Geophysical characteristics of the Tornquist Fan area, northwest Trans-European Suture Zone: indication of late Carboniferous to early Permian dextral transtension

Abstract

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.