Distribution and surface morphology of debris-covered glaciers and the latitude dependent mantle (LDM) in Phlegra Montes, Mars

Mars hosts mid-latitude debris-covered glaciers, also referred to as viscous flow features (VFFs) that record past climate and former surface ice stability. Using a newly developed Confinement Index (CI), we categorize 479 VFFs, ranging from fully confined (CI = 1) to fully unconfined (CI = 0). Our results show that CI values decrease at northern latitudes (>40° N), where low-relief landscapes host only unconfined glaciers. A focused analysis of 83 of these isolated lobate debris aprons (LDAs), a subtype of VFFs that encircle bedrock massifs, shows that massif centroids become increasingly offset southward relative to the centroids of their surrounding LDA complexes towards higher latitudes, indicating preferential ice accumulation or preservation on pole-facing slopes. SHARAD radar data from a small number of sites ( n = 3) implies that the total ice thickness increases with latitude, with a maximum thickness of ∼390 m at 48° N. We identify five surface textures associated with LDAs, Lineated, Knobby, Smooth-Undulating , and Scalloped texture classes, which exhibit latitudinal trends in occurrence and extent. We interpret the Lineated texture class (30-44° N) as a relict of glacier flow that commonly occurs adjacent to the Knobby texture class (28-44° N) with gradational lateral contacts. We interpret the Smooth-Undulating (∼40-46° N) and Scalloped (>44° N) texture classes as expressions of the latitude dependent mantle (LDM), a thin, ice- and dust-rich deposit that blankets the mid-latitudes and varies systematically with latitude. The Smooth-Undulating texture class reflects a range of surface roughness and the Scalloped texture class consists of clusters of quasi-circular depressions bounded by arcuate scarps and gently sloping floors. We interpret the Scalloped texture class as a degraded form of the LDM, consistent with relatively ice-rich material. Our findings suggest that the LDM, deposited episodically due to obliquity-driven climate variations, modulates and/or is modulated by the subsurface ice within VFFs. Over time, ice degradation, sublimation, and debris redistribution shape the LDM surface morphology, producing surface textures that reflect latitudinal variations in its emplacement and stability, and its interaction with underlying debris-covered glaciers.