Guangzhou Institute of Geochemistry
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Light iron isotopes in high-silica granites record fluid evolution in magmatic-hydrothermal systems
No full textHigh-silica (SiO2 > 70 wt%) granites in continental collisional zones are crucial for understanding formation and evolution of the upper continental crust. Fluids released from felsic magmas can help drive the transition from magmatic to magmatic-hydrothermal systems in shallow magma chambers. However, the influence of these fluids on compositional variations and Fe isotope fractionation during the later stages of evolution of felsic magmas are unclear. In this contribution, we report stable Fe-Mg isotope compositions for the Paleocene Zhengga leucogranite pluton, part of the Gangdese batholith in southern Tibet. The pluton consists of both biotite granite and garnet-bearing two-mica granite, the latter of which contains zoned plagioclase and patchy K-feldspar that show fluid-mediated partial replacement textures, recording complicated magmatic and hydrothermal processes. Compared to high-silica granites worldwide (delta Fe-57 = +0.10 parts per thousand to +0.74 parts per thousand), all rocks from the Zhengga leucogranite pluton have light and variable delta Fe-57 values (+0.03 parts per thousand to +0.28 parts per thousand relative to IRMM-014), which display wave-shaped variations with progressive magmatic differentiation. However, their delta Mg-26 values (relative to DSM-3) decrease from -0.12 parts per thousand to -0.72 parts per thousand with increasing SiO2. The variable Fe and Mg isotope signatures of the Zhengga pluton can be best explained by a three-stage process, comprising initial fractional crystallization of biotite and magnetite, followed by deuteric fluid exsolution with decreasing temperatures and pressures, and final interaction between trapped fluids and residual melts in the highly crystalline magma mush. In combination with previously published Sr-Nd-Mo isotopes on the same samples, our new results suggest that fluid exsolution is required to elevate the delta Fe-57 of the felsic melts by up to 0.15 permil, but subsequent fluid-melt reaction reduces the Fe isotopes and leads to similar light-Fe isotope compositions of final residual melts to their primary magma. Therefore, the high-silica granites can be enriched in light Fe isotopes due to the effects of magmatic fluids, which make a significant contribution to the formation and evolution of upper continental crust
Atomic Insights into the Heterogeneous Crystallization of Manganese (Oxyhydr)oxides on Typical Iron (Oxyhydr)oxides: from Adsorption to Oxidation to Crystallization
No full textHeterogeneous crystallization of manganese (oxyhydr)oxides (MnO x ) on iron (oxyhydr)oxides (FeO x ) is crucial for the biogeochemical cycling of Mn, yet atomic-level insights into this process are important but relatively limited. Herein, we revealed the distinct adsorption, oxidation, and crystallization mechanisms of Mn on hematite (Hem), ferrihydrite (Fhy), and goethite (Gth). Gth exhibited highest ability in Mn(II) removal and oxidation, followed by Hem and Fhy. Manganite and hausmannite were the main MnO x products with distinct proportions, and morphologies cross the systems. MnO x growth mechanisms involve surface-induced nucleation, crystallization by particle attachment (CPA), and self-catalyzed growth. On Fhy, self-catalyzed growth was dominant; for Gth, surface-induced nucleation was prevalent, supplemented by CPA; and Hem combined all three mechanisms. These distinct mechanisms led to nanoparticles primarily of hausmannite on Gth and nanowires of manganite and hausmannite on Hem and Fhy, with those on Hem displaying lower aspect ratios. Differences in MnO x structure and morphology were attributed to Mn(II)-FeO x complexation, FeO x electronic band structure, and crystal structure mismatch between MnO x and FeO x , which respectively influenced the direct and indirect electron transfer and heterogeneous nucleation efficiency. This work advances our understanding of MnO x crystallization on FeO x at the nanoscale, explaining the diverse morphology and structure of MnO x in different environments
From bedrock to life activity and atmospheric deposition: Drivers of soil element coupling across horizons
No full textUnraveling the intricate coupling of multiple elements and their underlying drivers in natural soils is crucial for comprehending ecosystem functions, yet this knowledge has remained elusive. Using a comprehensive dataset of 900 soil samples collected from 116 sites across 26 mountains, this study dissected the coupling relationship of 23 elements within three soil development horizons, spanning five climate zones in China. Our findings revealed a robust continental-scale coupling of soil elements, influenced by plants and environmental factors including spatial distance, climate, soil properties, and atmospheric nitrogen deposition, accounting for 36% of the observed variance in element coupling. Notably, our study unveiled the horizon-specific nature of element coupling mechanisms. In the parent horizon, rock type exerted the primary control on the dynamics of element coupling. However, as soil developed, life activities and atmospheric deposition of anthropogenic trace metals concurrently reshaped the element coupling patterns, particularly in the organic and surficial mineral horizons. Elements were divided into two distinct elemental groups, exhibiting opposite fitting trends with atomic mass and crustal abundance, and the effect of these properties on coupling diminished with soil depth. Heavy metals enriched by human activity deviated from property-based predictions with lower coupling. This study represents the first continental-scale quantification of multi-element coupling across soil horizons, underscoring the paramount importance of life activity and atmospheric deposition in modulating the initial lithological-mediated multi-element coupling. Our insights advance understanding of terrestrial ecosystem biogeochemistry and urge further research on the impacts of anthropogenic activities and environmental changes on these delicate elemental interactions
Fractionation of radiogenic Pb isotopes in meteorites and their components induced by acid leaching
No full textIn this study we test the possibility that radiogenic 207Pb/206Pb ratios (207Pb*/206Pb*) in meteorites can be fractionated during partial dissolution, and explore the consequences of this fractionation for Pb-isotope chronology of meteorites. We report the results of experiments tailored to detect Pb-isotope fractionation, induced by partial dissolution through acid leaching, in plutonic angrite Northwest Africa (NWA) 4801 and ungrouped achondrites NWA 10132 and Erg Chech (EC) 002. We also re-examine previously published U-Pb data for other achondrites and for Ca-Al-rich refractory inclusions (CAIs), to seek evidence of such fractionation. We observe that, in primitive achondrite NWA 10132, differences in 207Pb*/206Pb* ratios, corresponding to the age bias of ca. 1-2 Ma, exist between the 0.5 M hydrofluoric acid leachates of pyroxene or crushed rock, and the residues after such leaching. In angrite NWA 4801, similar acid treatment of pyroxene separates did not cause a resolvable age bias. In EC 002, three steps of partial dissolution in 0.2 M - 5 M HF caused irregular 207Pb*/206Pb* fractionation between leaching steps, and generally higher 207Pb*/206Pb* ratios in the residues than in HF leachates. These age biases were observed in leaching pairs with highly radiogenic Pb, and cannot be explained by mixing between radiogenic Pb, primordial Pb, and Pb introduced by terrestrial contamination. Instead, the observed isotope fractionation is attributed to the combined effects of the size difference between alpha-recoil tracks in the decay chains of 238U and 235U, and exsolution of primary pigeonite, leading to the formation of a lamellar structure consisting of augite and low-Ca pyroxene by either slow-cooling or subsequent metamorphic reactions. Where extensive acid leaching intended for removal of non-radiogenic Pb causes fractionation of radiogenic Pb isotopes, its detrimental effect can be reversed by performing a numeric recombination of partial leachate and residue data. Currently, it is unclear how common leaching-induced isotopic fractionation is in Pb-isotopic chronology to meteoritic materials. Acid leaching is an essential step for removal of non-radiogenic Pb in the precise Pb-isotopic dating of meteorites, which currently does not have viable alternatives. However, it is important to be aware of its possible side effects, and to continue search for new non-radiogenic Pb removal techniques that do not cause radiogenic 207Pb* and 206Pb* fractionation
Pegmatite lithium deposits formed within low-temperature country rocks
No full textThe global climate crisis is likely to lead to a potential supply risk of lithium (Li) over the coming decades. More than half of the world's production of Li is derived from Li-bearing pegmatites. Although pegmatites are widespread, only a small fraction host economically relevant Li mineralization. Revealing which factors cause some pegmatites to be enriched in Li and others to be barren is critical for understanding Li pegmatite formation and for guiding exploration for new Li resources. In this study, we used an approach involving the analysis of natural samples from the Jiajika pegmatite deposit (China), combined with thermal and diffusion modeling. Here we show that Li contents in pegmatites are controlled not only by the initial Li contents in pegmatite melts but also by the temperature of the surrounding country rocks at the time of pegmatite emplacement. Lithium-mineralized pegmatites form preferentially when Li-rich pegmatite melts intrude low-temperature country rocks
Sedimentary responses to climatic variations and Kuroshio intrusion into the northern South China Sea since the last deglaciation
No full textThe terrigenous sediment source-to-sink processes in marginal seas are governed by intricate interactions among climate, sea level, and ocean currents. The continental slope of the northern South China Sea (SCS) provides an excellent setting to examine these processes due to its substantial terrigenous influx and continuous sedimentation. In this study, we present a high-resolution sedimentary record from the northern SCS continental slope covering the last deglaciation. Analyses of Rare Earth Elements (REEs) and Sr-Nd isotopic compositions in the NH07 core indicate that the predominant source of terrigenous sediment was Taiwan. Grain size-standard deviation analysis identified two sensitive grain size components, with the sensitive component 2 used as a marker of the Kuroshio intrusion into the northern SCS through Luzon Strait. The intensity of the Kuroshio intrusion into the northern SCS was found to be inversely related to that of the open Pacific. The Asian monsoon and El Nino- Southern Oscillation (ENSO) significantly influenced the variability of the Kuroshio Current throughout the deglaciation period. During the interval 16, 000-11, 700 cal yr BP, variations in terrigenous influx were collectively driven by sea level changes and the intensity of the Kuroshio intrusion, while chemical weathering intensity was affected by the reworking of previously exposed shelf sediments due to sea level fluctuations. During the Holocene, however, the East Asian summer monsoon intensity became the primary factor influencing variations in terrigenous influx and chemical weathering
Molecular simulation on Cs, Rb retention in Na/K-montmorillonite interlayer coupling clay swelling/collapse
No full textA key issue about radioactive waste disposal and nuclear accident contamination control is the retention of radionuclides in clay minerals. The cation (Cs+, Rb+, Na+, K+) selectivity in montmorillonite (Mt) interlayers have not been quantitatively studied. This work employs classical molecular dynamics (CMD) to systematically investigate the interlayer structure, swelling properties, diffusion dynamics, and cation exchange processes. The selectivity of alkali ions within the interlayer space coupled with clay swelling/collapse under different water activity (a(w)) and cation activity, has been quantified. Both Cs-, Rb-Mt demonstrate a monolayer hydrate configuration as the most stable state. The mobility of intercalated species, as indicated by self-diffusion coefficients, exhibits a stepwise trend with increasing water content. The cationic selectivity within the interlayer follows the order Cs+ > Rb+ > K+ > Na (+) at a(w) = 1.0. The logarithm values of the selectivity coefficients for Cs/Rb relative to Na/K are as follows: logK(c)(Cs/K) = 0.73, logK(c)(Cs/Na) = 1.62, logK(c)(Rb/K) = 0.62, and logK(c)(Rb/Na) = 1.57 at a(w) = 1.0. A model correlating selectivity coefficients with water activity has been proposed. It is noted that Cs+ and Rb+ ions tend to accumulate within the interlayer as water activity decreases, and interlayer Rb+ competes with Cs+ for exchange positions at low water activity. These results can be used to quantify cationic partitioning during the remediation of radiocesium contamination in soil and weathering processes of sediments
Microbial recruitment and microbial ecological roles in soil nutrient cycling of Populus cathayana males and females
No full textSoil nitrogen (N) availability influences plant production and soil nutrient cycling. However, how it influences sex-specific microbial community composition and rhizosphere nutrient cycling in dioecious plant species is poorly understood. We examined the rhizospheric bacterial and fungal community assemble and their influences on soil nutrient cycling under different N backgrounds in 30-year-old experimental stands and a soil microbial reshaping-controlled experiment. In comparison to male trees, female trees increased fungal community diversity, and the relative abundance of taxa related to nutrient availability; elevated phosphorus (P) mobilization by increasing acidic phosphatase activity and carboxylic acid release; and decreased the counts of denitrification nirS, nirK, and nosZ genes at high N supply. Males increased the nifH gene counts related to microbial N fixation at high N supply. Low N supply increased N fixation nifH gene counts in the rhizosphere of females. Males decreased bacterial and fungal diversity, increased enzymatic activities related to organic N and P mineralization, and elevated soil nitrate-nitrogen levels at low N supply. Our results indicate that sex-specific responses to N availability are associated with rhizospheric bacterial and fungal community composition and diversity and their effects on rhizospheric nutrient cycling, which may explain sex-specific resource utilization and niche differentiation
A comparative study on the formation of nitrogen-containing organic compounds in cloudd roplets and aerosolp articles
No full textNitrogen-containing organic compounds (NOCs)maypotentiallycontributetoaqueoussec-ondaryorganicaerosols,yet the different formationofNOCsinaerosolparticlesand clouddropletsremainsunclear. With the in-situmeasurementsperformedatamountainsite(1690ma.s.l.)in southernChina,weinvestigatedtheformationofNOCsintheclouddropletsandthecloud-freeparticles,basedontheirmixingstateinformationofNOCs-containingparticlesbysingleparticlemassspectrometry.TherelativeabundanceofNOCsinthecloud-freeparticleswassignificantlyhigherthanthoseincloudresidual(cloudRES)particles.NOCswerehighlycorrelatedwithcarbonylcompounds(includingglyoxalateandmethylglyoxal)inthecloud-freeparticles,however,limitedcorrelationwasobservedforcloudRESparticles.AnalysisoftheirmixingstateandtemporalvariationshighlightsthatNOCswasmainlyformedfromthecarbonylcompoundsandammoniuminthecloud-freeparticles,ratherthaninthecloud RES particles.Theresultssupportthattheformation of NOCsfromcarbonylcompoundsisfacilitatedinconcentratedsolutionsinwetaerosols,ratherthanclouddroplets.In addition,we have identified the transport of biomass burnin
Size-segregated nitrated aromatic compounds in PM10 and potential health risks in Guangzhou, South China
No full textNitrated aromatic compounds (NACs) are toxic, light-absorbing components of particulate matter, impacting both human health and climate. This study conducted a 14-day field campaign at an urban site in Guangzhou, southern China, collecting size-segregated aerosol samples at cutting points of 0.49, 0.95, 1.5, 3.0, 7.2, and 10 mu m, to analyze NAC size distribution, light absorption, and toxicity. Nearly 90% of NACs were concentrated in particulate matters with aerodynamic diameter smaller than 1.5 mu m (PM1.5). Their concentrations on polluted days strongly correlated with molecular markers from primary emissions, especially from coal combustion. Backward trajectory analysis indicated that northern coal-fired sources significantly contributed to pollution levels. Filter-based light absorption measurements showed that over 90% of brown carbon (BrC) were concen- trated in PM0.95. Despite lower mass concentrations of the 9 toxic NACs compared to the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs), their Benzo[a]pyrene toxic equivalency quotients (TEQBaP) were substantially higher, with 1,6-dinitropyrene, 1,8-dinitropyrene, and 6-nitroperylene accounting for 95% of the TEQBaP. 1,6-dinitropyrene was the dominant contributor to NACs' TEQBaP on both clean and polluted days. The TEQBaP of NACs exceeded 1.0 ng m-3, indicating substantial health risks associated with exposure. These findings highlight the urgent need for emission control to mitigate the health impact of NACs