Late Cretaceous blueschist facies metamorphism in southern Thrace (Turkey) and its geodynamic implications

Abstract

A blueschist facies tectonic sliver, 9 km long and 1 km wide, crops out within the Miocene clastic rocks bounded by the strands of the North Anatolian Fault zone in southern Thrace, NW Turkey. Two types of blueschist facies rock assemblages occur in the sliver: (i) A serpentinite body with numerous dykes of incipient blueschist facies metadiabase (ii) a well-foliated and thoroughly recrystallized rock assemblage consisting of blueschist, marble and metachert. Both are partially enveloped by an Upper Eocene wildflysch, which includes olistoliths of serpentinite-metadiabase, Upper Cretaceous and Palaeogene pelagic limestone, Upper Eocene reefal limestone, radiolarian chert, quartzite and minor greenschist. Field relations in combination with the bore core data suggest that the tectonic sliver forms a positive flower structure within the Miocene clastic rocks in a transpressional strike-slip setting, and represents an uplifted part of the pre-Eocene basement. The blueschists are represented by lawsonite-glaucophanebearing assemblages equilibrated at 270-310°C and 0.8 GPa. The metadiabase dykes in the serpentinite, on the other hand, are represented by pumpellyite-glaucophane-lawsonite-assemblages that most probably equilibrated below 290°C and at 0.75 GPa. One metadiabase olistolith in the Upper Eocene flysch sequence contains the mineral assemblage epidote + pumpellyite + glaucophane, recording P-T conditions of 290-350°C and 0.65-0.78 GPa, indicative of slightly lower depths and different thermal setting. Timing of the blueschist facies metamorphism is constrained to c. 86 Ma (Coniacian ⁄ Santonian) by Rb-Sr phengite-whole rock and incremental 40 Ar-39 Ar phengite dating on blueschists. The activity of the strike-slip fault post-dates the blueschist facies metamorphism and exhumation, and is only responsible for the present outcrop pattern and post-Miocene exhumation (2 km). The high-P ⁄ T metamorphic rocks of southern Thrace and the Biga Peninsula are located to the southeast of the Circum Rhodope Belt and indicate Late Cretaceous subduction and accretion under the northern continent, i.e. the Rhodope Massif, enveloped by the Circum Rhodope Belt. The Late Cretaceous is therefore a time of continued accretionary growth of this continental domain.

Pressure–temperature evolution of eclogites from the Kechros complex in the Eastern Rhodope (NE Greece)

“…Blueschist and eclogite-facies metamorphic rocks are reported from the southern part of East Thrace and the Biga peninsula of Turkey (Topuz et al 2008;Okay and Satir 2000; Fig. 1 insert).…”

“…All the above HP metamorphic complexes, the Kimi Complex in East Rhodope, the Circum Rhodope Belt and the HP rocks from East Thrace and Biga peninsula, are transgressively covered by Middle (Bartonian in East Thrace) to Upper Eocene sediments (Papadopoulos 1980;Topuz et al 2008;Satir 2000, Okay et al 2010) having thus been exhumed to the surface clearly earlier than the Kechros Complex.…”

“…In the Biga peninsula, the HP unit comprises quartz-mica schists with minor calc-schists, marble, quartzite and metabasite metamorphosed at P-T conditions of 510°C and 1.1 GPa minimum pressure. Timing of the blueschist facies metamorphism is constrained to c. 86 ± 1.5 Ma in East Thrace and 65-69 ± 1 Ma of the eclogite facies in the Biga peninsula by Rb-Sr phengitewhole rock dating (Topuz et al 2008;Okay and Satir 2000). Pre-Alpine lithologies are not involved in both highpressure units.…”

A review for genesis of continental arc magmas: U, Th, K and radiogenic heat production data from the Gümüşhane Pluton in the Eastern Pontides (NE Türkiye)

“…1), in NE Turkey, delineates a Late Cretaceous magmatic arc built on a pre-Liassic basement (Şengör and Yılmaz, 1981;Yılmaz et al, 1997;Okay and Şahintürk, 1997;Okay and Tüysüz, 1999;Topuz et al, 2004aTopuz et al, , 2004bTopuz et al, , 2007. This magmatic belt is subdivided into three sub-tectonic units from north to south as Northern, Southern and Axial zones depending on their lithological and facies changes and tectonic characteristics (Bektaş et al, 1995;Eyüboğlu et al, 2006).…”

Diverse tectonic settings of formation of the metaigneous rocks in the Jurassic metamorphic accretionary complexes (Refahiye, NE Turkey) and their geodynamic implications

“…Deeply subducted parts of the accretionary complexes are mostly subjected to high-pressure metamorphism whereby primary structures of the accreted materials are mostly obliterated (e.g. Agard, Yamato, Jolivet, & Burov, 2009;Ernst, 2003;Topuz, Okay, Altherr, Satır, & Schwarz, 2008). Geochemistry of the metabasic rocks provides the best means to determine the nature of the accreted materials in ancient metamorphic accretionary complexes provided that the fluid flow during the accretionary processes have not strongly modified rock composition.…”