Guangzhou Institute of Geochemistry
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Enhanced daytime secondary aerosol formation driven by gas-particle partitioning in downwind urban plumes
No full textAnthropogenic emissions from city clusters can significantly enhance secondary organic aerosol (SOA) formation in the downwind regions, while the mechanism is poorly understood. To investigate the effect of pollutants within urban plumes on organic aerosol (OA) evolution, a field campaign was conducted at a downwind site of the Pearl River Delta region of China in the fall of 2019. A time-of-flight chemical ionization mass spectrometer coupled with the Filter Inlet for Gases and Aerosols (FIGAERO-CIMS) was used to probe the gas- and particle-phase molecular composition and thermograms of organic compounds. For air masses influenced by urban pollution, strong daytime SOA formation through gas-particle partitioning was observed, resulting in higher OA volatility. The obvious SOA enhancement was mainly attributed to the gas-particle partitioning of high-volatility (semi-volatile organic compounds + intermediate volatility organic compounds + volatile organic compounds, mu g m(-3)) organic vapors. Using the equilibrium equation could underestimate the contribution of high-volatility organic vapors, since the volatility of these species in the particle phase was lower than that in the gas phase. We speculated that the elevated NOx concentration could suppress the formation of highly oxidized products, resulting in a smooth increase of low-volatility (extremely low volatility organic compounds + low volatility organic compounds, mu g m(-3)) organic vapors. Evidence has shown that urban pollutants (NOx and VOCs) could enhance the oxidizing capacity, while the elevated VOCs were mainly responsible for promoting daytime SOA formation by increasing the RO2 production rate. Our results highlight the important role of urban anthropogenic pollutants in SOA control in the suburban region
Polystyrene microplastics exposure: Disruption of intestinal barrier integrity and hepatic function in infant mice
No full textThe pervasive presence of microplastics (MPs) in infant formula and care products has emerged as a significant and underappreciated risk to public health. Notably, infants are at an elevated risk due to their underdeveloped intestinal defenses and liver detoxification capabilities, factors that could heighten their vulnerability to MPs. This study presents a comprehensive evaluation of the health implications linked to polystyrene microplastics (PSMPs) exposure during early life, examining both environmentally plausible and elevated levels. Based on histological analysis, in vivo imaging analysis, biochemical analysis and 16S rRNA sequencing results, our study found that oral PSMPs exposure in infant mice led to profound toxicological consequences, such as intestinal barrier impairment and hepatic injury, in a dose-dependent manner. Strikingly, even low ambient concentration of PSMPs (20 ppb) was sufficient to inflict considerable harm, disrupting the intestinal barrier, manifested that lessened mucus secretion, elevated iFABP level (276.50+10.73 pg/mL), decreased sIgA levels (0.60+0.03 mg/g), and pathological damage of intestinal tissues, allowing PSMPs accumulation and leakage into blood, inducing hepatotoxicity, such as increased TG levels (0.99+0.05 mmol/gprot) and lipid droplet accumulation. Furthermore, PSMPs exposure gives rise to aberrant bacterial colonization, dropping the abundance of probiotics as well as altering the abundance of pathogenic bacteria, which may contribute to the toxicity outcomes. The study underscores the critical need for vigilance regarding the insidious effects of PSMPs at environmental-relevant concentrations, especially in the context of infant exposure
A modified genetic model for multiple pulsed mineralized processes at the giant Qulong porphyry Cu-Mo mineralization system
No full textPorphyry copper deposits are economically significant sources of Cu and Mo, formed when metal-rich fluids precipitate at shallow levels, exsolving from underlying magmatic reservoirs at depth. However, the origin and evolution of these metal-rich fluids, whether through episodic enrichment from multiple pulses or a single continuous fluid-release event, remain a subject of controversy. To gain deeper insights into these processes, data on cathodoluminescence (CL) imaging, in situ trace elements, and Sr isotopes of newly discovered scheelite (Sch 1, Sch 2, and Sch 3) found in three generations of vein types within the giant Qulong porphyry Cu-Mo mineralization system are presented. The anhedral Sch 1 occurs in quartz + magnetite + anhydrite + chalcopyrite veins, exhibiting no obvious zoning in the CL image. These scheelite samples show high concentrations of Mo, Nb, Ta, and 87Sr/86Sr ratios ranging from 0.70688 to 0.71109. Moreover, they demonstrate enriched rare earth elements (REE) and negative Eu anomalies in the chondrite-normalized pattern, indicative of their formation in relatively oxidized metal-rich fluids during the early high-temperature alteration stage. Among the discovered scheelite varieties, the most volumetrically significant is the subhedral Sch2, which occurs in veins composed of quartz + pyrite + chalcopyrite. In its central region (Sch 2a), Cu-rich cores are dispersed, surrounded by an oscillatory Cu-poor mantle and rim (Sch 2b and 2c), as observed in the CL image. When compared to Sch 1, Sch 2 exhibits lower levels of REE, Nb, Ta, Mo, and 87Sr/86Sr ratios (ranging from 0.70502 to 0.70578), but higher Cu concentration and positive Eu anomalies. The gradual decrease in Cu content from the core to rim in Sch2, along with its rim's intergrowth with sulfide, suggests the precipitation of Cu during the second pulse of fluids. Euhedral Sch 3 is found in relatively moderate-temperature mineral assemblages within quartz + galena + sphalerite + molybdenite veins. It displays an oscillatory pattern with a Mo-rich core (Sch 3a), an extremely Mo-rich mantle (Sch 3b), and a Mo-poor rim (Sch 3c) in the CL image. Sch 3 shows lower REE, Cu, and Pb contents but variable Mo concentrations in different domains while consistently recording 87Sr/86Sr ratios ranging from 0.70498 to 0.70542. These characteristics indicate the precipitation process of Mo and Pb during the third pulse of fluid evolution. The observed shift in mineral assemblages, metal contents, and Sr isotopic components from Sch 1 to Sch 3 reflects the occurrence of different fluid pulses within a cooling porphyry Cu-Mo mineralization system. Overall, the three generations of scheelite found at the Qulong porphyry Cu-Mo deposit indicate the occurrence of multiple pulsed flows of magmatic fluids, revealing a more complex fluid evolution for porphyry Cu deposits than previously recognized. Notably, Sch 1 exhibits relatively high 87Sr/86Sr ratios, similar to the post-ore mafic porphyries, which are higher compared to Sch 2 and Sch 3, showing 87Sr/86Sr ratios similar to the pre- and syn-ore host granite and porphyry. This result implies that mafic magma has significantly contributed to the formation of the first pulse of magmatic fluids, whereas syn-ore granitic magma contributed to the ore fluids responsible for forming the veins containing Sch 2 and Sch 3 in the later stage. Therefore, we propose that volatiles from mafic magma, injected into the porphyry metallogenic system, play a crucial role in the formation of porphyry Cu deposits.
Additionally, for the first time, the presence of Cu-Mo-W metal endowment in the porphyry Cu deposits of the Gangdese magmatic belt is identified, providing valuable new insights into the metallogeny of porphyry Cu deposits and offering promising opportunities for tungsten exploration in the collision zone
Low-temperature crystallization of kumdykolite, a polymorph of albite, during mineral carbonation within fluid inclusions in hornblendite from the Dabie orogen, central China
No full textKumdykolite is a polymorph of albite that has been predominantly identified within crystallized melt inclusions in high-temperature metamorphic rocks. This study reports a new occurrence of kumdykolite that formed during internal mineral carbonation within amphibole-hosted fluid inclusions in post-collisional hornblendite from the Dabie orogen, central China. Amphibole in the hornblendite trapped CO2-rich fluid inclusions at the magmatic stage, and mineral carbonation, referring to the reaction of mineral rich in divalent cations and CO2 into carbonate, occurred in situ within the fluid inclusions due to the interaction between trapped CO2-rich fluids and host amphibole during cooling of the hornblendite. Kumdykolite was produced along with calcite, dolomite, chlorite, talc, a SiO2 phase (quartz or cristobalite), a TiO2 phase (rutile or anatase), and mica during internal mineral carbonation within the fluid inclusions. It is estimated that kumdykolite in the fluid inclusions crystallized under near-surface conditions, which are significantly different from the conditions of crystallization proposed in previous studies. It is further inferred that kumdykolite may crystallize metastably across the stability field of albite, and the presence of kumdykolite is not indicative of extreme thermobaric and fluid-absent conditions
Nanoparticle attachment promotes nugget effect of Au-rich metallic melts in hydrothermal ore deposits
No full textThe role of bismuth melts in scavenging Au from hydrothermal fluids has been increasingly recognized in the last decade, but the question of how the Au extracted by such melts transforms into nuggets to form high-grade ores remains obscure. Here, we have characterized the nanostructure of gold nanoparticles (AuNPs) in Bi-rich gold ores that precipitated from Bi-Au melts and propose a novel model to explain the genesis of gold nuggets. This model comprises three consecutive processes of Au crystallization in these melts into coarse grains: the initial formation of atomic clusters equivalent to Au nucleation, the coalescence of these clusters into low-crystalline AuNPs followed by their transformation into well-structured ones, and finally the preferential attachment of these NPs along the {111} lattice plane. This atomic crystallization pathway bridges the gap between Au scavenging by metallic melts and nugget formation, thus making the picture of the formation of high-grade gold ores in the context of melt-fluid interaction more complete
Carbonyl Compounds Observed at a Suburban Site during an Unusual Wintertime Ozone Pollution Event in Guangzhou
No full textCarbonyl compounds are important oxygenated volatile organic compounds (VOCs) that play significant roles in the formation of ozone (O3) and atmospheric chemistry. This study presents comprehensive field observations of carbonyl compounds during an unusual wintertime ozone pollution event at a suburban site in Guangzhou, South China, from 19 to 28 December 2020. The aim was to investigate the characteristics and sources of carbonyls, as well as their contributions to O3 formation. Formaldehyde, acetone, and acetaldehyde were the most abundant carbonyls detected, with average concentrations of 7.11 +/- 1.80, 5.21 +/- 1.13, and 3.00 +/- 0.94 ppbv, respectively, on pollution days, significantly higher than those of 2.57 +/- 1.12, 2.73 +/- 0.88, and 1.10 +/- 0.48 ppbv, respectively, on nonpollution days. The Frame for 0-D Atmospheric Modeling (F0AM) box model simulations revealed that local production accounted for 62-88% of observed O3 concentrations during the pollution days. The calculated ozone formation potentials (OFPs) for various precursors (carbonyls and VOCs) indicated that carbonyl compounds contributed 32.87% of the total OFPs on nonpollution days and 36.71% on pollution days, respectively. Formaldehyde, acetaldehyde, and methylglyoxal were identified as the most reactive carbonyls, and formaldehyde ranked top in OFPs, and it alone contributed 15.92% of total OFPs on nonpollution days and 18.10% of total OFPs on pollution days, respectively. The calculation of relative incremental reactivity (RIR) indicates that ozone sensitivity was a VOC-limited regime, and carbonyls showed greater RIRs than other groups of VOCs. The model simulation showed that secondary formation has a significant impact on formaldehyde production, which is primarily controlled by alkenes and biogenic VOCs. The characteristic ratios and backward trajectory analysis also indicated the indispensable impacts of local primary sources (like industrial emissions and vehicle emissions) and regional sources (like biomass burning) through transportation. This study highlights the important roles of carbonyls, particularly formaldehyde, in forming ozone pollution in megacities like the Pearl River Delta region
Provenance shift of the abyssal plains in the Southwest sub-basin of the South China Sea at 8 Ma: Tectonics & climate changes implication
No full textTectonic processes and climatic changes are recognized as two major drivers of erosion along the southeastern margin of the Tibetan Plateau and consequently are the main factors controlling depositional patterns along the margins of the South China Sea. However, the role of tectonics and climate in governing the types and patterns of sedimentation in the abyssal plains is relatively little known. The results of International Ocean Discovery Program (IODP) drilling in the abyssal plains of the Southwest sub-basin of the South China Sea show that the multi-trace element and rare earth element (REE) character of sediments older than 8 Ma are in disorder. 8Nd (0) and 87Sr/86Sr values exhibit large fluctuations, which implies temporally variable sediment sources during the early post-spreading stage of the South China Sea. High 8Nd(0) and low 87Sr/86Sr values and abundant Cenozoic (13-35 Ma) zircon grains in the sediments suggest relatively juvenile sources for their origins, such as the Cagayan Ridge and Palawan Block in the south before 8 Ma. Multi-trace element and REE patterns of sediments younger than 8 Ma are more uniform. Low 8Nd(0) and high 87Sr/86Sr values of the sediments indicate that more continentally-derived sediments were transported to the abyssal plain. Coastal rivers in SE Vietnam, and the Mekong and Red Rivers in the west gradually became the major detrital sources of abyssal sediments in the Southwest sub-basin after 8 Ma. The switching of the sediment sources from the south to the west is consistent with the progressive uplift of the Vietnamese Central Highlands (VCH) and the SE Tibetan Plateau margin during the Late Miocene. The strengthened summer monsoon since 5 Ma affected not only the marginal basins, but also the deep abyssal basins. We argue that the regional tectonics shaped and controlled the shift of provenance and sediment routing system, whereas the East Asian monsoon affected the sediment flux to the abyssal plains of the Southwest sub-basin in the South China Sea
Magmatic flare-ups in arcs controlled by fluctuations in subduction water flux
No full textThe tempo of subduction-related magmatic activity over geological time is episodic. Despite intense study and its importance to crustal growth, the fundamental drivers of this episodicity remains unclear. We demonstrate quantitatively a first order relationship between arc flare-up events and high subduction flux. The volume of oceanic lithosphere entering the mantle is the key parameter that regulates the proportion and rate of H2O 2 O entering the sub-arc. New estimates of subduction zone H2O 2 O flux over the last 150 million-years indicate a three- to five-fold increase in the proportion of H2O 2 O entering the sub-arc during the most recent global pulse of magmatism. Step changes in H2O 2 O flux enable proportionally greater partial melting in the sub-arc mantle leading to a flare-up episode. Similar magmatic flare-ups in the ancient Earth could be related to variability in slab flux associated with supercontinent cycles
Formation of a granite-related Sn-Pb-Zn-(Ag) deposit from three discrete mineralization events around a common magmatic-hydrothermal center over a span of ～45 million years at Changpu, eastern Guangdong, South China
No full textMagmatic-hydrothermal Sn-(W) mineral- ization is commonly associated with Pb-Zn- Ag mineralization, forming Sn-polymetallic deposits that typically exhibit a zonation from proximal Sn-(W) to distal Pb-Zn-Ag, alongside a paragenetic sequence from early Sn-(W) to late Pb-Zn-Ag mineralization. Tra- ditional models generally propose that these deposits formed from a single magmatic- hydrothermal event characterized by con- tinuously decreasing temperatures. However, our study of the Changpu Sn-Pb-Zn-(Ag) deposit in eastern Guangdong, South China, reveals a more intricate mineralization his- tory. There, metal zonation results from three distinct mineralization events occurring over a prolonged period. The Sn orebodies at Changpu occur as cassiterite-tourmaline- quartz-(muscovite) veins and breccia zones in the central part of the deposit, whereas the Pb-Zn-Ag orebodies occur mainly as sulfide- (cassiterite) veins peripheral to the Sn ore- bodies. The hydrothermal processes related to mineralization are divided into three peri- ods, and each corresponds to a unique miner- alization event. Period 1 is characterized by tourmalinization with minor Sn mineraliza- tion, period 2 represents the main Sn miner- alization, and period 3 features predominant Pb-Zn-Ag mineralization. Different isotopic dating methods were used to obtain the ages of these mineralization periods: ca. 150 Ma for period 1 (U-Pb dating of cassiterite and Ar-Ar dating of fluid inclusions in quartz), ca. 130 Ma for period 2 (U-Pb dating of cas- siterite), and ca. 105 Ma for period 3 (Ar- Ar dating of muscovite). These ages over- lap with the reported zircon U-Pb ages for quartz porphyry dike (144.1 +/- 1.2 Ma) and rhyolite (153.9 +/- 1.3 Ma) in the deposit area. Fluid inclusions in cassiterite and quartz are of the H2O-CO2-CH4-NaCl compositional system in all of the periods and show a de- crease in temperature and salinity from the early to late stages within each period. The H isotopes of fluid inclusions in cassiterite and quartz fall within the field of magmatic water, and the O isotopes of the ore-forming fluids calculated from the O isotopes of cas- siterite and quartz are slightly shifted away from the field of magmatic water toward meteoric water. These geochronological and isotopic data, together with fluid pressures calculated from fluid inclusion data, suggest that three distinct magmatic-hydrothermal Sn-Pb-Zn mineralization events occurred at the same location over similar to 45 m.y., resulting in the observed metal zonation due to the evolu- tion of the magmatic system and continuous surface erosion. The magmas responsible for the three mineralization events are linked via deep fault to a crustal source region, where discrete partial melting processes are related to episodic slab-foundering or slab rollback of the paleo-Pacific plate during the Mesozoic in South China. This proposed model has significant implications for mineral explora-tion at depth within the study area and offers valuable insights for areas with similar geo- logical contexts globally
Fluid evolution and genesis of the Yidinan granitoid-hosted orogenic gold deposit (China)
No full textThe metamorphic model explaining orogenic gold ore formation has become widely accepted. However, there has been extensive debate regarding whether a magmatic-hydrothermal system contributes fluids or metals in the source of orogenic gold deposits. The Yidinan gold deposit is hosted by Triassic quartz diorite in the West Qinling Orogen, China, which is controlled by NNE-trending high-angle brittle-ductile faults. The gold mineralization is characterized by vein and disseminated type ores comprising auriferous pyrite and arsenopyrite. Magmatic apatite U-Pb and magmatic biotite Ar-Ar dating pinpoint the emplacement and the cooling of ore-hosting quartz diorite at 241.8 +/- 2.8 Ma and 241.7 +/- 0.32 Ma, respectively. In situ U-Pb dating of hydrothermal monazite yield an age of 234.6 +/- 2.8 Ma for the gold mineralization. Systematic fluid inclusion investigation suggests that the ore-forming fluids belong to a NaCl-H2O-CO2 +/- CH4 system with low salinity (5.76-10.09 wt% NaCl equiv.) and medium temperatures (253-395 degrees C). During fluid evolution, phase separation occurred, with CO2 and other gases preferentially fractionating into the vapor phase. The sulfur isotope data range from 5.50%o to 7.85%o and are higher than those from the nearby magmatic-hydrothermal deposits. Such results support that the gold-bearing fluids were sourced from devolatilization of underlying sedimentary rocks during regional metamorphism. Fluid immiscibility caused by fault-valve processes might be the critical mechanism for the gold deposition. Although the geological and geochronological evidence suggested gold mineralization was spatially and temporally associated with the quartz diorite, the ore-forming fluids are not consistent with a magmatic source; therefore, the Yidinan gold deposit is of an orogenic type. This study reveals that despite orogenic gold mineralization and magmatic activities showing a broad temporal or spatial overlap during orogenesis processes, there is no genetic link between gold mineralization and granitic magmatism in many hydrothermal gold deposits. The low-salinity auriferous metamorphic fluid was released from underlying metasedimentary sequences during orogenesis. The rapid cooling of the granitoid after emplacement further prevented it from contributing to gold-bearing fluid formation or creating the necessary pressure-temperature conditions for gold deposition