Sea floor spreading history, VI, Labrador sea, Plate reconstruction, Closure magnetic anomaly

Geophysical data collected during a detailed survey in Baffin Bay have shown that lineated magnetic anomalies trending north-northwest occupy the deep central region. These anomalies exhibit maximum amplitudes of about 300 nT and can be modelled by a 1-km thick magnetic source layer divided into blocks of normal and reversed polarity. The magnetizations required are comparable with those of oceanic basalts. A striking feature of the gravity field is a 20 mGal gravity low, about 20 km wide, which runs through the centre of the bay with approximately the same trend as the magnetic lineations. The gravity low is associated with a change in crustal structure measured from seismic refraction data and sometimes with a deepening of the sediment-basement interface, reminiscent of a median valley. These results suggest that the magnetic anomalies were produced by sea-floor spreading and that the gravity low marks an extinct spreading centre in Baffin Bay. Comparisons of the magnetic anomaly profiles with a model profile computed for magnetic anomalies 13–24 (38 to 60 Ma), show good correlation between the observed and computed anomalies in the time period represented by anomalies 13–21, with slow spreading rates of about 0.3–0.4 cm yr−1 perpendicular to the spreading axis. These results are in reasonable agreement with magnetic anomaly identifications and spreading rates deduced from geophysical data in the Labrador Sea. The direction of plate motion in Baffin Bay is not well defined from the data, but the Labrador Sea data require plate motions at a highly oblique angle to the spreading centre in the bay. Peculiarities of the postulated spreading centre, including the change in crustal structure beneath the gravity low along its strike from south to north, and the decrease in coherence and amplitude of the magnetic anomalies immediately north of the survey area, may be the result of these very low spreading rates, oblique spreading and changes in spreading direction, or the proximity of this area to the junction with a possible major transform fault through the Nares Strait.

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Sea-floor spreading in the Labrador Sea: A new reconstruction

Geology ◽

10.1130/0091-7613(1989)017<1000:sfsitl>2.3.co;2 ◽

1989 ◽

Vol 17 (11) ◽

pp. 1000 ◽

Cited By ~ 224

Author(s):

W. R. Roest ◽

S. P. Srivastava

Keyword(s):

Labrador Sea ◽

Sea Floor ◽

Sea Floor Spreading

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Fission Track Age of Magnetic Anomaly 10: A New Point on the Sea-Floor Spreading Curve

Science ◽

10.1126/science.164.3887.1516 ◽

1969 ◽

Vol 164 (3887) ◽

pp. 1516-1517 ◽

Cited By ~ 9

Author(s):

B. P. Luyendyk ◽

D. E. Fisher

Keyword(s):

Magnetic Anomaly ◽

Fission Track ◽

Sea Floor ◽

Sea Floor Spreading

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Geology of the Northern End of Juan de Fuca Ridge and Sea-Floor Spreading

Canadian Journal of Earth Sciences ◽

10.1139/e74-134 ◽

1974 ◽

Vol 11 (10) ◽

pp. 1384-1406 ◽

Cited By ~ 33

Author(s):

Sandra M. Barr ◽

R. L. Chase

Keyword(s):

Magnetic Anomaly ◽

Fracture Zone ◽

Juan De Fuca Ridge ◽

Transform Fault ◽

Sea Floor ◽

Fuca Ridge ◽

Juan De Fuca ◽

Low Potassium ◽

Sea Floor Spreading ◽

Ocean Ridge

The northern end of Juan de Fuca Ridge consists of a series of basement ridges and valleys, inundated with sediment except for the axis of most recent sea-floor spreading. This axis is associated with the western of two branches of the Brunhes magnetic anomaly. The eastern branch of the magnetic anomaly is associated with a largely sediment-covered ridge, apparently produced by spreading early in the Brunhes Epoch. The intervening negative anomaly is probably caused by reversely magnetized rocks older than 0.7 m.y. Basalts dredged from the region of the northern end of Juan de Fuca Ridge have compositions typical of low-potassium ocean ridge basalts. They differ from basalts reported from the southern part of Juan de Fuca Ridge which have higher K2O, TiO2, FeOT, and FeOT/MgO. This difference is compatible with the hypothesis that a mantle plume exists under the southern part of the ridge. Distribution of earthquake epicenters suggests that the Queen Charlotte Fault Zone presently extends south of Explorer Ridge to intersect Juan de Fuca Ridge at 49°N and that the Sovanco Fracture Zone no longer functions as a transform fault.

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