Guangzhou Institute of Geochemistry
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Synthesis and high-pressure properties of (Nd<sub>0.2</sub>Li<sub>0.2</sub>Ba<sub>0.2</sub>Sr<sub>0.2</sub>Ca<sub>0.2</sub>)TiO<sub>3</sub> high-entropy perovskite
No full textThe recent development of high-entropy perovskites has demonstrated their tremendous promise for various applications. To meet the expanding needs for extreme environment applications, however, the critical properties of high-entropy perovskite at high pressure remain to be disclosed. In the present work, an A-site high-entropy perovskite (Nd0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 was synthesized. High-pressure investment on the phase stability, dielectric properties, and bandgap was conducted using diamond anvil cell combined with comprehensive in-situ measurements. The results reveal that (Nd0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 remains the perovskite structure at the pressure up to similar to 15 GPa. The grain resistance exhibits an exponential decrease with the increasing pressure, whilst an unusual change of the grain boundary resistance was observed at similar to 7 GPa. Furthermore, (Nd0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 shows a slight increase of the bandgap upon compression. Our multifaceted approach provides a comprehensive understanding of the high-pressure behavior of high-entropy perovskite, offering valuable insights for the design and optimization of advanced functional materials for high-pressure environments
Sediment-derived granites as the precursor of rare-metal pegmatites in the Paleo-Tethys tectonic zone - evidence from the Bailongshan Li-Rb-Be pegmatite ore field and factors controlling mineralization
No full textThe Paleo-Tethys tectonic zone has been recognized as a world-class rare-metal (Li-Rb-Be-Nb-Ta) pegmatite belt. Previous studies indicate that the rare-metal pegmatite mineralization is related to the Late Triassic-Early Jurassic granitoids. However, it remains debated which granites, among the various coeval I-, A- and S-type granitoids in the tectonic belt, are responsible for the rare-metal pegmatite mineralization. We address these questions through a systematic geochemical study of the Bailongshan granite complex, which is composed of both biotite granites and two-mica granites and is related to the largest Li deposit in this zone. The similarities in Sr-Nd-Hf-O isotopic compositions between the two-mica granites (ISr=0.7176 to 0.7183, epsilon Nd(t)= - 10.7 to - 10.1, epsilon Hf(t)= - 14.12 to - 4.58, delta 18O = 10.11 to 13.46 parts per thousand) and rare-metal pegmatites (ISr=0.7181 to 0.7189, epsilon Nd(t)= - 11.72 to - 10.68, epsilon Hf(t)= - 12.15 to - 5.37, delta 18O = 10.37 to 12.37 parts per thousand), both showing affinity with sedimentary source, provide convincing evidence that the rare-metal pegmatites were derived from the two-mica granites. The differences in these parameters between the two-mica granites and the biotite granites (ISr=0.7083 to 0.7086, epsilon Nd(t)= - 5.9 to - 5.7, epsilon Hf(t)= - 6.64 to - 1.50, delta 18O = 7.27 to 9.36 parts per thousand, characteristic of I-type granites) indicate that they were derived from different sources. Trace element modeling indicates that the pegmatites were produced via extremely high fractional crystallization (> 90%) of the two-mica granites, which is also supported by the difference in delta 7Li values between the two-mica granites (-0.6 to 0.5 parts per thousand) and pegmatites (2.04 to 4.94 parts per thousand). Comparison of the geochemical data between the two-mica granites and metasedimentary rocks in the area suggests that the rare metals in the mineralizing magmas were most likely derived from the partial melting of metapelites of the Triassic Bayanharshan Group. The relatively high temperatures (771 to 830 degrees C) estimated from the Ti-in-zircon thermometer for the two-mica granites favor extraction of rare metals from both biotite and muscovite in the source rocks during the partial melting. The results of this study, together with published data of Late Triassic to Early Jurassic granitoids in the Paleo-Tethys tectonic zone, indicate that the rare-metal pegmatite mineralization is related to S-type granites, but not all S-type granites are fertile. The combination of rare-metal-rich source rocks (metapelites), high temperatures due to an external heat source favoring the release of rare metals from the source rocks, and high degrees of fractional crystallization facilitating further enrichment of rare-metals in the pegmatite magmas, is critical for the rare-metal mineralization
Contribution of bismuth melts to gold endowment in the Baolun gold deposit, Hainan Island, South China
No full textBismuth (Bi) melts and related polymetallic alloys can efficiently scavenge gold (Au) from Au-unsaturated aqueous solutions, contributing to the Au endowment in many hydrothermal deposits. However, original evidence for Au-Bi melts is often poorly preserved due to post-precipitation alteration. This complicates investigation of the liquid bismuth collector model in hydrothermal Au deposits. Here we present primary evidence for the occurrence of Au-Bi melt in hydrothermal systems through an examination of the Au-Bi phases and textures in the Baolun Au deposit (Hainan Island). This study found that maldonite, native bismuth, Au-Bi symplectite and Au-Bi melt blebs appeared successively following the precipitation of native gold. Notably, large Au-Bi melt blebs were well preserved in natural systems due to the rapid cooling of fluids. The mineral assemblages and their corresponding fluid physiochemical conditions suggest that the evolution of the ore fluids at Baolun was characterized by a continuous reduction in Au and Bi concentrations and Au/Bi ratios alongside decreasing fluid temperatures and sulfur fugacity (fS(2)). These observations offer direct evidence for Au scavenging by Bi melts in a mesothermal (275-450 degrees C), low-fS(2) and reduced hydrothermal system, aligning well with the Au-Bi binary phase evolution established in metallurgy. As the fluid cooled further, the Au-Bi phases were subsequently overprinted by later Te-S-rich fluids, as evidenced by the formation of bismuthinite, jonassonite, and jos & eacute;ite-A around the Au-Bi phases. Importantly, our study reveals that the Baolun Au deposit is characterized by a Au-Bi-Te hydrothermal system and that the metamorphic country rocks at Baolun are the major source of Au, Bi, and Te
SPATIAL HETEROGENEITY OF ALIPHATIC COMPOUNDS AND THEIR LINK WITH PHYLLOSILICATES AS A RESULT OF AQUEOUS ALTERATION OF RYUGU SAMPLES.
No full textModulating effects of temperature on CO<sub>2</sub>-inhibited isoprene emissions in <i>Eucalyptus urophylla</i>
No full textTerrestrial vegetation emits substantial amounts of highly reactive isoprene, significantly impacting atmospheric chemistry and climate change. Both atmospheric carbon dioxide (CO2) concentration and temperature can influence plant isoprene emissions; however, whether these factors have a synergistic effect remains unclear, particularly for tropical/subtropical plants. In this study, we conducted in-situ controlled experiments on Eucalyptus urophylla, a representative tropical/subtropical species, to investigate the seasonal variation in the response of isoprene emissions to CO2 concentrations (ISOP-CO2 response) and to identify potential controlling factors. The results showed that high CO2 exerts a nearly linear inhibitory effect on isoprene emissions, as indicated by the slope of the ISOP-CO2 response curve. This inhibitory effect exhibited evident seasonal changes, with stronger suppression during cooler seasons and weaker suppression during warmer seasons. This finding contrasts with the default ISOP-CO2 response in the MEGAN model, which ignored seasonal variation. Further analysis showed a significant correlation between the slope of the ISOP-CO(2 )response curve and growth temperature from the past 10 days, indicating that these metrics are effective indicators for predicting seasonal changes. Our findings reveal a synergistic mechanism between temperature and CO2 concentration effects on isoprene emissions. By coupling the effects of growth temperature with the ISOP-CO2 response, this mechanism can be integrated into models to provide more accurate predictions of future isoprene emissions, reducing prediction biases, especially during cooler seasons
Human bare and clothing-covered skin exposure to chlorinated paraffins for the general populations: Exposure pattern differential and significance of indirect dermal exposure via clothing-to-skin transport
No full textTo investigate human exposure to short-chain chlorinated paraffins (SCCPs) and medium-chain chlorinated paraffins (MCCPs) through dermal and oral intake via hand-to-mouth contact, wipes from the face, forearm, hand, and foot of 30 volunteers were sampled. The concentration of SCCPs and MCCPs ranged from 0.66 to 119 and 0.71 to 565 mu g/m2, respectively. Hands exhibited significantly higher CPs concentrations than other skin areas, indicating that direct contact with indoor surfaces contributed considerable CP levels on this bare skin area. Gender differences in CP levels were observed in wipes from all locations, except for the hands, possibly because of the significant variability in residuals on the hands. A significant positive relationship was found between CP levels on the hands and faces, and the CP ratios of the hands/faces were related to log KOA. Bare skin showed more significant variations in CP partitioning among related congeners and between genders than skin covered by clothing, as elucidated by the linear analysis of RSD and log KOA. Although concentrations on clothing-covered areas were relatively lower than on bare skin, the median estimated dermal absorption doses of SCCPs and MCCPs (152 and 737 ng/kg bw/day, respectively) for the entire body were approximately 1-2 orders of magnitude higher than those for oral ingestion (1.62 and 7.94 ng/kg bw/day, respectively), emphasizing indirect dermal uptake as a significant exposure pathway for humans
Evolution of mechanical properties of organic-rich shale during thermal maturation
No full textAccurate assessment of the mechanical properties of organic matter, clay matrix, and bulk shale during maturation remains a challenge. Here, we aim to assess the mechanical properties of organic-rich shale during maturation using a combination of nanoindentation methods and various geochemical analyses, i.e., mineral composition, mass loss rate, chemical structure of organic matter, and Rock-Eval analyses. Results show that the evolution of mechanical properties of organic matter in shale during maturation can be divided into: the main oil-generation stage, and the condensate oil and gas generation stage. The stiffening of organic matter in the shale is mainly due to increased aromaticity and condensation of aromatic groups. The clay matrix experiences a slight decrease in hardness and Young's modulus at low maturity levels due to the generation of liquid hydrocarbons. However, overall, the clay matrix becomes stiffer as the shale matures due to shale dehydration, expulsion or cracking of liquid hydrocarbons, transformation of clay minerals, and hardening of organic matter. The Young's modulus and hardness of bulk shale generally increase with increasing maturity. This is closely related to the hardening of organic matter and clay matrix, as well as the development of the more compact and dense microstructure in the shale
Microtopography and hydrological regulation alter CO2 and CH4 fluxes in urban wetlands: Evidence from the Pearl River Delta, China
No full textInland urban wetlands are significant sources of CO2 2 and CH4. 4 . Wetland carbon fluxes can be influenced by management (e.g., restoration), impacting atmospheric carbon emissions. However, the regulatory mechanisms underlying the variations in CO2 2 and CH4 4 fluxes affected by microtopography and hydrological regulation, such as the water table, remain unclear, and field monitoring is inadequate. This study measured CO2 2 and CH4 4 fluxes and soil physicochemical properties across various micro-terrains in the restored Guangdong Guangzhou Haizhu Wetland in China and analyzed the direct and indirect effects of these factors on carbon flux. The results showed that the CO2 2 flux was lower than most previously reported urban wetland fluxes, with means of 3.41, 2.08, and 1.04 mmol center dot m-- 2 center dot d- 1 for hummocks, transition zones, and hollows, respectively. Similarly, the CH4 4 flux was lower than most previously reported fluxes in natural wetlands, with averages of 0.00027, 0.435, and 0.0087 mmol center dot m-2 center dot d-1- 2 center dot d- 1 for hummocks, transition zones, and hollows, respectively. Microtopography significantly reduced the CO2 2 flux, while saturated regions such as transition zones and hollows released CH4. 4 . Water level fluctuations primarily caused the elevated CO2 2 and CH4 4 emissions from transition zones compared to hollows. Redundancy analysis indicated that hydrolytic enzyme activity (73.85 %) and temperature (70.96 %) explained most of the variation in carbon flux. Path analysis revealed that microtopography influenced soil temperature, iron oxide contents, and enzyme activity via regulating the water level to affect CO2 2 and CH4 4 fluxes indirectly, with total variances of 69 % and 66 %, respectively. Overall, microtopography alters the patterns of CO2/CH4 2 /CH 4 flux, and appropriate hydrological regulation can reduce carbon emissions. Based on the complex changes in urban hydrology, this study emphasizes that wetland restoration strategies must consider topographic structures and hydrological management to mitigate carbon emissions
Characterizing Wall Loss Effects of Intermediate-Volatility Hydrocarbons in a Smog Chamber with a Teflon Reactor
No full textIntermediate-volatility organic compounds (IVOCs) serve as pivotal precursors to secondary organic aerosol (SOA). They are highly susceptible to substantial wall losses both in indoor environments and within smog chambers even with Teflon walls. Accurately characterizing the wall loss effects of IVOCs is thus essential for simulation studies aiming to replicate their atmospheric behaviors in smog chambers to ensure precise modeling of their physical and chemical processes, including SOA formation, yet a comprehensive understanding of the wall loss behavior of IVOCs remains elusive. In this study, we conducted a thorough characterization of wall losses for typical intermediate-volatility hydrocarbon compounds, including eight normal alkanes (n-alkanes) and eight polycyclic aromatic hydrocarbons (PAHs), using the smog chamber with a 30 m3 Teflon reactor. Changes in the concentrations of gaseous IVOCs with the chamber were observed under dark conditions, and the experimental data were fitted to the reversible gas-wall mass transfer theory to determine the key parameters such as the wall accommodation coefficient (alpha w) and the equivalent organic aerosol concentration (Cw) for different species. Our results reveal that Cw values for these hydrocarbon IVOCs range from 0.02 to 5.41 mg/m3, which increase with volatility for the PAHs but are relative stable for alkanes with an average of 3.82 +/- 0.92 mg/m3. alpha w span from 1.24 x 10-7 to 1.01 x 10-6, with the values for n-alkanes initially showing an increase followed by a decrease as carbon numbers rise and volatility decreases. The average alpha w for n-alkanes and PAHs are 3.34 x 10-7 and 6.53 x 10-7, respectively. Our study shows that IVOCs exhibit different loss rates onto clean chamber walls under dry and dark conditions, with increasing rate as the volatility decreases. This study demonstrates how parameters can be acquired to address wall losses when conducting smog chamber simulation on atmospheric processes of IVOCs
A Prograde Dual-Segmented Geotherm for (Retro-) Eclogite From Western Dabie and Implications for Maximum Decoupling Depths During Continental Subduction
No full textRobust quantification of the prograde P-T trajectories of eclogite exhumed from subduction zones is fundamental for deciphering the thermal structure evolution and understanding the geodynamic processes during continental subduction. In this study, we investigate four metabasites located in Hong'an within the western Dabie HP/UHP metamorphic belt. Based on detailed petrographic observations and mineral chemistry analyses, combined with phase equilibrium modelling, average-T calculation and conventional thermobarometry, we quantify the prograde to peak P-T paths for each of the four metabasites and the retrograde P-T conditions for two samples. The results show that three of the four metabasites have similar prograde P-T paths evolving from 15.5-18.5 kbar, 440-485 degrees C (M0 stage) to 18.5-20.5 kbar, 500-525 degrees C (M1 stage). On the other hand, although the fourth sample shares a similar P-T evolution for a segment of the late prograde stage from 18.0-19.0 kbar, similar to 500 degrees C to 20.0-22.0 kbar, similar to 550 degrees C, it attains P-max at a notably higher pressure of similar to 26.0 kbar at 550-560 degrees C (M2 stage). During exhumation, we identify an early retrograde stage occurring at 9.0-12.5 kbar, 545-580 degrees C (M3 stage), followed by a later retrograde stage at 3.5-8.0 kbar, 540-580 degrees C (M4 stage). In combination with previous studies, we propose a common dual-segmented P-T path for the late prograde evolution of the HP/UHP rocks in western Dabie. The initial segment exhibits a gentle slope with apparent geotherms of 7-8 degrees C/km, whereas the subsequent segment displays a steeper slope with apparent geotherms of 5-6 degrees C/km. We interpret the turning point at 20.0-23.0 kbar (corresponding to depths of 70-80 km) as marking the maximum decoupling depths (MDD) between the subducting slab and the overlying mantle wedge. Notably, this prograde dual-segmented geotherm for eclogite in western Dabie and the corresponding MDD are similar to computational geodynamic models