Lamprophyres are widespread in the Xiongcun porphyry copper-gold district in the southern margin of the Lhasa terrane. They represent the latest magmatism and cut all other rock types as well as orebodies in the Xiongcun district. Herein, we report the zircon LA-ICP-MS U-Pb age, whole-rock major and trace elements and Sr-Nd-Pb isotopic compositions of lamprophyre from the Xiongcun district. LA-ICP-MS zircon U-Pb dating yields crystallization ages in Eocene at 47.03 ± 0.61Ma for the Xiongcun lamprophyre. The major element contents of the Xiongcun lamprophyres exhibit high Mg# along with calc-alkaline and ultrapotassic characteristics. The lamprophyres are enriched in LILEs (e.g., K, Rb, and Ba) and LREEs but depleted in HFSEs (e.g., Nb, Ta, and Ti). The Xiongcun lamprophyres are characterized by high (87Sr/86Sr)i ratios ranging from 0.71846 to 0.71858, low εNd(t) values ranging from –14.44 to –15.09, and enriched in radioactive Pb with (206Pb/204Pb)i, (207Pb/204Pb)i and (208Pb/204Pb)i ranging from 18.53–18.97, 15.62–15.75, and 38.75–39.53, respectively. On the basis of the geochemistry of the Xiongcun lamprophyres, we propose that they were derived from the partial melting of an enriched lithospheric mantle source that was metasomatized by fluids released from the subducted Neo-Tethyan oceanic slab and Indian continental crust. This enriched lithospheric mantle source is characterized by phlogopite- and garnet-bearing lherzolite. The break-off of the subducted Neo-Tethyan oceanic slab from the Indian continental lithosphere at 45~50 Ma resulted in asthenospheric upwelling through the slab window. Subsequently, the enriched lithospheric mantle was heated by the underlying hot asthenosphere and partially melted, generating the magma that ascended to form the Xiongcun lamprohyres in an extensional tectonic setting. The parent magmas were fractionated during their ascent, whereas the effect of crustal assimilation on the magma was limited.
Fertilization and irrigation (FI) are exerting an important impact on the fluxes of carbon, both between and within ecosystems in an agricultural area. However, the impacts of urea, diammonium phosphate ((NH4)2HPO4) and animal manure, as the most common fertilizers in Northern China, and irrigation on carbonate weathering in soil are still relatively unknown due to the complicated biogeochemical process of these added fertilizers. In this study, four soil columns with different treatments (control (CK), fresh cow manure (FM) urea (NF) and diammonium phosphate (PF)), were established to explore the influence of fertilization and irrigation on carbonate weathering in an agricultural area in Northern China. The pH, K+, Ca2+, Na+, Mg2+, NH4+, NO3–, NO2–, free CO2, HCO3–, Cl–, SO42–, COD and HPO42– in leachates from the soil columns were analyzed. The results showed that Ca2+ and NO3–, HCO3–, SO42– were the dominant cations and anions (>25% in meq%) in the leachate from the CK and FM columns, respectively, while Ca2+ and NO3– were the dominant cations and anions in NF and PF treatments, respectively. The addition of fresh cow manure had no distinct effect on the hydro-chemical characteristics in the soil solution, and the weathering rate of carbonate, whereas an increase in the weathering rate of carbonate, CO2 concentration, Ca2+, Mg2+ and NO3– was observed after the addition of urea and (NH4)2HPO4, which was mainly attributed to the release of protons from the nitrification reaction. The co-precipitation of phosphate ions with calcium carbonate had a blockage effect on the leaching of phosphate, but has no apparent effect on the weathering rate of carbonate when (NH4)2HPO4 was added to the carbonate-enriched soil column. The widespread application of urea and (NH4)2HPO4 along with irrigation in the agricultural area of Northern China increases the rate of carbonate weathering and soil CO2 emission. The enhanced Ca2+, Mg2+ and DIC (free CO2 + HCO3– + CO32–) due to the addition of urea and (NH4)2HPO4 as well as irrigation should not be disregarded when evaluating CO2 consumption by mineral weathering in the agricultural area.
Isotope dilution analysis can provide precise elemental concentration and isotopic composition data in a single measurement run. However, mass fractionation correction in isotope dilution analysis can be challenging. This study presents two iterative calculation methods, based on isotopic ratios and abundances, for isotope dilution analysis of elements with at least two internal reference isotopic ratios. The strontium isotope system was used to show the details of the calculations. For convenience, a MATLAB program was created based on these calculation methods. Replicate analyses of three reference materials demonstrate that the obtained Rb and Sr concentrations and 87Sr/86Sr isotopic ratios are in good agreement with previously published values. In addition, two mineral Rb-Sr isochronal ages, which agree with accepted zircon U-Pb ages, demonstrate the validity of the methods presented in this study.
Mesoproterozoic shales of low metamorphic grade from the Jixian section, northern China, were geochemically analyzed for bulk organic contents, molecular and isotopic compositions. One organic-rich sample from the Hongshuizhuang Formation is characterized by high total organic carbon and extractable organic material contents, high hydrocarbon generation potential, while four other organic-lean samples have almost no hydrocarbon generation potentials. Molecular compositions differ greatly between the organic-rich and lean samples. n-Alkanes in the organic-rich sample consist mainly of low molecular weight components with a maximum at n-C12, while the organic-lean samples are enriched in medium molecular weight n-alkanes with the maximum around n-C16. The monomethylalkanes and cyclic alkanes in the organic-rich sample are much more abundant than in the organic-lean counterparts, while acyclic isoprenoid alkanes are enriched in the organic-lean samples. Almost no steranes can be detected in the organic-rich sample, while a reasonable amount of steranes, dominated by pregnanes, occurs in the organic-lean samples. Bicyclic sesquiterpanes and pentacyclic terpanes are relatively concentrated in the organic-rich sample, while tricyclic terpanes are the major terpane compounds identified from the organic-lean samples. Alkylphenanthrenes are the major compound class in the aromatic hydrocarbon fractions. The ratios of parent to methylated aromatic homologues are higher in the organic-rich sample than in the organic-lean samples. All these provide convincing evidence for the existence of cyanobacteria organisms in the organic-rich Hongshuizhuang Formation. While both prokaryotes and eukaryotic organisms are likely contributors in the organic-lean samples, contamination from the Phanerozoic biomass cannot be ruled out.
Transformations of nitrogen and hydrogen defects in natural octahedral and cuboid diamonds after multi-stage annealing at P = 6 GPa and T = 2200°C are presented. It has been observed that nitrogen aggregation from A- to B-defects in octahedral diamonds has gradually increased. This transformation of nitrogen has proceeded more rapidly in cuboid diamonds. One may confirm that most of the cuboid diamonds characterized by a low nitrogen aggregation state were not annealed over a long period at mantle conditions and their formation occurred shortly before transportation to the Earth’s surface. Unlike octahedral diamonds, cuboid diamonds show a considerable increase in the intensity of the primary hydrogen-related peaks after the annealing, thus implying involvement of sites to which the hydrogen can bond and become IR-active, but these sites are simply not available in the octahedral diamonds. The magnitude to which peak 3107 cm–1 is increased after annealing has been found to be correlated with the total nitrogen content in cuboid diamonds. This supports the suggestion that the vibrational system with a primary line at 3107 cm–1 corresponds to a C-H vibration bonded to some form of aggregated nitrogen.
90Sr released into seawater from nuclear bomb testing and nuclear facility accident sites requires long-term monitoring. However, measuring 90Sr in seawater is still difficult and time-consuming. This study is aimed at improving the preconcentration method for successive purification using DGA Resin chromatography, which is applied to 90Sr analysis in seawater. At natural pH, the oxalate coprecipitation technique effectively collected Sr (84% in Sr yield) from seawater without Mg or Na. For 90Sr determination, 90Y in secular equilibrium with 90Sr was directly extracted using Fe coprecipitation and DGA Resin chromatography. The proposed method simplifies the analytical processes associated with the conventional method. Analytical results for surface seawater in the western North Pacific (0.81 ± 0.06 Bq m–3, n = 5) were consistent with those obtained using the conventional method (0.81 ± 0.07 Bq m–3, n = 5).
The apparent partition coefficients (DMe) of Na, Mn, Sr and Ba (Me) between dolomite and MgCl2 solutions at 130 and 200°C, DMe = (XMe/XCa+Mg)dolomite/([Me]/[Ca+Mg])solution, were experimentally investigated, and the obtained average values were 0.0016, 5.3, 0.059 and 0.021, respectively. The Na partition coefficient was smaller than those of the above divalent ions, reflecting the valence discrepancy between Ca and Na. The partition coefficients of divalent ions decreased from Mn to Ba, which is consistent with the effect of the cation site size in the crystal lattice and the ionic radii of substituting elements. Comparing these solid/liquid partition coefficients for dolomite with those for calcite and aragonite seen in the literature, the former values resemble those for calcite, but are rather different from those for aragonite. These findings may reflect the sizes of the respective cation sites, since the cations in calcite and dolomite occupy relatively compact six-fold coordination sites, but aragonite has relatively large nine-fold sites.
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