Jökull - 01.12.1979, Síða 59

8. Outline of the petrology of Iceland
SVEINN PETER JAKOBSSON
Museum of Natural History, P. 0. Box 5320, Reykjavík
INTRODUCTION
Until in the early nineteen sixties the petrology
of Iceland was generally thought to be fairly simple
and monotonous. The bulk of the igneous rocks was
believed to be basaltic, in the main tholeiitic, with
only a few per cent being rhyolitic. Intermediate
rocks were considered very rare, and the chemical
variation within the two above mentioned groups
negligible.
However, within the last decade, mainly because
of the development of ideas on sea-floor spreading
and hot mantle plumes, a vast number of papers
dealing with the geochemistry and petrology of
Icelandic rocks has been produced, adding to the
complexity of the picture, and indeed showing that
the petrology of Iceland is probably more diverse
and variable than in any other area of the North
Atlantic ridge system.
Volcanism seems to have been more vigorous in
this part of the North Atlantic than elsewhere, since
the opening of the basin by sea-floor spreading in
the early Tertiary. Approximately 90% of Iceland
Fig. 1. Map of Iceland showing the Postglacial petrological zones, (shaded), Plio-Pleistocene
formations (oblique lines) and Tertiary formations (white).
JÖKULL 29. ÁR 57