Genesi ed evoluzione del magmatismo basico nelle successioni carbonatiche triassiche nel Complesso Alpujárride (Cordigliera Betica) e nelle Unità Appenniniche della Calabria settentrionale

Abstract

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.