ORIGIN OF MAFIC LAVAS AT HASANDAG STRATOVOLCANO, CENTRAL ANATOLIAN VOLCANIC ZONE

Hasandag stratovolcano is located within the transtensional Central Anatolian Fault Zone. We analyzed 24 samples for major and trace element concentrations and Nd-Pb-Hf isotopic data. The samples comprise mildly alkaline basalts, basaltic andesites, trachybasalts, basaltic trachyandesites and andesites; prior studies also sampled abundant andesitic to rhyolitic compositions. Major element variations document an abundant suite of parental basalts within a narrow range of compositions (9-10 wt.% MgO) suggesting homogenous thermal conditions for melting. Major element trends consistently suggest fractional crystallization as the main process responsible for creating andesite lavas, however abundant textural features recorded in hand sample lead to the interpretation of significant magma mixing. Primitive mantle-normalized incompatible trace element abundances differ from typical ocean island basalt ranges with enrichment in Th, Ba and U, and depletions in Nb, Ta and TiO₂ that likely record the influence of slab derived fluids and melts, suggesting a mantle source modified by subduction processes despite the absence of active convergence. εHf-εNd variations are linear and fall along the mantle array, ranging in composition from values found in MORB and/or the common mantle component “C” of Hanan and Graham (1995) to lower values more typical of the mantle lithosphere. Pb-Pb isotopic variations define steep arrays that are almost perpendicular to the Northern Hemisphere Reference Line. These isotopic signatures do not include values similar to the C component, but rather show a possible mixing trend between ocean sediment and Indian Ocean MORB. We suggest that the Pb isotopic signatures of Hasandag mafic lavas are controlled by small contributions from subducted sediments that overprint the isotopic characteristics of both the regional asthenosphere (shown by Pickard et al. 2014 to be C-like in composition) and the local lithosphere.