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SUMMARY
Magma chambers in the
volcanic zones
of Iceland
by
Ágúst Guðmundsson
Nordic Volcanological Institute
University of Iceland, Reykjavík
This paper reviews and extends the
author’s models for the formation and
dynamics of magma chambers in the volca-
nic zones of Iceland (Ágúst Guðmundsson
1986a, 1986b, 1987). The main conclusions
of the paper may be summarized as
follows.
1) The volcanic zones of Iceland consist
of some 30 volcanic systems (Fig. 1), each
one composed of volcanic and tectonic
fissures and some also containing a central
volcano. In this paper all volcanic systems
are considered to be fed by partially mol-
ten magma reservoirs, located at the depth
of 8—10 km within the volcanic zones. The
average magma content of the reservoirs is
25%, but the uppermost parts of them are
probably totally molten. The cross-sectio-
nal area of a reservoir is thought to be
similar to the area of the associated volca-
nic system. The maximum thickness of the
reservoirs is 14 km.
2) In addition to a reservoir, some vol-
canic systems have a shallow, totally mol-
ten magma chamber, located in the crust
(Fig. 2). The chambers are fed by reser-
voirs, are located at a depth of 1—3 km,
and have volumes of 20-200 km3. They
are either sill-like, spherical or stock-like.
3) Magma reservoirs form in those
areas, at the boundary of the crust and
upper mantle, where the crust is relatively
thin and weak. These are also the regions
where the crust is most likely to yield as a
result of plate movements. The magma
flows towards these regions to accumulate
and from reservoirs. Each part of the vol-
canic zone is fed by one or many magma
reservoirs (Fig. 3).
4) The formation of shallow magma
chambers is envisaged as follows. Dike
intrusions build up, temporary, high hori-
zontal compressive stresses that lead to
formation of a sill which, subsequently,
J