ISOTOPIC RECORDS IN HYDROTHERMAL MINERALIZATION AS A TRACER OF THE CRUSTAL ARCHITECTURE OF THE CYCLADES, GREECE (Invited Presentation)

The lithological heterogeneity and complex structural framework of the Cyclades, Greece, is a consequence of nappe stacking, exhumation within the subduction channel, rapid extension along low-angle detachment systems, and erosion. The consequent complexity renders drawing connections between scattered exposure of basement rocks across the Cycladic islands a challenge. Mid-Miocene to modern seafloor hydrothermal mineralization in the upper crust records one of the latest events in the geodynamic evolution of the Cyclades. We investigated over 30 mineral occurrences from Lavrion, Attica on the Greek mainland, across the Cycladic islands to Milos and Santorini along the active South Aegean volcanic arc, encompassing ~40,000 km² of the arc- to back-arc system. Lead isotope ratios of galena (PbS) and Sr isotope ratios of barite (BaSO₄) indicate distinct regional similarities in the isotopic signature of these hydrothermal minerals. The west Cyclades and the north-central Cyclades exhibit resolvable isotopic signature patterns despite differences in the age of mineralization, immediate host-rock and occurrence in the hanging wall or footwall of the detachment systems. High Pb and Sr isotope ratios are indicative of radiogenic crustal sources as supported by published isotope ratios of basement lithologies, which confirm the regional trends observed in Cycladic galena and barite data. These regional patterns largely correlate with the exposures of the Upper and Lower Cycladic Blueschist Nappe and allow us to further delineate the trace of the Trans-Cycladic Thrust. Our study highlights that the isotopic composition of hydrothermal minerals can provide an alternative tool for the paleogeographic reconstruction of juxtaposed tectono-stratigraphic units across the Cyclades and other complex continental back-arc systems.