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Pierre Voinchet Christophe Falgures Hlne Tissoux Jean-Jacques Bahain Jackie Desprie Florence Pirouelle 《Quaternary Geochronology》2007,2(1-4):363-366
An ESR experimental study of artificial optical bleaching of sedimentary quartz has shown that the aluminum center was maximally bleached after a 6-month illumination equivalent to natural light. This duration seems too long to apply in natural conditions. Nevertheless, the measurement of the ESR intensity of aluminum centers in quartz extracted from modern sediments and deposited in sandy bars shows that the maximum bleaching has effectively been reached.
In order to determine the relationship between the bleaching and the distance covered by a quartz grain in a river, samples were collected along the Creuse River (France) from its spring to about 170 km downstream, where maximum bleaching levels were observed in previous studies. The ESR intensities of the aluminum and titanium centers in quartz were measured, using X-band spectroscopy, before and after artificial bleaching. The difference measured between these sub-samples shows that the maximum bleaching level is obtained in the course of the first kilometer. Hence, the assumption that ESR dating of fluvial sediment is based on the optical bleaching was validated. 相似文献
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Jackie L. Cooper Geoffrey V. Bicknell Ralph S. Sutherland Joss Bland-Hawthorn 《Astrophysics and Space Science》2007,311(1-3):99-103
In order to better understand the formation of a starburst-driven wind, we have performed a series of three-dimensional hydrodynamical
simulations in an inhomogeneous interstellar medium. We present the results of these simulations, which provide new insights
into the formation of the optical filaments and the origin of the soft X-ray emission. 相似文献
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Juliet G. Crider David Frank Stephen D. Malone Michael P. Poland Cynthia Werner Jacqueline Caplan-Auerbach 《Bulletin of Volcanology》2011,73(2):175-189
Mount Baker volcano displayed a short interval of seismically-quiescent thermal unrest in 1975, with high emissions of magmatic
gas that slowly waned during the following three decades. The area of snow-free ground in the active crater has not returned
to pre-unrest levels, and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval. A relative
microgravity survey revealed a substantial gravity increase in the ~30 years since the unrest, while deformation measurements
suggest slight deflation of the edifice between 1981–83 and 2006–07. The volcano remains seismically quiet with regard to
impulsive volcano-tectonic events, but experiences shallow (<3 km) low-frequency events likely related to glacier activity,
as well as deep (>10 km) long-period earthquakes. Reviewing the observations from the 1975 unrest in combination with geophysical
and geochemical data collected in the decades that followed, we infer that elevated gas and thermal emissions at Mount Baker
in 1975 resulted from magmatic activity beneath the volcano: either the emplacement of magma at mid-crustal levels, or opening
of a conduit to a deep existing source of magmatic volatiles. Decadal-timescale, multi-parameter observations were essential
to this assessment of magmatic activity. 相似文献
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We develop a new Proper Orthogonal Decomposition (POD) reduced order model for saturated groundwater flow, and apply that model to an inverse problem for the hydraulic conductivity field. We use sensitivities as the POD basis. We compare the output when the optimizer uses the reduced order model against results obtained with a full PDE based model. The solutions generated using the POD reduced model are comparable in residual norm to the solutions formed using only the full-scale model. The material parameters are similarly comparable. The time to solution when using the reduced model is reduced by at least an order of magnitude, as are the number of calls to the full model. 相似文献
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Timescales of partial melting in the Himalayan middle crust: insight from the Leo Pargil dome, northwest India 总被引：5，自引：0，他引：5
Graham W. Lederer John M. Cottle Micah J. Jessup Jackie M. Langille Talat Ahmad 《Contributions to Mineralogy and Petrology》2013,166(5):1415-1441
The Leo Pargil dome (LPD) in northwest India exposes an interconnected network of pre-, syn-, and post-kinematic leucogranite dikes and sills that pervasively intrude amphibolite-facies metapelites of the mid-crustal Greater Himalayan sequence. Leucogranite bodies range from thin (5-cm-wide) locally derived sills to thick (2-m-wide) crosscutting dikes extending at least 100 m. Three-dimensional exposures elucidate crosscutting relations between different phases of melt injection and crystallization. Combined laser ablation inductively coupled plasma mass spectrometry U–Th/Pb geochronology and trace element analysis on well-characterized monazite grains from nineteen representative leucogranites yields a large, internally consistent data set of approximately 700 U–Th/Pb and 400 trace element analyses. Grain-scale variations in age correlate with trace element distributions and indicate semi-continuous crystallization of monazite from 30 to 18 Ma. The youngest U–Th/Pb ages in a given sample are consistent with the outcrop-scale crosscutting relations, whereas older ages within individual samples record inheritance from partially crystallized melt and source metapelites. U–Th/Pb isotopic and trace element data are incorporated into a model of melting within the LPD that involves (1) steady-state equilibrium batch melting of compositionally homogeneous metapelitic sources; (2) pulses of increased melt mobility lasting 1–2 m.y. resulting in segregation of melt from its source and amalgamation into mixed magmas; and (3) rapid emplacement and final crystallization of leucogranite bodies. Melt systems in the LPD evolved from locally derived, in situ melt in migmatitic source rocks into a vast network of dikes and sills in the overlying non-migmatitic host rocks. 相似文献
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RésuménDans certaines régions où les sédiments récents (plio-quaternaires) sont rares ou inutilisables comme enregistreurs de déformations, seule l’analyse morpho-strcturale peut mettre en évidence des indices de néotectonique. Deux types d’objets morphologiques se révèlent particulièrement utiles : les surfaces (d’érosion et de comblement) et le réseau hydrographique. Leur prise en compte et leur analyse s’effectuent essentiellement à partir des cartes topographiques à différentes échelles (de 1/50 000 à 1/500 000).* La démarche est la suivante: 1 – Des traitements appropriés sont développés, mettant en évidence des discontinuités et des anomalies au sein des surfaces enveloppes et du réseau hydrographiques; 2 – Ces discontinuités sont analysées puis interprétées afin de déterminer les causes de leur existence dans le cadre d’un modèle d’évolution du relief qui tient compte de facteurs internes (la lithologie, la structure), et de facteurs externes (le climat, la végétation et les actions humaines); 3 – Des travaux de terrain confirment et précisent les caractéristiques de ces facteurs (nature et quantification de la déformation : âge. amplitude, sens des mouvements). * Les principaux résultats de cette démarche appliquée à l’Kst du Bassin parisien sont les suivants: 1 – Les cuestas orientales du Bassin parisien apparaissent structurées par des accidents NK-SW (prolongement du fossé de Sarre Nahe) et NNW-SSK ( Argonne-Bar-le-Due); 2 – Les discontinuités morpho-structurales sont localisées et caractérisées par des mouvements récents. 相似文献
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de Jong Geoffrey Rotherham Jackie Phillips G. Neil Williams Patrick J. 《Geologie en Mijnbouw》1997,76(4):311-319
In Mid Proterozoic crystalline rocks of the Mount Isa Inlier, around Cloncurry, Australia, 2000 km2 of alteration and brecciation are the product of high-temperature (> 450 °C) concentrated saline solution activity. During retrogression, this fluid was locally responsible for mobility of V, Y, Nb and light rare-earth elements (15 × enrichment). Copper and S were leached during alteration and this may have been a significant source of components in nearby Cu-Au deposits. Similar rare-earth-element behaviour has been observed in the hematite breccias which host Cu-sulfides at the giant Olympic Dam Cu-Au deposit. 相似文献