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51.
Lev J. Spivak‐Birndorf Audrey Bouvier Gretchen K. Benedix Samantha Hammond Gregory A. Brennecka Kieren Howard Nick Rogers Meenakshi Wadhwa Philip A. Bland Pavel Spurný Martin C. Towner 《Meteoritics & planetary science》2015,50(5):958-975
Bunburra Rockhole is a unique basaltic achondrite that has many mineralogical and petrographic characteristics in common with the noncumulate eucrites, but differs in its oxygen isotope composition. Here, we report a study of the mineralogy, petrology, geochemistry, and chronology of Bunburra Rockhole to better understand the petrogenesis of this meteorite and compare it to the eucrites. The geochemistry of bulk samples and of pyroxene, plagioclase, and Ca‐phosphate in Bunburra Rockhole is similar to that of typical noncumulate eucrites. Chronological data for Bunburra Rockhole indicate early formation, followed by slow cooling and perhaps multiple subsequent heating events, which is also similar to some noncumulate eucrites. The 26Al‐26Mg extinct radionuclide chronometer was reset in Bunburra Rockhole after the complete decay of 26Al, but a slight excess in the radiogenic 26Mg in a bulk sample allows the determination of a model 26Al‐26Mg age that suggests formation of the parent melt for this meteorite from its source magma within the first ~3 Ma of the beginning of the solar system. The 207Pb‐206Pb absolute chronometer is also disturbed in Bunburra Rockhole minerals, but a whole‐rock isochron provides a re‐equilibration age of ~4.1 Ga, most likely caused by impact heating. The mineralogy, geochemistry, and chronology of Bunburra Rockhole demonstrate the similarities of this achondrite to the eucrites, and suggest that it formed from a parent melt with a composition similar to that for noncumulate eucrites and subsequently experienced a thermal history and evolution comparable to that of eucritic basalts. This implies the formation of multiple differentiated parent bodies in the early solar system that had nearly identical bulk elemental compositions and petrogenetic histories, but different oxygen isotope compositions inherited from the solar nebula. 相似文献
52.
Rochelle-Newall EJ Chu VT Pringault O Amouroux D Arfi R Bettarel Y Bouvier T Bouvier C Got P Nguyen TM Mari X Navarro P Duong TN Cao TT Pham TT Ouillon S Torréton JP 《Marine pollution bulletin》2011,62(11):2317-2329
Phytoplankton diversity, primary and bacterial production, nutrients and metallic contaminants were measured during the wet season (July) and dry season (March) in the Bach Dang Estuary, a sub-estuary of the Red River system, Northern Vietnam. Using canonical correspondence analysis we show that phytoplankton community structure is potentially influenced by both organometallic species (Hg and Sn) and inorganic metal (Hg) concentrations. During March, dissolved methylmercury and inorganic mercury were important factors for determining phytoplankton community composition at most of the stations. In contrast, during July, low salinity phytoplankton community composition was associated with particulate methylmercury concentrations, whereas phytoplankton community composition in the higher salinity stations was more related to dissolved inorganic mercury and dissolved mono and tributyltin concentrations. These results highlight the importance of taking into account factors other than light and nutrients, such as eco-toxic heavy metals, in understanding phytoplankton diversity and activity in estuarine ecosystems. 相似文献
53.
We present synthetic images of accretion disks around young stars computed from a model where the disk's vertical structure is solved assuming hydrostatic equilibrium. The disk's brightness results from three emission processes: (1) the reprocessing of stellar photons in the optically thick disk's regions; (2) the scattering of stellar photons in the optically thin parts of the disk; and (3) the thermal emission of the disk due to viscous energy dissipation during the accretion process.We discuss the relative importance of these emission processes at wavelengths ranging from 1.2 to 20m.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
54.
Pavel Kroupa † Jerome Bouvier 《Monthly notices of the Royal Astronomical Society》2003,346(2):369-380
55.
Sophie Blain Ian K. Bailiff Pierre Guibert Armel Bouvier Maylis Baylé 《Quaternary Geochronology》2010,5(2-3):311-316
A luminescence dating study has been applied to inform the history and archaeology of two early medieval buildings in north western France. Five bricks were sampled from the medieval churches (10th–11th centuries A.D.) of Rugles and Condé-sur-Risle in Normandy. The samples were divided and tested in the luminescence laboratories of the University of Durham (UK) and of Iramat-CRP2A, University of Bordeaux 3 (France). The fine grain and quartz inclusion techniques were applied, and tests included an examination of the anomalous fading of the luminescence signal from fine grain samples and coarse grains of feldspar. With one exception, the dates produced using the fine grain technique, although corrected for fading, were significantly younger than those produced with quartz inclusions. Although most of the corrected fine grain dates were consistent with the medieval construction of the churches, the brick fabric is of Roman type by archaeological assessment, and this is supported by the quartz coarse grain dates. We conclude that the bricks sampled are re-used, likely to be of Roman origin, and that the reliability of measurements with feldspars in brick fabrics requires wider investigation. 相似文献
56.
We analyse the distribution of projected equatorial velocities ( v sin i ) for a magnitude-limited sample of stars in Taurus, in order to assess whether this sample can contain a population of fast rotators (missed in previous photometric monitoring campaigns) similar to those recently discovered in Orion by Stassun et al. We find strong evidence, in line with the results of photometric monitoring campaigns in Taurus, that there is no such population of stars in Taurus that rotate at a large fraction of breakup velocity. We thus demonstrate that the stellar rotation distributions in the two star-forming regions are intrinsically different (with a statistical significance of this discrepancy in excess of 3 σ ), and discuss possible origins for this difference. 相似文献
57.
Recent work, quoted in the introduction, concerning a scale covariant theory of gravitation and corresponding astrophysical tests, has called for a revival of the geometrical considerations put forward by Weyl half a century ago, together with a better understanding of the mathematical foundation of Weyl's geometry. The present paper is to be regarded as a contribution in that direction. 相似文献
58.
Situated at the foot of the Pichincha volcano, the city of Quito is frequently subjected to hydroclimatic hazards. In 1995 an 11·2 km2 watershed, located in the vicinity of the city, was equipped with eight rain gauges and two flow gauges to better understand the local rainfall/runoff transformation processes. Rainfall simulation experiments were carried out on more than 40 one‐square‐metre plots to measure infiltration point‐processes. The high density of measurement devices allowed us to identify the origin and nature of the various contributions to runoff for the different physiographic units of the watershed: urban area from an altitude of 2800 to 3200 m; farmland, pasture and forested land, and finally páramo above 3900 m. Runoff occurs mainly in the lower part of the basin and is caused by urbanization; however, the natural soils of this area can also produce Hortonian runoff, which is predominant in a few events. This contribution can be studied through rainfall simulation experiments. In the upper natural zone, the younger and more permeable soils generate less runoff on the slopes. However, almost permanently saturated contributing areas, which are located in the bottom of the quebradas, may generate flood events, the size of which depends on the extent of the area concerned. Variations in the runoff coefficients are related first to the baseflow and second to the amount of rainfall in the previous 24 h. This analysis, which underlines the complexity of a small, peri‐urban, volcanic catchment, is a necessary preliminary to runoff modelling in an area where very few experiments have been carried out on small catchments. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
59.
Guillaume?SironEmail authorView authors OrcID profile Lukas?Baumgartner Anne-Sophie?Bouvier 《Contributions to Mineralogy and Petrology》2018,173(8):63
The hydroxyl (O(4)) site composition of biotite can in principle be used to retrieve information about fluid composition during fluid–rock interaction; however, due to low F and Cl content, as well as difficulties involved with analyzing the H2O content using in situ techniques, measuring these species in biotite has remained an elusive goal. Here we present high-precision secondary ion mass spectrometry (SIMS) OH–F–Cl measurements from biotite within metapelites from the Western Adamello Tonalite (WAT) contact aureole, Northern Italy. Fluorine, chlorine and hydrogen are analyzed on the SIMS sequentially by peak-hopping at the same biotite spot; H2O, F and Cl content were measured with a precision (1σ) οφ 0.06 ωτ%, 50 ανδ 5 ππµ, ρεσπεχτι?ελψ. The compositions of isolated biotite crystals in andalusite are compared with that of biotite in the matrix, documenting that halogens and H2O behave refractory in biotite during the time scale of contact metamorphism. The H2O and halogen contents of biotite are mostly locked in during the prograde to peak formation of biotite, and are not reset during further heating or cooling, unless significant biotite recrystallization occurs. It also appears that both Ti content and XMg of the biotite from the Western Adamello contact aureole were not significantly reset during cooling. The concentration of F and Cl does not vary systematically with metamorphic grade, which indicates that these species reflect initial compositions. No significant Rayleigh fractionation behavior was observed for these elements. H2O variations in the biotite from samples throughout the Western Adamello contact aureole suggest that Al-oxy substitution partially controls the variations in OH content through charge balance of the type R2+,VI + OH? = Al3+,VI + O2? + H2, while the Ti-oxy substitution does not seem to influence the O(4) site occupation. The main titanium substitution appears to be the Ti-vacancy (\({\text{2}}{{\text{R}}^{{\text{2}}+}}~=~{\text{T}}{{\text{i}}^{{\text{4}}+}}~+\,{\square ^{{\text{VI}}}}\)) exchange. Variations in H2O and halogen concentrations in biotite define sub mm-scale areas of localized equilibration, even for biotite recrystallized during dehydration reactions that produced large amounts of fluid (chlorite or muscovite breakdown). Similar systematics were observed for Ti4+ and Al3+. These findings further support the increasing number of observations that kinetics control much of the mineralogical reactions occurring in contact aureoles, and hence care is advised in using equilibrium thermodynamics in this environment. 相似文献
60.
Li isotopes and trace elements as a petrogenetic tracer in zircon: insights from Archean TTGs and sanukitoids 总被引:1,自引:0,他引:1
Anne-Sophie Bouvier Takayuki Ushikubo Noriko T. Kita Aaron J. Cavosie Reinhard Kozdon John W. Valley 《Contributions to Mineralogy and Petrology》2012,163(5):745-768
We report δ7Li, Li abundance ([Li]), and other trace elements measured by ion probe in igneous zircons from TTG (tonalite, trondhjemite,
and granodiorite) and sanukitoid plutons from the Superior Province (Canada) in order to characterize Li in zircons from typical
Archean continental crust. These data are compared with detrital zircons from the Jack Hills (Western Australia) with U–Pb
ages greater than 3.9 Ga for which parent rock type is not known. Most of the TTG and sanukitoid zircon domains preserve typical
igneous REE patterns and CL zoning. [Li] ranges from 0.5 to 79 ppm, typical of [Li] in continental zircons. Atomic ratios
of (Y + REE)/(Li + P) average 1.0 ± 0.7 (2SD) for zircons with magmatic composition preserved, supporting the hypothesis that
Li is interstitial and charge compensates substitution of trivalent cations. This substitution results in a relatively slow
rate of Li diffusion. The δ7Li and trace element data constrain the genesis of TTGs and sanukitoids. [Li] in zircons from granitoids is significantly
higher than from zircons in primitive magmas in oceanic crust. TTG zircons have δ7Li (3 ± 8‰) and δ18O in the range of primitive mantle-derived magmas. Sanukitoid zircons have average δ7Li (7 ± 8‰) and δ18O higher than those of TTGs supporting genesis by melting of fluid-metasomatized mantle wedge. The Li systematics in sanukitoid
and TTG zircons indicate that high [Li] in pre-3.9-Ga Jack Hills detrital zircons is a primary igneous composition and suggests
the growth in proto-continental crust in magmas similar to Archean granitoids. 相似文献