3-3-Geochemical data from the Neogene volcanic rocks 
The eastern Anatolian lavas’ modal and normative compositions show a broad spectrum from nepheline normative basalts to quartz normative felsic lavas (Yılmaz et al. 1987A.B; 1998; Pearce et al. 1990; Keskin 2003;). The southern volcanic centers produced large quantities of basic and intermediate lavas. The northern volcanoes extruded voluminous intermediate volcanic edifices in which pyroclastic rocks dominate, particularly in the northeast of the Erzurum city (Fig 2).
Based on the geochemistry of the Eastern Anatolian Neogene lavas, the previous studies (e.g., Yılmaz et al. 1987A; B 1988; Yılmaz 1990; Pearce et al. 1990; Notsu et al. 1995; Keskin et al. 1998; 2003; 2006; 2007;2012; Lustrino et al. 2012; Özdemir and Güleç 2014; Oyan et al. 2016 A; 2016 B; Lebedev et al. 2016 A and B; Kaygusuz et al. 2018; Açlan et al. 2020; Üner 2021) reached the following conclusions on the magma compositions.
1-The magmas were derived from the heterogeneous mantle source and retained their compositions during the transit with minor modifications.
2- Magma chemistry of the alkaline, mildly alkaline, and calc-alkaline lavas displays distinct enrichment by the subduction components (enriched in LILE and LREE and depleted in HFSE) (e.g., Pearce et al. 1990; Jean et al. 2010; Lebedev et al. 2018 A and B. Kaygusuz et al. 2018; Üner 2021 and the references therein) and also boninitic enrichment (Üner 2021). In accordance with this conclusion, the seismic images obtained by various analytical methods demonstrate a remnant subducted oceanic lithosphere that is broken into pieces underneath Eastern Anatolia (Piromallo and Morelli 2003; Piromallo and Regard 2006; Facenna et al. 2006; Gans et al., 2009; Warren et al., 2013) (for the discussion on the time, place, and role of the subducting events in the development of the surrounding orogenic belts, see the two accompanying papers by Yılmaz et al. in this volume). The enriched mantle source generated a wide compositional range in the consecutive magma batches.
3- The Sr 86/ Sr 87 ratios of lavas of the eastern Anatolian volcanic provinces are on an average of 0.704, which varies in a narrow range commonly between 0.703 and 0.705. The Nd 143 Nd/144 Nd ratio ranges between 0.5127 and 0.5128 (e.g., Kaygusuz 2018 and the references therein). The isotope values plot in the mantle array (Kaygusuz et al. 2018). The isotope ratios together with the magma composition compare favorably with the OIB lavas (Üner 2021; Yang et al 2019; McNabb et al. in 2018).
4- The petrochemical characteristics indicate that the eastern Anatolian magmas were derived from an ophiolitic host and underwent significant fractionation in the magma chamber and during the transit.
5-Upper crustal contribution into the magmas is negligible (Kaygusuz et al., 2018; Üner 2021).
The petrochemical data derived from the Eastern Anatolian magmas may be used to test the validity of the hypothesis that assumes the presence of a thick continental crust under eastern Anatolia. Substantial chemical modifications would be expected in the magma composition if they passed through the thick and hot continental crust. These may be listed as follow; 1-higher Sr and Nd isotope values, 2-increasing amount of continental crustal components, 3-large volumes of magmas of continental crust origin (granitic magmas), 4-mixing and mingling of magmas of diverse compositions.
The petrochemical properties of the lavas from the entire eastern Anatolian region show boninitic or metasomatic enrichment but do not confirm these alternatives and thus do not support presence of a thick continental crust.