Abstract

Serifos is located in the Aegean Sea, 100 km southeast of Athens and belongs to the Cycladic Islands. Geologically, Serifos belongs to the Attic-Cycladic massif and the island is largely dominated by a Late Miocene shallow-level I-type granodiorite pluton in the central and SE portion of the island. The pluton intruded into mylonitized orthogneisses, amphibolites, schists, calc-silicates, marbles and marble meta-conglomerates. Because the host-rocks near the largely undeformed granodiorite pluton contain weakly deformed Ca-Fe-Mg high-temperature skarns, Fe-ores and extensive hydrothermal alteration, the intrusion has been generally considered to be post-tectonic.

Although the granodiorite intrusion clearly crosscuts the regional metamorphic fabric, the uppermost structural levels of the granodiorite, together with its host-rocks, are strongly overprinted by networks of greenschist-facies to cataclastic shear zones that record a notably consistent stretching lineation direction, associated with non-coaxial SSW-directed shear. The immediate host-rocks near the intrusion are mainly mylonitic orthogneisses and amphibolites that were highly deformed at temperatures > 450 °C. This deformation, similar to the lower-temperature greenschist-facies overprint, also records a consistent stretching lineation direction associated with non-coaxial SSW-directed shear. Skarns crosscut the mylonitic orthogneisses and amphibolites and also show evidence of ductile deformation, requiring them to pre-date the emplacement of the mainly undeformed granodiorite.

Higher structural levels, which are separated by a N-dipping high-angle normal fault zone, are mainly exposed in the northern parts of Serifos. The rocks typically consist of greenschists intercalated with marbles. In addition to several generations of folding, the rocks also record W-E trending stretching lineations. Relics of glaucophane suggest that the rocks were affected by an earlier high-pressure metamorphic event, typical for the Cycladic Blueschist Unit.

Based on these observations, we suggest that Serifos represents a major metamorphic core complex in the Aegean region that was exhumed during the Miocene: An earlier SSW-directed mid-crustal shear zone mylonitized an older granitic body together with its host-rocks. In the Late Miocene, this shear zone (exhumed by ongoing extension in the intervening period to higher crustal levels) was, in turn, intruded and cross-cut by the main Serifos granodioritic pluton and its associated dykes. Although these granodioritic intrusions cut the pre-existing metamorphic fabric at structurally deeper levels, they are themselves deformed by a network of south-directed brittle / ductile low-angle shear zones at structurally higher levels, as a result of ongoing N-S extension. This N-S extension is further documented by the intrusion of numerous, approximately W-E trending granodioritic sheets and dykes that typically cross-cut the detachment and are parallel with the also W-E striking, high-angle conjugate normal fault system.

This guide outlines a three-day field excursion showcasing the cross-cutting relationship between the granodiorite intrusion and the host-rocks containing the high-temperature skarns, as well as the kinematics of ductile to brittle low- and high-angle normal faults.