Regional Geochemical Trends in Young Basalts Along the Central Anatolian Fault Zone, Turkey

The regional neotectonics and volcanism along the margins of the Anatolian microplate (Turkey) are broadly well-constrained. The African and Arabian plates currently push Anatolia against the relatively stable Eurasian plate and as a result, Anatolia has had a west-southwest movement for the last 12 Ma in what is called ‘escape tectonics’. The tectonic environments and their associated volcanism include slab rollback in Western Anatolia (post-Miocene alkaline basalts and basanites) and slab detachment in Eastern Anatolia (mid-Miocene calc-alkaline to Quaternary alkaline). However, the situation in Central Anatolia is less clear: extensional forces govern the neo-tectonic environment and Pliocene-Recent basalts through basaltic andesites and dacites form large stratovolcanoes in extensional basins as well as both small and large basalt fields. The geochemistry of these basalts requires contributions from a poorly-defined mantle source lithology that has been enriched by subduction processes. However, available plate reconstructions indicate that the leading edge of the subducted African plate did not reach Central Anatolia, suggesting that the subduction environment could be related to closure of the neo-Tethyan Ocean in Paleozoic time. Geochemical compositions of mafic lavas along the Central Anatolian Fault Zone (CAFZ) provide new clarity on the question of the extent of lithospheric melting and the influence of the subducting slab. Moving southward along the CAFZ, incompatible trace element compositions of Central Anatolian basalts increase systematically in La/Nb concentrations and other incompatible trace element indicators trend from MORB and OIB signatures to more enriched values. Small negative Nb and no Ta anomalies are present in basalts from the northern CAFZ, and increase to larger negative Nb anomalies and Ta anomalies in the north. The incompatible trace element variations along the CAFZ point to an increase in lithospheric or slab involvement toward the leading edge of the African plate, i.e., to the south. Here we present new Pb and Hf isotopic data on recent (<15 Ma) mafic lavas along the CAFZ previously analyzed for major and trace elements. Isotopic ratios show greater source heterogeneity than suggested by the trace element data and show no apparent relationship with latitude. The Pb-Pb isotope ratios define a data field similar to modern oceanic sediment, intermediate in composition to Western Anatolia SCLM and the C component and enriched Central Atlantic MORB. In the 206Pb/204Pb-ɛHf diagram the Central Anatolian lavas are consistent with mixing between a C-like component on the enriched end of the Central Atlantic MORB trend, and Western Anatolia-like SCLM. The isotopic data support a mixing model between oceanic mantle and subduction modified SCLM sources.