Magmatism and the emergence of lithological structure in Io — Model Predictions

Io’s tidal heating and extensive volcanic activity has inspired decades of research. Previous models have provided significant insight into how tidal heating operates [1][2], how melt forms and migrates in the mantle [3], and how eruptions affect lithospheric structure [4][5]. However, little has been done to couple these processes. In this work we present results from 1D models that couple magmatic segregation and volcanism to illuminate the controls on Io’s magma distribution, compositional evolution, lithosphere thickness, and long-wavelength lithosphere thickness and topography variations [7][8]. Radial melt transport [3], leading order spherical symmetry [6], and degree-2 forcing [1] mean that 1D models are useful in investigating such coupling.

We show that lithospheric thickness can reach a steady state within observational constraints when the burial of cold surface material is balanced by a heat source in the lithosphere. We propose that this heat source is the formation of permanent magmatic intrusions [7]. We show that melting and buoyant segregation of a more-fusible component of Io’s mantle leads to chemical stratification. Hot, refractory melts form in the lower mantle, and if able to migrate to the surface, can provide an explanation for Io’s highest temperature eruptions [8]. Finally, we couple a suite of 1D columns to a tidal heating model. With this we predict that crustal thickness should either correlate with surface heat flux, or be largely uniform.

Future work can expand these models to higher-dimensions and more realistic compositional systems, explore the propensity for convection, and predict heterogeneity in erupted products.

1. Segatz et al. (1988), Icarus, 10.1016/0019-1035(88)90001-2.

2. Bierson & Nimmo (2016), JGR:Planets, 10.1002/2016JE005005.

3. Moore (2001), Icarus, 10.1006/icar.2001.6739.

4. O’Reilly & Davies (1981), GRL, 10.1029/GL008i004p00313.

5. Mckinnon et al. (2001), Geology, 10.1130/0091-7613(2001)029<0103:COIAMF>2.0.CO;2.

6. Kirchoff et al. EPSL, 10.1016/j.epsl.2010.11.018.

7. Spencer, Katz, and Hewitt (2020), JGR:Planets, 10.1029/2020JE006443.

8. Spencer et al, (in review).