18-3 Putative volcaniclastic inverted channels on Hadriacus Mons, Mars: Martian model for hydrothermal alteration of tuff

Session: Surface Processes Across the Solar System

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Abstract:

Sinuous ridges with locally anatomizing, segmented morphologies have been observed on Hadriacus Mons, Mars (31.29°S, 91.86°E), originating proximal to the summit caldera complex (Hadriaca Patera) and extending down the shallow flanks (<2°) of this volcano. Mapping at Thermal Emission Image System Daytime Infrared (THEMIS Daytime IR; 100m/pixel) scale, with ConTeXt Camera images (CTX; ~6m/pixel) as needed, reveals that the sinuous ridges are generally oriented radial to, and reach distances up to 50 km downflank from, Hadriaca Patera. Their topographic relief appears to be similar to that of adjacent flank materials, suggesting that the ridges originate within these materials and are exhumed as flank materials are eroded. The sinuous ridges exhibit consistent widths (~300 m) over lengths of tens of kilometers; are locally separated into ~0.4-1 km-long segments; may intersect with other sinuous ridges; and on occasion, cross valley floors. We propose that these sinuous ridges are volcaniclastic inverted channels, formed by hydrothermal alteration of welded tuff from groundwater interaction with heated pyroclastic deposits.

Hadriacus Mons’ edifice is interpreted to be pyroclastic deposits (ignimbrite and welded tuff) with an extensive history of valley network modification from groundwater processes. Comparison of the sinuous ridges’ morphologies to terrestrial and putative Martian eskers, sediment-capped (fluvial) and lava-capped inverted channels, and volcanic and clastic dikes, reveals some similarities; however, we observe no diagnostic associated features or landforms typically seen in fluvial, glacial, or effusive volcanic environments. The sinuous ridge’s spatial distribution on Hadriacus Mons’ flanks, ridge crest morphology, and equidistant widths, are consistent with an origin relating to Hadriacus Mons’ pyroclastic formational and groundwater history. Hydrothermal alteration of tuff may explain these features, similar to the fumarolic pinnacles of the tuff of Valley of Ten Thousand Smokes, southwest Alaska, and Crater Lake, Oregon, USA. We propose the following formational model. 1) Formation of paleo-channels from flowing water dissecting the flank. 2) Deposition of tuff into pre-exisiting channels, which had either wetted banks or contained liquid water. 4) Subsequent hydrothermal alteration of heated tuff deposits with the wetted channel banks and subsurface water. Continual groundwater movement aided in hydrothermal welding as deposits cooled over time. 5) Exhumation of the indurated, differentially welded tuff through subsequent erosion.

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