An Early Cretaceous paleomagnetic pole from Ponta Grossa dikes (Brazil): Implications for the South American Mesozoic apparent polar wander path

Abstract

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 Paleozpic‐Mesozoic Parana 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; α95 = 2.0°; k = 43.8). This pole along with the available paleomagnetic poles for the Paraná 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 tp 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, α95 = 2.9°) which can be discriminated from the Middle‐Late Jurassic (191.3°E, 86.2°S; N = 3, α95 = 7.8°) and Late Cretaceous (346.5°E, 84.1°S; N = 5, α95 = 4.9°) mean poles for South America, indicating a more complex movement of the continent than the simple east‐west drift generally proposed.