¹Cyril Sturtz,¹Angela Limare,¹Marc Chaussidon,¹Édouard Kaminski
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115100]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris, F-75005, France
Copyright Elsevier

Meteorites are interpreted as relics of early formed planetary bodies, and they provide information about the processes that occurred in the first few of our solar system. The ages measured for some differentiated meteorites (achondrites), indicate that planetesimals formed a differentiated silicate crust as early as after the beginning of the solar system. The composition of the recently discovered achondrite Erg Chech 002 (EC002), the oldest andesitic rock known so far, betokens partial melting of a chondritic source taking place as early as before all other known achondrites. However, thermal models of early accreted planetesimals predict massive melting of the planetesimal during core/mantle differentiation and cannot account for the preservation of a substantial amount of chondritic material. In this paper, we propose a way to interpret petrological and geochemical constraints provided by differentiated meteorites by introducing a refined thermal model of planetesimals formation and evolution. We demonstrate that continuous, protracted accretion of cold undifferentiated material upon a magma ocean over a timescale 2 times larger than the lifetime of the 26Al heat source leads to the preservation of a few km thick chondritic crust. During accretion, the heat released by radioactive decay further induces episodes of partial melting at the base of the crust, which can led to the formation of andesitic rocks such as EC002. Using the available constraints on the age of EC002 and its cooling rate, the application of our model constraints the terminal radius of its parent body between 70 and .

¹Andrew Rodriguez,¹Lindsey Hunt,²Charity Phillips-Lander,³Daniel Mason,¹Megan Elwood Madden
Icarus (in Print) Link to Article [https://doi.org/10.1016/j.icarus.2022.115111]
¹OU School of Geosciences, United States of America
²Southwest Research Institute, United States of America
³UNM School of Earth and Planetary Sciences, United States of America
Copyright Elsevier

Salts and basalt are widespread on the surface of Mars. Therefore, basalt-brine interactions may have significant effects on both the aqueous history of the planet, and near-surface alteration assemblages. Raman spectra were collected from McKinney Basalt samples that were immersed in eight near-saturated brines composed of Na-Cl-H2O, Na-SO4-H2O, Na-ClO4-H2O, Mg-Cl-H2O, Mg-SO4-H2O, and two salt mixtures (Mg-Cl-SO4-H2O and Na-ClO4-SO4-H2O), as well as ultra-pure water for up to one year. Secondary minerals were observed in the Raman specta, including iron oxides, hydrated sulfates, amorphous silica, phosphates, and carbonates. Detection of these secondary minerals demonstrates the utility of Raman spectroscopy to identify basalt-brine alteration assemblages on Mars. This work also demonstrates that major classes of alteration phases can be distinguished using Raman spectra with resolution similar to those expected from the Raman instruments aboard the Perseverance and Rosalind Franklin Mars rovers. In addition, observations of carbonate minerals within alteration assemblages suggest CO2 from the atmosphere readily reacted with ions released from the basalt during alteration in near-saturated brines.