Greinar (Vísindafélag Íslendinga) - 01.01.1976, Blaðsíða 107

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are subsided has no effect or almost no effect on the relief; in some
places a reversed relief is observed. The latter is especially clearly
expressed in the Snaefellsnes zone, which structually is a gently
sloping depression.
Usually the large grabens of Iceland are called rifts, i.e. Western
and Eastern rift zones. These latter names are used on our map
(Fig. 1), though their terminological correctness is subject to doubt.
The term “rift” should, apparently, mean large structural com-
plexes consisting of a nrnnber of grabens and horsts. From this
viewpoint the entire inner zone of Iceland is a rift. Particular
structures should, obviously, be called just grabens and horsts. Any-
way, the use of this or that term largely depends on the assumed
scale applied in a given case to the structure.
The Hreppar-Eyjafjördur uplift is a horst complicated by a gentle
domelike bend of the strata. The horst lifts to the north, such that
the Pliocene rocks forming it in the south are replaced by the
Miocene ones in the north. The bottom of the Western rift zone
lifts to the north in exactly the same way, owing to which, as al-
ready marked above, the northem part of this zone is composed
along its axis not by the Pleistocene-Holocene rocks, as in the south,
but b)r the Pliocene-Eopleistocene.
Besides these large grabens (“rifts”) and the rift between them,
the inner zone is complicated by a great number of much smaller
grabens and horsts.
These small grabens and horsts stretch along the rift zones and
the Hreppar-Eyjafjördur uplift. Due to the block movements within
the eastern rift zone, an uplift of the Tjömes Peninsula has been
formed in the north, where not only the Pliocene rocks outcrop on
the surface, but also those of the Miocene.
The valleys of Northem Iceland are mostly of biock origin: they
are grabens or graben-synclines, while the ridges dividing them are
horsts and horst-anticlines. Within their boundaries the grabens of
large valleys consist of a large number of smaller horsts and grabens
and also of monoclinal blocks. Especially numerous faults are found
in rift zones. Here faults, fault-wrenches, tension fissures are group-
ed into echelon-like distributed swarms.
The amplitude of individual faults does not exceed tens or few
hundreds of meters. But groups of numerous parallel faults can