Nappe Imbrication Within the Phyllite‐Quartzite Unit of West Crete: Implications for Sustained High‐Pressure Metamorphism in the Hellenide Subduction Orogen, Greece

Abstract

AbstractWe report four K‐Ar fault‐gouge and eight U‐Pb calcite ages from the high‐pressure Phyllite‐Quartzite Unit (PQ) and the overlying, strongly thinned non‐high‐pressure Tripolitza and Pindos units of western Crete, Greece. We relate consistent 26–21 Ma fault‐gouge ages to a discrete top‐to‐the‐S, brittle‐ductile, contractional shear zone (Intra‐PQ Thrust) that formed during high‐pressure conditions within the Phyllite‐Quartzite Unit. The Intra‐PQ Thrust separates the Phyllite‐Quartzite Unit into an upper and a lower unit and is associated with gypsum deposits and high finite strain. Below the Intra‐PQ Thrust, U‐Pb calcite ages between about 16 and 13 Ma are also associated with top‐to‐the‐S kinematic indicators and, in part, developed during aragonite stability. The brittle‐ductile contact zone to the overlying Tripolitza and Pindos units yielded U‐Pb calcite ages of 13 to 12 Ma. Our data imply that the upper Phyllite‐Quartzite Unit underwent high‐pressure metamorphism at the commonly envisaged time of 24–21 Ma. However, the lower Phyllite‐Quartzite Unit started to be underthrust at 26–21 Ma and was high‐pressure metamorphosed at 16–13 Ma, as suggested by the U‐Pb calcite ages of aragonite‐bearing samples and published zircon fission track ages. We discuss a tectonic model of successive underthrusting, high‐pressure metamorphism and subsequent exhumation of both Phyllite‐Quartzite units in extrusion wedges until 12–11 Ma, after which Crete underwent crustal extension. Our work suggests that there might be more than one Cretan Detachment. It also has implications for sustained underthrusting and exhumation of continental crust in subduction zones.