Geological setting
Rocks in Amorgos have been sub-divided into the following tectonostratigraphic units (Rosenbaum et al., 2007): the Metabasite Unit, the Basal Conglomerate Unit, the Marble Unit, and the Flysch Unit.
The two lowermost units are found only in the area northwest of Katapola (Itinerary 1). They consist of two distinct blueschist-facies assemblages associated with (1) garnet/blue-amphibole metabasites, and (2) carpholite-bearing micaschists, quartzites and meta-conglomerates.
Overlying these units is a thick (>1000 m) Triassic to Eocene marble sequence. This includes, from bottom to top, massive marbles, meta-dolomites, well bedded pelagic marbles with abundant meta-chert replacements, and thick massive marbles with a few small lenses of Cretaceous meta-bauxites (Dürr et al., 1978; Fytrolakis et al., 1981; Dürr, 1985). The meta-bauxites can be found in the northern part of the island, where they contain the assemblage diaspore, hematite and Fe-carpholite (Minoux et al., 1980), estimated by Theye et al. (1997) to represent metamorphic conditions of 300-400°C and >8 kbar.
The top of the stratigraphic sequence in Amorgos is made up of a Flysch unit, which consists of shales, schists, greywackes, conglomerates and large marble olistoliths. The flysch conglomerates are characterised by centimetre- to decimetre-scale pebbles of marbles and greywackes, shales, schists and quartzites.
The structural history of Amorgos involved at least three phases of deformation (Rosenbaum et al., 2007). The earliest one is associated with isoclinal recumbent folds (F1) and is responsible for the development of the dominant penetrative foliation. The large-scale F1 folds have axes that are generally perpendicular to the stretching lineation (L1). The latter is commonly associated with kinematic criteria showing top-to-SE sense of shear.
The earliest deformation D1 is locally overprinted by a second deformational event D2. These structures are associated with top-to-NW kinematic indicators and sub-horizontal to gently plunging fold axes and crenulations (F2) with vergence towards the NW. Most of these structures are found close to detachment faults and are attributed to the role of detachment faulting (Rosenbaum et al., 2007).
Figure 2. IMap of itinerary 1 and locations of the excursion stops. Geology is after Rosenbaum et al. (2007).
The whole sequence in Amorgos has been affected by late F3 folds. These are predominantly N-S trending folds with sub-horizontal fold axes, ranging from gently inclined tight folds to long wavelength open folds.
The actual morphology of Amorgos is largely attributed to the role of Quaternary high-angle normal faulting (Stiros et al., 1994). These faults are generally oriented NE-SW. One of these faults are supposedly responsible for the juxtaposition of the Pelagonian amphibolite-facies rocks of Nikouria on top of Amorgos’ marble unit (Figure 1). The contact itself is not exposed.