A seismic model of the Precambrian crust along the coast of southeastern Sweden: the Coast Profile wide-angle airgun experiment and the southern partof FENNOLORA revisited
Ce. Lund et al., A seismic model of the Precambrian crust along the coast of southeastern Sweden: the Coast Profile wide-angle airgun experiment and the southern partof FENNOLORA revisited, TECTONOPHYS, 339(1-2), 2001, pp. 93-111
Within the framework of the EUROBRIDGE project, the P-wave velocity structu
re along the coast of southeastern Sweden was determined from 2-D forward m
odeling of seismic refraction and wide-angle reflection airgun data on a pr
ofile named the Coast Profile. Previously obtained results of the FENNOLORA
Profile were also used.
The studied traverse extends from the ca. 1.90-1.86 Ga Svecofennian orogeni
c domain in the north to the Blekinge-Bornholm region (BBR) in the south wh
ere the dominant crust-forming granitoid rocks were emplaced between ca. 1.
78 and 1.72 Ga. In the intervening area, the crust has ages between these e
xtremes, the rocks of the different age groups and lithologies mostly being
arranged in roughly EW-trending belts. However, there are also substantial
ly younger shear zones and granite intrusions.
The obtained results show a crustal structure typical of shield areas, with
velocities of ca. 5.9-6.5 km/s in the upper and 6.5-6.9 km/s in the lower
parts of the final model. The crustal levels below approximately 40 km have
velocities above 7 km/s. The Moho is situated at depths of ca. 36 km benea
th the BBR and 40-42 krn beneath most of the modeled part of the Svecofenni
an Orogen. The thickest now identified crust is about 52 km. It forms a wid
e belt along the southern edge of the latter domain. The variations of crus
tal thickness do not appear to occur smoothly but rather stepwise. The part
iculars of the resultant Moho topography are described.
In a genetic interpretation, it is suggested that the metamorphic island-ar
c environment in the southern part of the Svecofennian Domain developed by
a subduction-related process ending ca. 1.85 Ga ago, but that similar devel
opments, including mafic underplating, continued still later, until at leas
t ca. 1.77 Ga, farther to the south. Between ca. 1.55 and 1.45 Ga, the BBR
and adjoining area were affected by largely granitoid magmatism associated
with foliation and the formation of major zones of shearing. Together, the
various episodes of underplating, subduction and crustal stacking appear to
have been responsible for the varying depths and present step-like topogra
phies of Moho and the crust. (C) 2001 Elsevier Science BN. All rights reser
ved.