Aktağ, Alican; Sayit, Kaan; Furman, Tanya; Peters, Bradley J.

The Sr-Nd-Hf-Pb isotope geochemistry of the Late Miocene Tunceli Volcanics suggests that they are the products of mixed asthenospheric and lithospheric mantle melts. The combined elemental and mineral chemistry data additionally indicate that a pyroxenite component of lithospheric origin is involved in their genesis. Calculations favor melting depths of ∼2 GPa for the Tunceli lavas, that is, deeper than the current lithosphere-asthenosphere boundary beneath Eastern Anatolia. Geochemical data suggest that during regional Neo-Tethyan subduction, dense (i.e., pyroxenite-bearing) domains formed by progressive melt intrusion into the lower lithosphere resulted in gravitational instabilities. This unstable density configuration eventually led to the foundering of the eastern Anatolian lithosphere in the Late Miocene, resulting in progressive melting of fusible pyroxenite-bearing domains at asthenospheric depths. We demonstrate that these pyroxenitic melts mixed with ambient asthenospheric melts and generated the Tunceli lavas.

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Aktağ, Alican; Sayit, Kaan; Peters, Bradley J.; Furman, Tanya; Rickli, Jörg

Quaternary Elazığ mafic alkaline volcanism is part of the anorogenic volcanic system of the circum-Mediterranean region, and it provides crucial insights into the chemical nature of the mantle source domains beneath eastern Turkey. Elemental and isotope geochemistry reveals that these mafic lithologies are mainly free of crustal contamination, reflecting geochemical signatures inherited from partial melting of their mantle sources. The trace element and Sr-Nd-Hf-Pb isotope systematics of the most primitive members of this volcanism are consistent with a predominant contribution from a sub-lithospheric component which compositionally resembles component C, believed to be common to global OIBs and MORBs. However, the total range of the isotope data also requires the involvement of two additional mantle components into their genesis: a depleted asthenospheric component (DM) and an enriched component (EM-type) representing metasomatized lithospheric mantle. We propose that the recycled oceanic lithologies with C-like signatures are dispersed in the asthenospheric mantle beneath eastern Anatolia and have undergone mixing with the depleted mantle matrix. When considering these with the melting models, it appears that the garnet-facies partial melts of the C-DM mixture have experienced a small degree of interaction with the melts from an SCLM domain modified by slab-derived melts and/or fluids. The metasomatized SCLM domain may be intrinsic to the eastern Anatolian lithosphere or occur as pods embedded in the asthenosphere. The chemical characteristics of the Elazığ Volcanics may confirm the wide-range dispersal of the common component in the sub-lithospheric mantle beneath the region extending from western Europe to eastern Turkey. However, the common component resides beneath Anatolia appear to have distinct composition (i.e., Pb isotope systematics) than the ubiquitous component shared mostly by European intraplate volcanics (i.e., LVC/EAR).

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