Gelatine as a crustal analogue: Determining elastic properties for modelling magmatic intrusions

Gelatine has often been used as an analogue material to model the propagation of magma-filled fractures in the Earth's brittle and elastic crust. Despite this, there are few studies of the elastic properties of gelatine and how these evolve with time. This important information is required to ensure proper scaling of experiments using gelatine. Gelatine is a viscoelastic material, but at cool temperatures (T-r similar to 5-10 degrees C) it is in the solid 'gel' state where the elastic behaviour dominates and the viscous component is negligible over short to moderate timescales. We present results from a series of experiments on up to 30 litres of maximum 30 wt.% pigskin gelatine mixtures that document in detail how the elastic properties evolve with time, as a function of the volume used and gel concentration (C-gel). Gelatine's fracture toughness is investigated by measuring the pressure required to propagate a pre-existing crack. In the gel-state, gelatine's Young's modulus can be calculated by measuring the deflection to the free-surface caused by an applied load. The load's geometry can affect the Young's modulus measurement; our results show its diameter needs to be 10% of both the container diameter and the gelatine thickness (H-gel) for side-wall and base effects to be ignored. Gelatine's Young's modulus increases exponentially with time, reaching a plateau (E-infinity) after several hours curing. E-infinity depends linearly on C-gel, while T-r, H-gel and the gelatine's thermal diffusivity control the time required to reach this value. Gelatine's fracture toughness follows the same relationship as ideal elastic-brittle solids with a calculated surface energy gamma(s) = 1.0 +/- 0.2 J m(-2). Scaling laws for gelatine as a crustal analogue intruded by magma (dykes or sills) show that mixtures of 2-5 wt.% gelatine cured at similar to 5-10 degrees C ensure the experiments are geometrically, kinematically and dynamically scaled. (C) 2012 Elsevier B.V. All rights reserved.