Mississippian olistostromes of Iberia revisited: tectonic drivers of synorogenic carbonate platform/reef destruction

Abstract

This paper reviews the synorogenic basins formed on the Gondwana side of the Variscan Orogen of Iberia, highlighting the widespread occurrence of calciturbiditic formations and olistostromes containing reef limestone olistoliths in Iberia's Variscan basins. Using key examples from the Variscan Orogen for comparison (the Azrou–Khenifra and Rhenohercynian basins), the significance of these olistostromes and flyschoid deposits is discussed. Our tectonic models of the Variscan belt in Iberia propose possible drivers of synorogenic carbonate platform/reef destruction responsible for the origin of calciturbidites and olistostromes. One model proposes the formation of an orogenic plateau via the lateral flow of partially molten orogenic roots in the context of Laurussia–Gondwana convergence following the destruction of the Rheic Ocean and slab retreat of the Gondwana (lower) plate. An alternative model invokes subduction of Palaeotethys oceanic lithosphere beneath the Gondwana (upper) plate. Both emphasize the Mississippian occurrence of a significant thermal anomaly beneath Gondwana that favoured strong lithosphere thinning, creating ideal conditions for synorogenic carbonate platform/reef destruction and the formation of calciturbidite deposits and olistostromes in Iberia. The Variscan palaeotopography would look similar in both situations. Distinguishing between these models is therefore not straightforward, with differences in the kinematics of regional tectonic transport in the superstructure of Mississippian gneiss domes. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists