Osman Candan

Correlation of syn-orogenic tectonic and metamorphic events in the Cyclades, the Lycian nappes and the Menderes massif : Geodynamic implications

The recent discovery of HP-LT parageneses in the basal unit of the Lycian nappes and in the Mesozoic cover of the Menderes massif leads us to reconsider and discuss the correlation of this region with the nearby collapsed Helle-nides in the Aegean domain. Although similarities have long been pointed out by various authors, a clear correlation has not yet been proposed and most authors insist more on differences than similarities. The Menderes massif is the eastern extension of the Aegean region but it has been less severely affected by the Aegean extension during the Oligo-Miocene. It would thus be useful to use the structure of the Menderes massif as an image of the Aegean region before a significant extension has considerably reduced its crustal thickness. But the lack of correlation between the two regions has so far hampered such comparisons. We describe the main tectonic units and metamorphic events in the two regions and propose a correlation. We then show possible sections of the two regions before the Aegean extension and discuss the involvement of continental basement in the Hellenic accretionary complex. In our interpretation the Hellenic-Tauric accretionary complex was composed of stacked basement and cover units which underwent variable P-T histories. Those which were not exhumed early enough later followed a high-T evolution which led to partial melting in the Cyclades during post-orogenic extension. Although the Menderes massif contains a larger volume of basement units it does not show significant evidence for the Oligo-Miocene migmatites observed in the center of the Cyclades suggesting that crustal partial melting is strictly related to post-orogenic extension in this case.

Eclogites within the Menderes Massif/western Turkey

Metagabbros in the core series of the Menderes Massif, for some time considered as post orogenic Miocene intrusives, revealed a strong poly-metamorphic history. The metagabbro bodies exhibit a pronounced zonation. Within their cores, igneous minerals are still preserved. Coronitic textures are interpreted as results of a high temperature, possibly granulitic overprint. The outer parts of the metagabbro bodies mostly consist of strongly to completely retrograded garnet-amphibolites, but occasionally contain relics of eclogites. Petrologic investigations confirmed a high pressure overprint and allowed preliminary P, T estimates (650°C, ≥ 1.3 GPa). The intensity of the HP metamorphism seems to rise from south to north within the Menderes basement, thus pointing to a northward subduction as the cause. The age of the high pressure event still awaits clarification. However, its very existence reanimates the question, how close the relationship between Menderes and the Cyclades evolution might have been.

The wide distribution of HP-LT rocks in the Lycian Belt (Western Turkey): implications for accretionary wedge geometry

Abstract In SW Turkey, Fe-Mg-carpholite has recently been recognized in the basal metasediments of the Lycian Nappes, which overthrust the Menderes Massif on its southern flank. This high-pressure-low-temperature (HP-LT) metamorphic index mineral was widely found in the Bodrum peninsula region. Our new metamorphic and structural data on similar carpholite-bearing rocks found farther north in several klippen of the Lycian Nappes located on top of the Menderes Massif show that HP-LT rocks in SW Turkey occur over a distance of >200 km in both north-south and east-west directions, thus indicating a wide HP-LT metamorphic belt. The deformation pattern from the Bodrum peninsula to Çivril, all along the contact between the Lycian Nappes and the Menderes Massif, reveals the role played by major top-to-the-NE shear zones contemporaneous with exhumation of the Lycian HP-LT rocks. This deformation shows an oblique direction of opposite shear sense relative to the earlier southward translation of the Lycian Nappes over the Menderes Massif, for which top-to-the-south displacements are preserved in the upper units of the Lycian Nappes on the Bodrum peninsula, as well as at the base of the Lycian nappe klippen located farther north. The widespread distribution of well-preserved Fe-Mg-carpholite-bearing rocks in the Lycian Nappes has implications for the geometry of the accretionary wedge responsible for HP-LT metamorphism in SW Turkey.

Natural radioactivity (226Ra, 232Th and 40K) and assessment of radiological hazards in the Kestanbol granitoid, Turkey.

The surveys of natural gamma-emitting radionuclides in rocks and soils from the Ezine plutonic area were conducted during 2007. Direct dose measurement using a survey meter was carried out simultaneously. The present study, which is part of the survey, analysed the activity concentrations of (238)U, (232)Th and (40)K in granitoid samples from all over the region by HPGe gamma spectrometry. The activity concentrations of (226)Ra ranged from 94 to 637 Bq kg(-1), those of (232)Th ranged from 120 to 601 Bq kg(-1)and those of (40)K ranged from 1074 to 1527 Bq kg(-1) in the analysed rock samples from different parts of the pluton. To evaluate the radiological hazard of the natural radioactivity in the samples, the absorbed dose rate (D), the annual effective dose rate, the radium equivalent activity (Ra(eq)) and the external (H(ex)) hazard index were calculated according to the UNSCEAR 2000 report. The thorium-to-uranium concentration ratios were also estimated.

Alpine high pressure evolution of the eastern Bitlis complex, SE Turkey

Abstract The Bitlis complex, SE Anatolia, constitutes a crystalline complex derived from the north of the Arabian Plate, accreted to the South Armenian block. Metamorphic studies in the cover sequences of the Bitlis complex allow constraining the thermal evolution of the massif by metamorphic index minerals. A regionally distributed low temperature-high pressure (LT-HP) metamorphic evolution is documented by glaucophane, relics of carpholite in chloritoid-bearing schists and pseudomorphs after aragonite in marbles. The metamorphic age of these HP assemblages is constrained by Ar isotope dating as 74±2 Ma. This indicates that (i) the Bitlis complex represents a terrane detached from the Arabian indenter that was subducted and stacked to form a nappe complex during the closure of the Neo-Tethys and (ii) that during Late Cretaceous to Cenozoic evolution the Bitlis complex never underwent temperatures over 450 °C. The consequences of the metamorphic evolution of the Bitlis complex (a cold continental block within a hot environment) for the Eastern Anatolian plateau are complied in a crustal section.

Late Cretaceous eclogitic high-pressure relics in the Bitlis Massif

A new occurrence of eclogites was found in the Kesandere valley in the eastern most part of the Bitlis complex, SE Anatolia. These high-pressure (HP) relics were preserved in calc-arenitic metasediments within the high-grade metamorphic basement of the Bitlis complex. The eclogitic parageneses were strongly overprinted during decompression and heating. These new eclogites locality complements the evidence of blueschist-facies metamorphism documented recently in the meta-sedimentary cover sequence of this part of the Bitlis complex. Thermodynamic calculations suggest peak conditions of ca. 480–540 °C/1.9–2.4 GPa. New U/Pb dates of 84.4 ± .9 and 82.4 ± .9 Ma were obtained on zircons from two Kesandere eclogite samples. On the basis of geochemical criteria, these dates are interpreted to represent zircon crystallization during the eclogitic peak stage. Kesandere eclogites differ from those previously described in the western Bitlis complex (Mt. Gablor locality) in terms of lithologic association, protolithic origin, and peak P–T conditions (600–650 °C/1.0–2.0 GPa, respectively). On the other hand, eclogitic metamorphism of Kesandere metasediments occurred shortly before blueschist-facies metamorphism of the sedimentary cover (79–74 Ma 40Ar/39Ar white mica). Therefore, the exhumation of Kesandere eclogites started between ca. 82 and 79 Ma, while the meta-sedimentary cover was being buried. During this short time span, Kesandere eclogite were likely uplifted from ~65 to 35 km depth, indicating a syn-subduction exhumation rate of ~4.3 mm/a. Subsequently, eclogite- and blueschist-facies rocks were likely retrogressed contemporarily during collision-type metamorphism (around 72–69 Ma). The Bitlis HP rocks thus sample a subduction zone that separated the Bitlis–Pütürge (Bistun?) block from the South-Armenian block, further north. To the south, Eocene metasediments of the Urse formation are imbricated below the Bitlis complex. They contain (post Eocene) blueschists, testifying separation from the Arabian plate and southward migration of the subduction zone. The HT overprint of Kesandere eclogites can be related to the asthenospheric flow provoked by subducting slab retreat or break off.

East Anatolian plateau constructed over a continental basement: No evidence for the East Anatolian accretionary complex

The East Anatolian plateau (Turkey) is extensively covered by Neogene to Quaternary volcanic-sedimentary rocks, and is characterized by an attenuated lithospheric mantle. Its pre-Neogene basement is commonly considered to consist entirely of Late Cretaceous to Oligocene oceanic accretionary complexes, formed at the junction of several continental blocks. Here we report on three main exposures of the pre-Neogene basement in this region. The exposed areas consist mainly of amphibolite-to granulite-facies metamorphic rocks, including marble, amphibolite, metapelite, metagranite, and metaquartzite. An upper amphibolite-to granulitefacies domain is equilibrated at similar to 0.7 GPa and similar to 800 degrees C at 83 +/- 2 Ma (2 sigma). U-Pb dating of magmatic zircons from the metagranite yielded a Late Ordovician-early Silurian protolith age (444 +/- 9 Ma, 2 sigma). The detrital zircons from one metaquartzite point to a Neoproterozoic-early Paleozoic provenance. Ophiolitic rocks tectonically sit on the metamorphic rocks. Both the metamorphic and ophiolitic rocks are in turn unconformably covered by lower Maastrichtian clastic rocks and reefal limestones, suggesting that the whole exhumation process and juxtaposition with the ophiolitic rocks had occurred by the early Maastrichtian. Several lines of evidence, such as (1) the absence of any indication of a former high-pressure metamorphism in the metamorphic rocks, (2) the allochthonous nature of the ophiolitic rocks, (3) the presence of metagranite with a Late Ordovician-early Silurian protolith age, and (4) the Neoproterozoic- early Paleozoic provenance of detrital zircons in the metaquartzite (in contrast to the dominance of late Paleozoic-Mesozoic crystalline rocks in the adjacent continental blocks) indicate a substantial component of continental basement beneath the Neogene to Quaternary cover. Thus, the loss of the lithospheric mantle probably resulted from lithospheric foundering processes beneath the plateau, rather than just slab steepening and break-off.

A radiological survey of the Eğrigöz granitoid, Western Anatolia/Turkey.

A radiological survey of the granitoid areas throughout Western Anatolia was conducted during 2007-14. As a part of this radiological survey, this article presents results obtained from Eğrigöz pluton, which lies in the northeastern region of Western Anatolia. In the investigated area, the activity measurements of the natural gamma-emitting radionuclides ((226)Ra, (232)Th and (40)K) in the granitic rock samples and soils have been carried out by means of the NaI(Tl) gamma-ray spectrometry system. The activity concentrations of the relevant natural radionuclides in the granite samples appeared in the ranges as follows: (226)Ra, 28-95 Bq kg(-1); (232)Th, 50-122 Bq kg(-1) and (40)K, 782-1365 Bq kg(-1), while the typical ranges of the (226)Ra, (232)Th and (40)K activities in the soil samples were found to be 7-184, 11-174 and 149-1622 Bq kg(-1), respectively. Based on the available data, the radiation hazard parameters associated with the surveyed rocks/soils are calculated. The corresponding absorbed dose rates in air from all those radionuclides were always much lower than 200 nGy h(-1) and did not exceed the typical range of worldwide average values noted in the UNSCEAR (2000) report. Furthermore, the data are also used for the mapping of the surface soil activity of natural radionuclides and the corresponding gamma dose rates of the surveyed area.

The Rosetta Marbles from Fesleğen, Ören Unit, SW Anatolia

Rosetta Marble (Rimmelé et al. 2003) refers to radiating, rosette-like structures made of decimeterto meter-scale calcitic rods observed in a metamorphosed carbonate platform succession in SW Anatolia. Candan et al. (2005), Oberhänsli et al. (2010) and Pourteau et al. (2010) reported similar structures from Alpine metamorphic belts of western, central and south-eastern Anatolia. The presented GeoSite (37 03.390N 27 47.480E, near Fesleğen village in the Bodrum Peninsula, SW Anatolia) exhibits spectacular examples and wide morphological diversity of Rosetta Marble structures. Surprisingly, these features, in this location and anywhere else across Anatolia, were not reported in previous works that tackled detailed regional stratigraphy and its lateral continuations (e.g. Graciansky et al. 1967; Brunn et al. 1970; Bernoulli et al. 1974; Poisson 1977; Gutnic et al. 1979). Interestingly, cm-sized, Rosette-like pseudomorphs after gypsum were reported from Neogene–Quaternary lake sediments of SW Anatolia (Alçiçek and Jiménez-Moreno 2013). This occurrence differs considerably from the Fesleğen Rosetta Marble in terms of dimensions, depositional environment, stratigraphic age and metamorphic evolution. Fesleğen Marbles, which are intercalated with thin cherty and calcarenitic layers, represent the upper, pelagic section of the Triassic–Cretaceous carbonate platform sequence of the Ören Unit. The latter underwent low-grade high-pressure metamorphism during the latest Cretaceous–early Palaeocene (Rimmelé et al. 2003; Pourteau et al. 2013). Rosetta textures are absent in calcarenitic levels and restricted to the almost pure limestone horizons. Typical Rosetta structures at this locality are made of *0.5–1.5-m-long calcitic rods (Fig. 1). This marble usually contains a fine-grained grey calcitic matrix and dark marly material that rims calcite rods. However, pure marble layers are found composed entirely of long, three-dimensional, straight rods forming palmate structures (Fig. 1). Some rods present a remarkable swallowtail structure (Fig. 2), in which calcite forms parallel set of fibres oblique to the rod axis. Prior chemical analyses of fibrous crystals from this area yielded abnormally high Sr concentrations (1,500 ppm; Rimmelé et al. 2005) for calcite but typical for aragonite (e.g. Gillet and Goffé 1988; Brady et al. 2004). That the Rosetta structures are primary features is indicated by their imprints as bottom marks of radiolarian-bearing meta-chert beds.