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GEODINAMICA ACTA, vol.19, no.5, pp.363-390, 2006 (SCI-Expanded)
Granitoid rocks of the southern Menderes Massif, SW Turkey include widespread possibly Ediacaran high-grade granitic orthogneisses and younger (Tertiary) sheets, sills and/or dikes of variably deformed tourmaline-bearing leucogranites. The latter are confined to the immediate footwall of the regional-scale ductile southern Menderes shear zone. Although both sets of granitoid rocks are essentially calc-alkaline and peraluminous, the syn- to post-collisional tourmaline-bearing leucogranites are chemically distinguishable from both the granitoid orthogneisses and from two sets of mostly sodic siliceous dyke rocks. The leucogranites were generated by partial melting induced by shear heating during the waning stages of the Eocene main Menderes metamorphism and associated top-to-the-NNE thrusting along the southern Menderes ductile shear zone, which transported schists northwards over the granitoid orthogneisses of the core Menderes complex. Upward migration and emplacement of leucogranitic melt weakened formerly sheared rocks, so that when thrust-related deformation ceased it facilitated rapid crustal extension along the shear zone. The emplacement of leucogranites, in turn, promoted the reactivation of the southern Menderes shear zone as a top-to-the-SSW extensional feature. Continued extensional deformation affected the leucogranites which became parallel to the shear-zone foliation; local S-C fabrics were also generated. The additional occurrence of less or almost undeformed leucogranites suggests that the latest stages of extension might have induced adiabatic decompressional melting. Hence the leucogranite melt generation and emplacement in the southern Menderes Massif occurred in pulses. Both compressional and extensional processes played key roles in melt generation, emplacement, deformation and exhumation of the massif.