Mineralogical and petrological features of the Cemilkoy ignimbrite, Cappadocia, Turkey


Dogan-Kulahci G. D. , TEMEL A. , GOURGAUD A.

CHEMIE DER ERDE-GEOCHEMISTRY, cilt.78, ss.103-115, 2018 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 78 Konu: 1
  • Basım Tarihi: 2018
  • Doi Numarası: 10.1016/j.chemer.2017.11.002
  • Dergi Adı: CHEMIE DER ERDE-GEOCHEMISTRY
  • Sayfa Sayıları: ss.103-115

Özet

The Cemilkoy ignimbrite is one of the voluminous ignimbrite deposits in Cappadocia. The Cemilkoy ignimbrite contains pumice and lithic clasts of volcanic and ophiolitic origin in an ash matrix. The unwelded Cemilkoy ignimbrite is distinguished from other deposits in Cappadocia by flattened pumices, elongate vesicles and a slaty fabric. The mineral assemblage of the Cemilkoy ignimbrite is plagioclase, biotite, quartz and oxides (magnetite and Ti-magnetite) and the matrix is glassy. Eutaxitic texture is dominant and all pumice clasts have a vitrophyric-porphyritic texture. The same textural properties were observed throughout the spatial distribution of CemilkOy ignimbrite. Microprobe studies reveal that plagioclase compositions range from albite through oligoclase-andesine. Estimated plagioclase-liquid temperatures (T) and pressures (P) are varying between 806 and 847 degrees C and 4.2-7.1 (kbar), and the H2O content of the melt is estimated to have been 5 wt.% from the pumice clasts. Based on geochemical data, the Cemilkoy ignimbrite is rhyolitic and calc-alkaline in character, and all pumice clasts are enriched in LIL and LRE elements relative to I-IFS elements. Negative Nb, Ta and Ti anomalies, ratios of Ba/Nb > 28 (56-77), Ba/Ta (>)450 (590-700) and Th/Yb vs. Ta/Yb are consistent with a subduction-related origin. According to the geochemical and mineralogical-petrographical data, the Cemilkoy ignimbrite originated from partial melting of a mantle source which was enriched during previous subduction processes with variable degrees of assimilation fractional crystallization (AFC) through time and Cemilkoy ignimbrite erupted from a crustal magma chamber at shallow to intermediate depth.