Deciphering the Variscan tectonothermal overprint and deformation partitioning in the Cadomian basement of the Teplá-Barrandian unit, Bohemian Massif
Abstract
The Teplá-Barrandian unit (TBU) has long been considered as a simply bivergent supracrustal 'median massif' above the Saxothuringian subduction zone in the Variscan orogenic belt. This contribution reveals a much more complex style of the Variscan tectonometamorphic overprint and resulting architecture of the Neoproterozoic basement of the TBU.
For the first time, we describe the crustal-scale NE-SW-trending dextral transpressional Krakovec shear zone (KSZ) that intersects the TBU and thrusts its higher grade northwestern portion severely reworked by Variscan deformation over a southeastern very low grade portion with well preserved Cadomian structures and only brittle Variscan deformation. The age of movements along the KSZ is inferred as Late Devonian (~380-370 Ma).
On the basis of structural, microstructural, and anisotropy of magnetic susceptibility (AMS) data from the KSZ we propose a new synthetic model for the deformation partitioning in the Teplá-Barrandian upper crust in response to the Late Devonian to early Carboniferous subduction and underthrusting of the Saxothuringan lithosphere. We conclude that the Saxothuringian/Teplá-Barrandian convergence was nearly frontal during ~380-346 Ma and was partitioned into pure shear dominated domains that accommodated orogen-perpendicular shortening alternating with orogen-parallel high-strain domains that accommodated dextral transpression or bilateral extrusion.
The syn-convergent shortening of the TBU was terminated by a rapid gravity-driven collapse of the thickened lithosphere at ~346-337 Ma followed by, or partly simultaneous with, dextral strike-slip along the Baltica margin-parallel zones, driven by the westward movement of Gondwana from approximately 345 Ma onwards.