Publication Date:
2011-07-28
Description:
Sheet intrusions (inclined sheets and dykes) in the deeply eroded volcanoes of Geitafell and Dyrfjöll, eastern Iceland, were studied at the surface to identify the location, depth, and size of their magmatic source(s). For this purpose, the measured orientations of inclined sheets were projected in three dimensions to produce models of sheet swarm geometries. For the Geitafell Volcano, the majority of sheets converge toward a common focal area with a diameter of at least 4 to 7 km, the location of which coincides with several gabbro bodies exposed at the surface. Assuming that these gabbros represent part of the magma chamber feeding the inclined sheets, a source depth of 2 to 4 km below the paleoland surface is derived. A second, younger swarm of steeply dipping sheets crosscuts this gabbro and members of the first swarm. The source of this second swarm is estimated to be located to the SE of the source of Swarm 1, below the present-day level of exposure and deeper than the source of the first swarm. For the Dyrfjöll Volcano, we show that the sheets can be divided into seven different subsets, three of which can be interpreted as swarms. The most prominent swarm, the Njardvik Sheet Swarm, converges toward a several kilometers wide area in the Njardvik Valley at a depth of 1.5 to 4 km below the paleoland surface. Two additional magmatic sources are postulated to be located to the northeast and southwest of the main source. Crosscutting relationships indicate contemporaneous, as well as successive activity of different magma chambers, but without a resolvable spatial trend. The Dyrfjöll Volcano is thus part of a complex volcanic cluster that extends far beyond the study area and can serve as fossil analog for nested volcanoes such as Askja, whereas in Geitafell, the sheet swarms seem to have originated from a single focus at one time, thus defining a single central volcanic complex, such as Krafla Volcano.
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
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