CONSTRAINTS ON THE TEMPORAL SUCCESSION OF DEEP UNDERPLATING IN THE NW CYCLADIC SUBDUCTION COMPLEX, GREECE.

The deformation and metamorphic processes operating along subduction zone interfaces vary dramatically with depth, from the accretion zone to underplating along the deep plate interface. This deformational and rheological transition has been studied through geophysical and numerical modeling. However, information from the rock record is sparse. The rock record is important for understanding depth-dependent variations in the subduction interface. This study focuses on quantifying the temporal and spatial processes associated with intermediate to deep coherent underplating (>20km) in the NW portion of the Cycladic Subduction Complex (CSC). Constraining the deformation and P-T-t history of these rocks clarifies the processes of syn-metamorphic coherent underplating, the timing and depth of underplating, and the rheology of the interface. On the islands of Evia, Andros, and Tinos, a series of underplated and stacked HP-LT metamorphic slices were exhumed during large-magnitude back-arc extension. These include the Basal Unit (BU) and Cycladic Blueschist Unit (CBU), which are separated by the Almyropotamos flysch on Evia. These rocks experienced Eocene to Oligocene HP-LT metamorphism during progressive underplating. Systematic structural, metamorphic, petrochronologic, and thermochronologic constraints are integrated to define these underplated tectono-stratigraphic slices and to reconstruct the spatial and temporal progression of subduction underplating. Understanding the conditions and progression of Eocene to Oligocene coherent underplating in the CSC provides insights into long-term progressive underplating, including the impact of deformation and fluid-rock interaction on the subduction interface and the temporal sequencing of underplating.