Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid?          下载免费PDF全文

Pavel P. Povinec  Matthias Laubenstein  A. J. Timothy Jull  Ludovic Ferrière  Franz Brandstätter  Ivan Sýkora  Jozef Masarik  Juraj Beňo  Andrej Kováčik  Dan Topa  Christian Koeberl 《Meteoritics & planetary science》2015,50(2):273-286

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long‐lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of ¹⁴C, ²²Na, ²⁶Al, ⁵⁴Mn, ⁵⁷Co, ⁵⁸Co, and ⁶⁰Co, which indicate that the pre‐atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed ²⁶Al activities of the investigated samples, Monte Carlo simulations, and taking into account the ²⁶Al half‐life (0.717 Myr), the cosmic‐ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, ¹⁴C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of ¹⁴C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic ¹³⁷Cs and primordial ⁴⁰K in some of the Chelyabinsk fragments.  相似文献   

Velocity structure of the lithosphere on the 2003 Mongolian-Baikal transect from <Emphasis Type="Italic">SV</Emphasis> waves     

V. V. Mordvinova  A. Deschamps  T. Dugarmaa  J. Deverchére  M. Ulziibat  V. A. Sankov  A. A. Artem’ev  J. Perrot 《Izvestiya Physics of the Solid Earth》2007,43(2):119-129

The S wave velocity distribution in the Earth’s crust and the first two hundred kilometers of the upper mantle is inferred from data of a seismological linear network including 18 broadband stations installed in the framework of the international teleseismic experiment carried out in 2003 in the south of Siberia and in Mongolia. Models were constructed by using P-to-S received function inversion beneath each station. Vertical cross sections of S wave velocities from the surface to depths of 65 and 270 km covering the entire 1000-km profile are constructed by the linear spline interpolation of individual velocity models. The vertical sections are also represented as anomalies relative to the standard velocity model. The most intense low velocity anomalies (from ?3 to ?6%) in the crust and upper mantle are identified beneath the Sayan, Khamar-Daban, and Khangai highlands and the Djida fold zone and agree both with other geophysical data and with the distribution of Late Cenozoic volcanic fields. The results of this work suggest that the activation of Mongolian-Siberian highlands is largely connected with uplift of the asthenosphere to the base of the crust.  相似文献   

Direct imaging with highly diluted apertures – II. Properties of the point spread function of a hypertelescope     

F. Patru  N. Tarmoul  D. Mourard  O. Lardière 《Monthly notices of the Royal Astronomical Society》2009,395(4):2363-2372

In the future, optical stellar interferometers will provide true images thanks to larger number of telescopes and to advanced cophasing subsystems. These conditions are required to have sufficient resolution elements (resel) in the image and to provide direct images in the hypertelescope mode. It has already been shown that hypertelescopes provide snapshot images with a significant gain in sensitivity without inducing any loss of the useful field of view for direct imaging applications. This paper aims at studying the properties of the point spread functions of future large arrays using the hypertelescope mode. Numerical simulations have been performed and criteria have been defined to study the image properties. It is shown that the choice of the configuration of the array is a trade-off between the resolution, the halo level and the field of view. A regular pattern of the array of telescopes optimizes the image quality (low halo level and maximum encircled energy in the central peak), but decreases the useful field of view. Moreover, a non-redundant array is less sensitive to the space aliasing effect than a redundant array.  相似文献   

POLAR investigation of the Sun—POLARIS     

T. Appourchaux  P. Liewer  M. Watt  D. Alexander  V. Andretta  F. Auchère  P. D’Arrigo  J. Ayon  T. Corbard  S. Fineschi  W. Finsterle  L. Floyd  G. Garbe  L. Gizon  D. Hassler  L. Harra  A. Kosovichev  J. Leibacher  M. Leipold  N. Murphy  M. Maksimovic  V. Martinez-Pillet  B. S. A. Matthews  R. Mewaldt  D. Moses  J. Newmark  S. Régnier  W. Schmutz  D. Socker  D. Spadaro  M. Stuttard  C. Trosseille  R. Ulrich  M. Velli  A. Vourlidas  C. R. Wimmer-Schweingruber  T. Zurbuchen 《Experimental Astronomy》2009,23(3):1079-1117

The POLAR Investigation of the Sun (POLARIS) mission uses a combination of a gravity assist and solar sail propulsion to place a spacecraft in a 0.48 AU circular orbit around the Sun with an inclination of 75° with respect to solar equator. This challenging orbit is made possible by the challenging development of solar sail propulsion. This first extended view of the high-latitude regions of the Sun will enable crucial observations not possible from the ecliptic viewpoint or from Solar Orbiter. While Solar Orbiter would give the first glimpse of the high latitude magnetic field and flows to probe the solar dynamo, it does not have sufficient viewing of the polar regions to achieve POLARIS’s primary objective: determining the relation between the magnetism and dynamics of the Sun’s polar regions and the solar cycle.

T. AppourchauxEmail:

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European Venus Explorer (EVE): an in-situ mission to Venus   总被引：1，自引：0，他引：1  

E. Chassefière  O. Korablev  T. Imamura  K. H. Baines  C. F. Wilson  D. V. Titov  K. L. Aplin  T. Balint  J. E. Blamont  C. G. Cochrane  Cs. Ferencz  F. Ferri  M. Gerasimov  J. J. Leitner  J. Lopez-Moreno  B. Marty  M. Martynov  S. V. Pogrebenko  A. Rodin  J. A. Whiteway  L. V. Zasova  J. Michaud  R. Bertrand  J.-M. Charbonnier  D. Carbonne  P. Raizonville 《Experimental Astronomy》2009,23(3):741-760

The European Venus Explorer (EVE) mission was proposed to the European Space Agency in 2007, as an M-class mission under the Cosmic Vision Programme. Although it has not been chosen in the 2007 selection round for programmatic reasons, the EVE mission may serve as a useful reference point for future missions, so it is described here. It consists of one balloon platform floating at an altitude of 50–60 km, one descent probe provided by Russia, and an orbiter with a polar orbit which will relay data from the balloon and descent probe, and perform science observations. The balloon type preferred for scientific goals is one which oscillates in altitude through the cloud deck. To achieve this flight profile, the balloon envelope contains a phase change fluid, which results in a flight profile which oscillates in height. The nominal balloon lifetime is 7 days—enough for one full circumnavigation of the planet. The descent probe’s fall through the atmosphere takes 60 min, followed by 30 min of operation on the surface. The key measurement objectives of EVE are: (1) in situ measurement from the balloon of noble gas abundances and stable isotope ratios, to study the record of the evolution of Venus; (2) in situ balloon-borne measurement of cloud particle and gas composition, and their spatial variation, to understand the complex cloud-level chemistry; (3) in situ measurements of environmental parameters and winds (from tracking of the balloon) for one rotation around the planet, to understand atmospheric dynamics and radiative balance in this crucial region. The portfolio of key measurements is complemented by the Russian descent probe, which enables the investigation of the deep atmosphere and surface.  相似文献   

Single crystal U-Pb zircon age and Sr-Nd isotopic composition of impactites from the Bosumtwi impact structure, Ghana: Comparison with country rocks and Ivory Coast tektites     

Ferrière L  Koeberl C  Thöni M  Liang C 《Chemical Geology》2010,275(3-4):254-261

The 1.07?Myr old Bosumtwi impact structure (Ghana), excavated in 2.1-2.2?Gyr old supracrustal rocks of the Birimian Supergroup, was drilled in 2004. Here, we present single crystal U-Pb zircon ages from a suevite and two meta-graywacke samples recovered from the central uplift (drill core LB-08A), which yield an upper Concordia intercept age of ca. 2145?±?82?Ma, in very good agreement with previous geochronological data for the West African Craton rocks in Ghana. Whole rock Rb-Sr and Sm-Nd isotope data of six suevites (five from inside the crater and one from outside the northern crater rim), three meta-graywacke, and two phyllite samples from core LB-08A are also presented, providing further insights into the timing of the metamorphism and a possibly related isotopic redistribution of the Bosumtwi crater rocks. Our Rb-Sr and Sm-Nd data show also that the suevites are mixtures of meta-greywacke and phyllite (and possibly a very low amount of granite). A comparison of our new isotopic data with literature data for the Ivory Coast tektites allows to better constrain the parent material of the Ivory Coast tektites (i.e., distal impactites), which is thought to consist of a mixture of metasedimentary rocks (and possibly granite), but with a higher proportion of phyllite (and shale) than the suevites (i.e., proximal impactites). When plotted in a Rb/Sr isochron diagram, the sample data points (n?=?29, including literature data) scatter along a regression line, whose slope corresponds to an age of 1846?±?160?Ma, with an initial Sr isotope ratio of 0.703?±?0.002. However, due to the extensive alteration of some of the investigated samples and the lithological diversity of the source material, this age, which is in close agreement with a possible "metamorphic age" of ～?1.8-1.9?Ga tentatively derived from our U-Pb dating of zircons, is difficult to consider as a reliable metamorphic age. It may perhaps reflect a common ancient source whose Rb-Sr isotope systematics has not basically been reset on the whole rock scale during the Bosumtwi impact event, or even reflect another unknown geologic event.  相似文献   

Environmental conservation and the production of new territories: the example of French départements     

Pech Pierre  Dizière Sophie  Gillet Anne-Gabrielle  Mamder Julie  Tichit Marion 《GeoJournal》2010,75(2):149-161

Very important initiatives have been taken and policies have been adopted in the European Union to protect areas of great importance for threatened species and habitats. Protected areas differ broadly in terms of category, natural conditions and administrative organisation, from international initiative such as Biosphere Reserves, European ones with Natura 2000 network until the institution of national and regional protected areas. In France, the administrative subdivisions known as “départements” were created with the French Revolution in the end of the eighteenth century; in 1985 an original and autonomous procedure to establish special protected areas, called “Sensitive Natural Spaces” (SNS) was devolved to them. The scope of this paper is to present an overview of these devolved powers which enable French départements to create protected areas and to levy a departmental tax on sensitive natural spaces (DTSNS). We statistically studied some parameters by multivariate methods in order to explain the choices of this policy by the départements. The huge variations in the way these powers are implemented prove the development of new environmental territories.  相似文献   

Multi-tracer tests to evaluate the hydraulic setting of a complex aquifer system (Brévilles spring catchment, France)     

Pascal Goderniaux  Serge Brouyère  Alexis Gutierrez  Nicole Baran 《Hydrogeology Journal》2010,18(7):1729-1740

For good management of groundwater resources, and to comply with European and national regulations, a detailed understanding of an aquifer’s hydraulic setting is required. In order to better characterize a sandy aquifer that is affected by diffuse pollution (Brévilles spring catchment, Val d’Oise, France), and to quantify the transfer time in the saturated zone, a multi-tracer test involving a new technique, the ‘finite volume point dilution method’, has been performed in natural flow conditions. In November 2005, injections of four different tracers took place in four piezometers involving different locations and depths in the aquifer. Recovery of the tracers was observed at two different places near the aquifer outlet. A particularly long and unusual monitoring exercise (27 months) demonstrated the existence of several different velocities within the sandy layer, which seems to be linked to the decrease of hydraulic conductivity with depth. The new insight and parameter quantification brought by interpretation of these tests contribute to a better characterization of the saturated zone. The particularly long-term monitoring exercise also gives new information to understand and forecast the trend and persistence of groundwater contamination by pesticides in the catchment.  相似文献   

Hydrodynamic characterization of the Arcachon Bay,using model-derived descriptors     

M. Plus  F. Dumas  J.-Y. Stanisière  D. Maurer 《Continental Shelf Research》2009,29(8):1008-1013

A numerical model (MARS-2D) was developed, with the aim of describing the hydrodynamics that prevail in Arcachon Bay. Direct model results as well as derived mixing and transport time-scales (tidal prism, local and integrated flushing times, age of water masses), were used to understand the behaviour of water masses and exchanges between the Bay and its frontiers. Particular attention was paid to the processes that drive the hydrodynamics (tides, wind and rivers), in order to understand their respective influence.The Arcachon Bay hydrodynamic system appears primarily to be highly influenced by tides; secondarily, by winds. About two third of the lagoon total volume is flushed in and out at each tidal cycle, which represent a mean tidal prism of 384 millions of cubic meters. The percentage of seawater flushed out during the ebb, that returns into the lagoon during the following flood flow is very high (return flow factor=0.95). This pattern leads to calculated integrated flushing times (IFT) ranging from 12.8 to 15.9 days, respectively, for the winter 2001 and summer 2005 simulations (two contrasting climatological situations: in summer, light northwesterly winds and low discharges in the rivers and, in winter, stronger southwesterly winds and higher river flows). Moreover, it has been found that northerly and westerly winds tend to reduce the flushing time, whilst southerly and easterly winds tend to hinder the renewal of the water in the Bay. The behaviour of the waters originating from the two main rivers of the lagoon, was studied also by means of the mean age assessment, under varying conditions of river flow and wind regime.  相似文献   

Holocene fire regime changes from multiple-site sedimentary charcoal analyses in the Lourdes basin (Pyrenees,France)     

Damien Rius  Boris Vannière  Didier Galop  Hervé Richard 《Quaternary Science Reviews》2011,30(13-14):1696-1709

One lake and three peat bogs from the Lourdes glacial basin (France) were used for macrocharcoal analyses and fire frequency reconstruction over the entire Holocene (11700 years). The chronology was based upon thirty-three 14C AMS dates. Comparison of the distribution of both CHarcoal Accumulation Rate (CHAR) and fire return intervals showed that charcoal accumulation significantly differs between the lake and the peat bogs, but that frequency calculation overcomes the disparity between these site types. A composite frequency was built from the four individual records to assess regional versus local variability and fire regime controls by comparisons with regional fire activity, Holocene climatic oscillations and vegetation history. The millennial variability can be depicted as follows: relatively high frequency between 8000 and 5000 cal a BP (up to 5 fires/500 yrs), relatively low frequency between 5000 and 3000 cal a BP (down to 0 fires/500 yrs), and an increase between 3000 and 500 cal a BP (up to 4 fires/500 yrs). From 8000 to 5000 cal a BP, fire frequency displays strong synchrony between sites and appears to be mostly driven by increased summer temperature characterizing the Holocene Thermal Maximum (HTM). On the contrary, during the last 3000 years fire frequency was heterogeneous between sites and most probably human-driven. However, higher frequency at the millennial scale during the mid-Holocene strongly suggests that the perception of human-driven fire regime depends on the strength of natural controls.  相似文献