Fróðskaparrit - 01.01.1971, Side 20

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Magnetic Anomalies Around The Faeroe Islands
now show that the anomaly over the northern islands is local
and about — 65 mGal. The geological models on the invisible
part of the Faeroes presented by Saxov and Abrahamsen (1964)
and Noe-Nygaard (1966) only needed to explain an anomaly
of — 7 mGal; neither a hidden mound consisting of submarine
palagonite tuffs and pillow breccias, nor a local depression in
the crust mantle boundary, however, can explain the anomaly
we now see (Fig. 4).
A combination of the above mentioned causes might ex-
plain the anomaly (if the tuffs and breccias are allowed to
be several times thicker than the 300 m earlier considered).
Flowever, it seems more obvious to interpret the — 65 mGal
anomaly as caused by a concealed body of salic (continental)
rocks; Fig. 4 shows the approximate extension of such a body.
Isostatic movements of the salic rock-body might then explain
the domestructure.
The recent theories on the sea-floor spreading in the Nor-
wegian Sea presented in Vogt et al. (1970) also seems to favour
a continental origin of the invisible part of the Faeroe Islands.
Vogt et al. show that the axis of rifting between the Iceland-
Faeroe Ridge and the Jan Mayen Fracture Zone has been
shifting; they show that the now active Jan Mayen-Iceland
Ridge may be as young as 4 m. y. and suggest that the spread-
ing in the Norwegian Sea between about 60—42 m. y. B.P.
took place around a now extinct axis (N-S striking along the
4° W median).
This shifting of spreading axis might explain that a conti-
nental rest could be left behind; the position of the spreading
axis northeast of the Faeroe Islands, at the time when the
basalts poured out, may explain that we find the youngest
series in the eastern part of the islands.
Acknowledgement
I wish to thank J. Rasmussen, statsgeolog, for advice and
discussion during the survey; A. Toft, master, and Egmont
Nielsen, mate, for their excellent navigation; S. W. Platou
for assistance in the model calculations, and Anneli Damgaard