Conditions for complex or simple flow during magma ascent: Insights from 3D laser imaging of analogue dykes
Janine L. Kavanagh , Caitlin Chalk and Kate Williams
Affiliations: Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, L69 3GP, UK
Presentation type: Poster
Presentation time: Friday 16:30 - 18:00, Room Poster Hall
Poster Board Number: 5
Programme No: 1.5.12
Abstract
It is widely recognized that the physical, chemical and thermal properties of magma strongly impact how explosive a volcanic eruption will be and how long it will last. However, how these are controlled by the ascent dynamics of dyking is relatively understudied. Magma flow in dykes is often assumed to be simple and unidirectional, however geological evidence of magma flow recorded in fossil dykes often suggests complex multidirectional flow patterns have occurred. Existing dyke models are insufficient to explain their emplacement and need to account for magma flow which varies across the dyke breadth and thickness over time as the dyke ascends through the crust. We conducted dynamically scaled analogue dyke experiments using a laser-based stereoscopic imaging system to measure three-dimensional (3D) flow dynamics inside flux-driven fractures for the first time. An elastic, transparent host medium (gelatine) was intruded by either a simple Newtonian fluid (a glycerol solution or salt water) or more complex shear-thinning fluid (a xanthan gum-salt water solution) to represent magma with variable proportions of melt, crystals and bubbles. Our results show that the Newtonian magma model exhibits complex and strong 3D effects, whereas the shear-thinning magma model produces simple, 2D unidirectional flow. This challenges major assumptions of most numerical and conceptual models of magma ascent, impacting the dynamics of magma connections between deep crustal reservoirs and the dynamics of shallow feeder dykes.