A model for a continental accretionary wedge developed by oblique collision: the NE Bohemian Massif

Abstract

Structural and metamorphic investigations of the northeastern margin of the Bohemian Massif indicate three main sequential Devonian–Carboniferous tectonic events: (1) Devonian rifting; (2) Early Carboniferous oblique underthrusting and formation of a continental accretionary wedge; (3) eduction of the wedge and Late Carboniferous transpression. Devonian rifting of the Brunia microcontinent resulted in the formation of two crustal‐scale boudins associated with the development of two syn‐rift Devonian basins. This extensional template strongly influenced the nature of the ensuing Variscan contractional deformation. Early Carboniferous (350–330 Ma), progressive, highly oblique underthrusting of the two crustal boudins beneath the Lugian terrane to the west, generated syn‐deformational Barrovian metamorphism and the formation of a continental accretionary wedge. The wedge was further compressed by continued underthrusting of Brunia which resulted in the successive vertical extrusion (eduction) of an upper and lower allochthon, derived from the more deeply underthrust crustal boudin. The eduction was terminated by a Late Carboniferous (330–310 Ma) transpressional event resulting from continued plate convergence. Release of mantle‐derived magma during late‐stage eduction thermally softened the transpressional zones in the more external parts of the wedge. The resultant differential displacements gave rise to extensional unroofing of the internal part of the wedge.