Magma ocean solidification and the dichotomous lunar crust (fully funded PhD studentship, DAMTP)

Plate tectonics on Earth is often thought to have emerged as a the terrestrial magma ocean solidified following the giant Earth-moon impact (Ćuk & Stewart, 2012). However, on the active Earth’s surface, this process is difficult to reconstruct. Instead the remains of this early lunar crust are relatively well preserved, which exhibits a relatively light anorthosite crust with a remarkable hemispherical dichotomy in the observed crustal thickness (Wieczorek et al. 2013). Fluid motion driven by the cooling of the early magma ocean is also recorded in the early paleomagentic field, which shows peak strengths comparable to the present day terrestrial field (Weiss & Tikoo, 2014). Understanding the compositional differentiation and solidification of the magma ocean and the formation of the lunar crust therefore provide a unique opportunity to understand processes of planetary formation with direct implications for the Early Earth.

This project will explore three aspects of planetary evolution:

  1. By coupling a model of a convection with compositional boundary layers at the top of the solidifying magma ocean the timescale of lunar crustal formation will be constrained.
  2. Using laboratory experiments on fluids with a temperature-dependent viscosity, an experimental map of the transition from overturning to stagnant-lid convection will be made, and extrapolated to constrain the start of crustal preservation on the moon.
  3. The heat flux from the base of magma ocean will be used to drive a simple lunar dynamo model, and compared to paleomagnetic measurements.

The student will help develop a set of parameterised models of convection in a solid-fraction and temperature dependent medium, the crystallising lunar magma ocean. The output of these simple parameterised models will be compared with modern re-analysis of Apollo era samples, remote geophysical measurements of the lunar topography and gravity anomaly, as well as some seismic and paleomagentic records. In parallel, the student will help design, run and analyse a suite of experiments to study the transition between overturning convection (in which the surface is recycled) and stagnant-lid convection (in which the crust is preserved). The project will involve some visits to ENS-Lyon to work with Prof. Michaut.

  • Ćuk, M., Stewart, S.T. (2012) Making the Moon from a fast-spinning Earth: A giant impact followed by resonant despinning. Science. 338(6110), 1047-1052.
  • Wieczorek, M.A. et al. (2013) The crust of the Moon as seen by GRAIL. Science. 339(6120), 671-675.
  • Weiss, B.P., Tikoo, S.M. (2014) The lunar dynamo. Science. 346(6214), 1198-1208.

For additional information please contact Jerome Neufeld.