¹J.C. Noest, ¹M.J. Sluis, ^1,2J. Alsemgeest, ¹H.J.L. Van der Lubbe, ¹S.J.A. Verdegaal, ¹F.M. Brouwer
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117068]
¹Geology and Geochemistry Cluster, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1105, 1081, HV, Amsterdam, the Netherlands
²Department of Applied Earth Sciences, Science and Earth Observation (ITC), University of Twente, Hallenweg 8, 7522, NH, Enschede, the Netherlands
Copyright Elsevier

Hydrothermal systems can provide a habitat for early life on planetary bodies throughout the Solar System. For Mars, impact-generated hydrothermal systems (IGHSs) are especially interesting, because of its high crater density and the presence of hydrous minerals in Martian craters. However, it is uncertain whether these hydrous minerals formed in an IGHS, or if they formed earlier and were then excavated by the impact. It is also unknown whether conditions in these systems are hospitable for life.
To gain further insight into these open questions, this study investigates two types of vein-forming hydrothermal alteration in the Vargeão Dome impact structure (Brazil) residing in basaltic host rock similar to the Martian surface. Rare Earth Element (REE) patterns of the veins and the surrounding host rock and stable C and O isotopes in calcite were studied using linear regression modelling and thermodynamic modelling to constrain fluid conditions.
REE analysis as proxy for major elements and modelling suggest that elevated amounts of Al, Fe, Mg, and to a lesser extent Na and Ca are needed for the formation of white and red veins. They also suggest that the white veins form under reducing conditions and with limited aquifer influence, whereas the opposite is true for the red veins. Stable isotope signatures indicate that all calcite formed from a meteoric fluid in the same hydrothermal stage as part of the white veins. Furthermore, the thermodynamic modelling suggest that this calcite precipitated from a fluid that underwent gradual heating from 27 to 55 °C combined with degassing of CO2. Together with observed calcite amygdales close to the vein rim and geodes outside of the impact structure, which are both isotopically similar to the calcite in veins, this suggests that the white veins all formed before the impact.
If Martian impact craters are similar to Vargeão Dome, the hydrous minerals are more likely to have been excavated by the impact and did not form as part of an IGHS. However, gradual heating in the Vargeão pre-impact hydrothermal system, as well as the high-nutrient content related to the hydrothermal system, could favour the development of mesophiles in impact-excavated systems on Mars.

¹Timo Hopp, ¹Shengyu Tian, ¹Thorsten Kleine
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117057]
¹Max Planck Institute for Solar System Research; 37077, Göttingen, Germany
Copyright Elsevier

Understanding the origin of the Earth requires determining the original formation location of its building material. Based on the similar Fe isotopic composition of Earth’s mantle and Ivuna-type (CI) chondrites, a prior study has argued that Earth formed by accretion of sunward-drifting pebbles from the outer Solar System. Here, using new high-precision Fe isotopic data, we show however that CI chondrites and Earth’s mantle have distinct Fe isotopic composition when the neutron-rich 58Fe is also considered. This observation rules out that the Fe in Earth’s mantle derives from CI chondrite-like material and demonstrates that Earth did not form by accretion of sunwards-drifting pebbles. We show that the Fe in Earth’s mantle instead derives from the inner Solar System, and has been partly or wholly delivered by bodies from the innermost disk that remained unsampled among meteorites. This provenance of terrestrial Fe is consistent with the classical model of Earth’s formation by hierarchical growth among inner Solar System planetesimals and planetary embryos.