Rit (Vísindafélag Íslendinga) - 01.06.1971, Page 112

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GUÐMUNDUR PÁLMASON
Reykjanes Ridge is 5-6 km (Ewing and Ewing, 1959) while in SW-
Iceland it is 8—9 km. This change in depth of the 3—4 boundary may
be related to the gradual weakening of the axial zone anomahes to-
wards Iceland. A relationship between the magnetic pattern and the
depth to the 3-4 boundary may thus be indicated.
11.5. Magnetotelluric soundings.
Hermance and Garland (1968a, 1968b) have carried out mag-
netotelluric measurements at several locations in Iceland. The latest
measurements (Hermance, pers.comm.) indicate that the electrical
resistivity decreases to a depth of several kilometers, and then in-
creases again at a depth which is between 10 and 20 km. Whether
or not the conductivity changes can be correlated with seismic boun-
daries is not clear, but it seems possible that the increase in resistivity
may occur near the boundary between layers 3and 4.
11.6. Dips of the Tertiary flood basalts.
A comparison of the dips of the Tertiary flood basalts with the
depth variations of the seismic boundaries is of importance for the
interpretation of these boundaries in geological terms. It has heen
pointed out by Einarsson (1965, 1967b) that the seismic boundaries
do not conform to the dip of the plateau basalts, which is perhaps
most obvious in eastem and western Iceland. A closer comparison of
the dips with the depth to layer 3 will therefore be made here.
The most detailed map available of the dip of the plateau basalts
in westem and northern Iceland has been prepared by Einarsson
(1960) and for eastern Iceland by Walker (1964). Einarsson’s
map is shown in Fig. 44. These maps will be compared with the depth
contours to layer 3 given in Fig. 37.
In eastern Iceland the regional dip of the flood basalts is on the
average about 6° towards the volcanic zone. Local variations are
found near the Tertiary volcanic centres, which are partly deposi-
tional dips (Walker, 1966). No direct relationship of the depth to
layer 3 to the regional dip is visible. Even though the depth to the
seismic boundary increases generally towards the volcanic zone, the
corresponding dip is much smaller than the regional dip of the flood
basalts in eastem Iceland.
In westem Iceland the situation is similar. The dips are mostly