Guangzhou Institute of Geochemistry
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Molybdenum isotopes demonstrate that multistage upgrading is required to generate heavy rare earth element-enriched carbonatites
No full textCarbonatites with heavy rare earth element (HREE) enrichment are a rare and intriguing prospect for economic geology research, due to the growing global demand for HREEs in various industries. However, debate persists over the mechanism responsible for HREE enrichment in carbonatites, with the mantle source, magmatic-hydrothermal evolution, or a combination of these factors proposed to be responsible. This study examines three adjacent Late Triassic carbonatites (from the Huanglongpu, Huayangchuan, and Jialu carbonatite dike systems) in the Lesser Qinling of Central China and uses Mo isotope systematics to provide unique insights into the HREE enrichment process of these magmas. All three carbonatites exhibit elevated total REE (Sigma REE) concentrations (up to 4600 ppm), along with significant HREE enrichment (Sigma HREE/Sigma REE = 0.1-0.4). Notably, Jialu carbonatite stands out for having the highest total HREE concentrations (>= 360 ppm) and Sigma HREE/Sigma REE ratios (0.2-0.4). Regardless of their variable degrees of HREE enrichment, the three carbonatites display similar Sr-Nd-Pb isotope signatures, which indicates a shared enriched mantle source. The Huanglongpu and Huayangchuan carbonatites mostly display significantly lighter delta Mo-98/95 (-1.71 parts per thousand to -0.15 parts per thousand) values than the depleted mantle, which indicates an origin from an enriched mantle influenced by recycled pelagic clays and Fe-Mn nodules. Both types of marine sediments are enriched in REEs and would have undergone initial HREE enrichment during slab dehydration and metamorphism, resulting in an HREE-enriched mantle source region. In contrast, Jialu carbonatite possesses significantly heavier delta Mo-98/95 (0.13 parts per thousand-1.89 parts per thousand), which is indicative of the subsequent influence of hydrothermal processes. Additional evidence of this hydrothermal influence at Jialu is preserved in calcite crystal fluid inclusions, elevated delta O-18 (8.71 parts per thousand-10.72 parts per thousand), non-charge-and-radius-controlled (CHARAC) Y/Ho ratios (36-41), and low Sr concentrations (<4800 ppm). Secondary upgrading of HREEs at Jialu occurred due to preferential complexation and transportation during hydrothermal exsolution. This study demonstrates that maximum HREE enrichment in carbonatites is achieved through a two-stage process that involves both a refertilized mantle source and late-stage hydrothermal exsolution
Ultrahigh-pressure to high-pressure eclogite in Cuban ophiolitic melange reveals proto-Caribbean spreading ridge subduction
No full textProto-Caribbean oceanic crust produced during ocean-floor spreading between diverging North and South American plates was subsequently subducted beneath the Caribbean plate. However, the timing and spatial configuration of proto-Caribbean spreading ridge subduction remain subjects of debate. High-pressure (HP) basaltic metamorphic rocks, representing relics of the sub ducted proto-Caribbean oceanic crust, commonly occur in Cuban ophiolitic m & eacute;langes. In this study, an integrated set of petrological, geochemical, and geochronological data is presented for eclogite from the Las Villas m & eacute;lange, central Cuba. The typical geochemical signature of mid-ocean-ridge basalt (MORB) indicates that the protolith of eclogite formed at the proto-Caribbean spreading ridge. Based on pressure-temperature (P-T) estimates obtained by pseudosection analysis as well as Zr-in-rutile and Ti-in-zircon thermometry, the following P-T paths for representative samples can be derived: a prograde path from 24-25 kbar and 510-520 degrees C to peak conditions of 29-31 kbar and 525-575 degrees and a complex retrograde path initially following almost isothermal exhumation to 25-27 kbar, followed by near-isobaric heating to 610-640 degrees C before final exhumation. This is the first documentation of prograde oceanic ultrahigh-pressure (UHP) metamorphism in the northern Caribbean area. U-Pb dating of magmatic zircon with steep heavy rare earth element (HREE) patterns and negative Eu anomalies yielded a protolith age of 126.3 +/- 0.7 Ma. In contrast, metamorphic zircon with flat HREE patterns and without an Eu anomaly yielded a weighted mean age of 118.6 +/- 1.6 Ma. The short time interval of >8 m.y. between MORB magmatism and UHP metamorphism suggests that the oceanic crust was subducted to great depth (similar to 100 km) shortly after generation in an oceanic ridge, which provides robust evidence for subduction of the proto-Caribbean spreading ridge. Furthermore, this work demonstrates high potential to trace ancient spreading ridge subduction by joint petrological, geochemical, and geochronological study of oceanic eclogite
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
Inhibition Effect of H<sub>2</sub>O on the Heterogeneous Reaction between Isoprene and Fe-Substituted Cryptomelane
No full textThe transportation and transformation of biogenic isoprene are vital for the organic carbon cycle in the troposphere. As a typical mineral with high oxidation potential, Fe-substituted cryptomelane oxidizes the surface monolayer of isoprene into formic and acetic acids, and simultaneously, the Mn4+ ions in the structure are reduced to Mn3+ and Mn2+. The flow of H2O in isoprene decreases the adsorption and oxidation of isoprene significantly, even at low relative humidity (10%). As physisorbed H2O retains Fe-substituted cryptomelane's crystal structure and oxidation ability, the adsorption and oxidation capacity recovers when H2O is absent in the isoprene flow. Theoretical calculations on (001) surfaces show that isoprene prefers to be adsorbed by the Fe3+ site and H2O tends to form hydrogen bonds. Due to the decrease in total adsorption energy of H2O and isoprene, Fe-substituted cryptomelane favors the adsorption of H2O in the flow of humid isoprene. The low oxidation performance at ambient relative humidity suggests that direct oxidation by aerosols of mineral dust might not be the transformation pathway of biogenic isoprene at night
Polyhalogenated carbazoles in the environment: Analysis, origins, occurrence, and toxicity
No full textPolyhalogenated carbazoles are a class of emerging organic compounds characterized by the substitution of one to eight hydrogen atoms in the carbazole structure with halogen atom(s). Polyhalogenated carbazoles originate from natural and anthropogenic sources and are widely distributed in the environment. They are persistent in the environment and present a range of toxic effects, notably dioxin-like activity. This review focused on recent progress in determining their distribution, analytical methodologies, toxicity, origins, and transformation in the environment, highlighting their potential ecological and health risks. It confirmed the critical need for ongoing research regarding their environmental behavior and fate, to ensure a comprehensive understanding of the resulting environmental risks. This review also identified future research needs regarding these compounds
Coupling of sulfate reduction and dissolved organic carbon degradation accelerated by microplastics in blue carbon ecosystems
No full textMicroplastics have increasingly accumulated in sulfate- and organic matter-rich mangrove ecosystems, yet their effects on microbially mediated carbon and sulfur cycling in sediments remains poorly understood. In this study, we performed a 70-day anaerobic microcosm experiment to examine the effects of polylactic acid (PLA) microplastics with different sizes on sulfate reduction and dissolved organic carbon (DOC) degradation in mangrove sediments. Our results demonstrated that millimeter-scale PLA (mm-PLA) more effectively enhanced sulfate reduction, sulfur isotope fractionation, reduced sulfide production, and carbon dioxide (CO2) emission compared to micrometer-scale PLA (m-PLA). These results suggested that mm-PLA had a more pronounced impact on the carbon and sulfur cycles. Integrated 16S rRNA gene amplicon sequencing and metagenomic analyses revealed that mm-PLA preferentially enriched key functional microorganisms, including acetate-producing bacteria (e.g., Acetobacteroides), completely oxidizing sulfate-reducing bacteria (e.g., Desulfobacter), and incompletely oxidizing sulfate-reducing bacteria (e.g., Desulfobulbus). These microorganisms exhibited higher abundances and greater genetic potential for carbon metabolism and sulfate reduction under mm-PLA treatment. Their relative abundances showed positive correlations with sulfate reduction rates, sulfur isotope fractionation, and CO2 emission, identifying them as crucial drivers of coupled carbon-sulfur cycling. Furthermore, the synergistic interactions among Acetobacteroides, Desulfobacter, and Desulfobulbus facilitated the oxidation of sediment-derived DOC, highlighting significant implications for carbon sequestration in blue carbon ecosystems
Dual-pressure pyrolysis apparatus unravelling how fluid and lithostatic pressure matter in hydrocarbon expulsion
No full textImprovement in thermal simulation technology will increases the accuracy of predictive geochemistry. A dual- pressure pyrolysis apparatus was developed, to precisely control the fluid pressure and lithostatic pressure during simulated source rock maturation. Two series of pyrolysis experiments were carried out, simulating the same generation process but different expulsion fluid pressure condition. Episodic hydrocarbon expulsion from source rocks under controlled lithostatic pressure and fluid pressure was for the first time observed through thermal simulation experiments. The results were applied to (1) hydrocarbon expulsion efficiency (HEE) analysis, and (2) compositional analysis of oil and gas expelled under different pressures. Results show that HEE is strongly influenced by both fluid and lithostatic pressures. If the oil discharged during depressurization and normal pressure is taken into account, the calculated HEE was 2-31 times the HEE that only considers the high fluid pressure expelled oil. Compared with previous experimental results, HEE under controlled dual pressure is also lower. Therefore, before applying the results of thermal simulation experiments to unconventional and deep oil/gas evaluation, sufficient attention should be paid to the pressure conditions of the experiments. Within the oil window, when the temperature and hydrostatic pressure of source rocks are dropped due to tectonic events such as uplift, they can discharge more oil and gas than before uplift, as a consequence of adjustment of overpressured fluid to re-equilibrate to the adjacent hydrostatic conditions. In addition, during pressure and temperature reduction, the expelled fluids have a higher gas to oil ratio. This helps to indicate that sedimentary basins that experienced tectonic events still have great exploration potential. The temperature program, pressure setup, expulsion conditions in the two-series experiments is a tentative work tested on a representative source rock from the Triassic Yanchang Formation (Ordos Basin), indicating that control of fluid and lithostatic pressure are essential for improving the accuracy of thermal simulation predictions. The dual-pressure pyrolysis apparatus has high exploration relevance, particularly when quantitative results are integrated with the depositional, tectonic and thermal histories of specific source rocks
Transitional chromitites within the Maqsad crust-mantle transition zone of the Semail ophiolite formed above the nascent forearc setting
No full textThe Semail ophiolite is a classic example of a well-preserved ophiolite, hosting over 450 documented podiform chromite deposits. This study investigates a transitional chromitite occurrence in the crust-mantle transition zone (CMTZ) of the Maqsad area within the Sumail massif of the Semail ophiolite. The chromitites, enveloped by dunites, exhibit massive and disseminated textures. Host harzburgites, representing upper mantle residues, underwent similar to 20-35 % partial melting followed by metasomatism from subducting slab-derived melts/fluids. These peridotites show geochemical affinities with Izu-Bonin-Mariana (IBM) forearc peridotites, indicating a forearc tectonic setting. The Maqsad chromitites, with Cr# values of 54.3-66.2, are classified as transitional chromitites. Their geochemical features resemble chromites crystallized from mid-ocean ridge basalt (MORB) melts. Elevated oxygen fugacity (f(O2)) values compared to abyssal peridotites further support their formation in a supra-subduction zone (SSZ)environment. Based on the petrogeological and geochemical characteristics of the host rocks, we propose that the parental magma of the Maqsad transitional chromitites derived from a nascent forearc mantle above an SSZ setting, with MORB-like affinity
Ultrahigh-pressure to high-pressure eclogite in Cuban ophiolitic melange reveals proto-Caribbean spreading ridge subduction
No full textProto-Caribbean oceanic crust produced during ocean-floor spreading between diverging North and South American plates was subsequently subducted beneath the Caribbean plate. However, the timing and spatial configuration of proto-Caribbean spreading ridge subduction remain subjects of debate. High-pressure (HP) basaltic metamorphic rocks, representing relics of the sub ducted proto-Caribbean oceanic crust, commonly occur in Cuban ophiolitic m & eacute;langes. In this study, an integrated set of petrological, geochemical, and geochronological data is presented for eclogite from the Las Villas m & eacute;lange, central Cuba. The typical geochemical signature of mid-ocean-ridge basalt (MORB) indicates that the protolith of eclogite formed at the proto-Caribbean spreading ridge. Based on pressure-temperature (P-T) estimates obtained by pseudosection analysis as well as Zr-in-rutile and Ti-in-zircon thermometry, the following P-T paths for representative samples can be derived: a prograde path from 24-25 kbar and 510-520 degrees C to peak conditions of 29-31 kbar and 525-575 degrees and a complex retrograde path initially following almost isothermal exhumation to 25-27 kbar, followed by near-isobaric heating to 610-640 degrees C before final exhumation. This is the first documentation of prograde oceanic ultrahigh-pressure (UHP) metamorphism in the northern Caribbean area. U-Pb dating of magmatic zircon with steep heavy rare earth element (HREE) patterns and negative Eu anomalies yielded a protolith age of 126.3 +/- 0.7 Ma. In contrast, metamorphic zircon with flat HREE patterns and without an Eu anomaly yielded a weighted mean age of 118.6 +/- 1.6 Ma. The short time interval of >8 m.y. between MORB magmatism and UHP metamorphism suggests that the oceanic crust was subducted to great depth (similar to 100 km) shortly after generation in an oceanic ridge, which provides robust evidence for subduction of the proto-Caribbean spreading ridge. Furthermore, this work demonstrates high potential to trace ancient spreading ridge subduction by joint petrological, geochemical, and geochronological study of oceanic eclogite
Step characteristics and formation mechanism of strike slip faults in Wuerhe asphalt vein, Junggar Basin
No full textIn order to define the geometric characteristics, formation mechanism and fault wall movement direction of steps about mini-extensional shear strike-slip fault zone in Wuerhe asphalt vein. Field outcrop observation, 3D seismic data interpretation, fracture formation time and stress mechanism analysis were carried out. There is no friction in the vein section and the initial fracture shape is maintained. Not only negative steps but also steps is developed, and even steps and negative steps coexist in a cross section. The step is the microtension rupture surface associated with the strike-slip fault plane, which does not have the pointing significance of the fault wall relative movement. The outcrop features are typical, which overturns the consensus of domestic and foreign scholars based on the structural physics simulation experiments that the small steepness generated at the early stage of normal fault, reverse fault and strike-slip fault sections are all negative steps