High-pressure Rocks From The Southern Menderes Massif and The Lycian Nappes: Implications For Tectonic Evolution of Southwest Turkey.
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Geologic units of Bafa Lake and Akbuk Gulf, which have very importance in point of geologic and tectonic structure, are generally are classified by high-grade metamorphic units of the Menderes Core Complex, Cycladic Complex (schist, marble, eclogite), Afyon zone meta sedimentary and Pan-African basement rocks, Neogene volcanic-sedimentary rocks and alluvium. As for tectonic structures of study areas are; Izmir-Balikesir Transfer Zone also affected the Buyuk Menderes Graben, Bornova Flysch Zone, Menderes Massif and Lycian Nappes. Regional researches were studied to reveal using Turkey Bouguer Anomaly and Turkey Aeromagnetic regional map with gravity method used for geologic structures analysis and magnetic method used to explain main structure, tectonic conditions of underground. General geologic structure and tectonic lineaments of region were examined and interpretated compatibility with gravity and magnetic values. When the geologic and tectonic structures on the terrestrial areas are generally investigated, graben systems and linearities are clearly seen on the Bouguer Anomaly map. Positive values are seen in the Bornova Flysch Zone and Menderes Massif areas at the north of study areas arising from high-density ophiolitic and metamorphic units. Graben areas in the Menderes Massif are observed negative gravity values on the low-density young alluviums. Positive gravity values are increased up to 50-60 mgal on the metamorphic rocks that are named Cycladic Complex located southwest of study areas.At the aeromagnetic regional magnetic map, gamma values about -100 observed on the Menderes Massif region are indicated metagranite rocks that are Paleozoic crystalline structure. Gamma values, which are changed between -100 and +100 at the transition areas granite with schists, are obviously revealed this transition region. Located northwest of study areas Upper Miocene-Pliocene aged from sedimentary rocks on the terrestrial carbonates and nonsegregated terrestrial clastics units +100 gamma values are interpreted as values observed on the sedimentary rocks. For the marine geologic and tectonic structures, at the total magnetic field measurements mapped weren't quite run across to residual values. Gamma values that are changed between -60 and +400 acquired at the marine magnetic datas with gamma values that are changed between -100 and +300 in lake at the aeromagnetic anomaly map are very close values each other. In the lake, high anomaly datas are caused by islands. Showing between -100 and +100 of gamma values observed in the Akbuk Gulf are interpreted as to see effects of terrestrial geologic units at the environment in the gulf. Also, Akbuk Gulf marine magnetic datas will be collected for the detailed study.
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Abstract A transition from construction to collapse of the Alpine orogen in Middle to Late Eocene time is recorded in the structural fabrics of gneissic rocks in the southern Menderes Massif, western Turkey. Augen gneiss in the southern Menderes Massif indicates a spatial switch of shear sense along a north–south section through the complex (top-to-north shear in the north and top-to-south in the south). This ‘kinematic hinge’ corresponds to a broad zone of dominant pure shear where crust underwent vertical thinning and approximate north–south extension. During this extension, foliation became corrugated with fold axes parallel to lineation, indicating inflow from neighbouring crust to the east and the west. Published geochronologic work suggests a Middle to Late Eocene age for this dominant fabric. Thermal weakening of felsic Menderes crust beneath Alpine nappes may have triggered this orogenic collapse. Deformation fabrics developed at temperatures of c. 550 °C, and progressive cooling during collapse generated strain localization within a kilometre-thick shear zone at the southern margin of the Menderes Massif. In the southern Menderes, the corrugation of foliation indicates that Middle to Late Eocene flow was constricted into an orogen-perpendicular direction. This behaviour is similar to the collapse and orogen-parallel extension of the European Alps (Lepontine dome, Tauern Window).
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The Early Eocene to Early Oligocene tectonic history of the Menderes Massif involves a major regional Barrovian-type metamorphism (M1, Main Menderes Metamorphism, MMM), present only in the Palaeozoic-Cenozoic metasediments (the so-called "cover" of the massif), which reached upper amphibolite faciès with local anatectic melting at structurally lower levels of the cover rocks and gradually decreased southwards to greenschist facies at structurally higher levels. It is not present in the augen gneisses (the so called "core" of the massif), which are interpreted as a peraluminous granite deformed within a Tertiary extensional shear zone, and lie structurally below the metasediments. A pronounced regional (S1) foliation and approximately N-S trending mineral lineation (L1) associated with first-order folding (F1) were produced during D1 deformation coeval with the MMM. The S1 foliation was later refolded during D2 by approximately WNW-ESE trending F2 folds associated with S2 crenulation cleavage. It is now commonly believed that the MMM is the product of latest Palaeogene collision across Neo-Tethys and the consequent internal imbrication of the Menderes Massif area within a broad zone along the base of the Lycian Nappes during the Early Eocene-Early Oligocene time interval. However, the meso- and micro-structures produced during D1 deformation, the asymmetry and change in the intensity and geometry of the F2 folds towards the Lycian thrust front all indicate an unambiguous non-coaxial deformation and a shear sense of upper levels moving north. This shear sense is incompatible with a long-standing assumption that the Lycian Nappes were transported southwards over the massif causing its metamorphism. It is suggested here that the MMM results from burial related to the initial collision across the Neo-Tethys and Tefenni nappe emplacement, whereas associated D1 deformation and later D2 deformation are probably related to the northward backthrusting of the Lycian nappes.
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