USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
A Magmatic Model of Medicine Lake Volcano, California
--
Julie M. Donnelly-Nolan, 1988,
A Magmatic Model of Medicine Lake Volcano, California:
Journal of Geophysical Research, v.93, p.4412-4420.
Abstract
Medicine Lake volcano is a Pleistocene and Holocene shield volcano
of the southern Cascade Range. It is located behind the main Cascade arc
in an extensional tectonic setting where high-alumina basalt is the most
commonly erupted lava. This basalt is parental to the higher-silica
calc-alkaline and tholeiitic lavas that make up the bulk of the shield.
The presence of late Holocene, chemically identical rhyolites on opposite
sides of the volcano led to hypotheses of a large shallow silicic magma
chamber and of a small, deep chamber that fed rhyolites to the surface via
cone sheets. Subsequent geophysical work has been unable to identify a
large silicic magma body, and instead a small one has apparently been
recognized. Some geologic data support the geophysical results. Tectonic
control of vent alignments and the dominance of mafic eruptions both in
number of events and volume throughout the history of the volcano indicate
that no large silicic magma reservoir exists. Instead, a model is proposed
that includes numerous dikes, sills, and small magma bodies, most of which
are too small to be recognized by present geophysical methods.
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04/06/00, Lyn Topinka