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251.
252.
Prosper Rakotovao Andrianjakavah Stefano Salvi Didier Béziat Michel Rakotondrazafy Gaston Giuliani 《Mineralium Deposita》2009,44(7):817-835
The Ianapera emerald deposit is located in the Neoproterozoic Vohibory Block of southern Madagascar. The local geology consists
of intercalated migmatitic gneissic units and calcareous metasedimentary rocks, containing boudinaged metamorphosed mafic/ultramafic
lenses, all intruded by pegmatite veins. These units occur near the hinge of the tightly folded Ianapera antiform, within
a few kilometers of the Ampanihy shear zone. Emerald mineralization is hosted by metasomatic phlogopite veins, and bodies
developed within the mafic/ultramafic rocks. Based on field and textural relationships, we distinguish proximal and distal
styles of mineralization. Proximal mineralization occurs at the contact of pegmatite veins with mafic/ultramafic units; in
the distal style, pegmatites are not observed. Three types of emeralds could be distinguished, mainly on the basis of color
and mineral zoning. Some of these emeralds have the most Al-depleted and Cr-rich composition ever recorded. Another characteristic
feature to the Ianapera deposit and, to our knowledge, yet unreported, is the association of some emeralds with scapolite
in metasomatised mafic rocks. Mineral inclusions are common in most emeralds and include phlogopite, carbonates, barite, K-feldspar,
quartz, pyrite, zircon, monazite, bastnaesite, phenakite, plus Fe and Cr oxides. However, feldspar and rare earth element-bearing
minerals occur predominantly in proximal emeralds, which also have a more incompatible trace-element signature than distal
emeralds. We propose a model related to syn- to post-tectonic magmatic-hydrothermal activity. Pegmatitic bodies intruded units
of the Ianapera antiform probably during tectonic relaxation. Exsolution of fluids rich in halogens and incompatible elements
from the cooling pegmatites caused hydrothermal metasomatism of Cr-bearing mafic/ultramafic rocks in direct contact with the
pegmatites. Local fracturing favored fluid infiltration, permitting the formation of distal mineralization. Emerald composition
was controlled by the chemistry of the host rock. The presence of carbonate mineral inclusions in the emeralds and the high
F-activity indicated by elevated F-contents in newly formed minerals suggest transport of Be as a fluoride-carbonate complex.
It seems likely that beryl formation was triggered by precipitation of F-rich phlogopite, which removed the complexing ligand
from the fluid. 相似文献
253.
Emmanuel Damien Rivière Michel Pirre Gwenaël Berthet Jean-Baptiste Renard Franck Lefèvre 《Journal of Atmospheric Chemistry》2004,48(3):261-282
Two cases of simultaneous nighttime measurements of NO2 and OClO in the winter polar stratosphere are analyzed in order to test our present knowledge of halogen chemistry in the presence of high amount of NO2 at low temperature. Comparisons with Lagrangian model calculations using several hypotheses are performed. First simulations, using the admitted constant rates of chemical reaction, strongly underestimate the measured OClO while the NO2 profiles are correctly reproduced. If uncertainties in actinic fluxes calculations are taken into account, simulation results do not show a significant reduction of the underestimation. A better agreement can be achieved if the formation of unstable isomers of ClONO2 and of BrONO2 occurs in the cold conditions of the polar stratosphere. An approximate value of the branching ratios of the channels leading to ClONO2 and ClOONO, and to BrONO2 and BrOONO, necessary to reproduce both OClO and NO2 is given and discussed. 相似文献
254.
255.
Michel Pichavant 《Contributions to Mineralogy and Petrology》1981,76(4):430-439
An experimental study of the effect of boron in the water saturated Q-Or-Ab-B2O3-H2O system has been performed at P=1 Kbar to provide experimental data and explain the role of boron in some late magmatic and early hydrothermal events. Experiments were conducted between 500° C and 800° starting from a gel, or a previously crystallized gel, and variable amounts of boron (0 to 18% B2O3) added to water. The phases obtained were: quartz, sanidine, albite, silicate liquid quenched to glass, and aqueous vapour phase. Boric acids, borates and isotropic low index materials were found in the quenched vapour phase. An aluminium silicate-like mineral, not yet fully identified, is also present.The solidus temperature of the Q-Or-Ab composition is lowered by 60° C when 5 wt. % B2O3 is added and by more than 130° C when 17wt. % B2O3 is added. Compositions of equilibrated silicate melts and vapours were obtained between 780° C and 750° C for various B2O3 concentrations. The vapour phase is B and Si rich. It is also enriched in Na with respect to K, and in alkalis with respect to Al. Its silicate solute content is higher than in experiments with pure water. The solubility of water is increased by the addition of boron in Q-Or-Ab melts. Microprobe data show that the melts equilibrated with vapour phases become hyperaluminous and more potassic than sodic. The partition coefficient of boron is in favour of the vapour (k
D=B2O3% in melt/B2O3% in vapour=0.33±0.02). The effect of the interaction between the silicate phases and the vapour is discussed. Comparison is made between the behaviour of boron and that of chlorine and fluorine. Geological applications are also provided, which concern the influence of boron on minimum melting, on muscovite stability and on the hypersolvus-subsolvus transition. 相似文献
256.
Determination of Halogens (F, Cl, Br, I), Sulfur and Water in Seventeen Geological Reference Materials 总被引:5,自引:0,他引:5
Fluorine, chlorine, bromine, iodine and sulfur were determined in seventeen geological reference materials after extraction by pyrohydrolysis. Fluorine, Cl and S (as sulfate ions) were determined in the extraction solution by ion chromatography with detection limits of around 0.2 mg l−1 . Bromine and I were measured by ICP-MS with detection limits of 1 μg l−1 for Br and 0.1 μg l−1 for I. For rock samples, using normal extraction conditions (500 mg of sample and 100 ml of final solution) detection limits were 40 mg kg−1 for F and Cl, 15 mg kg−1 for S, 0.2 mg kg−1 for Br and 0.02 mg kg−1 for I. These detection limits may be improved by increasing the amount of sample and hence the concentration of the final solution. Water was also determined using an extraction technique based on H2 O degassing, reduction on zinc at 1000 °C and H2 manometry. Our results for fluorine, chlorine, sulfur and water are in good agreement with literature data. Very few reference materials have recommended values for bromine and especially for iodine. Among the analysed samples, three are new reference materials: BHVO-2, BCR-2 and AGV-2. 相似文献
257.
Wei Lin Nicolas Charles Yan Chen Ke Chen Michel Faure Lin Wu Fei Wang Qiuli Li Jun Wang Qingchen Wang 《Gondwana Research》2013,23(1):78-94
Granitoids play an important role in deciphering both crustal growth and tectonic evolution of Earth. In the eastern end of the Yinshan–Yanshan belt of North China Craton, the Yiwulüshan massif is a typical region that presents the tectonic evolution features of this belt. Our field work on the host rocks has demonstrated two phases of opposite tectonics: compressional and extensional, however, the deformation is almost invisible in the intrusive rocks. To improve the understanding of the tectonic evolution of the Yiwulüshan massif and the Late Mesozoic tectonics of East Asia, a multidisciplinary study has been carried out. In this study, anisotropy of magnetic susceptibility (AMS) and gravity modeling have been applied on these Jurassic plutons (Lüshan, Jishilazi and Guanyindong), which intrude into the Yiwulüshan massif. According to laboratory measurements and microscopic observations on thin sections, the AMS of the Yiwulüshan massif is characterized by secondary fabrics, indicating that the intensive post solidus deformation has reset the (primary) magmatic magnetic fabrics. A relatively gentle NW dipping magnetic foliation has been identified with two distinct groups of magnetic lineations of N34°E and N335°E orientations, namely LM1 and LM2, relatively. Gravity modeling reveals a southward thinning of the massif with a possible feeding zone rooted in the northern part of the massif. Integrating all results from structural observation, geochronological investigation, AMS measurement and gravity modeling, two tectonic phases have been identified in the Yiwulüshan massif, posterior to the Jurassic (180–160 Ma) magmatism in the Yinshan–Yanshan area. The early one concerns a Late Jurassic–Early Cretaceous (~ 141 Ma) compressional event with a top-to-the-south to southwest sense of shear. The second one shows an Early Cretaceous (~ 126 Ma) NW–SE ductile extensional shearing. At that time, sedimentary basins widened and Jurassic plutons started to be deformed under post solidus conditions. In fact, the NW–SE trend of the maximum stretching direction is a general feature of East Asian continent during Late Mesozoic. 相似文献
258.
Assessment of groundwater recharge processes through karst vadose zone by cave percolation monitoring
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Amaël Poulain Arnaud Watlet Olivier Kaufmann Michel Van Camp Hervé Jourde Naomi Mazzilli Gaëtan Rochez Romain Deleu Yves Quinif Vincent Hallet 《水文研究》2018,32(13):2069-2083
Recharge processes of karst aquifers are difficult to assess given their strong heterogeneity and the poorly known effect of vadose zone on infiltration. However, recharge assessment is crucial for the evaluation of groundwater resources. Moreover, the vulnerability of karst aquifers depends on vadose zone behaviour because it is the place where most contamination takes place. In this work, an in situ experimental approach was performed to identify and quantify flow and storage processes occurring in karst vadose zone. Cave percolation monitoring and dye tracing were used to investigate unsaturated zone hydrological processes. Two flow components (diffuse and quick) were identified and, respectively, account for 66% and 34% of the recharge. Quickflow was found to be the result of bypass phenomenon in vadose zone related to water saturation. We identify the role of epikarst as a shunting area, most of the storage in the vadose zone occurring via the diffuse flow component in low permeability zones. Relationship between rainfall intensity and transit velocity was demonstrated, with 5 times higher velocities for the quick recharge mode than the diffuse mode. Modelling approach with KarstMod software allowed to simulate the hybrid recharge through vadose zone and shows promising chances to properly assess the recharge processes in karst aquifer based on simple physical models. 相似文献
259.
260.
F. E. analysis of field consolidation curves obtained with the modified borehole shear device (BHSD)
A modified version of the bore hole sheat device (BHSD) was used to obtain field consolidation curves in a soft sensitive clay. The Porewater pressure dissipation was monitored at the centre of one of the shear plates. This paper describes briefly the in situ device employed and demonstrates the basic features of the linearelastic F. E. program ‘SOL’. A detailed study is made to simulate the field behaviour with the finite element approach. Comparisons are made between the field and analytical consolidation behaviour. Difficulties in predicting the value of the coefficient of consolidation of a sensitive clay using the BHSD consolidation curves are discussed. 相似文献