GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.2 225 Fig. 1 – Tectonic outline of the Alps and northern Apennines with the locations of igneous and metamorphic pre- Alpine relicts as labeled in Spalla et al. (2014) and Marotta et al. (2016). a pre-Alpine burial of continental crust at convergent plate margins, in a context of oceanic lithosphere subduction underneath continental upper plate, characterized by a low thermal regime, and followed by continental collision (e.g. Marotta and Spalla, 2007; von Raumer et al., 2013; Spalla et al. , 2014). Permian-Triassic remnants (300-220 Ma) of high-temperature metamorphism, mainly occurring within Austroalpine and Southalpine domains (belonging to Adria plate) and associated with widespread basic to acidic igneous activity testified by large gabbro bodies (Fig. 1), indicate an increase of the lithospheric thermal regime (e.g. Lardeaux and Spalla, 1991; Schuster and Stüwe, 2008; Marotta et al. , 2009; Spalla et al. , 2014) related to asthenospheric upwelling and lithospheric thinning (e.g. Thompson, 1981; Sandiford and Powell, 1986; Beardsmore and Cull, 2001). During Late Triassic-Early Jurassic an important extensional stage leads to the break-up of the Pangaea continental lithosphere and the opening of the Alpine Tethys Ocean, accounted by the occurrence of ophiolitic sequences in the western Alps and Apennines (Fig. 1). The geodynamic significance of the Permian-Triassic high temperature and low pressure metamorphic event has been widely debated and recent numerical models suggest an origin consequent to successive lithospheric extension and thinning events