Guangzhou Institute of Geochemistry
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First identification of Mid-Miocene north-south trending dikes in the eastern Qiangtang terrane, eastern Tibet: Mantle melting and implications for plateau uplift
No full textThe uplift of the Tibetan Plateau during the Miocene is crucial to understanding continental deformation processes and global climatic events. However, the eastern Tibetan Plateau remains poorly investigated. Mantlederived magmatism provides crucial insights into the deep dynamic processes and surface uplift of the plateau. In this paper we report the first discovery of north-south trending lamprophyre dikes from the Aduo Basin in the eastern Qiangtang terrane, eastern Tibet. Our new age data show that these lamprophyre dikes were generated in Mid-Miocene (15-13 Ma). This new discovery has bridged the Mid-Miocene mantle-derived magmatic gap in the Qiangtang terrane. Trace element and Nd-Sr isotopic data indicate that they were derived by partial melting of enriched subcontinental lithospheric mantle. Our study implies that the eastern Tibetan Plateau had its attained near-maximum elevation by the Mid-Miocene. Combined with previous research results, we propose that the entire plateau almost simultaneously reached its near-maximum elevation by the MidMiocene
Switching From Subduction Zone Advance to Retreat Explains the Late Paleozoic Evolution of the East Junggar System, Central Asian Orogenic Belt
No full textThe geodynamic evolution of the East Junggar is examined by means of satellite imaging and field-based structural studies, U-Pb zircon geochronology and analysis of potential field geophysical data in the Yemaquan arc and the Dulate back-arc systems. The northern Yemaquan arc shows a pervasive WNW-ESE steep S1 foliation that is related to the exhumation of Armantai ophiolitic m & eacute;lange in an F1 antiformal structure. The bedding of the Dulate sequences is folded by N-S-trending F1 upright folds that are preserved in low strain domains. The timing of D1 is estimated between 310 and 280 Ma. During D2, previously folded Dulate sequences were orthogonally refolded by E-W-trending F2 upright folds, resulting in Type-1 basin and dome interference pattern and pervasive E-W trending S2 cleavage zones. The age of D2 is constrained to be 270-250 Ma based on the dating of syn-tectonic pegmatites and deposition of syn-orogenic sedimentary rocks. The boundary between the Yemaquan arc and Dulate back-arc basin experienced reactivation through D2 dextral transpressive shear zones. The D1 fabrics are the consequence of the closure of the Dulate back-arc basin due to the advancing mode of Kalamaili subduction. Almost orthogonal Permian D2 fabrics were generated by the N-S shortening of the East Junggar and the northward movement of the Junggar Block indenter. This D2 deformation was associated with the anticlockwise rotation of the southern limb of the Mongolian Orocline, the scissor-like closure of the northerly Mongol-Okhotsk Ocean and the collision of the Mongolian and the Tarim-North China craton collages.
The Yemaquan arc and Dulate back-arc are affected by 310-280 Ma D1 and 270-250 Ma D2 events D1 results from advancing mode of the Kalamaili subduction zone, and the closure of the Dulate back-arc basin D2 results from the collisional reworking of the East Junggar system and indentation of Junggar promontor
Grain transportation and consumption reshapes the α-HCH exposure picture of China
No full textSocio-economic activities like food trade can increase the uncertainty of human risk of persistent organic pollutants (POPs). We compared the change in model predicted alpha-hexachlorocyclohexane (alpha-HCH) cancer risk (CR) with and without grain trade in mainland China. In scenario without grain logistics, alpha-HCH moved fast away from southern and southeastern China via northward atmospheric transport. However, the grain logistics from northeastern China delivers the alpha-HCH previously accumulated in northeastern sink back to densely populated areas in recent years, which enhance CR by >50 % in the southern seaboard of China. The northward movement of grain production center and recent grain deficiency in southern provinces induced by dietary pattern changes is identified as the major driving factors of the reversed transport of alpha-HCH. The finding highlights the potential of socio-economic activities that can otherwise offset the risk reduction effect of the geochemical cycle of POPs
Water distribution in pore systems and its influences on gas-bearing property of deep shale: A case study of the Longmaxi Formation in the Luzhou area, southern Sichuan Basin
No full textThe deeply-buried (>3500 m) Longmaxi Formation (LMX) shale in the southern Sichuan Basin, China, has become an attractive target for shale gas exploration owing to its huge resource potential. Exploration shows that the deep shale has a wide range of gas-in-place (GIP) contents, with variable gas yields, but the reason remains unclear, especially the impact of pore water on gas-bearing property lacks systematic research. In the present study, a suite of deep LMX shale samples was collected from the well FB1 in the Luzhou area of the southern Sichuan Basin, and techniques such as the pore water content measurements, low-pressure gas (CO2 and N-2) adsorption and high-pressure methane adsorption experiments of the moist and dry samples were employed to investigate the distribution of water in the nanopores and its effects on the gas-bearing property. The results show that the deep shale is characterized by a high water content, with a high water saturation (average up to 69.80%), and the water occurs in both the inorganic and organic pores. The water reduces the effective specific surface area and pore volume of the shale averagely by 79.01% and 22.56%. Consequently, the water results in the decrease of methane adsorption capacity averagely by 45.13%. The GIP content models of two typical shale samples indicate that their total gas content is 3 m(3)/t with decreasing water saturation to <40-50%, especially under overpressure conditions. The gas-bearing property of deep LMX shale reservoirs in the complex faulted zones or structural-complex zones would mainly depend on the pore water content except for the properties of shale itself (e.g., maturity, TOC content, mineral composition, porosity and pore structure)
Mantle contributions to granitoids associated with Sn mineralization: Geochemical and isotopic evidence from the giant Dachang deposit, South China
No full textMajor Sn deposits are commonly linked to crust-derived and highly evolved granites, with magma generation aided by mantle heating. However, whether and how the mantle components contribute to Sn polymetallic mineralization remains unclear. In this study, in combination with a compilation of equivalent data in the region, we provide new constraints on this issue based on detailed investigations on the petrogenesis and metallogenic significance of granitoids including the causative batholith and later granodiorite porphyry dike in the giant Dachang Sn deposit from South China. The former has zircon U-Pb ages of 93-91 Ma and belongs to highly evolved S-type biotite granite, which experienced fractionation of massive feldspar. The latter shows zircon U-Pb ages of 90 Ma and displays I-type granite features. The batholith was mainly derived from the dehydration melting of biotite in the metasedimentary sources, as revealed by the relatively low whole-rock Pb contents (850 degrees C), whole-rock Mg-# (52 to 58), apatite epsilon(Nd)(t) (-9.2 to -6.5) and zircon epsilon(Hf)(t) (-7.6 to 2.5) values but lower zircon delta O-18 values (6.33 to 8.30 parts per thousand) of the later granodiorite porphyry dike than those of the batholith also suggest that mantle material was involved in the generation of the dikes, which is evident by the variational features of zircon and apatite trace elements. In addition, at the zircon Hf 0.05, the higher zircon Delta FMQ values (mostly from -1.8 to 2.0) and H2O contents (100-1100 ppm) of the Dachang granitoids than the pure crust-derived S-type granites (Delta FMQ = mostly from -3.7 to -1.5; H2O < 100 ppm) imply that mantle materials involved are relatively rich in water and oxidized. These suggest that the addition of mantle components is conducive to the extraction of Sn from metasedimentary sources, and moderately facilitates the increase of oxygen fugacity which still maintains the incompatibility of Sn in magmas with Delta FMQ < 2. Also, the involvement of mantle components upgrades the H2O contents in S-type magmas, favoring the migration of ore-forming elements from magmas to hydrothermal fluids. The sediment-derived causative granites displayed higher epsilon(Hf)(t) and epsilon(Nd)(t) values with greater Sn tonnages of their associated world-class Sn polymetallic deposits, supporting the opinion that the contributions of mantle components play an important role in the generation of giant Sn deposits
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
Green synthesis of diatom-allophane bio-nanocomposites for highly efficient oxytetracycline adsorption
No full textThe extensive use of the antibiotic oxytetracycline (OTC) has led to considerable environmental contamination and other negative impacts, prompting an urgent need for a green, effective, and innovative OTC adsorption material. In this study, diatom-allophane bio-nanocomposites were synthesized using a simple and eco-friendly method, yielding a homogeneous coating of allophane nanoparticles on diatom surfaces. The resultant bio-nanocomposites were found to have hierarchically porous structures and abundant active sites derived from successful allophane loading and dispersion on diatom surfaces. The OTC adsorption capacity of this novel adsorbent is remarkable (219.112 mgg(-1)), surpassing the capacities of raw allophane and diatoms by >5 and 10 times, respectively. Mechanistically, OTC adsorption by the bio-nanocomposites was found to be driven primarily by chemisorption through a process involving complexation between the amide and amino groups on OTC and the aluminum hydroxyl and carboxyl groups on the adsorbent surface. Electrostatic interactions and hydrogen bonding also contribute significantly to OTC capture. Furthermore, the diatom-allophane bio-nanocomposites exhibit excellent performance over a wide pH range (4-7), in the presence of various cations (Na+, K+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO42-), and in real water bodies. These findings demonstrate the potential of the diatom-allophane bio-nanocomposite as a green, efficient, and promising biological-mineral adsorbent for environmental remediation, leveraging the combined utilization of biological and mineral resources
Effects of fluid pressure on the occurrence of multi-phase oil and accumulation of light oil and condensate from crude oil cracking: Insights from modified gold tube pyrolysis experiments
No full textAn oil with an initial equivalent maturity of 0.74 %Ro, was pyrolyzed in a closed gold tube pyrolysis system with added silica sand and no added water under simulated conditions spanning 0.7 %-2.1 % EasyRo. The internal fluid pressure, ranging from 0 to >150 MPa at individual maturities states of 1.0 %, 1.5 % and 2.1 % EasyRo, was controlled by increasing sample mass and setting external confining pressure (50, 100 and 150 MPa). Results indicate that the increasing fluid pressure initially promoted and then gradually retarded crude oil cracking. The free-radical reaction mechanism (hydrogen radical supply), free space of vessels, and characteristics of pressure medium control the influence of fluid pressure on the chemical reaction process. The decreasing free space of volume-constant vessels and the difference of hydrogen radicals supplied in various thermal maturity stages together gradually reduce the reaction rate of crude oil cracking. Thus, the yields of methane, wet gas, and light and heavy hydrocarbons increase at low fluid pressure ranges and then decrease at high-pressure conditions. Moreover, the physical controls of fluid phase behaviors include the evolution of fluid phase states influencing the increased rates of fluid pressure and fluid pressure influencing the production of multi-phase hydrocarbons. The increase in fluid pressure is faster in the saturated gas-liquid phase than in the unsaturated phase; thus, the phase behaviors induce the yields of product change. The increasing fluid pressure induces the occurrence of multi-phase hydrocarbons and accumulation of light oil and condensate. This study introduces a novel approach to investigate the influence of fluid pressure on reservoir oil cracking, emphasising phase behavior analysis, and shedding light on the evolution of organic matter in deep and ultra-deep strata
Wintertime ozone surges: The critical role of alkene ozonolysis
No full textOzone (O3) pollution is usually linked to warm weather and strong solar radiation, making it uncommon in cold winters. However, an unusual occurrence of four high O3 episode days (with maximum hourly concentrations exceeding 100 ppbv and peaking at 121 ppbv) was recorded in January 2018 in Lanzhou city, China. During these episodes, the average daytime concentration of total non-methane volatile organic compounds (TVOCs) reached 153.4 +/- 19.0 ppbv, with alkenes-largely emitted from the local petrochemical industry-comprising 82.3 +/- 13.1 ppbv. Here we show a photochemical box model coupled with a Master Chemical Mechanism to elucidate the mechanisms behind this unusual wintertime O3 pollution. We find that the typically low temperatures (-1.7 +/- 1.3 degrees C) and weak solar radiation (263.6 +/- 60.7 W m-2) of those winter episode days had a minimal effect on the reactivity of VOCs with OH radicals. Instead, the ozonolysis of alkenes generated Criegee intermediates, which rapidly decomposed into substantial ROx radicals (OH, HO2, and RO2) without sunlight. This radical production led to the oxidation of VOCs, with alkene ozonolysis ultimately contributing to 89.6 +/- 8.7% of the O3 formation during these episodes. This mechanism did not activate at night due to the depletion of O3 by the NO titration effect. Furthermore, the findings indicate that a reduction of alkenes by 28.6% or NOx by 27.7% in the early afternoon could significantly mitigate wintertime O3 pollution. Overall, this study unravels the unique mechanism of alkene-induced winter O3 pollution and offers a reference for winter O3 reduction strategies in the petrochemical industrial regions. (c) 2024 The Authors. Published by Elsevier B.V. on behalf of Chinese Society for Environmental Sciences, Harbin Institute of Technology, Chinese Research Academy of Environmental Sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Tire Wear Chemicals in the Urban Atmosphere: Significant Contributions of Tire Wear Particles to PM<sub>2.5</sub>
No full textTire wear particles (TWPs) containing tire wear chemicals (TWCs) are of global concern due to their large emissions and potential toxicity. However, TWP contributions to urban fine particles are poorly understood. Here, 72 paired gas-phase and PM2.5 samples were collected in the urban air of the Pearl River Delta, China. The concentrations of 54 compounds were determined, and 28 TWCs were detected with total concentrations of 3130-317,000 pg/m(3). Most p-phenylenediamines (PPDs) were unstable in solvent, likely leading to their low detection rates. The TWCs were mainly (73 +/- 26%) in the gas phase. 2-OH-benzothiazole contributed 82 +/- 21% of the gas-phase TWCs and benzothiazole-2-sulfonic acid contributed 74 +/- 18% of the TWCs in PM2.5. Guangzhou and Foshan were "hotspots" for atmospheric TWCs. Most TWC concentrations significantly correlated with the road length nearby. More particulate TWCs were observed than model predictions, probably due to the impacts of nonexchangeable portion and sampling artifacts. Source apportionment combined with characteristic molecular markers indicated that TWPs contributed 13 +/- 7% of urban PM2.5. Our study demonstrates that TWPs are important contributors to urban air pollution that could pose risks to humans. There is an urgent need to develop strategies to decrease TWP emissions, along with broader urban air quality improvement strategies