GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.2 241 metamorphism (i.e. Austroalpine and Penninic domains) from rocks that recorded only shallow structural level deformation (i.e. Southalpine domain). The Periadriatic line is interpreted as the ascent path for the late collisional Oligocene magmas, which emplaced to form the Periadriatic plutons (Rosenberg, 2004). The Periadriatic plutons are traditionally considered as derived from the Alpine slab breakoff (Von Blanckenburg and Davies, 1995). However recently the Tertiary magmatic rocks south of the Periadriatic line, such as the southern Adamello pluton, Veneto Volcanic province, and dykes in the central Southalpine, are supposed to be generated during Alpine subduction �������� (Tiepolo et al., 2011; Bartoli et al., 2013; Bergomi et al., 2015). ��� The Austroalpine domain of the western Alps consists of continental rocks tectonically sampled by the margin of Adria plate during subduction ����� ���� (e.g. Roda et al. , 2012) ��� �� �������� ������� and is actually divided into two main tectonic units, namely the Sesia-Lanzo Zone (SLZ) and Dent Blanche nappe. Both tectonic units were subducted and exhumed during the Alpine cycle when the oceanic subduction was still active (Spalla et al., 1996; ������ Babist et al., 2006� ���� ; Roda et al., 2012)� ������� . Between 60 and 80 Ma the SLZ reached the P-peak during subduction ������ (Bussy et al., 1998� ��������� ; Cenki-Tok et al., 2011), corresponding to eclogite conditions at about 550°C and ≥ 2 GPa (Zucali et al., 2002; Zucali and Spalla, 2011). Eclogite metamorphism is followed by decompression blueschist and greenschist re-equilibrations ��������� (Pognante et al., 1980� ������ ; Zucali et al., 2002), related to later Fig. 2 – Summary of P-T evolution in Biella aureole at different distances from the pluton margin. Thick line: P-T from calculated petrogenetic grids; thin line: P-T from independent thermobarometry only.