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Turkish Journal of Earth Sciences

Petrology and 40Ar-39Ar Age of the Bimodal Orduzu Volcanics (Malatya) from the Western end of the Eastern Anatolian Neogene Volcanism, Turkey

AYTEN ÖNAL1, DURMUŞ BOZTUĞ2, MEHMET ARSLAN3,
TERRY L. SPELL4 & SEVCAN KÜRÜM5

1 Department of Mining Engineering, İnönü University, TR-44280 Malatya, Turkey
2 Department of Geological Engineering, Cumhuriyet University, TR-58140
Sivas, Turkey
(E-mail: durmus.boztug@gmail.com )
3 Department of Geological Engineering, Karadeniz Technical University, TR-61080 Trabzon, Turkey
4 Department of Geosciences, University of Nevada, Las Vegas, Nevada 89154, USA
5 Department of Geological Engineering, Fırat University, TR-23119 Elazığ, Turkey

Abstract: The Orduzu volcanics, which are part of the Yamadağ volcanics in the Malatya region, include rhyolite, rhyolitic dykes, trachyandesite and basaltic trachyandesitic dykes. Mafic globular occurrences within the basaltic trachyandesitic dykes, the existence of basaltic trachyandesite enclaves within the trachyandesite, and other textural and geochemical evidence all indicate magma mingling/mixing. Incremental 40Ar-39Ar dating on plagioclase from the rhyolite, from rhyolite dykes and basaltic trachyandesite yielded consistently 16 Ma (Middle Miocene). Primordial mantle-normalized spider diagrams of the rhyolite and rhyolitic dykes represent enrichments in some large ion lithophile elements (Cs, Rb, Ba, K, Th, U) but remarkably depletion in Sr, Nb, Ti, Eu and slight depletion in some high field strength elements (Hf, Zr) relative to the trachyandesites and basaltic trachyandesitic dykes. Chondrite-normalized rare earth element spidergrams yield a high (La/Lu)CN(18-47) and Eu/Eu* (0.57-0.92) ratios for the rhyolites and rhyloitic dykes, but a low (La/Lu)CN (7-13) and Eu/Eu* (0.86-1.05) values for the trachyandesites and basaltic trachyandesitic dykes. From the field relations and geochemical data, it is concluded that three distinct magma sources were spatially and temporally involved in the genesis of the Orduzu volcanics, that include a calc-alkaline, crustal-derived rhyolitic melt, another calc-alkaline, lithospheric mantle-derived andesitic magma, and a mildly alkaline, lithospheric mantle-derived basaltic magma.

Key Words: petrology, Ar-Ar dating, Neogene volcanism, Malatya, Eastern Anatolia, Turkey

Turkish J. Earth Sci., 17, (2008), 85-109.
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Other articles published in the same issue: Turkish J. Earth Sci.,vol.17,iss.1.