Guangzhou Institute of Geochemistry
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Carboniferous Barrovian to Permian Buchan-type metamorphic cycles in the Mongolian Altai Zone: Implication for pressure cycles in accretionary orogens
No full textIn the Altai Accretionary Wedge, several periods of Barrovian- and Buchan-type metamorphic cycles were dated from Ordovician to Permian. However, the timing and link between these cycles are not clear, and their causes are debated. In order to contribute to the understanding of Barrovian- to Buchan-type evolution of the accretionary wedges, we studied an area composed of three parallel belts in the easternmost extremity of the Hovd domain located in Mongolian Altai Zone: garnet gneiss in the north, garnet-staurolite-kyanite schist overprinted by +/- sillimanite +/- cordierite +/- andalusite-bearing assemblages in the centre and garnet-sillimanite gneiss in the south. Petrography, garnet zoning and thermodynamic modelling indicate that the garnet gneiss from the northern belt records burial from similar to 510 degrees C and similar to 3-4 kbar to similar to 600 degrees C and similar to 5 kbar, followed by heating to similar to 660 degrees C and decompression to similar to 4.5 kbar. The garnet-staurolite-kyanite schist from the central belt records burial from similar to 550 degrees C and similar to 3-4.5 kbar to similar to 640-680 degrees C and similar to 7 kbar, followed by decompression to the sillimanite stability field at similar to 650 degrees C and similar to 6 kbar. Crystallization of cordierite, andalusite, late muscovite and chlorite in some samples indicates cooling on decompression to similar to 540 degrees C and similar to 3.5 kbar. In the southern gneiss belt, the garnet-sillimanite gneiss with almost unzoned garnet suggests re-equilibration at similar to 6 kbar and similar to 710 degrees C. In situ U-Pb monazite and xenotime dating carried out inclusions in porphyroblasts and matrix grains revealed Carboniferous and Permian ages. The monazite and xenotime from gneisses of the northern and southern belts record Carboniferous and Permian ages, which are interpreted as Carboniferous crystallization at c. 347 Ma associated with metamorphic peak, followed by Permian (re)crystallization at c. 300 and 283 Ma. In the central belt, rare Carboniferous xenotime grains in a garnet-staurolite-kyanite-andalusite-muscovite schist indicate a possible Carboniferous age of the prograde metamorphism. Predominant ages between c. 280 and 260 Ma recorded by monazite are interpreted as a result of complete recrystallization during an LP metamorphic overprint. The Carboniferous ages from the gneisses can be interpreted as constraining the timing of the exhumation of deep crustal rocks to shallow crustal levels. This event corresponds to the formation of crustal-scale migmatite-magmatite domes in the Mongolian Altai Zone. The prograde Barrovian assemblages in the central schist belt are interpreted as having formed contemporaneously during burial in a synform between the migmatite-magmatite domes. The Permian ages reflect LP-HT metamorphism, best recorded by the Buchan-type assemblages in the central schist belt, and are related to massive heat flux from tectonically mobile deep partially molten crust. Correlation with similar Barrovian- and Buchan-type episodes from the Chinese Altai Zone indicates multiple compressional and extensional events in the upper plate accretionary wedge, probably related to retreating and advancing modes of the subduction zone
Human dermal exposure to short- and medium-chain chlorinated paraffins: Effect of populations, activities, gender, and haze pollution
No full textHuman dermal exposure to chlorinated paraffins (CPs) has not been well documented. Therefore, hand wipes were collected from four occupational populations to analyze short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) in order to estimate dermal uptake and oral ingestion via hand-to-mouth contact. The total CP levels (& sum;SCCPs and & sum;MCCPs) in wipes ranged from 71.4 to 2310 mu g/m(2) in security guards, 37.6 to 333 mu g/m(2) in taxi drivers, 20.8 to 559 mu g/m(2) in office workers, and 20.9 to 932 mu g/m(2) in undergraduates, respectively. Security guards exhibited the highest levels of & sum;SCCPs among four populations (p < 0.01). In undergraduates engaged in outdoor activities, C-13 emerged as the most dominant SCCPs homologue group, followed by C-12, C-11, and C-10. The levels of & sum;SCCPs and & sum;MCCPs in males in light haze pollution were significantly higher than that in heavy haze pollution (p < 0.05). The median estimated dermal absorption dose of SCCPs and MCCPs via hand was 22.2 and 104 ng (kg of bw)(-1) day(-1), respectively, approximately 1.5 times the oral ingestion [12.3 and 74.4 ng (kg of bw)(-1) day(-1)], suggesting that hand contact is a significant exposure source to humans
Comparative analysis of DNA-SIP and magnetic-nanoparticle mediated isolation (MMI) on unraveling dimethoate degraders
No full textMicroorganisms are crucial in the bioremediation of organophosphorus pesticides. However, most functional microorganisms (> 99%) are yet to be cultivated. This study applied two cultivation-independent approaches, DNA-SIP and magnetic-nanoparticle mediated isolation (MMI), to identify the functional microorganisms in degrading dimethoate in agricultural soils. MMI identified five dimethoate degraders: Pseudomonas, Bacillus, Ramlibacter, Arthrobacter, and Rhodococcus, whereas DNA-SIP identified three dimethoate degraders: Ramlibacter, Arthrobacter, and Rhodococcus. Also, MMI showed higher resolution than DNA-SIP in identifying functional microorganisms. Two organic phosphohydrolase (OPH) genes: ophC2 and ophB, were involved in dimethoate metabolism, as revealed by DNA-SIP and MMI. The degradation products of dimethoate include omethoate, O,O,S-trimethyl thiophosphorothioate, N-methyl-2-sulfanylacetamide, O,O-diethyl S-hydrogen phosphorodithioate, O,O,O-trimethyl thiophosphate, O,O,S-trimethyl thiophosphorodithioate, and O,O,O-trimethyl phosphoric. This study emphasizes the feasibility of using SIP and MMI to explore the functional dimethoate degraders, expanding our knowledge of microbial resources with cultivation-independent approaches
Microstructural constraints for the formation of net-textured Fe-Ti oxide ores of the Baima layered intrusion in the Emeishan large igneous province, SW China
No full textThe mafic-ultramafic layered intrusions in the Emeishan large igneous province (LIP) host significant amounts of Fe, Ti and V resources. The Fe-Ti oxide ore layers hosted in these layered intrusions are variable in thickness and it is enigmatic how the large amounts of Fe-Ti oxides are accumulated to form the Fe-Ti oxide ore layers. The Fe-Ti oxide ore layers are mainly composed of net-textured ores, however, the processes to form the net-textured ores have not yet been well constrained due to lack of diagnostic microstructural evidence of Fe-Ti oxides in the ores. Here we use the electron back-scattered diffraction (EBSD) technique to characterize the microstructures of Fe-Ti oxides in the net-textured ores of the Baima layered intrusion in the Emeishan LIP, e.g., crystallographic orientation and neighbor-/random-pair misorientation, and to assess the formation model of net-textured ores. The net-textured ores are composed of silicate crystals (olivine, and minor plagioclase and clinopyroxene) isolated by interconnected matrix composed of Fe-Ti oxides (titanomagnetite and ilmenite) and minor sulfides. It is likely that the Fe-Ti oxides simultaneously crystallized from a common Fe-Ti-(P)-rich melt, but postdated olivine and other cumulus minerals. The compaction induced by the gravity of overlying cumulus minerals only caused weak intragrain deformation of Fe-Ti oxides so that the Fe-Ti oxides did not experience intense dynamic recrystallization. Instead, the relatively high temperature and water-rich condition facilitated the operation of static recrystallization, resulting in the straight or smoothly curved grain boundaries of Fe-Ti oxides. The neighbor-pair misorientation patterns of Fe-Ti oxides show the preference for low-angle misorientation, supporting the idea that adjacent crystallized Fe-Ti oxides were rotated to coincident orientation in a melt. This study provides new microstructural evidence for the presence of immiscible Fe-rich melt from which the Fe-Ti oxides crystallized to form the net-textured ores
Decontamination promotes the release of incorporated organic contaminants in hair: Novel insights into non-invasive biomonitoring
No full textHuman hair is increasingly employed as a non-invasive biomonitoring matrix for exposure to organic contaminants (OCs). Decontamination procedures are generally needed to remove external contamination from hair prior to analysis of OCs. Despite various existing decontamination protocols, their impacts on internally incorporated (endogenous) OCs in hair remain poorly understood. This study aims to quantitatively assess the impact of decontamination procedures on endogenous OCs in hair, and investigate optimal decontamination processes and factors influencing the removal of endogenous OCs. In this study, guinea pig was exposed to 6 OCs (triphenyl phosphate (TPHP), tris(1,3-dichloro-2-propyl) phosphate (TDCPP), and tri-n-butyl phosphate (TNBP), bisphenol A (BPA), perfluorooctanoic acid (PFOA), and phenanthrene (PHE)), and 6 decontamination procedures with different solvents (methanol, n-hexane, acetone, ultrapure water, Triton X-100, and sodium dodecyl sulfate) were used to rinse exposed guinea pig hair. All OCs and three metabolites (diphenyl phosphate (DPHP), dibutyl phosphate (DBP), and bis(1,3-dichloro-2-propyl) phosphate (BDCPP)) were detected in the majority of washing solutions. The decontamination procedures apparently resulted in the release of endogenous OCs from hair. The percentages of residual OCs in hair exhibited a linear or exponential decrease with more washing cycles. Furthermore, the residuals of OCs in hair washed with organic and aqueous solvents showed negative correlations with molecular weight, polarizability, and their initial concentrations. Although these findings need to be validated with a broader range of OCs, the results obtained in this study provide compelling evidence that current hair decontamination procedures have significant impacts on the analysis of endogenous OCs in hair. Therefore, it is important to interpret quantitative data on hair OC concentrations with caution and to thoroughly consider each decontamination procedure during analysis
Application of geological and short wavelength infrared (SWIR) spectroscopy mapping in the Mailong gold deposit, East Kunlun: Implications for exploration targeting
No full textWidespread regolith cover makes it difficult to identify the anomalous size of their mineralogical or geochemical footprint at the surface in gold exploration. Short wavelength infrared (SWIR) spectroscopy with effective identification of clays and other hydrous minerals shows potential application in gold exploration. The detailed geological and short wavelength infrared (SWIR) spectroscopy mapping was conducted in the newly-discovered orogenic-type Mailong gold deposit (13.06 t @ 6.29 g/t Au), East Kunlun, to determine alteration stage and mineral assemblages and discuss the potential values of SWIR spectral in gold exploration. In the Mailong area, magmatic rocks consist of granodiorite, biotite granodiorite, plagiogranite and mafic dikes, and the gold mineralization shows a close spatial and temporal relationship with mafic dikes. The earliest chloritization (chlorite-quartz) is widely distributed in granodiorite, biotite granodiorite and plagiogranite. The following potassic alteration (hydrothermal K-feldspar and quartz) is developed along high-angle fault/fracture, which cut through granodiorite, biotite granodiorite and plagiogranite. The subsequent sulfide alteration (chlorite-muscovite-sulfide-carbonate) overprints the former potassic and chloritization alteration, and shows spatial association with mafic dikes. Native gold occurs in fracture arsenopyrite or associated with minerals such as pyrite, and chalcopyrite during the early sulfide stage. Supergene alteration is characterized by limonite and malachite. At Mailong, the SWIR data indicate that the most abundant alteration minerals (chlorite, white micas and ankerite) mainly occurred in the northern area. White mica Al-OH absorption occurs at longer wavelengths (Pos2200 = 2202.5 similar to 2203 nm) and higher Illite crystallinity (IC = 1.2 similar to 3.1) probably reflecting a higher temperature and pH conduit at the bottom of ZK0001 and ZK0801. The sharp shift of IC values near the bottom reflects the control of fault. This area is also situated at the V-shaped intersections of the three granitic intrusions and structural transection, indicating more of a possible hydrothermal fluid channel than a mineralization center. Low-grade Au mineralization (Au = 0.1 similar to 0.5 g/t) is mainly distributed within hydrothermal channels with higher Pos2200 (mainly 2022.5 similar to 2203 nm) and IC values (mainly 1.2 similar to 3.1), while high-grade Au endowment associated with mafic dikes has low Pos2200 (mainly 2201 similar to 2202.5 nm) and IC values (mainly 0.43 similar to 1.2). Meanwhile, an equation of distance = -15*IC + 31 (R-2 = 0.47) can be summarized for low-grade orebodies vectoring. Integrating geological mapping and spectral data, target areas for high-grade ore bodies can be outlined using the criteria of white mica, shorter wavelength of Al-OH absorption position (Pos2200 = 2201 similar to 2202.5 nm), lower IC values (IC = 0.43 similar to 1.2), and chlorite Fe-OH absorption position Pos2250 (>2247 nm) along with occurrences of mafic dikes. This study demonstrates that utilizing the detailed SWIR identification in conjunction with accurate geological mapping has great potential for greenfield exploration of orogenic gold deposits
Rapid Identification of Greigite in Lacustrine Sediments Using SIRM/χ and χ<sub>ARM</sub>: Insights From the Cuo E Core, Tibetan Plateau, China
No full textThe Cuo E (CE) core contains the entire Quaternary stratigraphy of the CE Lake (31 degrees 24 '-31 degrees.32 ' N, 91 degrees 28 '-91 degrees 33 ' E, Tibetan Plateau, China). Here, we study the magnetic properties of 1,748 samples from the CE core, combined with scanning electron microscopy and X-ray energy dispersive spectrometer analysis on selected samples. The main magnetic minerals appear to be magnetite and greigite. To further quantify the presence of greigite in CE core, 84 samples were analyzed using rock magnetism in more detail including: susceptibility (chi) versus temperature, coercivity component analysis of acquisition curves of the isothermal remanent magnetization (IRM), and principal component analysis of the first-order reversal curve (FORC) diagrams. The greigite content and saturation IRM over susceptibility (SIRM/chi) appear to be exponentially related. SIRM/chi can be used as greigite concentration indicator. We also propose a rapid way to identify greigite in the CE core: When SIRM/chi increases and anhysteretic remanent susceptibility (chi(ARM)) increases only slowly, the sample contains greigite. Samples with SIRM/chi < 15 kA/m also follow this relation. This greigite detection method has a lower limit of detection than the traditionally used SIRM/chi parameter. It is also faster than FORC analysis and thus particularly suitable for analysis of large sample collections. Twenty greigite-bearing layers were identified in the CE core using this method. The location of the Jaramillo subchron in the CE core is controversial in the currently available magnetostratigraphy, possibly related to the presence of greigite in this core interval
Nontarget analysis and characterization of p-phenylenediamine-quinones and -phenols in tire rubbers by LC-HRMS and chemical species-specific algorithm
No full textBackground N,N '-disubstituted p-phenylenediamine-quinones (PPDQs) are oxidization derivatives of p-phenylenediamines (PPDs) and have raised extensive concerns recently, due to their toxicities and prevalence in the environment, particularly in water environment. PPDQs are derived from tire rubbers, in which other PPD oxidization products besides reported PPDQs may also exist, e.g., unknown PPDQs and PPD-phenols (PPDPs). Results This study implemented nontarget analysis and profiling for PPDQ/Ps in aged tire rubbers using liquid chromatography-high-resolution mass spectrometry and a species-specific algorithm. The algorithm took into account the ionization behaviors of PPDQ/Ps in both positive and negative electrospray ionization, and their specific carbon isotopologue distributions. A total of 47 formulas of PPDQ/Ps were found and elucidated with tentative or accurate structures, including 25 PPDQs, 18 PPDPs and 4 PPD-hydroxy-quinones (PPDHQs). The semiquantified total concentrations of PPDQ/Ps were 14.08-30.62 mu g/g, and the concentrations followed the order as: PPDPs (6.48-17.39) > PPDQs (5.86-12.14) > PPDHQs (0.16-1.35 mu g/g). Significance The high concentrations and potential toxicities indicate that these PPDQ/Ps could seriously threaten the eco-environment, as they may finally enter the environment, accordingly requiring further investigation. The analysis strategy and data-processing algorithm can be extended to nontarget analysis for other zwitterionic pollutants, and the analysis results provide new understandings on the environmental occurrence of PPDQ/Ps from source and overall perspectives
Nontarget analysis and characterization of p-phenylenediamine-quinones and -phenols in tire rubbers by LC-HRMS and chemical species-specific algorithm
No full textBackground N,N '-disubstituted p-phenylenediamine-quinones (PPDQs) are oxidization derivatives of p-phenylenediamines (PPDs) and have raised extensive concerns recently, due to their toxicities and prevalence in the environment, particularly in water environment. PPDQs are derived from tire rubbers, in which other PPD oxidization products besides reported PPDQs may also exist, e.g., unknown PPDQs and PPD-phenols (PPDPs). Results This study implemented nontarget analysis and profiling for PPDQ/Ps in aged tire rubbers using liquid chromatography-high-resolution mass spectrometry and a species-specific algorithm. The algorithm took into account the ionization behaviors of PPDQ/Ps in both positive and negative electrospray ionization, and their specific carbon isotopologue distributions. A total of 47 formulas of PPDQ/Ps were found and elucidated with tentative or accurate structures, including 25 PPDQs, 18 PPDPs and 4 PPD-hydroxy-quinones (PPDHQs). The semiquantified total concentrations of PPDQ/Ps were 14.08-30.62 mu g/g, and the concentrations followed the order as: PPDPs (6.48-17.39) > PPDQs (5.86-12.14) > PPDHQs (0.16-1.35 mu g/g). Significance The high concentrations and potential toxicities indicate that these PPDQ/Ps could seriously threaten the eco-environment, as they may finally enter the environment, accordingly requiring further investigation. The analysis strategy and data-processing algorithm can be extended to nontarget analysis for other zwitterionic pollutants, and the analysis results provide new understandings on the environmental occurrence of PPDQ/Ps from source and overall perspectives
Large magnesium isotopic fractionation in lunar agglutinatic glasses caused by impact-induced chemical diffusion
No full textImpact glasses are abundant in the lunar regolith, and Mg isotopes have the potential to trace components from various lunar crustal reservoirs, which have recently been shown to exhibit large Mg isotopic fractionations. However, it remains unclear whether Mg isotopic fractionation occurs during the formation of impact glasses. In this study, we report in situ Mg isotopic and elemental compositional data for agglutinatic glasses returned by the Chang'e 5 mission and obtained using the laser ablation split stream technique. Vesicular textures, Fe-Ni alloys, tiny Fe droplets, and high Ni contents suggest the studied agglutinatic glasses had an impact origin. The agglutinatic glasses exhibit large Mg isotopic fractionation, with delta 26Mg values ranging from -1.36 %o to -0.01 %o. The lack of correlations between delta 26Mg values, Ni contents, and ratios between volatile and relatively refractory elements (K/La, Rb/Sr, and Ce/Pb) indicate the addition of a meteoritic component and evaporation was not the major process responsible for the measured Mg isotopic variations. In fact, the MgO profiles and correlations between delta 26Mg and MgO, Na2O, Sc, Sr, CaO/Al2O3, and delta Eu reflect Mg isotopic fractionation caused by Mg diffusion from a region with high Mg contents (i.e., more melted pyroxene) to one with lower contents (i.e., more melted plagioclase). Diffusion modeling shows that the duration of diffusion was less than a fraction of a second. Our results indicate that chemical diffusion can produce large Mg isotopic fractionation in impact glasses on a scale of at least tens of microns, and that isotopic fractionation driven by chemical diffusion needs to be considered when the Mg isotopic compositions of impact glasses are used to identify different lunar rock reservoirs