HR: 1340h
AN: U33A-0028    [Abstracts]
TI: Paleomagnetically Testing the Integrity of South America
AU: * Taylor, G K
EM: GTaylor@plymouth.ac.uk
AF: University of Plymouth, School of Earth, Ocean and Environmental Sciences, Drake Circus, Plymouth, PL4 8AA United Kingdom
AU: Vizan, H
EM: haroldo@gl.fcen.uba.ar
AF: Universidad de Buenos Aires, CONICET- Departamento de Ciencias Geol¢gicas, FCEyN, Pabellon (2), Buenos Aires, 1428 Argentina
AU: Somoza, R
EM: rsomoza@sinectis.com.ar
AF: Universidad de Buenos Aires, CONICET- Departamento de Ciencias Geol¢gicas, FCEyN, Pabellon (2), Buenos Aires, 1428 Argentina
AB: The Falkland Plateau is, physiographically, one of the most unusual pieces of continental crust extending some 1500 miles eastward from South America into the South Atlantic. The Falkland Islands/Malvinas have been shown palaeomagnetically to have undergone a very substantial (~120$^{o}$) Jurassic-Early Cretaceous clockwise rotation (Mitchell et al. 1986; Taylor & Shaw 1989; Randall pers comm. 1999) and this was part of a more general rotation of microplates during the break-up of Gondwana. More recently paleomagnetic studies of Jurassic and Cretaceous units in the North Patagonian Massif of Argentina, associated with the Gastre Fault system, the postulated onshore continuation of the Falkland Fracture zone, have shown 25-30$^{o}$ of clockwise rotation occurred in latest Jurassic to earliest Cretaceous times (Geuna et al. 2000). This led us to investigate the pre-Jurassic paleomagnetic record of the Deseado Massif, the closest continental region to the Malvinas/Falkland Islands, to determine whether it too records a Jurassic-Cretaceous rotation history. We present results from a range of Late Triassic-Jurassic units, both sedimentary and intrusive, which suggest the occurrence of clockwise vertical-axis rotations in Mesozoic localities from the Deseado Massif comparable in both magnitude and sense to those in the North Patagonian Massif but considerably smaller than those in the Falklands/Malvinas. This latter contrast suggests that the intervening region between the Deseado Massif and the islands, in the present Argentine shelf, would have been a zone of major structural discontinuity although offshore exploration has yet to identify any such zone. Alternatively it may be a zone of distributed deformation with rotation decreasing eastward. In either case the observed rotations in all these areas were roughly coeval. The continuity of rotations within Patagonia requires further clarification and investigation to determine whether there was a distinct southern Patagonian microplate.
DE: 8110 Continental tectonics--general (0905)
DE: 8155 Plate motions--general
DE: 8157 Plate motions--past (3040)
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
SC: Union [U]
MN: 2004 AGU Fall Meeting