Widespread ancient anorthosites in the lower crust of Mars

Understanding when and how evolved rocks formed on terrestrial planets remains a fundamental question in planetary geology. Mars preserves ancient surface rocks, providing unique opportunities to study early crustal formation. Here we report extensive detections of feldspathic, possibly anorthositic, rocks uplifted by the Argyre basin-forming impact using orbital remote sensing. The radial distribution of these feldspathic outcrops indicates they originated from the lower martian crust, positioned stratigraphically between olivine-bearing materials and low-calcium pyroxene-bearing upper crustal rocks. This stratigraphy resembles observations at the Hellas basin, suggesting feldspar-rich rocks are widespread in the lower crust. The spatial association of plagioclase-rich outcrops with pyroxene and olivine-bearing units resembles layered mafic intrusions on Earth, suggesting large-scale melting early in Mars’s history produced differentiated igneous complexes. These observations offer direct evidence to support and refine existing models of early crust formation, addressing key questions regarding crustal properties and formation that have lacked widespread observational constraints. Spectrally feldspathic lithologies, stratigraphically located in the lower crust above olivine-bearing material and below low-Ca pyroxene bearing rocks, are exposed in the Argyre impact basin and observed in data from the Mars Reconnaissance Orbiter.