P-T conditions for the Ikaria unit (see stops 3.1 and 3.4 below for details of samples) were estimated via pseudosections using the KFMASH system based on whole-rock analyses and constrain P-T estimates for IK02-06a at 6-8 kbar for a temperature of 600-650°C and >6-<7 kbar for IK02-16 (Figure 11).
Figure 11. Pseudosections and AFM diagrams
Pseudosections and AFM diagrams; phengitic substitution in white mica is shown by dashed lines in both pseudosections; the projection of the bulk-rock composition is labelled bulk for both samples in the AFM diagrams. (a) Sample IK02-06a; projections into an AFM diagram are based on mineral formulae of muscovite (pure end member), quartz and water; same projections calculated by THERMOCALC are also shown; inferred pressure is 6-8 kbar for a temperature of 600-650°C (hatched field in pseudosection); a possible P-T path is shown. (b) Sample IK02-16; projections based on mineral formulae (observed) and calculated by THERMOCALC are shown; P-T conditions of 6 kbar and 600°C (hatched field in pseudosection) are indicated. Abbreviations: bi = biotite, cd = cordierite, chl = chlorite, ctd = chloritoid, ep = epidote, fsp = plagioclase, g = garnet, ky = kyanite, and = andalusite, sill = sillimanite, mu = muscovite, q = quartz, st = staurolite.
A very important conclusion is that there is no evidence for any high-pressure metamorphism pre-dating amphibolite-facies metamorphism in samples IK02-6a and IK02-16 from the Ikaria nappe. Reconnaissance metamorphic analyses of other samples from the Ikaria nappe also do not show any signs for high-pressure relics. Altherr et al. (1982) also did not report any evidence for high-pressure metamorphism in the Ikaria nappe.
The absence of any sign of high-pressure metamorphism suggests that the Ikaria nappe does not belong to the Cycladic blueschist unit and might in fact be an exotic non-high-pressure unit in the Aegean. To which tectonic unit does the Ikaria nappe then belong? The only mid-amphibolite-facies units, which have no Tertiary high-pressure overprint in the region are the Çine and Bozdağ nappes of the Menderes nappes of western Turkey (Ring et al. 1999a; Gessner et al. 2001; Régnier et al. 2003). Large parts of the Çine nappe consist of ~550 Ma old augengneiss, which does not occur in the Ikaria nappe. We tentatively correlate the Ikaria nappe with the Bozdağ nappe of western Turkey, which also comprises a very thick metapelite sequence and minor marble, amphibolite and quartzite (Ring et al. 2001). The Çine and Bozdağ nappes belong to the lowest tectonic unit (Menderes nappes) of western Turkey, which was overthrust by the Cycladic blueschist along the Cyclades-Menderes thrust unit in the Eocene (Gessner et al. 2001). We speculate that the Cyclades-Menderes thrust emplaced the Messaria nappe onto the Ikaria nappe.
Our correlation of the Ikaria nappe with the Bozdağ nappe of the Menderes nappes results in a major geometric problem in the eastern Aegean. On Samos Island east of Ikaria, the Cycladic blueschist unit rests on the Basal unit (External Hellenides), which in general makes up the lowest tectonic unit in the Aegean (see Ring et al. this volume). If the Ikaria nappe indeed belongs to the Menderes nappes it would have been derived from Anatolia (Figure 5) and this implies that the interfingering of Adria and Anatolia has a complex geometry in the eastern Aegean.