Contribution of lithospheric remanent magnetization to satellite magnetic anomalies over the world's oceans

Abstract

Regional studies have shown that remanent magnetization of the Cretaceous quiet zones (CQZs), created during the long period of geomagnetic normal polarity at 118–84 Ma, produce well‐defined magnetic anomalies at satellite altitudes. We investigate the effects of the remanent magnetization of the oceanic lithosphere on satellite magnetic anomalies on a global scale. We consider entire oceanic areas because oceanic lithosphere formed during periods other than CQZ, but with a predominant polarity, also have appreciable contributions to the satellite anomalies. The magnetic anomalies of the world's oceans are calculated from a distribution of vertically integrated remanent magnetization that is computed using age map, plate relative motions, and the apparent polar wander path of Africa. Three magnetization models are examined: thermoremanent magnetization confined to extrusive layer 2A, and thermoviscous remanent magnetization of the crust and uppermost mantle down to a maximum depth of 12 km or 30 km. Although all models lead to rather similar anomaly distributions, the amount of magnetization required suggests the need for deeper sources. All models produce the satellite anomalies associated with the CQZ in the North Atlantic and parts of the Indian and Pacific Oceans, with slight differences in location, depending on the models. Low‐amplitude observed anomalies associated with areas created at fast and intermediate spreading rates in the Indian and Pacific Oceans are successfully modeled. A major difference between models and observation is the north‐south elongated model anomalies associated, for instance, with the CQZs in the South Atlantic and the fast spreading East Pacific Rise. These elongated anomalies are systematically absent on the observed map, probably because they were removed by along‐track filtering in the early stages of processing the satellite data. A careful comparison of the model anomalies with observation favors model with thermoviscous magnetization down to 12 km and saturation magnetizations of 4, 0, 1, and 0.6 A/m for the extrusive basalts, intrusive basalts, gabbros, and peridotites, respectively.