The island of Samos in the Aegean Sea exposes high-pressure metamorphic rocks of the Cycladic blueschist unit which are sandwiched between the mildly blueschist-facies Kerketas nappe below and the overlying non-metamorphic Kallithea nappe. The general architecture of the island is depicted in two generalized cross sections in Figure 4. Overall the nappe pile is dipping to the east.
Figure 4. Serial cross sections
(a) and (b). Serial cross sections A-A' and B-B' through Samos Island showing general architecture of the island (refer to Fig. 2 for transect positions). The trace of the main foliation illustrates the generally E-dipping structure.
The base of the Kerketas nappe is not exposed. At its northern end the dolomite of the Kerketas nappe can be followed from the top of Kerkis Mountain down to the sea. The contact of the Kerketas nappe with the Agios Nikolaos nappe has been excised, either by Eocene out-of-sequence thrusting, and/or subsequent Eocene normal shearing, or Miocene extensional shearing (see below). What is well exposed is the Pythagoras thrust separating the Kerketas nappe from the overlying Ampelos nappe (see field trip stop 3.2 below). Ring and Layer (2003) interpreted 40Ar/39Ar phengite ages of ~30-35 Ma to date shear-related phengite recrystallization during thrusting of the Cycladic blueschist unit onto the Kerketas nappe. The Pythagoras thrust was then reactivated as a top-E extensional fault in the Middle Miocene probably associated with the formation of the Middle Miocene basins.
The base of the Agios Nikolaos nappe is nowhere exposed. The upper contact of the Agios Nikolaos nappe is poorly exposed in the northern Ampelos Massif at the central north coast of the island. There is no unambiguous evidence as to whether this contact is a thrust-type or normal shear zone. Ring et al. (2007) speculated that the latest penetrative ductile deformation might be normal and related to the Eocene motion of the Selçuk normal shear zone (see below).
The Selçuk normal shear zone separates the Ampelos nappe from the overlying Selçuk nappe. Rb-Sr dating revealed that the Selçuk normal shear zone was active from 42-32 Ma (Ring et al. 2007). Normal shearing caused extensive retrogression of the high-pressure parageneses in the Selçuk nappe (see below). Normal shearing is a geometric effect facilitating the extrusion of the Ampelos nappe (together with its western Turkish equivalent, the Dilek nappe); it is not related to wholesale crustal extension of the region.
The next major contact in the tectonic sequence is the Kallithea detachment in western Samos. Figure 5 shows a detailed map and cross section of the Kallithea nappe and the Kallithea detachment at its base. Ring et al. (1999a) argued that the detachment was active between 10-8.5 Ma. Subsequent zircon fission-track dating by Stephanie Brichau (published in Kumerics et al. 2005) revealed that the Kallithea detachment, or a splay of it, continued moving until or was reactivated at ~7 Ma (see stop 4.3 below).
Figure 5. Map and cross section
(a) and (b) Detailed map and cross section of Kallithea nappe and adjacent units. The contact between the Katavasis complex and the Kallithea and Kerketas nappes, respectively, is marked by a conspicuous ~50 cm thick dark-grey cataclasite.
The Miocene basins on Samos have a complex architecture and tectonic history. It seems that formation of the basins was related to extensional reactivation of the Pythagoras thrust in the Middle Miocene in a transtensional setting. Ring et al. (1999a) argued that a transtensional scenario might best explain the abrupt lateral facies changes of the Hora and Pythagorion Formations. There is plenty of evidence for folding in the Hora and Pythagorion Formations caused by a short-lived shortening event at >8.6 to ~9 Ma (e.g. stop 2.3 below, see also Structural History).