Deformation and metamorphism in the Fenes Nappe (southern Apuseni Mountains,Romania)Déformation et métamorphisme dans la nappe de Fenes (monts Apuseni méridionaux,Roumanie)     

Alessandro Ellero  Leonardo Leoni  Michele Marroni  Ionel Nicolae  Luca Pandolfi  Franco Sartori 《Comptes Rendus Geoscience》2002,334(5):347-354

The Fenes Nappe belongs to the stack of tectonic units cropping out in the southern Apuseni Mts (Romania). It is characterised by a structural history consisting of two folding phases that developed during the time spanning from Early Aptian to Late Maastrichtian. The D1 phase produced west-northwest-verging, isoclinal to very tight folds, associated to a slaty cleavage. The main metamorphic imprint of the Fenes Nappe is linked to this deformation phase; illite and chlorite ‘crystallinity’ values indicate metamorphic conditions of the late diagenesis, close to the diagenetic zone/anchizone boundary. The subsequent D2 phase produced north-northwest-verging, parallel folds, not associated with synkinematic recrystallisation. These phases are interpreted as developed during a structural path, which includes burial at a depth of 8–10 km, followed by exhumation at shallower structural levels. To cite this article: A. Ellero et al., C. R. Geoscience 334 (2002) 347–354.  相似文献   

Magma contamination by direct wall rock interaction: constraints from xenoliths from the walls of a carbonate-hosted magma chamber (Vesuvius 1944 eruption)     

Aldo Del Moro  Paolo Fulignati  Paola Marianelli  Alessandro Sbrana   《Journal of Volcanology and Geothermal Research》2001,112(1-4)

During the 1944 eruption of Vesuvius different types of xenoliths were ejected. They represent fragments of the walls of a low volume (<0.5 km³) shallow (3–4 km depth) magma chamber. The study of these xenoliths enables us to estimate the amount of contamination occurring at the boundary of a high-T alkaline magma chamber hosted in carbonate rocks. The process of contamination of the magma by carbonates can be modelled, using isotopic and chemical data, as a mixing between magma and marbles. Mass exchanges occur at the boundary between the crystallizing magma and marble wall rocks, where endoskarn forms. The contamination of the solidification front of the chamber is very limited. The solidification front and the skarn shell effectively isolate the interior of the magma chamber from new inputs of contaminants from the carbonate wall rocks. Therefore, the main volume of magma, hosted in the magma chamber, did not undergo any significant mass exchange with the wall rocks.  相似文献   

Multiple sector collapses at stromboli volcano, Italy: how they work     

Alessandro Tibaldi 《Bulletin of Volcanology》2001,63(2-3):112-125

This paper demonstrates that four large sector collapses have affected the NW flank of the Stromboli volcano in the past 13 ka, alternating with growth phases, in order to contribute to the evaluation of the critical conditions which trigger lateral collapses, a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented, and a computation of the landslide volume. This reconstruction is based on new field data plotted in three dimensions. Prior to the initial 13-ka collapse, the volcano was 1125±100 m high above sea level. The collapse had a volume of 2.23±0.87 km³, whereas the pre-collapse volcano volume was 218.8±7.7 km³. The next edifice that failed was 900±70 m high a.s.l. The collapse volume was 1±0.54 km³, with a precollapse volcano volume of 201.4±5.4 km³. The edifice then grew to 1000±60 m a.s.l. The third collapse had a volume of 1.08±0.39 km³ and occurred within a volcano with a volume of 209.1±4.6 km³. This was followed by a new growth phase followed by the last collapse with a volume of 0.73±0.22 km³. The volcano volume was about the same as the present one. The present active crater zone is at 780 m a.s.l. in the first three collapses, sliding surfaces cut the main magma conduit. In the last collapse, the upper scarp coincided with the conduit location. Dyking along a main NE-trending weakness zone across the volcano summit exerted a lateral force for collapse inception. The decrease of the landslide volumes with the age, and the concentric scarps of the four collapses, suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent. This is interpreted as due to: (a) successively weaker eruptive products from dominantly lavas to dominantly pyroclastics; and (b) the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane.  相似文献   

Insights into present-day crustal motion in the central Mediterranean area from GPS surveys   总被引：3，自引：0，他引：3  

Marco Anzidei  Paolo Baldi  Giuseppe Casula  Alessandro Galvani  Enzo Mantovani  Arianna Pesci  Federica Riguzzi  Enrico Serpelloni 《Geophysical Journal International》2001,146(1):98-110

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The main secular resonances ν6, vs and ν16 in the asteroid belt     

Alessandro Morbidelli  Jacques Henrard 《Celestial Mechanics and Dynamical Astronomy》1991,51(2):169-197

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The 1906 eruption of Vesuvius: from magmatic to phreatomagmatic activity through the flashing of a shallow depth hydrothermal system     

Antonella Bertagnini  Patrizia Landi  Roberto Santacroce  Alessandro Sbrana 《Bulletin of Volcanology》1991,53(7):517-532

The April 1906 eruption of Vesuvius is the type-example of the final eruptions that close the short cycles of semi-persistent activity that characterized the volcano in the 1631–1944 period. The eruption had a marked explosive character that accompanied the emission of lava from several vents on the southern slopes of the volcano. The observed sequence of events was characterized by repeated fluctuations of the magma level within the conduit, by large lava fountains, by conduit partial collapses, and by the final explosive decapitation of the summit cone. Contemporary chronicles, although frequently contradictory, allow reconstruction of the eruption, which can be divided into four main phases: (1) lateral lava effusions; (2) lava fountains; (3) gas-pyroclasts column; (4) low dense clouds. Pyroclastic deposits of the Monte Somma ridge and northeastern slope can be related to observed and described events and mainly refer to the 2nd and 3rd phases. The increase in the degree of fragmentation of the juvenile component together with the marked increase of the lithic component and morphologic evidence emphasize the repeated occurrence of magmawater interaction. This was most spectacular in the 3rd phase of the eruption in which, after the decapitation of the cone, a high gas-pyroclasts eruption column was formed. Because of the nature of the lithic fragments (mainly hydrothermally altered and metasomatic rocks), the huge amount of steam, and the high lithic/juvenile ratio, it is unlikely that the largest part of the energy in play was related to the contact between magma and cold phreatic water. We suggest that most of the steam involved in this phase of the eruption came from flashing of the hydrothermal system connected to the very shallow feeding system of the volcano and formed as a consequence of repeated subsurface intrusions between 1872 and 1906. Juvenile products were ejected through the eruption, and represent (at least) two different magma bodies: the first (older) was erupted during the initial phase of the eruption and was exhausted at the beginning of the lava fountains phase, when fresh magma was involved in the eruption.  相似文献   

Search for Gamma Ray Bursts of energy Eγ ≥10 GeV and Eγ ≥ 100 TeV in correlation with BATSE events     

M. Aglietta  B. Alessandro  P. Antonioli  F. Arneodo  L. Bergamasco  M. Bertaina  A. Campos Fauth  A. Castellina  C. Castagnoli  A. Chiavassa  G. Cini  B. D'Ettorre Piazzoli  G. Di Sciascio  W. Fulgione  P. Galeotti  P. L. Ghia  M. Iacovacci  G. Mannocchi  C. Melagrana  C. Morello  G. Navarra  L. Riccati  O. Saavedra  G. C. Trinchero  P. Vallania  S. Vernetto 《Astrophysics and Space Science》1995,231(1-2):351-354

We present the results of a search for Gamma Ray Bursts at energies E 10 GeV and E 100 TeV made by the EAS-TOP Air Shower Array in correlation with 50 events detected by BATSE in the last 3 years.This analysis gives an indication of the sensitivity of air shower arrays in the detection of GRBs at energies beyond the range seen by satellite experiments.  相似文献   

PAssive COastal TOMography: an Innovative Approach for the Remote Monitoring of Sea Temperature     

Enrico De  Marinis  Paola Picco  Alessandro Crise  Otello Gasparini  Stefano Salon 《Marine Ecology》2002,23(S1):122-137

Abstract. This paper describes a new Ocean Acoustic Tomography (OAT) methodology - a passive tomography - presently in an advanced development phase. This technique has been developed for long-term, extensive, remote monitoring of the seawater temperature spatial distribution, which is estimated from the received noise emitted from ships of opportunity. To test the passive tomographic processor under controlled conditions, the components of the naval noise from different kinds of vessels was analysed and realistic naval noise was simulated. The feasibility of the proposed methodology was confirmed by test-runs on semi-synthetic data; its capability to resolve temperature profiles will be better assessed with the use of real acoustic and environmental data collected during the INTIMATE00 experiment performed in October 2000 in the Atlantic Ocean off the Portuguese coast. An analysis of the space and time variability of the Empirical Orthogonal Function (EOF) decomposition of the sound speed (SSP) in the Mediterranean Sea has been carried out to identify areas where acoustic tomography can be successfully applied. Results from simulations in the South Adriatic Sea, which was identified as a region with a high sound speed variability associated with the seasonal cycle and with the main oceanographic processes, are reported.  相似文献   

Intrusive mechanism of the 2002 NE-rift eruption at Mt Etna (Italy) modelled using GPS and gravity data     

Alessandro Bonforte  Daniele Carbone  Filippo Greco  Mimmo Palano 《Geophysical Journal International》2007,169(1):339-347

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Thermal expansion and dehydroxylation of phengite micas     

Mauro Gemmi  Marco Merlini  Alessandro Pavese  Nadia Curetti 《Physics and Chemistry of Minerals》2008,35(7):367-379

Phengite samples (2M ₁ and 3T politypes) and a synthetic end-member muscovite specimen were studied by in situ high-temperature synchrotron radiation X-ray diffraction. The measured volume thermal expansion of 2M ₁ phengite (<α _V> ≈ 36.6 × 10⁻⁶ K⁻¹) was systematically greater than <α _V> of the 3T polytype (≈33.3 × 10⁻⁶ K⁻¹). A positive linear correlation between the average thermal expansion on (001) plane and the mean tetrahedral rotation angle at ambient condition is proposed on the ground of new measurements and literature data. Dehydroxylation processes were observed in 2M ₁, starting at 1,000 K in 3T at 800 and 945 K in synthetic muscovite. Rietveld refinements allowed a determination of structural variations upon heating of phengite samples and their dehydroxylate phases. The phengite structure expands by regularizing the tetrahedral sheet and by reducing the bond length differences between the outer and inner coordination shell of the interlayer site. The dehydroxylate phase derived from 2M ₁ is characterized by fivefold polyhedra in the low temperature form as a consequence of two OH groups reacting to form H₂O + O (residual). The dehydroxylate exhibits an increase of the cation–cation distances along the M–Or–M bonds with respect to low-temperature phengite structures. For the 3T phase, we were unable to achieve completion of dehydroxylation. The refined structural model of the dehydroxylate phase shows two hydroxyl sites, but at a short distance from one another. This result suggests that the dehydroxylation reaction did not proceed to completion. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献