Preliminary paleomagnetic data from the Sierra Grande formation: Tectonic consequences of the first mid-Paleozoic paleopoles from Patagonia

Abstract

The first two mid-Paleozoic paleomagnetic poles from Patagonia were obtained from a preliminary paleomagnetic study of the Sierra Grande Formation, exposed at 65.4°W, 41.6°S in Argentina. The first pole, SG1, is located at 238.0°E, 3.4°N (N=14, D1=14.3°, D2=8.5°) and corresponds to a ferriferous horizon intercalated in the lower member of the formation, which is assigned to the Wenlockian. The second pole, SG2, located at 283.5°E, 42.0°S (N=10, D1=20.4°, D2=20.2°), belongs to the upper member of the formation and is assigned to the Late Silurian-Early Devonian. These pole positions are interpreted according to different tectonic hypotheses. The position of SG1 is more easily understood if Patagonia had an allochthonous origin, for it does not agree with the presently most accepted Silurian pole position of Gondwana. Nevertheless, the position of SG2, consistent with the Late Silurian-Early Devonian Gondwana poles, suggests that Patagonia was next to collide with South America in the Early Devonian. On the other hand, the hypothesis of an autochthonous Patagonia is supported by the consistent position of SG2 with respect to the coetaneous poles of Gondwana, while SG1 would indicate that the reversed polarity path of Schmidt and Morris (1977) should be taken as the most probable early-middle Paleozoic apparent polar wander path of Gondwana.