We used integrated analyses and forward and inverse modeling of potential field data to interpret the enigmatic Brunswick magnetic anomaly (BMA), a prominent negative magnetic lineation that is developed within the ocean-continent transition of the Southeast Georgia Embayment. From magnetic profiles extracted from gridded data, residual magnetic maps, and simultaneous 2.5-dimensional forward and 3-dimensional Euler inverse modeling of the gravity and magnetic fields, we suggest that the source of the BMA is a series of semicontinuous to discrete, late-stage rift-related mafic intrusions of Mesozoic age. This interpretation is supported by the observation that the BMA is independent of the East Coast magnetic anomaly, implying a predrift source, and that the amplitude and frequency of the anomaly change nearshore across a fracture zone that divides the offshore BMA, where continental breakup occurred, from the onshore BMA. Modeling demonstrates for the first time that a Mesozoic rift-related mafic body can explain the anomaly onshore. The lack of a BMA equivalent on the West African margin may indicate that Atlantic rifting began with a single lithospheric dislocation.

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