Crustal Structure and Tectonic Evolution of the Southern Baltic Sea
Interpreted from Seismic, Gravity and Magnetic Data
Abstract
The Teisseyre-Tornquist Zone (TTZ) is the longest pre-Alpine tectonic
lineament in Europe. Its nature and structural evolution are
controversially debated. In this study, we show its structural evolution
beneath the southern Baltic Sea both on crustal and basin scale by using
three seismic reflection profiles combined with 2-D potential field
data. The results demonstrate that the southern Baltic Sea is underlain
by a thick crust of the East European Craton (EEC) with a Moho depth in
the range of 38-42 km. The overall crustal architecture is shaped by
three phases of localized crustal stretching in early Paleozoic,
Devonian-Carboniferous, and Permian-Mesozoic. The most spectacular
feature of the southern Baltic Sea are zones of thick-skinned
compressional deformation produced by Alpine inversion along the TTZ and
Sorgenfrei-Tornquist Zone (STZ). Both zones include a system of thrusts
and back thrusts penetrating the entire crust in an 80-90 km wide
inversion zone superimposed on the EEC crust and its sedimentary cover.
ENE-vergent thrusts are traced from the top of the Cretaceous down to
the Moho and they are accompanied by back thrusts of opposite vergence,
also reaching the Moho. Inversion tectonics resulted in the uplift of a
block of cratonic crust as a pop-up structure, bounded by thrusts and
back thrusts, and the displacement of the Moho within the STZ and TTZ.
The similar mechanism of intra-cratonic inversion was recognized for the
Dnieper-Donbas Basin in Ukraine, and it may be characteristic of rigid
cratons, where deformation is localized in a few preexisting zones of
weakness.