A COMPREHENSIVE PALEOMAGNETIC STUDY FO THE ITARARE' GROUP FROM THE STATE OF SAO PAULO, BRAZIL, IN THE CONTEXT OF PANGEA RECONSTRUCTIONS: EVIDENCE FOR PERVASIVE SOUTH AMERICAN REMAGNETIZATIONS

It has long been recognized that Permo-Carboniferous paleomagnetic data throughout Pangea imposes an overlap between Laurasia and Gondwana in the traditional Pangea-A assembage. To obviate for this problem, the alternative Pangea-B configuration was proposed, that places Gondwana to the West of Laurasia between the Carboniferous and the Triassic. More recently, it was shown that the paleogeographies of the two landmasses may be brought into agreement if significant inclination shallowing is assumed for the sedimentary rock-derived paleopoles. However, increasing evidence for widespread remagnetization is becoming available for South American rocks.

 We performed an extensive paleomagnetic study, including rock-magnetic characterization and anisotropy, of the Permo-Carboniferous Itararé Group throughout the state of São Paulo, Brazil. This also includes three basalt sills that intruded the sedimentary rocks, most likely during the post-Jurassic breakup of Pangea. We obtained a wealth of paleomagnetic directions that are suspiciously consistent with the directions isolated from the basalts, whereas a limited number of sites appear independent of the volcanic rocks. These independent sites allowed us to calculate a paleopole that we believe to be primary Upper Carboniferous, and which has been corrected for inclination shallowing using the anisotropy of magnetic remanence.

However, rock-magnetic evidence, a fold test, and shape analysis of the distributions of directions and poles obtained from the bulk of the Itararé sites provides convincing evidence for these magnetizations to be secondary. A comparison of these paleopoles and data presented in the literature not only supports the notion that these rocks were remagnetized during the Cretaceous, but also suggests that many published Permo-Carboniferous poles throughout South America are affected by these secondary magnetizations.

Scrupulous revision of the Permo-Carboniferous Apparent Polar Wander path for South America, and elimination of all poles suspected to be remagnetized, yields a new path that is consistent with a Pangea-A assemblage, without the need to apply systematic blanket inclination shallowing corrections that are unjustified and scientifically unsound.