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 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 synconvergent 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.

From Crustal Thickening to Orogen‐Parallel Escape: The 120‐Myr‐Long HT‐LP Evolution Recorded by Titanite in the Paleozoic Famatinian Backarc, NW Argentina

“…Strain in such orogens can be partitioned into pure and simple shear during compression (Braathen et al, 2000; Carreras et al, 2013; Fletcher & Bartley, 1994; Hajná et al, 2012; Malavieille, 1993; Rubio Pascual et al, 2016; Sullivan, 2009; Sullivan & Law, 2007), extension (Jolivet et al, 2004; Mancktelow & Pavlis, 1994), and associated with constriction (Jolivet et al, 2004; Sullivan & Law, 2007), which are all end‐members of a more general scheme in transpressional or transtenstensional settings (Jones et al, 2004). More significantly, a number of papers documented tectonic transport directions that deviates from the direction perpendicular to the orogen.…”

Petrogenesis of fractionated nested granite intrusions: the Sedmihoří Composite Stock (Bohemian Massif)

“…1b) is one of the bestpreserved segments of the Avalonian-Cadomian belt which developed along the northern active margin of Gondwana during the late Neoproterozoic to the earliest Cambrian (Nance et al 2008, 2010 andreferences therein). The basement of the TBU is unique in that it exposes almost a complete section across the Cadomian active margin from a remnant meta-ophiolite complex to the NW, through an accretionary wedge, to a volcanic arc and intra-arc and back-arc basins to the SE (Hajná et al 2012(Hajná et al , 2013. The Teplá-Barrandian upper crust was intruded by several Late Devonian-early Carboniferous calc-alkaline granitoid plutons (Fig 1b).…”

A lifetime of the Variscan orogenic plateau from uplift to collapse as recorded by the Prague Basin, Bohemian Massif

“…During the Variscan plate convergence, the northwesterly oceanic domain (Saxothuringian Ocean) followed by the Saxothuringian continental margin were progressively subducted beneath the overriding Teplá–Barrandian upper crust (from >380 Ma to ~340 Ma), resulting in its overall ~NW–SE to ~WNW–ESE horizontal shortening (e.g. Zulauf, 1997, 2001; Konopásek & Schulmann, 2005; Schulmann et al 2009, 2014; Žák et al 2009; Franěk et al 2011; Hajná et al 2012). The Prague Basin was inverted, uplifted and multiply deformed (e.g.…”