HR: 1340h
AN: T23D-1662    [Abstracts]
TI: Crustal Reflectivity Underneath the Central Scandinavian Caledonides
AU: Dyrelius, D
EM: dan.dyrelius@geo.uu.se
AF: Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala, 75236, Sweden
AU: * Juhojuntti, N
EM: niklas.juhojuntti@sgu.se
AF: Geological Survey of Sweden, Villavägen 18, Uppsala, 75236, Sweden
AU: Juhlin, C
EM: christopher.juhlin@geo.uu.se
AF: Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala, 75236, Sweden
AB: We discuss data from a ca. 160 km long deep reflection seismic profile in the Swedish part of the Central Scandinavian Caledonides. The seismic data were acquired during 1988-1992, as part of the Central Caledonian Transect. The profile starts within the Precambrian basement to the east of the Caledonian thrust front and extends westwards onto the relatively thin Caledonian thrust sheets, which in this area largely consist of sedimentary rocks of Late Proterozoic or Early Palaeozoic age. One outstanding feature in the seismic image, observed throughout the profile, is the pattern of strong reflectivity down to depths of ca. 15 km. We interpret this reflectivity primarily as due to dolerites intruded in the Precambrian basement. Although the Caledonian thrust sheets cover large parts of the Precambrian basement in the study area, magnetic data reveals structures underneath the thrust sheets. We interpret the dolerites to be located in a homogeneous and highly magnetized granite belonging to the Transscandinavian Igneous Belt, stretching ca. 1400 km from southern Sweden to northern Norway. Based on the pattern of intrusion inferred by the seismic data as well as comparison with ground observations in exposed parts of the Precambrian basement in the region, the dolerites are believed to belong to an 1 Ga system. At the eastern end of the seismic profile, to the east of the thrust front, there are also seismic reflections which can be correlated with dolerites belonging to an older 1.2 Ga intrusion system. The dolerites to the east of the thrust front are clearly visible in magnetic maps. Coinciding with the location of the magnetic TIB granite, the seismic data shows a thinning of the crust, from ca. 50 km to 45 km, and a less distinct reflection Moho. We propose that the decrease in deep reflectivity is related to the emplacement of the TIB granite at 1.85-1.65 Ga. Based also on the observation of weak east-dipping reflections in the middle/lower crust we suggest that extension at ca. 1.0 Ga led to the thinning of the crust and allowed the dolerities to intrude the granites in the upper/middle crust. Later Caledonian compression sheared the granite/dolerite system, resulting in the pattern of reflections observed in the seismic image.
DE: 0935 Seismic methods (3025, 7294)
DE: 8108 Continental tectonics: compressional
DE: 8110 Continental tectonics: general (0905)
DE: 9335 Europe
DE: 9619 Precambrian
SC: Tectonophysics [T]
MN: 2007 Fall Meeting