Incipient continental collision and plate-boundary curvature: Late Pliocene–Holocene transtensional Hellenic forearc, Crete, Greece

Abstract

Geodynamic controls on Late Pliocene–Holocene kinematics of the Hellenic forearc are assessed using the fan–deltaic basin fill of the Messaras forearc basin of south–central Crete. Previously unrecognized 070° sinistral faults developed in wrench-dominated transtension with strike-slip:normal-slip ratios of 10:1 to 100:1. Coeval folds developed in proximity to the 070° sinistral faults during deposition of the Galini Formation, making them candidates to have developed in transtension, and new chronostratigraphic and 87 Sr/ 86 Sr data constrain the age of initial sinistral transtension and associated folding to c . 3.4 Ma. Sinistral fault activity continued through Late Holocene time based on the ages of displaced units with implications for seismic hazards in central Crete. The Messaras structural assemblages are symptomatic of the regional-scale Hellenic forearc with Plio-Pleistocene basins both offshore and onshore Crete controlled by sinistrally dominated 070° faults and secondary 020° extensional oversteps. Although the post-Miocene plate-convergence vectors became increasingly oblique, deformation in transtension, not transpression, has driven Hellenic forearc kinematics. Incipient collision with an African promontory blocked further outward expansion of the Aegean plate boundary along western Crete but induced forearc slivers to be displaced northeastward and sheared sinistrally off the free expanding edge of Aegea as the Cretan–Rhodes forearc was simultaneously stretched. Such a kinematic regime has probably operated since c . 3.4 Ma when the Messaras 070° wrench-dominated system became active and represents tectonic escape during incipient continental collision.