Yazar "Schmitt, Axel K." seçeneğine göre listele

Listeleniyor 1 - 2 / 2
  • Küçük Resim Yok
    Öğe
    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.
  • Küçük Resim Yok
    Öğe
    Quaternary bimodal volcanism in the Nigde Volcanic Complex (Cappadocia, central Anatolia, Turkey): age, petrogenesis and geodynamic implications
    (SPRINGER, 2014) Aydin, Faruk; Schmitt, Axel K.; Siebel, Wolfgang; Sonmez, Mustafa; Ersoy, Yalcin; Lermi, Abdurrahman; Duncan, Robert
    The late Neogene to Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia is one of the most impressive volcanic fields of Turkey because of its extent and spectacular erosionally sculptured landscape. The late Neogene evolution of the CVP started with the eruption of extensive andesitic-dacitic lavas and ignimbrites with minor basaltic lavas. This stage was followed by Quaternary bimodal volcanism. Here, we present geochemical, isotopic (Sr-Nd-Pb and delta O-18 isotopes) and geochronological (U-Pb zircon and Ar-Ar amphibole and whole-rock ages) data for bimodal volcanic rocks of the Ni g de Volcanic Complex (NVC) in the western part of the CVP to determine mantle melting dynamics and magmatic processes within the overlying continental crust during the Quaternary. Geochronological data suggest that the bimodal volcanic activity in the study area occurred between ca. 1.1 and ca. 0.2 Ma (Pleistocene) and comprises (1) mafic lavas consisting of basalts, trachybasalts, basaltic andesites and scoria lapilli fallout deposits with mainly basaltic composition, (2) felsic lavas consisting of mostly rhyolites and pumice lapilli fall-out and surge deposits with dacitic to rhyolitic composition. The most mafic sample is basalt from a monogenetic cone, which is characterized by Sr-87/Sr-86 = 0.7038, Nd-143/Nd-144 = 0.5128, Pb-206/Pb-204 = 18.80, Pb-207/Pb-204 = 15.60 and Pb-208/Pb-204 = 38.68, suggesting a moderately depleted signature of the mantle source. Felsic volcanic rocks define a narrow range of Nd-143/Nd-144 isotope ratios (0.5126-0.5128) and are homogeneous in Pb isotope composition (Pb-206/Pb-204 = 18.84-18.87, Pb-207/Pb-204 = 15.64-15.67 and Pb-208/Pb-204 = 38.93-38.99). Sr-87/Sr-86 isotopic compositions of mafic (0.7038-0.7053) and felsic (0.7040-0.7052) samples are similar, reflecting a common mantle source. The felsic rocks have relatively low zircon delta O-18 values (5.6 +/- 0.6 %) overlapping mantle values (5.3 +/- 0.3 %), consistent with an origin by fractional crystallization from a mafic melt with very minor continental crustal contamination. The geochronological and geochemical data suggest that mafic and felsic volcanic rocks of the NVC are genetically closely related to each other. Mafic rocks show a positive trend between Sr-87/Sr-86 and Th, suggesting simultaneous assimilation and fractional crystallization, whereas the felsic rocks are characterized by a flat or slightly negative variation. High Sr-87/Sr-86 gneisses are a potential crustal contaminant of the mafic magmas, but the comparatively low and invariant Sr-87/Sr-86 in the felsic volcanics suggests that these evolved dominantly by fractional crystallization. Mantle-derived basaltic melts, which experienced low degree of crustal assimilation, are proposed to be the parent melt of the felsic volcanics. Geochronological and geochemical results combined with regional geological and geophysical data suggest that bimodal volcanism of the NVC and the CVP, in general, developed in a post-collisional extensional tectonic regime that is caused by ascending asthenosphere, which played a key role during magma genesis.