GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.2 229 late-orogenic collapse; ii) a rifting developed on a thermally perturbed lithosphere agrees with a hyperextended configuration of the Alpine Tethys rifting and with the duration of the extension up to the oceanization. These results suggest that the Alpine Tethys rifting and oceanization developed on a lithosphere characterized by a thermo-mechanical configuration consequent to a post-Variscan extension affecting the European realm during Permian and Triassic. Therefore, a long lasting period of continuous active extension can be envisaged for the breaking of Pangea supercontinent, starting from the unrooting of the Variscan belts (300 Ma, Fig. 3a), followed by the Permian-Triassic thermal peak highlighted by HT-LP metamorphism and gabbros emplacement (Fig. 3b), and ending with the crustal breakup and the formation of the Alpine Tethys ocean (170-160 Ma, Fig. 3c). This process could be characterized by alternated period of active extension and stasis, as proposed for the Northern Atlantic rifting or as envisaged for the Ivrea-Verbano Zone on the basis of three metamorphic ages (Permian, Triassic and Jurassic; Langone and Tiepolo, 2015). In order to explore this issue a continuous and polycyclic numerical model is necessary to record the thermo-mechanical inheritance of different events during the entire extensional process, and use ages and P-T-t paths of natural data as constraints. References Beardsmore, G. R. and Cull, J. P.; 2001: Crustal Heat Flow: a guide to measurement and modelling . Cambridge University Press, 321 pp. Doré, A. G. and Stewart, I. C.; 2002 : Similarities and differences in the tectonics of two passive margins: the Northeast Atlantic Margin and the Australian North West Shelf , in: Keep, M., Moss, S.J. (Eds.), The Sedimentary Basins of Western Australia 3. Petroleum Exploration Society of Australia (PESA), pp. 89-117. Langone,A. and Tiepolo, M.; 2015: U-Th-Pb “multi-phase” approach to the study of crystalline basement: application to the northernmost sector of the Ivrea-Verbano Zone (Alps) . Periodico di Mineralogia, 84 , 633-655. Lardeaux, J. M. and Spalla, M. I.; 1991: From granulites to eclogites in the Sesia zone (Italian Western Alps): a record of the opening and closure of the Piedmont ocean . J. Metamorph. Geol, 9 , 35-59. Manatschal, G., Lavier, L. and Chenin, P.; 2015: The role of inheritance in structuring hyperextended rift systems: Some considerations based on observations and numerical modeling . Gondwana Research, 27 , 140-164. Marotta, A. M., Roda, M., Conte, K. and Spalla, M. I.; 2016: Thermo-mechanical numerical model of the transition from continental rifting to oceanic spreading: the case study of the Alpine Tethys . Geological Magazine, 1-30. Marotta, A. M. and Spalla, M. I.; 2007: Permian-Triassic high thermal regime in the Alps: Result of late Variscan collapse or continental rifting? Validation by numerical modeling . Tectonics, 26 , 1-27. Marotta, A. M., Spalla, M. I. and Gosso, G.; 2009: Upper and lower crustal evolution during lithospheric extension: numerical modelling and natural footprints from the European Alps , in: Ring, U., Wernicke, B. (Eds.), Extending a Continent: Architecture, Rheology and Heat Budget. The Geological Society, London, Special Publications, pp. 33-72. Mohn, G., Manatschal, G., Beltrando, M., Masini, E. and Kusznir, N.; 2012: Necking of continental crust in magma- poor rifted margins: Evidence from the fossil Alpine Tethys margins . Tectonics, 31 , 1-28. Sandiford, M. and Powell, R.; 1986. Deep crustal metamorphism during crustal extension: modern and ancient examples . Earth Planet. Sci. Lett., 79 , 151-158. Schuster, R. and Stüwe, K.; 2008: Permian metamorphic event in the Alps . Geology, 36 , 603-606. Spalla, M. I., Zanoni, D., Marotta, A. M., Rebay, G., Roda, M., Zucali, M. and Gosso, G.; 2014: The transition from Variscan collision to continental break-up in the Alps: insights from the comparison between natural data and numerical model predictions . Geol. Soc. London, Spec. Publ., 405 , 363-400. Spiess, R., Cesare, B., Mazzoli, C., Sassi, R. and Sassi, F.P.; 2010: The crystalline basement of the Adria microplate in the eastern Alps: a review of the palaeostructural evolution from the Neoproterozoic to the Cenozoic . Rend. Lincei Sci. Fis. Nat., 21 , 31-50. Thompson, A.B.; 1981: The pressure–temperature (P,T) plane viewed by geophysicists and petrologists . Terra Cogn., 1 , 11-20. von Raumer, J. F., Bussy, F., Schaltegger, U., Schulz, B. and Stampfli, G. M.; 2013: Pre-Mesozoic Alpine basements - Their place in the European Paleozoic framework . Geol. Soc. Am. Bull., 125 , 89-108.