Aeromagnetic profiles across the Reykjanes Ridge southwest of Iceland

Abstract

Six low‐level aeromagnetic profiles were obtained across the Reykjanes ridge southwest of Iceland during 1967. The 1300‐km long profiles spaced about 100 km apart were flown at right angles to the mid‐Atlantic ridge between the Greenland and European continental shelves. The magnetic anomalies have an excellent symmetry about the crest of the ridge, and the symmetry extends from the Greenland continental slope to about the 2000‐meter contour on the European side. A quantitative interpretaion of the results indicates that the intensity of magnetization (J) of the rock producing the axial anomaly is about 0.013 emu/cc. A plot of the average J over 20 km also shows excellent symmetry about the ridge axis, and the known geomagnetic polarity epochs have associated maxima and minima in the J plot. There appear to be twenty‐three polarity epochs in 480 km, so that the average length of an epoch is 2.1 m.y. if a constant spreading rate of 1 cm/yr is assumed. A power spectral analysis shows a major peak at 40 km, which is about the length of a complete reversal cycle. Digital filtering was, therefore, performed to separate the anomalies due to epochs and those due to events. There are sixty‐one reversals of the magnetic field in 500 km that are resolvable in the profiles. The magnetic anomaly pattern has a minimum amplitude and a maximum wavelength at points 260 km on either side of the ridge axes. The amplitude and wavelength are approximately symmetrical for distances of 160 km on either side of these 260‐km points. Two possible explanations of this symmetry are offered: (1) If it is assumed, as was suggested by Menard, that the thickness of the second layer is directly proportional to the spreading rate, both the change in anomaly wavelength and amplitude can be explained by a symmetrical 2:1 change in spreading rate. (2) The double axes of symmetry are the locus of two dormant ridges that were active in the middle Tertiary and migrated away from one another because the material between them could not itself migrate. Any continental crustal remnants would tend to be trapped between the double‐ridge system. When the two active ridges were approximately 320 km apart, they and possibly the Labrador Sea ridge became dormant. The present stage of single‐ridge ocean‐floor spreading began about 10 m.y. ago, and the unconformity between the two systems occurs at 100 km, where Ewing and Ewing have demonstrated that a discontinuity in the sediment thickness exists.

Reykjanes ridge crest: A detailed geophysical study

“…The evidence has been presented by (on the basis of Lamont data, as well as data obtained by Godby et al [1968]) and by Vogt et al [1970]. Whereas the suggestion of hiatus on a worldwide basis can almost certainly not be substantiated, magnetic anomalies have provided convincing evidence for a hiatus or a much lower spreading rate between anomaly 13 (38 m.y.…”

The Southern Labrador Sea—A Key to the Mesozoic and Early Tertiary Evolution of the North Atlantic

“…The magnetic anomalies of the outer parts of the Reykjanes Ridge were mapped by Godby, Hood and Bower (1968), and identifications with respect to the Heirtzler time scale can be made by relating these with the more closely mapped anomalies near Rockall Plateau (Aver<y, Vogt and Higgs, 1969). South of Rockall Plateau, anomaly trends have been mapped by Avery et al, and by Williams and McKenzie (1971).…”

Sites 403 and 404

“…in age (Ewing and Ewing, 1958;Godby et al, 1968;Vogt et al, 1969Vogt et al, , 1971Scrutton and Roberts, 1971;Ruddiman, 1972;Laughton, 1971;Vogt and Avery, 1974) (Figure 3). The age of the oceanic basement abutting the southwest margin is, by the position there of anomaly-32, 73 m.y.…”