Browsing by Author "Piluso, Eugenio"

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    Genesi ed evoluzione del magmatismo basico nelle successioni carbonatiche triassiche nel Complesso Alpujárride (Cordigliera Betica) e nelle Unità Appenniniche della Calabria settentrionale
    (2012-11-28) Matrangolo, Gilda; Piluso, Eugenio; Liberi, Francesca; Rojas, Iván Martin
    Permo-Mesozoic extension represents one of the most noticeable geological processes in the western Mediterranean. Triassic sedimentary sequences observed along the Dinaride-Hellenide orogenic belts and in Betic Cordillera are locally related with a basic magmatism in an extensional tectonic setting. Carbonates sequences which include basic rocks can be observed in the Alpujarride Complex (central-eastern Betic Cordillera, Spain) and in the Lungro-Verbicaro Unit (northern Calabria). Betic Cordillera represents an important orogenic belt sited in the southern and southeastern side of the Iberian Peninsula and it is commonly divided into three main geological units: the Betic External Zone, Campo de Gibraltar Complex and the Betic Internal Zone, which include various tectonostratigraphic units arising from previous paleogeographical domains developed during the Mesozoic, as a consequence of the break-up of the Pangaea supercontinent. According to Iannace et al. (2007), the Meso-Cenozoic carbonates sequences outcropping in northern Calabria can be grouped into three tectonic units: the Lungro-Verbicaro Unit, the Cetraro Unit and the Pollino-Ciagola Unit. The Lungro-Verbicaro Unit is represented by a thick sedimentary succession affected by HP-LT metamorphism and consisting of phyllites and metarenites with carbonate intercalations in its lowermost part of Middle Triassic. Basic rocks can be found as a small intrusive complex within the Anisian phyllites and the Ladinian-Carnian carbonates of the Lungro-Verbicaro Unit. As Mesozoic geodynamic processes, since the opening of the Tethys, are recorded in the above rocks, the attention was focused on these two areas. The aim of this research was to study these basic magmatic rocks in order to obtain a better interpretation of the extensional tectonic process and to recognize a possible hydrothermal metamorphic overprint. In fact, the latter process is suggested by significant mineralizations observed in the outcrops of the Alpujarride Complex, due to the activity of a hydrothermal metamorphism in the Betic area. Basic rocks were characterized from a petrological and geochemical standpoint with the purpose of determining the characteristics of their source. A multidisciplinary approach was followed in both areas. Firstly, a field geology work (with the addition of photo-geological analyses for the Betic area) was performed to constrain relationships between basic rocks and wall rocks. Secondly, laboratory analyses were carried out in order to determine petrographic, petrological and geochemical characteristics of study samples. Petrographic analyses were performed using both the optical and scanning electron microscopy techniques, whereas petrological data were obtained by the electron microprobe. Lastly, geochemical composition of study rocks was characterized by X-ray fluorescence spectroscopy (XRF), and the obtained data were processed using suitable diagrams.
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    Natura ed evoluzione delle rocce ultramefiche in Calabria settentrionale
    (2018-03-16) Caparelli, Sabina; Pantano, Pietro; Bloise, Andrea; Piluso, Eugenio
    Continental Sila and oceanic Gimigliano-Monte Reventino tectonometamorphic Units that outcrop in northern Calabria contain small ultramafic rocks bodies. The ultramafic rocks of the Sila Unit are embedded within the northern Calabria alpine chain and preserve evidence of the pre-alpine extensional tectonics related to lithospheric thinning in Permo-Triassic time. The Sila Unit consist of a continuous continental lithospheric section in which the ultramafic rocks represent the subcontinental upper mantle components. The ultramafic rocks of the Gimigliano-Monte Reventino Unit represent the suboceanic upper mantle and was interpreted as remnants of the Jurassic Alpine Tethys ocean realms subsequently involved in the Alpine accretionary wedge. The mantle rocks of the Sila Unit are made of layered alternations of serpentinized peridotities and concordant pyroxenites. The serpentinites are after Spl-harzburgites-dunites. The concordant pyroxenites range from olivine-bearing orthopyroxenite to orthopyroxenite in composition. The olivine-bearing orthopyroxenites and the orthopyroxenites have been produced by melt-rocks interaction processes under Spl-lherzolitic facies conditions. Locally the concordant pyroxenites shows extensional tectonic effects whit formation of drawn boudins. The subsolidus evolution of the Sila Unit upper mantle rocks can be described by four main stages from Spl-lherzolite facies to Chl-lherzolite facies followed by a severe serpentinization. Moreover, evidence of metasomatism produced by melt-rock interaction has been observed at meso- and microscale. On the base of field work and microstructural evidence two main metasomatizing agents have been observed: (i) discordant dykes orthopyroxenitic in composition; (ii) concordant orneblendites with tholeitic affinity. Melt-rock interaction processes was responsible for the local transformation of: (i) Spl-peridotites into hercynitic spinel-bearing peridotites and (ii) concordant pyroxenites into websterites. Gabbroic magmatism occurred at P ≈ 0.55 GPa (Liberi et al., 2011). Thermobarometric estimates based on Opx-Cpx pairs from olivine-bearing othopyoxenites and websterites given values of 808-855°C and 0,7 GPa respectively for T and P. These physical conditions are consistent with the transition from Spl- to Amph-lherzolite facies. Finally, greenschist facies retrogression is documented by static serpentinization and by the development of late vein systems filled by serpentine mineral groups. At this stage chrysotile and lizardite crystallize. This fact suggests equilibrium at T<300°C. The serpentinites and ophicarbonates occur in the Gimigliano-Monte Reventino Unit at the core of the antiform structures. The serpentinites are after depleted lherzolites and in some preserve the protogranular textures. The ophicarbonate shows typical brecciated textures given by clasts of peridotites severely serpentinized surrounded by a matrix made of carbonates and serpentine minerals. The ultramafic rocks are in tectonic contact with the metabasites along a narrow cataclastic-mylonitic shear zone where can be observed a grain size reduction of serpentinite clasts in a matrix made of calcite and tremolite. Therefore, the petrogenetic evolution of the northern Calabria ultramafic rocks document a Ocean Continent Transition (OCT) which was part of the Tethyan hyperextended margin. Again, northern Calabrian ultramafics preserve the signals of the transition from late-hercinian orogenic extention to Tethyan rift, followed by the Alpine and subsequent compression stages in the Apennine tectonic phases.