Guangzhou Institute of Geochemistry
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Mantle metasomatism by subducted Indian continental crust: Evidence from post-collisional basaltic ultrapotassic rocks in southern Tibetan plateau
No full textAt continental collisional zones, the continental crust is known to subduct, penetrating the deep lithospheric mantle and undergoing partial melting. However, the extent to which these melts can effectively alter, or metasomatize, the overlying mantle remains a contentious issue. This debate is especially pronounced in the Cenozoic Himalayan-southern Tibet collisional orogen. The complexity arises from the fact that previous research has predominantly concentrated on the post-collisional intermediate ultrapotassic rocks. However, these rocks could have originated either from the subducted Indian continental crust through a process of mantle assimilation or from melange rocks, thereby primarily reflecting crustal recycling rather than mantle metasomatism by subducted continental crust. In this study, we shift our focus to the less-well-studied post-collisional basaltic ultrapotassic rocks (BUPRs) from the Sailipu region in the Lhasa block of southern Tibet. Our aim is to evaluate the characteristics of the orogenic mantle and the dynamics of crust-mantle interactions. In this study we report major and trace elements and Sr-Nd-Pb-Mo-B isotopes for these Miocene post-collisional BUPRs. The rocks are typically characterized by alkaline affinity, arc-like trace element distribution patterns, and enriched Sr-Nd-Pb isotopes, which point to their derivation from an enriched mantle source. Moreover, the Mo-B isotope ratios of these BUPRs - delta 98/95Mo ranging from -0.85 %o to -0.27 %o and delta 11B from -20.2 %o to -14.4 %o - are notably lower than those found in Mid-Ocean Ridge Basalts (MORBs) and arc lavas. Instead, they are similar to the isotopic compositions of basalts associated with continental subduction, as well as intermediate ultrapotassic rocks from western Anatolia and the Lhasa block, and the gneisses and schists of the Himalayas. These similarities strongly suggest the input of subducted Indian continental crust to the mantle source for these rocks. In conclusion, our study supports the metasomatism of the mantle beneath southern Tibet by subducted Indian continental crust. These results show that continental subduction zones, much like their oceanic counterparts, are key regions for mantle metasomatism, and thus expands our understanding of the geological processes at work in these dynamic areas
Iron isotopic fractionation during seafloor hydrothermal alteration of oceanic upper crust, as recorded in Geotimes lavas of Semail ophiolite, Oman
No full textThe Semail ophiolite in Oman features a crustal stratigraphy akin to a fast-spreading modern oceanic lithosphere. Its Geotimes pillow lavas, the stratigraphically oldest extrusive sequence at the bottom, share geochemical traits with contemporary mid-ocean ridge basalts, offering a unique opportunity to examine iron (Fe) isotopic fractionation during hydrothermal alteration under varied redox conditions. Significant alteration transformed primary minerals, evidenced by the dissolution of clinopyroxene, plagioclase, and ilmenite, alongside the precipitation of chlorite, albite, and magnetite-hematite. The 87Sr/88Sr ratios of 18 basalt subsamples from altered pillow lava range from 0.705110 to 0.705680, indicating extensive seawater interaction. The delta 56Fe values show systematic variations at a centimeter scale (0.037-0.291 parts per thousand), primarily resulting from hydrothermal processes rather than source inheritance. Notably, the pillow lava's core displays higher delta 56Fe values, suggesting the initial dissolution of Fe-bearing minerals under reduced conditions. In contrast, the edges show lower delta 56Fe values akin to mean mid-ocean ridge basalt, indicating that strong oxidation conditions minimally affected these isotopic values. In conclusion, this study reveals the complex variations of the Fe concentrations and Fe isotopic compositions of altered basalt that suffered hydrothermal alteration during the various redox conditions
Examining the reliability of current micro-and nano-indentation-based rock mechanical upscaling schemes: a comprehensive comparison with uniaxial/triaxial macroscopic mechanical testing
No full textShale and marlstone are two typical rocks for gas reservoirs and caprocks for the underground storage of carbon dioxide. Accurately estimating their mechanical properties is challenging due to these rocks' multiphase and multiscale structures. In this study, we conducted triaxial compressive, microindentation, and nanoindentation tests on samples collected in a borehole to investigate Young's modulus at different scales. To upscale the mechanical properties, we utilized existing homogenization models, namely Mori-Tanaka (MT), Self-Consistent (SC), and Voigt-Reuss-Hill average (VRH), and compared the moduli upscaled from the nanoindentation technique and rock mineralogical method with those measured from microindentation and triaxial compressive tests. Results showed that the rock mineralogy-based MT and SC methods produced higher moduli than the nanoindentation-based MT method, and all of these were significantly larger than those obtained from the triaxial compressive tests. Additionally, the nanoindentation-based VRH method and the microindentation test yielded close moduli but still exhibited a certain gap compared to the macroscopic mechanical test results. This suggests that the current indentation-based mechanical upgrading method cannot accurately estimate the rock mechanics at the macroscale. Nevertheless, in the absence of a better solution, the above two methods can still be considered. The difference between the moduli measured by the compressive test and those upscaled through these homogenization models was attributed to the underestimation caused by the low elastic stiffness of pores, fractures, and grain contacts in the rocks. Therefore, more advanced methods are required to develop to make mechanical upscaling closer to the real situation of rocks
Green remediation of REEs-contaminated soil by biodegradable chelators with optimization and risk assessment
No full textThe omnipresence of rare earth elements (REEs) in the environment, driven by their extensive industrial applications and common occurrence in some weathered crusts, has raised significant concerns as emerging pollutants. Soil washing has been recognized as an effective approach to remediate REEs-contaminated soils. However, traditional washing agents frequently lead to soil acidification and salinization, adversely affecting soil microbial communities and plant growth. This study explored the use of biodegradable chelators (BCs)-specifically N,N-bis(carboxymethyl)-L-glutamic acid (GLDA), iminodisuccinic acid (ISA), and polyaspartic acid (PASP)-as alternatives for removing REEs from contaminated agricultural soils. Our findings demonstrated that the removal efficiency of REEs positively correlates with BCs concentration, liquid-to-solid ratio, and washing time, while showing a negative correlation with solution pH. Through response surface analysis, we determined the optimal parameters for the washing process, revealing that GLDA, ISA, and PASP achieved total REEs removal efficiencies of 50.8%, 40.5%, and 23.2%, respectively. Statistical analysis confirmed that the concentration of BCs was the primary factor influencing washing effectiveness. Moreover, washing with BCs significantly removed reducible REEs-those bound to iron/manganese oxides-thereby decreasing the mobility and bioavailability of REEs in soil. The reduction in bioavailable REEs significantly lowered the environmental risk associated with contaminated soil. Notably, the activity of soil enzymes improved post-washing with BCs, indicating a positive impact on soil health. This study provides valuable insights into the remediation of REEscontaminated soils using BCs, with GLDA emerging as a particularly effective agent
Generation characteristics of polybrominated and polychlorinated dibenzo-<i>p</i>-dioxins/furans (PBDD/Fs and PCDD/Fs) under varying incineration conditions of municipal solid waste
No full textMunicipal solid waste incinerators (MSWIs) are deemed important sources of polychlorinated and polybrominated dibenzo-p-dioxin/furans (PCDD/Fs and PBDD/Fs). However, compared to PCDD/Fs, the emission characteristics of MSWI-derived PBDD/Fs have been rarely studied. Here we selected a long-term operating MSWI, investigated the generation of PBDD/Fs under varying incineration conditions within the normal range, and compared them to those of PCDD/Fs. Generally, PBDD/Fs exhibited mass-based emission factors (mass-EFs) one order of magnitude higher than those of PCDD/Fs and were predominantly released via slag, as were PCDD/ Fs, though at lower percentages. Both PBDD/Fs and PCDD/Fs showed significant changes in emissions with the variations in waste load, O2 content, and waste composition, particularly PBDD/Fs. Comparatively, furnacederived PBDD/Fs demonstrated heightened sensitivity to waste load and composition, whereas PCDD/Fs were primarily influenced by O2 levels, followed by waste composition; PCDD/Fs consistently exhibited increasing mass-EFs under unconventional conditions and PCDD/Fs in filtered fly ash were highly sensitive to all the three variables, while filtered PBDD/Fs remained insensitive to these conditions. Data comparison between raw flue gas and filtered fly ash indicated secondary generation of PBDD/Fs and PCDD/Fs during gas purification, as well as the insufficient dioxin-trapping efficiency of bag filters, particularly for PBDD/Fs. Therefore, MSWI-derived PBDD/Fs and dioxins in slag and other MSWI-derived wastes warrant significant attention
Microwave Digestion for Re-Os Isotope Measurements in Geological Samples
No full textIn this study, we present the novel use of a microwave digestion system (CEM BLADE) to digest geological materials for Re-Os isotopic analysis. This technique employs quartz digestion vessels that are easy to clean and reusable, avoid the complicated steps of opening and sealing, and enable complete digestion of the samples within 30 min at high temperature (max. 310 degrees C) and pressure (max. 700 psi). The microwave digestion system was used to digest samples of four ultramafic rock reference materials (GBW07101, GBW07102, GBW07291, and WPR-1a), one basalt reference material (BIR-1a), and one black shale reference material (SGR-1b). The Re-Os isotope measurement results for GBW07291, BIR-1a, and SGR-1b were in agreement with previously published values, and we are the first to report Re-Os isotopes for GBW07101, GBW07102, and WPR-1a. Therefore, this new microwave digestion system is a simple, efficient, reliable, and safe sample digestion method for prospective applications in Re-Os isotopic analysis
Algorithm for improving the sizing accuracy in real-time bioaerosol single particle mass spectrometer
No full textThe newly developed bioaerosol single particle mass spectrometer (Bio-SPAMS) has been innovatively designed for its optical sizing system. The first laser beam in the previous single particle mass spectrometer was split into near distance double beams, similar to the design of APS (Aerodynamic Particle Sizer) and SBS-LIBS (Single Beam Splitting-Laser Induced Breakdown Spectroscopy). All the particles focused by the aerodynamic lens can be sized and got number concentration statistic. However, due to the imperfect beam quality and the large scattering intensity of the large-sized particles, there may be some noise in the scattered signals, particle diameter measured by this sizing system was often larger than actual value if the same trigger threshold was set. In this study, when measuring PSL microspheres with diameters of 1.9, 3.1, and 4.9 mu m, the identification rates of the fixed threshold algorithm were only 75.25%, 55.26%, and 0.27%, respectively. To address such issue, we developed a dynamic threshold waveform recognition algorithm based on field programmable gate array (FPGA), which could process the photoelectric signals collected by a photomultiplier tube (PMT) in real time. The algorithm can dynamically adjust the trigger threshold of the collected scattered signals and accurately calculate the interval time between the near distance double beam. For PSL microspheres with diameters of 1.9, 3.1, and 4.9 mu m, the accuracy of the dynamic threshold algorithm increased by 19.09%, 25.72%, and 88.20%, respectively. This algorithm effectively solves the problem of particle sizing deviation, and improves the particle size measurement accuracy of the bioaerosol mass spectrometer in a wide particle size range from 0.3-6 mu m
Evaluating Heavy Metal Contamination in Water and Tissues of <i>Tor putitora</i>: Implications for Human Health Risk Assessment
No full textAnthropogenic activities have led to the release of heavy metals, posing significant threats to both aquatic ecosystems and human health. This study focused on evaluating the concentrations of Chromium (Cr), Nickel (Ni), Zinc (Zn), Cadmium (Cd), and Lead (Pb) in water and Tor putitora fish along the River Kabul in Pakistan, considering upstream and downstream sites with varying anthropogenic influences. Our analysis revealed detectable levels of all studied heavy metals at both sites, with concentrations surpassing the permissible limits set by the World Health Organization (WHO), with except for Zinc. At Site-1, average concentrations (mg L- 1) were: Cr 1.46 +/- 1.03, Ni 1.61 +/- 0.53, Zn 0.65 +/- 1.09, Cd 0.23 +/- 0.28, and Pb 0.75 +/- 0.07, while Site-2 values were: Cr 1.57 +/- 0.03, Ni 1.54 +/- 0.94, Zn 1.55 +/- 0.98, Cd 1.12 +/- 0.46, and Pb 1.47 +/- 0.82. Analysis of Tor putitora fish indicated significant metal concentrations, particularly in metabolically active tissues such as the kidney and liver, with Cr showing significant accumulation across all tissues and Cd exhibiting the lowest accumulation. Notably, muscle, a less metabolically active tissue, demonstrated the lowest metal accumulation. Evaluation of the Target Hazard Quotient and Hazard Index revealed no considerable risk for non-carcinogenic effects. However, in Site-1, Pb exhibited a carcinogenic risk surpassing the acceptable threshold (< 1 x 10(- 4)), suggesting an elevated cancer risk associated with consuming Tor putitora. These findings emphasize the urgent need for comprehensive environmental policies in developing countries to address long-term heavy metal pollution and safeguard both ecosystems and human health
Uphill diffusion of lithium along phosphorus gradients in olivine from mafic layered intrusions
No full textLithium (Li) concentration and Li isotopes of olivine have been widely adopted to decipher the mantle-crust interaction and short-lived magmatic processes in the shallow magma chambers. However, the diffusion behavior of Li in olivine has not yet been fully understood, which may bias the interpretation of Li concentration and Li isotopes observed in natural olivine. In this study, high-resolution elemental mapping (Li, P, Fe, Mn, Ca, Al, and Ni) combined with in situ Li concentration and Li isotope analyses were conducted for olivine grains from two ca. 260 Ma mafic layered intrusions in SW China, to decode the origin of coupled Li-P zoning and multimode diffusion of Li in natural olivine. The 2-D elemental maps and compositional profiles reveal complex, coupled Li-P zoning patterns. The Li-P-rich zones contain 3.5 to 6.1 ppm Li and 187 to 776 ppm P, higher than those of Li-P-poor olivine domains that contain 0.7 to 2.8 ppm Li and 29 to 166 ppm P. Particularly, the Li-P-rich zones in each grain commonly have lower delta 7Li* than that of the Li-P-poor domains, with the maximum fractionation of Li isotopes in a single grain being up to 15 parts per thousand. Numerical modeling shows that rapid olivine growth can result in variable degrees of Li and P enrichment in concentration and an increase of delta 7Li* in the Li-P-rich zone of olivine, which is inconsistent with our observations. Instead, the inverse variations of Li concentration and Li isotopic profiles can be well simulated in an uphill diffusion mode of Li along pre-existing sharp P gradients, accompanying by simultaneous coupled and non-coupled diffusion of Li within a single olivine. The large variation of delta 7Li* is thus interpreted as kinetic fractionation, which may be caused by dehydration of olivine due to exsolution of a fluid phase from the interstitial liquid of a crystal mush. Three distinct Li-P variation trends of olivine are summarized in this study and can be used to distinguish the process of crystal growth from postcrystallization diffusion. Our results should have important bearings on the understanding of complex crystallization and solidification processes of crustal magma chambers
Revisiting the high temperature Darongshan-Shiwandashan granitoids in the South China: A response to slab tearing associated with diachronous collision between Indochina and South China blocks
No full textThe Darongshan-Shiwandashan granite belt (DSGB) is composed of S-type granites and granodiorite intrusions, which are characterized by high- or ultrahigh-temperature cordierite, orthopyroxene, and granulite xenoliths. The petrogenesis of these plutons is a subject of debate, and a thorough overview of regional tectonic evolution and geochemistry is still absent despite the numerous research conducted in this granite belt. This study is a comprehensive overview of geochronology, whole-rock major-trace elements, Sr-Nd isotopes, and zircon Hf-O isotopes in the DSGB, focusing on their petrogenesis and tectonic setting of formation. The geochronological data indicates that DSGB granitoids emplaced at ca. 250 Ma, with a southwestward-younging trend. Moreover, mineral assemblages of cordierite + orthopyroxene suggest that the DSGB was formed in a high-temperature (similar to 850 degrees C) and low-pressure (3.7-6 kbar) tectonic setting. Three main plutons (Darongshan, Jiuzhou, and Taima) of the DSGB exhibit distinctly different compositions. The Darongshan and Taima granitoids display high silica (SiO2 = 68.65-78.10 wt%), low-maficity (FeO + MgO = 1.97-7.28 wt%), along with negative whole-rock epsilon Nd(t) values (-13.9 to -9.7) and elevated initial Sr-87/Sr-86 values (0.71638 to 0.73165). The Jiuzhou granitoids, on the other hand, exhibit relatively low silica (SiO2 = 63.90-72.72 wt%) and high maficity (FeO + MgO = 3.03-9.88 wt%), with largely overlapping but relatively high epsilon Nd(t) values ranging from -12.9 to -9.9 and lower initial Sr-87/Sr-86 values from 0.71453 to 0.72401. Two-component mixing model results indicate these different compositions represent varying degrees of mixing between crust- and mantle-derived magmas, with 0-10 %, 0-20 % and 20-40 % basaltic melts involved for Taima, Darongshan and Jiuzhou plutons, respectively. The subducting slab tearing, induced by the diachronous collision between the South China Block (SCB) and Indochina Block (ICB), provide the most feasible interpretation for the petrogenesis and spatio-temporal geochemical pattern of the granitic rocks in the DSGB. The onset of the diachronous collision initiated at the Hainan-Yunkai massif, southwest of SCB, while the Tethys Ocean still existed in the northwest (Nanpanjiang area), causing notable disparities in the convergence velocities of the subducting ocean slab. The heterogeneous stresses resulting from the different subduction rates were accommodated by bending and tearing of the subducting slab. Then, ultrahigh-temperature basaltic melts derived from the decompression melting of the lithospheric mantle facilitated the melting of metasedimentary rocks, which resulted in the formation of high-temperature S-type granitoids. The Jiuzhou pluton, located at the center of slab tearing, received more mantle contributions than the Darongshan and the Taima plutons, which are emplaced away from the slab tearing center. The younging trend in age from the Darongshan to Jiuzhou and Taima plutons indicates a progressive tearing from the northeast (the far end of the subducting slab) to the southwest