Shackleton Mid-Atlantic Ridge Crest Survey near 45°N: No Evidence for Asymmetric Spreading

1974 ◽  
Vol 11 (6) ◽  
pp. 867-871
Author(s):  
C. A. Williams
Keyword(s):  
Conclusive Evidence ◽  
Sea Floor ◽  
Ridge Crest ◽  
Mid Atlantic Ridge ◽  
Spreading Rates ◽  
Sea Floor Spreading

An eastwards extension of the Hudson Geotraverse has been made aboard R.R.S. Shackleton. The spreading rates have been determined from the magnetic observations and compared with those of Loncarevic and Parker (1971), but they produce no conclusive evidence for asymmetric sea-floor spreading.

New estimates of rapid sea-floor spreading rates and the identification of young magnetic anomalies on the East Pacific rise, 6° and 11° S

1973 ◽  
Vol 19 (2) ◽  
pp. 225-229 ◽  
Author(s):  
David K. Rea ◽  
Jack Dymond ◽  
G. Ross Heath ◽  
Donald F. Heinrichs ◽  
Stephen H. Johnson ◽  
...  
Keyword(s):  
East Pacific Rise ◽  
Magnetic Anomalies ◽  
Sea Floor ◽  
East Pacific ◽  
Spreading Rates ◽  
Sea Floor Spreading

A revised magnetic polarity timescale for the Cretaceous and Cainozoic

1982 ◽  
Vol 306 (1492) ◽  
pp. 129-136 ◽  
Keyword(s):  
Magnetic Polarity ◽  
Geomagnetic Reversal ◽  
Sea Floor ◽  
Marine Magnetic Anomalies ◽  
Increasing Trend ◽  
Reversal Frequency ◽  
Spreading Rates ◽  
Sea Floor Spreading ◽  
Central Atlantic ◽  
Stage Boundaries

Magnetostratigraphic correlations of biostratigraphic stage boundaries have established calibration points for dating the polarity reversal sequence derived from marine magnetic anomalies. Interpolation between the best-estimate ages for these tie points gives a revised magnetic polarity timescale for the Cainozoic and Cretaceous. Recomputed sea-floor spreading rates for this time prove to be high during the Cretaceous quiet interval at several plate margins, but remained remarkably constant in the central Atlantic. The geomagnetic reversal frequency, when averaged over intervals of several megayears duration, has exhibited a steadily increasing trend since the late Cretaceous.

Fracture zones on the Mid-Atlantic Ridge between 43° N and 44° N

1970 ◽  
Vol 7 (5) ◽  
pp. 1352-1355 ◽  
Author(s):  
M. J. Keen
Keyword(s):  
Fracture Zone ◽  
Seismic Reflection ◽  
Seismic Reflection Profile ◽  
Fracture Zones ◽  
Sea Floor ◽  
Eastern Flank ◽  
Reflection Profile ◽  
Mid Atlantic Ridge ◽  
Sea Floor Spreading

A seismic reflection profile across the fracture zones on the Mid-Atlantic Ridge between 43° N and 44° N shows that the thickness of sediment increases markedly south of the fracture zone at 43° 05′ N on the eastern flank of the ridge. The thickness there is in accord with observations made west of the ridge in the region of the survey at 45° N. This suggests that the effects of rates of sea-floor spreading and sedimentation have been similar on this eastern part of the ridge to those west of the ridge farther north.

New geophysical evidence for sea-floor spreading in central Baffin Bay

1979 ◽  
Vol 16 (11) ◽  
pp. 2122-2135 ◽  
Author(s):  
H. R. Jackson ◽  
C. E. Keen ◽  
R. K. H. Falconer ◽  
K. P. Appleton
Keyword(s):  
Magnetic Anomaly ◽  
Crustal Structure ◽  
Magnetic Anomalies ◽  
Geophysical Data ◽  
Plate Motion ◽  
Labrador Sea ◽  
Sea Floor ◽  
Baffin Bay ◽  
Spreading Rates ◽  
Sea Floor Spreading

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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