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P‐T‐t evolution of the Cycladic blueschist unit in Western Anatolia / Turkey: Geodynamic implications for the Aegean region

Abstract : Eclogite and blueschist facies rocks occurring as a tectonic unit between the underlying Menderes Massif and the overlying Afyon Zone / Lycian Nappes and the Bornova Flysch Zone in western Anatolia represent the eastward continuation of the Cycladic Blueschist Unit in Turkey. This high-P unit is attributed to the closure of the Pindos Ocean and consists of (i) a Triassic to Upper Cretaceous coherent series derived from passive continental margin sediments and (ii) the tectonically overlying Upper Cretaceous Selçuk mélange with eclogite blocks embedded in a pelitic epidote-blueschist matrix. The coherent series has experienced epidote-blueschist facies metamorphism (490 ± 25°C / 11.5 ± 1.5 kbar; 38 km depth). 40 Ar/ 39 Ar white mica and 206 Pb/ 238 U monazite dating of quartz metaconglomerate from coherent series yielded middle Eocene ages of 44 ± 0.3 and 40.1 ± 3.1 Ma for epidote-blueschist facies metamorphism, respectively. The epidote-blueschist facies metamorphism of the matrix of the Selçuk mélange culminates at 520 ± 15°C / 13 ± 1.5 kbar, 43 km depth, and is dated 57.5 ± 0.3-54.5 ± 0.1 Ma (40 Ar/ 39 Ar phengite). Eclogite facies metamorphism of the blocks (570 ± 30°C / 18 ± 2 kbar, 60 km depth) is early Eocene and dated at 56.2 ± 1.5 Ma by 206 Pb/ 238 U zircon. Eclogites experienced a nearly isothermal retrogression (490 ± 40°C / ~ 6-7 kbar) during their incorporation into the Selçuk mélange. The retrograde overprints of the coherent series (410 ± 15°C / 7 ± 1.5 kbar from Dilek Peninsula and 485 ± 33°C / ~ 6-7 kbar from Selçuk-Tire area) and the Selçuk mélange (510 ± 15°C / 6 ± 1 kbar) are dated at 35.8 ± 0.5-34.3 ± 0.1 Ma by 40 Ar/ 39 Ar white mica and 31.6 ± 6.6 Ma by 206 Pb/ 238 U allanite dating methods, respectively. Regional geological constrains reveal that the contact between the Menderes Massif and the Cycladic Blueschist Unit originally formed a lithosphere-scale transform fault zone. 40 Ar/ 39 Ar white mica age from the contact indicates that the Cycladic Blueschist Unit and the Menderes Massif were tectonically juxtaposed under greenschist facies conditions during late Eocene, 35.1 ± 0.3 Ma.
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Soumis le : mercredi 29 janvier 2020 - 23:23:57
Dernière modification le : jeudi 9 avril 2020 - 05:46:05
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Mete Çetinkaplan, Osman Candan, Roland Oberhänsli, Masafumi Sudo, Bénédicte Cenki‐tok. P‐T‐t evolution of the Cycladic blueschist unit in Western Anatolia / Turkey: Geodynamic implications for the Aegean region. Journal of Metamorphic Geology, Wiley-Blackwell, In press, ⟨10.1111/JMG.12526⟩. ⟨hal-02460274⟩

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