The bedrock of Hymittos, Attic peninsula, Greece, exposes a pair of low-angle crustal-scale ductile-then-brittle detachment faults. The uppermost detachment fault separates sub-greenschist facies phyllite and marble of a Pelagonian Zone hanging wall, from greenschist facies metasedimentary schist, calc-schist, and marble correlated to the Cycladic Blueschist Unit. A second, structurally lower detachment fault subdivides the metamorphic rocks of the Cycladic blueschist unit footwall into middle and lower units. There is a marked step in metamorphic grade between the sub-greenschist facies uppermost package, and the middle-to-upper greenschist facies middle and lower packages. A suite of new white mica 40Ar/39Ar and zircon (U-Th)/He dates indicates accommodation of deformation along these faults occurred from the late Oligocene to the late Miocene with both faults active during the middle Miocene. The structures have clear top-S/SSW kinematics determined from flanking folds, sigmoids, shear bands, stair-stepping of strain shadows on porphyroclasts, and SCC' fabrics. The ductile-to-brittle deformation of the structures, morphology of the massif, and the increase in metamorphic grade suggest these low-angle structures are part of a major, crustal-scale extensional complex, located at the northwest end of the West Cycladic Detachment System, that accommodated Miocene bivergent exhumation of Attic-Cycladic metamorphic core complexes in the central Aegean. Taken together, the above data suggest that multiple coeval detachment branches may form in areas with high strain gradients to accommodate the mechanically necessary termination of Cycladic-style detachment systems.

Triassic rift-related volcanic rocks outcrop over all mainland Greece, comprising of trachybasalts and basaltic trachyandesites. Relatively immobile to the effects of alteration processes major and trace element abundances classify the volcanics into OIB and E-MORB lavas. They have mainly been distinguished based upon their: i) LREE contents, ii) silica-saturation index (S·I.), iii) Zr/Nb and Nb/Y ratio values; iv) Th, U, and Ta contents v) geotectonic discrimination diagrams. Their geochemistry indicates that most rocks were affected by moderate to extensive differentiation processes, mostly expressed by clinopyroxene fractionation. Some of the OIB and E-MORB volcanics are considered as primitive undersaturated, displaying (low SiO2, Zr/Nb and S.I. values, enhanced CaO/Al2O3 ratios). Calculated average mantle potential temperatures are comparable (1410 °C OIB; 1370 °C E-MORB), with melt fractions estimated at 3–5% for primary OIB magmas and 6–8% for primary E-MORB magmas. An asthenospheric origin is inferred for the OIB lavas, with melting in the garnet stability field (75–95 km; 2.5–3.0 GPa), whereas E-MORB parent magmas were formed with melting in the garnet/spinel (transitional) stability field (55–70 km; 1.8–2.2 GPa). The Hellenic Triassic rift-related lavas were most likely generated and erupted after lithospheric attenuation and extension, followed by subsequent asthenospheric upwelling of the mantle. The high calculated partial melting degrees and the observed thick and voluminous lava formations account for fast-spreading of the Tethys ridge during the Triassic. Temperature results suggest that the Hellenic Triassic rift-related magmas were generated from mantle at ambient temperature, render a mantle plume-based scenario improbable.