Rit (Vísindafélag Íslendinga) - 01.06.1967, Síða 179

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which indicate that a layer corresponding to the TPB, is
found below the Quaternary rock series in the so-called
“central graben” of N.-Iceland. The surface of the TPB
seems to be at or little below sea level within the central
zone (cf. Fig. 2).
ON THE STRUCTURE OF ICELAND
In the geological literature on Iceland it has often been
stated that the TPB dips towards the central zone, i.e. the so-
called “central graben”. But already in 1906 Thoroddsen re-
ports dips in the TPB in W- and NW-Iceland which do not
agree with this conclusion. Maps published by Trausti Ein-
arsson (1960, 1965) show the dips of the Tertiary basalts
in Iceland. From the maps it is clear that only 30% of the
TPB dips towards the central zone, and the rest has dips
which cannot he connected with the central zone. On Fig. 1
the main trend of the dips in the TPB (symbol 1) and in the
older Quaternary rock series (symbol 2) is shown. The map
reveals several gentle folds, not only confined to the TPB
areas but also found in the central zone. Smaller anti- and
synclines also exist (cf. Haraldur Sigurdsson, this sympo-
sium). The folding has certainly been going on for a long
time, very likely since the beginning of volcanic activity in
Iceland in the Tertiary and has been more or less continu-
ous since then. This can clearly he seen in the Hvalfjördur
area, SW-Iceland, which is on the SE-flank of the Borgames
anticline. The lowermost Tertiary basalt sequence in the area
has a dip of 12° SE, but the overlying sequence has a dip
of 6° SE and the lowest Pleistocene hasalt on top dip 3° SE
(cf. Rutten 1958, 1960). The dip-discordances reveal also
that the volcanic activity has not been wholly continuous
but there have been some lulls in the activity which are re-
sponsible for the discordances. The Hreppar-anticline shows
similar development: The Tertiary hasalts there have a dip