Pan-African high-pressure metamorphism in the Precambrian basement of the Menderes Massif, western Anatolia, Turkey

Abstract

The Menderes Massif is made up of Pan-African basement and a Paleozoic to Early Tertiary cover sequence imbricated by Late Alpine deformation. The Precambrian basement comprises primarily medium-to high-grade schists, paragneisses, migmatites, orthogneisses, metagranites, charnockites, and metagabbros. High-pressure relics in the Pan-African basement are divided into two groups: eclogites and eclogitic metagabbros. The mineral assemblage in the eclogites is omphacite (Jd 44)±garnet±clinozoisite± rutile. The eclogites occur as pods and boudinaged layers in the basement schists and paragneisses. Inclusions found in the cores of the garnets indicate a medium-pressure protolith. The eclogitic metagabbros are closely related to Precambrian gabbroic stocks. The igneous texture and relic magmatic phases are preserved in these high-pressure rocks, which are characterized by the mineral assemblage omphacite (Jd 25)±garnet±rutilekyanite. The P±T conditions of the Pan-African high-pressure metamorphism in the eclogites are estimated to be 644 C with a minimum pressure of approximately 15 kbar. The eclogites are partly to completely retrograded to garnet amphibolites by a Barrovian-type overprint which developed under isothermal decompression conditions. For this post-eclogitic event, the P±T estimates are 7 kbar and 623 C. The eclogite relics provide strong support for a correlation of the Menderes Massif with the Bitlis Massif in terms of common Pan-African high-pressure evolution.

Cretaceous and Triassic subduction-accretion, high-pressure-low-temperature metamorphism, and continental growth in the Central Pontides, Turkey

“…HP-LT metamorphic rocks of Precambrian (Candan et al, 2001), Late Triassic (Okay and Monié, 1997;Okay et al, 2002), mid-Cretaceous (this study), Late Cretaceous (Sherlock et al, 1999), and Eocene ages (Oberhänsli et al, 1998) occur within the relatively confi ned area of Anatolia and attest to its location along active plate boundaries throughout the Phanerozoic. Although oceanic subduction was a steady-state process during much of the Cretaceous along the Pontide margin, accretion of the subduction complexes to the continental margin was episodic and happened at different times in different segments of the margin.…”

Exhumation with a twist: Paleomagnetic constraints on the evolution of the Menderes metamorphic core complex, western Turkey

“…This MMM postdates a phase of HP metamorphism and eclogite formation in mafic pockets in the Pan-African orthogneisses Candan et al, 2001] and also postdates HP metamorphism [Régnier et al, 2007] under blueschist facies conditions Oberhänsli et al, 1998;Rimmelé et al, 2003b;Whitney et al, 2008] in the Paleozoic to Eocene sedimentary cover. The age of the eclogites and the age of the MMM are matter of fierce debate, with the majority of researchers now preferring a PanAfrican age of HP metamorphism in the Pan-African basement and a Paleogene age for HP metamorphism in the cover sequence [Satir and Friedrichsen, 1986;Lips et al, 1998;Bozkurt and Satir, 2000;Candan et al, 2001;Bozkurt, 2004Bozkurt, , 2007. The age of the MMM is debated as well, but an Eocene age seems most likely because Barrovian MMM-related metamorphism affected metasediments with Cretaceous Rudist fossils in the central Menderes Massif [Okay, 2001;Özer and Sözbilir, 2003].…”

“…The Menderes Massif is intensely sheared during hightemperature and medium-pressure (Barrovian) metamorphism (the so-called Main Menderes Metamorphism, or MMM [Akkök, 1983;Ashworth and Evirgen, 1984;Sengör et al, 1984;Satir and Friedrichsen, 1986;Bozkurt and Park, 1999;Whitney and Bozkurt, 2002;Sengün et al, 2006]. This MMM postdates a phase of HP metamorphism and eclogite formation in mafic pockets in the Pan-African orthogneisses Candan et al, 2001] and also postdates HP metamorphism [Régnier et al, 2007] under blueschist facies conditions Oberhänsli et al, 1998;Rimmelé et al, 2003b;Whitney et al, 2008] in the Paleozoic to Eocene sedimentary cover. The age of the eclogites and the age of the MMM are matter of fierce debate, with the majority of researchers now preferring a PanAfrican age of HP metamorphism in the Pan-African basement and a Paleogene age for HP metamorphism in the cover sequence [Satir and Friedrichsen, 1986;Lips et al, 1998;Bozkurt and Satir, 2000;Candan et al, 2001;Bozkurt, 2004Bozkurt, , 2007.…”

Supradetachment basin evolution during continental extension: The Aegean province of western Anatolia, Turkey

“…Eclogitic mafi c rocks and metasedimentary units in these orthogneisses also reveal geochronological evidence for Pan-African metamorphism (Hetzel and Reischmann, 1996;Loos and Reischmann, 1999;Bozkurt and Satir, 2000;Gessner et al, 2004;Koralay et al, 2004;Catlos and Çemen , 2005). On the other hand, the metasedimentary sequence at structurally higher levels, which includes fossil-bearing marble and schist units, widely known as the "Menderes cover sequence," displays Paleozoic to Eocene stratigraphy (Konak et al, 1987;Özer et al, 2001) and high-P-low-T metamorphic conditions (12-14 kbar and 470-500 °C; Rimmelé et al, 2003;Régnier et al, 2007;Candan et al, 2001;Oberhänsli et al, 1998). The entire stack of the Menderes Massif appears to have experienced a late-stage, high-T-medium-P (Barrovian) metamorphic event and penetrative deformation (Satir and Friedrichsen, 1986;Bozkurt and Park, 1999), which have been considered as the Main Menderes metamorphism of Alpine origin.…”