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

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.