A long-term rock uplift rate for eastern Crete and geodynamic implications for the Hellenic subduction zone.

Strobl M., Hetzel R., Fassoulas C., Kubik P.W.

Zusammenfassung

The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with local relief exceeding 2km. Based on the elevation of marine shorelines, rates of rock uplift during the Late Holocene were previously estimated to range between 1 and 4mm/a in different parts of the island. These rates may, however, not be representative for longer timescales, because subduction earthquakes with up to 9m of vertical coseismic displacement have affected Crete in the Late Holocene. Here we use a well preserved sequence of marine terraces near Kato Zakros in eastern Crete to determine the rate of rock uplift over the last ~600ka. Field investigations and topographic profiles document a flight of more than 13 marine bedrock terraces that were carved into limestones of the Tripolitza unit. Preliminary age constraints for the terraces were obtained by 10Be exposure dating of rare quartz-bearing sandstone clasts, which are present on some terraces. The 10Be ages of these samples, which have been corrected for an inherited nuclide component, yielded exposure ages between ~100ka and zero. Combined with geomorphologic evidence the two oldest 10Be ages suggest that the terraces T4 and T5, with shoreline angles at an elevation of ~68 and ~76m above sea level, respectively, formed during the marine isotope stage 5e about 120ka ago. The correlation of the higher terraces (T6 to T13) with regional sea-level highstands indicates sustained rock uplift at a rate of ~0.5 m/ka since at least ~600 ka. As normal faulting has dominated the tectonics of Crete during the last several million years, upper crustal shortening can be ruled out as a cause for rock uplift. We argue that the sustained uplift of the island results from the continuous underplating of sediments, which are transferred from the subducting African plate to the base of the crust beneath Crete.