Paleomagnetic evidence for a collision of Patagonia with Gondwana in the Permo-Triassic?

RAPALINI, A.E.; LÓPEZ DE LUCHI, M.G.,; LUPPO, T.; MARTINEZ DOPICO, C.I.

Cape Town

Congreso; Joint Assembly 2017 IAPSO-IAMAS-IAGA 27 August ? 1 September 2017; 2017

Joint Assembly 2017 IAPSO-IAMAS-IAGA 27

The "origin" of Patagonia has been an unsolved debate for the last three decades. The Permo- Ventana Fold Belt in central-eastern Argentina, and its continuation in the South African Cape Fold Belt, far-away from the southwestern Gondwana active margin has been the most conspicuous evidence in favour of a Late Paleozoic accretion of an allochtonous or para-authochtonous Patagoniaterrane. Correlation of Early Paleozoic basement rocks between northern Patagonia and the Pampean Ranges in central Argentina, on the other hand, has been interpreted as evidence for an "authochtonous" Patagonia. Scarce paleomagnetic data on Paleozoic rocks from Patagonia have suggested limited if any relative displacement with respect to Gondwana since Devonian times.However, not only this database is scarce but shows very loose age constraints for the paleomagnetic poles, turning ambiguous any comparison with a reference apparent polar wander path (APWP) for Gondwana. We present new paleomagnetic data on accurately dated volcanic rocks from the North Patagonian Massif. A paleomagnetic pole from the Collinao Dacite (253±2 Ma) based on seven sites,and validated by an inverse contact test, plus a single VGP from a Rhyolite Dome (264±2Ma) and twofrom subvertical basic dykes (255-246 Ma?) fall in an anomalous position with respect to the reference APWP of Gondwana. A second paleomagnetic pole, computed from 12 subvertical acidic dykes (244±2Ma) in the same region, agrees with 250-240 Ma Gondwana reference poles. To reconcile both observations a tectonic model in which Patagonia collided with the southern Gondwanamargin by the latest Permian-early Triassic, closing a small V-shaped oceanic basin is presented. Recently found evidence of Permo-Triassic highly deformed granitoids in northeastern Patagonia and timing of deformation in the Hesperides Basin offshore central Argentina is consistent with such model. Preliminary paleomagnetic results from a nearly continuous succession of volcanic rocks thatencompass the Permian-Triassic boundary in the same region would support this interpretation