HR: 0800h
AN: V21D-0640    [Abstracts]
TI: Infrastructure of the Geitafell Volcano, Southeast Iceland
AU: Burchardt, S
EM: sburcha@gwdg.de
AF: Department of Structural Geology and Geodynamics, Geoscience Center, University of Gottingen, Goldschmidtstrasse 3, Gottingen, 37077 Germany
AU: Krumbholz, M
EM: krumbholz@freenet.de
AF: Department of Structural Geology and Geodynamics, Geoscience Center, University of Gottingen, Goldschmidtstrasse 3, Gottingen, 37077 Germany
AU: Friese, N
EM: nfriese@gwdg.de
AF: Department of Structural Geology and Geodynamics, Geoscience Center, University of Gottingen, Goldschmidtstrasse 3, Gottingen, 37077 Germany
AU: * Gudmundsson, A
EM: Agust.Gudmundsson@gwdg.de
AF: Department of Structural Geology and Geodynamics, Geoscience Center, University of Gottingen, Goldschmidtstrasse 3, Gottingen, 37077 Germany
AB: The Geitafell Volcano is an extinct 5-6 Ma Tertiary composite (central) volcano with a collapse caldera, 4 km in diameter. Parts of the volcano are eroded to depths of about 2 km beneath its original top. The erosion provides an exceptionally well-exposed infrastructure of a typical composite volcano in Iceland. In the core of the volcano is a gabbro pluton which forms the uppermost part of its extinct shallow magma chamber. The pluton makes a sharp contact with, and acted as a source of, a swarm of (mostly basaltic) inclined sheets. Next to the contact with the gabbro the inclined sheets form 80-100% of the rock, but the intensity falls off rapidly with distance from the contact. To understand better the infrastructure and tectonic evolution of the Geitafell Volcano, we measured more than 500 inclined sheets and dikes, 68 (mostly normal) faults, more than 400 mineral veins, and nearly 1100 joints and minor faults. The inclined sheets dip from horizontal to vertical; they have a general circular strike distribution but with one minor E-W peak and a major NE peak, which coincides with the general trend of the volcanic zone within which the volcano developed. The strike of joints and minor faults has a more even distribution than the strike of sheets. Nevertheless, there are two minor peaks of N-S and NE-trending joints, and a major peak of E-W trending joints. For the mineral veins, the strike distribution is also generally circular with two peaks: E-W and N-S. Most joints are cooling (columnar) joints and occur in the outermost part of the gabbro pluton. Many joints were subsequently used by geothermal water, which is one reason why the attitudes of the joins and mineral veins are so similar. Some joints were used as pathways by the latest dykes and sheets to be injected from the chamber. These late-formed sheets passed through a cooled but still-hot envelope of the magma chamber on their way out to the main sheet swarm. The sheets that dissect the gabbro envelope, however, are few in comparison with those that constitute the high-intensity swarm at the margin of the gabbro pluton.
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
DE: 8145 Physics of magma and magma bodies
DE: 8164 Stresses: crust and lithosphere
DE: 8178 Tectonics and magmatism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005