Rocky Mountain (56th Annual) and Cordilleran (100th Annual) Joint Meeting (May 3–5, 2004)

Paper No. 6
Presentation Time: 10:20 AM


MUTTONI, Giovanni, Dipartimento di Scienze della Terra, Università di Milano, via Mangiagalli 34, Milano, I-20133, Italy, RONCHI, Ausonio, Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata 1, Pavia, 27100, KENT, Dennis V., Geological Sciences, Rutgers Univ. and Lamont-Doherty Earth Observatory, Piscataway, NJ 08854, BACHTADSE, Valerian, Earth and Environmental Sciences, Ludwig-Maximillians Univ, Theresienstrasse 41, Munich 2, 80333, MOSER, Elmar, Earth and Environmental Sciences, Univ, Theresienstrasse 41, Munich, G-80333, Germany and GARZANTI, Eduardo, Dipartimento Scienze Geologiche e Geotecnologie, UNIVERSITA' DI MILANO-BICOCCA, Piazza della Scienza 4, Milano, 20126, Italy,

The pre-drift Wegenerian model of Pangea, also known as Pangea 'A', is almost universally accepted, but debate exists on its pre-Jurassic configuration since Irving (1977) introduced Pangea ‘B’ by placing Gondwana farther to the east by ?3000 km with respect to Laurasia using paleomagnetic data. New paleomagnetic data from radiometrically dated Early Permian volcanic rocks from parts of Adria that are tectonically coherent with Africa (Gondwana) fully support Pangea 'B' in the Early Permian. Regarding the paleomagnetic evidence for Pangea 'B' as robust, we seek for geological evidence in support of an intra-Pangea dextral megashear system that presumably took place during the Permian after the cooling of the Variscan lithosphere. The Gondwana/Laurasia transcurrent plate boundary associated with Pangea 'B' to 'A' transformation was probably diffuse and the search for possible remnants should focus on mid-Permian shear zones, which may represent reactivation of terminal Variscan shear zones sensu Arthaud and Matte (1977). A possible example is the deep crustal shear synchronous with the emplacement of granitoids (dated at ~280 and ~270 Ma) from the Petite and Grande Kabylie of northern Algeria. The Petite and Grande Kabylie, as well as the Calabria and Corsica-Sardinia basements, were, prior to Alpine-Apennine deformation in the Cenozoic, members of the same 'Alboran' micro-plate(s) located in front of the French-Catalan margin. Paleomagnetic directions obtained from various (Early) Permian localities from Corsica and Sardinia are internally inconsistent and differ from either the Laurasian or the Gondwanan apparent polar wander path when restored for the well-known 'Balearic' counter-clockwise rotation of Cenozoic age. We therefore argue that the Cenozoic 'Alboran' terranes were Paleozoic tectonostratigraphic terranes that may have been caught into the dextral mega-shear zone which developed during Pangea 'B' to Pangea 'A' transformation in the Permian. New paleomagnetic data from volcanic and sedimentary rocks from Sardinia have been collected by the writers in 2003 and are presently under investigation. With these new data we would like to verify if Sardinia underwent a post-Variscan, intra-Permian tectonic phase that could be reconciled with the Pangea 'B' to 'A' transformation.