HR: 0800h
AN: T51A-0442    [Abstracts]
TI: Origin of Breccia Deposit Within the Solund Devonian Basin, Western Norway
AU: * McGrath, E A
EM: e.a.mcgrath@fys.uio.no
AF: Physics of Geological Processes, University of Oslo P.O. Box 1048, Oslo, 0316 Norway
AU: Austrheim, H
EM: hakon.austrheim@geo.uio.no
AF: Physics of Geological Processes, University of Oslo P.O. Box 1048, Oslo, 0316 Norway
AU: Andersen, T B
EM: t.b.andersen@geologi.uio.no
AF: Physics of Geological Processes, University of Oslo P.O. Box 1048, Oslo, 0316 Norway
AU: Onderdonk, N W
EM: nate.onderdonk@fys.uio.no
AF: Physics of Geological Processes, University of Oslo P.O. Box 1048, Oslo, 0316 Norway
AB: The Solund basin of western Norway developed in the hanging-wall of a large extensional detachment zone in the lower Devonian. The basin consists of an approximately 10km thick succession of primarily conglomeratic sediments, but also includes an anomalous brecciated body composed of gabbro, rhyolite and metamorphosed quartzite of uncertain origin near the basal deposits of the basin. The body has been previously interpreted as an in-situ intrusive and volcanic rocks, as a thrust slice, and as a landslide. Previous U/Pb zircon dating of glassy felsic rocks within the body (439$\pm$3 Ma) suggest a lowermost Silurian age of the volcanic protolith. Detailed field mapping combined with microtexture analysis and laboratory modeling is currently used to determine the origin of this body and investigate the physical mechanisms that control the brecciation process. Based on the basal structure, the geometry of the body, and an unconformable upper contact with the conglomerate we present evidence to support the landslide interpretation. The unit is characterized by a large degree of brecciation, including "jigsaw breccias", particularly common within the foliated metamorphic rocks of the body. These breccias contain fragments ranging from microscopic grains to intact blocks up to 30m in length. The breccias are clast supported and the clasts have rotated around multiple axes, with little apparent space for these rotations to occur. The metamorphic rocks exhibit a higher degree of brecciation than the more massive gabbroic to granitoid rocks in contact with them. This apparent intrusive relationship, seen at many localities within the body, suggests that the majority of the jigsaw brecciation occurred prior to emplacement, with the body remaining quite coherent and preserving internal relationships through the emplacement event. A simple brecciation mechanism does not fully explain the observed morphology and arrangement of the breccia. We are currently addressing this problem and will present preliminary results from our analysis.
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting