The metamorphism and age of the Findicak metamorphite in the Yildizeli metasedimentary group

Abstract

The metamorphic rocks exposed in the Yildizeli region (west of Sivas) to the east of Kirsehir block (Central Anatolian massif or Kirsehir massif comprising metamorphic and associated magmatic rocks) are called as Yildizeli metasedimentary group. It is divided, into four units as based on the rock types, from bottom to top, the Asilik metamorphics including pelitic gneiss and migmatites, the Findicak metamorphics including the pelitic schist and gneiss, and calcsilicates, the Pelitlikaya quartzite consisting of quartzite and quartzitic schists, and the Kadikoy metacarbonate. Microscopicillay following mineralogical associations have been observed in the Findicak metamorphite: sillimanite + kyanite + muscovite + ortoclase + quartz; sillimanite + muscovite + biotite + orthoclase; quartz + plagioclase, diopside + hornblende + plagioclase + quartz; hornblende + plagioclase + quartz and diopside + hornblende + quartz + plagioclase + scapolite + calcite paragenesis. In addition to these paragenesis, post - tectonic epidote overgrowth in the hornblende - gneisses, replacement of diopside by tremolite in the diopsite - hornblende gneisses, transformation of calcsilicatic gneiss into talc - tremolite schist, and mica overgrowths on feldspars in the mica gneiss are also common and characteristic features of Findicak metamorphics were also determined. The hornblende - plagioclase, garnet - muscovite - biotite - plagioclase - kyanite, garnet - muscovite - biotite - plagioclase and muscovite - biotite - chlorite geobarometries show that the first metamorphism occurred under high pressure conditions. Following the high pressure metamorphism, the temperature increased, resulting in the transformation of kyanite into fibrolitic sillimanite. During the uplifting, a retrograde greenschist facies cataclastic metamorphism overprinted on the earlier fabrics due to decompressional regime. The last metamorphic event occurred during the Santonian - Maestrichtian time (K-Ar ages of muscovite and biotite, are 71.8 ± 2.3 Ma - 77.7 ± 1.8 and 68.1 ± 1.8 Ma - 72.3 ± 2.1 Ma, respectively).