New He-O-Sr-Nd isotopes and chronology of Quaternary lavas from the Kula volcanic field (western Türkiye): Implications for temporal changes in the magma source

The Quaternary Kula volcanic field in western Turkey comprises predominantly sodium-rich alkaline basaltic products from several eruption periods. We report new bulk-rock major-trace element, SrNd isotopes, helium and oxygen isotope determinations of olivine phenocrysts and Ar/Ar and cosmogenic He ages to investigate the mantle source characteristics and the temporal change in melt source isotope compositions. The volcanic activity in the Kula field continued episodically from 1.28 Ma to around 8 ka and can be divided into three main eruption phases characterized by distinct eruption type and lava morphology. The lava compositions from these phases evolve from basanite to phonolitic tephrite. Sr-87/Sr-86 and Nd-143/Nd-144 range from 0.703012 to 0.703407 and 0.512968 to 0.513032, respectively, becoming less enriched in time. The earliest basalts display a small degree of crustal contamination that reduces with time that may be the result of rapid ascent of magmas in the volcanic conduit, likely resulting from gradually increasing rate of extensional deformation and enhanced lithospheric fracturing. He-3/He-4 ratios vary from 3.50 to 8.04 Ra, while delta O-18 values vary from 4.7 to 5.2 parts per thousand. The less differentiated samples are characterized by higher He-3/He-4 with >7 Ra, indicating melt derivation from a low-He-3/He-4 OIB-type sub-lithospheric mantle source. The relatively large range in He-3/He-4 and delta O-18 values with insignificant change in Sr-87/Sr-86 for the entire suite further indicates mixing of melts from a multi-component mantle source.