Paleomagnetic data of Upper Jurassic-Lower Cretaceous rocks in Central Patagonia: evidence for tectonic rotations

GEUNA, SILVANA; SOMOZA, RUBÉN; VIZAN, HAROLDO; FIGARI, EDUARDO; RINALDI, CARLOS

Birmingham

Congreso; IAGA 9th Scientific Assembly; 1999

We report preliminary paleomagnetic datafrom a widespread distribution of sites of Upper Jurassic to lowermostCretaceous volcanic and sedimentary rocks in the Cañadón Asfalto basin, centralPatagonia. Monocomponent and multicomponent magnetizations were observed duringboth thermal and AF demagnetization procedures. Some sites show the presence ofboth normal and reverse polarities, while only one polarity is observed inothers. The resulting time-averagedpaleomagnetic vector of each site was compared with the expected LateJurassic-Early Cretaceous paleofield for South America. Despite problems withthe accurate definition of the APWP of this continent, the paleodeclinations ofthe studied rocks suggest the widespread occurrence of vertical axis rotations.In contrast, the unconformable overlying Cretaceous rocks in the region do notshow paleomagnetic evidence of vertical axis rotations. This indicates thatmost tectonic rotations detected in rocks of the Cañadón Asfalto basin arecoeval with, and perhaps closely related to the opening of the South AtlanticOcean.