Adria in Mediterranean paleogeography, the origin of the Ionian Sea, and Permo-Triassic configurations of Pangea

Abstract

The African affinity of the deformed Mesozoic continental margins surrounding the Adriatic Sea (a region known as Adria) was recognized in the 1920s. However, over the last several decades, the majority view of Mediterranean Mesozoic paleogeography has featured an ocean (Mesogea) that separated Adria and Africa in Mesozoic and early Cenozoic time. The presence of a Mesogea ocean has become an argument against the use of paleomagnetic data from Adria as a proxy for Africa, which has been central to the controversy surrounding alternative Permian configurations of Pangea (Pangea A or B). The rationale for Mesogea has been derived from the perceived need for oceanic lithosphere to feed Miocene to Recent subduction beneath the Tyrrhenian and Aegean seas, the apparent presence of Early Jurassic oceanic basement beneath the present-day Ionian Sea, and the presence of deep-water Permian and younger sedimentary rocks in Sicily. On the other hand, the presence of Mesogea is incompatible with the apparent continuity of Mesozoic sedimentary facies from North Africa and Sicily into Adria, and with increasingly well-documented consistency of paleomagnetic data from Adria and NW Africa. We argue that the subducting slabs beneath the Tyrrhenian and Aegean seas are delaminated continental-margin mantle lithosphere of Adria/Africa stripped of its sedimentary cover and most of its crustal basement by thrusting. We propose, rather than an early Mesozoic (Mesogea) ocean between Adria and Africa, a sinistral strike-slip fault system linked Atlantic spreading in the West to the Neo-Tethys in the East, during the Middle and Late Jurassic, and featured pull-apart basins that included the Ionian and Levant basins of the eastern Mediterranean. In our modelling, Adria moved with Iberia during initial opening of the Central Atlantic in the Early and Middle Jurassic (after 203 Ma until 170 Ma). From mid-Jurassic time (170 Ma), Adria began to break away from Iberia with onset of rifting in the Piemonte-Ligurian Ocean, and, as the rate of southeasterly motion of Adria relative to North America lagged that of Africa, the Ionian-Levant basins formed as pull-apart basins along a sinistral strike-slip fault system parallel to a small circle about the 170–154 Ma Euler stage pole for motion of Africa relative to Adria. From marine magnetic anomaly M25 time (154 Ma), Adria moved in synch with Africa and therefore pull-apart extension in the eastern Mediterranean came to a halt. The modeled opening of eastern Mediterranean pull-apart basins is consistent with the observed resemblance of Permian and younger paleomagnetic poles from Adria and NW Africa. The Atlantic Euler poles used to map these paleogeographic changes, when applied to Permian paleomagnetic poles from Adria, Africa, and elsewhere, support the existence of Pangea B in Early Permian time (280 Ma) with transformation to Pangea A by the Late Permian (260 Ma).