The study of magnetic anomalies over Davis Strait

Magnetic data collected during several cruises in Davis Strait show north-south lineations over most of the area. The central positive magnetic zone coincides well with a major gravity low. These results suggest that the magnetic anomalies were produced by seafloor spreading and that the gravity low marks an extinct spreading center in Davis Strait. Comparison between the geomagnetic polarity time-scale and dated anomalies in Labrador Sea suggests identification of anomalies 13–27 (37 to 62 MY). In southern Davis Strait (63°N), the spreading rates are 8.4 mm/y. east of the spreading center, and 2.7 mm/y to the west. In northern Davis Strait (66°N), the spreading rates are 4.5 mm/y east of the spreading center, and 2.1 mm/y to the west. Seafloor spreading in Davis Strait was there-fore very asymmetrical, with decreasing rates from south to north. Spreading is interpreted as having begun at 61–63 M and ending at 37 MY. Three fracture zones have been delineated, suggesting oblique spreading about the ridge axis in the Davis Strait. A distinct northeast-southwest anomaly zone is interpreted as the, expression of faults caused by volcanically-induced vertical crustal movements, and not by spreading-related horizontal crustal movement. Faulting along this northeast-southwest anomaly zone is inferred to have occurred after the spreading and before 30 MY. The magnetic anomalies off Cape Dyer are proposed to be different from the anomalies striking in northeast-southwest direction. The Cape Dyer anomaly is interpreted as being formed at 58 MY while the northeast-southwest anomaly zone formed more recently. This work was carried out at Department of Geology and Centre for Marine Geology, Dalhousie University, Halifax, N. S. Canada.