Early transient superplumes and the origin of the Martian crustal dichotomy

Abstract

[1] The large temperature difference between the core and mantle of Mars at the end of planetary accretion creates a hot, internally convecting thermal boundary layer at the base of the mantle, whose viscosity is several orders of magnitude lower than the viscosity of the mantle above it. Theoretical analysis and numerical simulations of the instability of this thermal boundary layer show that it is likely that only one large plume forms. This superplume may play a role in the formation of crustal dichotomy and generation of the magnetic field in the early history of Mars.

Experiments on metal–silicate plumes and core formation

“…The change from neutrally buoyant metal-silicate plumes relatively rich in core-forming metals to positively buoyant plumes relatively depleted in core-forming metals is likely to be a gradual transition, which might be expected to recycle significant amounts of metals back towards the Earth's surface. Reversal in the direction of coreforming plumes offers an explanation for why there were major pulses of volcanic activity and heterogeneous crust formation in the early history of some terrestrial planets, such as has been proposed for the crustal dichotomy on Mars (Ke & Solomatov 2006). It also suggests that plumes may have been the initial phase of whole mantle convection in the Earth.…”

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

“…Similarly, synthetic single harmonic patterns for planetary mantle heterogeneity, for example for the CMB conditions that prevailed during the paleo dynamo of Mars, are oversimplified. Even if the Martian anomaly was indeed large-scale (Elkins-Tanton et al 2005;Harder and Christensen 1996;Ke and Solomatov 2006;Roberts and Zhong 2006;Roberts et al 2009), it was likely more complex than a single harmonic pattern. Note finally that simulating the geodynamo at earlier times requires information about the time-dependent mantle convection pattern, which is not witnessed by presentday tomography (Yoshida and Santosh 2011;Zhang and Zhong 2011;Zhang et al 2010;Zhong et al 2007).…”

Hemispheres Apart: The Crustal Dichotomy on Mars

“…Widespread crustal extension (McGill & Dimitriou 1990) and volcanism (Zhong & Zuber 2001, Zuber 2001 in the northern lowlands likely accompanied the formation of the crustal dichotomy. A somewhat related mechanism to mantle convection for the formation of the dichotomy involves an early transient superplume (Ke & Solomatov 2006). Modeling suggests that the high thermal gradient at the core and the mantle expected at the end of planetary accretion results in a low viscosity layer at the base of the mantle that gives rise to a single large-scale mantle plume.…”

“…If the dichotomy formed as a result of mantle overturn, cold cumulates placed against the core-mantle boundary could create a heat flux that might have maintained a dynamo for ∼15 to 150 Myr (Elkins-Tanton et al 2005b). Likewise, an early transient superplume would be expected to result in a high heat flow at the core-mantle boundary (Ke & Solomatov 2006). …”

“…Modeling suggests that the high thermal gradient at the core and the mantle expected at the end of planetary accretion results in a low viscosity layer at the base of the mantle that gives rise to a single large-scale mantle plume. A superplume may have resulted in global-scale melting that contributed to the formation of the crustal dichotomy (Ke & Solomatov 2006). …”