HR: 13:40h
AN: V33G-01    [Abstracts]
TI: Regional and Local Flexure Zones in Iceland: Upper Crustal Structures in Magmatically Robust Spreading Systems
AU: * Karson, J A
EM: jkarson@duke.edu
AF: Division of Earth & Ocean Sciences, Duke University, Durham, NC 27708-0230 United States
AU: Varga, R J
EM: rvarga@wooster.edu
AF: Department of Geology, College of Wooster, Wooster, OH 44691 United States
AU: S$\ae$mundsson, K
EM: ks@isor.is
AF: Iceland GeoSurvey, Grens\'{a}svegur 9, Reykjavik, 108 Iceland
AB: Extensively uplifted and glaciated exposures of the Tertiary crust of Iceland provide a window into the architecture of oceanic crust formed near hot spots on ridges and may provide analogs for magmatically robust ridge segments in general. Upper crustal rock units on Iceland consist mainly of laterally continuous, sheet-like, lava flows cut by sparse dikes. These units reveal a surprising degree of structural complexity with asymmetrical flexure zones marking the sites of former spreading axes. In regional flexure zones ($>$10 km across), near-horizontal lava flows overlie inward-dipping (toward the rift) lavas in a downward -steepening geometry. Associated dikes increase in (outward) dip, but in some places steeply dipping dikes cut this entire assemblage. Paleomagnetic data on lavas and dikes help quantify these rotations. Along-strike variations in regional-scale flexures appear to show segmentation patterns with spreading segments a few tens of kilometers long separated by accommodation zones. Local flexures (1-2 km across) are characterized by packages of dipping lava flows unconformably overlain by later, less tilted flows. In some places, multiple episodes of subsidence, tilting and burial by later lavas have occurred. These areas document dramatic, 3-dimensional, subaxial subsidence (few hundred meters) near magmatically robust segment centers. Rapid subaxial subsidence during crustal construction may be a hallmark of spreading in magmatically robust systems.
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8100 TECTONOPHYSICS
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting