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The fluid dynamics of magma mingling and mixing during dyke propagation and eruption: Insights from analogue experiments

Tegan A. Havard 1, Janine L. Kavanagh1, Stefano Urbani1,2, & Caitlin M. Chalk1

  • Affiliations: 1 Department of Earth, Ocean and Ecological Sciences, University of Liverpool, United Kingdom 2 Department of Geological Survey of Italy, Institute for Environmental Protection and Research (ISPRA), Italy

  • Presentation type: Talk

  • Presentation time: Monday 08:45 - 09:00, Room R280

  • Programme No: 1.2.2

  • Theme 1 > Session 2

Abstract

Volcanic fissures can erupt magmas which have a range of physical and chemical properties that suggest mingling and mixing between distinct magma reservoirs. The timing and location of mingling/mixing however is uncertain, with interactions either happening within sill-like reservoirs at depth, between reservoirs, during transport to the surface within a dyke, or a combination of all these. Here, we use analogue experiments to explore the fluid dynamics of magmas mingling and mixing during ascent within a growing dyke and discuss how these impact chemical and petrological expressions. An array of Newtonian immiscible and miscible pairs of fluids with differing density, representing magmas of different compositions, were injected sequentially at low or high volumetric flux into a solid, elastic body (crustal analogue) to create experimental dykes. Photographs were captured in the planes along the dyke strike and across the dyke thickness and processed to measure dyke tip velocity and qualitatively assess the extent of mingling and mixing. The experiments were repeated using particle image velocimetry (PIV) to calculate flow velocities within the dyke. Our results show an internal high-velocity jet structure and recirculating flow forms during mixing, whereas low-velocity uniform upwards flow forms during mingling. We find that a higher flux promotes more effective mingling and mixing, and this is associated with greater dyke tip propagation velocity and greater internal velocities. We discuss our experimental results in terms of magma recharge events, evolving properties of eruptive products, and natural Icelandic fissure systems that display chemical and physical interaction of distinct magmas.