Thermochronologic and Geochronologic Investigations of the Pre-Volcanic Crystalline Basement of Thera (Santorini), Greece: Determining the Tectonostratigraphy and Deformational History of the Metamorphic Core

Abstract

The cores of most Cycladic Islands are formed as consequences of early Paleogene high-pressure subduction processes of the African plate beneath Europe, and Miocene extensional exhumation of the subduction trench. The island of Thera (Santorini) resides in the Hellenic Volcanic Arc, and is dominated by Quaternary eruptive volcanic material atop a pre-volcanic basement. The position of the island has led to debate as to the nature of the pre-volcanic basement, with connections drawn to either the Cycladic Blueschist Unit (CBU) or the Phyllite-Quartzite Unit (PQU). Field observations, which document a top-to-SSE detachment, in conjunction with geochronological techniques have been applied to assess the tectonostratigraphy of the pre-volcanic basement. The results resolve the pre-volcanic basement as belonging to the CBU which has been juxtaposed against Sub-Pelogonian marble by the SSE directed detachment. This firmly establishes Thera within the Cycladic realm, documents Miocene deformation, and changes the geologic map of the Hellenides.