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A scanning electron microscope study of post-depositional changes in the northeast Niğde ignimbrites, South Central Anatolia, Turkey

Published online by Cambridge University Press:  05 July 2018

S. Yurtmen  and
G. Rowbotham
S. Yurtmen
Affiliation:
Çukurova Üniversitesi, Mühendislik-Mimarlik Fakültesi, Jeoloji Mühendisligi Bölümü, 01330, Balcali, Adana, Turkey
G. Rowbotham
Affiliation:
Department of Earth Sciences, University of Keele, Keele, Staffordshire, ST5 5BG, UK
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Abstract

The ignimbrites of the northeast Niğde area, which are subdivided into the Lower, Middle and Upper ignimbrites on the basis of their compositional and stratigraphical characteristics, display textural variations from the base to the top. A large proportion of these ignimbrites have been altered and recrystallized by the processes of compaction, welding and devitrification, and as a result of volatile movement. The alteration and recrystallization processes include four stages: hydration, glassy and spherulitic stages accompanied by vapour-phase crystallisation. In the early phases of devitrification, detailed shard shapes are easily recognisable with the scanning electron microscope, but as alteration proceeds clarity of detail disappears because compaction results in collapse of the structure of the rock. Spherulitic and vapour-phase crystallisation usually involves the growth of alkali feldspar and cristobalite. These later stages are more common in the Upper Ignimbrite than the Middle and Lower ignimbrites.

Keywords

ignimbriteNiğdecompactionweldingdevitrificationhydrationglassyspheruliticvapour-phase
Type
Research Article
Information
Mineralogical Magazine , Volume 63 , Issue 1 , February 1999 , pp. 131 - 141
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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