Elastic-plated gravity currents with a temperature-dependent viscosity

Abstract

We develop a set of equations to explore the behaviour of cooling elastic-plated gravity currents for constant influx conditions. In particular, we introduce a temperature-dependent viscosity to couple the flow thermal structure with the velocity field. We show that this coupling results in important deviations from the isoviscous case. In particular, the bending and gravity asymptotic regimes, characteristic of the isoviscous case, both split into three different thermal phases: a first ‘hot’ isoviscous phase, a second phase where the spreading rate drastically decreases and the flow thickens and a third ‘cold’ isoviscous phase. The viscosity that controls the spreading rate differs in both asymptotic regimes; it is the average viscosity of a small peeling region at the current tip in the bending regime and the average flow viscosity in the gravity regime. In both regimes, we characterize the evolution of the thermal anomaly and determine the time scale of the phase changes in terms of the Péclet number and of the viscosity contrast. Finally, we show that the evolution with bending and gravity can result in six different evolution scenarios depending on the combination of dimensionless numbers considered. We provide a phase diagram which summarizes them as a function of the flow Péclet number and viscosity contrast.

Structural and Geochemical Interactions Between Magma and Sedimentary Host Rock: The Hovedøya Case, Oslo Rift, Norway

“…These features highlight the competition between solidification of the dike margin and tip and internal magma overpressure. Solidification is ignored in the conceptual models of Mode I, Mode II, and mixed‐mode magma‐induced fracturing but has been shown to result in pulsating propagation and temporary stalling of magma and 3‐D complexity of intrusions through numerical modeling (Fialko & Rubin, 1998; Thorey & Michaut, 2016) and laboratory experiments (Chanceaux & Menand, 2016; Currier & Marsh, 2015; Taisne & Tait, 2011).…”

Dynamics of Sill and Laccolith Emplacement in the Brittle Crust: Role of Host Rock Strength and Deformation Mode

“…Thus, the values of Π 6 in our models are in the same range as those of Π 6 in geological systems, showing that our models are similar to their geological equivalent in terms of balance between viscous stresses and host rock strength. Note that our experiments do not consider cooling effects: magma cooling induces viscosity increase which may locally affect the value of Π 6 in nature (Thorey & Michaut, 2016).…”

“…To date, two end-member types of magma emplacement models exist. On one hand, models for sheet intrusions consider "relatively low," often neglected, viscosity magma into purely elastic rock (Bunger & Cruden, 2011;Galland & Scheibert, 2013;Kavanagh et al, 2015;Malthe-Sørenssen et al, 2004;Michaut, 2011;Pollard & Johnson, 1973;Thorey & Michaut, 2016). On the other hand, models for massive intrusions consider very viscous magma intruding into a weak, usually plastic host rock (e.g., Brothelande et al, 2016;Merle & Borgia, 1996;Montanari et al, 2010;Roman-Berdiel et al, 1995).…”

An Approximate Approach to Nonisothermal Emplacement of Kilometer‐Sized Kilometer‐Deep Sills at Calderas

“…As a consequence, R stop will be larger than (and w s ∕w smaller than) what computed for a single-component magma at its solidification temperature, and magma properties, like viscosity, will remain similar to the initial ones in the core of the flow. Since magma viscosity increases with decreasing temperature, propagation slows down while magma cools near the tip, as also shown by Thorey and Michaut (2016) in the case of elastic-plated gravity currents; however, arrest by solidification is retarded as the arrest velocity is approximately inversely proportional to the square root of viscosity.…”