The timing of high-pressure metamorphism on Andros Island, Greece: evidence for both Cretaceous and Eocene blueschist-facies events?

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This proposal seeks funding for field-based geochemical, geochronological and isotope geochemical research and attempts to fill a gap in understanding of the tectono-metamorphic evolution of the central Aegean region. The proposed study aims at deciphering the enigmatic importance of Cretaceous blueschist-facies metamorphism that was postulated for the Makrotantalon Unit (MU) in northern Andros, and of the unique association of Jurassic meta-ophiolitic rocks and HP rocks in southern Andros (Cape Steno), currently considered to be a part of the Cycladic Blueschist Unit. This proposal suggests to systematically check the geological significance of these alternatives and to clarify the status of the Cape Steno succession by addressing the following questions: Is the MU a tectonic slice of the CBU with unusual preservation of pre-Eocene blueschist metamorphism? Is the apparently Cretaceous age for the HP/LT stage robustly constrained or compromised by extraneous Ar contamination? Did the MU experience different episodes of HP/LT metamorphism? Was Cretaceous blueschist facies metamorphism followed by an Eocene HP/LT event? Is the structural assignment of Eocene blueschists to the MU correct? What is the age of blueschist facies metamorphism at Cape Steno? Is this meta-ophiolitic HP rock suite an integral part of the CBU or representing an exotic subunit? To answer these questions, it is proposed (a) to date the HP/LT rocks from northern and southern Andros using the Rb-Sr method to provide robust age constraints for establishing a correlative relationship either to the CBU or to the Pelagonian Zone on continental Greece, and (b) to apply geochemical fingerprinting using a combination of bulk rock geochemistry, Sr–Nd isotope characteristics and spinel chemistry to further characterize ultramafic rocks that recently were assigned to different structural positions within the nappe stack. Further work on these aspects will help developing a better understanding of the metamorphic history and the geodynamic context. The overarching goal of the proposed research is to further unravel the internal architecture of the Cycladic Massif and to establish robust age constraints for an improved interpretation of the geological history.