Melt inclusion stratigraphy in plagioclase megacrysts from the Bárðarbunga-Veiðivötn volcanic system, Iceland

• Main Author: Daniel John Christopher Manns 1998-
• Other Authors: Háskóli Íslands
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: Jarðfræði (námsgrein); Jarðlög; Brandur; Veiðivötn; Iceland
• Online Access: http://hdl.handle.net/1946/41885

Major and minor element concentrations of plagioclase-hosted melt inclusions, plagioclase, olivine, and clinopyroxene crystals were analysed within plagioclase megacryst samples from the Bárðarbunga-Veiðivötn volcanic system in Iceland’s Eastern Volcanic Zone. Plagioclase megacryst samples were collected from the Brandur, Fontur, and Saxi tuff cones, located on the Veiðivötn volcanic fissure swarm. Plagioclase megacryst-hosted melt inclusions, once corrected for post-entrapment crystallisation, ranged in compositions from Mg# 50 – 64, with variable TiO2 and Al2O3 contents of 0.4 – 1.6 wt.% and 14 – 16 wt.%, respectively. The data as a whole show minimal systematic variation of melt inclusion MgO and TiO2 contents with respect to textural position within the megacrysts. However, significant compositional variation was observed between individual samples, and in some cases based on textural position within individual samples. Plagioclase megacrysts were observed to be homogeneous in their major and minor element contents, despite this significant variation in melt inclusion geochemistry. Crystallisation temperature calculated using a liquid-only thermometer gave a range of 1183 – 1243 ± 26 °C, with a modal range of 1190 – 1220 ± 26 °C. Crystallisation pressure calculated using olivine-plagioclase-augite-melt (OPAM) barometry had an estimated range of 1.6 – 7 ± 1.3 kbar (5.7 – 25 km), with a modal range of 3.0 – 3.7 ± 1.3 kbar (10.7 – 13.1 km). Modal values of both temperature and pressure decreased slightly from core to rim. However, as with geochemical variation, both temperature and pressure varied significantly in different megacryst samples. This suggests that despite being erupted during the same event, and from the same carrier liquid, individual megacrysts reveal significantly different formation histories. Secondly, the megacrysts preserve very different information and processes compared to what has been observed from macrocrysts from the same localities Styrkur aðalefna glers, plagíóklas, ólivín og ...