Correlation of ignimbrites in the central Anatolian volcanic province using zircon and plagioclase ages and zircon compositions

摘要

Episodes of high eruptive fluxes (> 10~(-3) km~3/year) in continental environments are associated with magma-tism related to subduction, post-orogenic collapse, intra-plate hot spots, or rifting. During such episodes, voluminous ignimbrite deposits are produced which cover landscapes over 10~4-10~5 km~2. In such sequences, brief eruptive recurrence and chemical similarity limit the applicability of geochronological and geochemical correlation methods. Here, we present complementary geochronological data (~(40)Ar/~(39)Ar plagioclase eruption and ~(206)Pb/~(238)U zircon crystallization ages) for ignimbrites from the Miocene-Holocene Central Anatolian Volcanic Province (CAVP). In addition, we successfully employed zircon geochemistry (trace elements, oxygen isotopes) as an alteration-resistant indicator to correlate rhyodacitic to rhyolitic ignimbrites whose eruption age differences are too brief to be resolved by ~(40)Ar/~(39)Ar geochronology. By applying this method, we dismiss previous correlations between stratigraphic members (i.e., Sofular and Goerdeles. Sofular and Sarimadentepe), but demonstrate close relationships for other CAVP ignimbrites (i.e., Kavak units 1 to 4; Cemilkoey ignimbrite and overlying fallout deposits). Our chronostratigraphy reveals two previously unrecognized eruptive pulses at ～9-8 Ma and 7-5 Ma which are characterized by increasing magmatic temperatures (～75-100 ℃ within each cycle). Despite a long-term (10 Ma) eruptive productivity that is about one order of magnitude smaller than in other magmatically active continental plateaus, the CAVP achieved high eruptive fluxes during brief (1-2 Ma) intervals.