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

• Published in: Geological magazine Vol. 156; no. 3; pp. 485 - 509
• Main Authors: VACEK, FRANTIŠEK, ŽÁK, JIŘÍ
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.03.2019
• Subjects: Bohemia; Bohemian Massif; Carboniferous; Central Europe; Collapse; crust; crustal thickening; Czech Republic; Deformation; Devonian; Domains; ductile deformation; Europe; exhumation; Extrusion; Fault lines; faults; folds; geodynamics; Geologic depressions; Geological faults; Geology; Geophysics; Gondwana; Gravitational collapse; Gravity; Laurussia; Lava; Lower Carboniferous; Magma; Massifs; Ordovician; Original Articles; Orogeny; Palaeotopography; Paleozoic; plate collision; Plate convergence; plate tectonics; Plateaus; Plates (structural members); Prague Basin; Shear zone; shear zones; solid Earth (tectonophysics); Stratigraphy; Synclines; Tepla-Barrandian Terrane; Thickening; Thrust faults; topography; Uplift; uplifts; Upper Devonian; Variscan Orogeny; orogenic plateau; Teplá–Barrandian Unit; Bohemian Massif; continental collision; basin inversion; gravitational collapse
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756817000875

The Ordovician to Middle Devonian Prague Basin, Bohemian Massif, represents the shallowest crust of the Variscan orogen corresponding to c. 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 accommodating c. 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 at c. 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.