The metamorphic evolution of the high-pressure Kechros complex in East Rhodope (NE Greece): Implications from Na–Al-rich leucocratic rocks within antigorite serpentinites.

The Rhodope Domain in NE Greece is comprised of different tectonometamorphic complexes involved in the Alpine collisional history between the Eurasian and African plates. The Kechros Complex represents the lowermost tectonic unit in East Rhodope, and contains a metamorphic suite of Na–Al-rich leucocratic rocks (i.e., alkali feldspar granites, alkali syenites and syenites) within the Virsini antigorite serpentinite. Based on the calculated P–T pseudosection and superimposed isopleths for a meta-syenite, we have determined a peak pressure and temperature of 1.55±0.03GPa and 550±25°C, suggesting HP metamorphism for leucocratic rocks enclosed in the Virsini serpentinized peridotites. The retrograde conditions suggest a prolonged exhumation history, with equilibration conditions first at P 1.1±0.03GPa and T 580±20°C and then at P 0.55±0.04GPa and T 430±30°C. The P–T conditions suggest an early rapid uplift event followed by a late-stage exhumation period, characterized by rapid cooling at relatively isobaric conditions. Similar metamorphic signatures are also recorded in continental rocks of the Kechros complex (i.e., orthogneisses, metapelites), suggesting that crustal and mantle rocks underwent a common Alpine tectonometamorphic evolution. The exact ages of HP metamorphism in the Kechros Complex are not well constrained, however, a Rb–Sr age of 37Ma from a neighboring orthogneiss records a stage of exhumation that may be contemporaneous with the Eocene HP metamorphism (49–55Ma; i.e., recorded in the Nestos Shear Zone of Central Rhodope). We interpret this to be the result of the eventual closure of the Axios/Vardar Ocean and subsequent subduction of the Apulian continental crust (a promontory of the Africa continent) under the southern margin of the European continent in the late Cretaceous and early Tertiary. [ABSTRACT FROM AUTHOR]