By Penny Wieser, University of Cambridge
Olivine is near ubiquitous in lavas from Kilauea volcano, Hawaii. It is particularly prevalent at depth – the difference in bulk MgO between primary and erupted magmas requires fractionation and storage of ~14 vol% olivine within the Kīlauea edifice! Seismic imaging shows that this “lost” olivine is highly concentrated into dunitic bodies around the summit caldera and rift zones. Crucially, catastrophic landslide events at Hawaiian volcanoes have been attributed to the presence of this weak material. The olivines commonly show extinction discontinuities, which for the last ~30 years have been suggested to arise from plastic deformation, or “creep”, in the dunitic bodies. However, it has also been suggested that these features may form during an early period of dendritic growth, and that the importance of dunitic bodies in the structural evolution of ocean islands is overstated.
Electron backscatter diffraction (EBSD) allows quantitative measurements of the orientation of the olivine crystal lattice. My research characterizes extinction discontinuities in Kilauean olivines, showing that they have crystallographic signatures consistent with experimental deformation of olivine at magmatic conditions, and different from the signature of dendritic growth. The spacing between extinction discontinuities allows estimation of the differential stress in dunitic bodies beneath Kilauea (~5-10Mpa).
Penny Wieser is a PhD student at the University of Cambridge, supervised by Marie Edmonds and John Maclennan. Her research is based on using geochemistry and petrology to investigate the controls on eruption style and volcanic plumbing in Hawaii. She particularly focuses on high fountaining eruptions at Kilauea, Hawaii. Follow Penny to find out more about her research: @Penny_Wieser