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

Abstract

The Ordovician to Middle Devonian Prague Basin, Bohemian Massif, represents the shallowest crust of the Variscan orogen corresponding toc.1–4 km palaeodepth. The basin was inverted and multiply deformed during the Late Devonian to early Carboniferous Variscan orogeny, and its structural inventory provides an intriguing record of complex geodynamic processes that led to growth and collapse of a Tibetan-type orogenic plateau. The northeastern part of the Prague Basin is a simple syncline cross-cut by reverse/thrust faults and represents a doubly vergent compressional fan accommodatingc.10–19 % ~NW–SE shortening, only minor syncline axis-parallel extension and significant crustal thickening. The compressional structures were locally overprinted by vertical shortening, kinematically compatible with ductile normal shear zones that exhumed deep crust in the orogen's interior atc. 346–337 Ma. On a larger scale, the deformation history of the Prague Syncline is consistent with building significant palaeoelevation during Variscan plate convergence. Based on a synthesis of finite deformation parameters observed across the upper crust in the centre of the Bohemian Massif, we argue for a differentiated within-plateau palaeotopography consisting of domains of local thickening alternating with topographic depressions over lateral extrusion zones. The plateau growth, involving such complex three-dimensional internal deformations, was terminated by its collapse driven by multiple interlinked processes including gravity, voluminous magma emplacement and thermal softening in the hinterland, and far-field plate-boundary forces resulting from the relative dextral motion of Gondwana and Laurussia.

Putative Ordovician green alga Krejciella reinterpreted as enteropneust hemichordate tube (Czech Republic)

“…The Prague Basin comprises Lower Ordovician to Middle Devonian sediments and volcanites preserved in a Variscan-developed syncline (see Havlíček, 1998;Vacek and Žák, 2017) in the central part of the Bohemian Massif, Czech Republic (Figure 1A). The Ordovician is dominated by siliciclastic sediments with local volcanites (Figure 1B).…”

Dead or alive? Brachiopods and other shells as substrates for endo- and sclerobiont activity in the early Devonian (Lochkovian) of the Barrandian (Czechia)

“…They are represented mostly by dark coloured calcisiltites. The overlying Givetian succession is siliciclastic and marked beginning of the Variscan orogeny (Chlupáč et al 1998, Vacek & Žák 2019.…”

First Record of Podichnus in Byronid Shell from the Lower Devonian (Pragian) of the Prague Basin, Czechia

“…It is characterized by two major lithofacies: shallow water biodetrital mostly crinoidal limestones which also comprise reefal bioskeletal accumulations of Pragian and, in limited extent, also Emsian and Eifelian age, and more pelagic lithofacies that is represented mostly by calcisiltites (Chlupáč 1998, Slavík & Hladil 2020. The overlying Givetian siliciclastic succession terminates the entire Ordovician to Middle Devonian volcano-sedimentary infill of the Prague Basin as a reflection of the Variscan orogeny (Vacek & Žák 2019).…”