TY - JOUR
T1 - Deep crustal seismic reflection profiling across two major tectonic zones in southern Sweden
AU - Dahl-Jensen, T.
AU - Dyrelius, D.
AU - Palm, H.
N1 - Funding Information:
Roland Gorbatschev, Anders Lindh, Carl-Henrik Wahlgren and Per H. Lundeg%rdh all discussed the geological and tectonic environments in the area with us, and so helped us to put the seismic information into a geological and tectonic context. Roland Gorbatschev also read an early draft of the paper, and provided us with extensive comments, which have helped us greatly. We also wish to gratefully acknowledge thorough reviews by Asger Berthelsen, Paul Valasek and Brigitte Schwendener, who made us reconsider several aspects of our work and, we believe. improve our discussions and conclusions. Special thanks are due to our colleagues Laust Biirsting Pedersen, Thorkild Rasmussen and Zhang Ping, who put their skill and computer programs at our disposal for a study of the problems of geophone response. This project was funded by the Swedish Natural Science Research Council (NFR).
PY - 1991/9/1
Y1 - 1991/9/1
N2 - A seismic reflection profile has been shot in Värmland, southwestern Sweden, across two major tectonic zones, the Protogine Zone and the Mylonite Zone. The crustal bedrock units separated by the tectonic zones are clearly distinguished in the seismic profile by changes in the reflection character in the upper 5-6 km. The Protogine Zone is represented by a 15-20 km wide band of dipping structures. The Mylonite Zone dips too steeply to be seen directly and a lack of clear reflectors at depth makes a continuation down through the crust hypothetical. In the uppermost 5-6 km between the two tectonic zones, stronger and more continuous reflections can be seen, and are interpreted as being connected with "hyperite" intrusions, which have been mapped at the surface. The lower crust shows generally little reflectivity, with only short and weak reflectors. An exception occurs at mid-crustal depths where a number of clearly recognizable bands of reflected energy are suggested to be major shear zones formed during Sveconorwegian-Grenvillian thrusting towards the east. A slight increase in reflectivity in the depth range 42-48 km correlates well with the Moho depth determined from refraction seismic studies. The possible relationships between data acquisition parameters and the observed scarcity and low strength of reflections from the deeper crust have been considered in some detail. It is shown that the use of 28 Hz single geophones instead of 10 Hz geophone strings along a major part of the profile did not reduce the signal-to-noise ratio for deep reflections. However, the varying source characteristics, in combination with the different quality of the recordings, made computation of the residual static corrections difficult, which may have resulted in a partly destructive stacking of seismic traces. In this way, the low reflectivity of the deeper crust in this area is further brought out in the stacked seismic sections.
AB - A seismic reflection profile has been shot in Värmland, southwestern Sweden, across two major tectonic zones, the Protogine Zone and the Mylonite Zone. The crustal bedrock units separated by the tectonic zones are clearly distinguished in the seismic profile by changes in the reflection character in the upper 5-6 km. The Protogine Zone is represented by a 15-20 km wide band of dipping structures. The Mylonite Zone dips too steeply to be seen directly and a lack of clear reflectors at depth makes a continuation down through the crust hypothetical. In the uppermost 5-6 km between the two tectonic zones, stronger and more continuous reflections can be seen, and are interpreted as being connected with "hyperite" intrusions, which have been mapped at the surface. The lower crust shows generally little reflectivity, with only short and weak reflectors. An exception occurs at mid-crustal depths where a number of clearly recognizable bands of reflected energy are suggested to be major shear zones formed during Sveconorwegian-Grenvillian thrusting towards the east. A slight increase in reflectivity in the depth range 42-48 km correlates well with the Moho depth determined from refraction seismic studies. The possible relationships between data acquisition parameters and the observed scarcity and low strength of reflections from the deeper crust have been considered in some detail. It is shown that the use of 28 Hz single geophones instead of 10 Hz geophone strings along a major part of the profile did not reduce the signal-to-noise ratio for deep reflections. However, the varying source characteristics, in combination with the different quality of the recordings, made computation of the residual static corrections difficult, which may have resulted in a partly destructive stacking of seismic traces. In this way, the low reflectivity of the deeper crust in this area is further brought out in the stacked seismic sections.
UR - http://www.scopus.com/inward/record.url?scp=0026311758&partnerID=8YFLogxK
U2 - 10.1016/0040-1951(91)90211-A
DO - 10.1016/0040-1951(91)90211-A
M3 - Article
AN - SCOPUS:0026311758
SN - 0040-1951
VL - 195
SP - 209
EP - 240
JO - Tectonophysics
JF - Tectonophysics
IS - 2-4
ER -