HR: 0800h
AN: T31A-1280    [Abstracts]
TI: Deep Crustal Seismic Investigation Across the Silkeborg Gravity High, Central Denmark
AU: * Sandrin, A
EM: ALSA@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AU: Thybo, H
EM: THYBO@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AU: Nielsen, L
EM: ln@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AU: Lyngsie, S B
EM: sbl@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AU: Keller, G R
EM: keller@utep.edu
AF: Department of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968 United States
AB: We recently completed a seismic refraction study across northwestern Denmark (the Jutland Peninsula) as part of our efforts to understand the origin and evolution of the Danish Basin. We were testing the hypothesis that the origin of the Mesozoic sedimentary basins in Denmark is related to extensional regimes and intensive magmatic activity during the Carboniferous and early Permian. Potential field data and existing seismic studies indicate that a large batholith is present within the lower crust below the Silkeborg Gravity High (Central Jutland). The goal of project ESTRID (Explosion Seismic Transect across a Rift In Denmark) is to define the shape and size of this batholith. Our main profile (more 140 km long) was laid out along the strike direction of the Silkeborg anomaly. Around 240 Texan instruments were deployed on this profile and ca. 150 more instruments where deployed in arcuate fan geometries, whose centres of curvature were located at the two extreme shotpoints on each end of the profile. These two shots were detonated in water, in the North Sea (shot 1) and in the Arhus Bay (shot 6). Additionally, 4 shots were fired at regular distances along the main profile. Preliminary analysis with seismic tomography locates the top of the crystalline crust at approximately 9 to 11 km depth, below a thick package of sedimentary rocks of Mesozoic and Palaeozoic age. This result is also confirmed by 1D modelling of the data. The tomographic study also defines the extension and depth to the top (ca. 12 km) of the supposed batholith and the depth to the Moho (ca. 30 km). The PmP (Moho reflection) signal is clearly identified along most of the profile, but not in a ca. 30 km long window at the centre of the gravity high. The Pn (diving waves in the upper mantle) is recognizable at the end of the profile. The reflection from the Moho shows a ringing which is interpreted as indicating a layered structure in the lower crust.
DE: 8180 Tomography
DE: 8105 Continental margins and sedimentary basins
DE: 7218 Lithosphere and upper mantle
DE: 1219 Local gravity anomalies and crustal structure
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting