A Microprobe Study of Subglacial Pillow Rim Glasses from the Hofsjökull Volcanic System, Central Iceland

• Main Author: Sigurbjörg Jónína Guðmundsdóttir 1997-
• Other Authors: Háskóli Íslands
• Format: Bachelor Thesis
• Language: English
• Published: 2020
• Subjects: Jarðfræði; Hofsjökull; Iceland
• Online Access: http://hdl.handle.net/1946/37124

The Hofsjökull volcanic system is a part of the Mid-Iceland Volcanic Zone and has two central volcanoes, Kerlingarfjöll and Hofsjökull. There is currently limited knowledge on the Mid-Iceland Volcanic Zone and its volcanic products, and most of the petrological studies conducted so far have been largely focused on Kerlingarfjöll. This thesis presents a microprobe study on 24 subglacial pillow rim glasses from the Hofsjökull volcanic system. The major element compositions of these glass samples were used to constrain their origin. It is demonstrated that the Hofsjökull glass samples have likely evolved from at least two parental magmas through fractional crystallization processes at different depths within the crust below the volcano. We found no evidence of contamination by the surrounding crust and/or by magma mixing, but such secondary processes cannot be excluded on the basis of the dataset presented. Depth of crystallization was estimated using the Olivine-Plagioclase-Augite-Melt (OPAM) barometer, suggesting that a network of magmatic intrusions/sills were present below the volcanic system. The most primitive magmas likely equilibrated deep in the crust, at about 9 ±1.32 kbar (~30 km depth), which is near the mantle-crust Moho boundary at ~35 km depth. In contrast, the more evolved magmas (<7 wt.% MgO) equilibrated under lower pressure at ~1.6 ±0.56 kbar which equates to a crustal depth of ~4.6 km below sea level. This study therefore provides important constraints on the likely magma plumbing structure of the Hofsjökull volcanic system. Hofsjökulseldstöðvakerfið er hluti af Mið-Íslands gosbeltinu (Hofsjökulsgosbeltið) og eru tvær megineldstöðvar í því kerfi, Kerlingarfjöll og Hofsjökull. Það er lítið vitað um Mið-Íslands gosbeltið og eldfjallaafurðir þess, en flestar storkubergs rannsóknir sem hafa verið gerðar hingað til hafa haft áherslu á Kerlingarfjöll. Ritgerðin setur fram og ræðir niðurstöður örgreina á 24 bólstraglers sýnum frá Hofsjökulseldstöðvakerfinu. Öll sýnin mynduðust undir jökli og eru ...