Tectono-sedimentary evolution of the External Liguride units (Northern Apennines,Italy): insights in the pre-collisional history of a fossil ocean-continent transition zone

Abstract

In the Northern Apennines, the External Liguride (EL) units are interpreted as derived from the domain that joined the Ligure–Piemontese oceanic basin to the Adriatic plate continental margin. The EL units can be divided into two different groups according to the lithostratigraphic features of the basal complexes underlying the Upper Cretaceous–Lower Tertiary carbonate flysch (e.g. Helminthoid flysch). The first group includes the western successions characterized by Santonian–Campanian sedimentary melanges where slide blocks of lherzolitic mantle, gabbros, basalts, granulites, continental granitoids are represented. The second group is represented by the eastern successions where the Cenomanian–Campanian basal complexes mainly consist of sandstones and conglomerates where the mafic and ultramafic rocks are scarce or completely lacking. Their original substrate is represented by the Middle Triassic to Lower Cretaceous, mainly platform carbonate deposits, found as slices at the base of the eastern successions.

The stratigraphic features shown by the basal complexes allow the reconstruction of their source area that is assumed to be also representative for the pre-Upper Cretaceous setting. The proposed reconstruction suggests the occurrence in the EL domain of two distinct domains. The eastern domain was characterized by a thinned and faulted continental crust belonging to the Adriatic continental margin. The western domain was instead floored by subcontinental mantle associated with lower and upper continental crust, representing the ocean–continent transition. This setting is interpreted as the result of the opening of the Ligure–Piemontese oceanic basin by passive rifting, mainly developed by simple shear, asymmetric extension of the continental crust. © 2001 Éditions scientifiques et médicales Elsevier SAS     

The quantitative analysis of OH in vesuvianite: a polarized FTIR and SIMS study

A well-characterized suite of vesuvianite samples from the volcanic ejecta (skarn or syenites) from Latium (Italy) was studied by single-crystal, polarized radiation, Fourier-transform infrared (FTIR) spectroscopy and secondary-ion mass-spectrometry (SIMS). OH-stretching FTIR spectra consist of a rather well-defined triplet of broad bands at higher-frequency (3,700–3,300 cm^–1) and a very broad composite absorption below 3,300 cm^–1. Measurements with E//c or Ec show that all bands are strongly polarized with maximum absorption for E//c. They are in agreement with previous band assignments (Groat et al. Can Mineral 33:609, 1995) to the two O(11)–H(1) and O(10)–H(2) groups in the structure. Pleochroic measurements with changing direction of the E vector of the incident radiation show that the orientation of the O(11)–H(1) dipole is OHc~35°, in excellent agreement with the neutron data of Lager et al. (Can Mineral 37:763, 1999). A SIMS-based calibration curve at ~10% rel. accuracy has been worked out and used as reference for the quantitative analysis of H₂O in vesuvianite by FTIR. Based on previous SIMS results for silicate minerals (Ottolini and Hawthorne in J Anal At Spectrom 16:1266, 2001; Ottolini et al. in Am Mineral 87:1477, 2002) the SiO₂ and FeO content of the matrix were assumed as the major factors to be considered at a first approximation in the selection of the standards for H. The lack of vesuvianite standards for quantitative SIMS analysis of H₂O has been here overcome by selecting low-silica elbaite crystals (Ottolini et al. in Am Mineral 87:1477, 2002). The resulting integrated molar absorption FTIR coefficient for vesuvianite is _i=100.000±2.000 l mol^–1 cm^–2. SIMS data for Li, B, F, Sr, Y, Be, Ba REE, U and Th are also provided in the paper.     

A baroclinic coastal trapped wave event in the Gulf of Naples (Tyrrhenian Sea)

In this study, a baroclinic coastal trapped wave, with period ~?4.5 days and cross-shore scale ~?3 km, is identified in the outputs of a very-high-resolution ocean circulation model of the Campania coastal system (central Tyrrhenian Sea; including the Gulfs of Salerno, Naples, and Gaeta). The outputs are from a simulation spanning June 2003, a month in which the surface winds were always weak, except for a strong northeasterly wind event that lasted 1 day (20 June). This event is found to generate a strong upwelling along the Campania coasts, whose relaxation—virtually free, because of the weakness of the winds—produces coastal current fluctuations that propagate to the north, spanning the three gulfs. The dynamics (analyzed with a focus on the Gulf of Naples) is found to share important features with baroclinic Kelvin waves in a two-layer model, such as the sharp cross-shore decrease of the perturbation amplitude and the vertical reversal of the long-shore current velocities. The simulated phase speed, cross-shore extension, and wavelength of the perturbation are also close to those obtained using a two-layer approximation of the dynamics. Moreover, the propagation described by the models is shown to be compatible with current measurements that were made in June 2003 at the southern entrance of the Gulf of Naples. Experimental implications related to the specific oceanographic problem are finally discussed, and an experimental strategy—inspired by our modeling approach—aimed at identifying the phenomenon is proposed.     

Finite element evaluation of the effects of faulting on a shallow tunnel in alluvial soil

A numerical estimation is presented on the effects induced in an existing tunnel by the development of a fault from the deep bedrock during a seismic event. The spreading of the fault within the alluvial deposit hosting the tunnel, and the consequent effects on its permanent liner, are studied in static conditions through a series of elastic-plastic, plane strain finite element analyses. They account for the reduction of the shear strength and stiffness characteristics of the faulting zone with increasing irreversible strains. Even though the calculations require only “standard”, e.g. peak and residual, material parameters it is shown that these properties can hardly be obtained for the alluvial deposit at hand. To overcome this drawback a relatively large scale in-situ tests could be performed and its results could be interpreted through a suitable back analysis. This would permit characterizing the numerical model to be subsequently adopted for the analysis of the faulting process.     

First Ar/Ar age of the Ceprano man (central Italy)

The Ceprano calvarium, found in 1994 in Italy and attributed to Homo cepranensis, is one of the most celebrated hominin remains of Europe. It was considered at least 700 ka-old until a recent investigation incorporating magnetostratigraphy and K-Ar ages from the literature assigned to the calvarium an age of ∼450 (+50, −100) ka. Here we pin down the age of the Ceprano calvarium to 353 ± 4 ka (±1σ external) by means of new ⁴⁰Ar/³⁹Ar dating on K-feldspars retrieved from the sediments that hosted the skull. In absence of evidence of reworking, this refined age sinks the conviction that H. cepranensis belonged to human evolution at the Brunhes–Matuyama boundary (c.a. 781 ka). Our refined age indicates that H. cepranensis lived in central Italy probably during the cold period of marine isotope stage (MIS) 10, and that despite his archaic morphology and lack of Neanderthal traits, he was contemporaneous with more advanced species such as H. heidelbergensis.     

A finite element analysis of direct shear tests on stiff clays

A finite element analysis is presented of some direct shear tests carried out on samples of a stiff, heavily overconsolidated clay. The effects of softening are accounted for through a simple material model which views this phenomenon as a consequence of an intrinsic loss of strength of the material taking place when plastic strains increase. After illustrating the main characteristics of the finite element approach, with particular reference to the correct determination of the non-reversible strains, its use in the interpretation of the mentioned shear tests is discussed. Some comments are also presented on the mesh dependence of the numerical results, and on the use of a relation between material parameters and element size which reduces this negative effect. Finally, the solution procedure is applied to the simulation of a compression test in order to investigate the possibility of numerically detecting the ‘spontaneous’ (i.e. not directly induced by the boundary conditions) formation of shear zones within the specimen.     

Back analysis procedures for the interpretation of field measurements in geomechanics

A survey is presented of some recent developments of the numerical techniques for back analysis in the field of geomechanics, with particular reference to tunnelling problems. In the spirit of Terzaghi's observational design method, these techniques are seen as practical tools for interpreting the available field measurements, in order to reduce the uncertainties that in many instances affect the parameters governing the solution of complex geomechanics problems. Both deterministic and probabilistic viewpoints are considered and some significant applications to practical problems are illustrated.     

Pore pressure tension cut off in two-phase finite element analyses

In the coupled finite element analysis of the two-phase, saturated soils the pore pressure could decrease below the atmospheric pressure in particular when the plastic dilation of the skeleton is accounted for. The consequent reduction of the bulk modulus of the liquid phase is here modelled in a simplified manner through a tension cut off on the pore pressure. Two alternative approaches are outlined in the framework of the finite element method. The first one introduces a unilateral constraint on the nodal pore pressures and involves manipulations on matrices of the assembled mesh, whilst the second approach requires calculations solely at the element level. The effects of the pore pressure tension cut off are illustrated through some undrained test examples in elastic–plastic regime.     

The Loci of Satellite Positions: A Constellation Design Approach

In special cases in which satellite constellations can be described by a limited set of parameters, a correlation between the latter and the constellation characteristics (i.e. shape and kinematics of the satellite configurations) has been investigated. Such cases may be a useful starting point for designing more complex constellations in order to achieve better the desired performances. Therefore, this proves to be one way to fix an initial set of parameters once the desired behaviour of the constellation has been established on the basis of the operational purposes required. This revised version was published online in August 2006 with corrections to the Cover Date.