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

Abstract

A review of the synorogenic basins formed on the Gondwana side of the Variscan orogen of Iberia is presented, highlighting the widespread ocurrence of calciturbiditic formations and olistostromes containing reef-limestone olistoliths in Iberia's Variscan basins. Using key-examples from the Variscan orogen for comparison (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 by lateral flow of partially molten orogenic roots in the context of Laurussia-Gondwana convergence, following the destruction of the Rheic Ocean and Gondwana (lower) plate slab retreat. An alternative model invokes subduction of Paleotethys oceanic lithosphere beneath the Gondwana (upper) plate. Both emphasize the Mississippian occurrence of a significant thermal anomaly beneath Gondwana that favored strong lithosphere thinning, creating ideal conditions for synorogenic carbonate platform/reef destruction, and for the formation of calciturbidite deposits and olistostromes in Iberia. Variscan paleotopography would look alike in both situations. Thus, distinguishing these models is not straightforward, with differences in the kinematics of the 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