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1.
Cosmogenic nuclide-based denudation rates and published erosion rates from recent river gauging in the Napo River basin (Peruvian Amazonia) are used to decipher erosion and sedimentation processes along a 600 km long transect from the headwaters to the lowlands. The sediment-producing headwaters to the Napo floodplain are the volcanically active Ecuadorian Andes, which discharge sediment at a cosmogenic nuclide-based denudation rate of 0.49 ± 0.12 mm/yr. This denudation rate was calculated from an average 10Be nuclide concentration of 2.2 ± 0.5 × 104 at/g(Qz) that was measured in bedload-derived quartz. Within the Napo lowlands, a significant drop in trunk stream 10Be nuclide concentrations relative to the Andean hinterland is recorded, with an average concentration of 1.2 ± 0.5 × 104 at/g(Qz). This nuclide concentration represents a mixture between the 10Be nuclide concentration of eroded floodplain deposits, and that of sediment eroded from the Andean hinterland that is now carried in the trunk stream. Evidence for addition of sediment from the floodplain to the trunk stream is provided by published decadal-scale sediment flux measurements from gauging stations operated in the Napo basin, from which an increase from 12 × 106 t/yr at the outflow of the Andes to ～47 × 106 t/yr at the confluence with the Solimões (upper Amazon River) is recorded. Therefore, approximately 35 × 106 t of floodplain sediment are added annually to the active Napo trunk stream. Combined with our nuclide concentration measurements, we can estimate that the eroded floodplain deposits yield a nuclide concentration of ～0.9 × 104 at/g(Qz) only. Under steady state surface erosion conditions, this nuclide concentration would translate to a denudation rate of the floodplain of ～0.47 mm/yr. However, we have no geomorphologic explanation for this high denudation rate within the low relief floodplain and thus suggest that this low-nuclide concentrated sediment is Andean-derived and would have been deposited in the floodplain at a time when erosion rates of the Andes were elevated. Therefore, the recently eroded floodplain sediment provides an Andean “paleo denudation rate” of 1.2 mm/yr that was calculated for high Andean production rates. A likely period for elevated erosion rates is the LGM, where climate and vegetation cover of the Andes differed from that of the Holocene. A possible cause for the erosion of the floodplain is the tectonic uplift of the Eastern Andes, which progressively shifts the Napo River northwards. Hence, the river cuts into ancient lowland sediment, which is admixed to the Andean sediment carried in the main Napo River.  相似文献   

2.
The adsorption capacity of seven organic wastes/by-products (slash pine, red gum and western cypress bark, composted green waste, prawn exoskeletons, spent brewery yeast and mill mud from a sugar mill) for transition metals were determined at two metal concentrations (10 and 100 mg L−1) and three equilibrium pH values (4.0, 6.0 and 8.0) in batch adsorption experiments. All tested materials indicate a positive affinity to adsorb metal cations from aqueous solution and spent yeast was the least effective. Adsorption generally increased with increasing pH and the order of selectivity of metals was: Cr3+ > Cu2+ > Pb2+ > Zn2+ ≥ Cd2+. For pine bark, compost, spent yeast and prawn shell, quantities of previously adsorbed Pb and Cd desorbed in 0.01 M NaNO3 electrolyte were negligible. However, 0.01 M HNO3, and more particularly 0.10 and 0.50 M HNO3 were effective at removing both adsorbed Pb and Cd. Using 0.10 M HNO3 as the regenerating agent, pine bark and compost maintained their Pb and Cd adsorption capacity over eight successive adsorption/regeneration cycles. For mill mud and prawn shell, there was a pronounced decrease in adsorption capacity after only one regeneration cycle. A subsidiary experiment confirmed that acid pre-treatment of the latter two materials appreciably reduced their Pb and Cd adsorption capacity. This was ascribed to the metal adsorption capacity of prawn shell and mill mud being partially attributable to their significant CaCO3 content and acid treatment induces dissolution of the CaCO3. It was shown that in relation to both adsorption capacity and desorption/regeneration capability, composted green waste showed the greatest potential.  相似文献   

3.
Natural hydrothermal ZnCO3 crystal aggregates are nominally anhydrous phases with interfacial water, with substitutional divalent cations and decarbonation c. 300°C. All these common features must be involved during the experimental heating of a thermoluminescence (TL) glow curve up to 500°C: dehydration–dehydroxylation, phase transition and ion transition of point defects in Zn2+ positions. A representative specimen of natural smithsonite was analysed by X-ray fluorescence spectrometry, field emission scanning electron microscopy (FESEM) with a chemical probe of energy dispersive spectrometer, high temperature in situ X-ray diffraction, differential scanning calorimetry, differential thermal analyses coupled to thermogravimetry, TL, radioluminescence and high resolution spectra thermoluminescence (3DTL), to gain an overview of the spectra emission and defects linkages modified by heating from room temperature up to 500°C. The ZnCO3 specimen contains minor amounts of Ca, Cu, Cr, Cd, Pb, Ce, Co, Ni, Mn and Fe. Under FESEM, it displays CaCO3 clusters and oscillatory zoning distribution with lamellae ranging from Ca0.11Zn0.89 to Ca0.19Zn0.81. The analytical results suggest assignments of defects and processes to measured 3DTL emission bands, as follows: (1) peak at ~260°C, ~360 nm bonds, breaking during the thermal decarbonation process; (2) peak ~120°C, ~340 nm: non-bridging oxygen centres associated to a complex dehydration–dehydroxylation process and (3) peak at ~170°C, ~650 nm, crystal field effects on the thermoluminescence of Mn2+ centres and associated transitional elements in the ZnCO3 phase. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

4.
Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3–2.3).Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mmol kg−1 (3080, 2200, and 2570 mg kg−1), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2-fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25–54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe phases, principally ferrihydrite. In surface samples (0–35 cm), metal(loid)s are found as sorbed species or incorporated into secondary Fe hydroxysulfate phases, such as schwertmannite and jarosites. Metal-bearing efflorescent salts (e.g., ZnSO4·nH2O) were detected in the surficial sample. Taken together, these data suggest the bioaccessibility and lability of metal(loid)s are altered by mineral weathering, which results in both the downward migration of metal(loid)s to the redox boundary, as well as the precipitation of metal salts at the surface.  相似文献   

5.
《Quaternary Research》2014,81(3):538-544
Measurements of 137Cs concentration in soils were made in a representative catchment to quantify erosion rates and identify the main factors involved in the erosion in the source region of the Yellow River in the Tibetan Plateau. In order to estimate erosion rates in terms of the main factors affecting soil loss, samples were collected taking into account the slope and vegetation cover along six selected transects within the Dari County catchment. The reference inventory for the area was established at a stable, well-preserved, site of small thickness (value of 2324 Bq·m− 2). All the sampling sites had been eroded and 137Cs inventories varied widely in the topsoil (14.87–25.56 Bq·kg− 1). The effective soil loss values were also highly variable (11.03–28.35 t·km− 1·yr− 1) in line with the vegetation cover change. The radiometric approach was useful in quantifying soil erosion rates and examining patterns of soil movement.  相似文献   

6.
The Pb contents and 206Pb/207Pb and 208Pb/206Pb isotopic ratios were studied in the soils and wines (2004 harvest) of three vineyard areas of the Czech Republic. The areas differ in their geological basements and anthropogenic loading. The isotopic compositions of wine in areas with intensive industry (Most, North Bohemia 206Pb/207Pbwine = 1.178 ± 0.004) and the agricultural areas of Central Bohemia (Roudnice nad Labem 206Pb/207Pbwine = 1.176 ± 0.007) are similar to the Pb isotopic composition of airborne particulate material typical of polluted and industrial environments (206Pb/207Pb = 1.17–1.19). The isotopic composition of wine from Prague (206Pb/207Pbwine = 1.174 ± 0.003) is different from that of the soil, which was severely contaminated in the past by vehicular Pb (206Pb/207Pbsoil = 1.147–1.168). This fact shows that interception of airborne Pb by plants is greater than its uptake by the root system.  相似文献   

7.
Subduction erosion, which occurs at all convergent plate boundaries associated with magmatic arcs formed on crystalline forearc basement, is an important process for chemical recycling, responsible globally for the transport of ~1.7 Armstrong Units (1 AU = 1 km3/yr) of continental crust back into the mantle. Along the central Andean convergent plate margin, where there is very little terrigenous sediment being supplied to the trench as a result of the arid conditions, the occurrence of mantle-derived olivine basalts with distinctive crustal isotopic characteristics (87Sr/86Sr ≥ 0.7050; εNd ≤ −2; εHf ≤ +2) correlates spatially and/or temporally with regions and/or episodes of high rates of subduction erosion, and a strong case can be made for the formation of these basalts to be due to incorporation into the subarc mantle wedge of tectonically eroded and subducted forearc continental crust. In other convergent plate boundary magmatic arcs, such as the South Sandwich and Aleutian Islands intra-oceanic arcs and the Central American and Trans-Mexican continental margin volcanic arcs, similar correlations have been demonstrated between regions and/or episodes of relatively rapid subduction erosion and the genesis of mafic arc magmas containing enhanced proportions of tectonically eroded and subducted crustal components that are chemically distinct from pelagic and/or terrigenous trench sediments. It has also been suggested that larger amounts of melts derived from tectonically eroded and subducted continental crust, rising as diapirs of buoyant low density subduction mélanges, react with mantle peridotite to form pyroxenite metasomatites that than melt to form andesites. The process of subduction erosion and mantle source region contamination with crustal components, which is supported by both isotopic and U-Pb zircon age data implying a fast and efficient connectivity between subduction inputs and magmatic outputs, is a powerful alternative to intra-crustal assimilation in the generation of andesites, and it negates the need for large amounts of mafic cumulates to form within and then be delaminated from the lower crust, as required by the basalt-input model of continental crustal growth. However, overall, some significant amount of subducted crust and sediment is neither underplated below the forearc wedge nor incorporated into convergent plate boundary arc magmas, but instead transported deeper into the mantle where it plays a role in the formation of isotopically enriched mantle reservoirs. To ignore or underestimate the significance of the recycling of tectonically eroded and subducted continental crust in the genesis of convergent plate boundary arc magmas, including andesites, and for the evolution of both the continental crust and mantle, is to be on the wrong side of history in the understanding of these topics.  相似文献   

8.
We report measurements of pH, total dissolved inorganic carbon (DIC), total or titration alkalinity (TAlk), Ca2+, Mg2+, sulfate, and sulfide data at the seawater-freshwater interface in a shallow groundwater aquifer in North Inlet, South Carolina. These measurements and a diagenetic modeling analysis indicate that the groundwaters at North Inlet are mixtures of seawater and freshwater end-members and are seriously modified by carbon dioxide inputs from organic carbon degradation via SO42− reduction across the entire salinity range and fermentation and CaCO3 dissolution in the low-salinity region. DIC and TAlk are several times higher than the theoretical dilution line, whereas Ca2+ is slightly higher and SO42− is somewhat lower than the dilution line. Partial pressure of CO2 in the groundwater is extremely high (0.05 to 0.12 atm). These deviations are consistent with theoretical predictions from known diagenetic reactions. Estimated groundwater DIC fluxes to the South Atlantic Bight from either the surficial aquifer (via salt marshes) or the Upper Floridan Aquifer (direct input) are significant when compared to riverine flux in this area.  相似文献   

9.
The production of organic matter and calcium carbonate by a dense population of the brittle star Acrocnida brachiata (Echinodermata) was calculated using demographic structure, population density, and relations between the size (disk diameter) and the ash-free dry weight (AFDW) or the calcimass. During a 2-year survey in the Bay of Seine (Eastern English Channel, France), organic production varied from 29 to 50 gAFDW m−2 year−1 and CaCO3 production from 69 to 104 gCaCO3 m−2 year−1. Respiration was estimated between 1.7 and 2.0 molCO2 m−2 year−1. Using the molar ratio (ψ) of CO2 released: CaCO3 precipitated, this biogenic precipitation of calcium carbonate would result in an additional release between 0.5 and 0.7 molCO2 m−2 year−1 that represented 23% and 26% of total CO2 fluxes (sum of calcification and respiration). The results of the present study suggest that calcification in temperate shallow environments should be considered as a significant source of CO2 to seawater and thus a potential source of CO2 to the atmosphere, emphasizing the important role of the biomineralization (estimated here) and dissolution (endoskeletons of dead individuals) in the carbon budget of temperate coastal ecosystems.  相似文献   

10.
本文报道了天然Ⅱ型CaCO3 矿物。该矿物发现于海洋表层沉积物,成分与方解石、文石及六方球方解石相同,但结构完全不同,它们共同组成了天然CaCO3 的同质多象变体。天然Ⅱ型CaCO3 矿物的空间群为P21/c,单位轴长为a0= 0.6290±0.0002 nm,b0= 0.4934±0.0002 nm,c0= 0.7979±0.0003nm,β= 107.571°±0.002°,Z= 4,单胞体积为0.23605±0.1749nm3;理论密度为2.82 g/cm3,实测值为2.76 g/cm3;实测硬度H= 4.天然Ⅱ型CaCO3 矿物是在深水环境中较高静水压力下形成的珊瑚体生物矿物。  相似文献   

11.
The reuse of waste materials as soil additives could be a welcome development in soil remediation. The mobility of Cd, Pb and As in a contaminated soil was investigated using natural and calcined poultry wastes (eggshell and chicken bone), CaCO3 and CaO at different application rates (0, 1, 3 and 5 %). The chemical composition accompanied with mineralogical composition indicated that CaCO3 and CaO were the major components in natural and calcined eggshells, respectively, while hydroxyapatite (HAP) dominated the natural and calcined chicken bones. The results showed that soil pH tended to increase in response to increasing application rates of all soil additives. The effectiveness of the additives in reducing Cd, Pb and As mobility was assessed by means of chemical extractions with 0.1 N HCl for Cd and Pb or 1 N HCl for As, according to Korean Standard Test (KST) method. Both calcined eggshell and chicken bone were equally effective with CaO or CaCO3 in reducing the concentration of 0.1 N HCl-extractable Cd from 6.17 mg kg?1 to below warning level of 1.5 mg kg?1, especially at the highest application rate. The application of calcined eggshell, CaO and CaCO3 also decreased the concentration of 0.1 N HCl-extractable Pb from 1,012 mg kg?1 to below warning level of 100 mg kg?1. The Pb concentration decreased significantly with an increasing application rate of chicken bone, but remained above warning level even at the highest application rate. On the contrary, natural and calcined chicken bones led to a significant increase in the mobility of As when compared with the control soil. These findings illustrate that calcined eggshell in particular is equally effective as pure chemical additives in stabilizing Cd and Pb in a contaminated agricultural soil. The presence of As in metal-contaminated soils should be taken into consideration when applying phosphate-containing materials as soil additives, because phosphate can compete with arsenate on adsorption sites and result in As mobilization.  相似文献   

12.
The spatial pattern of soil erosion can provide valuable insights into the soil erosion processes that require a rapid assessment in practical applications. Generally, quantitative technique is expensive and time-consuming. The objective of this paper is to reveal the spatial pattern of erosion with a rapid assessment method. The affecting factors such as land cover, vegetation fraction and slope gradient are integrated into this method using a qualitative means. Beijing-1 images in 2006 were used to produce land-cover and vegetation fraction, and 1:50,000 topographic maps were used to calculate slope gradient. The study area was classified into six grades. Results show that the upstream area of Guanting Reservoir, in general, is exposed to a moderate risk; there are 17,740.33 km2 of land that suffered from water soil erosion in 2006, occupied 40.69% of the total area, and most of the soil erosion area is on the light and moderate risk, which occupied 25.05 and 62.83% of the eroded area, respectively. Eight elevation zones and six slope gradient zones were overlaid with the assessed risk. The analyzed results show that: (1) the areas above 2,000 m have the lowest erosion risk, which is only 0.75% of the eroded area; 1,250–1,500 m elevation zone has the highest erosion risk, which is 34.72% of the eroded area. (2) The slope gradient zone less than 5 degrees and greater than 35 degrees have the lowest erosion risk, which is 0.02 and 0.75% of the eroded area, respectively; the slope gradient zone with 8–15 degrees has the highest erosion risk, which is 36.40% of the eroded area. These results will be useful for water and soil conservation management and the planning of mitigation measures.  相似文献   

13.
Lead isotope amount ratios are commonly used in diverse fields such as archaeometry, geochemistry and forensic science. Currently, five reference materials with certified lead isotope amount ratios are available, namely NIST SRM 981, 982 and 983, GBW‐04442 and NMIJ 3681‐a. Only NIST SRM 981 and NMIJ 3681‐a have approximately natural isotopic compositions, and NIST SRM 981 is predominantly used for correcting mass discrimination/mass fractionation in the applied mass spectrometric procedures. Consequently, there is no other certified reference material available to be used for validation and/or quality control of the analytical procedures applied to lead isotope amount ratio measurements. To fill this gap, two new reference materials have been produced and certified for their lead isotope amount ratios. For both certified reference materials, complete uncertainty budgets have been calculated and SI traceability has been established. This provides the users with independent means for validating and verifying their analytical procedures and for conducting quality control measures. ERM‐EB400 is a bronze material with a nominal lead mass fraction of 45 mg kg?1 and certified lead isotope amount ratios of n(206Pb)/n(204Pb) = 18.072(17) mol mol?1, n(207Pb)/n(204Pb) = 15.578(18) mol mol?1 and n(208Pb)/n(204Pb) = 38.075(46) mol mol?1 with the associated expanded uncertainties (k = 2) given in brackets. ERM‐AE142 is a high‐purity solution of lead in 2% nitric acid with a nominal mass fraction of 100 mg kg?1 and certified Pb isotope amount ratios of n(206Pb)/n(204Pb) = 21.114(17) mol mol?1, n(207Pb)/n(204Pb) = 15.944(17) mol mol?1 and n(208Pb)/n(204Pb) = 39.850(44) mol mol?1 with the associated expanded uncertainties (k = 2) given in brackets. Both materials are specifically designed to fall within the natural lead isotopic variation and to assist users with the validation and verification of their analytical procedures. Note that while one of these reference materials requires the chemical separation of Pb from its matrix (ERM‐EB400), the other does not (ERM‐AE142). As additional information, δ208/206PbNIST SRM981 values are provided for both materials. For ERM‐AE142, a delta value of δ208/206PbNIST SRM981 = ?28.21(30)‰ was obtained, and for ERM‐EB400, a delta value of δ208/206PbNIST SRM981= ?129.47(38)‰ was obtained, with the associated expanded uncertainties (k = 2) given in brackets.  相似文献   

14.
A simplified regression model is here calibrated on the basis of rainfall data records of Sicily (southern Italy), in order to show the model reliability in assessing the R-factor of the Universal Soil Loss Equation and its revised version (RUSLE) and to provide an estimate of long-term rainfall erosivity at medium-regional scale. The proposed model is a rearrangement of a former simplified model, formulated for the Italian environment, grouping three easily available rainfall variables on various time scales, which has been shown to be more successful than others in reproducing the rainfall erosive power over different locations of Italy. A geostatistical interpolation procedure is then applied for generating the regional long-term erosivity map with associated standard error. Areas with severe erosive rainfalls (from 2,000 up to more than 6,000 MJ mm ha−1 h−1) are pointed out which will correspond to areas suffering from severe soil erosion. Solving the problem of calculating the R-factor value in the RUSLE equation by means of such a simplified model here formulated will allow to predict the related soil loss. Moreover, given the availability of long time-series of concerned rainfall data, it will be possible to analyse the variability of rainfall erosivity within the last 50 years, and to investigate the application of RUSLE or similar soil erosion models with forecasting purposes of soil erosion risk.  相似文献   

15.
Palaeo-heat flow values and thicknesses of eroded Permo-Carboniferous sediments in the Saar Basin were evaluated using one dimensional thermal modelling techniques. Thermal, burial and erosion histories for 16 wells were calibrated by comparing measured and calculated vitrinite reflectance using the kinetic EASY%Ro algorithm and by comparing measured and calculated temperature data. On the basis of 37 wells, coalification maps were constructed revealing a syn-kinematic coalification pattern. Thermal maturity of the sediments can only be explained by deep burial and moderate heat flows during time of maximum burial, i.e., in the Permo-Carboniferous. Calculated heat flow data range between 50 and 75 mW/m2, which implies a crustal thickness between 30 and 40 km during the time of maximum burial. These values are in accordance with the geodynamic setting of the basin. The influence of the Permo-Carboniferous volcanism on the palaeo-temperature distribution was overwhelmed by the subsequent deep burial. During Permian times, between 1800 and 3000 m of Permo-Carboniferous sediments were eroded. Different sedimentation and erosion histories are characteristic for anticlines and synclines, respectively.  相似文献   

16.
《Chemical Geology》2007,236(3-4):291-302
The probable sources of some of the famous Indian diamonds are the 1.2 Ga old Krishna lamproites of Southern India, a rare Proterozoic occurrence of lamproites which are usually Cretaceous or younger in age. In this study we report Nd, Sr, Pb and Hf isotopes and multiple trace element concentrations of the Krishna lamproites. The goals are to evaluate mantle-processes and the petrogenesis of these ultrapotassic rocks of extreme chemical composition in light of these geochemical data, including their major element compositions.The Krishna lamproites show nearly uniform, parallel rare earth element (REE) distribution patterns with high concentrations and extreme light-REE enrichment (La/Yb(N) = 41–88), high average concentrations of Ba (∼ 1200 ppm), Sr (∼ 1200 ppm), Zr (∼ 930 ppm), La (∼ 230 ppm), high U/Pb and Th/U ratios with notable absence of any Eu-anomaly. These rocks are typically porphyritic without any evidence of crystal accumulation, and have moderately high Mg-numbers (59–73) along with high Ni (average ∼ 301 ppm, highest 819 ppm) and Cr (average ∼ 183 ppm, highest 515 ppm) concentrations that show a positive correlation with MgO (wt.%), implying a role of olivine in the melt source. The low SiO2 content (lowest 37.8%, average 49%) and high Nb (average 147 ppm), Zr, Sr, as well as Ni and Cr in these rocks indicate lack of upper continental crustal contribution in the genesis of these rocks. The initial Pb-isotopic composition of these lamproites is unusual in that in a 207Pb/204Pb vs. 206Pb/204Pb plot, these rocks plot to the left of the 1.2 Ga geochron (age of emplacement), unlike most mantle-derived rocks. This Pb-isotopic signature and the superchondritic Nb/Ta ratios (average 23.6) of these rocks rule out their derivation from a metasomatized sub-continental lithospheric mantle. The high 207Pb/204Pb at low 206Pb/204Pb indicates an Archean component in the source of these rocks. We argue that this Archean crustal component, which produced the low-SiO2 lamproites along with the high Ni and Cr must have been ultrabasic, and we propose a model in which these lamproites formed by partial melting of metasomatized, subducted Archean komatiite in a peridotite mantle-source assemblage. In addition, these rocks display initial Hf isotopic compositions similar to Al-depleted komatiites, and high Nb/U, Nb/Th, and TiO2 as well as low Al2O3/TiO2 ratios (1.1–4.2) and average CaO/Al2O3 of ∼ 1.6 that are also similar to Archean komatiites. This is also supported by the initial Pb isotopic composition of the Krishna lamproites, requiring evolution in a variably high U/Pb, Th/Pb reservoir early in earth history, possibly resulting from preferential segregation of Pb relative to U and Th in the sulfides of the komatiite.The Al-depleted subducted komatiitic component was enriched by carbonate metasomatism in the peridotitic mantle. This metasomatism was responsible for the observed Nd–Hf isotope characteristics, specifically variable εNd(T) at relatively constant εHf(T) in the lamproites. This Nd–Hf-isotopic characteristic seems to be common in global lamproites of all ages. Our proposed model for the genesis of the Krishna lamproites involving a subducted komatiitic source may also be applicable for other global lamproites from cratonic settings, as older komatiite-bearing subducted crustal components were possibly ubiquitous in the architecture of ancient cratonic mantle.  相似文献   

17.
The Wangjiazhuang porphyry–breccia Cu(–Mo) deposit is located in the Zouping volcanic basin, western Shandong Province. Seven molybdenite samples yield a Re–Os weighted mean age of 127.8 ± 0.7 Ma (2σ), which is identical within error to the zircon weighted mean 206Pb/238U age of 128.3 ± 1.3 Ma (2σ) determined for quartz monzonite samples. The host rock is characterized by high concentrations of K2O (4.26–4.53 wt.%), Na2O (4.97–5.76 wt.%), LILEs and LREEs, and high Mg# (> 40), and low concentrations of HFSEs and HREEs, with K2O/Na2O ratios of 0.76–0.88. The quartz monzonite also has high Sr/Y (69.9–112.5) and (La/Yb)N (22.0–30.0) ratios, similar to adakitic rocks worldwide. Relatively low initial 87Sr/86Sr ratios (0.70549–0.70556), high εNd(t) values (2.58–3.06), high radiogenic Pb [(206Pb/204Pb)i = 18.3424–18.4606, (207Pb/204Pb)i = 15.5692–15.5985, (208Pb/204Pb)i = 38.1714–38.2734] and high zircon εHf(t) values (− 2.1 to + 4.3) indicate that the magma was likely derived from the partial melting of subducted oceanic crust which then reacted with the peridotitic mantle wedge. Both the breccia and porphyry ores have a narrow range of δ34S (− 4.8 to + 2.1‰) and Pb isotopic compositions (206Pb/204Pb = 18.295–18.402, 207Pb/204Pb = 15.551–15.573, and 208Pb/204Pb = 38.215–38.331), suggesting that the ore metals were extracted primarily from the quartz monzonite or similar source. Subduction of the Paleo-Pacific slab during the Early Cretaceous resulted in the formation of the Wangjiazhuang quartz monzonite and associated Cu(–Mo) deposit in western Shandong Province.  相似文献   

18.
To better understand the formative mechanism of the Cretaceous Gyeongsang Basin in South Korea, we determined the geochemical compositions of Early Cretaceous syntectonic basaltic rocks intercalated with basin sedimentary assemblages. Two distinct compositional groups appeared: tholeiitic to calc-alkaline basalts from the Yeongyang sub-basin and high-K to shoshonitic basaltic trachyandesites from the Jinju and Uiseong sub-basins. All collected samples exhibit patterns of light rare earth element enrichment and chondrite-normalized (La/Yb)N ratios ranging from 2.4 to 23.6. In a primitive-mantle-normalized spidergram, the samples show distinctive negative anomalies in Nb, Ta, and Ti and a positive anomaly in Pb. The basalts exhibit no or a weak positive U anomaly in a spidergram, but the basaltic trachyandesites show a negative U anomaly. The basalts have highly radiogenic Sr [(87Sr/86Sr)i = 0.70722–0.71145], slightly negative εNd, positive εHf [(εNd)i = −2.7 to 0.0; (εHf)i = +2.9 to +6.4], and radiogenic Pb isotopic compositions [(206Pb/204Pb)i = 18.20–19.19; (207Pb/204Pb)i = 15.60–15.77; (208Pb/204Pb)i = 38.38–39.11]. The basaltic trachyandesites are characterized by radiogenic Sr [(87Sr/86Sr)i = 0.70576–0.71119] and unradiogenic Nd, Hf, and Pb isotopic compositions [(εNd)i = −14.0 to −1.4; (εHf)i = −17.9 to +3.7; (206Pb/204Pb)i = 17.83–18.25; (207Pb/204Pb)i = 15.57–15.63; (208Pb/204Pb)i = 38.20–38.70]. The “crust-like” signatures, such as negative Nb–Ta anomalies, elevated Sr isotopic compositions, and negative εNd(t) and εHf(t) values, of the basaltic trachyandesites resemble the geochemistry of Early Cretaceous mafic volcanic rocks from the southern portion of the eastern North China Craton. Considering the lower-crust-like low U/Pb and high Th/U ratios and the unradiogenic Pb isotopic compositions, the basaltic trachyandesites are considered to be derived from lithospheric mantle modified by interaction with melts that originated from foundered eclogite. Basaltic volcanism in the Yeongyang sub-basin is coeval with the basaltic trachyandesite magmatism, but it exhibits an elevated 87Sr/86Sr ratio at a given 143Nd/144Nd and highly radiogenic Pb isotopic compositions, which imply an origin from an enriched but heterogeneous lithospheric mantle source. Melts from subducted altered oceanic basalt and pelagic sediments are considered to be the most likely source for the metasomatism. An extensional tectonic regime induced by highly oblique subduction of the Izanagi Plate beneath the eastern Asian margin during the Early Cretaceous might have triggered the opening of the Gyeongsang Basin. Lithospheric thinning and the resultant thermal effect of asthenospheric upwelling could have caused melting of the metasomatized lithospheric mantle, producing the Early Cretaceous basaltic volcanism in the Gyeongsang Basin.  相似文献   

19.
In Korea, soils adjacent to abandoned mines are commonly contaminated by heavy metals present in mine tailings. Further, the disposal of oyster shell waste by oyster farm industries has been associated with serious environmental problems. In this study, we attempted to remediate cadmium (Cd)- and lead (Pb)-contaminated soils typical of those commonly found adjacent to abandoned mines using oyster shell waste as a soil stabilizer. Natural oyster shell powder (NOSP) and calcined oyster shell powder (COSP) were applied as soil amendments to immobilize Cd and Pb. The primary components of NOSP and COSP are calcium carbonate (CaCO3) and calcium oxide (CaO), respectively. X-ray diffraction, X-ray fluorescence and scanning electron microscope analyses conducted in this study revealed that the calcination of NOSP at 770°C converted the less reactive CaCO3 to the more reactive CaO. The calcination process also decreased the sodium content in COSP, indicating that it was advantageous to use COSP as a liming material in agricultural soil. After 30 days of incubation, we found that the 0.1 N HCl-extractable Cd and Pb contents in soil decreased significantly as a result of an increase in the soil pH and the formation of metal hydroxides. COSP was more effective in immobilizing Cd and Pb in the contaminated soil than NOSP. Overall, the results of this study suggest that oyster shell waste can be recycled into an effective soil ameliorant.  相似文献   

20.
The Yinchanggou Pb-Zn deposit, located in southwestern Sichuan Province, western Yangtze Block, is stratigraphically controlled by late Ediacaran Dengying Formation and contains >0.3 Mt of metal reserves with 11 wt% Pb + Zn. A principal feature is that this deposit is structurally controlled by normal faults, whereas other typical deposits nearby (e.g. Maozu) are controlled by reverse faults. The origin of the Yinchanggou deposit is still controversial. Ore genetic models, based on conventional whole-rock isotope tracers, favor either sedimentary basin brine, magmatic water or metamorphic fluid sources. Here we use in situ Pb and bulk Sr isotope features of sulfide minerals to constrain the origin and evolution of hydrothermal fluids. The Pb isotope compositions of galena determined by femtosecond LA-MC-ICPMS are as follows: 206Pb/204Pb = 18.17–18.24, 207Pb/204Pb = 15.69–15.71, 208Pb/204Pb = 38.51–38.63. These in situ Pb isotope data overlap with bulk-chemistry Pb isotope compositions of sulfide minerals (206Pb/204Pb = 18.11–18.40, 207Pb/204Pb = 15.66–15.76, 208Pb/204Pb = 38.25–38.88), and both sets of data plotting above the Pb evolution curve of average upper continental crust. Such Pb isotope signatures suggest an upper crustal source of Pb. In addition, the coarse-grained galena in massive ore collected from the deep part has higher 206Pb/204Pb ratios (18.18–18.24) than the fine-grained galena in stockwork ore sampled from the shallow part (206Pb/204Pb = 18.17–18.19), whereas the latter has higher 208Pb/204Pb ratios (38.59–38.63) than the former (208Pb/204Pb = 38.51–38.59). However, both types of galena have the same 207Pb/204Pb ratios (15.69–15.71). This implies two independent Pb sources, and the metal Pb derived from the basement metamorphic rocks was dominant during the early phase of ore formation in the deep part, whereas the ore-hosting sedimentary rocks supplied the majority of metal Pb at the late phase in the shallow part. In addition, sphalerite separated from different levels has initial 87Sr/86Sr ratios ranging from 0.7101 to 0.7130, which are higher than the ore formation age-corrected 87Sr/86Sr ratios of country sedimentary rocks (87Sr/86Sr200 Ma = 0.7083–0.7096), but are significantly lower than those of the ore formation age-corrected basement rocks (87Sr/86Sr200 Ma = 0.7243–0.7288). Again, such Sr isotope signatures suggest that the above two Pb sources were involved in ore formation. Hence, the gradually mixing process of mineralizing elements and associated fluids plays a key role in the precipitation of sulfide minerals at the Yinchanggou ore district. Integrating all the evidence, we interpret the Yinchanggou deposit as a strata-bound, normal fault-controlled epigenetic deposit that formed during the late Indosinian. We also propose that the massive ore is formed earlier than the stockwork ore, and the temporal-spatial variations of Pb and Sr isotopes suggest a certain potential of ore prospecting in the deep mining area.  相似文献   

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