Guangzhou Institute of Geochemistry
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Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones
No full textEarth's continental crust is hypothesized to originate from mantle melting in subduction zones. However, mantle melts are typically Fe-rich, with light Fe isotopes (delta Fe-56 = 0.05 parts per thousand), unlike the Fe-depleted and heavy Fe isotope (delta Fe-56 can be up to 0.2 parts per thousand) compositions of continental crust. The mechanisms responsible for this paradox remain elusive. Here, we report Fe isotope data from a suite of co-magmatic Middle Triassic continental arc rocks in the Ailaoshan tectonic zone (Yunnan, SW China). Gabbroic diorites have light Fe isotopes (delta Fe-56 = 0.04 parts per thousand-0.09 parts per thousand), while granodiorites and normal-arc granites have slightly heavier values (delta Fe-56 = 0.07 parts per thousand-0.14 parts per thousand). Adakitic granites, with high Sr/Y (61-183) and La/Yb (47-90) ratios, exhibit the heaviest delta Fe-56 (0.16 parts per thousand-0.19 parts per thousand). Rayleigh fractionation modeling results suggest that fractionation of isotopically light Fe minerals (e.g., olivine, pyroxene, and amphibole) can reproduce the Fe isotopic variations in most samples, but fails to explain the high Sr/Y, La/Yb, and delta Fe-56 values of adakitic granites, which would require Fe-rich garnet fractionation. Notably, the different Fe isotopes of the adakitic granites and non-adakitic rocks reveal two distinct transcrustal magmatic differentiation pathways: lower crustal, high-pressure, garnet-dominated fractionation; and middle-upper crustal, amphibole-dominated fractionation. The heavy Fe isotopic and Fe-depleted characteristics of the Ailaoshan magmatic arc suites are more comparable to the calc-alkaline arc magmas from normal to thick crust arcs (e.g., the Andean arc), but remarkably different from the tholeiitic arc magmas from thin crust arcs (e.g., the Mariana arc). This study highlights the role of amphibole and garnet fractionation in magmatic calc-alkaline differentiation. We propose that a thickened crust would permit a longer magmatic differentiation column, thus facilitating felsic and Fe-depleted continental crustal formation. The fractionated Fe-rich, garnet-bearing arc cumulates with light Fe isotopes are density-unstable and may be recycled into the mantle by lower crustal foundering
Biogenic emission as a potential source of atmospheric aromatic hydrocarbons: Insights from a cyanobacterial bloom-occurring eutrophic lake
No full textAs important precursors of ozone (O3 ) and secondary organic aerosol (SOA), reactive aromatic hydrocarbons (AHs) have typically been classified as anthropogenic air pollutants. However, biogenic emission can also be a potential source of atmospheric AHs. Herein, field observations in a eutrophic lake were combined with laboratory incubation experiments to investigate the biogenic AH emission. Field work showed that the water-air fluxes of AHs measured at sites with high cyanobacteria abundance could reach an order of magnitude greater than those at sites with low cyanobacteria abundance, suggesting that cyanobacteria could be the important contributor to measured AHs. Laboratory incubation experiments further confirmed the AH emission of cyanobacteria and revealed that the emission could change significantly over the lifespan of cyanobacteria and varied to their growing conditions. By combining field observations and laboratory incubation experiments, it has been suggested that the emission of different AH species from cyanobacteria could be modulated by variable biogeochemical mechanisms and that the biochemical process of toluene could be different from that of other AHs. This study investigates AH emissions from inland aquatic ecosystem and suggests that biogenic emission could be a potential source of atmospheric AHs. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V
On using an aerosol thermodynamic model to calculate aerosol acidity of coarse particles
No full textThermodynamic modeling is still the most widely used method to characterize aerosol acidity, a critical physicochemical property of atmospheric aerosols. However, it remain unclear whether gas-aerosol partitioning should be incorporated when thermodynamic models are employed to estimate the acidity of coarse particles. In this work, field measurements were conducted at a coastal city in northem China across three seasons, and covered wide ranges of temperature, relative humidity and NH3 concentrations. We examined the performance of different modes of ISORROPIA-II (a widely used aerosol thermodynamic model) in estimating aerosol acidity of coarse and fine particles. The M0 mode, which incorporates gas-phase data and runs the model in the forward mode, provided reasonable estimation of aerosol acidity for coarse and fine particles. Compared to M0, the M1 mode, which runs the model in the forward mode but does not include gas-phase data, may capture the general trend of aerosol acidity but underestimates pH for both coarse and fine particles; M2, which runs the model in the reverse mode, results in large errors in estimated aerosol pH for both coarse and fine particles and should not be used for aerosol acidity calculations. However, M1 significantly underestimates liquid water contents for both fine and coarse particles, while M2 provides reliable estimation of liquid water contents. In summary, our work highlights the importance of incorporating gas -aerosol partitioning when estimating coarse particle acidity, and thus may help improve our understanding of acidity of coarse particles. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V
Coupled effects of iron (hydr)oxides and clay minerals on the heterogeneous oxidation of aqueous Mn(II) and crystallization of manganese (hydr)oxides
No full textThe formation of nanominerals and mineral nanoparticles (NMMNs) has drawn broad attention due to their high reactivity and omnipresence in the environment. While the heterogeneous formation of NMMNs on surfaces of various minerals has been extensively studied, there is limited understanding of how mineral heteroaggregates influence this process. In this study, we investigated how heteroaggregates of iron (hydr)oxides and clay minerals affect the heterogeneous oxidation of aqueous Mn(II) and crystallization of manganese (hydr)oxides (MnOx). Our results revealed that iron (hydr)oxides (ferrihydrite) and clay minerals (kaolinite or montmorillonite) in heteroaggregates exerted coupled effects on these processes, dictating the distribution of Mn and the morphology of MnOx. Specifically, ferrihydrite catalyzed gradual oxidative removal of Mn(II) and triggered MnOx nucleation; in contrast, kaolinite/montmorillonite rapidly adsorbed Mn(II) but hardly catalyzed its oxidation. These reactions collectively resulted in fast adsorption and gradual oxidation of Mn(II) on the heteroaggregates. Further, MnOx nanoparticles formed on ferrihydrite surfaces migrated to kaolinite/montmorillonite surfaces, leading to interactions between MnOx and various component minerals within the heteroaggregates. This significantly altered the subsequent growth pathways and the eventual morphology of MnOx. Consequently, while MnOx nanoparticles in the ferrihydrite-only system aggregated freely and formed well-extended nanowires, those in the ferrihydrite-kaolinite system predominantly became short nanorods due to the immobilization by kaolinite surfaces; in the ferrihydrite-montmorillonite system, considerable MnOx nanoparticles attached to montmorillonite surfaces due to strong electrostatic attraction, and subsequently grew into blocky particles via particle attachment. These findings illustrate that surface reactivities of heteroaggregated ferrihydrite and kaolinite/ montmorillonite are coupled when they interact with aqueous Mn(II) or MnOx. Our work exemplifies, for the first time, the cooperation between surfaces of various minerals during the heterogeneous formation of NMMNs. Findings from this study also enhance our understanding of MnOx formation on surfaces with diverse atomic structures, and contribute to the knowledge of Mn cycling in the environment
Formation and evolution of supercritical geofluid
No full textIn this work, we provide a comprehensive review on the formation, evolution, properties, and effects of supercritical geofluid. In Earth's interior, enhanced miscibility between H2O and silicate by the addition of special components or by the increase of pressure and temperature gives rise to supercritical geofluid with a significant amount of both H2O and silicate solute. The formation of supercritical geofluid in magmatic-hydrothermal systems, typified by pegmatite system, is governed by meltfluid critical curve. The formation of supercritical geofluid in metamorphic systems, typified by subducted slab, is governed by the second critical end point. Experimental results suggest that the presence of boron and fluorine in pegmatite system makes it possible to form supercritical geofluid at crustal depths, but the release of supercritical geofluid from subducted slab is withheld until almost 100 km depth. A major presence of both H2O and depolymerized structural units (monomers, dimers, etc.) endows supercritical geofluid with unique physical properties including low density, low elastic moduli, low viscosity, high diffusivity, and high electrical conductivity. Supercritical geofluid can effectively mobilize a variety of elements even including high field strength elements and heavy rare earth elements. The chemical signatures of supercritical geofluid can be inherited by metasomatized mantle and mantle-derived melts, and this could give an explanation of the oxidation of arc magmas. Phase separation of supercritical geofluid through the mechanism of spinodal decomposition leads to formation of a melt network. Multiphase fluid inclusions recovered from subduction zone rocks and pegmatites are possible relics of supercritical geofluid. Supercritical geofluid can cause electrical anomaly and low seismic velocity near the top of subducted slab, and can be linked with intermediate-focus earthquakes. Supercritical geofluid may have played a crucial role in the formation of pegmatites and associated ore deposits
Bimetal-organic framework derived single-atom-like Co/Fe catalysts for peroxydisulfate activation: The dual amplification of radical and nonradical pathways
No full textA novel single-atom-like Co/Fe catalyst (i.e., Co/Fe-N-C) was synthesized by pyrolysis of a Zn/Co/Fe zeolitic imidazolate framework, and applied in peroxydisulfate (PDS) activation for removal of organic contaminants from wastewater. The isolated diatomic metal-nitrogen sites were detected by X-ray adsorption fine-structure. The degradation of four contaminants (i.e., phenol, bisphenol A, 2,4-dichlorophenol, and N-methyl-2-pyrrolidone) with a concentration of 100 mg/L could be degraded separately within 20 min by the Co/Fe-N-C system with 10 mmol/L of PDS, 0.5 g/L of catalyst dosage, and initial pH of 3. Besides, 79.2 % of phenol could be mineralized in 120 min, and the turn-over frequency value of the catalyst was calculated to be 27.17 min(-1), which was higher than the commonly reported homogeneous PS-AOPs. Moreover, the Co/Fe-N-C exhibited high stability (mineralization rate over 70 % after 5 cycles), a wide initial pH range (3-9), and high catalytic performance at 5-20 mmol/L of PDS concentrations. Based on the analysis of radical scavenging experiments and electron spin resonance spectra, the radical and non-radical pathways for PDS activation were proved in the system, and the contribution of phenol degradation by each pathway was clarified
Mushroom-shaped growth of crystals on the Moon
No full textOver the past three decades, advances in crystal nucleation and growth have led to the understanding that crystallization proceeds through various pathways, ranging from the conventional atom-by-atom model to the particle aggregation- or amorphous transformation-based non-classical modes. Here, we present a novel mineralization mechanism exemplified by a lunar chromite formed via solid-liquid interface reactions through investigations of a lunar breccia returned by the Chang'e 5 mission. The chromite occurs in the middle of a whisker-shaped intergrowth structure made by olivine at the bottom and nanospheres of troilite and metallic iron at the top. Morphological observation and size statistics of the nanospheres, including those within the whisker structure and the others dispersed in glass, suggest the nanophases attached to olivine with coherent crystallographic orientations, possibly through an oriented aggregation process. The chromium deficiency in the olivine near the interface between olivine and chromite suggests that Cr in chromite originated from olivine, but the significantly reduced ferrous concentration in the glass surrounding chromite indicates the iron was derived from surrounding impact-induced glass. Based on laboratory observations and simulated calculations of energy and lattice mismatch, we propose that chromite crystallized at the interface between troilite and olivine in the impact melts, during which the nanospheres were lifted and transported away from olivine surface and formed a mushroom-shaped structure. This finding suggests that oriented attachment growth, chiefly confined to homogeneous systems thus far, can also occur in heterogeneous systems far from equilibrium, such as that produced by the impacts. It is conceivable that the studied crystallization pathway occurring on the heterogeneous interfaces may have been a common mineralization mode at highly nonequilibrium conditions
Effects of fine terrain complexity on cloud and precipitation changes over the Tibetan Plateau: a modeling study
No full textInaccurate characterization of complex topography leads to the wet bias in climate models, particularly affecting terrain effects in regions like the Tibetan Plateau (TP). This study utilizes the Weather Research and Forecasting (WRF) model with multiple terrain datasets and introduces the terrain complexity index (TCI) to quantify the degree of terrain changes, aiming to evaluate how terrain complexity affects the cloud and precipitation processes over the TP. The results indicate that fine terrain complexity primarily causes earlier cloud formation and precipitation, resulting in more heavy precipitation on the southern slope of the TP (SSTP) and more light precipitation on the TP platform. The structure of moisture transport and microphysical processes further reveals that this promotes the formation of more medium and high clouds, increasing the proportion of solid precipitation over the SSTP. Over the TP platform, the restriction of medium and high cloud development with enhancing the proportion of low clouds for more liquid precipitation. These findings deepen the understanding of the TP's complex terrain effect on cloud and precipitation changes in the Asian water cycle
Impacts of anthropogenic disturbances on antibiotic resistomes in biological soil crusts on the Qinghai-Tibetan Plateau
No full textBiological soil crusts (BSCs) are the main landscape on the Qinghai-Tibetan Plateau and an ecological indicator of human disturbance. Information about antibiotic resistomes in BSCs on the Qinghai-Tibetan Plateau can provide baseline for the risk assessment and management of resistomes and yet to be explored. This work investigated the profiles and geographic patterns of antibiotic resistomes in BSCs along the Lhasa River and their response to anthropogenic activities for the first time. Various antibiotic resistance genes (ARGs) were widely distributed in BSCs, but had relatively lower detection frequency and abundance comparing to soils from human disturbed sites. ARGs profiles in BSCs were separated by altitude from 3860 to 3880 m, possibly attributing to the difference in anthropogenic activities. Above 3860 m, resistomes exhibited lower abundance including total ARGs, aadA, blaSFO and tnpA-04 owing to the rare human activities; at human disturbed sites with altitude <3860 m, the detection frequency and relative abundance of tetG02, oprJ, qacEdelta1-01, and ARGs with the mechanism of efflux pump were higher and viewed as potential indicators of human activities. Anthropogenic activities potentially promoted the horizontal gene transfer of ARGs in BSCs at human disturbed sites from co-occurrence network analysis. Our findings provided fundamental information of antibiotic resistomes in BSCs on the Qinghai-Tibetan Plateau, and unraveled possible mechanisms of human disturbance in shaping antibiotic resistomes
Geochemical constraints on subduction-related mantle metasomatism of the Tiebaghi ophiolitic lherzolite in New Caledonia
No full textThe geochemical evolution of mantle peridotite during subduction initiation (SI) remains an issue in geosciences. This study presents geochemical and Ca isotopic data for Tiebaghi lherzolites from the New Caledonia ophiolite to constrain their petrogenesis and the nature of melt-rock interaction during the nascent stage of subduction. Petrographic and geochemical analyses reveal that the Tiebaghi lherzolites are characterized by olivine with Fo contents of 89.5-90.7, high-Al Spinel (Cr# = 45.1-50.9; Al2O3 = 24.99-29.29 wt%), orthopyroxene with high CaO (0.87-2.47 wt%) and Al2O3 (2.19-4.91 wt%) coupled with relatively low Mg# (89.4-91.3), and clinopyroxene with high Al2O3 (2.72-6.44 wt%) and relatively low Mg# (90.4-92.5). Lherzolites from northwestern New Caledonia are thought to have escaped the suprasubduction re-melting, resulting in the formation of the highly depleted harzburgites that form the bulk of the ophiolite. They display a restricted range of 5 44/40 Ca values (0.75-0.93 parts per thousand), which are lower than the proposed 5 44/40 Ca value of Earth's upper mantle. This isotopic signature is interpreted to reflect interaction with a low 5 44/40 Ca metasomatic agent, possibly a carbonate-rich melt derived from the subducting slab. These findings suggest that the Tiebaghi lherzolites preserve a geochemical record of the early stages of melt-rock interaction during subduction initiation, emphasizing the role of carbonate melt metasomatism in altering the composition of the nascent mantle wedge