The Tornquist Fan is a northwestward widening splay of late
Carboniferous–early Permian fault
zones in the region of Denmark emanating from the Teisseyre-Tornquist Zone
in
northern Poland. The
crust–mantle boundary shows an undulating topography which correlates
with the main tectonic features of
the area. Zones of high average velocity through the consolidated crust
coincide
with pronounced positive
Bouguer gravity anomalies in the deep basins and in the border zone of
the
shield. Less pronounced, similar
correlation to gravity is found for the thickness of the lower crust, whereas
the thickness of the upper crust in
parts is inversely related to the gravity anomalies. Some magnetic anomalies
appear to be related to the gravity
anomalies. The positive features are interpreted as magmatic bodies that
formed during late
Carboniferous to early Permian transtensional movement along the faults
of
the Tornquist Fan, which
explains pull-apart structures in the area and the Ringkøbing-Fyn basement
High.
The magmatism has
strong implications for the subsequent formation of the regional Mesozoic
basins. Localized dextral strike-slip
movement on the Teisseyre-Tornquist Zone became distributed over the Tornquist
Fan, which formed
part of the rigid Baltic Shield and was situated at the northwestern end
of
this major, long-reaching Central
European zone. As defined by late Cretaceous–early Tertiary
compressional inversion structures, the
Sorgenfrei-Tornquist Zone cuts across the Tornquist Fan area.