Greinar (Vísindafélag Íslendinga) - 01.01.1976, Blaðsíða 106

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phery of the island, and with the dominating steep north-west dip
on the north-eastern peninsula. But these two regions differ con-
siderably in the number of dikes: in the north-west the number of
dikes is much less than in the eastern region. In the north-west only
separate dikes with different strikes are observed (34, 40). In the
east the dikes are grouped into several large swarms with north and
north-north-east strike (19, 20, 49, 50). The length of individual
swarms may reach 40 km and the width commonly is 3—5 km (but
sometimes reaches 10 km). Within the swarms the dikes, varying
in thickness from several meters to 17 m, are located parallel to each
other and with distance between them from 4 to 30 m. In some
places dike zones without dividing basalts are found up to 65 m
wide. But outside the swarms only 4-5 dykes are found per km if
counted in transversal direction. Buried central volcanoes, formed
mostly of acid rocks, are scattered within the layers of the plateau-
basalts.
The Inner Zone is composed mainly of rocks of the Pliocene and
Pleistocene, though in its marginal parts (and in the north of Ice-
land in its middle part) the Miocene basalts outcrop on the surface.
The zone is 250 km across and is characterised by block and folded-
block structures, being divided into uplifted and suhsided areas
bordered by faults and sometimes hy steep flexures.
The north-western boundary of this zone, separating it from the
quiet zone of the North-Western peninsula, crosses in the narrowest
part the isthmus which joins the peninsula with the main part of
the island. The tectonic boundary expressed by a flexure is pierced
by a large number of dikes parallel to it. The eastern boundary of
the inner zone is expressed by numerous echelon-like faults.
Within the inner zone in tum a number of subzones can be
defined. In the south there are two Neovolcanic subzones mentioned
above: the Western and the Eastern, the intermediate Hreppar-
subzone, which divides these two; and two peripherial or transition
subzones. There is also the separately located neovolcanic Snaefells-
nes zone.
Structurally the neovolcanic zones are tectonic depressions almost
everywhere framed by systems of normal faults, in connection with
which they should be called grabens, though in some places their
limitation has the character of flexures. The fact that these zones