EarthRef.org Reference Database (ERR) -- Bartolomeu Raposo & Ernesto 1995

Paleomagnetic results from the Early Cretaceous Ponta Grossa dike swarm are reported. These dikes crosscut sediments and basement rocks associated with the Ponta Grossa Arch, a tectonic feature in the eastern border of the Paleozoic-Mesozoic Paran¿ Basin. These dikes are vertical or subvertical and trend mainly NW and NE. Samples from 127 dikes were submitted to both alternating field and thermal demagnetizations; 121 of them yielded characteristic directions interpreted as original thermal remanent magnetizations. Both normal and reversed polarities as well as intermediate directions (6 dikes) are recorded. The paleomagnetic pole is located at 30.3¿E, 82.4¿S (N=115; a95=2.0¿; k=43.8). This pole along with the available paleomagnetic poles for the Paran¿ Basin volcanics (Serra Geral Formation), recalculated in this paper in the light of reported 40Ar/39Ar ages describe an apparent polar wander path segment corresponding to a clockwise rotation (~6.9¿) of the South American plate. This movement is compatible with the initial phase of the South Atlantic opening with rifting progressing from south to north. However, the calculated plate velocity is higher than the predicted velocities reported so far based on oceanic floor magnetic anomalies. The new data reported in this paper allowed the calculation of a mean Early Cretaceous pole (60.3¿E, 83.8¿S; N=7, a95=2.9¿) which can be discriminated from the Middle-Late Jurassic (191.3¿E, 86.2¿S; N=3, a95=7.8¿) and Late Cretaceous (346.5¿E, 84.1¿S; N=5, a95=4.9¿) mean poles for South America, indicating a more complex movement of the continent than the simple east-west drift generally proposed. ¿ American Geophysical Union 1995 Paleomagnetic results from the Early Cretaceous Ponta Grossa dike swarm are reported. These dikes crosscut sediments and basement rocks associated with the Ponta Grossa Arch, a tectonic feature in the eastern border of the Paleozoic-Mesozoic Paran¿ Basin. These dikes are vertical or subvertical and trend mainly NW and NE. Samples from 127 dikes were submitted to both alternating field and thermal demagnetizations; 121 of them yielded characteristic directions interpreted as original thermal remanent magnetizations. Both normal and reversed polarities as well as intermediate directions (6 dikes) are recorded. The paleomagnetic pole is located at 30.3¿E, 82.4¿S (N=115; a95=2.0¿; k=43.8). This pole along with the available paleomagnetic poles for the Paran¿ Basin volcanics (Serra Geral Formation), recalculated in this paper in the light of reported 40Ar/39Ar ages describe an apparent polar wander path segment corresponding to a clockwise rotation (~6.9¿) of the South American plate. This movement is compatible with the initial phase of the South Atlantic opening with rifting progressing from south to north. However, the calculated plate velocity is higher than the predicted velocities repo