Post-delamination magmatism in south-central Anatolia

Abstract

Quaternary mafic lavas in Central Anatolia provide geochemical insights into melt generation processes following regional delamination of the subducted Tethyan slabs. New geochemical data from the Pleistocene Hasandağ Cinder Cone Province (HCCP) and Karapınar Volcanic Field (KVF) record contributions from subduction-modified lithospheric and sub-lithospheric source domains that are distinct from those sampled elsewhere across Anatolia (e.g., Pearce et al., 1990; Aldanmaz et al., 2006; Keskin, 2007; Chakrabarti et al., 2012; Reid et al., 2017). Hasandağ cinder cones are primarily basaltic, with subordinate trachybasalt and basaltic trachyandesite; Karapınar lavas comprise basalts and andesites with subordinate basaltic trachyandesite and basaltic andesite. Anomalously high Li, Na, Ti and Zr abundances and Ba/Rb values in these South-Central Anatolian primitive mafic lavas suggest significant contribution from metasomatic phases (i.e., amphibole, zircon and rutile); Dy/Ybn values measured in the mafic volcanics indicate melting in the spinel stability field. Correlation between 87Sr/86Sr and εNd in HCCP and KVF lavas indicate pseudo-binary mixing between enriched and depleted endmembers, while εNd-εHf isotopic values that plot above the terrestrial array extend toward sediment compositions sampled from the eastern Mediterranean Sea (Klaver et al., 2015). Together, trace element chemistry and Sr-Nd-Hf-Pb isotope compositions suggest input from a spatially heterogeneous mantle with contributions from depleted MORB-like and recycled sediment sources. The apparent presence of pyroxenite and hydrous metasomes within the HCCP and KVF source regions, and abundant dense mafic cumulates associated with the adjacent Hasandağ stratovolcano, support an unstable small-scale lithospheric density structure in South-Central Anatolia. We suggest regional delamination of the Neotethyan slab on a regional scale caused upwelling asthenosphere to destabilize the remaining Central Anatolian lithosphere and resulted in localized drip melting to produce the mafic volcanism at the HCCP and KVF. Geochemical similarities to Miocene alkali basalts from Galatia and Sivas (Wilson et al., 1997; Varol et al., 2014; Kürkcüoğlu et al., 2015) suggest that this mechanism occurred across Central Anatolia subsequent to Tethys subduction, and thus the ages of monogenetic volcanic activity record the descent of the slab beneath Anatolia. We infer that slab foundering played a more important role in this process than lithospheric loss beneath a tectonically shortened orogen (Göğüs et al., 2017) although further mapping of sedimentary basins and structures is required to resolve this interpretation.