Active simultaneous uplift and margin-normal extension in a forearc high, Crete, Greece

• We present new field observations and geochronology from southern Crete, Greece.
• Two active E–W striking extensional faults are identified that extend offshore.
• The footwalls and hanging walls of active normal faults preserve marine terraces.
• Kinematic analyses show that offshore structures are synthetic to onshore faults.
• Underplating accompanied by upper crustal extension best explains forearc growth.

The island of Crete occupies a forearc high in the central Hellenic subduction zone and is characterized by sustained exhumation, surface uplift and extension. The processes governing orogenesis and topographic development here remain poorly understood. Dramatic topographic relief (2–6 km2–6 km) astride the southern coastline of Crete is associated with large margin-parallel faults responsible for deep bathymetric depressions known as the Hellenic troughs. These structures have been interpreted as both active and inactive with either contractional, strike-slip, or extensional movement histories. Distinguishing between these different structural styles and kinematic histories here allows us to explore more general models for improving our global understanding of the tectonic and geodynamic processes of syn-convergent extension. We present new observations from the south–central coastline of Crete that clarifies the role of these faults in the late Cenozoic evolution of the central Hellenic margin and the processes controlling Quaternary surface uplift. Pleistocene marine terraces are used in conjunction with optically stimulated luminesce dating and correlation to the Quaternary eustatic curve to document coastal uplift and identify active faults. Two south-dipping normal faults are observed, which extend offshore, offset these marine terrace deposits and indicate active N–S (margin-normal) extension. Further, marine terraces preserved in the footwall and hanging wall of both faults demonstrate that regional net uplift of Crete is occurring despite active extension. Field mapping and geometric reconstructions of an active onshore normal fault reveal that the subaqueous range-front fault of south–central Crete is synthetic to the south-dipping normal faults on shore. These findings are inconsistent with models of active horizontal shortening in the upper crust of the Hellenic forearc. Rather, they are consistent with topographic growth of the forearc in a viscous orogenic wedge, where crustal thickening and uplift are a result of basal underplating of material that is accompanied by extension in the upper portions of the wedge. Within this framework a new conceptual model is presented for the late Cenozoic vertical tectonics of the Hellenic forearc.

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