Middle Eocene to Early Miocene sedimentary evolution of the western Lombardian segment of the South Alpine foredeep (Italy)     

Andrea Di Giulio  Barbara Carrapa  Roberto Fantoni  Luciano Gorla  Antonio Valdisturlo 《International Journal of Earth Sciences》2001,90(3):534-548

The main steps of the sedimentary evolution of the west Lombardian South Alpine foredeep between the Eocene and the Early Miocene are described. The oldest is a Bartonian carbonate decrease in hemipelagic sediments linked with an increase in terrigenous input, possibly related to a rainfall increase in the Alps. Between the Middle Eocene and the early Chattian, a volcanoclastic input is associated with an extensional tectonic regime, coeval with magma emplacement in the southern-central Alps, and with volcanogenic deposits of the European foredeep and Apennines, suggesting a regional extensional tectonic phase leading to the ascent of magma. During Late Eocene to Early Oligocene, two periods of coarse clastic sedimentation occurred, probably controlled by eustasy. The first, during Late Eocene, fed by a local South Alpine source, the second, earliest Oligocene in age, supplied by the Central Alps. In the Chattian, a strong increase in coarse supply records the massive erosion of Central Alps, coupled with a structures growth phase in the subsurface; it was followed by an Aquitanian rearrangement of the Alpine drainage systems suggested by both petrography of clastic sediments and retreat of depositional systems, while subsurface sheet-like geometry of Aquitanian turbidites marks a strong decrease in tectonic activity.  相似文献   

Time-clustering analysis of volcanic occurrence sequences     

Luciano Telesca  Vincenzo CuomoVincenzo Lapenna  Maria Macchiato 《Physics of the Earth and Planetary Interiors》2002,131(1):47-62

We investigate the time dynamics of worldwide volcanic activity in order to find the presence of time correlation structures, by applying the Fano factor (FF) method. The analysis, performed on 35 time-occurrence volcanic eruptive sequences with volcanic explosivity index (VEI≥0) has revealed fractal behaviors in the most of the data sets considered, with fractal exponent α ranging from ∼0.2 to 0.9.  相似文献   

Discovery of a highly dispersed pulsar at l=304°     

Luciano Nicastro  & Simon Johnston 《Monthly notices of the Royal Astronomical Society》1998,293(3):L65-L67

We report the discovery of a pulsar with a Galactic longitude of 304° and a dispersion measure (DM) of 875 cm⁻³ pc. PSR J1302−63 has the second largest DM of any known pulsar. It is also relatively weak, with a flux density of only 0.2 mJy at 1500 MHz. This is the 13th pulsar with a DM greater than 400 cm⁻³ pc located more than 50° from the Galactic Centre. It provides further evidence for a significant pulsar population and enhanced electron densities within the major spiral arms.  相似文献   

Scintillation parameters for 49 pulsars     

Simon Johnston  Luciano Nicastro  & Bärbel Koribalski 《Monthly notices of the Royal Astronomical Society》1998,297(1):108-116

We report on multi-epoch, multifrequency observations of 64 pulsars with high spectral and time resolution. Scintillation parameters were obtained for 49 pulsars, including 13 millisecond pulsars. Scintillation speeds were derived for all 49, which doubles the number of pulsars with speeds measured in this way. There is excellent agreement between the scintillation speed and proper motion for the millisecond pulsars in our sample using the simple assumption of a mid-placed scattering screen. This indicates that the scaleheight of scattering electrons is similar to that of the dispersing electrons. In addition, we present observations of the Vela pulsar at 14 and 23 GHz, and show that the scintillation bandwidth scales as ν^3.93 over a factor of 100 in observing frequency. We show that for PSR J0742−2822, and perhaps PSR J0837−4135, the Gum nebula is responsible for the high level of turbulence along their lines of sight, contrary to previous indications. There is a significant correlation between the scintillation speeds and the product of the pulsar's period and period derivative for the 'normal' pulsars. However, we believe this to be caused by selection effects both in pulsar detection experiments and in the choice of pulsars used in scintillation studies.  相似文献   

Crystal-chemistry and cation ordering in the system diopside-jadeite: A detailed study by crystal structure refinement     

Giuseppe Rossi  David C. Smith  Luciano Ungaretti  M. Chiara Domeneghetti 《Contributions to Mineralogy and Petrology》1983,83(3-4):247-258

The Nybö eclogite pod in Norway is characterized by a great variety of clinopyroxene compositions with Jd contents ranging from less than 5% up to nearly 80%, whilst Ac+Hd contents remain almost constant (mostly within 10±5%).Unconstrained X-ray structure refinement has been carried out on 16 pyroxene crystals (8 with C2/c and 8 with P2/n space group) from the Nybö eclogite, and also on one omphacite crystal (from Lago Mucrone in the Sesia-Lanzo Zone, Western Alps) which displays the highest degree of cation ordering yet described. The final discrepancy factors range from 0.014 to 0.029. The population of the sites has been determined on the basis of bond length considerations and of the results of the site occupancy refinement. Six of these crystals were subsequently analysed by electron microprobe.The tetrahedral sites are occupied by Si with negligible amounts of Al. Al, Mg, Fe³⁺ and Fe²⁺ occur at the octahedral sites; in the ordered P2/n crystals Al and Fe³⁺ are concentrated at the M11 site, whilst Mg and Fe²⁺ are concentrated and the M1 site. The eight-coordinated sites contain Ca and Na with negligible amounts of Fe and/or Mg. Ordering of Ca and Na takes place in the P2/n samples in such a way that in the most ordered crystal the M2 site contains almost exactly 0.75 Na+0.25 Ca and the M21 site 0.25 Na+0.75 Ca.Some geometrical features of the tetrahedra as well as of the octahedra (e.g. tetrahedral quadratic elongation and TILT angle) are not a simple linear function of composition, even when no change in space group occurs. The crystals evidently do not behave like a binary system of the two components, Di and Jd, but behave rather as if the composition Di_0.50 Jd_0.50 was a distinct end member.The boundaries between disordered and ordered phases in the Nybö pyroxenes fall at about 0.35 and 0.65 Jd/(Di+ Jd), in close agreement with the previous TEM investigations.The degree of order varies with composition following a bell-shaped curve: different coaxial bell-shaped curves can be drawn for crystals which have similar compositions but come from different metamorphic environments. The order vs composition diagrams may be useful for the interpretation of the P-T-t histories of the host rocks.  相似文献   

Pumpellyite in low-grade metamorphic rocks from Ligurian and Lucanian Apennines,Maritime Alps and Calabria (Italy)     

Luciano Cortesogno  Gabriella Lucchetti  Piera Spadea 《Contributions to Mineralogy and Petrology》1984,85(1):14-24

In the Ligurian Apennines and the Brianzonese area of the Maritime Alps (Northern Italy), and in the Lucanian Apennines and Calabria (Southern Italy), pumpellyite formed during the Alpine metamorphism is widespread in terranes of Late Paleozoic to Miocene age, particularly in mafic ophiolites (Tethyan ophiolites of Jurassic-Early Cretaceous age).Pumpellyite developed under variable metamorphic conditions, which include zeolite, prehnite-pumpellyite, pumpellyite-actinolite, lawsonite-albite and blueschist facies. Pumpellyite from rocks belonging to all these facies was studied in 30 specimens of different chemistry, derived mostly from ophiolitic basalt and gabbro, but also from gneiss, amphibolite, and greywacke protoliths.Microprobe data give evidence of strong compositional variations of pumpellyite. The ranges are extreme for Al and Fe^tot (Al₂O₃=18.74–30.91; FeO_tot=0.46–12.71), to a lesser extent for Mg (MgO=0.58–4.00), with a reciprocal variation of Al and Fe^tot which suggests that most Fe is Fe³⁺.Pumpellyite compositions can be related with the metamorphic conditions, particularly an increase of the Al/Fe^tot ratio with increasing pressure, but larger compositional variation for each facies in the Al-Fe^tot-Mg diagram than those previously described was recognized. Particularly the compositions of pumpellyite from the pumpellyite-actinolite and blueschist fades assemblages extend towards higher Fe^tot contents. Moreover, pumpellyites of the lawsonite-albite facies rocks result to be more aluminous than in blueschist facies; such relations appear to be inconsistent with that expected by the effects of pressure on the Al content.As the rocks are generally incompletely re-equilibrated, their bulk chemistry is not an important factor of pumpellyite composition; in fact the correlations of Al, Fe^tot and Mg are low. The local environment of crystallization, more evidently the composition of the precursor minerals, seems to be a major controlling factor. The observed topologic relations indicate that either the nature of the precursor mineral, or the presence of relict phases have a great influence on the pumpellyite composition. The observed variations within individual specimens, as well as the interspecimen ones, can be explained by small-scale inhomogeneities and in some cases by differences in the activity of O₂.It can be therefore concluded that the composition of pumpellyite often reflects disequilibrium crystallization and cannot be generally used as an indicator of metamorphic conditions.  相似文献   

1980–1990: Ten years of geochemical investigation at Phlegrean Fields (Italy)     

Marino Martini  Luciano Giannini  Antonella Buccianti  Franco Prati  Paola Cellini Legittimo  Paolo Iozzelli  Bruno Capaccioni 《Journal of Volcanology and Geothermal Research》1991,48(1-2)

A systematic geochemical investigation on the thermal manifestations of the volcanic area of Phlegrean Fields started in 1980, with the aim of obtaining useful information about the changes possibly occurring at the same time of vertical ground movements, termed as “bradyseismic”, which frequently interested this area.The attention was initially given to the fumaroles and the boiling pools of Solfatara and Pisciarelli, then subsequently extended to thermal springs, dug wells, and crater lakes.Analytical data pertaining to a period preceding the last crisis of 1982–1984 were then available, as well as other data collected during the previous crisis of 1970; a comprehensive picture of the variations observed before, during and after the acceleration of vertical movement has been drawn.According to the results obtained, the intrusion of a magmatic body as the trigger of the observed ground deformation is considered unrealistic. The whole area appears now in a quiet stage, and no further perturbation is expected without previous significant tectonic activity; chemical precursors appear suitable for an early detection of changes occurring at depth, to forecast possible consequences to be expected in the surface environment.  相似文献   

Potential effects of climate changes on soil–atmosphere interaction and landslide hazard     

Guido Rianna  Luca Comegna  Paola Mercogliano  Luciano Picarelli 《Natural Hazards》2016,84(2):1487-1499

  相似文献   

The mechanics of mudslides as a cyclic undrained–drained process     

Luca Comegna  Luciano Picarelli  Gianfranco Urciuoli 《Landslides》2007,4(3):217-232

Data collected by monitoring suggest that the movement of mudslides essentially develops through alternating stages of undrained–drained deformation. Undrained conditions are established as a consequence of landslide mobilisation or reactivation. Every acceleration phase is followed by progressive deceleration associated with dissipation of excess pore pressure. This paper reports the results of some simple numerical analyses performed to investigate the role of pore pressure on mudslide behaviour.  相似文献   

Non-extensivity analysis of seismicity within four subduction regions in Mexico     

Sharon M. Valverde-Esparza  Alejandro Ramírez-Rojas  E. Leticia Flores-Márquez  Luciano Telesca 《Acta Geophysica》2012,60(3):833-845

The non-extensivity approach based on the Tsallis entropy has been applied to seismicity that occurred from 1988 to 2010 along the Mexican South Pacific coast. We analyzed four different regions, characterized by different subduction patterns. Our results indicate a possible correlation between the non-extensive parameters and the seismicity pattern associated with the inclination angle of each subduction region.  相似文献