Magmatic Intrusions Control Io's Crustal Thickness

Abstract

Io, the most volcanically active body in the solar system, loses heat through eruptions of hot lava. Heat is supplied by tidal dissipation and is thought to be transferred through the mantle by magmatic segregation, a mode of transport that sets it apart from convecting terrestrial planets. We present a model that couples magmatic transport of tidal heat to the volcanic system in the crust, in order to determine the controls on crustal thickness, magmatic intrusions, and eruption rates. We demonstrate that magmatic intrusions are a key component of Io's crustal heat balance; around 80% of the magma delivered to the base of the crust must be emplaced and frozen as plutons to match rough estimates of crustal thickness. As magma ascends from a partially molten mantle into the crust, a decompacting boundary layer forms, which can explain possible observations of a high‐melt‐fraction region.

Compositional Layering in Io Driven by Magmatic Segregation and Volcanism

“…The model, shown schematically in Figure 1, considers the evolution and dynamics of a tidally heated body composed of a mixture of two chemical components. It is an extension of that described in Spencer, Katz, and Hewitt (2020) using the same equations and also solved in one dimension. Here it is extended to consider conservation of chemical species and the effect of composition on melting behavior, using a phase diagram described below.…”

“…As in Spencer, Katz, and Hewitt (2020), we assume spherical symmetry motivated by the global distribution of Io's volcanoes (Kirchoff et al, 2011; Williams et al, 2011). The one‐dimensional approach of this work precludes our ability to investigate processes such as thermochemical convection that may be a consequence of stratification, a point we discuss in section 4.5.…”

“…Conservation of energy () tells us that changes in bulk enthalpy occur by the advection of sensible and latent heat, diffusion of sensible heat, tidal heating, the energy removed by extraction, and the energy delivered by emplacement. We note that in Spencer, Katz, and Hewitt (2020) bulk enthalpy was normalized by the volumetric heat capacity ρC . Conservation of mass () in the plumbing system tells us that the plumbing system flux increases when material is extracted from the mantle and decreases when material is emplaced back into the continuum.…”

“…As in Spencer, Katz, and Hewitt (2020) we assume that the emplacement rate of magma from the plumbing system to the continuum is proportional to the temperature difference between the plumbing system material and the local continuum where T e is an elastic limit temperature below which no emplacement occurs (Spencer, Katz, & Hewitt, 2020). The emplacement rate constant h is discussed at length in Spencer, Katz, and Hewitt (2020), but here we propose that it may have different values in the mantle h M and the crust h C (the crust is where T < T A ). The mechanisms by which magma propagates through a partially molten medium are likely to be very different to those in a solid, and so would be expected to have a different efficiency of magma transport.…”

“…In this work we present a fluid dynamical model of crust and mantle dynamics that builds on the recent work of Spencer, Katz, and Hewitt (2020) by including compositional evolution. The compositional model is in the form of a two‐component phase diagram between hypothetical refractory and fusible components.…”