INTERPRETATION OF THE SATELLITE MAGNETIC ANOMALY OF THE NOVA-SCOTIA MARGINAL BASIN

Satellite magnetic anomaly maps show well-defined negative anomalies o ver some deep sedimentary marginal basins, such as the Nova Scotia mar ginal basin. A possible explanation would be the thermal demagnetizati on of the oceanic upper crust due to thermal blanketing by the sedimen ts and the oceanic lower crust and uppermost mantle due to subsidence into hotter regions beneath. We examine this possibility by computing the thermoviscous remanent magnetization of the oceanic lithosphere be neath the Nova Scotia basin using a detailed thermal evolution model w hich takes into account the continental rifting, sea-floor spreading, and subsequent subsidence. It is concluded that the thermal demagnetiz ation is not sufficient to explain the entire observed negative magnet ic anomaly over the basin; it contributes similar to 40% to the anomal y. We suggest that a major part, similar to 60%, of the anomaly arises from the particular location of the early Mesozoic oceanic lithospher e beneath the basin, which has a relatively weaker bulk remanent magne tization compared with a highly magnetic continental crust in the west and north and the strong magnetic oceanic lithosphere of the Cretaceo us Quiet Zone in the east.