Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53f..04b&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53F-04
Other
[5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering, [5422] Planetary Sciences: Solid Surface Planets / Ices
Scientific paper
The use of Shallow Radar (SHARAD) on Mars Reconnaissance Orbiter (MRO) to map the oldest ice-rich members of the Planum Boreum stratigraphic column has revealed a complex irregular surface. As a distinction between the Rupes Tenuis and Planum Boreum Cavi units is difficult to ascertain with radar, the older term basal unit (BU) applies to both units. The BU is not a simple mounded deposit with post-depositional erosion of the margins, as hypothesized in earlier works [Byrne and Murray, 2002; Fishbaugh and Head, 2005]. Zones of strong relief on the BU correspond in several regions to surface features that are poorly understood indicating that paleotopography might play a controlling role in the formation of Mars’ north polar layered deposits (NPLD). Small graben features and associated pits have been identified on Planum Boreum Mars in the region above western Olympia Cavi [Nunes, 2006; Nunes et al., 2007; Tanaka et al., 2008]. Shear stress modeling indicates that internal stresses alone are not sufficient to cause brittle failure at the surface [Nunes et al., 2007]. Another explanation [Tanaka et al., 2008] for these zones of brittle failure is that differential stress within Planum Boreum has allowed for normal fault nucleation at depth, with propagation to the surface. A further hypothesis states that differential compaction of material above the Cavi unit resulting from the presence of troughs on its surface, could account for normal fault formation [Tanaka et al., 2008]. BU mapping of this zone indicates that while troughs may not have been prevalent on the surface of Cavi there is a distinct topographic signature in this region not found elsewhere. The correlation of unique BU topography and unique NPLD surface topography indicates a probable link between the two. While this spatial correspondence does not necessarily indicate causation it does provide a new context for analyzing topographic expression on the NPLD of Mars and evaluating stress states. Furthermore, the western Olympia Cavi grabens and their correspondence to BU mapping is not the only example of BU correspondence to modern topographic expression. Two additional regions identified thus far are the Abalos Colles reentrant and a large, linear ridge on the poleward side of Chasma Boreale. In general, the location of cutbacks and reentrants in the BU has a strong correspondence to irregular NPLD topography. Mapping of the early Amazonian BU has therefore revealed a correlation between modern topography and BU topography, a correlation that is likely to expand our understanding of Planum Boreum evolution.
Brothers T. C.
Holt Jeremy William
Tanaka Ken L.
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