Constraints on the geodynamical evolution of Crete: insights from illite crystallinity, Raman spectroscopy and calcite twinning above and below the ‘Cretan detachment’

Abstract

The Alpine nappes of Crete are commonly subdivided into a Lower and an Upper Nappe pile, both of which are considered to be separated by a low-angle extensional shear zone referred to as ‘Cretan detachment’. The presence of a detachment at the originally suggested position, however, is not supported by our data: (1) Neogene rocks are sandwiched between Tripolitza Unit and the Lower Nappes. (2) Calcite twinning analyses indicate that the major nappes on Crete were largely affected by subhorizontal, layer-parallel shortening rather than subvertical shortening. (3) Metamorphic Tripolitza carbonates resting on top of non-metamorphic Neogene strata on the one hand and illite crystallinity data on the other indicate inverse metamorphism along the ‘Cretan detachment’. (4) Raman spectra of carbonaceous material from rocks below the detachment are locally indicative for very low-grade or an absence of metamorphism within the Lower Nappes, indicating weaknesses of their present tectono-stratigraphical assignment to the Phyllite-Quartzite Unit. (5) Illite crystallinity in the Pindos Unit is substantially lower than in the Tripolitza Unit, although both Units are considered as the Upper Nappes. (6) Oxygene Isotope data indicate precipitation of twinned calcite veins at supercrustal conditions. These findings point to Miocene thrusting at supercrustal conditions, which postdates the exhumation of the Lower Nappes.