Exponential Gaussian approach for spectral modelling: The EGO algorithm II. Band asymmetry     

Loredana Pompilio  Giuseppe Pedrazzi  Michael A. Craig 《Icarus》2010,208(2):811-823

The present investigation is complementary to a previous paper which introduced the EGO approach to spectral modelling of reflectance measurements acquired in the visible and near-IR range (Pompilio, L., Pedrazzi, G., Sgavetti, M., Cloutis, E.A., Craig, M.A., Roush, T.L. [2009]. Icarus, 201 (2), 781-794). Here, we show the performances of the EGO model in attempting to account for temperature-induced variations in spectra, specifically band asymmetry.Our main goals are: (1) to recognize and model thermal-induced band asymmetry in reflectance spectra; (2) to develop a basic approach for decomposition of remotely acquired spectra from planetary surfaces, where effects due to temperature variations are most prevalent; (3) to reduce the uncertainty related to quantitative estimation of band position and depth when band asymmetry is occurring.In order to accomplish these objectives, we tested the EGO algorithm on a number of measurements acquired on powdered pyroxenes at sample temperature ranging from 80 up to 400 K. The main results arising from this study are: (1) EGO model is able to numerically account for the occurrence of band asymmetry on reflectance spectra; (2) the returned set of EGO parameters can suggest the influence of some additional effect other than the electronic transition responsible for the absorption feature; (3) the returned set of EGO parameters can help in estimating the surface temperature of a planetary body; (4) the occurrence of absorptions which are less affected by temperature variations can be mapped for minerals and thus used for compositional estimates.Further work is still required in order to analyze the behaviour of the EGO algorithm with respect to temperature-induced band asymmetry using powdered pyroxene spanning a range of compositions and grain sizes and more complex band shapes.  相似文献   

Transpressional tectonics and nappe stacking along the Southern Variscan Front of Morocco   总被引：1，自引：0，他引：1  

Andrea Cerrina Feroni  Alessandro Ellero  Marco G. Malusà  Giovanni Musumeci  Giuseppe Ottria  Riccardo Polino  Leonardo Leoni 《International Journal of Earth Sciences》2010,99(5):1111-1122

The Southern Variscan Front in the Tinerhir area involves Palaeozoic allochthonous units (Ouaklim and Tilouine units) thrust onto the northern edge of the West African Craton during late Carboniferous time. Illite crystallinity data highlight an anchizonal grade for the Ouaklim Unit, and a diagenesis-anchizone transition for the Tilouine Unit during deformation phase D1. The tectonic stack is crosscut by major dextral reverse faults bounding E–W trending domains of dominant shortening deformation (central domain) and strike-slip deformation (northern and southern domains), later segmented by a network of post-Variscan faults. This complex deformation pattern is the result of kinematic partitioning of dextral transpression along the Southern Variscan Front, coeval with the Neovariscan (300–290 Ma) oblique convergence observed at the scale of the whole Moroccan Variscides. Partitioning of dextral transpression described in the Tinerhir area is consistent with dextral wrench faulting along the Tizi n’ Test Fault, and with Appalachian-style south-directed thrusting in the Tinerhir and Bechar-Bou Arfa areas.  相似文献   

Relationship between soil CO<Subscript>2</Subscript> flux and volcanic tremor at Mt. Etna: Implications for magma dynamics     

Andrea Cannata  Gaetano Giudice  Sergio Gurrieri  Placido Montalto  Salvatore Alparone  Giuseppe Di Grazia  Rocco Favara  Stefano Gresta  Marco Liuzzo 《Environmental Earth Sciences》2010,61(3):477-489

Large variations of the CO₂ flux through the soil were observed between November 2002 and January 2006 at Mt. Etna volcano. In many cases, the CO₂ flux was strongly influenced by changes in air temperature and atmospheric pressure. A new filtering method was then developed to remove the atmospheric influences on soil CO₂ flux and, at the same time, to highlight the variations strictly related to volcanic activity. Successively, the CO₂ corrected data were quantitatively compared with the spectral amplitude of the volcanic tremor by cross correlation function, cross-wavelet spectrum and wavelet coherence. These analyses suggested that the soil CO₂ flux variations preceded those of volcanic tremor by about 50 days. Given that volcanic tremor is linked to the shallow (a few kilometer) magma dynamics and soil CO₂ flux related to the deeper (~12 km b.s.l.) magma dynamics, the “delayed similarity” between the CO₂ flux and the volcanic tremor amplitude was used to assess the average speed in the magma uprising into the crust, as about 170–260 m per day. Finally, the large amount of CO₂ released before the onset of the 2004–2005 eruption indicated a deep ingression of new magma, which might have triggered such an eruption.  相似文献   

Rhyacian (2.23–2.20 Ga) juvenile accretion in the southern São Francisco craton,Brazil: Geochemical and isotopic evidence from the Serrinha magmatic suite,Mineiro belt     

Ciro Alexandre Ávila  Wilson Teixeira  Umberto Giuseppe Cordani  Candido Augusto Veloso Moura  Ronaldo Mello Pereira 《Journal of South American Earth Sciences》2010,29(2):464-482

The Serrinha magmatic suite (Mineiro belt) crops out in the southern edge of the São Francisco craton, comprising the Brito quartz-diorite, Brumado de Cima and Brumado de Baixo granodiorites, granophyres and felsic sub-volcanic and volcanic rocks, part of which intruded into the Nazareno greenstone belt. The suite rocks have petrographic features that are consistent with magma supercooling due to the low water content combined with volatile loss, leading to crystallization of quartz and alkaline feldspar at the rims of plagioclase phenocrysts (granophyric intergrowth). The investigated rocks are sub-alkaline, calc-alkaline and show low content in rare earth elements. The U–Pb zircon crystallization ages for the Brumado de Cima granodiorite [2227 ± 22 (23) Ma] and a coeval granophyre [2211 ± 22 (23) Ma], coupled with available single-zircon Pb evaporation ages for the Brito and Brumado de Baixo plutons, are significantly older than the “Minas orogeny” (ca. 2100–2050 Ga) of Quadrilátero Ferrífero area, eastward from the Serrinha suite. Our data establish an early Rhyacian event tectonically linked with the evolution of the Mineiro belt. The bulk Nd isotopic signature [low negative to positive ε_Nd(t) values] of the Serrinha samples are consistent with the important role of Paleoproterozoic mantle components in the magma genesis. The integrated geologic, geochemical and isotopic information suggests that Paleoproterozoic evolution of the Mineiro belt initiated in a passive continental margin basin with deposition of the Minas Supergroup at ca. 2500 Ma. This stage was succeeded by outboard rupture of the oceanic lithosphere with development and coalescence of progressively younger magmatic arcs during Rhyacian time. One of the earliest arcs formed the Serrinha suite. The tectonic collage of the Serrinha and Ritápolis (2190–2120 Ma) arcs produced the NE–SW Lenheiro shear zone, resulting in mylonitization and recrystallization of both the granitoid intrusions and host rocks. As a matter of fact juxtaposition of distinct magmatic units in age and origin took place along the Lenheiros structure in this sector of the Mineiro belt.  相似文献   

The potential for Earth-mass planet formation around brown dwarfs     

Matthew J. Payne  Giuseppe Lodato 《Monthly notices of the Royal Astronomical Society》2007,381(4):1597-1606

Recent observations point to the presence of structured dust grains in the discs surrounding young brown dwarfs, thus implying that the first stages of planet formation take place also in the substellar regime. Here, we investigate the potential for planet formation around brown dwarfs and very low-mass stars according to the sequential core accretion model of planet formation. We find that, for a brown dwarf mass 0.05 M_⊙, our models predict a maximum planetary mass of  ∼5   M_⊕  , orbiting with semimajor axis ∼ 1 au. However, we note that the predictions for the mass–semimajor axis distribution are strongly dependent upon the models chosen for the disc surface density profiles and the assumed distribution of disc masses. In particular, if brown dwarf disc masses are of the order of a few Jupiter masses, Earth-mass planets might be relatively frequent, while if typical disc masses are only a fraction of Jupiter mass, we predict that planet formation would be extremely rare in the substellar regime. As the observational constraints on disc profiles, mass dependencies and their distributions are poor in the brown dwarf regime, we advise caution in validating theoretical models only on stars similar to the Sun and emphasize the need for observational data on planetary systems around a wide range of stellar masses. We also find that, unlike the situation around solar-like stars, Type II migration is totally absent from the planet formation process around brown dwarfs, suggesting that any future observations of planets around brown dwarfs would provide a direct measure of the role of other types of migration.  相似文献   

The role of preconditioning in the solution to FE coupled consolidation equations by Krylov subspace methods     

Massimiliano Ferronato  Giorgio Pini  Giuseppe Gambolati 《国际地质力学数值与分析法杂志》2009,33(3):405-423

The repeated solution in time of the linear system arising from the finite element integration of coupled consolidation equations is a major computational effort. This system can be written in either a symmetric or an unsymmetric form, thus calling for the implementation of different preconditioners and Krylov subspace solvers. The present paper aims at investigating when either a symmetric or an unsymmetric approach should be better used. The results from a number of representative numerical experiments indicate that a major role in selecting either form is played by the preconditioner rather than by the Krylov subspace method itself. Two other important issues addressed are the size of the time integration step and the possible lumping of the flow capacity matrix. It appears that ad hoc block constrained preconditioners provide the most robust algorithm independently of the time step size, lumping, and symmetry. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Repeated GPS surveys across the Ionian Sea: evidence of crustal deformations   总被引：1，自引：0，他引：1  

Marco Anzidei  Paolo Baldi  Giuseppe Casula  Mattia Crespi  Federica Riguzzi 《Geophysical Journal International》1996,127(2):257-267

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Ground deformations in collapsed caldera structures     

Giuseppe De Natale  Folco Pingue 《Journal of Volcanology and Geothermal Research》1993,57(1-2)

A method is presented to analyze the effect of stress-strain discontinuities on the ground deformations generated by a pressure source. This is meant to simulate the effects due to caldera structures, likely to present fractured zones at the borders of the collapsed area. A method originally developed by Crouch (1976) to solve plane-strain problems has been used to simulate deformation curves for several source and discontinuity geometries. The main result is that the location of the discontinuities controls the extension of the deformed zone, and always reduces it with respect to a continuous medium. With respect to a homogeneous medium the presence of lateral discontinuities also acts towards lowering the overpressure required to produce a given amount of deformation. These results indicate that, when analyzing ground deformations in calderas, the use of classical methods involving continuous media should be avoided, or at least taken with caution. These methods, in fact, assume that the extension of the deformed zone is only linked to the source depth.Some examples of ground deformations in active calderas have been analyzed in the framework of the results obtained from theoretical modeling. Four calderas recently affected by ground deformations have been considered: Rabaul (New Guinea), Campi Flegrei (Italy), Long Valley and Yellowstone (U.S.A.). The effects of collapsed structures on the deformation field are possibly evidenced for all the four calderas. At Rabaul and Campi Flegrei, the fracture systems mainly affecting the ground deformations probably represent younger, innermost collapses and are well evidenced by seismicity studies. Ground deformations are here concentrated in an area much smaller than the one enclosed by geologically visible caldera rims. In particular, at Rabaul, the effect of the innermost collapse can explain the high concentration of the uplift in the period 1971–1985, previously modeled by a very shallow source (1–3 km) in terms of overpressure in the main magma chamber, probably located at 4–5 km of depth.  相似文献   

Crystal-chemistry of a unique jadeite-rich acmite-poor omphacite from the Nybø eclogite pod,Sørpollen,Nordfjord, Norway     

David C. Smith  Annibale Mottana  Giuseppe Rossi 《Lithos》1980,13(3):227-236

An omphacite from the Nybø eclogite pod, Norway, has a chemical composition which plots within the gap, often regarded as a miscibility gap, which is evident in all previous compilations of natural jadeite-rich acmite-poor omphacite compositions. Its cation site populations determined by crystal structure refinement accord well with its chemical composition analysed by electron microprobe. Its disordered space group C2/c symmetry extends the known compositional range of C2/c pyroxene. The postulated miscibility gap is regarded as real and wide at low temperatures, but it appears to narrow with increasing temperature or ultimately with increasing acmite proportion. The adjacent primitive symmetry field appears to initially widen with increasing temperature or increasing acmite proportion, at the expense of the diminishing miscibility gap, before finally closing with further increase.  相似文献   

Trace elements in tentacles from the jellyfish Pelagia noctiluca     

Giuseppe Cimino  Maria Alfa  Giuseppina La Spada 《Marine pollution bulletin》1983,14(5):197-198

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