Geochemical approach to magmatic evolution of Mt Erciyes stratovolcano central Anatolia, Turkey

Erciyes stratovolcano, culminating at 3917 m, is located in the Cappadocian region of central Anatolia. During its evolution, this Quaternary volcano produced pyroclastic deposits and lava flows. The great majority of these p roducts are calc-alkaline in character and they constitute Kocdag and Erciy es sequences by repeated activities. Alkaline activity is mainly observed i n the first stages of Kocdag and approximately first-middle stages of Erciy es sequences. Generally, Kocdag and Erciyes stages terminate by pyroclastic activities. The composition of lavas ranges from basalt to rhyolite (48.4- 70.5 wt.% SiO2). Calc-alkaline rocks are represented mostly by andesites an d dacites. Some compositional differences between alkaline basaltic, basalt ic and andesitic rocks were found; while the composition of dacites remain unchanged. All these volcanics are generally enriched in LIL and HFS elemen ts relative to the orogenic values except Rb, Ba, Mb depleted alkaline basa lt. Sr-87/Sr-86 and Nd-143/Nd-144 isotopic composition of the volcanics ran ge between 0.703344-0.703964, 0.512920-0.512780 for alkaline basalts and ch ange between 0.704322-0.705088, 0.512731-0.512630 for alkaline basaltic roc ks whereas calc-alkaline rocks have relatively high Sr and Nd isotopic rati os (0.703434-0.705468, 0.512942-0.512600). Low Rb, Ba, Mb content with high Zr/Nb, low Ba/Nb, La/Yb ratio and low Sr isotopic composition suggest an d epleted source component, while high Ba, Rb, Mb content with high La/Yb, Ba /Nb, low Zr/Nb and low Sr-87/Sr-86 ratios indicate an GIB-like mantle sourc e for the generation of Erciyes alkaline magma. These elemental and ratio v ariations also indicate that the different mantle sources have undergone di fferent degree of partial melting episodes. The depletion in Ba, Rb, Mb con tent may be explained by the removal of these elements from the source by s lab-derived fluids which were released from pre-collisional subduction, mod ified the asthenospheric mantle. The chemically different mantle sources in teracted with crustal materials to produce calc-alkaline magma. The Ba/Nb i ncrease of calc-alkaline samples indicates the increasing input of crustal components to Erciyes volcanics. Sr and Nd isotopic compositions and elevat ed Ln, and HFS element content imply that calc-alkaline magma may be derive d from mixing of an GIB-like mantle melts with a subduction-modified asthen ospheric mantle and involvement of crustal materials in intraplate environm ents. (C) 1998 Elsevier Science B.V. All rights reserved.