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Low-pressure - high-temperature metamorphism during extension in a Jurassic magmatic arc, Central Pontides, Turkey

Okay, A. I.; Sunal, G.; Tüysüz, O.; Sherlock, S.; Keskin, M. and Kylander-Clark, A. R. C. (2014). Low-pressure - high-temperature metamorphism during extension in a Jurassic magmatic arc, Central Pontides, Turkey. Journal of Metamorphic Geology, 32(1) pp. 49–69.

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Magmatic arcs are zones of high heat flow; however, examples of metamorphic belts formed under magmatic arcs are rare. In the Pontides in northern Turkey, along the southern active margin of Eurasia, high temperature–low pressure metamorphic rocks and associated magmatic rocks are interpreted to have formed under a Jurassic continental magmatic arc, which extends for 2800 km through the Crimea and Caucasus to Iran. The metamorphism and magmatism occurred in an extensional tectonic environment as shown by the absence of a regional Jurassic contractional deformation, and the presence of Jurassic extensional volcaniclastic marine basin in the Pontides, over 2 km in thickness, where deposition was coeval with the high‐T metamorphism at depth. The heat flow was focused during the metamorphism, and unmetamorphosed Triassic sequences crop out within a few kilometres of the Jurassic metamorphic rocks. The heat for the high‐T metamorphism was brought up to crustal levels by mantle melts, relicts of which are found as ultramafic, gabbroic and dioritic enclaves in the Jurassic granitoids. The metamorphic rocks are predominantly gneiss and migmatite with the characteristic mineral assemblage quartz + K‐feldspar + plagioclase + biotite + cordierite ± sillimanite ± garnet. Mineral equilibria give peak metamorphic conditions of 4 ± 1 kbar and 720 ± 40 °C. Zircon U–Pb and biotite Ar–Ar ages show that the peak metamorphism took place during the Middle Jurassic at c. 172 Ma, and the rocks cooled to 300 °C at c. 162 Ma, when they were intruded by shallow‐level dacitic and andesitic porphyries and granitoids. The geochemistry of the Jurassic porphyries and volcanic rocks has a distinct arc signature with a crustal melt component. A crustal melt component is also suggested by cordierite and garnet in the magmatic assemblage and the abundance of inherited zircons in the porphyries.

Item Type: Journal Item
Copyright Holders: 2013 John Wiley & Sons Ltd.
ISSN: 0263-4929
Project Funding Details:
Funded Project NameProject IDFunding Body
Not Set109Y049TUBITAK
Not SetITU BAP 33342Not Set
Not SetNot SetTUBA
Keywords: extension; LP–HT metamorphism; magmatic arc; Pontides; Turkey
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 55900
Depositing User: Sarah Sherlock
Date Deposited: 25 Jul 2018 08:17
Last Modified: 07 Dec 2018 11:09
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