An intrusive origin for the Nili Fossae regional olivine-bearing unit

Abstract The origin of the olivine-bearing unit in Nili Fossae has been debated for over two decades, with leading hypotheses ranging from pyroclastic falls to aeolian deposits. However, recent in situ data from the Perseverance rover at Jezero crater favor an igneous cumulate origin for intra-crater olivine-rich outcrops, creating a paradox with orbital observations of ‘draping’ morphologies. Here, we present orbital evidence that the regional olivine-bearing unit was emplaced as an extension-controlled intrusion. We identify ‘Large Linear Features’ that exhibit triple junctions, raised bounding ridges, and tapering geometries consistent with feeder dikes aligned with the fracturing of the Nili Fossae. Their characteristics indicate that extensional fracturing of the Noachian crust due to the mass loading of the Isidis basin assisted the ascent of magma in the Nili Fossae region. We resolve the morphological conflict by reinterpreting the unit’s ‘draping’ nature as eroded saucer-shaped sills. This geologic framework implies that the olivine unit formed after Jezero crater and requires extensive erosion in the region, revising the geological timeline of the Perseverance landing site.