Lateral slab deformation and the origin of the western Mediterranean arcs

TLDR

The western Mediterranean subduction zone extends from the northern Apennine to southern Spain, forming the Calabrian and Gibraltar Arcs, and its evolution involves an initial orogenic wedging phase followed by trench retreat and back‑arc extension from about 30 Ma. The study seeks to describe the evolution of the WMSZ over the last 35 Myr. The authors combine new and previous geological data, mantle tomography, and plate kinematics to reconstruct this evolution. The reconstruction shows that the two arcs formed by fragmentation of the 1500 km long WMSZ into small, narrow slabs that retreat outward, causing back‑arc extension and large‑scale flank rotation; the Gibraltar Arc formed in the middle Miocene and the Calabrian Arc later, and the similar rupture and backward migration mechanisms on both sides suggest slab deformation is driven by lateral mantle flow in a restricted upper‑mantle convection style.

Abstract

The western Mediterranean subduction zone (WMSZ) extends from the northern Apennine to southern Spain and turns around forming the narrow and tight Calabrian and Gibraltar Arcs. The evolution of the WMSZ is characterized by a first phase of orogenic wedging followed, from 30 Ma on, by trench retreat and back‐arc extension. Combining new and previous geological data, new tomographic images of the western Mediterranean mantle, and plate kinematics, we describe the evolution of the WMSZ during the last 35 Myr. Our reconstruction shows that the two arcs form by fragmentation of the 1500 km long WMSZ in small, narrow slabs. Once formed, these two narrow slabs retreat outward, producing back‐arc extension and large scale rotation of the flanks, shaping the arcs. The Gibraltar Arc first formed during the middle Miocene, while the Calabrian Arc formed later, during the late Miocene‐Pliocene. Despite the different paleogeographic settings, the mechanism of rupture and backward migration of the narrow slabs presents similarities on both sides of the western Mediterranean, suggesting that the slab deformation is also driven by lateral mantle flow that is particularly efficient in a restricted (upper mantle) style of mantle convection.