Earth Planets Space, Vol. 58 (No. 10), pp. 1283-1293, 2006
Mabel Mena1,2, María Julia Orgeira1,2, and Silvia Lagorio2
1CONICET- INGEODAV, Argentina
2Dto. Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina
(Received December 20, 2005; Revised May 25, 2006; Accepted June 1, 2006; Online published November 8, 2006)
The basalts of the Posadas Formation were extruded during the huge continental volcanism that affected the Paraná Basin in the Lower Cretaceous. We have carried out a paleomagnetic and rock-magnetic study on samples collected along a basalt outcrop section in Misiones, Argentina and determined that rocks classified as tholeiitic basalts and andesi-basalts are characterized by a low to intermediate content of Ti. Paleomagnetic and rock-magnetic studies suggest that the main magnetic mineral is low-Ti titanomagnetite of superparamagnetic (SP) to single-domain (SD) sizes, and very low amounts of multi-domain (MD) particles. The stable magnetic remanence enabled us to define characteristic remanent magnetizations (ChRMs) with a maximum angular deviation (MAD) <5° in most cases; and in all the cases, a MAD <10°. The sequence has registered at least two polarity reversions, starting from a normal polarity at the base. The calculated virtual geomagnetic poles (VGPs) present an elongated distribution similar to other distributions of VGPs published for the Paraná Magmatic Province. The elongated distribution of the VGPs could be a real feature of the geomagnetic field at a time of frequent changes of polarity.
Key words: Paleomagnetism, rock-magnetism, basalts, Paranv Magmatic Province, Cretaceous.