Revisiting the source characteristics of Quaternary monogenetic basalts in Central Anatolian Volcanic Province: asthenospheric or lithospheric melts?

The Neogene-Quaternary Central Anatolian Volcanic Province (CAVP) is characterized by widespread polygenetic and monogenetic volcanism. About 800 monogenetic volcanoes were identified within the CAVP and these mainly include scoria cones and related flows (basaltic and andesitic), with subordinate maars (of both basaltic and rhyolitic composition), and domes (generally rhyolitic in composition).
   Despite the occurrence of q-normative, ol-hy-normative, and ne-normative basalts, CAVP monogenetic basalts (s.l.) have been generally considered as alkaline. Based on this fact, they are recently evaluated as tholeiitic, transitional, and mildly alkaline (<5% normative ne), respectively. Similar patterns and HFS anomalies of monogenetic basalts on mantlenormalized diagrams to CAVP calc-alkaline lava flows from the polygenetic volcanoes were also noted. These andesitic-dacitic lava flows from the CAVP stratovolcanoes display orogenic trace element fingerprint, reflecting enrichment of their source regions by subduction-related fluids. So, this brings about the need for revisiting the source characteristics of CAVP monogenetic basalts. Compilation and re-evaluation of all available geochemical data from previous studies, and interpretation of our own data from monogenetic
volcanoes enabled us reviewing source characteristics of monogenetic basalts in CAVP.
   CAVP monogenetic samples are transitional to calc-alkaline according to their Zr and Y contents. All CAVP monogenetic basalts display similar variably enriched LIL/HFS patterns and HFS anomalies on mantle-normalized diagrams. They all have incompatible element ratios intermediate between orogenic andesites and within-plate basalts. High La/Nb (>1.6), Al₂O₃/TiO2 (10-17) and low Sm/Yb ratios (<2.5) imply that the melts must have been derived from shallow depths (<80 km), that is within the lithospheric mantle, just like the calc-alkaline volcanics of CAVP. There is also evidence which might account for crustal contamination such as highly variable range in HFS and other incompatible element ratios Zr/Nb, Y/Nb, La/Yb, and presence of slight negative Ba anomaly on multielement diagrams. Presence of U peaks on mantle-normalized multielement diagrams for most monogenetic CAVP basalts, and variation in ⁸⁷Sr/⁸⁶Sr ratios reported for monogenetic volcanoes in the western part of CAVP imply crustal contribution as well.
   The driving mechanism for generation and ascent of Neogene-Quaternary volcanism in the CAVP is the transtensional and rotational tectonics in central Anatolia from Miocene onwards. This is evidenced by exposure and vent distribution of the central Anatolian volcanics confined to two major fault zones namely, the Central Anatolian Fault Zone (or Ecemis Fault Zone) and the Tuz Gölü Fault Zone. In a wider regional context, CAVP monogenetic basalts are comparable to Apuseni Mountains (Romania) and Big Pine (Basin and Range) volcanics, except CAVP basalts have depleted Ba contents. There is a need for systematic petrological study to expand the database and have a better picture of monogenetic volcanism within the CAVP.