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G. Iezzi F. Cámara R. Oberti G. Della Ventura G. Pedrazzi J-L Robert 《Physics and Chemistry of Minerals》2004,31(6):375-385
This work reports the synthesis of ferri-clinoholmquistite, nominally Li2(Mg3Fe3+2)Si8O22(OH)2, at varying fO2 conditions. Amphibole compositions were characterized by X-ray (powder and single-crystal) diffraction, microchemical (EMPA) and spectroscopic (FTIR, Mössbauer and Raman) techniques. Under reducing conditions ( NNO+1, where NNO = Nickel–Nickel oxide buffer), the amphibole yield is very high (>90%), but its composition, and in particular the FeO/Fe2O3 ratio, departs significantly from the nominal one. Under oxidizing conditions ( NNO+1.5), the amphibole yield is much lower (<60%, with Li-pyroxene abundant), but its composition is close to the ideal stoichiometry. The exchange vector of relevance for the studied system is M2(Mg,Fe2+) M4(Mg,Fe2+) M2Fe3+–1 M4Li–1, which is still rather unexplored in natural systems. Amphibole crystals of suitable size for structure refinement were obtained only at 800 °C, 0.4 GPa and NNO conditions (sample 152), and have C2/m symmetry. The X-ray powder patterns for all other samples were indexed in the same symmetry; the amphibole closest to ideal composition has a = 9.428(1) Å, b = 17.878(3) Å, c = 5.282(1) Å, = 102.06(2)°, V = 870.8(3) Å3. Mössbauer spectra show that Fe3+ is strongly ordered at M2 in all samples, whereas Fe2+ is disordered over the B and C sites. FTIR analysis shows that the amount of CFe2+ increases for increasingly reducing conditions. FTIR data also provide strong evidence for slight but significant amounts of Li at the A sites. 相似文献
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A. G. Szulc Y. Najman† H. D. Sinclair M. Pringle‡ M. Bickle§ H. Chapman§ E. Garzanti¶ S. Andò¶ P. Huyghe&#; J-L. Mugnier&#; T. Ojha P. DeCelles† 《Basin Research》2006,18(4):375-391
40Ar–39Ar dating of detrital white micas, petrography and heavy mineral analysis and whole‐rock geochemistry has been applied to three time‐equivalent sections through the Siwalik Group molasse in SW Nepal [Tinau Khola section (12–6 Ma), Surai Khola section (12–1 Ma) and Karnali section (16–5 Ma)]. 40Ar–39Ar ages from 1415 single detrital white micas show a peak of ages between 20 and 15 Ma for all the three sections, corresponding to the period of most extensive exhumation of the Greater Himalaya. Lag times of less than 5 Myr persist until 10 Ma, indicating Greater Himalayan exhumation rates of up to 2.6 mm year?1, using one‐dimensional thermal modelling. There are few micas younger than 12 Ma, no lag times of less than 6 Myr after 10 Ma and whole‐rock geochemistry and petrography show a significant provenance change at 12 Ma indicating erosion from the Lesser Himalaya at this time. These changes suggest a switch in the dynamics of the orogen that took place during the 12–10 Ma period whereby most strain began to be accommodated by structures within the Lesser Himalaya as opposed to the Greater Himalaya. Consistent data from all three Siwalik sections suggest a lateral continuity in tectonic evolution for the central Himalayas. 相似文献
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The isomeric compositions of the eicosenoic and docosenoic fatty acids of four freshwater fish oils (from sheepshead Aplodinotus grunniens, tullibee Coregonus artedii, maria Lota lota and alewife Alosa pseudoharengus, respectively) were examined by open-tubular gas—liquid chromatography. The 22:1ω11 isomer, usually the dominant isomer in marine-fish oils, was unimportant relative to 22:1ω9. The unsaponifiables lacked fatty alcohols and pristane and were mostly cholesterol. The probability that the 22:1ω1 in marine fish oils is strictly of an exogenous origin (primarily originating as the fatty alcohol in copepod wax esters) is reviewed and it is proposed that docosenoic acids have no obligatory role in the lipid biochemistry of either marine or freshwater fish. 相似文献
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Boisson F Cotret O Teyssié JL El-Baradeï M Fowler SW 《Marine pollution bulletin》2003,46(12):1549-1557
The relative importance of dissolved and food pathways and the influence of food type in the bioaccumulation and retention of lead in the shrimp Palaemonetes varians were examined using a radiotracer method. Shrimp were exposed to 210Pb-labelled seawater or fed two types of 210Pb-labelled food, viz. mussels or worms. The amount of radiotracer accumulated by shrimp was examined over a 7-day period, followed by a 1-month and a 7-day depuration period for the dissolved and food source, respectively. Steady state in the uptake was reached after 2 days exposure to dissolved lead, with a resultant estimated concentration factor of 98 ± 3. Transfer factors following ingestion of contaminated mussels and worms were lower than unity for both food types, with lead transfer from worms being significantly higher than that from mussels. Accumulation of dissolved Pb by shrimp was found to occur mainly through adsorption on the exoskeleton with a minor accumulation in the internal tissues probably resulting from the intake of seawater for osmoregulation. In contrast, lead taken up from contaminated food was readily absorbed and bound in the internal tissues of P. varians. Although the transfer of lead to P. varians through the ingestion of contaminated food was low (TF < 1%), it still represented 4 to 8% of the lead content in the prey which is a significant additional contribution of lead to the shrimp body burden. Independent of food type, following ingestion of contaminated food, approximately 23–27% of total lead accumulated in shrimp was located in the edible parts (e.g. muscle). Therefore, the food pathway is suggested to be a significant contributor to the lead transfer to humans through ingestion of contaminated shrimp. After exposure to contaminated food, lead loss kinetics were described by a two-component model, whereas Pb loss following direct uptake from seawater was best described by a three-component model. The additional compartment representing 64% of total Pb retained and characterized by a turnover < 10 min, corresponded to lead weakly adsorbed on the exoskeleton and incorporated in the hepatopancreas. Nevertheless, a significant fraction of lead accumulated from the dissolved (2%) and food (52–57%) pathways remained irreversibly retained in the tissues, suggesting that this organism could also serve as an effective long-term bioindicator of lead contamination in marine waters. 相似文献
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Canopy Structure Parameters Derived from Multi-Angular Remote Sensing Data for Terrestrial Carbon Studies 总被引：1，自引：0，他引：1
J-L. WIDLOWSKI B. PINTY N. GOBRON M. M. Verstraete D. J. Diner A. B. Davis 《Climatic change》2004,67(2-3):403-415
Recent studies have highlighted the importance of vegetation structure, both in the context of landscape dynamics and with regard to ecosystem productivity. This paper addresses the feasibility to retrieve information on canopy structure on the basis of quasi-simultaneous multi-spectral and multi-directional remote sensing measurements from space. After a brief summary of both active and passive remote sensing approaches that are commonly used to address vegetation structure retrievals, this contribution focuses on the state-of-the-art in physically based interpretations relating the anisotropy of multi-directional reflectance measurements to the structure and heterogeneity of the underlying surface. New sets of ecology-oriented parameters are identified that permit a geophysical interpretation of the directional signature of the surface leaving radiation field. The availability of such terrestrial surface structure information, at the within-pixel scale and for the entire globe, will undoubtedly lead to better estimates of ecosystem productivity, carbon stocks and fluxes, as well as changes thereof. 相似文献
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Montero N Belzunce-Segarra MJ Gonzalez JL Larreta J Franco J 《Marine pollution bulletin》2012,64(1):31-39
In this contribution, the potential use of diffusive gradients in thin-films (DGTs) for the chemical evaluation of transitional water bodies within the Water Framework Directive (WFD) has been studied. The water metal concentration has been evaluated in 13 estuaries in the southeastern Bay of Biscay. The DGTs were deployed in triplicate at two stations in each estuary, delimiting the tidal influence. The DGT results were in the ranges of 2-1570 ng L(-1) for cadmium, 66-515 ng L(-1) for copper, 30-3650 ng L(-1) for nickel and 0.8-95.5 μg L(-1) for zinc. The DGTs provided reliable average labile metal concentrations in highly dynamic systems that were comparable with DGT measurements in coastal and estuarine waters worldwide. In addition, it was possible to discriminate those estuaries more susceptible to environmental impacts, being consistent with the historical contamination of each estuary. Based on the obtained results, a sampling strategy for the monitoring of transitional water bodies using DGTs is proposed. 相似文献
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