CONTRIBUTION OF LITHOSPHERIC REMANENT MAGNETIZATION TO SATELLITE MAGNETIC-ANOMALIES OVER THE WORLDS OCEANS

Regional studies have shown that remanent magnetization of the Cretace ous 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 mag netization of the oceanic lithosphere on satellite magnetic anomalies on a global scale. We consider entire oceanic areas because oceanic Li thosphere formed during periods other than CQZ, but with a predominant polarity, also have appreciable contributions to the satellite anomal ies. 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 pola r wander path of Africa. Three magnetization models are examined: ther moremanent magnetization confined to extrusive layer 2A, and thermovis cous 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 s uggests the need for deeper sources. All models produce the satellite anomalies associated with the CQZ in the North Atlantic and parts of t he Indian and Pacific Oceans, with slight differences in location, dep ending 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 betwee n 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 system atically absent on the observed map, probably because they were remove d by along-track filtering in the early stages of processing the satel lite data. A careful comparison of the model anomalies with observatio n favors model with thermoviscous magnetization down to 12 Irm and sat uration magnetizations of 4, 0, 1, and 0.6 A/m for the extrusive basal ts, intrusive basalts, gabbros, and peridotites, respectively.