Crustal structure along the EGT profile across the Tornquist Fan interpreted from seismic, gravity and magnetic data

The Tornquist Fan is a northwestward widening splay of late Carboniferous t o early Permian fault tunes in the Danish area which emanates from the Teis seyre-Tornquist Zone in the Baltic Sea. It is located over an area of deep sedimentary basins around Denmark in the southwestern corner of the former Baltica plate. This paper presents an integrated model of seismic velocity, density, and magnetic properties along the EGT profile across the Tornquis t Fan between southern Sweden and northern Germany. The model shows distinc t features that may be related to the main tectonic events in the area. The Caledonian crustal suture between Baltica and Eastern Avalonia is interpre ted from changes in physical parameters at all crustal levels; most noticea ble as an abrupt, lateral change in seismic velocity in the lowest crust at Moho level from 6.9 km/s in Baltica to only 6.4 km/s in Eastern Avalonia. Thick sedimentary successions beneath the Mesozoic sequence are interpreted as Palaeozoic sedimentary rocks, which may have been deposited on the sout hern margin of the Baltica plate, in a deep Caledonian foreland basin, and in late Carboniferous-early Permian rifts and extensional basins. Rift rela ted magmatism is indicated by the presence of zones of high velocity, densi ty and magnetic susceptibility as well as strong remanent magnetization. Th ermal subsidence following the emplacement of these bodies may be the origi n of regional subsidence of the Danish and North German basins of late Pale ozoic and Mesozoic age. Late Cretaceous to early Cenozoic inversion of basi n structures is detected at the Sorgenfrrei-Tornquist Zone (STZ) in the tra nsition between shield and basin areas. The STZ coincides with a pronounced change in crustal thickness and the southwestern edge of a major magmatic intra-crustal body. Significant, abrupt changes in Moho depth exist along t he profile: 26-30 km beneath the deep basins, ca. 35 km beneath the Ringkob ing-Fyn basement High, and its km beneath the Baltic Shield around the Sorg enfrei-Tomquist inversion Zone. The basement in the Tornquist Fan area is o f Proterozoic age. The Moho topography indicates strong thinning of the cru st during its Phanerozoic evolution. The model supports the hypothesis that existing tectonic structures and weakness zones are continuously being rea ctivated during subsequent tectonic activity. (C) 2001 Elsevier Science B.V . All rights reserved.