The 61st GRC & The 6th MEXT Shin-Gakujutsu "Core-Mantle Coevolution”
International Frontier Seminar

Thermo-chemical-tectonic
evolution of terrestrial planets:
the key influence of magmatism
Dr. Paul J. Tackley (Professor, ETH Zurich, Zurich, Switzerland)
Date: 1.16.2017 (Mon.) 16:30 – 18:30
Venue: Meeting Room #486, Science Research Bldg 1, Ehime Univ.
Convection of the rocky mantle is the key process that drives the evolution of Earth’s
interior: it causes plate tectonics, controls heat loss from the metallic core (whichgenerates the magnetic field) and drives long-term volatile cycling between theatmosphere/ocean and interior. It is now possible to numerically model the evolution of aterrestrial planet from the magma ocean stage to the present day using a 2D or 3D model ofthe mantle-lithosphere system couped to a parameterized model of the core (andsometimes, atmosphere), including the effects of magmatism and variations in tectonicmode. Previous works have identified stagnant lid, episodic overturn and mobile lid (platetectonics) as possible tectonic modes, depending on the effective strength of thelithosphere and convective parameters. Simple scalings [1] as well as more complex
models [2] indicate that plate tectonics should be easier on larger planets (super-Earths),
other things being equal. Our recent models find that melting has several key effects onplanetary evolution. Firstly, it produces compositional heterogeneity in the lithosphere,
including continental cratons [3] and basaltic crust [4], which facilitate plate tectonics byfocussing or producing stresses, making it ‘easier’ for the lid to break. Thus, scaling lawsthat are based on purely thermal convection cannot be literally applied to planetaryevolution. Secondly, magmatism acts as a thermostat on mantle temperature, losing large
amounts of heat when the mantle is hot, when internal heat production is high such as
early in a planet’s evolution [5] or in a stagnant-lid mode – [6] showed that in a stagnant-lid
Venus-like planet most of the heat loss is accommodated by magmatic heat pipe volcanism.
Thirdly, it can produce compositional stratification in the deep mantle, which modules heat
flux from the core, determining geodynamo evolution [7]. Additionally crust may besubstantially weaker, and regional models that take this weakness into account find thatsignificant crustal deformation or even internal convection may take place under Venus-likeconditions [8], which would mean that Venus-like planets do not have a real stagnant lid but
rather a “squishy-lid” tectonic mode.

Contact: Prof. Taku Tsuchiyatsuchiya.taku.mg@ehime-u.ac.jp

Figure 1. Simulations of the terrestrial planets as labelled.

References[1] H. van Heck and P.J. Tackley, Earth Planet. Sci. Lett. 310, 252-261 (2011).
[2] P.J. Tackley, M. Ammann, J.P. Brodholt, D.P. Dobson & D. Valencia, Icarus
225, 50-61 (2013).
[3] T. Rolf & P.J. Tackley, Geophys. Res. Lett. 38, doi:10.1029/2011GL048677(2011).
[4] D. Lourenco, A. Rozel & P. J. Tackley, Earth Planet. Sci. Lett., in press.
(2016).
[5] T. Nakagawa & P.J. Tackley, Earth Planet. Sci. Lett. 329-330, 1-10 (2012).
[6] M. Armann & P.J. Tackley, J. Geophys. Res. 117, doi:10.1029/2012JE004231(2012).
[7] T. Nakagawa & P.J. Tackley, Geophys. Geochem. Geosyst. 11,doi:10.1029/2010GC003031 (2010).
[8] Gerya T. V., Earth Planet. Sci. Lett. 391, 183-192 (2014).

Key words Mantle convection, plate tectonics, Mars, Venus, stagnant lid.