Early exhumation of high-pressure rocks in extrusion wedges: Cycladic blueschist unit in the eastern Aegean, Greece, and Turkey

[1] Structural, metamorphic, and geochronologic work shows that the Ampelos/Dilek nappe of the Cycladic blueschist unit in the eastern Aegean constitutes a wedge of high-pressure rocks extruded during early stages of orogeny. The extrusion wedge formed during the incipient collision of the Anatolian microcontinent with Eurasia when subduction and deep underthrusting ceased and the Ampelos/Dilek nappe was thrust southward over the greenschist-facies Menderes nappes along its lower tectonic contact, the Cycladic-Menderes thrust, effectively cutting out a similar to 30- to 40-km-thick section of crust. The upper contact of the Ampelos/Dilek extrusion wedge is the top-to-the-NE Selcuk normal shear zone, along which the Ampelos/Dilek nappe was exhumed by similar to 30-40 km. Detailed Rb-Sr and Ar-40/Ar-39 dating of mylonites demonstrates that both shear zones operated between 42 and 32 Ma. There is no evidence for episodic motion during the similar to 10 Myr life span of the shear zones, suggesting that both shear zones operated in a steady, nonepisodic fashion. Our data provide supporting evidence that simultaneous thrust-type and normal sense shearing can accomplish the early exhumation of deep-seated rocks