Paleomagnetic poles and paleosecular variation of basalts from Paraná Magmatic Province, Brazil: geomagnetic and geodynamic implications

Abstract

A paleomagnetic study was carried out along two sections (altogether 35 lava flows, 300 samples) in the central Paraná Magmatic Province (PMP), Brazil. The two sections, distanced ca. 200 km apart, yield statistically indistinguishable paleomagnetic poles. The combined paleomagnetic pole with coordinates −85.7°N, 197.9°E ( A95=2.6°, N=35) is statistically different from previously published paleomagnetic poles for other sections of PMP. We suggest that this angular difference, as well as differences between previously published poles, is caused by undetected local tectonic rotations not easily identified in the often-poorly exposed lavas of the PMP. A joint analysis of all published PMP paleomagnetic data indicate that paleosecular variation, estimated as the angular standard deviation ( S F) of the virtual geomagnetic pole distribution, does not support the suggestion of anomalously high secular variation at low latitudes in the 110–195 Ma period [J. Geophys. Res. 96 (1991) 3923]. All S F estimates are, in fact, in better accordance with latitudinal dependence estimates derived from the curve for the 0–5 Ma period. Moreover, we find that all PMP paleomagnetic poles lie ∼10° away from the pole predicted by an assumed fixed hotspot reconstruction of South America. The PMP paleomagnetic poles, therefore, call for either true polar wander or motion of Indo-Atlantic hotspots.