An impact melt flow scenario to form the pure native sulfur deposit at Gale crater

The Curiosity rover recently discovered a deposit of native sulfur (S⁰) in Gediz Vallis, Gale crater, composed of decimetric light-toned blocks forming a 60 m wide talus. Such accumulations are rare on Earth and typically require volcanic, hydrothermal, or bio-mediated processes, yet the Martian deposit challenges direct terrestrial analogies. While previous studies proposed subsurface clathrate decomposition as a source, we propose an alternative scenario involving a sulfur flow produced by meteoritic impact melting of the light-toned yardangs unit upstream, hypothesized to be enriched in volcanic native sulfur. A 390 m-diameter, 80 m-deep breached crater is identified as the possible source of the melt flow that traveled 4 km down Gediz Vallis. Considering the low viscosity of sulfur, thermal modeling of the flow confirms that the travel time would be shorter than its crystallization time. The molten sulfur would then pool, crystallize, and exsolve the remaining gases, including H₂S, forming subspherical cavities as observed in the blocks. The sulfur outcrop is also laterally wedged with a near-horizontal upper contact, consistent with a low viscosity melt filling the channel. The high purity and rhombic crystal habit of the sulfur blocks, along with an apparent increase of the number of gas bubbles from bottom to top, further support in-situ crystallization from a single melt pool. In-situ reflectance spectroscopy reveals that dust obscures the native sulfur signal on naturally exposed blocks, explaining why its presence could not be detected from the orbit.

This scenario implies that the light-toned yardangs unit, previously interpreted as eolian deposits and possibly linked to the Medusae Fossae formation, may represent a new type of distal volcanic deposit enriched in native sulfur. Such deposits could provide new insights into Hesperian atmospheric and volcanic processes, as well as Mars’ magmatic evolution. The Curiosity rover is planned to investigate this unit during its fifth extended mission, offering an opportunity to test this hypothesis and refine our understanding of sulfur cycling on early Mars.