Jökull - 01.12.1992, Page 23

NW
Seaíloor
SE
Figure 5. A schematic NW-SE cross-section showing the main crustal interfaces in the Axarfjarðardjúp profile
and P-velocities at layer boundaries.
Þversnið eftir Axarfjarðardjúpi. Setlagaþykkt er um 2km.
present day rift axis. Sæmundsson (1974) suggests
that the Axarfjarðardjúp trough became active during
late Matuyama - early Brunhes time. Although the
positive Brunhes magnetic anomaly extends from the
northern volcanic zone into Axarfjarðardjúp it is dis-
turbed by tectonics offshore (Jónsson et al. 1991) and
does not necessarily reflect the magnetic field of the
basement. Judging from these sedimentation rates,
the sedimentary thickness indicates that the Axar-
fjarðardjúp basement is late- Gilbert, Gauss or early-
Matuyaina in age.
CONCLUSIONS
1- A 1.9-2.3 km thick sediment layer occurs in
the N10°W aligned Axarfjarðardjúp which is the
eastemmost trough in Tjömes fracture zone. A
continuous interface divides the sediments which
may represent different sedimentary sequences,
separated in time.
2. A higher velocity layer, thickening landwards, is
indicated within the upper sedimentary sequence,
at the southem end of the profile. The existence
of this layer is supported by observations on land
in Axarfjörður where coarse sediments and well-
cemented volcaniclastic sediments with higher
velocities have been drilled.
3. The sedimentary pile is deposited on an igneous
basement with a P-wave velocity of 4.3 km/s
which can be traced horizontally along the 70 km
long profile. Crustal velocities below the sedi-
JÖKULL, No. 42, 1992 21