Petrographic and geochemical characteristics of upper Miocene Tekkedag volcanics (Central Anatolia-Turkey)

Abstract

The Tekkedag volcanic complex, which extends as a ridge in the direction of NW-SE, is one of the poorly known volcanic centers and is exposed to the southwest of Kayseri located within the Central Anatolian Volcanic Province (CAVP) of Turkey. The mineralogical composition of Tekkedag volcanics reveals an assemblage of plagioclase (labradorite, bytownite)+pyroxene (augite, diopside and enstatite)+Fe-Ti oxide (magnetite, rutile)±olivine (forsterite) mineral composition having hypocrystaline porphryric, hypohyaline porphryric, gleomeroporphryric and seriate textures under the microscope. Confocal Raman Spectroscopy (CRS) has been used to define the mineral types. Tekkedag volcanics have medium K 2 O contents and are calc-alkaline in character. Geochemically, Tekkedag volcanics show a narrow range of major element compositions and are classified as augite andesite/basaltic andesite. On the variation diagrams based on MgO versus major and trace elements, they show good positive and negative correlations, indicating fractional crystallization of plagioclase, clinopyroxene and Fe-Ti oxide. Tekkedag volcanics display enrichment in large-ion lithophile elements (LILEs) relative to high field-strength elements (HFSEs) in chondrite, MORB, E-MORB and lower crust normalized multi-element diagrams. In all normalized multi-element diagrams, the trace element patterns of all samples are similar in shape and exhibit depletions in Ba, Nb, P and Ti as characteristics of subduction-related magmas. Rare earth element (REE) patterns for Tekkedag volcanics show REE enrichment with respect to chondrite values. They exhibit marked enrichment in light rare earth elements (LREEs) ((La/Sm) N =4.13-4.62) relative to heavy rare earth elements (HREEs) ((Sm/Lu) N =1.34-1.92). Furthermore, all samples have negative Eu anomalies ((Eu/Eu * ) N =0.77-0.90), indicating the significant role of plagioclase in the fractional crystallization. Elemental ratios such as K/P (15.46-21.69), La/Nb (2.01-4.26), Rb/Nb (8.74-10.59), Ba/Nb (38.54-75.77), Nb/Ta (1.16-2.14), Ce/P (2.13-4.32) and Th/U (1.77-3.97) propose that the magma was subjected to conceivable crustal contamination during the evolution of these Tekkedag volcanics. This statement is supported by the AFC modeling based on the trace elements. As a result, despite the lack of isotopic data, the petrographic and geochemical results suggest a significant role of plagioclase, clinopyroxene and Fe-Ti oxide fractionation during the evolution of the Volcanic Arc Basalts (VAB) nature of the Tekkedag volcanics. Furthermore, these results reveal that the volcanics of Tekkedag were produced from a parental magma derived from an enriched source of mixed subduction and/or crustal products. © 2010 Elsevier GmbH.