Guangzhou Institute of Geochemistry
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Microscopic slickenside as a record of weak shock metamorphism in the surface layer of asteroid Ryugu
No full textThe surface morphology of regolith grains from the C-type asteroid Ryugu was studied in search of evidence of impact events on the asteroid. Scanning electron microscopy revealed that similar to 8% of C0105-042 Ryugu grains have a smooth surface on one side of the grains. One of these grains has striated linear grooves (striations) on its smooth surface. Transmission electron microscopy of the grain showed that a porous fine-grained Mg-Fe phyllosilicate assemblage, which is the main component of Ryugu grains, is compacted near the smooth surface. The smooth surface with striations closely resembles a slickenside, a characteristic texture found in terrestrial fault rocks formed by shear deformation. There is no evidence of melting/decomposition in the Mg-Fe phyllosilicates near the smooth surface, indicating that the shear heating temperature is less than similar to 1100 K. Assuming that the average length of the striations corresponds to the minimum displacement of the micro-fault, the shock pressure recorded in the C0105-042 Ryugu grain is estimated to be similar to 3.9 GPa) in previous studies suggest that the impact velocities recorded in these grains are < similar to 0.89-1.63 km s(-1). Based on the impact velocities, these grains may record an impact event that occurred when asteroid Ryugu was in the orbit in Main Belt
Garnet as a carrier of HREEs in highly fractionated peraluminous granite: Implications for the formation of ion-absorption HREE deposits
No full textIon-absorption rare earth element (REE) deposits in South China are the world's most important source of heavy REEs (HREEs). These deposits were formed by the weathering of granitic rocks whose formation involved primary HREE enrichment. Previous studies have identified the key role of late-stage magmatic evolution, especially the magmatic-hydrothermal transition stage played in HREE enrichment, but the detailed processes need further investigation. Garnet is a common HREE carrier in parent rocks and also a main contributor of these elements in formation of ion-absorption HREE deposits. Here, we investigate textural and compositional variations in garnets from parent rock (muscovite granite) of the Dabu ion-absorption HREE deposit to constrain the primary HREE enrichment of the parent rock during late-stage magmatic evolution. Mass-balance calculations reveal that garnet accounts for similar to 67 % of the Y and 64 % of the REEs in the Dabu muscovite granite. The garnets can be classified into three types: i) magmatic garnets (Grt-1A) are intergrown with plagioclase, K-feldspar, and quartz, host both melt and mineral inclusions, and have high REE + Y contents (6488-19,215 ppm); ii) magmatic-hydrothermal garnets (Grt-1B) occur as overgrowths on Grt-1A, host both melt and fluid inclusions, and have intermediate REE + Y contents (2681-8683 ppm); and iii) hydrothermal garnets (Grt-2) are intergranular with quartz and altered biotite, host primary fluid inclusions, and have the lowest REE + Y contents (476-1247 ppm). The texture and composition of the three types of garnet indicate that the magma have undergone a transition from a volatile-undersaturated to a volatile-oversaturated aqueous system. The fluid, from which some REE minerals precipitated, present in the magma system was derived from the magma itself rather than from an external source, as evidenced by the similarity in Nd isotopic composition between the REE minerals and the whole-rock samples. During this transition, the presence of high-HREE garnet prevents the HREE partitioning into refractory minerals (e.g., zircon, REE-bearing phosphate) or extracting from the magma system by the fluid. Our findings show that granites containing high-HREE garnet have high potential for forming ion-absorption HREE deposits and that garnet can reliably record their magmatic evolution
Study on the Suppression of Vitrinite Reflectance: A Thermal Simulation Experiment
No full textVitrinite reflectance is the most widely used parameter for reconstructing the thermal history of sedimentary basins and evaluating the maturation of source rocks. However, suppression of vitrinite reflectance has also been reported, which could affect the accuracy of evaluating the degree of thermal evolution. In this article, the influence of hydrocarbon generation on vitrinite reflectance during thermal evolution is studied based on thermal simulation experiments in a closed system. The results show that hydrocarbon absorption and overpressure can lead to the suppression of vitrinite reflectance. For R-0 values between 0.6% and 2.1%, the suppression of vitrinite reflectance is primarily attributed to the impregnation of the telocollinite texture with hydrocarbons generated from type I kerogen. At R-0 values exceeding 2.1%, overpressure becomes the dominant cause of the anomalous reflectance. Under closed-system conditions, the retention of volatile products within the pore network of vitrinite hinders the structural reorganization, leading to reflectance suppression
Experimental constraints on serpentinite carbonation in the presence of a H<sub>2</sub>O-CO<sub>2</sub>-NaCl fluid
No full textSerpentinite carbonation contributes to the deep carbon (C) cycle. Recently, geophysical and numerical studies have inferred considerable hydrothermal alteration in plate bending faults, opening the possibility of significant C storage in the slab mantle. However, there is a lack of quantitative determination of C uptake in serpentinized mantle rocks. Here, we experimentally constrain serpentinite carbonation in H2O-CO2-NaCl fluids to estimate C uptake in hydrated mantle rocks. We find that serpentinite carbonation results in the formation of talc and magnesite along the serpentinite surface. The presence of porous reaction zones (49.2% porosity) promotes the progress of carbonation reactions through a continuous supply of CO2-bearing fluids to the reaction front. Added NaCl effectively decreases the serpentinite carbonation efficiency, particularly at low salinities (< 5.0 wt%), which is likely attributed to the reduction in fluid pH and the transport rate of reactants, and the increase in magnesite solubility. Based on previous and our experiments, we fit an empirical equation for the reaction rate of serpentinite carbonation. Extrapolation of this equation to depths of plate bending fault systems suggests that serpentinite carbonation may contribute to an influx of up to 7.3-28.5 Mt C/yr in subduction zones. Our results provide new insights into serpentinite carbonation in environments with high fluid salinities and potentially contribute to the understanding of the C cycle in subduction zones
Impact of Nitrate and Iron Ions on Uptake Coefficients and Condensed Phase Products From the Reaction of Gaseous NO<sub>2</sub> With HULIS Proxies
No full textHumic-like substances (HULIS) are a ubiquitous reactive component of atmospheric aerosol. They participate in the formation of secondary organic aerosols via chemical reactions with atmospheric oxidants. Here, we assess the influence of transition metal ions (namely ferric iron, Fe(III)), and nitrate ions (NO3-) on the heterogeneous reaction of gaseous NO2 with an aqueous film containing gallic acid (GA) or tannic acid (TA) as proxies for HULIS. Using a vertical wetted wall flow tube technique, the uptake coefficients of gaseous NO2 on GA and TA increased nonlinearly with increasing [Fe(III)], in dark and under light irradiation. However, the combined effect of both ions, Fe(III) and NO3-, led to a substantial decrease in NO2 uptake in the dark and under simulated near-UV sunlight irradiation (300 < lambda < 400 nm). The lifetime of GA in dilute aqueous phase, which corresponds to cloud water, due to reaction with NO2 would be 6 hr during both nighttime and daytime. However, the lifetime of GA in aerosol particles which contain both ions, that is, Fe(III) and NO3-, would increase to 27 hr during nighttime and 11 days and 6 hr due to light-induced reaction with NO2. Also, we observed, using Fourier transform ion cyclotron resonance mass spectrometry, the formation of nitrocatechols compounds (e.g., methyl-nitrocatechol), which contribute to brown carbon. Compounds with reduced functional groups such as amines were also observed in the presence of iron and nitrate ions in the dark and under irradiation, indicating that Fe(III) and NO3-, can influence the kinetics and product distribution in deliquescent aerosol particles
A modified surface to volume (SVR) method to calculate nuclear magnetic resonance (NMR) surface relaxivity: Theory and a case study in shale reservoirs
No full textSurface relaxivity (rho(2)) is a critical parameter for converting nuclear magnetic resonance (NMR) T-2 data to pore size distribution (PSD). The surface-to-volume ratio (SVR) method, known for its simplicity and ease of operation, has been widely used for rho(2) calculation in unconventional reservoirs. However, previous studies often overlooked the equivalence of pore ranges characterized when directly applying the classical SVR model. Moreover, shale reservoirs generally develop layered fractures, whose rho(2) values are different from matrix pores. The logarithmic mean value of the T-2 distribution (T-2LM) is significantly influenced by layered fractures, therefore, relying solely on the T-2LM value of a whole sample under fluid-saturated state will lead to inaccurate rho(2) values of matrix pores, particularly in laminated shales where fractures are well developed. However, insufficient attention has been paid to the effect of fractures on the rho(2) calculation. In this study, a modified SVR method based on the theory of NMR relaxation in partially fluid-saturated pores was proposed to characterize the rho(2) of shale matrix pores. Twenty-four shale core samples from the Shahejie Formation in the Jiyang Depression, China were selected, and subjected to series of NMR experiments at varying oil-bearing conditions, and low-temperature nitrogen adsorption (LTNA) analysis. The results indicate a strong linear correlation (R-2 > 0.85) between the inverse T-2LM (1/T-2LM) and the inverse fluid saturation (1/f) when oil molecules across the entire surface layer participate in the exchange process. For a whole core sample, rho(2) values obtained using the modified SVR model are higher than those obtained using the classical SVR model, especially in samples with numerous fractures. The modified SVR method effectively reduces the impact of fractures on the characterization of rho(2) of matrix pores. For shale pore rho(2) characterization, the classical SVR model may be more suitable for pores smaller than 300 nm, with a recommended T-2 range of 100 nm) within individual samples were estimated. It is found that the rho(2) values of smaller pores is greater than those of larger pores, which may be due to differences in mineralogy of the pores across various size ranges. The small pores are more associated with clay minerals while large pores are surrounded by quartz and rigid minerals. In addition, rho(2) is lower in larger pores and fractures that do not contain organic matter and clays, thus the underestimation of rho(2) by the classical SVR method can be corrected by modified SVR method. This study represents the first attempt to examine rho(2) variations across different pore ranges in shale reservoirs. The methodology presented can be applied to other formations, enhancing NMR data application in both laboratory settings and well logging
Transition metals in alkaline Lost City vent fluids are sufficient for early-life metabolisms
No full textDespite the importance of alkaline seafloor hydrothermal vents in broadening our understanding of deep-sea hydrothermal ecosystems, little is known about the mobility and concentrations of micronutrient transition metals in these environments. Here, we present new analyses of micronutrient transition metal concentrations in vent fluids from the iconic Lost City Hydrothermal Field (LCHF) and report concentrations of Fe = 2.9-18.3 mu mol/kg, Zn = 1.30-5.86 mu mol/kg, Cu = 0.43-5.06 mu mol/kg, Ni = 86.4-556 nmol/kg, Mn = 8.3-274 nmol/kg, V = 25.9-127 nmol/kg, Mo = 24-94 nmol/kg, Co = 8.0-135 nmol/kg, W = 4.8-16 nmol/kg, and Cd = 1.7-4.5 nmol/kg. We additionally present results of a hydrothermal lherzolite alteration experiment conducted at 300 degrees C, 500 bar. Transition metal concentrations and major chemical parameters of experimental reaction fluids are broadly similar to LCHF vent fluids, indicating that transition metal concentrations in LCHF vent fluids, and alkaline hydrothermal fluids more generally, reflect metal solubility controlled by underlying rock-buffered hydrothermal reactions. Concentrations of Ni and Mo are especially noteworthy because of their recognized importance for biological methanogenesis (Ni) and nitrogen fixation (Mo). When compared with known biological thresholds, our findings indicate that Ni concentrations in LCHF vent fluids are sufficient to support the robust methane-metabolizing microbial communities observed in the immediate vicinity of LCHF vents and suggest that Ni availability influences the spatial distribution of LCHF methanogens. Furthermore, our laboratory hydrothermal experiments demonstrate that Mo concentrations of similar magnitude to those observed in LCHF vent fluids (and also modern seawater) can be obtained by hydrothermal alteration of ultramafic rocks with Mo-free (Na, Ca) Cl aqueous solution. Thus, we conclude that alkaline hydrothermal fluids were likely similarly enriched in Mo prior to oxidation of the Earth's atmosphere and ocean, providing localized Mo-rich geochemical environments capable of supporting Mo-dependent nitrogen fixation at currently recognized threshold concentrations
Recent Advances in Machine Learning-Enhanced Joint Inversion of Seismic and Electromagnetic Data
No full textSeismic and electromagnetic (EM) imaging are essential tools for characterizing velocity and conductivity. However, the separate inversion of seismic and EM data is challenging due to the noisy measurements, inadequate data collection, and reliance on prior information, consequently resulting in uncertainty and ambiguity of the solutions. Moreover, the two methods are different in sensitivity and spatial resolution, making it difficult to discover consistencies in the inverted models. Joint inversion of seismic and EM data takes advantage of both methods and significantly improves the imaging capability of subsurface structures. In this paper, we review various coupling strategies for the joint inversion of seismic and EM data and highlight the application advances from 1-D to 3-D inversion. Specifically, we investigate the integration of machine learning techniques to tackle ill-posed inverse problems and showcase their effectiveness in coupling. Following this, we construct a deep-learning-based joint inversion workflow and provide a synthetic test to demonstrate its superiority by applying an attention mechanism, which enhances the model's capability to focus on specific features within the data. This study proves the potential of integrating artificial intelligence into joint inversion and understanding the deep Earth interior by incorporating multiple geophysical data
Reaction kinetics and molecular characterization of the compounds formed by photosensitized degradation of the plastic additive bisphenol A in the atmospheric aqueous phase
No full textBisphenol A (BPA, 4,4'-(propane-2,2-diyl)diphenol) is a common plasticizer that is very widespread in the environment and is also found at significant concentrations in the global oceans, due to contamination by plastics. Here we show that triplet sensitization is an important degradation pathway for BPA in natural surface waters, which could prevail if the water dissolved organic carbon is above 2-3 mgC L-1. Bromide levels as per seawater conditions have the potential to slow down BPA photodegradation, a phenomenon that could not be offset by reaction of BPA with Br2 center dot- (second-order reaction rate constant of (2.54 +/- 0.09) x 108 M-1 s-1). Ultra-high resolution mass spectrometry revealed that the presence of inorganic salts (NaCl and NaBr) markedly increased the complexity of the observed CHO product compounds formed upon photosensitized degradation of BPA. The obtained results suggest that bisphenols can be efficiently removed by photosensitized reactions and generate higher number of oligomers and polyaromatic compounds in the sea surface and liquid water of marine aerosols compared to freshwaters and/or dilute cloud-water. Considering that polyaromatic compounds absorb solar actinic radiation, these results suggest that inorganic salts could significantly affect the photosensitized degradation of bisphenols and consequently influence the light-absorbing properties of marine aerosols and, ultimately, the Earth's radiative balance
Effects of EDTA and Bicarbonate on U(VI) Reduction by Reduced Nontronite
No full textWidespread Fe-bearing clay minerals are potential materials capable of reducing and immobilizing U(VI). However, the kinetics of this process and the impact of environmental factors remain unclear. Herein, we investigated U(VI) reduction by chemically reduced nontronite (rNAu-2) in the presence of EDTA and bicarbonate. U(VI) was completely reduced within 192 h by rNAu-2 alone, and higher Fe(II) in rNAu-2 resulted in a higher U(VI) reduction rate. However, the presence of EDTA and NaHCO3 initially inhibited U(VI) reduction by forming stable U(VI)-EDTA/carbonato complexes and thus preventing U(VI) from adsorbing onto the rNAu-2 surface. However, over time, EDTA facilitated the dissolution of rNAu-2, releasing Fe(II) into solution. Released Fe(II) competed with U(VI) to form Fe(II)-EDTA complexes, thus freeing U(VI) from negatively charged U(VI)-EDTA complexes to form positively charged U(VI)-OH complexes, which ultimately promoted U(VI) adsorption and triggered its reduction. In the NaHCO3 system, U(VI) complexed with carbonate to form U(VI)-carbonato complexes, which partially inhibited adsorption to the rNAu-2 surface and subsequent reduction. The reduced U(IV) largely formed uraninite nanoparticles, with a fraction present in the rNAu-2 interlayer. Our results demonstrate the important impacts of clay minerals, organic matter, and bicarbonate on U(VI) reduction, providing crucial insights into the uranium biogeochemistry in the subsurface environment and remediation strategies for uranium-contaminated environments