source of the gold and provides new evidence for establishing a geochemical link between metasomatized SCLM, derivative magmas, and the giant gold deposits, supporting the model that subduction-related metasomatism plays a key role in the enrichment of volatiles and gold in the SCLM for large-scale gold mineralization
Formation mechanism of Gulong shale oil: Insights from semiclosed hydrous pyrolysis
No full textAs a typical lacustrine shale oil, Gulong shale oil has enormous resource potential. The current lack of understanding regarding the formation process of this oil has affected its development. This study uses a low-mature shale sample from the first member of the Qingshankou Formation in the Songliao Basin and analyzes the hydrocarbon generation, expulsion, and retention characteristics by conducting hydrous pyrolysis in a semiclosed system. The results show that the formation process of the Gulong shale oil can be divided into three stages. The slow hydrocarbon generation stage occurs when organic matter maturity (Ro) 1.1 % indicates the stage of oil cracking and rapid gas generation. Light component oil (C-6-C-14) and gaseous hydrocarbons (C-1-C-5) are formed when heavy components oil (C15+) begins to crack. The light-to-heavy ratio of the hydrocarbon products (C-1-C-14/C15+) rapidly increases with maturity. The hydrous pyrolysis experiment in a semiclosed system is more in line with actual geological conditions of Qingshankou Formation compared to other experimental systems and can simultaneously consider the influence of geological factors such as temperature, pressure, hydrocarbon expulsion, and formation water