The Wegenerian configuration of Pangea at Jurassic times is not questioned among Earth scientists. Debate exists on its pre-Jurassic configuration since Ted Irving in 1977 introduced Pangea 'B' by placing Gondwana to the East by ≈3000km with respect to Laurasia on the basis of paleomagnetic data. Pangea 'B' and its tectonic implications have not been however broadly accepted by the scientific community. We review data from Gondwana and Laurasia strictly from igneous rocks, and conclude that Pangea 'B' is indeed paleomagnetically acceptable in the Early Permian. Importantly, the exclusive use of paleomagnetic data from igneous rocks virtually excludes possible effects of sedimentary inclination error as an explanation for Pangea 'B' as envisaged by Rochette and Vandamme (1998). The ultimate option to reject Pangea 'B' is to abandon the geocentral axial dipole (GAD) hypothesis by introducing a specific octupole component of a specific amount with a specific sign in the Late Paleozoic time-averaged geomagnetic field (Van der Voo and Torsvik, 2001). We demonstrate, however, by using a dataset made exclusively and entirely of paleomagnetic directions with low inclinations from the northern hemisphere, that the effects of an octupole field contamination can not account for Pangea 'B' in the Early Permian. We therefore review geological data from the literature in support of Pangea dextral mega-shear. The transformation from Pangea 'B' to Pangea 'A' occurred after the cooling of the Varisican lithosphere during the Permian at a minimum plate speed of ≈15cm/yr. No Triassic transformation is herein envisaged. The transformation is coeval with the opening of the Neotethys Ocean, which took place along the eastern margin of Gondwanan between India/Arabia and the Cimmerian continents, and widespread lithospheric wrenching and magmatism in the west, along the margin of the Adriatic promontory. We show that the "push-pull" driving forces associated with the Gondwana grand plate circuit are qualitatively consistent with a right-lateral shear couple between Gondwana and Laurasia during the Permian.
|Titolo:||Pangea B: a plausible impossibility is always preferable to an uncommitting possibility (Aristotle, Poetics 7)|
MUTTONI, GIOVANNI (Primo)
GAETANI, MAURIZIO (Ultimo)
|Data di pubblicazione:||apr-2003|
|Settore Scientifico Disciplinare:||Settore GEO/03 - Geologia Strutturale|
|Citazione:||Pangea B: a plausible impossibility is always preferable to an uncommitting possibility (Aristotle, Poetics 7) / G. Muttoni, D.V. Kent, E. Garzanti, P. Brack, N. Abrahamsen, M. Gaetani. ((Intervento presentato al convegno Joint Assembly tenutosi a Nice nel 2003.|
|Appare nelle tipologie:||14 - Intervento a convegno non pubblicato|