Lunar Thermo-Chemical Evolution

Asymmetric evolution of the Moon

M. Laneuville (IPG, Paris), M.A. Wieczorek (IPG, Paris), D. Breuer (DLR, Berlin) and N. Tosi (DLR/TU, Berlin)

or how to melt the nearside...

44th LPSC18-22 March, 2013

magmatic asymmetry

Motivation

LRO/WAC

NEARSIDE FARSIDE

compositional asymmetryLP/GRS/Mimoun et al., 2011

NEARSIDE FARSIDE

0 2 4 6 8 10 12Thorium (ppm)

Motivation

Observation

1. 99% of volcanism occured on the nearside (~107 km3)

2. Nearside volcanism stopped ~1 Ga ago

3. Sporadic farside volcanism occur until ~3 Ga ago

Constraints

✓ strong heat sources enrichment on the nearside

What do successful models predict?

➡ Initial temperature profile follows magma ocean crystallization

➡ The heat sources are already localized below the PKT

• 2D conduction model (Wieczorek & Phillips, 2000; Hess and Parmentier, 2001)

• 3D thermo-chemical evolution code GAIA (DLR)

• assume rheologie

• assume initial conditions

Method

Model: initial temperature profile

Model: initial heat source distribution

3 possible distribution:- below the crust- at the bottom of the crust- within the crust

Results: cold start, KREEP below the crust

not enoughvolcanism!

Results: hot start, KREEP below the crust

too muchvolcanism!

Results: intermediate start, KREEP below the crust

successful!1. NS melt volume2. NS melt duration3. FS melt volume4. FS melt duration

Results: predicted gravitational signature

result: total gravity signature estimate

- heating the nearside mantle actually increases the heat flow

- it may help having a long lasting chemical dynamo

Results: CMB heat flow evolution and magnetic field

Conclusion & take home messages

1. lunar volcanism can be explained by heat sources enrichment in the PKT

2. it predicts a present temperature anomaly

- Laneuville et al. (2013), submitted to J. Geophys. Res.

3. it influences core evolution

- work in progress