Subsurface Structure and Morphometry of the Wrinkle Ridges in the Late Amazonian Volcanic Unit on Mars

Abstract

Wrinkle ridges are widespread compressional tectonic features on Mars and are important records of the planet's global contractional history. However, their formation, evolution and subsequent modification by other geologic processes remain poorly constrained. Combining radar data, elevation data and high-resolution imagery, we find that the uppermost layer of the Late Amazonian volcanic (lAv) unit is ∼50 m thick and exhibits dielectric properties consistent with porous basalt (${\epsilon }^{\prime }$ = 7.50 ± 0.69; $\tan \delta$ = 0.011–0.077). Stratigraphic analyses and crater dating within the Amazonis Planitia west of Olympus Mons reveal multiple resurfacing events at ∼1.3 Ga, ∼240 Ma, and ∼28 Ma. The estimated volume of the youngest flow is ∼7.50 × 10⁴ km³, and flow thicknesses appear to have progressively decreased over time. Radar and image data demonstrate that the latest lava flow completely buried the preexisting ridges while preserving their subsurface geometry. Wrinkle ridges within the lAv unit differ from global averages, showing enhanced widths, lower heights, larger width-to-height ratios, and reduced elevation offsets. These morphometric deviations suggest substantial post-formational modification by volcanic flooding, topography inflation and sedimentation with potential contributions from varying fault geometry and slip. The modification may have led to an underestimation of derived strain by up to ∼22%. These findings reveal that volcanism both alters surface ridge topography and preserves underlying structure, emphasizing the necessity of radar constraints to reconstruct tectonic history on Mars.