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71.
Fragments of unaltered andesite found at all levels in the deposits of the catastrophic flank-failure, directed-blast eruption of the Soufrière of Guadeloupe in 3100 bp are thought to be remnants of the cryptodome. They were observed in analytical transmission electron microscopy for clues to the evolution of the intrusion prior to the eruption. Several features that could potentially be used as temperature markers were identified, among which the angle between microexsolutions of magnetite in augite phenocrysts was used to find an upper boundary of the temperature of the intrusion before the eruption: 600–700°C. Calculation of the time a dyke or sphere-shaped intrusion may have taken to cool from the emplacement temperature down to the temperature of exsolution of the magnetite leads to an estimate of the time between emplacement of the intrusion and the eruption, which could not have been less than a few tens of years. It therefore seems probable that the emplacement of the magmatic intrusion was not the immediate cause of the flank destabilization and catastrophic eruption of the Soufrière in 3100 bp. 相似文献
72.
G. Budetta D. Condarelli M. Fytikas N. Kolios G. Pascale A. Rapolla E. Pinna 《Bulletin of Volcanology》1984,47(3):447-466
A program of geophysical research was carried out as a preliminary stage of study of the Santorini volcanic group. This area is of remarkable geothermal and volcanological interest, and the definition of a volcanological structural model is the starting point for an understanding of the local geodynamic processes. Gravity, magnetic and geoelectrical data proved that:
- the core of the volcanic edifice consists of a sedimentary-metamorphic basement;
- the basement is tectonically disturbed and a linear tectonic system produces a graben-type structure in the middle part of the area.
73.
Jean‐Paul Bravard Ashraf Mostafa Romain Garcier Gaëlle Tallet Pascale Ballet Yael Chevalier Herv Tronchre 《Geoarchaeology》2016,31(6):467-486
The present study examines the geoarchaeological history of an oasis in Kharga Depression in central Egypt. El‐Deir is renowned for its Ptolemaic temple and Roman fortress on the road from former Hibis (Kharga) to the Nile Valley. During the survey, spring mounds and irrigation soils belonging to an ancient agricultural zone were discovered, and further documented by ceramics found on the site. Our methodology combines the geomorphological interpretation of landforms (especially yardangs) with ceramics and 14C‐dated charcoal to distinguish and date former agricultural areas in El‐Deir. The results show that the oasis experienced several phases of soil accretion and destruction through time. Playa sediments were deposited in the humid early Holocene and severely eroded by deflation before the onset of irrigated agriculture between Pharaonic and Persian times. Very fast vertical soil accretion occurred in the Ptolemaic period, but irrigation soils were later destroyed during the Roman period by a combination of wind deflation and flash floods (second to fourth century A.D.), suggesting a period of climate instability. The case of El‐Deir invites reevaluation of constructive agencies for the development of irrigated land and destructive agencies as limiting factors for the sustainability of agricultural practices in late antiquity. 相似文献
74.
Dawsonite synthesis and reevaluation of its thermodynamic properties from solubility measurements: Implications for mineral trapping of CO2 总被引:1,自引:0,他引:1
Pascale Bénézeth Donald A. Palmer Juske Horita 《Geochimica et cosmochimica acta》2007,71(18):4438-4455
Over the last decade, a significant research effort has focused on determining the feasibility of sequestering large amounts of CO2 in deep, permeable geologic formations to reduce carbon dioxide emissions to the atmosphere. Most models indicate that injection of CO2 into deep sedimentary formations will lead to the formation of various carbonate minerals, including the common phases calcite (CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), siderite (FeCO3), as well as the far less common mineral, dawsonite (NaAlCO3(OH)2). Nevertheless, the equilibrium and kinetics that control the precipitation of stable carbonate minerals are poorly understood and few experiments have been performed to validate computer codes that model CO2 sequestration.In order to reduce this uncertainty we measured the solubility of synthetic dawsonite according to the equilibrium: , from under- and oversaturated solutions at 50-200 °C in basic media at 1.0 mol · kg−1 NaCl. The solubility products (Qs) obtained were extrapolated to infinite dilution to obtain the solubility constants (. Combining the fit of these values and fixing at 25 °C, which was derived from the calorimetric data of Ferrante et al. [Ferrante, M.J., Stuve, J.M., and Richardson, D.W., 1976. Thermodynamic data for synthetic dawsonite. U.S. Bureau of Mines Report Investigation, 8129, Washington, D.C., 13p.], the following thermodynamic parameters for the dissolution of dawsonite were calculated at 25 °C: , and . Subsequently, we were able to derive values for the Gibbs energy of formation (, enthalpy of formation ( and entropy ( of dawsonite. These results are within the combined experimental uncertainties of the values reported by Ferrante et al. (1976). Predominance diagrams are presented for the dawsonite/boehmite and dawsonite/bayerite equilibria at 100 °C in the presence of a saline solution with and without silica-containing minerals. 相似文献
75.
A non-linear non-hydrostatic model (MIT-gcm) is used to study the generation and propagation of internal tides. The model domain covers a continental slope and neighbouring parts of the deep ocean and shelf. Uniformity in the along-slope direction is assumed. We focus on the non-linear evolution of the internal tide once generated. In particular, we show that in the main region of generation, over the upper part of the slope, small-scale features occur, indicative of breaking and mixing. Far from the generation region, non-linear processes are important in the reflection of the beam at the bottom, where higher harmonics are generated. This implies an energy transfer toward higher frequencies and the resulting shape of the energy spectra is consistent with observations. Turbulent and mixing processes are analysed by employing an adiabatic sorting method; thus, we calculate the development in time of the available potential energy, the variation in the background potential energy due to irreversible processes, and the distribution of the Cox number (the local turbulent diffusivity normalized by the background diffusivity) over the slope. With rotation, the transfer of energy to higher harmonics is reduced. 相似文献
76.
Using a multivariate model testing procedure that distinguishes between model inadequacies and data uncertainties, we investigate the ability of the LODYC GCM to simulate the evolution of the 20°C isotherm depth during the 1982–1984 FOCAL/SEQUAL experiment in the equatorial Atlantic. Two different versions of the model are considered: the Ri version which has a Richardson number dependent parameterization of vertical mixing and the new TKE version which uses a local estimation of the turbulent kinetic energy to parameterize vertical mixing. Some effects of the forcing uncertainties are considered by forcing the TKE version with three equally plausible wind stress fields whose differences are consistent with the measurement and sampling errors, and the drag coefficient indeterminacy. The resulting uncertainties in the model response are substantial and can be as large as the differences between simulations with the two GCM versions, which stresses the need to take the forcing uncertainties into account. Although only one Ri run is available, it is shown that the TKE parameterization significantly improves the representation of the equatorial upwelling and the simulation of the depth of the thermocline in the eastern Atlantic. However, there remain significant differences with the observations which cannot be explained by the forcing uncertainties that were considered. The two model versions perform better in the equatorial wave guide than in the 12°N-12°S domain, and they are better distinguished over large domains than along sections, which shows that a global multivariate view point must be used in model-reality comparisons. Finally, a comparison with a linear multimode model emphasizes the need for greater model complexity to properly simulate the equatorial upwelling and the thermocline variability in the tropical Atlantic.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max-Planck-Institute for Meteorology. Guest Editor for these papers is L. Dümenil 相似文献
77.
78.
Variations of Indian and African monsoons induced by insolation changes at 6 and 9.5 kyr BP 总被引:2,自引:2,他引:0
This study investigates the role of insolation in controlling the Indian and African monsoon evolutions during the Holocene using coupled ocean-atmosphere simulations of 0, 6, 9.5 kyr BP climates, for which only the variations of Earth’s orbital configuration are considered. The two monsoon systems are enhanced at 6 and 9.5 kyr BP, compared to 0 kyr BP, as a result of the intensified seasonal cycle of insolation in the Northern Hemisphere. The analysis of daily climatologies indicates that even though the length of the “celestial” summer season is shorter at 9.5 kyr BP, the rainy season is longer than at present. Emphasis is put on the impact of the precession on the seasonality, which partly explains why the relative amplification of the Indian and African monsoon varies between 9.5 and 6 kyr BP. Moreover, the changes in snow cover over the Tibetan Plateau play a critical role in reinforcing the 9.5 kyr BP monsoon in India during spring. The results suggest that the teleconnection between convection over India and subsidence over the Mediterranean regions, through the Rodwell and Hoskins mechanism, has an impact on the development of the African monsoon at 9.5 kyr BP. 相似文献
79.
Ralf Srama Thomas Stephan Eberhard Grün Norbert Pailer Anton Kearsley Amara Graps Rene Laufer Pascale Ehrenfreund Nicolas Altobelli Kathrin Altwegg Siegfried Auer Jack Baggaley Mark J. Burchell James Carpenter Luigi Colangeli Francesca Esposito Simon F. Green Hartmut Henkel Mihaly Horanyi Annette Jäckel Sascha Kempf Neil McBride Georg Moragas-Klostermeyer Harald Krüger Pasquale Palumbo Andre Srowig Mario Trieloff Peter Tsou Zoltan Sternovsky Oliver Zeile Hans-Peter Röser 《Experimental Astronomy》2009,23(1):303-328
The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We
propose a new mission concept, SARIM, that collects interstellar and interplanetary dust particles and returns them to Earth.
SARIM is optimised for the collection and discrimination of interstellar dust grains. Improved active dust collectors on-board
allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important
constraints for subsequent laboratory analysis.
The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and
inside the solar-wind charging environment. SARIM is three-axes stabilised and collects interstellar grains between July and
October when the relative encounter speeds with interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection
period several hundred interstellar and several thousand interplanetary grains will be collected by a total sensitive area
of 1 m2. At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule.
SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of interstellar
samples by latest laboratory technologies. 相似文献
80.
Climate and vegetation: Simulating the African humid period 总被引:1,自引:0,他引:1
Christelle Hély Pascale Braconnot Julie Watrin Weipeng Zheng 《Comptes Rendus Geoscience》2009,341(8-9):671-688
The outputs of the climate simulated by two General Circulation Models (GCMs), (IPSL and UGAMP) have been used to force a vegetation model (LPJ-GUESS) to analyze the Holocene African humid period (AHP) and related vegetation changes over the 18°W-35°E, 5°S-25°N region. At the continental scale, simulations with the two models confirm the intensified African monsoon during the Holocene as compared to now, and the early but gradual termination of the AHP in eastern regions as compared to western regions. At the regional scale, the two GCMs results present important differences in the timing of the AHP, its spatial extent and the summer rainfall amplitude. Consequently, the vegetation model simulates changes that are globally in agreement with pollen data, but with large differences according to the region and the model considered. During the AHP, the IPSL climate induced proper vegetation changes in the eastern Sahara and in the Sahel, whereas the UGAMP climate induced correct changes in the western Sahara and in the equatorial zone. 相似文献