Guangzhou Institute of Geochemistry
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Variations of the atmospheric polycyclic aromatic hydrocarbon concentrations, sources, and health risk and the direct medical costs of lung cancer around the Bohai Sea against a background of pollution prevention and control in China
No full textThe Bohai Sea (BS) region, an area of China that is severely polluted with atmospheric polycyclic aromatic hydrocarbons (PAHs), has received wide attention in recent decades. To characterize the variations of the concentrations and sources of PAHs from June 2014 to May 2019, 15 PAH congeners (Sigma(15)PAHs) were measured in atmospheric samples (N=228) collected at 12 sites around the BS, and the health risk and direct medical costs associated with lung cancer caused by exposure to PAHs were also estimated. The annual daily average concentration of Sigma(15)PAHs was 56.78 +/- 4.75ng m(-3), which was dominated by low molecular weight PAHs (LMW-PAHs) containing three rings (58.7 +/- 7.8%). During the 5-year sampling period, the atmospheric Sigma(15)PAHs concentration reduced by 17.5% for the whole BS region, with an especially large drop of 51.7% observed in the tightly controlled area of Tianjin (TJ), which was mainly due to a decrease in the concentration of high molecular weight PAHs (HMW-PAHs) containing five or six rings. Generally, the concentration of Sigma(15)PAHs was highest in winter and lowest in summer, which can mainly be attributed to the change in LMW-PAH concentration. Based on the positive matrix factorization (PMF) model, PAHs in the BS region were mainly ascribed to coal combustion and biomass burning. The PAH contributions of coal combustion and motor vehicles showed different trends for the BS region (PAHs from coal combustion rose by 7.2% and PAHs from motor vehicles fell by 22.4%) and for TJ (PAHs from coal combustion fell by 12.6% and PAHs from motor vehicles rose by 6.9%). The incidence of lung cancer (ILCR) caused by exposure to atmospheric PAHs decreased by 74.1% and 91.6% from 2014 to 2018 in the BS region and in TJ, respectively. This was mainly due to the decrease in the concentration of highly toxic HMW-PAHs and was reflected in USD10.7 million of savings in direct medical costs of lung cancer caused by exposure to PAHs, which represent a decrease of 46.1% compared to the corresponding costs before air pollution prevention and control was implemented around the BS. There was an even higher reduction in medical costs of 54.5% in TJ. Hence, this study proves that implementing pollution prevention and control not only effectively reduced the concentration of pollutants and the risks caused by them, but it also significantly reduced the medical costs of diseases caused by the corresponding exposure
Measurement report: Effects of transition metal ions on the optical properties of humic-like substances (HULIS) reveal a structural preference - a case study of PM<sub>2.5</sub> in Beijing, China
No full textHumic-like substances (HULIS) are complex macromolecules in water-soluble organic compounds (WSOCs) containing multiple functional groups, and transition metal ions (TMs) are ubiquitous in atmospheric particles. In this study, potential physical and chemical interactions between HULIS and four TM species, including Cu2+, Mn2+, Ni2+, and Zn2+, were analyzed by optical method under acidic, weakly acidic, and neutral conditions. The results showed that Cu2+, Mn2+, and Zn2+ only slightly enhanced mass absorption efficiency (MAE(365)) of HULIS in winter and had indiscernible effects on the absorption & Aring;ngstr & ouml;m exponent (AAE) of HULIS in both seasons under all acidity conditions. All four TMs had fluorescence quenching effects on winter HULIS, and only Cu2+ had similar effects on summer HULIS, with the highest quenching coefficients found under weakly acidic conditions in both seasons. The H-1-nuclear magnetic resonance (H-1-NMR) and Fourier-transform infrared (FTIR) spectra revealed that Cu2+ mainly bound with aromatic species and tightened the molecule structures of HULIS. The parallel factor analysis (PARAFAC) results extracted four components of HULIS, including low-oxidized humic-like substances (C1), N-containing compounds (C2), highly oxidized humic-like substances (C3), and the mixing residuals (C4), from the fluorescence spectra in both winter and summer. The spectral characteristic of HULIS with Cu2+ additions under three acidity conditions indicated that electron-donating groups of HULIS mainly corresponded to C1 and C3, with Cu2+ binding with HULIS by replacing protons, while electron-withdrawing groups of HULIS could correspond to C2, with its connection with Cu2+ through electrostatic adsorption or colliding-induced energy transfer
Contribution of abiotic methane polymerization of C2+hydrocarbons in highly mature natural gas reservoirs
No full textThe formation and evolution of thermogenic gases were investigated using a combination of intermolecular and intramolecular isotope analyses of 32 natural gas samples collected from the Sichuan and Tarim basins (China) and the Arkoma Basin (USA). Three evolution stages (I-III) were identified: In stage I, hydrocarbon gases are produced through thermal decomposition of organic matter, and kinetic isotope effects in C-C bond breakage control their isotopic distributions; In stage II, C2-C5 hydrocarbons crack with increasing thermal maturity, with their formation and decomposition tending toward thermodynamic equilibrium, and at the end of this stage, the intermolecular and intramolecular isotopic compositions of gaseous hydrocarbons are in thermodynamic equilibrium; A remarkable feature of stage III is the surface-catalyzed abiotic polymerization of methane, which provides a critical origin of C2+ hydrocarbons in this stages and leads to isotopic anomalies in C2+ hydrocarbons, including the reversal of 613C distributions of C1-C3 and the reverse evolution trend of SP value of propane (i.e., tending to be positive). The contribution of C2+ hydrocarbons from the abiotic polymerization of methane can be determined based on a two-end member model. C2+ hydrocarbons in the Changning shale gases are all generated from abiotic methane polymerization, and the contribution ratio in the Weiyuan shale gases is about 85 %, while, the contribution of C2+ hydrocarbons in dry gases from the Tarim Basin formed by this way is no more than 55 %. High methane abundance, high temperature, and abundant catalyst are beneficial to abiotic methane polymerization
Paleozoic Episodic Magmatism in Western Tianshan: Insight Into Assembling the Northeastern Pangea
No full textThe late-stage union of Pangea was associated with the convergence of Siberia with Laurussia, but the exact timing remains unclear. The orogenic duration of the Kazakhstan block can provide geochronological constraints as it connects Siberia, Baltica, and Tarim. Zircon petrochronology offers a reliable approach for ascertaining the lifespan of an ancient orogen. In this study, we explore three phases of magmatism recorded in detrital zircons from late Paleozoic and Mesozoic sandstone-siltstones in Western Tianshan, that is, 400-470 Ma, 320-380 Ma, and 280-320 Ma. Based on their age-propagated Hf isotopes, melt SiO2 contents, and crustal thicknesses, our findings suggest that the southern limb of Kazakhstan underwent the early Paleozoic amalgamation of microcontinents with arcs, the late Paleozoic maturation of an Andean-like continental arc, and the late Carboniferous collision of Kazakhstan with the Junggar oceanic basin and the Tarim craton. Such characteristics manifest the long-term orogenic progression of Kazakhstan. Combining published timelines and paleolatitudes of major orogens and blocks, we propose that the Kazakhstan block welded northeastern Pangea along with the cessation of these orogenic activities around it. Consequently, by docking Kazakhstan with surrounding cratons, the fundamental configuration of Pangea could have been established in the late Carboniferous.
Pangea was suggested to have assembled at ca. 250 Ma upon paleogeographic reconstructions. However, the assembling time remains a matter of debate due to low-quality Permo-Carboniferous paleomagnetic data on the northeast of Pangea; thus, other geochronological records need to be determined. Here, we employ the method of zircon petrochronology to trace the orogenic processes of Kazakhstan because it serves as a pivot in welding peripheral Siberia, Baltica, and Tarim blocks. Our results demonstrate that episodic variations in melt compositions, crustal thicknesses, and Hf isotopes reveal the long-lived orogenic progression of the southern limb of Kazakhstan and constrain its incorporation into Pangea to the late Carboniferous. Such an event was almost contemporaneous with the assembly of Baltica and Siberia with the northern limb of Kazakhstan but occurred slightly later than the collision of Laurussia with Gondwana. As such, the fundamental configuration of Pangea could have been established in the late Carboniferous rather than the Permian, as previous paleogeographic reconstructions postulated.
Detrital zircons in Western Tianshan record three phases of Paleozoic magmatism Zircon petrochronology can trace orogenic processes of the southern limb of Kazakhstan Docking Kazakhstan with surrounding cratons in the late Carboniferous marked the major assembly of the northeastern Pange
Identification of carbonated eclogitic source for Cenozoic intraplate alkaline basalts from western Central Asia and its geodynamic implication
No full textCarbonated eclogite has been identified as a significant component in the formation of intraplate alkaline basalts, typically attributed to stagnated subducted oceanic slabs, such as the Pacific plate beneath eastern China. However, it is unclear whether this component exists in other tectonic settings. Here, we present new zircon U-Pb geochronology, mineral chemistry, and geochemical analyses of Cenozoic Tuoyun basanites and alkaline basalts from western Central Asia, where stagnated subducted oceanic slabs are absent, to elucidate the source properties and associated geodynamic processes. Olivine compositions (e.g., moderate Ni concentrations, low Mn/Fe and Ni/(Mg/Fe) ratios) and whole-rock chemistry (e.g., high Fe/Mn, Ca/Al, and Zr/Hf ratios, TiO2 contents, and weak anomalies of Zr-Hf-Ti) suggest a carbonated eclogite in the mantle source of the Tuoyun basanites. Trace elements (positive Nb-Ta anomalies and absence of positive Eu anomaly) and depleted to slightly enriched Sr-Nd-Hf isotopic compositions indicate that the basanites originated from mantle sources composed of variable proportions of altered oceanic crust (AOC) and carbonates. Synthesizing regional geochemical, geophysical studies and tectonic history, we propose that the continuous India-Eurasia collision triggered mantle upwelling, leading to the formation of a widespread carbonated eclogitic mantle source beneath western Central Asia. Our findings suggest that carbonate-rich mantle sources may also be present in areas without stagnated subduction slabs
Magmatic degassing and fluid metasomatism promote compositional variation from I-type to peralkaline A-type granite in the late Cretaceous Fuzhou felsic complex, SE China
No full textA-type granites generally have much lower water, higher temperature, and incompatible element concentrations than I-type granitoids. Yet it remains unclear why I-A-type granitic complexes occur in convergent plate margins. Here we conduct geochemical analyses on apatite and mafic minerals from the late Cretaceous I-A-type granitic complex in Fuzhou area, SE China, aiming to decipher differentiation, fluid metasomatism, and degassing that primarily control the compositional diversity of felsic magmas. Apatites in both rock types are F-rich and show large H2O and delta D variations, i.e., 341-3892 ppm H2O and -325 to +336 parts per thousand delta D in I-type granitoids; 67-1366 ppm H2O and -251 to +1439 parts per thousand delta D in A-type granites. H2O in apatite is negatively correlated with La/Sm and Sr/Y in the I-type granitoids, whereas it is positively correlated with Ce and total rare earth element (REE) concentrations in the A-type granites. Once H2O increases up to hundreds of ppm, both rock types show a rapid decrease of H2O/Ce, an increase of F/Cl, and extensive H isotope fractionation. Arfvedsonite occurs as a late crystallizing mineral in the A-type granite and has much higher contents of Na2O, K2O, F, and high field strength elements (HFSE) than hornblende in the I-type granitoids, indicating the addition of F-HFSE-rich alkaline fluids during its magmatic evolution. The consumption of arfvedsonite and formation of aegirine further indicate the role of fluid metasomatism and H-2 degassing via a reaction of 3Na(3)Fe(5)Si(8)O(22)(OH)(2) + 2H(2)O = 9NaFeSi(2)O(6) + 2Fe(3)O(4) + 6SiO(2)+5H(2). The combined geochemical data demonstrate that the systematic differences in mineral assemblage, whole-rock composition, magma temperature, H2O content, and delta D of apatite between the I- and A-type granites are likely attributed to varying degrees of differentiation, fluid metasomatism and magmatic degassing. The I-type granitoids experienced hornblende, biotite, plagioclase, K-feldspar, and apatite fractionation and close-system degassing. The A-type granite was likely formed from the I-type monzogranitic magma that was metasomatized by the mantle-derived F-HFSE-rich alkaline fluids to produce the peralkaline magma, which further experienced K-feldspar + plagioclase + biotite + apatite fractionation and open-system degassing. Further numerical estimation indicates that the primary magma of Fuzhou granitic complex contained similar to 3.0 wt% H2O, and the lower water content of A-type granite was likely attributed to strong degassing during its emplacement. Our results indicate that some peralkaline A-type granites can be generated from relatively water-poor I-type granitic magmas by fluid metasomatism and degassing
Dual-carbon isotope analysis of benzene polycarboxylic acids for tracking black carbon across different environments
No full textBlack carbon (BC) is ubiquitous in the environment and is a significant component of the refractory carbon pool. However, its sources, biogeochemical processes, and environmental residence times are poorly understood. One important reason is that the technical protocols for isolating/analyzing BC vary across different matrices, thereby bringing inconsistency among studies on BC in different environment media. Benzene polycarboxylic acids (BPCA), produced by nitric acid oxidation of the condensed aromatic structure that is common in BC and BC-like substances, has been proven to be a useful molecular proxy for tracking BC in the Earth's surface. Here, we introduce a new technical approach for the compound-specific dual-carbon isotope (813C and A14C) analysis of BPCA. The BPCA compounds are isolated using preparative liquid chromatography, in which trifluoroacetic acid is used in the mobile phase instead of phosphoric acid. This allows complete removal of solvent from the isolated BPCA fraction, so that conversion of BPCA isolates into CO2 can be done by conventional oxidation methods for off-line Delta 14C analysis with accelerator mass spectrometry. Liquid chromatography (void column)-stable carbon isotope ratio mass spectrometry is employed to measure 813C of the isolated BPCA, leaving as much BPCA carbon amount as possible for 14C analysis. Blockage of oxidation chamber due to incomplete oxidation of other organic acids in the samples is avoided thanks to preliminary isolation of BPCA. We tested the approach by applying it to solid and dissolved BC species in a suite of environmental reference materials, including maize char, coal, riverine natural organic matter (NOM 2R101N), marine sediment (SRM 1941b), urban dust (SRM 1649b), and coke-polluted soils. We assessed the offsets of BPCA-813C and BPCA-A14C values caused by procedural carbon contaminations to correct measured carbon isotopic values. Paired 813C-A14C data of individual BPCA were plotted to validate and demonstrate the ability of this dual carbon isotope technique in tracking BC across different environmental matrices. We observed slightly different 813C-A14C signatures among individual BPCA, indicating that the less condensed BC may have younger apparent radiocarbon ages
The bending of a supra-subduction zone produced crustal thickening and arc migration of the Mongolian Orocline
No full textOrogenic curvatures have been widely recognized along global convergent plate boundaries. Understanding the impact of such curvatures on the tectonic evolution of orogens and their three-dimensional architecture has been challenging. Here we address this issue by studying magmatism around the tightly curved Mongolian Orocline in Central Asia. Our results show that during the Permian-Triassic, arc magmatism around the inner hinge of the orocline became younger towards the core of the orocline. During the same period, the crust was thickened, as indicated by Lanthanum-Ytterbium ratio proxy. These findings, together with the observation that the present-day hinge zone of the Mongolian Orocline is wider, indicate that this zone was subjected to significant crustal-scale contraction. This contractional deformation accounts for the relatively thicker crust around the inner hinge of the Mongolian Orocline, and offers a novel perspective on the formation of elevated topography around the hinge of curved plate boundaries.
Significant contractional deformation produced crustal thickening in the inner hinge of the Mongolian Orocline, according to geochemical data from Permian-Triassic granitoids
Using pyrite composition to track the multi-stage fluids superimposed on a porphyry Cu system
No full textThe Yulekenhalasu porphyry Cu-Mo deposit (0.2 Mt Cu at 1.04 wt% and 0.012 Mt Mo at 0.06 wt%) is located in the Devonian Halasu copper belt, East Junggar block, northwest China. At Yulekenhalasu, Cu and Mo mineralization commonly occurs as disseminated sulfides or veinlets in porphyry-related alteration zones. Five alteration stages have been identified, including porphyry-type alteration, i.e., sodic-calcic (stage I), potassic (stage IIa), propylitic (stage IIb), and phyllic (stage III) alteration, and widespread late Cu sulfide-bearing veins (stage IV) cross-cutting porphyry-type alteration, plus a post-ore fault-controlled argillic alteration (stage V). Stages IV and V have overprinted porphyry-type alteration (stages I-III).
Anomalous concentrations of trace elements in stage IIb pyrite (e.g., Ti, Zr, Gd, and Hf) are due to the presence of micro-inclusions (e.g., zircon and rutile) in the low-temperature (similar to 200 degrees C) propylitic zone. Cu, Ag, Co, and Mn, occurring as stoichiometric substitutions or as tetrahedrite inclusions in overprinting stage IV pyrite, were sourced directly from the primary hydrothermal fluid. The enrichment of distal pathfinder elements (e.g., Cr, Au, and Tl) in overprinting stage V pyrite was caused by a low-temperature (similar to 160 degrees C) hydrothermal event related to regional orogenic Au mineralization. The spatial variation of Se/S in pyrite among various paragenetic stages were influenced by changes in the hydrothermal fluid composition and temperature, with the latter having the effect of decreasing pyrite Se/S. Lower Se concentrations in pyrite of stages IIb and III close to the orebody are explained by relatively higher temperatures in the locus of mineralization. This may provide a potential vectoring tool to mineralization using pyrite geochemistry in porphyry deposits.
Systematic thermodynamic calibrations were applied to pyrite compositions to fingerprint the corresponding Se/S and Co/Ni ratios of fluids and further to develop a complete metallogenic model for Yulekenhalasu. The Devonian diorite porphyry generated fluids that produced the early porphyry-type alteration. High Co/Fe (average similar to 1 x 10(-4)) and Ni/Fe (average similar to 3 x 10(-6)) ratios of fluid for late Cu sulfide-bearing veins, combined with higher Se/S (average similar to 6 x 10(-7)) than orogenic Au deposits (average similar to 3 x 10(-8)), indicate that the fluids possibly derived from a Late Devonian-Carboniferous mafic intrusion. Argillic alteration assemblages forming at ca. 280 Ma host pyrite relatively enriched in Au (average 0.1 ppm, with native gold inclusions). Therefore it is likely related to a regional orogenic gold mineralizing event in the Early Permian that overprinted Devonian mineralization. Although spatially contiguous, hydrothermal alteration and hypogene mineralizing stages identified herein represent discrete episodes of hydrothermal activities at Yulekenhalasu. The multi-stage alteration features observed at Yulekenhalasu may provide insights into the complete evolutionary history of Paleozoic porphyry Cu deposit systems in the Central Asian orogenic belt. This study contributes to a better understanding of the metallogenic and exploration models of porphyry Cu deposits overprinted by multi-stage hydrothermal events, which is economically important in Phanerozoic orogenic belts
Air-plant interaction and air-soil exchange of polycyclic aromatic hydrocarbons in a large human-influenced reservoir in southwest China*
No full textThe Three Gorges Reservoir (TGR) is totally manmade, strongly influenced by anthropogenic activity, and lies on the upper reaches of Yangtze River. The periodic storage and discharge of water from the Three Gorges Dam could have altered the original air-plant/soil interactions of contaminants in TGR. Herein, paired atmospheric gas-particle, air-plant, and air-soil samples were collected to investigate the air-plant interaction and air-soil exchange of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). The air-plant interaction based on McLachlan's framework to our datasets suggests that PAHs were absorbed via gaseous deposition that was restricted by the plant-gas dynamic equilibrium. The equilibrium indicates a dynamic balance between the gaseous phase and plant surface in PAH absorption. The main limiting factor influencing the PAH uptake was the plant species rather than the atmospheric PAH concentration. The air-soil exchange of PAHs exhibited a net volatilization flux of 16.71 ng/m2/d from the soil to the air based on annual average. There was more volatilization and less deposition in summer and more deposition and less volatilization in autumn and winter. The soil serves as a secondary source of atmospheric PAHs. As the first attempt on probing the multi-interface geochemical process of PAHs, this study highlights the influence of manual water level manipulation from the TGD and environmental factors (such as temperature, humidity, and soil properties) on the regional fate of PAHs in the TGR