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Bedrock fission‐track analysis, high‐resolution petrography and heavy mineral analyses of sediments are used to investigate the relationships between erosion and tectonics in the Western Alps. Along the Aosta Valley cross‐section, exhumation rates based on fission‐track data are higher in the fault‐bounded western block than in the eastern block (0.4–1.5 vs. 0.1–0.3 mm yr−1). Erosion rates based on the analysis of bed‐load in the Dora Baltea drainage display the same pattern and have similar magnitudes in the relative sub‐basins (0.4–0.7 vs. 0.04–0.08 mm yr−1). Results highlight that climate, relief and lithology are not the controlling factors of erosion in the Western Alps. The main driving force behind erosion is instead tectonics that causes the differential upward motion of crustal blocks. 相似文献
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Richard P. BINZEL Ettore PEROZZI Andrew S. RIVKIN Alessandro ROSSI Alan W. HARRIS Schelte J. BUS Giovanni B. VALSECCHI Stephen M. SLIVAN 《Meteoritics & planetary science》2004,39(3):351-366
Abstract— Using an H‐plot analysis, we identify 234 currently known near‐Earth objects that are accessible for rendezvous with a “best case” delta‐V of less than 7 km/s. We provide a preliminary compositional interpretation and assessment of these potential targets by summarizing the taxonomic properties for 44 objects. Results for one‐half (22) of this sample are based on new spectroscopic measurements presented here. Our approach provides an easy‐to‐update method for giving guidelines to both observers and mission analysts for focusing on objects for which actual mission opportunities are most likely to be found. Observing prospects are presented for categorizing the taxonomic properties of the most accessible targets that are not yet measured. 相似文献
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Gabriele Giuli Eleonora Paris Giovanni Pratesi Christian Koeberl Curzio Cipriani 《Meteoritics & planetary science》2003,38(8):1181-1186
Abstract— Libyan Desert Glass (LDG) is an enigmatic type of glass that occurs in western Egypt in the Libyan Desert. Fairly convincing evidence exists to show that it formed by impact, although the source crater is currently unknown. Some rare samples present dark‐colored streaks with variable amounts of Fe, and they are supposed to contain a meteoritic component. We have studied the iron local environment in an LDG sample by means of Fe K‐edge highresolution X‐ray absorption near edge structure (XANES) spectroscopy to obtain quantitative data on the Fe oxidation state and coordination number in both the Fe‐poor matrix and Fe‐rich layers. The pre‐edge peak of the high‐resolution XANES spectra of the sample studied displays small but reproducible variations between Fe‐poor matrix and Fe‐rich layers, which is indicative of significant changes in the Fe oxidation state and coordination number. Comparison with previously obtained data for a very low‐Fe sample shows that, while iron is virtually all trivalent and in tetrahedral coordination ([4]Fe3+) in the low‐Fe sample, the sample containing the Fe‐rich layers display a mixture of tetra‐coordinated trivalent iron ([4]Fe3+) and penta‐coordinated divalent iron ([5]Fe2+), with the Fe in the Fe‐rich layer being more reduced than the matrix. From these data, we conclude the following: a) the significant differences in the Fe oxidation state between LDG and tektites, together with the wide intra‐sample variations in the Fe‐oxidation state, confirm that LDG is an impact glass and not a tektite‐like glass; b) the higher Fe content, coupled with the more reduced state of the Fe, in the Fe‐rich layers suggests that some or most of the Fe in these layers may be directly derived from the meteoritic projectile and that it is not of terrestrial origin. 相似文献
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Marcello Franceschelli Isabella Memmi Giovanni Gianelli 《Contributions to Mineralogy and Petrology》1991,109(2):151-158
Low temperature metamorphosed clastic rocks of northern Apennines (Verrucano) contain detrital and metamorphic muscovite along with aggregates of interleaved phyllosilicate grains. The extent of celadonite substitution in the metamorphic muscovite progressively increases from Al-rich pyrophyllite-bearing samples to Al-poor K-feldspar-bearing samples and appears to be compatible with the phase relation in the AKF and AKNa diagrams. Some detrital muscovite grains, not equilibrated with the present metamorphic mineral assemblages, seem to be unreacted grains retaining their premetamorphic composition. The chemistry of the re-equilibrated detrital muscovite is mainly controlled by the activity of Al2O3 that is implied by mineral assemblages in the host rocks and is independent of the original composition of detrital mica. Four types of phyllosilicate associations in the interleaved phyllosilicate grains were recognized: 1) muscovite- pyrophyllite-sudoite; 2) muscovite-pyrophyllite-chlorite; 3) muscovite-paragonite-chlorite; 4) muscovite-chlorite. A microstructural and petrological model is proposed for the origin of interleaved phyllosilicate grains in the Verrucano rocks. The model supports the idea that the interleaved phyllosilicate grains are the result of the trend towards equilibrium between detrital muscovite, metamorphic mineral assemblages and the fluid phase. 相似文献