ACS Earth and Space Chemistry最新文献

The mechanism of the Triassic continental crust growth in the East Kunlun Orogenic Belt (EKOB) is highly controversial. In this contribution, we present comprehensive data on the Yuegelu granodiorite and its mafic microgranular enclaves (MMEs) from the eastern segment of the EKOB, including zircon U–Pb geochronology and Hf isotope, mineral chemistry, whole-rock geochemistry and Sr–Nd isotopes, and in situ plagioclase Sr isotope, to constrain the genesis of these rocks and shed new insights on the continental crust growth. The MMEs are coeval with the host granodiorite at ∼240 Ma and display abundant quenching textures such as acicular apatites and quartz phenocrysts rimmed by amphibole. They typically exhibit low SiO₂ but high TiO₂, Fe₂O₃^T, MnO, and MgO concentrations and have similar Sr–Nd–Hf isotopic compositions to the host rock. We suggest that the Yuegelu MMEs are late cognate cumulates derived from the same parental magma with the host rock as a result of pressure quenching rather than the hybrids of crustal and mantle magmas. The granodiorite is medium- to high-K calc-alkaline, metaluminous I-type granite with relatively high SiO₂, but low Al₂O₃, CaO, and Fe₂O₃^T contents. The granodiorite is enriched in Rb, K, and Pb but depleted in Nb, Ta, Sr, P, and Ti, resembling a bulk continental crust. However, Yuegelu granodiorite has much more depleted Sr–Nd–Hf isotopic compositions than those of the mature crustal materials, indicating a significant mantle contribution. Based on Sr–Nd isotopic modeling, the Yuegelu granodiorite could be generated by partial melting of the Paleo-Tethys Oceanic crust (∼80%) with the overlying terrigenous sediments (∼20%). The partial melting of oceanic crust fragments in the syn-collisional setting in the Middle Triassic contributed substantially to the continental crust growth in the EKOB.

This study presents field experiments conducted in a contaminated aquifer in Rifle, CO, to determine the speciation and accumulation of uranium in sediments during in situ bioreduction. We applied synchrotron-based X-ray spectroscopy and imaging techniques as well as aqueous chemistry measurements to identify changes in U speciation in water and sediment in the first days follwing electron donor amendment. Limited changes in U solid speciation were observed throughout the duration of this study, and non-crystalline U(IV) was identified in all samples obtained. However, U accumulation rates strongly increased during in situ bioreduction, when the dominant microbial regime transitioned from iron- to sulfate-reducing conditions. Results suggest that uranium is enzymatically reduced during Fe reduction, as expected. Mineral grain coatings newly formed during sulfate reduction act as reduction hotspots, where numerous reductants can act as electron donors [Fe(II), S(II), and microbial extracellular polymeric substances] that bind and reduce U. The results have implications for identifying how changes in the dominant reducing mechanism, such as Fe versus sulfate reduction, affect trace metal speciation and accumulation. The outcomes from this study provide additional insights into uranium accumulation mechanisms in sediments that could be useful for the refinement of quantitative models describing redox processes and contaminant dynamics in floodplain aquifers.

The alunite supergroup of minerals contains several hydroxysulfate mineral phases that commonly occur in acidic natural and engineered environments. The main division of the mineral supergroup defines two minerals, jarosite and alunite, based on the relative structural occupancy by Al or Fe, respectively. However, intermediate members of the jarosite-alunite solid solution have not been extensively characterized, especially in the environment. Here, we link the mineral unit cell sizes measured by X-ray diffraction, peak shifts in Raman spectra, fitting parameters in Mössbauer spectroscopy, and elemental quantification by EDX spectroscopy to known amounts of Al substitution in two synthetic series of Al-substituted jarosite (up to Al-for-Fe substitution of 9.5%) and unknown Al substitution in a natural jarosite isolated from an acid sulfate soil. Strong correlations were observed between the Al substitution of the jarosite samples and unit cell size, position of several vibrational peaks in Raman spectroscopy, and the temperature of magnetic ordering. In addition, elemental mapping provided a robust way to characterize the Al content of jarosite. As the techniques were effective in quantifying the Al or Fe content of jarosite-alunite supergroup mineral samples, without the need for sample dissolution, the findings support the application of these spectroscopy techniques to characterize natural jarosite-alunite samples. Using these techniques, we demonstrate at least 5% Al-for-Fe substitution in a jarosite sample from an acid sulfate soil. Application to environmental samples is especially useful in cases where it is otherwise difficult to directly measure the Al content of a mineral sample or when Al-for-Fe substitution influences the spectral responses to substitution at other sites in the crystal structure.

The late Proterozoic tectonic evolution of the North China Craton (NCC) has long been a matter of debate, and A-type granites in the region can provide valuable constraints for resolving this issue. In this paper, the Baojiashan and Longwangzhuang granites from the southern margin of the NCC were studied using a combination of LA-ICP-MS zircon U–Pb dating, Hf–Nd isotopic analyses, and whole-rock geochemical analyses to constrain their magmatic ages and sources. The Baojiashan and Longwangzhuang granites yield intrusion ²⁰⁷Pb/²⁰⁶Pb ages of 1803 ± 29 and 1607 ± 21 Ma, respectively. They show significant geochemical similarities to the A-type granites, with high SiO₂ and K₂O content, high FeO^T/(FeO^T + MgO) and 10,000 Ga/Al ratios, strong Eu-negative anomaly, and high zircon saturation temperature (813–982 °C). Among them, the Baojiashan granites display a lower Nb/Ta ratio and a higher Y/Nb ratio, consistent with the characteristics of A₂-type granites. Longwangzhuang granites exhibit opposite ratios of the above, following the characteristics of A₁-type granites. The zircon ε_Hf(t) values (−6.5 to −3.0) and ε_Nd(t) values (−6.7 to −2.4) of both are similar, and the second-stage model ages (T_DM2) are 2588–2730 and 2462–2953 Ma, indicating that they mainly originated from the partial melting of the Neoarchean crust. Combined with previous analytical results, the southern margin of the NCC experienced a process of postorogenic extension toward intracontinental rift at 1.8–1.6 Ga and represents a response to the breakup of the Columbia supercontinent.

Chemical composition is an essential aspect of classifying iron meteorites. In this study, we developed and validated a stand-alone procedure for the chemical characterization of iron meteorites using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The adopted innovative approach to the analytical sequence included new features in data reduction software, such as external calibration with more than one measurement standard, yield corrections, and normalization for matrix elements. The obtained results of As, Au, Co, Cr, Cu, Fe, Ga, Ge, Ir, Ni, Os, Pd, Pt, Re, Rh, Ru, and W in nine known iron meteorites agreed with the published values, their recognized chemical classifications, and distribution on normalized chondrite diagrams. Moreover, the results obtained closely correlate with those employed to classify three Brazilian iron meteorites (Conceicao do Tocantins─H, IIAB; Nova Olinda─Ogg, IIAB; and Augusto Pestana─Og, IIIE), which have recently been included in the Meteoritical Bulletin Database. Additionally, we illustrate that LA-ICP-MS elemental mapping, conducted within regions featuring diverse phases of the Augusto Pestana meteorite, serves as a potent tool for chemical classification even without prior knowledge regarding natural structural variations.

The physicochemical properties of particles affect many important atmospheric processes; yet, they are challenging to measure in situ. Herein, fluorescence aerosol flow tube (F-AFT) spectroscopy is applied to directly probe the ionic strength and pH in model systems of inorganic aerosol particles. The pH-sensitive probe molecule quinaldine red (QR) is incorporated into aerosol particles of sodium chloride, ammonium sulfate, ammonium bisulfate, and their mixtures. Fluorescence spectra are collected for variable particle acidity and ionic strength as mediated by composition and relative humidity. Results show that shifts in fluorescence wavelength are driven by changes in both ionic strength and pH. A two-dimensional regression analysis of the sulfate particle fluorescence line shape as a linear function of both molality and pH results in R² = 0.75. For comparison, R² values of 0.17 and 0.64 are found for molality and pH considered separately, respectively. The regression model calculated from the sulfate particle system did not fit the sodium chloride particle data well, suggesting that there are chemically specific effects governing the pH and ionic strength interactions with the dye molecule. Overall, these findings indicate the potential of F-AFT spectroscopy for in situ elucidation of the physicochemical properties of submicrometer aerosol particles, contingent upon a detailed understanding of the controlling factors in the fluorescence behavior of the chosen probe molecules in common aerosol particle-phase chemical environments.

To improve our understanding of the formation of sedimentary copper deposits, the reaction of cuprite with 0.2 m HAc-KAc or pure H₂O solutions is studied systematically at 100–250 °C and 5–30 MPa. The experiments were carried out for periods of up to 72 h in a Parr autoclave, allowing for the in situ sampling of the fluid phase. The experiments conducted in this study demonstrate that cuprite (Cu₂O) underwent a series of changes: (i) simple dissolution, (ii) Cu(I) disproportionation to native Cu and Cu(II), and (iii) subsequent oxidation into tenorite (CuO). In pure water, only (i) and (ii) steps can be discerned, whereas all three processes have been observed in an acetate-bearing system. In HAc-KAc solutions, the maximum dissolved Cu content correlates inversely with temperature, i.e., 378 to 168 μg/g at 100 and 200 °C, respectively. However, equilibrium has not been reached in our experiments and these values may be treated as minimum cuprite solubility. In situ Cu isotope analyses have been carried out by laser ablation combined with a multicollector inductively coupled plasma-mass spectrometer. The data imply that copper isotope fractionation during cuprite replacement reactions is small. Both the microscopic observations on cross sections and the analytical data support the idea that the mineral replacement reaction is controlled by a coupled dissolution-reprecipitation (CDR) mechanism. This applies to both the deposition of metallic copper and the formation of tenorite. As suggested by the formation of pore spaces in the deposited layers, only a portion of the dissolved copper is redeposited directly in situ. The isotopic analyses of the solution and solid phases show that the partial transfer of copper into the surrounding solution is not associated with a significant isotopic effect, e.g., a measured difference between Cu and Cu₂O is within 0.32 ± 0.06‰. Our study indicates that acetate plays a dual role in copper transport and deposition. On one hand, the presence of acetate strongly enhances the Cu content in solution up to 400 μg/g, implying that acetate complexation can be responsible for metal transport in hydrothermal fluids. On the other hand, decarboxylation of acetate substantially decreases the dissolved Cu and aids the precipitation of tenorite. This may lead to the co-occurrence of Cu-bearing minerals with different oxidation valence states at low temperatures in a variety of geological settings such as supergene hydrothermal systems.

Elucidating how organic matter and iron oxide particles interact will advance the understanding of geochemical processes and facilitate the development and implementation of methods to address groundwater pollution. The sorption and fractionation of three well-characterized organic matter isolates, Suwannee River natural organic matter (SRNOM), Suwannee River fulvic acid (SRFA), and Eliot Soil humic acid (ESHA), onto goethite nanoparticles in batch reactors and goethite-coated sand in column reactors were studied. Total organic carbon, molecular size, and optical properties were measured before and after exposure to solids in batch and column reactors, as well as in solution after the resuspension of equilibrated solids in a fresh buffer. Fluorescent, aromatic, high-molecular-weight material more strongly sorbed and stayed sorbed upon exposure to fresh solution. The effects of the different organic matter fractions on reduction of 4-chloronitrobenzene (4-ClNB) were also quantified. In both batch and column reactors, the reactivity of NOM-treated particles toward 4-ClNB in the presence of Fe(II) was inhibited by all isolates as compared to that in NOM-free reactors, with SRFA inhibiting reaction rate constants the most followed by ESHA and SRNOM. There are clear spectral and size differences in the organic matter that remains in the liquid medium compared to the NOM that binds to the mineral surfaces, but both of these materials inhibit Fe(II)-mediated reactions on the surface. Materials high in aliphatic and carboxylate contents, rather than the more strongly sorbing fluorescent aromatic material, appear to inhibit reactivity.

Distributions of amino acids, based on either enantiomeric excess or relative abundances of amino acid type, are key chemical measurements in the search for life on potential future astrobiology missions. This study investigates the impact of subcritical water extraction (SCWE) at different pH values on the measurement of these amino acid distributions when the starting material contains microorganisms. Cells of Pseudoalteromonas haloplanktis at pH 2, 6, and 12 underwent SCWE at 200 °C for 30 min, and the released amino acids were analyzed by capillary electrophoresis with laser-induced fluorescence detection. The overall extraction yield was improved under both acidic and alkaline conditions relative to neutral ones. The characteristic biotic distributions of amino acid types present in these samples were preserved under all conditions, although some degradation was observed as a relative increase in the amount of simpler amino acids like glycine. Contrarily, while biotic enantiomeric excesses remained preserved under acidic conditions, racemization was observed under alkaline conditions. This work shows the power of SCWE for converting polypeptide biopolymers into amino acid monomers, independent of the initial pH of the sample. However, it also highlights the need to understand the physiochemical properties of the sample to allow the mitigation of undesirable changes to the native distributions of amino acids.

Iron is a key element that affects bioactivity in the global environment as a nutrient and also as an adsorbent that controls the circulation of other elements in the hydrosphere. This element is abundant in sea ice and is released into the aquatic environment during the thawing process. Due to the low solubility of iron compounds, they exist as solid materials, such as oxides and oxyhydroxides, which effectively adsorb transition metal ions and affect their circulation in the hydrosphere. This process occurs not only in the hydrosphere but also in the cryosphere. In this study, adsorption of first-row transition metal cations on ferric oxyhydroxide (FeOxH) under frozen conditions is evaluated by ex-situ measurements with sample thawing and also by in situ X-ray fluorescence (XRF) measurements without thawing. The adsorption and desorption characteristics of transition metal cations on FeOxH are discussed from the difference in the adsorption ratio between these two measurements. For in situ XRF measurements, linear regression analysis assuming two states of analytes, i.e., adsorbed on FeOxH and dissolved in the freeze-concentrated solution (FCS) is efficient in estimating adsorption ratios. While complete adsorption is found for all metal cations studied here (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) at pH > 8, the adsorption ratio determined by in situ XRF is larger than the corresponding value obtained with the ex situ method with thawing at lower pH. This strongly suggests that metal cations are well adsorbed on FeOxH when concentrated in the FCS under frozen conditions but are desorbed upon thawing. The comparison of the adsorption ratios obtained by in situ and ex situ methods reveals specific adsorption of Mn²⁺ and Co²⁺. Interestingly, the specific adsorption of Mn²⁺ is irreversible, and desorption does not occur upon thawing. In contrast, thawing causes the desorption of specifically adsorbed Co²⁺, suggesting that different mechanisms are responsible for the specific adsorption.