Topographical Analysis of Fretted Terrain: Implications for Ancient Martian Super-eruptions
Abstract
Recent work has identified Late Noachian to Early Hesperian plains-style caldera complexes on Mars in western Arabia Terra (AT), eruptions from which might have produced widespread volcanic deposits throughout AT and the entire planet. AT is composed of 2 km thick friable and fretted Late Noachian to Early Hesperian material. Although an ash deposit origin has been suggested for the friable material due to its low thermal inertia, layering, thickness, sulfate abundance, zonal indurations and draped morphology, prior to 2013 no volcanic sources with ability to produce such a deposit were known, and therefore the existence of extensive ash deposits on AT was thought unlikely. Due to recent identification of evidence for ancient super-eruptions in AT such as Eden Patera, the geomorphology of the fretted material warrants reexamination. This study involves a quantitative analysis of eroded valleys throughout the fretted terrain visible at Mars Orbiter Laser Altimeter (MOLA) Digital Elevation Model (DEM) resolution (463 m). These erosion features are mapped objectively via the D8 flow direction algorithm, a technique developed for delineating watersheds with DEMs. The features are then partitioned based on depth and location. Valley orientations are measured for each feature segment and plotted on rose diagrams. To study valley formation mechanisms we use the ratio between high and low stream order lengths (bifurcation ratio) as well as the variance between orientation and primary slope direction. On Earth, bifurcation ratios > 3 and < 5 indicate fluvial erosion is the dominant formation mechanism while values < 3 or > 5 indicate other processes principally formed the valleys and are consistent with the deformation of welded and fractured volcanic deposits. Valleys east of Isidis basin (IB) have bifurcation ratios < 3. West of IB the bifurcation ratios are between 3 and 5, indicating these deposits may be less indurated. Valleys in either location display preference for orientations contrary to down-slope directions. These results suggest that gravity driven erosion is not the single valley formation process throughout the study area. We propose that the AT fretted terrain resembles a network of valleys formed by exploiting angular cooling and compaction fractures in a Late Noachian to Early Hesperian volcanic deposit.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.P13B1938M
- Keywords:
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- 6299 General or miscellaneous;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 5464 Remote sensing;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5470 Surface materials and properties;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5499 General or miscellaneous;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS