The Rheic riddle: ocean closed, but no orogen

Abstract

Abstract Although the Rheic Ocean was the widest to be closed during the assembly of Pangaea, its suture zone is dominated by a younger (Rhenohercynian) Wilson Cycle. The present paper briefly summarizes the Rhenohercynian and reviews the relicts of the Rheic. The absence of a Rheic orogen is mainly due to bipolar subduction of the Rheic Ocean, which created two magmatic arcs and largely destroyed the passive margin prisms, thus depriving the collision zone of building material. Also, displacement of Variscan zones in England, France and Germany along a curvature of the dextral Bristol/Bray/Bohemia shear zone has effected their anticlockwise rotation. Younger, ENE-trending reverse faults have truncated the NE-trending structural boundaries and excised pre-Devonian, Rheic-related rocks west of the River Rhine, while the northern Rheic Arc and Cambrian–Silurian deposits of the Rheic Ocean have been preserved further east. Opening of the Rhenohercynian successor ocean to the Rheic put a brake on plate convergence and hindered formation of a large collisional belt. Scarce relicts of the southern Rheic Arc and rocks with Silurian deformation exist in the (largely eroded) upper plate of the Rhenohercynian collisional belt, mostly in the form of clasts and detrital zircons in Upper Devonian/lower Carboniferous flysch and in tectonic mélange at the base of the allochthon.