The tectonometamorphic evolution of high-pressure low-temperature metamorphic rocks of eastern Crete, Greece: constraints from microfabrics, strain, illite crystallinity and paleodifferential stress

Abstract

Analysis of strain, paleodifferential stress, illite crystallinity, and microfabrics of quartz and calcite suggest that multiply alternating late Oligocene/early Miocene N–S convergence and N–S extension caused significant vertical discontinuities in the grade of high-pressure/low-temperature metamorphism of the Phyllite–Quartzite unit (PQU) of eastern Crete. Constrictional fabrics and parallelism of D2 stretching lineations and fold axes are attributed to enhanced slab pull forces at greater depth of subduction. A major D3 extensional detachment is present in the upper part of the PQU where slates with lowest metamorphic grade (diagenesis/anchizone transition) are resting on top of anchimetamorphic rocks. The highest metamorphic grade (anchi-/epizone transition) has been determined for Skythian rocks on top of pre-Alpine basement. Revived N–S convergence (D4) led to E–W-trending map-scale folds and top-to-the-S directed brittle thrusts. There is a clear correlation between D2-related metamorphic grade, finite strain, differential stress, and deformation mechanisms. At the anchi-/epizone transition, solution–precipitation and dislocation creep of quartz and calcite caused maximum finite strains (RXZ=up to 7) at high strain rates and moderate differential stresses (80–200MPa). At the diagenesis/anchizone transition, deformation was accommodated by cataclasis, dislocation glide and solution–precipitation creep resulting in relatively low finite strains (RXZ<2) at high differential stresses of up to 300MPa.