Francesca Liberi

Asbestos and other fibrous minerals contained in the serpentinites of the Gimigliano-Mount Reventino Unit (Calabria, S-Italy)

Serpentinites are metamorphic rocks with good technological properties and valuable ornamental characteristics, which have been exploited since ancient times. Actually, their use is limited and monitored in several countries worldwide because they can contain fibrous asbestos minerals that may be carcinogenic. Furthermore, certain types of fibrous minerals can be confused with asbestos, and must therefore be carefully investigated. We have investigated the possible presence of the asbestos and non-asbestos fibrous phases contained in serpentinitic rocks in a meta-ophiolitic sequence from the Gimigliano-Mount Reventino Unit (Southern Italy), which had not been previously assessed. The detection and quantification of asbestos and the correct distinction of the fibrous non-asbestos minerals are very important not only from a scientific point of view, but also from a legislative one. This is especially the case for the administrative agencies that have to take decisions with regards to the implementation of public and occupational health protection measures (e.g., in road yards and quarry excavations). As a consequence of this, serpentinitic rock samples have been characterized in detail through X-ray powder diffraction, scanning and transmission electron microscopy combined with energy-dispersive spectrometry, analytical electron microscopy (SEM–EDS and TEM–AEM), differential scanning calorimetry, thermogravimetry and micro-Raman spectroscopy. Two kinds of asbestos and four kinds of non-asbestos fibrous silicates have been detected in the examined samples. In order of decreasing abundance these are polygonal serpentine, chrysotile, fibrous antigorite, tremolite, gedrite and magnesiohornblende. The size, morphology, crystallinity and chemical composition of the fibres were also discussed, in the light of the possible role these properties could play in the carcinogenic effect on human health.

Tectonometamorphic evolution of the ophiolitic sequences from Northern Calabrian Arc

Ophiolites crop out discontinuously in the Northern Calabrian Arc (Southern Italy). They consist of high pressure/low temperature metamorphic ophiolitic sequences of Late Jurassic-?Early Cretaceous age, in which a metabasic and metaultramafic association is the base of a complex metasedimentary cover ranging from pelagic to flyschoid type sediments. These ophiolitic sequences, interpreted as slices of oceanic lithosphere belonging to the Jurassic Tethys realm, occupy an intermediate position in the northern Calabrian Arc nappe pile, between the overlying Hercynian continental lithosphere (Calabride nappe) and the underlying Apenninic carbonate units.In the literature, these ophiolitic sequences are subdivided into several tectonometamorphic units; some authors distinguished between an upper slightly metamorphic ophiolitic unit and a lower HP-metamorphic ophiolitic unit. This subdivision contrasts with new petrological data and geothermobarometric modelling. In fact, the overall P-T evolution for several ophiolitic sequences from the northern Calabrian arc describes comparable paths, characterized by a HP-LT metamorphism followed by retrogression under greenschist facies conditions. The metamorphic climax is calculated at pressures ranging between 0,9 and 1,1 GPa and a temperature around 380°C.Moreover, structural analysis of rocks characterized by HP syn-metamorphic ductile deformation suggests that tectonic evolution is quite homogeneous and similar, although different degrees of deformation can be observed. The high-pressure mineral assemblage defines a pervasive foliation developed during a compressive tectonic event (D1) that transposed the earlier structures. A second tectonic event (D2) which occurred during decompression at 0,4 GPa, produced millimetre to decametre scale asymmetric folds. Later extensional brittle structures are responsible for final exhumation of the HP rocks.The tectonometamorphic evolution of the ophiolitic sequences of Northern Calabrian Arc is well explained in a context in which the oceanic-derived rocks underwent subduction and exhumation as tectonic slices inside an accretionary wedge.

Geology map of the central area of Catena Costiera: insights into the tectono-metamorphic evolution of the Alpine belt in Northern Calabria

The 1:25.000 scale geological map of the central area of Catena Costiera aims to provide a picture of the tectonic setting of the metamorphic units belonging to the Alpine collisional belt of Northern Calabria, Italy. The exposed successions of the study area have been investigated by structural analyses, petrographic, petrological and geochemical studies whose results are summarised in the geological map. In this area, two HP-LT metamorphic, oceanic-derived units, referred as the Mongrassano and Cozzo Cervello units, have been distinguished on the base of their stratigraphic and tectono-metamorphic evolution. Both the oceanic-derived units show a polyphase deformation history developed under retrograde metamorphism in a subduction zone by underplating and exhumation into an accretionary wedge. These units are overthrust by continental-derived units, referred as the Sila and Castagna units, consisting of medium and high-grade metamorphic rocks. While the Castagna unit displays an Alpine HP/LT metamorphic overprint, the Sila unit escaped any subduction-related metamorphism.

Structural style of Quaternary extension in the Crati Valley (Calabrian Arc): Evidence in support of an east-dipping detachment fault

New geological field data, integrated with commercial seismic lines, allowed us to constrain the geometry and time-space evolution of the fault system that ruled the tectono-sedimentary evolution of the NS-striking Crati graben, in the axial portion of the northern Calabrian Arc.We highlight that this basin is controlled by a 60-km long east-dipping master fault, referred to as the Crati Graben Detachment Fault (CGDF).On the seismic sections, the CGDF appears as an east-dipping low-angle reflection reaching the surface along the eastern slope of the Catena Costiera Calabra. Its surface expression corresponds to an alignment of moderately-inclined (30° to 45°) left-stepping en-echelon faults.More to the East, a number of E- and W-dipping high-angle normal faults branch upward from the CGDF. Their reconstructed timing suggest that the westernmost faults are active since the Early Pleistocene and show a progressive eastward rejuvenation trend.The conversion to depth of a W-E oriented seismic section, crossing the entire Crati graben, highlights that the CGDF has a staircase geometry, with an average angle of 30°, and reaches a depth of 7-8 km below the east side of the basin. The evolutionary stages of the related fault system were reconstructed by restoring the section through the Move suite software (Midland Valley Exploration), in order to verify the kinematic consistency of our subsurface interpretation and estimate the amount of associate extension.Finally, the present activity and the possible seismogenic role of the CGDF is preliminarily discussed, by comparing the geometry of the extensional fault system with the available historical and seismological instrumental datasets.