Miocene core complex development and coeval supradetachment basin evolution of Paros, Greece, insights from (U–Th)/He thermochronometry

Abstract

The Aegean region of Greece hosts a series of crustal-scale extensional detachment systems that have accommodated the southward retreating Hellenic subduction zone. Extension has overprinted and dissected the Alpine nappe pile and locally exhumed Cordilleran-type metamorphic core complexes. On the island of Paros, a low-angle extensional detachment fault separates metamorphic footwall rocks from an unmetamorphosed sedimentary succession of the hanging wall. Basement orthogneisses were extensionally sheared in the footwall of the detachment until after 16Ma (zircon U–Pb age of a slightly deformed granite), but pervasive ductile deformation had ceased by 7Ma (zircon U–Pb age of an undeformed rhyolite dike that intrudes gneisses). Apatite and zircon (U–Th)/He ages from the gneisses confirm a period of cooling at rates >100°C/Ma from 16 to 7Ma. In the upper-plate, the basal sedimentary unit yields reset detrital apatite (U–Th)/He (DAHe) ages from 17 to 7Ma and detrital zircon (U–Th)/He (DZHe) ages ranging from 270 to 18Ma. DAHe ages from the stratigraphically higher fanglomerate units are reset to 10–7Ma. The DZHe data have a primary thermal signature of 12–7Ma, but preserve ages up to 113Ma. The uppermost conglomerates exhibit completely reset DAHe ages of 15–9Ma and reset DZHe ages from 10 to 8Ma, with DZHe ages up to 104Ma. Reset DAHe ages indicate late exposure of the footwall and constrain the depositional age of most sedimentary rocks on Paros to be from 14 to 7Ma. Unreset DZHe ages preserve thermal signatures from the major Mesozoic–Tertiary tectonic events in the Aegean Region: [1] Cretaceous Pelagonian-type metamorphism; [2] Eocene peak HP metamorphism; and [3] Miocene Barrovian overprinting. Preservation of these signatures indicates long-term upper-plate recycling prior to syn-extensional deposition. The Paros supradetachment basin represents a classic inverted unroofing sequence deposited during progressive core complex exhumation in the Middle to Late Miocene.