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Can a fractionally crystallized magma ocean explain the thermo-chemical evolution of Mars?

Plesa, A.-C. and Tosi, Nicola and Breuer, D. (2014) Can a fractionally crystallized magma ocean explain the thermo-chemical evolution of Mars? Earth and Planetary Science Letters, 403, pp. 225-235. Elsevier. DOI: 10.1016/j.epsl.2014.06.034 ISSN 0012-821X

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Official URL: http://www.sciencedirect.com/science/article/pii/S0012821X14004191

Abstract

The impact heat accumulated during the late stage of planetary accretion can melt a significant part or even the entire mantle of a terrestrial body, giving rise to a global magma ocean. The subsequent cooling of the interior causes the magma ocean to freeze from the core-mantle boundary (CMB) to the surface due to the steeper slope of the mantle adiabat compared to the slope of the solidus. Assuming fractional crystallization of the magma ocean, dense cumulates are produced close to the surface, largely due to iron enrichment in the evolving magma ocean liquid. A gravitationally unstable mantle thus forms, which is prone to overturn. We investigate the cumulate overturn and its influence on the thermal evolution of Mars using mantle convection simulations in 2D cylindrical geometry. We present a suite of simulations using different initial conditions and a strongly temperature-dependent viscosity. We assume that all radiogenic heat sources have been enriched during the freezing-phase of the magma ocean in the uppermost 50 km and that the initial steam-atmosphere created by the degassing of the freezing magma ocean was rapidly lost, implying that the surface temperature is set to present-day values. In this case, a stagnant lid quickly forms on top of the convective interior preventing the uppermost dense cumulates to sink, even when allowing for a plastic yielding mechanism. Below this dense stagnant lid, the mantle chemical gradient settles to a stable configuration. The convection pattern is dominated by small-scale structures, which are difficult to reconcile with the large-scale volcanic features observed over Mars' surface and partial melting ceases in less than 900 Ma. Assuming that the stagnant lid can break because of additional mechanisms and allowing the uppermost dense layer to overturn, a stable density gradient is obtained, with the densest material and the entire amount of heat sources lying above the CMB. This stratification leads to a strong overheating of the lowermost mantle, whose temperature increases to values that exceed the liquidus. The iron-rich melt would most likely remain trapped in the lower part of the mantle. The upper mantle in that scenario cools rapidly and only shows partial melting during the first billion year of evolution. Therefore a fractionated global and deep magma ocean is difficult to reconcile with observations. Different scenarios assuming, for instance, a hemispherical or shallow magma ocean, or a crystallization sequence resulting in a lower density gradient than that implied by pure fractional crystallization will have to be considered.

Item URL in elib:https://elib.dlr.de/114232/
Document Type:Article
Title:Can a fractionally crystallized magma ocean explain the thermo-chemical evolution of Mars?
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Plesa, A.-C.ana.plesa (at) dlr.deUNSPECIFIED
Tosi, Nicolanicola.tosi (at) dlr.deUNSPECIFIED
Breuer, D.doris.breuer (at) dlr.deUNSPECIFIED
Date:1 October 2014
Journal or Publication Title:Earth and Planetary Science Letters
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:403
DOI :10.1016/j.epsl.2014.06.034
Page Range:pp. 225-235
Editors:
EditorsEmail
Sotin, C.Jet Propulsion Laboratory M/S 321-625 4800 Oak Grove Drive Pasadena, CA 91109
Publisher:Elsevier
ISSN:0012-821X
Status:Published
Keywords:Mars,magma ocean, mantle reservoirs, mantle overturn, chemical gradient, thermo-chemical convection
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Vorhaben Exploration des Sonnensystems
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research
Institute of Planetary Research > Planetary Physics
Deposited By: Rückriemen, Tina
Deposited On:20 Sep 2017 10:31
Last Modified:01 Dec 2018 19:53

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