1. Evidence for post-depositional diffusional loss of hydrogen in quartz phenocryst fragments within ignimbrites
- Author
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Judit K. Sándorné, Tamás Fancsik, György Falus, Tamás Biró, Dávid Karátson, Roland Stalder, István Kovács, and Edit Király
- Subjects
chemistry.chemical_classification ,010504 meteorology & atmospheric sciences ,Base (chemistry) ,Hydrogen ,Geochemistry ,Mineralogy ,chemistry.chemical_element ,Pyroclastic rock ,010502 geochemistry & geophysics ,01 natural sciences ,Crystal ,Igneous rock ,Geophysics ,chemistry ,Geochemistry and Petrology ,Phenocryst ,Foreland basin ,Quartz ,Geology ,0105 earth and related environmental sciences - Abstract
Ignimbrite-hosted quartz phenocryst fragments contain much lower hydroxyl defect concentration than quartz in igneous rocks. Pre-eruptive and post-depositional loss of hydrogen were hypothesized as the main processes for lowering the initial magmatic concentrations of hydroxyl defects. The aim of this study was to examine the hydroxyl defect concentration of quartz phenocryst fragments from various vertical positions above the base of pyroclastic density current (PDC) deposits. It aims to record the vertical variations of hydroxyl defect concentrations to have an insight into potential post-depositional hydrogen loss of PDC deposits. Ignimbrite-hosted quartz phenocryst fragments were examined from two different ignimbrites in the Bukk Foreland Volcanic Area (North Hungary). Unpolarized micro-FTIR measurements on 23–35 unoriented crystal fragments from each sample were performed representing four different vertical positions of each site. Present results imply that hydroxyl defect concentrations show a pronounced decrease upward from the base of the deposits. The initial ~12 ppm hydroxyl defect concentration decreases to
- Published
- 2017
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