Author: Tamer KOROLAY, Oğuz ZOROĞLU, Yusuf Kağan KADIOĞLU
Publishing Date: 2009
Volume: 24 Issue: 2
Fiamme structures, defined as flattened, dark color and glassy inclusions within in the pyroclastic rocks. They may form the characteristic features of many welded and non welded ignimbrites and bears important clues in the determination of magma compositin before the eruption. The use of the term “Fiamme” is very chaotic in terms of its genesis meaning and interpretation of occurrences. This study deals with the petrographic and geochemical properties of fiamme structures which are basically described as elongated, flame like lenses and dark color inclusions within the welded İncesu ignimbrite from Central Anatolian Volcanic Province (CAVP). Two types of fiamme can be identified based on petrographical, mineralogical properties and geochemical variations of some major oxides (Fe2O3*, CaO, K2O, TiO2, MnO) and trace (Rb, Sr, Y, Zr, Th, Pb, Hf, La, Ce) elements within the İncesu ignimbrite. First type of the fiamme, which is defined as Type A, has no mineral component. The second type of the fiamme, is defined as Type‐B and is composed of plagioclase (oligoclase, andesine) + pyroxene (augite, clinoenstatite) + opaque minerals. Both types of Fimme have calc‐alkaline in character and andesite/basaltic andesite (B‐type) to dacite/rhyolite (A‐type) in composition. B‐type fiamme have relatively high; CaO, Fe2O3*, TiO2, P2O5, MnO ve Sr and low K2O, Rb, Y, Zr, Hf, Th, La, Ce contents with respect to A type fiamme. Fiamme display an enrichment in large ion lithophile elements (LILE) relative to high field‐strength elements (HFSE) in Chondrite, MORB and E‐MORB normalized multi‐element diagrams. In Chondrite, MORB and E‐MORB normalized multi‐element diagrams, the trace element patterns of all samples are similar in shape and exhibit depletions in Sr, Ba, Nb, P and Ti. In UC normalized multi element diagram, A and B type fiamme show positive Ta anomaly and have very similar trace element patterns of UC values. Rare earth element (REE) pattens for fiamme show REE enrichment with respect to chondrite values. They exhibit marked enrichmet in light rare earth elements (LREE) relative to heavy rare earth elements (HREE). Furthermore, all amples have negative Eu anomalies, indicating the significant role of plagioclase in the fractional crystallization. Elemental ratios such as Rb/Nb, Ba/Nb, Nb/Ta propose that the magma was subjected to conceivable crustal contamination during the evolution of these fiamme.
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 A and B type fiamme. Furthermore, these results reveal that the fiamme types of Incesuignimbrite were produced from same parental magma derived from an enriched source of mixed subduction and/or crustal products.
Key Words: Fiamme; İgnimbrite; Central Anatolian Volcanic Province (CAVP), Subduction Component; Crustal Contamination.