Intrusion age of Pan-African augen gneisses in the southern Menderes Massif and the age of cooling after Alpine ductile extensional deformation

Abstract

Pb-Pb single zircon ages of 546.2 ± 1.2 Ma demonstrate that the augen gneisses in the southern Menderes Massif were generated from Pan-African intrusions. During the Alpine orogenic evolution of the Menderes Massif these granites were metamorphosed and transformed into augen gneiss in an extensional top-to-the-south shear zone, located between augen gneisses and overlying schists. Quartz fabrics suggest a pronounced static recrystallization that post-dates the ductile deformation in the shear zone. Ar-Ar muscovite ages of 43-37 Ma from augen gneisses and schists suggest that ductile deformation and subsequent cooling occurred in the Eocene. These results contradict previous models that (1) interpret the extensional shear zone as late Oligocene in age and (2) regard the augen gneisses as syntectonic with respect to ductile extensional deformation.

Late Neoproterozoic granulite facies metamorphism in the Menderes Massif, Western Anatolia/Turkey: implication for the assembly of Gondwana

“…U/Pb and Pb/Pb zircon ages cluster at around~550 Ma and are interpreted as intrusion ages of the precursors of the orthogneisses Gessner et al, 2004;Hasözbek et al, 2011;Hetzel & Reischmann, 1996;Koralay et al, 2011Koralay et al, , 2012Koralay et al, , 2004Loos & Reıschmann, 1999). The orthogneisses are interpreted as syn-to post Pan-African intrusions, related to the latest Neoproterozoic final amalgamation of the Gondwana Candan, Oberhän-sli et al, 2011;Hetzel & Reischmann, 1996;Koralay, Candan et al, 2011;Koralay et al, 2012). The granite to orthogneiss transformation is ascribed to both Neoproterozoic, and to the later Eocene Alpine metamorphism.…”

“…Based on the mineralogical compositions and textural properties, several different types of orthogneisses have been distinguished: biotite orthogneiss, leucocratic tourmaline orthogneiss and amphibole orthogneiss (Bozkurt, Winchester, Mittwede, & Ottley, 2006;Koralay, Candan, Chen et al, 2012). U/Pb and Pb/Pb zircon ages cluster at around~550 Ma and are interpreted as intrusion ages of the precursors of the orthogneisses Gessner et al, 2004;Hasözbek et al, 2011;Hetzel & Reischmann, 1996;Koralay et al, 2011Koralay et al, , 2012Koralay et al, , 2004Loos & Reıschmann, 1999). The orthogneisses are interpreted as syn-to post Pan-African intrusions, related to the latest Neoproterozoic final amalgamation of the Gondwana Candan, Oberhän-sli et al, 2011;Hetzel & Reischmann, 1996;Koralay, Candan et al, 2011;Koralay et al, 2012).…”

“…Within this general tectonic framework, the Menderes Massif forms the largest crystalline basement of the Anatolides. In addition to Alpine overprint, petrological, petrographical and geochronological data indicate that the basement of the massif has experienced late Neoproterozoic poly-phase metamorphic events under granulite-, eclogite-and amphibolite-facies conditions (Candan, 1995;Candan & Dora, 1998;Candan, Dora, Dürr, & Oberhänsli, 1994;Candan et al, 2001;Oberhänsli, Candan, Dora, & Dürr, 1997;Oberhänsli, Candan, & Wilke, 2010) and was intruded by late Neoproterozoic basic and acidic magmas (Candan, 1996;Candan et al, in press;Gessner et al, 2004;Hasözbek, Akay, Erdoğan, Satır, and Siebel 2011;Hetzel & Reischmann, 1996;Koralay et al, 2011Koralay et al, , 2012Koralay et al, , 2004Loos & Reıschmann, 1999).…”

An overview on the main stratigraphic and structural features of a geothermal area: the case of Nazilli-Buharkent section of the Büyük Menderes Graben, SW Turkey

“…The core rocks are composed mostly of augen gneiss, metagranite (granitic gneiss), schist and metagabbro (Candan, 1995;Satır & Friedrichsen, 1986). The age of the granitic protolith of the augen gneiss is Late Precambrian and Early Cambrian (521-572 Ma) based on the U-Pb and Pb-Pb single zircon evaporation methods (Gessner et al, 2001;Hetzel & Reischmann, 1996;Loos & Reischmann, 1999). The second major rock assemblage comprising the Menderes Massif is known informally as the Cover.…”

“…The nature of the discontinuity or contact between the so-called "Core" and "Cover" rocks is still under debate. There are three ideas about it: (1) it is a regional unconformity (the supra Pan-African unconformity) (Şengör, Satır, & Akkök, 1984), (2) it is a south-facing extensional shear zone including preserved igneous contact along which Oligo-Miocene granites were intruded into the cover rocks (Bozkurt, 2004;Bozkurt, Park, & Winchester, 1993;Bozkurt & Satır, 2000;Hetzel & Reischmann, 1996); these authors have also reported that the core rocks had been exhumed into their present-day positions in the footwall of this shear zone during a top-to-the SSW operating deformational event of Oligo-Miocene age, and (3) it is a south-facing thrust fault contact (Gessner et al, 2001;Ring, Gessner, Güngör, & Passchier, 1999). The Menderes Massif has attained its massif character under the high-T (500°)/ moderate-P (≤5 kbar) conditions or Barrovian-type of tectono-metamorphic event termed "main Menderes metamorphism (MMM)" (Whitney & Bozkurt, 2002).…”