Geodynamics along an increasingly curved convergent plate margin: Late Miocene‐Pleistocene Rhodes, Greece

Abstract

Neogene‐Holocene outward migration of the absolute position of the convergent Hellenic plate boundary produced simultaneous increased curvature of the plate boundary, changing obliquity of plate convergence vectors and boundary‐parallel stretching of the forearc region. To study the effects of the plate boundary migration and curvature, a tectonostratigraphy is constructed from the middle Miocene–Pleistocene Apolakkia basin on Rhodes, whose easternmost location makes it a key island to assess the inner forearc's kinematic response to expansion of the overriding Aegean‐Anatolian block and thus obliquity of convergence with the African plate. The basin fill provides temporal and paleogeographic control to interpret its syndepositional and postdepositional structural assemblages. Five fault populations in the Apolakkia basin record two neotectonic deformation phases separated by a kinematic change at ∼4.5 Ma, both of which are consistent with outward expansion of the Aegean‐Anatolian block. The Apolakkia basin originated as a late Miocene fault wedge basin in response to syndepositional southwest‐northeast D1 extension with similar strain patterns in the adjacent offshore Hellenic inner forearc. The kinematic change at ∼4–5 Ma is attributed to a threshold of obliquity whereby the inner forearc started to experience sinistral‐oblique divergence. The Plio‐Pleistocene D2 transtensional phase reoriented the basin and resulted in combined syndepositional west‐northwest‐east‐southeast extension (283°) and 070° sinistral shear, orientations that are best attributed to simultaneous outward expansion of the Hellenic forearc, increasing curvature of the plate boundary and associated boundary‐parallel stretching of the forearc. Principal shear zones offshore also occur consistently at ∼070°, mimicking the D2 kinematic history of the Apolakkia basin and suggesting a consistent geodynamic regime throughout the inner eastern Hellenic forearc. Effects of sinistral‐oblique plate convergence along the subduction zone appear confined to the outer forearc and the accretionary prism of the Mediterranean Ridge. Thus the upper crust of the expanding Aegean‐Anatolian block behaved independently at its leading edge, and the Pliny “trench” constitutes a major boundary separating partitioned forearc slivers, a post‐4.5 Ma partitioning recorded reliably by the Pliocene fill of the Apolakkia basin.