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Journal Articles Geochimica et Cosmochimica Acta Year : 2022

Early differentiation processes on Mars inferred from silicon isotopes


Accretion of terrestrial planets involved partial or global melting events such as magma oceans or magma ponds. Mars experienced large-scale differentiation very early in its history, as shown by its 146 Sm-142 Nd and 182 Hf-182 W record. The broad variations in e 142 Nd and e 142 W of SNC meteorites highlight the presence of mantle sources that must have remained isolated, at least partly, after the crystallization of a global magma ocean. In this study, we have investigated whether the crystallization of the martian magma ocean could have generated mantle reservoirs characterized by different silicon isotope signatures, as the fractionation of Si isotopes between minerals and melts is known to depend on pressure. Thus, the goal of this study was to investigate whether there were any relationships between magma ocean crystallisation and possible variations in the Si isotope record of SNC meteorites. High resolution silicon isotope measurements were performed on twelve meteorites from the Shergottite, Nakhlite and Chassignite groups using a Neptune Plus MC-ICP-MS in dry plasma mode. The d 30 Si values are in good agreement with previous studies but display a narrower range of variations with a mean value at À0.46 ‰ ± 0.07 (2SD). A magma ocean crystallization model shows that the range of d 30 Si in SNCs is consistent with that generated by magma ocean crystallisation. In particular, there is a correlation between calculated 147 Sm/ 144 Nd for the moderately depleted mantle sources with d 30 Si values; this correlation is consistent with the crystallization model if one includes trapped melt in the cumulates. In contrast, enriched shergottites displayed a very homogenous composition in Sm/Nd ratios, despite significant variability in d 30 Si. This observation could be related to either fluid-rock interactions or redox effect during magma differentiation. Altogether, silicon isotope compositions of SNC provide new constraints about magma ocean crystallization processes in Mars.
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Dates and versions

insu-03868762 , version 1 (23-11-2022)



Delphine Losno, Caroline Fitoussi, Bernard Bourdon. Early differentiation processes on Mars inferred from silicon isotopes. Geochimica et Cosmochimica Acta, 2022, 338, pp.11-23. ⟨10.1016/j.gca.2022.10.002⟩. ⟨insu-03868762⟩
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