The relationship between accretion and deep exhumation: an example from the Hellenic Subduction wedge (Crete, Greece)

The island of Crete, Greece, exposes high-pressure, low-temperature (HP/LT) metamorphic rocks (~400 C, 1.0 GPa) exhumed in the forearc high of the modern Hellenic subduction zone. We present new thermochronologic data and re-analyze existing results that lead to a new interpretation for the time- temperature history of the HP/LT rocks. Our synthesis reveals a punctuated cooling history with significant rate changes through time. Tectonic exhumation primarily controls the cooling rate, suggesting that the variable cooling reflects changes in the rate of within-wedge thinning. In the absence of significant erosion, the deformation rate in an active wedge scales approximately linearly with its accretionary flux. In the Hellenic wedge, this flux is primarily controlled by the subduction velocity of the African plate. We argue that the Hellenic wedge has been in a flux steady-state since at least 25 Ma, meaning that volume of material added to the wedge through frontal offscraping and underplating is balanced by the material that leaves the system by erosion and advection out the rear of the wedge. We show that slow cooling and exhumation beginning at ~19 Ma corresponds with a period of slow subduction while rapid cooling at 12 Ma corresponds to the onset of backarc extension and subduction zone retreat. Slab rollback may cause horizontal extension not just by asthenospheric stretching beneath the backarc but also by accelerating the rate of accretion and deformation within the forearc subduction wedge.