Kinematic Evolution of the Cephalonia‐Lefkada Transform Fault Zone: Strain Partitioning in Response to Subduction Margin Dynamics

Abstract The eastern Adriatic margin is composed by an Ocean‐Continent Transition lithosphere (OCT), resulting in the southwards along‐strike variation from collision to subduction. The Cephalonia‐Lefkada Transform Fault zone (CTF) is a right‐lateral strike‐slip fault system located above the OCT and associated to this kinematic transition. The CTF is generally considered a proto‐STEP fault, that is the surface expression of the early‐stage propagation of a vertical slab tear (STEP) from the subducting lithosphere to the overriding plate. However, the existence of a slab tear is debated. The poorly constrained structural evolution of the CTF prevents to understand how the upper plate accommodates deformation above the OCT. We fill this gap by exploring onset, kinematic evolution, and geodynamics of the CTF system using onshore field observations and structural analysis. We find that the CTF developed as a right‐lateral transpressional system characterized by strain partitioning into thrusting and strike‐slip faulting since at least the late Pliocene. As the margin along the CTF progressively rotated clockwise due to differential convergence rates, the margin‐normal component of deformation, accommodated by thrusts, decreased, while shear strain, accommodated by strike‐slip faulting, increased. This ongoing strain partitioning is supported by published focal mechanisms and offshore seismic‐reflection data. Our observations are consistent with a proto‐STEP fault interpretation for the CTF. Joint evidence from the geometry of the fault system onshore and offshore, coupled with distinct partitioning of the strain along the CTF, suggest the absence of a slab tear below the CTF, favoring the hypothesis of a bent but still‐intact slab.