A basal magma ocean dynamo to explain the early lunar magnetic field

Scheinberg, Aaron; Soderlund, K. M.; Elkins‐Tanton, L. T.

doi:10.1016/j.epsl.2018.04.015

Cited by 41 publications

(72 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To obtain a better insight into our modeling results, we use here the theory of Rayleigh‐Taylor instability to analyze the overturn of IBC (Scheinberg et al, ). A growing Rayleigh‐Taylor instability can be described using the relation:

w = w_{0} \exp ((), \frac{t}{t_{onset}})

where w is the dimensional vertical velocity, w 0 its initial amplitude, and t onset is the so‐called (dimensional) onset time.…”

Section: Rayleigh‐taylor Instability Analysismentioning

confidence: 99%

See 1 more Smart Citation

Overturn of Ilmenite‐Bearing Cumulates in a Rheologically Weak Lunar Mantle

Tosi

Schwinger

et al. 2019

JGR Planets

View full text Add to dashboard Cite

The crystallization of the lunar magma ocean (LMO) determines the initial structure of the solid Moon. Near the end of the LMO crystallization, ilmenite‐bearing cumulates (IBC) form beneath the plagioclase crust. Being denser than the underlying mantle, IBC are prone to overturn, a hypothesis that explains several aspects of the Moon's evolution. Yet the formation of stagnant lid due to the temperature dependence of viscosity can easily prevent IBC from sinking. To infer the rheological conditions allowing IBC to sink, we calculated the LMO crystallization sequence and performed high‐resolution numerical simulations of the overturn dynamics. We assumed a diffusion creep rheology and tested the effects of reference viscosity, activation energy, and compositional viscosity contrast between IBC and mantle. The overturn strongly depends on reference viscosity and activation energy and is facilitated by a low IBC viscosity. For a reference viscosity of 1021 Pa s, characteristic of a dry rheology, IBC overturn cannot take place. For a reference viscosity of 1020 Pa s, the overturn is possible if the activation energy is a factor of 2–3 lower than the values typically assumed for dry olivine. These low activation energies suggest a role for dislocation creep. For lower‐reference viscosities associated with the presence of water or trapped melt, more than 95% IBC can sink regardless of the activation energy. Scaling laws for Rayleigh‐Taylor instability confirmed these results but also showed the need of numerical simulations to accurately quantify the overturn dynamics. Whenever IBC sink, the overturn occurs via small‐scale diapirs.

show abstract

w = w_{0} \exp ((), \frac{t}{t_{onset}})

where w is the dimensional vertical velocity, w 0 its initial amplitude, and t onset is the so‐called (dimensional) onset time.…”

Section: Rayleigh‐taylor Instability Analysismentioning

confidence: 99%

“…To obtain a better insight into our modeling results, we use here the theory of Rayleigh-Taylor instability to analyze the overturn of IBC (Scheinberg et al, 2018). A growing Rayleigh-Taylor instability can be described using the relation:…”

Section: Rayleigh-taylor Instability Analysismentioning

confidence: 99%

Overturn of Ilmenite‐Bearing Cumulates in a Rheologically Weak Lunar Mantle

Tosi

Schwinger

et al. 2019

JGR Planets

View full text Add to dashboard Cite

show abstract

“…The oldest lunar magnetic intensity of 20-40 μT dates back to 4.25 Ga (Garrick-Bethell et al, 2016). Such high magnitude of paleomagnetic intensity suggests a robust lunar core dynamo although this high strength is difficult to explain using our current understanding of small core size and the scaling between core heat flux and surface field strength (see summary by Scheinberg et al, 2018). Lunar paleomagnetism has been explained with different mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…Lunar paleomagnetism has been explained with different mechanisms. These mechanisms include the internal convection energy (Evans et al, 2014;Laneuville et al, 2013;Scheinberg et al, 2018;Zhang et al, 2013a), the impact event (Hood & Artemieva, 2008; Le Bars et al, 2011), and the precession movement (Dwyer et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Lunar Cumulate Mantle Overturn: A Model Constrained by Ilmenite Rheology

Zhang

Liang

et al. 2019

JGR Planets

View full text Add to dashboard Cite

Lunar cumulate mantle overturn has been proposed to explain the abundances of TiO2 and heat‐producing elements (U, Th, and K) in the source region of lunar basalts. Ilmenite‐bearing cumulates (IBCs) that were formed near the end of lunar magma ocean solidification are the driving force for overturn. IBCs are enriched with dense TiO2 and FeO contents and have lower viscosity and solidus than those of the underlying lunar cumulate mantle. We investigate the effects of temperature‐ and ilmenite‐dependent mantle rheology on the dynamic process of lunar cumulate mantle overturn and conditions for long‐wavelength downwellings of an IBC layer in a 3‐D spherical geometry. Our results show that the ilmenite‐induced rheological weakening is necessary to decouple the IBC layer from the top stagnant lid and facilitate overturn. Models with IBC viscosity derived from the experimental scaling can only produce short‐wavelength downwellings (spherical harmonic degree >3) and show an overturn timescale more than 100 Ma. A viscosity of the IBC layer at least 10−4 lower than that of the ambient mantle can produce the long‐wavelength (spherical harmonic degree ≤3) downwellings in ~10 Ma and even a hemispheric downwelling. Such low IBC viscosity requires additional weakening mechanisms, such as remelting or/and water enrichment. During the overturn, the cold downwellings displace upward the materials from hot lower mantle and produce partial melting in upper mantle, which may serve as a viable mechanism for early lunar magmatisms. The settling of cold downwellings on the core‐mantle boundary stimulates a transient high heat flux, which may contribute to generating an early lunar dynamo event.

show abstract

“…Unresolved questions about the lunar dynamo also prompted research into dynamos generated within basal magma oceans 37 (layers of molten silicates immediately above the core-mantle boundary), as has been proposed for the [38][39][40][41] . For example, core convection in Earth's Moon may provide insufficient energy to sustain a lunar dynamo for the duration and at the intensities indicated by palaeomagnetic data 42 .…”

Section: Core and Dynamo Formationmentioning

confidence: 99%