An exposed magmatic feeder system for the regional olivine unit in Nili Fossae, Mars

The origin of the >100,000 km² regional olivine unit in the Nili Fossae-Jezero region has been variously attributed by orbital studies to airfall, effusive lavas, impact melt, or intrusive emplacement. In situ characterization of olivine-bearing igneous rocks in Jezero crater by the Mars 2020 Perseverance rover has revealed olivine cumulate textures indicative of effusive or intrusive magmatism, but conduits in the shallow-crustal feeder system that transported olivine-saturated magma have not been identified. Here we combine sub-meter pansharpened imagery from the Colour and Stereo Surface Imaging System (CaSSIS) and the High Resolution Imaging Science Experiment (HiRISE) with near-infrared spectral analysis from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to characterize a population of olivine-rich ridges and elongated features that crosscut the Fe/Mg-smectite basement at the "Horseshoe" site in Nili Fossae, ∼200 km north of Jezero. The features display a continuum of morphologies, from planar dike-like ridges through sinuous and braided lineaments that locally crosscut topography. Analysis of the 1 µm olivine near-infrared absorption places the features along the same compositional trend as the regional olivine–carbonate assemblage, and CRISM spectra resolve weak 1.9 and 2.32 µm absorptions diagnostic of hydrated/hydroxylated phases, indicating partial alteration of the intrusive olivine. We interpret these features as exhumed magmatic intrusions in a hydrated smectite basement, possibly exploiting pre-existing fault networks, and propose that they form part of a broader Jezero-Nili Fossae magmatic province. Magma-clay contact zones of this kind may provide a unique class of habitable environments in the shallow Noachian crust of Mars.