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21.
Virtually all of the economic Ni–Cu–(platinum group element (PGE)) mineralization in the central part of the Cape Smith Belt
of New Québec is hosted by thick olivine cumulate units in the Katinniq Member of the Raglan Formation at the base of the
1.9 Ga Chukotat Group. These units transgress underlying gabbros and pelitic metasediments, forming 50–200-m deep and 300–1,000-m
wide V-shaped embayments and have been interpreted on the basis of surface geology, deep diamond core drilling, and magnetic
inversion models to represent the remnants of one or more large, long (at least 20 km, possibly ≥50 km), sinuous, komatiitic
basalt lava channels that formed by thermomechanical erosion of their substrates. We have used a mathematical model to test
these hypotheses regarding komatiitic lava emplacement and erosion by lava. Our modeling predicts that an initially 10-m thick
komatiitic basalt flow should have flowed turbulently near the vent and should have thermomechanically eroded unconsolidated
pelitic sediment during emplacement to reach the observed degree of contamination of ≤10% at distances of ~30–60 km downstream
from the source. Furthermore, our models predict that, at these distances downstream, a fully inflated 100-m thick komatiitic
basalt flow would have had thermal erosion rates over consolidated gabbroic substrate of ~0.7–1.5 m/day, requiring ~70–140 days
to incise a 100-m deep channel, depending on the initial temperature of the lava, the paleoslope, and the initial temperature
and solidus temperature of the gabbro. These erosion rates would have been associated with volumetric flow rates of >105–106 m3/s and eruption volumes of >103–104 km3. Although these flow rates are orders of magnitude larger than those of most modern terrestrial basaltic flows, they are
of the same order as those estimated for the largest terrestrial flood basalt flows and with those inferred for some of the
largest extraterrestrial flows. Our predicted flow volumes are also of the same order as those of the largest terrestrial
flood basalt units, consistent with the great thickness and widespread distribution of the Chukotat Group. Our modeling of
thermomechanical erosion of gabbro by komatiitic basalt results in negligible contamination (<1%), and geochemical studies
show that the spatially and petrogenetically related Chukotat basalts are uncontaminated, suggesting that the observed enrichments
in U–Th–Light Rare Earth Elements (REE) > Middle REE–Heavy REE > Nb–Ta–Ti represent contamination by underlying Povungnituk
semipelites. This result is consistent with present models for the genesis of the Ni–Cu–(PGE) mineralization in the Raglan
Formation that involve thermomechanical erosion of unconsolidated, sulfidic semipelitic sediments, and decoupling of the miscible
silicate and immiscible sulfide components. 相似文献
22.
Diana Prado Garzón Christiano G.M. Brum Ezequiel Echer Néstor Aponte Michael P. Sulzer Sixto A. González Robert B. Kerr Lara Waldrop 《Journal of Atmospheric and Solar》2011,73(11-12):1568-1574
We analyze the data obtained using the Arecibo incoherent scatter radar to examine the response of the topside ionosphere to a moderate geomagnetic storm that occurred during the period March 7–11, 2008. During this time period a magnetic storm with a non-monotonic main phase decrease in the Dst index occurred. The recovery phase also exhibited a secondary Dst decrease. During the initial phase of the storm, Te and Ti increased coincident with the arrival of the solar wind. The main phase registered an increase in proton concentration proportional to Ne while temperatures reached the lowest values. Variations in O+ concentration were not significant but a reduction in helium fraction was observed. Soon after the peak of the storm, the transition height between the topside ionosphere and the protonosphere, where H+ ions dominate composition, was lower than would be expected during quiet conditions and this behavior lasted for approximately 12 h. 相似文献
23.
F. M. Kerr A. Gouveia R. W. Lee P. K. Patel O. Renner S. J. Rose H. A. Scott J. S. Wark 《Astrophysics and Space Science》2005,298(1-2):171-176
An astrophysically relevant experiment is compared to the output of a multidimensional radiation transfer code in which populations
and radiation are self-consistently treated. Experimental Al Ly α spectra obtained with a very high-resolution spectrometer
are presented as quantitative evidence of dot plasma non-planar expansion. Analysis of these spectra using the code is performed,
in particular examining the effects of velocity gradients in directions other than that of the primary expansion. These calculations
are found to be in good agreement with the experimental results. Usage of the Ly α doublet as a planarity diagnostic is discussed. 相似文献
24.
25.
Delphine Yeghicheyan Cécile Bossy Martine Bouhnik Le Coz Chantal Douchet Guy Granier Alexie Heimburger Francois Lacan Aurélie Lanzanova Tristan C. C. Rousseau Jean‐Luc Seidel Mickaël Tharaud Frédéric Candaudap Jérôme Chmeleff Christophe Cloquet Sophie Delpoux Marie Labatut Rémi Losno Catherine Pradoux Yann Sivry Jeroen E. Sonke 《Geostandards and Geoanalytical Research》2013,37(4):449-467
The natural river water certified reference material SLRS‐5 (NRC‐CNRC) was routinely analysed in this study for major and trace elements by ten French laboratories. Most of the measurements were made using ICP‐MS. Because no certified values are assigned by NRC‐CNRC for silicon and 35 trace element concentrations (rare earth elements, Ag, B, Bi, Cs, Ga, Ge, Li, Nb, P, Rb, Rh, Re, S, Sc, Sn, Th, Ti, Tl, W, Y and Zr), or for isotopic ratios, we provide a compilation of the concentrations and related uncertainties obtained by the participating laboratories. Strontium isotopic ratios are also given. 相似文献
26.
27.
P. G. Jonker G. Nelemans Z. Wang A. K. H. Kong D. Chakrabarty M. Garcia P. J. Groot M. van der Klis T. Kerr B. Mobasher M. Sullivan T. Augusteijn B. W. Stappers P. Challis R. P. Kirshner J. Hjorth A. Delsanti 《Monthly notices of the Royal Astronomical Society》2003,344(1):201-206
We have obtained optical and near-infrared images of the field of the accreting millisecond X-ray pulsar XTE J1751−305. There are no stars in the 0.7-arcsec error circle (0.7 arcsec is the overall uncertainty arising from tying the optical and X-ray images and from the intrinsic uncertainty in the Chandra X-ray astrometric solution). We derive limiting magnitudes for the counterpart of R > 23.1, I > 21.6, Z > 20.6, J > 19.6 and K > 19.2 . We compare these upper limits with the magnitudes one would expect for simple models for the possible donor stars and the accretion disc subject to the reddening observed in X-rays for XTE J1751−305 and when put at the distance of the Galactic Centre (8.5 kpc). We conclude that our non-detection does not constrain any of the models for the accretion disc or possible donor stars. Deep, near-infrared images obtained during quiescence will, however, constrain possible models for the donor stars in this ultracompact system. 相似文献
28.
The Barra Nova inlet, in south Portugal, is known to migrate progressively southeastwards under wave action. The morphodynamics
of this system during a representative year suggests that this long-term evolution is dependent on a seasonal behavior of
the tidal inlet which can be described through a three-stage model of post-storm, transition and extended fair-weather conditions.
Processes involved in this evolution indicate that the historical migration of the Barra Nova is not dependent on the longshore
drift forcing constricting the channel on the updrift coast, but rather on the adjustment of the system to a major erosion
of the downdrift coast during short storm events. 相似文献
29.
30.