Great circle analysis of South American VGP-distributions suggests widespread Cretaceous remagnetizations: case study of the Itararé Group Rocks from Brazil

South American Jurassic/Cretaceous rocks has been troubled by elongated virtual geomagnetic pole (VGP) distributions, while many discordant poles from the Carboniferous to the Triassic have also been recognized, rendering the South American apparent polar wonder path (APWP) problematic. 

We have conducted a paleomagnetic study of the sedimentary Permo-Carboniferous Itararé Group rocks within the state of São Paulo, Brazil, including three intruding mafic sills that are attributed to Early Cretaceus magmatic activity. The site-mean VGP distributions obtained from the sedimentary rocks define elongations that include the VGPs of the mafic intrusions, and are interpreted as remagnetization paths toward the directions characteristic of the sills. These interpretations are supported by extensive rock-magnetic data that provide a viable mechanism for the secondary magnetizations. Careful analysis of the paleomagnetic data of the sedimentary rocks enables isolation of a primary VGP distribution that is consistent with the reference Carboniferous pole position.

Analysis of other Carboniferous to Triassic South American paleomagnetic VGPs reveals that the majority of these data are also elongated: regardless of the age of the rocks, the elongations dominantly intersect at the location of the Late Cretaceous reference pole, and a second location similar to the intersection of the VGP elongations of some Jurassic/Cretaceous rock formations, and also coincides with the cusp of the debated loop in the Carboniferous-Triassic APWP. Based on multiple lines of evidence, we interpret the elongations and their intersections to reflect remagnetizations that occurred as a result of the widespread magmatism associated with the opening of the South Atlantic. We suggest that the extent of the remagnetizations is formation-specific, and that other rock-formations should be carefully re-evaluated.