Propriedades Magnéticas dos Peridotitos do Arquipélago São Pedro e São Paulo: Uma Janela Para o Manto Oceânico

The contribution of the different layers of the oceanic lithosphere to the seafloor magnetic anomaly patter is still a matter of debate, in part due to the scarce knowledge on the magnetism of its deepest sectors: the mantle peridotites. Here we present magnetic results on the serpetinized peridotites that crop out in the San Peter-San Paul archipelago. Sampling was performed in four islands and comprises 274 specimens distributed along 19 sites for standard scalar parameters: magnetic susceptibility (k) and natural remanence (NRM). Our results show k values range from 1.53e-6 to 2.54e-2 and NRM values range from 3.88e-4 to 1.16 A/m, the highest values being found in the Challenger island. Remanence in these rocks is carried by pure magnetite in the pseudo-single domain range, probably formed during serpentinization of the original peridotites. Koenigsberger ratios (for a local field of 22 μT) vary between .036 and 6.54, suggesting that the deepest layer of the oceanic lithosphere must contribute to some extent to the anomalies observed on the sea floor.