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41.
Determination of Rare Earth Elements, Sc, Y, Zr, Ba, Hf and Th in Geological Samples by ICP-MS after Tm Addition and Alkaline Fusion 总被引:2,自引:0,他引:2
Germain Bayon Jean Alix Barrat Joël Etoubleau Mathieu Benoit Claire Bollinger Sidonie Révillon 《Geostandards and Geoanalytical Research》2009,33(1):51-62
We present a revised method for the determination of concentrations of rare earth (REE) and other trace elements (Y, Sc, Zr, Ba, Hf, Th) in geological samples. Our analytical procedure involves sample digestion using alkaline fusion (NaOH-Na2 O2 ) after addition of a Tm spike, co-precipitation on iron hydroxides, and measurement by sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS). The procedure was tested successfully for various rock types (i.e., basalt, ultramafic rock, sediment, soil, granite), including rocks with low trace element abundances (sub ng g−1 ). Results obtained for a series of nine geological reference materials (BIR-1, BCR-2, UB-N, JP-1, AC-E, MA-N, MAG-1, GSMS-2, GSS-4) are in reasonable agreement with published working values. 相似文献
42.
Nadir Benhamiche Lamia Sahi Sabrina Tahar Hassiba Bir Khodir Madani Benoit Laignel 《水文科学杂志》2013,58(4):775-792
ABSTRACTFive-year monitoring of physicochemical parameters was performed with two campaigns in low and high water periods of the Lower Soummam catchment. Data from 18 wells were processed by multivariate statistical tools in order to identify the principal factors influencing groundwater chemistry. Two matrices of 14 and 8 physicochemical parameters with 18 groundwater samples collected in wells were obtained. The correlation matrix showed strong associations between nine variables: K+, Ca2+, Na+, SO42?, Cl?, Mg2+, NO2?, Zn2+ and Sr2+. Principal component analysis and factor analysis showed that the cumulated variance of high and low water periods was of 83.19% and 78.55%, respectively. The variables assigned to the mineralization effect or to pollution indicators were presented by the factor analysis. The bivariate plots confirmed a mineralization model, ascribed to dissolution of geological materials, and to high levels of saline contamination attributed to leakages from sanitary systems. They also showed an increase “upstream to downstream” of the mineralization, visualization of temporal variations, and a dilution process identification of the natural mineralization during the recharge of the aquifer.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen 相似文献
43.
The influence of magma expansion due to volatile exsolution and gas dilation on dyke propagation is studied using a new numerical code. Many natural magmas contain sufficient amounts of volatiles for fragmentation to occur well below Earth's surface. Magma fragmentation has been studied for volcanic flows through open conduits but it should also occur within dykes that rise towards Earth's surface. The characteristics of volatile-rich magma flow within a hydraulic fracture are studied numerically. The mixture of melt and gas is treated as a compressible viscous fluid below the fragmentation level and as a gas phase carrying melt droplets above it. The numerical code solves for elastic deformation of host rocks, the flow of the magmatic mixture and fracturing at the dyke tip. With volatile-free magma, a dyke fed at a constant rate in a uniform medium adopts a constant shape and width and rises at a constant velocity. With volatiles involved, magma expands and hence the volume flux of magma increases. With no fragmentation, this enhanced flux leads to acceleration and thinning of the dyke. Simple scaling laws allow accurate predictions of dyke width and ascent rate for a wide range of conditions. With fragmentation, dyke behaviour is markedly different. Due to the sharp drop of head loss that occurs in gas-rich fragmented material, large internal overpressures develop below the dyke tip and induce swelling of the nose region, leading to deceleration of the dyke. These results are applied to the two-month long period of volcanic unrest that preceded the May 1980 eruption of Mount St Helens. An initial phase of rapid earthquake migration from the 7–8 km deep reservoir to shallow levels was followed by very slow progression of magma within the edifice. Such behaviour can be accounted for by magma fragmentation at the top of a dyke. 相似文献
44.
Garrelt Mellema Léon V. E. Koopmans Filipe A. Abdalla Gianni Bernardi Benedetta Ciardi Soobash Daiboo A. G. de Bruyn Kanan K. Datta Heino Falcke Andrea Ferrara Ilian T. Iliev Fabio Iocco Vibor Jelić Hannes Jensen Ronniy Joseph Panos Labroupoulos Avery Meiksin Andrei Mesinger André R. Offringa V. N. Pandey Jonathan R. Pritchard Mario G. Santos Dominik J. Schwarz Benoit Semelin Harish Vedantham Sarod Yatawatta Saleem Zaroubi 《Experimental Astronomy》2013,36(1-2):235-318
The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope. 相似文献
45.
46.
47.
A stepwise stalagmite sample screening process was applied in order to select a stalagmite as a sensitive recorder of recent tropical cyclone rainfall events near Belize. Field and laboratory criteria were combined in series, to screen out candidate stalagmites whose characteristics indicated lower sensitivity to stormwater infiltration. The approach described here was designed to increase the likelihood that selected stalagmites would increase the signal:noise ratio of the target phenomenon in the resulting proxy records. This four-stage method for sample selection may be an important methodological consideration for researchers attempting to use speleothems for stable isotope paleotempestology. Hallmarks of this approach include: (1) establishing a priori scientific targets, (2) applying sample criteria in the form of contra-indicators, and (3) organizing the sample screening protocol into a series of practical stages. The overall approach to stalagmite selection presented here supports cave conservation, and can be adapted readily by others in support of different scientific goals. It is hoped that other investigators will also publish field and laboratory sample selection schemes, as increased transparency will provide new information invaluable to replication efforts and to advancing the field of speleothem paleo-environmental studies. 相似文献
48.
François Gibert Bernard Moine Jacques Schott Jean-Louis Dandurand 《Contributions to Mineralogy and Petrology》1992,112(2-3):371-384
Scheelite-bearing calc-silicate gneisses (CSG) oceur in the Montagne Noire within a series of dominant micaschists. Detailed petrographical and mineralogical studies reveal three successive stages of metamorphism and hydrothermal alteration: (1) stage 1, a regional metamorphism at 550°C and 4.5 kb where no mineralization is formed; (2) stage 2a, a hydrothermal alteration at 500 to 450°C and 4 to 3 kb which is characterized by an intense sericitization of feldpars and deposition of Sn in Sn-bearing cale-silicates; and (3) stage 2b, a hydrothermal alteration characterized by the crystallization of idocrasegrossular in CSG with concomittant precipitation of scheelite. Tungsten was transported through the micaschist environment and deposited as scheelite only in the CSG of stage 2b at relatively low pressures. To characterize the mechanism of tungsten transport, tungsten speciation at high P-T and scheelite solubility in aqueous solations buffered by the CSG and by the micaschists assemblages were calculated. It was found that H2WO
0
4
, HWO
-
4
and WO
2-
4
are the dominant tungsten aqueous species in H2O–NaCl (one molal) solutions at 500°C and 2–4 kb. Calculations also indicate that scheelite deposition is controlled by decreasing pressure and increasing activity of aqueous calcium in this system. This is consistent with the petrographical and mineralogical observations. The consequences of the presence of volatiles (N2, CH4, CO2) in the regional fluids were examined by determining the effect of N2 on tungsten speciation and scheelite solubility. The addition of N2 (up to 10 mol%) to the mineralizing fluids results in a marked increase in H2WO
0
4
and HWO
-
4
concentrations relative to WO
2-
4
and in a large decrease of scheelite solubility. This mechanism favours scheelite precipitation and accounts for the commonly observed association of W (and Sn) deposits with graphitic series generating mixed volatiles fluids. 相似文献
49.
Miroslav Nastev Michel Parent Nicolas Benoit Martin Ross Danielle Howlett 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(3):200-212
Shear-wave velocity of the top 30?m, VS30, is commonly used for prediction of the seismic site response. This paper presents development, validation and uncertainty assessment of a regional VS30 model based on a combination of simplified 3D geology and statistically representative velocity values. Results identify soft marine sediments in deep sedimentary basins as zones most susceptible to seismic shaking. Compared to the available urban-scale seismic zonation studies, the regional model showed a success rate of roughly 64% in predicting local site category. The standard deviation was in average 30% of the expected VS30 value. 相似文献
50.
Putting the principles of the Sustainable Livelihoods Approach into fisheries development policy and practice 总被引:1,自引:1,他引:1
The Sustainable Livelihoods Approach (SLA) combines a conceptual framework with a set of operational principles to provide guidance on policy formulation and development practice. The SLA has been widely used in coastal and fisheries development research and has informed the design of development programmes but experience of operationalising it remains largely undocumented. In the Sustainable Fisheries Livelihoods Programme, which involves 25 West African countries, the SLA has helped to align fisheries policy with wider poverty reduction initiatives and to identify means of contributing to poverty reduction that do not directly increase pressure on fully or over-exploited fish resources. 相似文献