Lefkos Shear Zone of Karpathos, Greece (SE Aegean): Pleistocene to recent transtensional forearc basin and paleoseismicity

Abstract

Pleistocene–recent transtensional forearc basins and associated island uplift could be driven by sinistral–oblique convergence along the eastern Hellenic subduction zone, Greece, or by simultaneous trench retreat attributable to subduction of Permo-Triassic Tethyan lithosphere. Structural mapping and basin analysis of the Lefkos Basin, Karpathos indicate deformation best related to oblique trench retreat in which Karpathos drifts southeastward more slowly than Rhodes. Lefkos Basin, perched on a corner of the offshore Karpathos Basin, comprised two Early Pleistocene marine sub-basins developed under northwest extension. Unusually long-wavelength hummocky cross-stratification (>10 m) and clinoforms (15–20 m high) constitute distinctive marker facies. Facies architecture reflects inter-related fault-controlled subsidence, syn-depositional uplift/tilting, glacioeustacy, and fan-delta-lobe avulsion. A 230U/234Th coral age of ∼600 ka and a deer mandible date a Middle Pleistocene transition to southwestward fan-delta progradation and basin uplift. Following ∼0.5 Ma fan-delta-plain deposition, the Lefkos Slide dropped a ∼3.7 km2 coastal plain. Subsequent steep north–south dextral–normal faults dominate Lefkos Basin, with subordinate steep east–west sinistral–normal and northeast-trending normal–oblique faults. Faults signify wrench domination based on their steepness, rare slip indicators, slip reversals and co-genetic upright isoclinal folds. These structures are integral to a forearc-scale dextral–normal shear zone, the Lefkos Shear Zone, an active crustal discontinuity spanning the southeastern forearc from eastern Crete through Kasos–Karpathos to Rhodes. Vertical coherence exists between upper-crustal dextral–normal shear in the Lefkos Shear Zone, crustal seismic anisotropy and deeper mantle processes. Hydraulic fractures, fluid-expulsion pipes, and ruptured cobbles record intermittent significant seismicity (Mw ≥5–6) that permeated the entire Lefkos basin fill spanning ∼2 million years, ultimately involving Late Roman–Early Byzantine archeological remains through ∼1000 years ago. This study encourages re-evaluation of seismic, landslide and tsunami hazards in the sector of the Hellenic forearc surrounding the Lefkos and Karpathos Basins.