Structural and geochemical evolution of an extensional metamorphic core complex, Paros, Greece.

Lower Miocene crustal extension on the island of Paros resulted in the generation of two low-lying, north-vergent extensional detachment faults that exhumed deep levels of the ductile, partially molten crust in the footwall, whilst simultaneously accumulating lower Miocene age (Aquitanian-Burdigalian) sedimentary basin deposits in the hangingwall. Continued progressive extension, during the regional D2a event, led to the development of two elongate migmatitic gneiss domes; the NW Paros Dome (NPD), and the Main Paros Dome, (MPD) in the footwall of each detachment fault. Voluminous partial melting of the footwall during the D2b event resulted in the profuse emplacement of hybrid, Hs - type granitoids into the lower plate of the NW Paros extensional detachment fault. It is proposed that a similar, deep-seated D2b pluton / migmatite dome exists beneath the core of the Main Paros Dome, over which the Eastern Paros Detachment Fault was additionally uplifted and warped. The granitoids are derived from the concomitant dehydration melting of a mixed gneiss-amphibolite source during decompression of the lower plate rocks. The hybrid nature of the granitoid suite is reflected in their major- and trace-element variations and isotopic characteristics. Rb/Sr whole rock dating yields an errorchron age of circa. 21 Ma for the granitoid suite, which is correlated to the M2b upper amphibolite facies thermal event in the Aegean. The NW Paros Detachment Fault and associated footwall dome are here described for the first time, and provide valuable insights into the deformational mechanisms of a developing gneiss dome. The Monasteri-Naoussa section of NW Paros is thought to expose the deepest levels of the lower plate on Paros, and essentially provides a "tectonic window" into the ductile mid-lower crust. It is accepted that continental extension in the Aegean was superimposed onto an overthickened crust related to an Eocene HPLT D1 compressional event. It is proposed that D1 tectonic stacking of the Attic-Cycladic litho-tectonic units is related to a process of continuous subduction-accretion, as opposed to pure continental collision. New structural data are presented regarding the mid Miocene NW-SE directed horizontal compression phase on Paros, related to a regional, dextral simple shear event (D3). The D3 compressional event is associated with ubiquitous brittle structures that cross-cut and deform the earlier, higher temperature ductile fabrics related to D2 crustal extension.