Trace element geochemistry of Bitlis ignimbrites sourced by Quaternary Nemrut Volcano: inferences for A2-type magma generation in Eastern Anatolia post-collisional extensional setting

Abstract

In the study presented here, we investigated the whole-rock K-Ar dating and petrological significance of trace element compositions Bitlis (Eastern Anatolia) ignimbrites associated with explosive activities of the well-known Quaternary Nemrut volcano. Considering the previous age determinations (40.9 ka – 264.1 ka) of ignimbrites sourced in Nemrut volcano, and because they contain lithic clasts, obtained whole-rock K-Ar age of Bitlis ignimbrite flow deposits suggest that they are younger than late Pleistocene (< 790 ka), and occurred as the first products of pre-caldera stages of Nemrut stratovolcano. Bitlis trachydacitic ignimbrites with shoshonitic affinity are characterized by the typical negative anomalies of Eu, Nb-Ta, and Ti in chondrite-normalized spider and multi-element variation diagrams, and plot in the fields of within-plate and post-collisional tectonic setting in Rb vs Y+Nb discrimination diagram. Accordingly, similar to that of Nemrut volcanic products, trace element signatures (e.g., high Nb, Ce, Y, and Zr contents) of Bitlis ignimbrites show coincidence with geochemical characteristics of A2-type silicic magmas. Relative to the upper crust, higher La/Ba and Nb/La, and lower Ba/Ta and La/Ta ratios of Bitlis ignimbrites, which are close to that of Nemrut basalts previously reported as the most recent volcanic products, suggest an interaction between OIB-like basaltic magma and upper crust. Our results point to A2-type silicic magma generation in Eastern Anatolia post-collisional extensional setting, and Nemrut lava and pyroclastic rocks (e.g., Bitlis ignimbrites) formed by partial melting of upper crustal rocks at shallow level via interaction with OIB-like basaltic magma derived from a common mantle source.