Continuous mush disaggregation during the long-lasting Laki fissure eruption, Iceland ...

• Main Authors: Neave, DA, Buisman, I, Maclennan, JC
• Format: Article in Journal/Newspaper
• Language: English
• Published: Mineralogical Society of America 2017
• Subjects: mush disaggregation; basalt; automated mineralogy; crystal size distributions; textures; Laki; Iceland
• Online Access: https://dx.doi.org/10.17863/cam.10513; https://www.repository.cam.ac.uk/handle/1810/266946

Plagioclase textures were investigated in the products of the voluminous AD 1783–1784 Laki eruption from the Eastern Volcanic Zone (EVZ) of Iceland to establish whether mush disaggregation occurred solely at the onset of the eight-month eruption or throughout its whole duration. Phase proportions and plagioclase size distributions were determined using standard optical and manual techniques as well as automated approaches based on Quantitative Evaluation of Minerals by SCANing electron microscopy (QEMSCAN). Based on optical microscopy and the explicit combination of textural and compositional information in QEMSCAN images, plagioclase crystals were divided into two populations: small (<0.5 mm long), high-aspect ratio (length/width > 4) microcrysts with low-anorthite (0.5 mm long), low-aspect ratio(length/width = 2–3) macrocrysts with high-anorthite (An₈₄–An₉₂) cores. Small microcrysts grew from their carrier liquid during the final phase of pre-eruptive crystallization while large macrocrysts, which ...