Date

2008-03-28

Author

Toksoy Köksal, Fatma
Köksal, Serhat

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The petrology of the granitic and volcanic rocks cropping out in Avanos (Nevşehir) area sheds light on the nature of magmatism in central Anatolia. In the region while granitoids intrude the Precambrian-Paleozoic-Mesozoic metamorphic basement rocks, volcanic rocks are found as dykes cutting granitoids and blocks in Late Cretaceous (?)- Early Paleocene olistostromal unit (Göncüoğlu et al., 1997; Köksal et al., 2001). The felsic intrusive rocks in the Avanos area are quartz-syenite and alkali-feldspar quartz-syenite while volcanic rocks are trachydacite, trachyandesite and dacite. Both type of rock assemblages, in general, have similar mineral constituents which are K-feldspar, plagioclase, amphibole, biotite ± quartz ± clinopyroxene ± muscovite of essential minerals, and accessory phases of zircon, titanite, apatite and opaque. In the quartz-free volcanic rocks, there is limited amount of pseudoleucite in addition to these minerals. The granitoids and volcanic rocks, showing similarities also within the aspect of whole-rock element geochemistry, are alkaline and metaluminous-slightly peraluminous (molar A/CNK<1.1). The rocks can be described as A-type and post-collisional based on Whalen et al. (1987) and Pearce et al. (1984) classifications. Variation of elements against silica shows that both rock groups are characterized by same elemental distributions and trends. Moreover, these rocks display similar enrichment and depletion ranges and analogous patterns. In the multi-element diagram, Nb, Ta, Ti depletion and Rb, Th, K, Pb, U enrichment are noteworthy, besides in the rare earth element diagram LREEs are enriched compared to HREEs ([La/Yb]N = 12–97), and negative Eu anomaly is not very significant ([Eu/Eu*]N=0,65–0,92). Petrographic observations and whole-rock element geochemistry data point out that the granitic and volcanic rocks are cogenetic. Furthermore, the initial Sr, Nd, and Pb isotope ratios of both rock groups overlap in small ranges ([87Sr/86Sr]T= 0,708479–0,709896; εNd(T)= -7,2 – -9,1; [206Pb/204Pb]T = 18,84–18,98; [207Pb/204Pb]T = 15,72–15,76; [208Pb/204Pb]T = 38,98–39,24; n=24). Thus isotopic data also support the cogenetic relationship between these rocks. The data obtained show that the volcanics are shallow intrusive and extrusive equivalents of the granitic rocks in the Avanos area. Furthermore, it is suggested that both rocks are derived from mantle sourced magma that is affected from crustal contamination. These rocks are thought to be products of post-collisional magmatism generated due to the crustal thickening during the closure of Neotethyan İzmir-Ankara-Erzincan branch.

Subject Keywords

Magmatism, Volkanic rock, Granitoid, Isotope, Central Anatolia, Avanos, Magmatizma, Volkanik kayaç, Granitoyid, İzotop, Orta Anadolu

URI

https://hdl.handle.net/11511/78552

Collections

Department of Geological Engineering, Conference / Seminar