Download Partial melting and the thermo-chemical evolution of terrestrial planets

Unraveling the interior dynamics of planetary bodies
Partial melting and the thermo-chemical evolution of terrestrial planets
N. Tosi, A.-C. Plesa, C. Huettig, M. Maurice, S. performance scales nearly linearly with up to several
Padovan, A. Nikolaou, Department of Astronomy thousand cores (Figure 1). This makes Gaia one of
and Astrophysics, Technische Universität Berlin
the few mantle convection capable to make effective
use of large-scale computational infrastructures.
In Short
• Motivation: Surface features like volcanoes and
tectonic plates observed on terrestrial bodies of
the Solar System are a direct consequence of the
dynamics of the deep interior, which is strongly
affected by the production of partial melt.
• Goals: Understand the thermo-chemical evolution of the interior of terrestrial bodies by linking
present-day observations with state-of-the-art numerical simulations of solid-state convection in
planetary mantles.
• Constraints: Space missions deliver data on the
morphology and composition of the surface and
crust of planetary bodies, on their gravity and magFigure 1: Code performance using a grid with 11.5 × 106 (red
netic field, and surface heat flow, all of which can line) and 54 × 106 (green line) computational points. With the
be used to constrain models of the thermochemi- largest mesh, Gaia scales nearly linearly with up to 54000 cores.
cal evolution of the interior.
Mercury’s Thermal Evolution and Impacts
• HPC features: To investigate the interior dynamThe surface of Mercury is covered by craters,
ics of planetary bodies we use the mantle convecmostly
formed in the early phases of the planet’s evotion code Gaia: a finite volume, massively parallel
lution.
Each impact generates a shock front which
code capable to run efficiently on several tens of
propagates
in the interior. The associated shockthousand cores.
energy is ultimately converted into a temperature
anomaly which, for very large events, can interact
Solid-state mantle convection is the primary mecha- with and modify the underlying convection pattern
nism that controls the dynamics and thermal evolu- (Figure 2).
tion of the Earth and terrestrial planets. Thermal and
compositional buoyancy drive the slow creeping flow
of silicate mantles, which is ultimately responsible
for the heat transport from planetary interiors to the
surface and for the formation of geological structures
impact
such as volcanoes, rifts, and tectonic plates.
location
As the style of convection is known rather poorly
either from seismological observations – available
solely for the Earth and to a lesser extent, the Moon,
and representative only of the present-day state of
Temperature
0
1
the mantle – or, indirectly, from the study of geological structures, our main understanding stems from
Figure 2: Temperature distribution in the interior of Mercury
numerical simulations of the dynamics of the mantle. shortly after a basin-forming impact. Such phenomena strongly
In the present project we perform numerical simu- modify the planform of convection and the production of partial
lations of thermochemical mantle convection using melt.
the 2D-3D code Gaia [1], with the goal of constraining the thermochemical evolution of the interior of
We focused on the effects of large impacts on
Mercury, the Moon, and Mars. Gaia’s performance the melt production in the basin area and on the
has been tested using meshes with up to 54 million depth of the source region for this melt. Our models
grid-points. For a sufficiently large mesh, the code show that the properties (volume and depth of the
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source region) of the melt sheets observed within
large basins are mostly the result of the state of the
mantle at the time of impact. By tuning the models
to the properties of the well-studied melt sheet of the
Caloris basin, our model can explain the observed
properties of the major impact basins on Mercury.
This result indicates that the combination of numerical models of the effects of large impacts on the
interior dynamics with remote sensing observations
of the melt sheets can place important constraints
on the mantle evolution as a function of time.
Present-day mantle plumes on Mars
The presence of mantle plumes at present-day
in the interior of Mars has been inferred from geologic mapping of young lava flows of only several
million years in the Elysium and Tharsis volcanic
provinces. Another indication comes from the analysis of the Martian meteorites, which suggests that
the temperatures derived from shergottitic samples,
which are the youngest samples from Mars, possibly indicate the presence of thermal anomalies in
the interior of Mars. However, whether such thermal
anomalies in the interior of Mars are active at present
and how long have they been stable underneath
large volcanic centers on Mars is unknown (Figure
3). We have started investigating what are the condi-
InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport), due to launch
in 2018 (http://insight.jpl.nasa.gov), will aim at improving our understanding of the thermochemical
evolution and present-day state of Mars [2].
Early Stage of Planetary Evolution and Mantle
Mixing
On Earth and other terrestrial bodies, large scale
compositional heterogeneities may have formed during the early stage of planetary evolution by fractional crystallization of a liquid magma ocean or later
by partial melting of the mantle. The mixing efficiency of such heterogeneities is directly linked to
the convection vigor and style (i.e., mobile or stagnant lid). In order to make reliable predictions of the
mixing efficiency in a 3D geometry using a strongly
temperature-dependent viscosity as appropriate for
the interior of terrestrial bodies, numerical simulations with high spatial resolution need to be employed (Figure 4). Such simulations need to be carried out until they reach statistical steady state in
order to accurately quantify mantle mixing and to
derive suitable scaling laws. Because of these requirements, up to now, most of the studies of mixing
in a 3D geometry have been limited to simple isoviscous models. Nevertheless, thanks to the good
parallel scalability of our code, Gaia we will be able
to investigate scenarios with strongly variable viscosity for 3D configurations.
(a)
(b)
0.9
Temperature
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Figure 4: 3D numerical simulations of thermal convection with
a strongly temperature-dependent viscosity that will be used to
accurately quantify mantle mixing in the stagnant lid regime.
WWW
Figure 3: Present-day mantle plumes in the interior of Mars
shown together with the MOLA topography for the southern highlands.
https://sites.google.com/site/nictosi/
More Information
[1] C. Hüttig, N. Tosi, W.B. Moore (2013),
tions leading to the formation and survival of mantle
Phys. Earth Planet. Inter., doi:
plumes in the interior of Mars up to the present-day.
10.1016/j.pepi.2013.04.002
Preliminary results show that while the depth dependence of the viscosity plays an important role for the [2] Plesa et al., (2016). J. Geophys. Res. – Planets, manuscript in press.
presence of strong thermal anomalies, the crustal
structure may influence their location. Furthermore,
Funding
our models together with the upcoming seismic and
heat flow measurements from the NASA mission Helmholtz Gemeinschaft (VH-NG-1017)
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