Abstract

We apply low-temperature thermochronology, Rb/Sr geochronology, petrological data, and structural mapping to constrain the timing and kinematics of the Ios metamorphic core complex. Top-to-north extension in the lower plate Headland Shear Zone was active at 18-19 Ma under metamorphic conditions of 475-610 degrees C and 0.65-1.1 GPa. The South Cyclades Shear Zone/Ios Detachment Fault (SCSZ/IDF) system shows top-to-south extensional shear active at c. 19 Ma at 380-550 degrees C, with local top-to-north bands. Extensional shear above the SCSZ/IDF is dominantly top-to-south to top-to-SW. PT estimates from an eclogite boudin constrain Eocene high-pressure metamorphism to 430-560 degrees C and 1.21 +/- 0.42 GPa to 0.66 +/- 0.37 GPa. Similar low-temperature thermochronometric ages across Ios demonstrate that ductile extensional movement ceased by c. 15 Ma. Exhumation to shallow crustal levels took place between c. 15 and 9 Ma at cooling rates of up to 120 degrees C Ma(-1) with a slow down to 20 degrees C Ma(-1) between 12 and 9 Ma, most likely accommodated by extensional slip at rates of c. 3 km Ma(-1) along the top-to-SW Coastal Fault System. We propose a model of bivergent extension for exhumation of the Ios core complex between 19 and 9 Ma, with Ios forming a secondary antithetic top-to-south to top-to-SW extensional fault system to a more dominant top-to-north Naxos/Paros detachment system.