Syn-extensional granitoids in the Menderes core complex and the late Cenozoic extensional tectonics of the Aegean province

Abstract

The Miocene granitoid plutons exposed in the footwalls of major detachment faults in the Menderes core complex in western Anatolia represent syn-extensional intrusions, providing important geochronological and geochemical constraints on the nature of the late Cenozoic magmatism associated with crustal extension in the Aegean province. Ranging in composition from granite, granodiorite to monzonite, these plutons crosscut the extensional deformation fabrics in their metamorphic host rocks but are foliated, mylonitized and cataclastically deformed in shear zones along the detachment faults structurally upward near the surface. Crystallization and cooling ages of the granitoid rocks are nearly coeval with the documented ages of metamorphism and deformation dating back to the latest Oligocene–early Miocene that record tectonic extension and exhumation in the Menderes massif. The Menderes granitoids (MEG) are represented by mainly metaluminous-slightly peraluminous, high-K calc-alkaline and partly shoshonitic rocks with their silica contents ranging from 62.5 to 78.2 wt%. They display similar major and trace element characteristics and overlapping inter-element ratios (Zr/Nb, La/Nb, Rb/Nb, Ce/Y) suggesting common melt sources. Their enrichment in LILE, strong negative anomalies in Ba, Ta, Nb, Sr and Ti and high incompatible element abundances are consistent with derivation of their magmas from a subduction-metasomatized, heterogeneous sub-continental lithospheric mantle source. Fractional crystalization processes and lower to middle crustal contamination also affected the evolution of the MEG magmas. These geochemical characteristics of the MEG are similar to those of the granitoids in the Cyclades to the west and the Rhodope massif to the north. Partial melting of the subduction-metasomatized lithospheric mantle and the overlying lower-middle crust produced the MEG magmas starting in the late Oligocene–early Miocene. The heat and the basaltic material to induce this partial melting were provided by asthenospheric upwelling caused by lithospheric delamination. Rapid slab rollback of the post-Eocene Hellenic subduction zone may have peeled off the base of the subcontinental lithosphere, triggering the inferred lithospheric delamination. Both slab retreat-generated upper plate deformation and magmatically induced crustal weakening led to the onset of the Aegean extension, which has migrated southward through time.

Geochemistry and tectonic development of Cenozoic magmatism in the Carpathian–Pannonian region

“…In the Aegean and Anatolian areas where slab retreat was southward, similar extension and lower-middle crust exhumation occurred (e.g. Dilek et al, 2009;Jolivet and Brun, 2010;Tirel et al, 2009;van Hinsenberg et al, 2010).…”

Zagros orogeny: a subduction-dominated process

“…From our present-day knowledge of magmatism, the Iranian plateau may thus resemble E Turkey, where magmatism and deformation take place through a mixture of slab break-off, mantle delamination and strike-slip faulting (Keskin, 2003;Al-Lazki et al 2004;Keskin, Genç & Tüysüz, 2008;Sengör et al 2008). Such complex magmatic patterns are now recognized below W Turkey too (Dilek & Sandvol, 2009;Dilek, Altunkaynak & Oner, 2010). Future research should therefore aim at better documenting gradients in magmatic type such as were reported for Turkey (i.e.…”

“…In principle this could result from mantle delamination below Iran (although this is not supported, at least at the scale of the whole of Iran, by the seismic profiles of Paul et al 2010) or from abundant subduction-related magma ascent through (extensional) deforming areas of the upper plate. We envision an intermediate hypothesis, whereby extension within the upper plate (as indicated in the crust by core-complex formation in Central Iran and extension in the Alborz) relates to vigorous, ablative subduction (as a result of the entrance of a more shallow-dipping slab after SB1) with traction-driven flow (and/or rapid thermal convection in a low viscosity asthenospheric mantle; Currie et al 2004;Dilek, Altunkaynak & Oner, 2010) leading to only partial removal of the lithospheric mantle below Iran.…”

Surprisingly young Rb/Sr ages from the Simav extensional detachment fault zone, northern Menderes Massif, Turkey

“…1). The evolution of the massif occurred during two distinct but successive events: (1) continental collision and consequent crustal thickening of pre-Alpine basement during the closure of Neotethys along theİzmir-Ankara suture zone (Ş engör et al, 1984;Satır and Friedrichsen, 1986;Bozkurt and Oberhänsli, 2001;Gessner et al, 2001a;Jolivet et al, 2004;Bozkurt, 2007;Akal et al, 2011) and (2) subsequent post-orogenic extension during which metamorphic rocks of the massif exhumed progressively in the footwall of: (i) ductile southern Menderes shear zone in the southern submassif (Bozkurt and Park, 1994;Bozkurt and Satır, 2000;Lips et al, 2001;Satır and Taubald, 2001;Seyitoglu et al, 2004;Bozkurt, 2007) and (ii) first ductile, then brittle detachment faults in the central and northern submassifs, namely Büyük Menderes detachment fault along the northern margin of the Büyük Menderes Graben (Bozkurt, 2001;Gessner et al, 2001b), the Gediz detachment fault along the southern margin of the Gediz Graben (Hetzel et al, 1995a,b;Emre, 1996;Koç yigit et al, 1999;Seyitoglu et al, 2004;Gessner et al, 2001c;Sözbilir, 2001Sözbilir, , 2002Iş ık et al, 2003;Ring et al, 2003;Bozkurt and Sözbilir, 2004;Glodny and Hetzel, 2007;Dilek et al, 2009;Ç iftç i and Bozkurt, 2010;Catlos et al, 2010;Öner et al, 2010) and Simav detachment fault around the Simav Graben (Iş ık and Tekeli, 2001;Ring et al, 2003;Iş ık et al, 2003Iş ık et al, , 2004…”