Geochemistry and petrology of the lower Miocene bimodal volcanic units in the Tunçbilek–Domaniç basin, western Anatolia

ABSTRACT

The lower Miocene (~22–19 Ma) volcanic units in the NE–SW-trending Tunçbilek–Domaniç basin, located in the northeastern-most part of the Neogene successions in western Anatolia, are composed of (1) high-K, calc-alkaline dacitic to rhyolitic volcanic rocks of the Oklukdağı volcanics; (2) calc-alkaline low-MgO (evolved) basalts; and (3) high-MgO mildly alkaline basalts of the Karaköy volcanics. Sr isotopic ratios of the volcanic units increase from high-MgO (~0.7055–0.7057) to low-MgO basaltic rocks (~0.7066–0.7072) and then to dacitic-rhyolitic rocks (0.7081–0.7086). Geochemical features of the volcanic rocks reveal that the calc-alkaline evolved basalts were formed by mixing of basic and acidic magmas.

Geochemical studies in the last decade show that the Miocene mafic volcanic rocks in western Anatolia are mainly composed of high-MgO shoshonitic-ultrapotassic rocks (SHO-UK), of which mantle sources were variably, but also intensely metasomatized with crustally derived materials during collisional processes in the region. However, geochemical comparison of the high-MgO basalts of the Karaköy volcanics with the SHO-UK rocks in this region reveal that that the former has too low ⁸⁷Sr/⁸⁶Sr_(i) and high ¹⁴³Nd/¹⁴⁴Nd_(i) ratios, with lower LILE and LREE abundances, which are firstly described here. These features are interpreted to be derived from more slightly enriched lithospheric mantle sources than that of the SHO-UK. Accepting the SHO-UK rocks in the region were derived from mantle sources that had been metasomatized by northward subduction of crustal slices during Alpine collisional processes, it is proposed that the imbrication and direct subduction of crustal slices were not reached to, and were limited in the mantle domains beneath the basin. The dacites of the Oklukdağı volcanics might be formed either by high-degree melting of the same sources with the SHO-UK, or by melting of the lower crustal mafic sources as previously proposed, and then evolved into the rhyolites via fractional crystallization with limited crustal contribution.

KEYWORDS:

• Western Anatolia
• NE–SW-trending basins
• Tunçbilek–Domaniç basin
• Miocene volcanism
• mantle metasomatism

Acknowledgments

We greatly thank Özgür Karaoğlu, Bülent Kasapoğlu, and Uğur Öven for their help in the field studies. Samuele Agostini and one anonymous reviewer are thanked for their constructive suggestions and revisions of the earlier version of the manuscript. Robert J. Stern is thanked for editorial handling.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This study was supported by the Dokuz Eylül University Scientific Investigation Projects [grant number DEÜ BAP, 2010.KB.FEN.36].