Neogene alkaline volcanism of the Afyon-Isparta area, Turkey: petrogenesisand geodynamic implications

In the Kirka-Afyon and Isparta areas, potassic and ultrapotassic alkaline m agmatism followed Upper Eocene - Middle Miocene calc-alkaline volcanism, wh ich was related to the northward subduction of the African Plate beneath Eu rasia. The alkaline volcanism lasted from 14.8 Ma (in the north) to 4 Ma (i n the south) and was associated with a presently still active extensional t ectonic regime. It is mainly located along a N-S fault, which marks the lim it between the Aegean Are and the Cyprus Are (Isparta Angle). In the Kirka- Afyon area the potassic to ultrapotassic rocks range from silica saturated (trachybasalts to trachytes) to highly undersaturated (phonolitic leucitite s). In the Isparta area ultrapotassic rocks occur together with rhyolitic l avas. In both areas, the ultrapotassic magmatism is transitional between la mproitic and Roman type, with a more lamproitic character for the Isparta r ocks. The potassic suites of both the Kirka-Afyon and Isparta areas are cha racterised by rocks with Sr isotope ratios increasing from mafic to silicic rocks. The rocks from Kirka-Afyon area have an orogenic affinity, whereas those from Isparta area exhibit orogenic (the potassic suite) and within-pl ate (the ultrapotassic suite) affinities. Extreme enrichments in LIL elemen ts characterise the Afyon phonolitic leucitites, whereas enrichments in Sr and REE are observed in Isparta potassic rocks. A residual, probably lithos pheric mantle metasomatised by fluids and/or melts of different origin (sub duction-related for the Kirka-Afyon rocks; deep astenospheric origin for th e Isparta rocks), is considered to be the source of the ultrapotassic magma s. A more "fertile" and probably deeper mantle, enriched by subduction-rela ted components, is believed to be the source of the potassic rocks. Lower d egrees of partial melting, in the mantle, at higher pressure, and probably at higher X-CO2, may account for the genesis of the phonolitic leucitite pa rental magmas. Partial melting of the mantle took place simultaneously in b oth sources, probably due to post-collision extensional tectonics, which wa s also responsible for the uprise of deep astenospheric mantle.