Greinar (Vísindafélag Íslendinga) - 01.01.1976, Blaðsíða 40

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netic relief is very low, and one suspects the presence of at least
a few hundred meters thickness of sediments here, cf. the seismic
results of Talwani et al. (18) farther to the southwest.
Fig. 8 shows the extent of low-magnetic-relief areas near Ice-
land, as estimated from the present surveys and published data
(9, 17, 18) as well as the unpublished Project Magnet map re-
ferred to above. These areas also probably correspond to the maxi-
mum present extent of thick sediments near Iceland (presumably
volcanic, and of Quaternary age), but more seismic work is re-
quired to delineate these. Central volcanoes may be present below
the sediments, though none have been identified yet.
D. Tectonic considerations
Fleischer et al. (9) conclude from their thorough survey of the
Iceland-Faeroe ridge that linear magnetic anomalies are generally
lacking but that a large number of localized magnetic gravity and
magnetic anomalies occur on the ridge. Their dimensions and
amplitudes are similar to those in Table I and II, with a clear
tendency for magnetic and gravity anomalies to coincide. These
authors do not make explicit comparisons with research results
from Iceland, but it is fairly certain that these anomalies are due
to central volcanoes. In particular, one near-shore anomaly region
studied in detail by Fleischer et al. may coincide with the eroded
Bardsnes volcanic center of Walker (3).
The density of localized gravity anomalies on the Iceland-Faeroe
ridge appears to average one per 1100 km2, but Fleischer et al.
(9) do not quote a corresponding figure for magnetic anomalies.
In the main belt of our Fig. 7, the density of central volcanoes
appears to be about one per 600 km2, but in the westem part of
the Northwest peninsula and offshore, this density may be as low
as one per 3000 km2 (even after allowing for the suspected pre-
sence of a few unmapped centers on the peninsula).
Bullerwell (20) has discussed similar locahzed geophysical ano-
malies offshore west of Scotland, and considers them to be due to
(Lower) Tertiary volcanic centers similar to those on shore.
Central volcanoes hence seem to be a characteristic feature of the
Iceland-Faeroe-Britain volcanic area, but are apparently rare on