Paleomagnetism of Upper Carboniferous Sedimentary and Volcanic units from the Río Blanco Basin, Central West Argentina

GEUNA, SILVANA; ESCOSTEGUY, LEONARDO; FAUQUE, LUIS

Rio de Janeiro

Congreso; 31st International Geological Congress; 2000

The Punta de Agua and Río del Peñón Formations are part of the fillingof the Río Blanco Basin in the Argentine Precordillera and Cordillera Frontal(29oS, 68o30W). The Punta de Agua Formation is a volcanic complex mainlycomposed of andesites, breccias and conglomerates. This is conformably overlaidby the Río del Peñón Formation, a marine clastic sequence of Late Carboniferousage. Thirty-eight sites composing 121 block samples of these units werecollected from both flanks of the Rincón Blanco syncline. After removal of asmall present-day field overprint by 300°C or 15mT, a characteristic steeplydown direction was isolated during thermal and alternating-field treatment, inmost of the volcanics and sedimentary rocks. This reversed polaritycharacteristic magnetization passes a fold test at the 95% confidence levelsuggesting that the remanence is pre-tectonic. The formation of the RincónBlanco syncline might have begun with the San Rafael orogenic phase (EarlyPermian). Then the age of the magnetization is restricted to theKasimovian-Gzelian (beginning of the Kiaman reversed interval) to Asselian. Thedirections calculated from 30 sites yield a paleomagnetic pole at 73.3°S283.4°E, with A95=8.1. This direction is not in agreement with the UpperPaleozoic apparent polar wander path of Gondwana, indicating a possibleclockwise rotation of the sampling area, of about 40 degrees.