CALCITE TWINNING CONSTRAINTS ON ALPINE NAPPE EMPLACEMENT, HELLENIC ARC, CRETE, GREECE

The Alpine orogen throughout the Hellenic arc in Greece is characterized by SSE emplacement of thrust-cored nappes that young toward the arc (SSE), as constrained by the ages of synorogenic flysch deposits that are now preserved between the nappes. The peak metamorphic age within the belt is ~24 Ma. The frontal (external) Plattenkalk and Phyllite-Quartzite (PQU) nappes contain high P, low T mineral assemblages and are overlain by the Tripolitza and Pindos nappes that are composed of marblized limestones without any distinctive metamorphic mineral assemblages. This metamorphic juxtaposition has led to a number of tectonic models that utilize the Tripolitza-PQU boundary as a normal fault detachment within a thrust belt. In eastern Crete carbonates were sampled from the Tripolitza and PQU nappes, as well as limestones and calcite veins from the synorogenic flysch, and a presumed synorogenic, thrust fault-normal series of large calcite (‘travertine’) veins. Twenty-seven calcite twinning strain results indicate that N-S subhorizontal shortening is the dominant shortening fabric for Tripolitza limestones and veins (n=9), PQU marbles and veins (n=11), flysch limestones (n=2) and ‘travertine’ veins (n=2). Subvertical shortening was observed in two Tripolitza limestones (n<10 grains) near the PQU-Tripolitza boundary. Veins in the synorogenic flysch preserve an E-W sub-horizontal shortening strain complimetary to top-to-the east striations on horizontal planes in outcrop. We observe a consistent sub-horizontal shortening strain parallel to the inferred nappe transport direction for a diverse suite of carbonates with no evidence of any “detachment”, where vertical shortening would be pervasive.