Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p21c..11c&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P21C-11
Other
5480 Volcanism (8450), 5764 Surfaces, 6225 Mars, 8135 Hydrothermal Systems (8424), 8404 Ash Deposits
Scientific paper
Large mounds and mesas of interior layered deposits (ILDs) in Valles Marineris Chasmata have been suggested to be sub-ice volcanoes based on MGS and Viking data [1,2,3]. Similar to terrestrial sub-ice volcanoes, spectral investigation indicates the bright mounds are hydrothermally altered, palagonitic rocks [4]. These putative edifices are associated with outcrops of dark materials that have each been interpreted previously as young, volcanic ash deposits of mafic composition [5,6]. Spectral investigation also indicates that the dark materials are less water-altered and mafic in composition [4]. TES-detected concentrations of crystalline hematite have been noted to occur in these dark materials [7]. Mars Observer Camera (MOC) images indicate that the dark materials locally blanket chasmata floors and embay ILDs and are associated with small volcanic vents. These apparent vents may have emitted some of the ash-like deposits. The vent features appear very young, lacking impact craters and having non-eroded rims. Where they embay the ILDs, the vents have low rims similar to terrrestrial maar or tuff cones, which possibly indicates interaction with groundwater or ice. In support of ground-ice within the ILDs, MOC data show (1) channels that occur on the flanks of the bright mounds, and (2) theatre-headed gullies are eroded into caprock of the ILDs and the heads of valleys, formerly interpreted by Viking data to be wind flutes on ILD flanks. Both features may be related to spring sapping. MOC images also show that dark materials on the floor of many chasmata and Aram Chaos are associated with small fissures or cone-shaped mounds with central depressions that do not appear to have interacted with ground-ice. Perhaps late-stage water/ice circulated or was stored within the interior mounds after removal of large ponds of surface ice elsewhere. Young, dark, volcanic ash in the chasmata could be a product of both "dry" volcanism and water/magma interactions, which may have exobiologic implications. References: [1] Croft, S.K., 1990. NASA TM 4210, 539-541. [2] Lucchitta, B.K., N.K. Isbell, A. Howington-Kraus 1994. J. Geophys. Res. 99, 3783-3798. [3] Chapman, M.G. and K.L. Tanaka 2001. J. Geophys. Res. 106, 10,087-10,100. [4] Murchie, S., L. Kirkland, S. Erard, J. Mustard, and M. Robinson 2000 Icarus 147, 444-471. [5] Geissler, P.E., R.B. Singer, and B.K. Lucchitta 1990. J. .Geophys. Res. 95, no. B9, 14,399-14,413. [6] Lucchitta, B.K. 1990. Icarus 86, 476-509. [7] Noreen, E., K.L. Tanaka, and M.G. Chapman 2000. GSA abs. with progs. 32, no. 7, A303.
Chapman Mary G.
Smellie John L.
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