Fractionation mechanism of iron isotopes in highly fractionated granites from the Xinxian Pluton,Western Dabie Orogen,Central China

Iron isotopes are important for tracing the magmatic process.The fractionation of iron isotopes in granite is up to 0.55‰.In this study,Wangjiagou(XWJ)granite and Tayueping(XTY)granite in the Xinxian pluton of the Western Dabie orogen were evaluated.Both the XTY and XWJ granite belong to monzogranites,with high SiO2(74.42-76.82 wt.%)contents.The granites are depleted of Nb and Ti but enriched with Pb and K,and they display negative Eu anomalies(Eu/Eu^(*)=0.40-0.52)on REE plots that are normalized by chondrite.Theδ^(56)Fe values of the XTY granites vary from 0.19±0.03‰to0.27±0.04‰,and theδ^(56)Fe values of the XWJ granites are 0.34±0.02‰and 0.36±0.01‰,respectively.Both the XTY and the XWJ granites belong to highly fractionated granites due to their SI(solidification index),DI(differentiation index),and content of CaO.Evidence from the iron isotopes shows that neither fluid exsolution,alteration,weathering,nor partial melting can explain the enrichment of the heavy iron isotopes.The results modeled using the Rayleigh equation showed that fractional crystallization can produceΔ^(56)Femelt-crystalwith the value of0.08-0.15‰.In conclusion,fractional crystallization was the main factor controlling the fractionation of iron isotopes,and the change of melt composition may also lead to the enrichment of heavy iron isotopes in the residual melt.

Atmospheric Methane over the Past 2000 Years from a Sub-tropical Ice Core, Central Himalayas

A high-resolution 2000-year methane record has been constructed from an ice core recovered at 7200 m a.s.l. on the Dasuopu Glacier in the central Himalayas. This sub-tropical methane record reveals an increasing trend in the concentration of methane during the industrial era that is similar to observations from polar regions. However, we also observed the differences in the atmospheric methane mixing ratio between this monsoon record and those from polar regions during pre-industrial times. In the time interval 0-1850 A.D., the average methane concentration in the Dasuopu ice core was 782±40 ppbv and the maximum temporal variation exceeded 200 ppbv. The difference gradient of methane concentration in Dasuopu ice core with Greenland and Antarctica cores are 66±40 ppbv and 107±40 ppbv, respectively. This suggests that the tropical latitudes might have acted as a major global methane source in pre- industrial times. In addition, the temporal fluctuation of the pre-industrial methane records suggests that monsoon evolution incorporated with high methane emission from south Asia might be responsible for the relatively high methane concentration observed in the Dasuopu ice core around A.D. 800 and A.D. 1600. These results provide a rough understanding of the contribution of tropical methane source to the global methane budget and also the relationship between atmospheric methane and climate change.

Stable isotope analysis of diet confirms niche separation of two sympatric species of Namib Desert lizard

We used stable isotopes of carbon and nitrogen to study the trophic niche of two species of insectivorous lizards,the Husab sand lizard Pedioplanis husabensis and Bradfield’s Namib day gecko living sympatrically in the Namib Desert.We measured theδ13C andδ15N ratios in lizard blood tissues with different turnover times(whole blood,red blood cells and plasma)to investigate lizard diet in different seasons.We also measured theδ13C andδ15N ratios in available arthropod prey and plant tissues on the site,to identify the avenues of nutrient movement between lizards and their prey.Through the use of stable isotope mixing models,we found that the two lizard species relied on a largely non-overlapping but seasonally variable array of arthropods:P.husabensis primarily fed on termites,beetles and wasps,while R.bradfieldi fed mainly on ants,wasps and hemipterans.Nutrients originating from C3 plants were proportionally higher for R.bradfieldi than for P.husabensis during autumn and late autumn/early winter,although not summer.Contrary to the few available data estimating the trophic transfer of nutrients in ectotherms in mixed C3 and C4/crassulacean acid metabolism(CAM)plant landscapes,we found that our lizard species primarily acquired nutrients that originated from C4/CAM plants.This work adds an important dimension to the general lack of studies using stable isotope analyses to estimate lizard niche partitioning and resource use.

Liming Characteristics of a High-Calcium Dry Flue Gas Desulfurization By-Product and a Class-C Fly Ash

Due to coal’s availability and low cost, coal combustion continues to be the United States’ primary energy source. However, coal combustion produces large quantities of waste material. Some coal combustion by-products (CCBs) have chemical and physical characteristics that make them potentially useful as soil amendments. The objectives of this study were to characterize a relatively new, high-calcium dry flue gas desulfurization (DFGD) by-product and compare its agronomic liming potential to a Class-C fly ash (FA) and reagent-grade calcium carbonate (CaCO3). Calcium car-bonate equivalence (CCE), degree of fineness (DOF), and effective neutralizing value (ENV) for each CCB were determined using standard methods. The CCBs and CaCO3 were also incubated with an acidic (~4.5) clay sub-soil at application rates equiva-lent to 0, 0.5, 1, and 2 times the soil’s lime requirement and compared to an una-mended control. Soil pH was then measured periodically during a 40-day incubation. The ENV of 79.4% for the DFGD by-product and 57.3% for the FA were comparable to those of commercially available liming materials, but were significantly lower (P < 0.05) than that of reagent-grade CaCO3. After 40 days of incubation at the 0.5× ap-plication rate, both CCBs raised the pH of the clay soil to only 5.0, while the CaCO3 raised the pH to 6.5. After 40 days at the 1× rate, all three materials had raised the soil pH to between 6.5 and 7.0, although the FA increased the soil pH more slowly than did the other two materials. At the 2× rate, both CCBs increased the soil pH to between 7.5 and 8.0, while the CaCO3 increased the soil pH to only 7.0. Both CCBs appear to be useful as soil liming materials, although care should be taken to avoid over-application, as this may make the soil too alkaline for optimum plant growth.

内部物质的外溢:深部碳与深时碳循环

The Ediacaran Shuram excursion(SE)is widely regarded as oneof the largest carbon isotope(δ^(13)C)negative excursions in Earthhistory,with carbonate δ^(13)C values down to ca.-12%e(VPDB)[1].This event has been reported in Ediacaran strata on a global scale,and is closely associated with the earliest emergence of macro-scopic animal life in fossil record[2].Numerous hypotheses havebeen proposed to account for this profound carbon cycle anomaly,including both primary[2-7]and diagenetic[8-11]origins.Amongall the published hypotheses,a common ground is the long-standing and fundamental assumption of a marine origin for thebedded carbonates that record the SE.