Jökull - 01.01.2014, Side 1

Reviewed research article
Paleomagnetic studies on the lava pile between Skálavík and
Álftafjörður, Northwest Iceland
Leó Kristjánsson
Institute of Earth Sciences – Science Institute, University of Iceland, Sturlugata 7, 101 Reykjavík, leo@hi.is
Abstract — This paper focuses on the lava pile in the westernmost part of the south coast of the Ísafjarðardjúp
fjord in the Northwest peninsula of Iceland, between Skálavík and Álftafjörður. New laboratory measurements
on the paleomagnetism of over 60 lava flows in four profiles are utilized in the completion of a tentative polarity
column for a composite section of 3.4 km thickness along Ísafjarðardjúp. The magnetic results which among
other things document the occurrence of several excursions of the geomagnetic field, are consistent with other
available data from the area. They also strengthen correlations with a composite section running south from
Skálavík to Breiðafjörður. Some relevant previous studies on the Northwest peninsula are reviewed, with em-
phasis on the question whether the presence of the oldest lignite-containing sediments there is related to major
volcano-tectonic events. Judging from the thickness of polarity zones, the rate of buildup of lavas below these
sediments seems to have been of similar order of magnitude as elsewhere in Iceland.
INTRODUCTION: PREVIOUS
RESEARCH RELEVANT TO THE
GEOLOGY AND PALEOMAGNETISM
OF THE NORTHWEST PENINSULA
The lava piles in the older regions of Iceland at the
northwestern and eastern coasts of the island are fairly
similar in appearance, consisting of sequences of pre-
dominantly basaltic lava flows of average thickness 8–
10 m. Successive lavas are separated by scoria zones
as well as by thin layers of volcanoclastic sediments.
The lava pile in the Northwest peninsula (Vestfirðir,
Figure 1) is somewhat monotonous compared to that
of the eastern fjords, especially away from its eroded
central volcanoes. Thus the tectonic tilts are small
(mostly < 7◦) and rather uniform, there are fewer in-
trusions or acidic lava flows and tuffs, and alteration
minerals such as zeolites are less common. Although
more is known of the age and stratigraphy of lavas in
the Northwest peninsula than in many other parts of
Iceland, much remains to be studied. The project to be
described here attempts to fill a few small gaps in our
knowledge of the older lava formations of the penin-
sula. In particular it extends downwards (from Álfta-
fjörður to Skálavík) the geomagnetic polarity column
of Kristjánsson and Jóhannesson (1996) for the lava
pile on the south side of Ísafjarðardjúp. Some other
previously published results are reviewed in the next
few sections, especially as regards rates of buildup of
the lava pile and the significance of hiatuses in this
buildup.
Findings up to 1960
Walker (1959) was able to trace petrographically dis-
tinct groups of feldspar-porphyritic or olivine-rich
flows for distances up to tens of km in the mostly
tholeiitic lava pile of East Iceland, while such group-
ing seems to be less persistent in the Northwest. On
the other hand the Northwest peninsula has some geo-
logical features which are almost absent in the East
fjords, such as the presence of sediments containing
JÖKULL No. 64, 2014 1