Plate boundary re-organization in the western Mediterranean

The TOPO-EUROPE ESF Collaborative Research Project TOPOMED addresses an intriguing process of plate boundary re-organization, considered to be active in the western Mediterranean region. The opening of the Algero-Provencal Basin (between Spain, Corsica-Sardinia and NW Africa) by roll-back of the African lithosphere, led to collision of the migrating arc-trench system with the NW African (Maghrebian) continental margin, in the M. Miocene. TOPOMED investigates the hypothesis that this event prompted the subsequent and probably still ongoing evolution of the Calabrian Arc in the east, and possibly that of the Gibraltar Arc in the west. In this contribution we focus on the role of STEP faults (Subduction-Transform-Edge-Propagators [Govers and Wortel, EPSL 2005]) in the evolution of the arcs. Furthermore, seismic activity along the margins of NW Africa and northern Sicily indicates the possibility that a new subduction zone is being formed, accommodating the continuing ~ N-S motion between Africa and Eurasia (Europe) after arc-continent collision. The postulated processes involved are subduction polarity reversal and subduction initiation along a STEP fault. The Mediterranean setting offers unique opportunities to study the arcs’ evolution and the subduction initiation process in a natural setting. We explore the differences between the margins’ settings on the basis of observations and report on numerical modeling results pertaining to the inferred processes of subduction initiation.