Candidate Mud Volcanoes in the Northern Plains of Mars

Details Candidate Mud Volcanoes in the Northern Plains of Mars Candidate Mud Volcanoes in the Northern Plains of Mars

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.v13b1346k&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #V13B-1346

Mathematics

Probability

1824 Geomorphology: General (1625), 5462 Polar Regions, 5480 Volcanism (6063, 8148, 8450), 6225 Mars, 8426 Mud Volcanism

Scientific paper

Domes in the the `Borealis back-basin' (centre 76N 160W) on Mars resemble products of mud volcanism (MV) on Earth. Description of domes: Our mapping shows ~30 Early Amazonian domes in the back-basin (~50 x 40 km, height ~300 m). Many have marginal and central peaks (~7 x 5 km, height ~400 m), and moats ~2.5 km wide. Domes are rough at km-scale; some have central depressions; some have annular ridges. Mean rise/run is (0.93±0.22)%. Dome orientations, and alignments of multiple domes, run parallel to the continuation of grabens associated with Alba Patera diking [1]. Distributary channels are found in association with one dome. Aspect-frequency plots for the domes region show significant deviations from randomness. (Detrended) slopes facing S or N are more common than other aspects; local maxima are (S±5°) and (N±5°). N-facing slopes are more abundant than S-facing slopes, so mean S- facing slope must be steeper. A control region at the same latitude shows no comparable anomaly. Interpretation: Many worlds show igneous volcanism, but only Earth has confirmed MV. So, when assessing an extraterrestrial construct, one should assign a high prior probability to igneous volcanism. However, (1) Dome morphologies can be matched with MV in the Caspian Basin and Cadiz Gulf [2], though Martian domes have diameters ~5 times greater. (2) Moat morphometry excludes flexural origin and suggests a collapse origin. Collapse moats are often associated with MV on Earth. (3) Aspect anomalies suggest that near-surface dome material was subject to insolation-driven processing, requiring dome near-surface material to have been partially volatile [3]. (4) Volcanic constructs are rare closer to Alba Patera, inferred to have triggered dome construction. So there must be a major increase in the fusibility of materials in our basin. In the absence of Martian granites, volatile-rich deposits satisfy this requirement. (5) Mars' thick sediment piles permit MV. Crater fill studies suggest that the Scandia and Borealis back- basins contain the greatest thickness of cover in the Northern Plains, making these preferred MV locations [4]. We infer that domes may well result from MV. Outstanding puzzles: We currently lack a compelling mechanism for expulsion in the extensional tectonic setting required for dyking. One possibility is direct triggering of MV through intersection of dyke fluids with a volatile-rich sediment column. OMEGA spectra of domes show no significant differences between dome and non-dome terrain. Band depth methods and linear unmixing models [5] yield compositions uniformly dominated by ferric oxides and pyroxenes. This may be due to recent mantling, or MV may tap a source layer of similar composition to adjacent plains. Implications: Post-Hesperian cover in our study area is too thin for MV; older sediments are probably the source. These may record catastrophic flooding or oceans. Our results have implications for the ease of future drill-rig access to these ancient deposits. There is also a tempting geographic link with young evaporates [6]. [1] K.L.Tanaka (2006), 4th Mars Polar Sci., Abs. #8024. [2]L.Somoza et al. (2003), Mar. Geol. 195, doi:10.1016/S0025-3227(02)00686-2. [3] M.A.Kreslavsky and J.W.Head (2003),GRL 30, doi:10.1029/2003GL017795. [4] D.Buczkowski(2007),JGR-E, doi:10.1029/2006JE002836. [5] J.- P.Combe(2005),PhD thesis, U. Nantes. [6] K.E.Fishbaugh et al.(2007),JGR-E 112, doi:10.1029/2006JE00286.

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