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    Correlation of ignimbrites in the central Anatolian volcanic province using zircon and plagioclase ages and zircon compositions
    (ELSEVIER SCIENCE BV, 2012) Aydar, Erkan; Schmitt, Axel K.; Cubukcu, H. Evren; Akin, Lutfiye; Ersoy, Orkun; Sen, Erdal; Atici, Gokhan
    Episodes of high eruptive fluxes (>10(-3) km(3)/year) in continental environments are associated with magmatism 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 (Ar-40/Ar-39 plagioclase eruption and Pb-206/U-238 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 Ar-40/Ar-39 geochronology. By applying this method, we dismiss previous correlations between stratigraphic members (i.e., Sofular and Gordeles, Sofular and Sanmadentepe), but demonstrate close relationships for other CAVP ignimbrites (i.e., Kayak units 1 to 4; Cemilkoy 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 degrees C 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. (C) 2011 Elsevier B.V. All rights reserved.
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    Volcanological evolution and caldera forming eruptions of Mt. Nemrut (Eastern Turkey)
    (ELSEVIER SCIENCE BV, 2012) Ulusoy, Inan; Cubukcu, H. Evren; Aydar, Erkan; Labazuy, Philippe; Ersoy, Orkun; Sen, Erdal; Gourgaud, Alain
    Mt. Nemrut volcano, situated at the west of Lake Van, is one of the historically active volcanoes of the Eastern Anatolia. It has an 8.5 x 7 km diameter summit caldera. Volcanic activity of Mt. Nemrut started similar to 1 Ma ago; the most recent eruptions were in 1441, 1597 and 1692 A.D. Among the Eastern Anatolian volcanoes, Mt. Nemrut is the most hazardous volcano for its vicinity. Present day volcanic activity is represented by intra-caldera hydrothermal and fumarolic output and low-level volcano-seismic events. Geological evolution and chronostratigraphy of the volcano is subdivided in three stages: pre-caldera, syn-caldera and post-caldera stages. Pre-caldera products are dominated by felsic lava flows and domes. Trachytic Nemrut and Kantasi pyroclastics represent the caldera forming activity, of which sequences are composed of fallout units and ignimbrite flows. Both Nemrut and Kantasi ignimbrite units are low-aspect ratio ignimbrites, they are generally densely welded and present columnar jointed outcrops locally. Extent of Nemrut ignimbrite (volume: 32.6 km(3)) is greater than the Kantasi ignimbrite (volume: 3.8 km(3)). Post-caldera activity of the volcano is marked by peralkaline rhyolitic (comendite) intra-caldera lava flows and explosive hydrovolcanic activities. Historical activity of the volcano is represented by bimodal basaltic-rhyolitic effusive activity along Nemrut rift zone. (c) 2012 Elsevier B.V. All rights reserved.