The First Petrographic Textural Data of Sferulitic Rhyolites Observed in the west of İdrisyayla (Kırka-Eskişehir)

Spherulitic structures are classically defined as concentrically zoned crystal clusters that form in igneous systems (especially alkaline rocks), and usually occur different mineral layers or shells.
 The volcano-sedimentary series observed the Kırka region, south of Eskişehir, within Kırka-Afyon-Isparta Volcanic Province, Western Anatolia, consists predominantly Lower Miocene volcanic pyroclastic sequences with rhyodacitic-rhyolitic composition, lacustrine limestones, borate-bearing claystones, tuff, stromatolitic limestones basalts. formation mechanisms spherulitic marginal zone sub-alkaline rhyolitic lava dome outcropping Neogene west İdrisyayla (Eskişehir) region were described for first time this study. rhyolites grayish light brown color, have hypocrystalline hyalopilitic-holohyaline texture present spherical spherulites. These rocks a completely flowing structure composed glass containing rarely euhedral plagioclase quartz microcrystals, on surface up to 10-15 cm size. spherulites, which almost round shape, appear concentric rings flow bands. band phase presents continuity inner structures.
 This study suggests sferulitic (Kırka-Eskişehir) formed by devitrification mechanism result high temperature rapid cooling. petro-mineralogical features show during early magmatic stage, oversaturated liquid crystallized silica-rich fluid phases relatively densities, radial quartz-feldspar growths from center, caused structure. It is also suggested lithophysae-like representing solid axial cavities due locally folding bands following phase, changed laminated rhyolite.