An experimental approach to dike propagation : the effects of stress, solidification and internal flow

Abstract

This thesis provides a broad view on the factors controlling dike propagation and evolution, from analysis on the driving forces of propagation to the effect of the stresses in the medium to the thermal viability and vulnerability to solidification. Since magmatic dikes propagate in response to such various processes, this approach offers valuable and fundamental insights into their nature. General methodologyThroughout this thesis, I rely heavily on analogue modeling, which entails performing small, laboratory-scale experiments to understand what happens at the much-larger, natural, volcanic scale. In each experiment, I prepare a block of gelatin, which represents Earth's crust, and inject a fluid of some kind to represent the migrating magma. Since gelatin is brittle and elastic (like the Earth's crust on the spatial-and temporal-scale of a propagating dike), the injected fluid fractures the gelatin to create a small dike. This solid medium, by its very nature, produces planar dike geometries, similar to those found around volcanoes. In each chapter, I discuss in more detail the particulars of each specific If we choose to study a dike with a constant influx, we can non-dimensionalize the flux in different ways. A typical method is to consider the influx into the tail, so that magma flux, Q, and viscosity, μ, correspond to a thicker tail, whereas buoyancy draws magma upwards and corresponds to a thinner tail. The scale tail thickness, H∞, is quantified by H∞ = (Qμ/Δρg) 1/3 (Roper & Lister, 2007). The scale influx Q∞ is then quantified by Q∞ = Q/H∞. Note that in this methodology, Q is a 2D flux, meaning the flux per unit length (Roper & Lister, 2007;. When the parameter is large, it indicates that the dike is relatively thick. Another way to non-dimensionalize the flux is thermally, via a balance between heating a cooling. The influx provides heat to the dike at a rate determined by the influx, Q (now regular 3D flux) and dike thickness, H, while the cooling via conduction of heat into the surrounding crust depends on the surface area and the thermal diffusivity, α. If the dike has an approximate surface area of its vertical length, L, by its horizontal breadth, B, the dimensionless flux, Φ, is quantified by Φ = QH/(αLB) . When the value is large, it indicates that the flow is high and heat flows upward through the dike; when small, the heat is lost into the crust. Via the material selection and dimensionless numbers, we can control how the liquid and solid interact, as well as the relative size, shape and dynamics of a dike, so that they match nature. Chapter 1: Application of the Okada model to propagating dikes in analogue experiments: Comparing inversion estimates to lab measurements 15 Chapter 1: Application of the Okada model to propagating dikes in analogue experiments: Comparing inversion estimates to lab measurements