Background heatflow on hotspot planets: Io and Venus

Abstract

Abstract. On planets where most of the heat is transported to the surface by igneous activity (extrusive volcanism or near-surface intrusions), the surface heat flow at localities well away from regions of current igneous activity need not be even approximately the conductive heatflow through the entire lithosphere but may instead be dominated by the residual heat leaking out from the last igneous event in that locality. On lo, it is likely that (~tr) 1 1 2 <t:: lithosphere thickness (~t = thermal diffusivity, r = typical time between "resurfacing" events} and the background heatflow may be very large, comparable or even larger than the current observational heat flow, which is associated with the hotspots alone. This upward revision of lo's heatflow is compatible with observations and with recent indications of a non-steady tidal and thermal evolution. On Venus, (~tr) 1 1 2 is probably comparable to the lithosphere thickness and the resulting upward revision of heatflow may be only marginally significant, unless magmatic activity is enormously greater than on Earth.

Venus: A Contrast in Evolution to Earth

“…Ifheat removal by sea-floor spreading is slight (26), an evident mechanism is heat pipes (39), which entail mechanical and thermal nonlinearities not yet well understood. If this heat is delivered to the surface by volcanism, it is estimated that a volcanic flux of about 200 km3/year is required (39).…”

Formation of mountains on Io: Variable volcanism and thermal stresses

“…This may not be the case generally, in that magma may be injected laterally along sills at shallow levels and not reach the surface (Stevenson and McNamara, 1988;Leone and Wilson, 2001;Davies et al, 2006). This is plausible if Io's crust is pervasively layered as widely suspected (e.g., McEwen et al, 2004) and if the magma is close to neutrally buoyant with respect to the crust (consistent with patera observations; Davies et al, 2006).…”

“…This is plausible if Io's crust is pervasively layered as widely suspected (e.g., McEwen et al, 2004) and if the magma is close to neutrally buoyant with respect to the crust (consistent with patera observations; Davies et al, 2006). The effect on temperatures in the crust of magma intrusions was modeled by Stevenson and McNamara (1988), who were focused on how much conductive heat flow might be missing from ground-based IR estimates of Io's heat flow.…”

Io: Heat flow from dark volcanic fields

“…Only the most northern parts of Lei-Kung Fluctus (i.e., ID 14 and ID 15) appear to make a small contribution to the 'excess' polar heat flow (Veeder et al, 2004;Rathbun et al, 2004). The 'background' heat flow outside of dark paterae, dark volcanic fields and other active sources is still not very well constrained (Stevenson and McNamara, 1988).…”

“…This activity is powered by strong tidal interactions (Peale et al, 1979;Yoder, 1979;Yoder and Peale, 1981;Segatz et al, 1988;Moore et al, 2007). Io's heat flow, which is more than predicted by tidal dissipation models, produces observed thermal infrared emission in excess of the re-radiation of absorbed solar insolation (Matson et al, 1981;Sinton, 1981;O'Reilly and Davies, 1981;Pearl and Sinton, 1982;Sinton and Kaminski, 1988;Stevenson and McNamara, 1988;Spencer et al, 1990Spencer et al, , 2000Veeder et al, 1994;Rathbun et al, 2004). Surface manifestations of the volcanic activity on Io include paterae, flows and plume deposits as well as fumaroles and molten lava (Schaber, 1982;Strom and Schneider, 1982;McEwen et al, 1998b;Geissler et al, 1999Geissler et al, , 2004Keszthelyi et al, 2001;Leone et al, 2008; see also general Io overviews by Nash et al (1986), Spencer and Schneider (1996), Davies (2001Davies ( , 2007, Geissler (2003), McEwen et al (2004), Lopes and Williams (2005), and Perry et al (2007)).…”