Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological-geophysical record of spreading and subduction in the Alps

A new reconstruction of Alpine Tethys combines plate-kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution, from sea-floor spreading through subduction to collision in the Alps. Unlike previous models, which relate the fate of Alpine Tethys solely to relative motions of Africa, Iberia and Europe during opening of the Atlantic, our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record. The motions of these microplates (Adria, Iberia, Alcapia, Alkapecia, and Tiszia) relative to both Africa and Europe during Late Cretaceous to Cenozoic time involved the subduction of remnant Tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces: (1) 131-84 Ma intra-oceanic subduction of the Ligurian part of Alpine Tethys attached to Iberia coincided with Eo-alpine orogenesis in the Alcapia microplate, north of Africa. These events were triggered primarily by foundering of the older (170-131 Ma) Neotethyan subduction slab along the NE margin of the composite African-Adriatic plate; subduction was linked by a sinistral transform system to E-W opening of the Valais part of Alpine Tethys; (2) 84-35 Ma subduction of primarily the Piemont and Valais parts of Alpine Tethys which were then attached to the European plate beneath the overriding African and later Adriatic plates. NW translation of Adria with respect to Africa was accommodated primarily by slow widening of the Ionian Sea; (3) 35 Ma-Recent rollback subduction of the Ligurian part of Alpine Tethys coincided with Western Alpine orogenesis and involved the formation of the Gibraltar and Calabrian arcs. Rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable, retreating Adriatic and African slabs during slow convergence of Africa and Europe. The upper European-Iberian plate stretched to accommodate this slab retreat in a very mobile fashion, while the continental core of the Adriatic microplate acted as a rigid indenter within the Alpine collisional zone. The subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the Alps and Apennines, as well as beneath parts of the Pannonian Basin, the Adriatic Sea, the Ligurian Sea, and the Western Mediterranean. The predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10-30%, indicating that parts of slabs may be superposed within the mantle transition zone and/or that some of this subducted lithosphere became seismically transparent. (C) 2010 Elsevier B.V. All rights reserved.