Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusm.p31b..03v&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #P31B-03
Physics
6250 Moon (1221)
Scientific paper
The Tycho impact crater is an 85 km diameter complex crater thought to be of Copernican age (50 to 100 Ma) [1]; evidence of its young age is provided by the rays that spread outwards radially [1]. In addition to the large coherent melt sheet in the crater interior, impact melt ponds are also abundantly observable in and around the Tycho impact crater; they range from the lowest topographic area within the crater, to isolated slumped portions along the crater walls and on the crater rim. They have also been observed well beyond the crater as far as 74.8 km away (0.88 crater radii) [2]. In this study, we investigate the nature, origin, and emplacement of impact melt materials within and around the Tycho impact crater, using a GIS database of lunar imagery and terrestrial analogue studies. It is notable that the majority of the melt ponds are observed in the eastern sector of the crater (within and outside of the rim), with the highest melt pond concentration within the crater in the east-northeast corner. This geographic distribution is thought to originate from the obliquity of the impact [1, 2]. Emplacement of melt along the crater rim occurred on top of the ballistic ejecta. Thus, melt emplacement and ponding must have occurred following the deposition of the ballistic ejecta blanket during the modification stage of crater formation (within minutes after the initial impact). Around the Tycho melt ponds, there are signs of fluidic flow patterns, indicating the melt flowed in a viscous state shortly after deposition; there are also cooling cracks, which form as the melt contracts while cooling rapidly. As the impact melt has a tendency to follow topography, it will inevitably accumulate in areas of lowest elevation [2]. But what is the emplacement mechanism(s) for these melt ponds? The evidence above suggests these melt bodies were emplaced as flows outwards from the crater centre during the modification stage of crater formation. Refs: [1] Morris, A.R., et al., 2000, Impact melt distribution and emplacement on Tycho: a new look at an old question: LPSC. [2] Hawke, B.R. and Head, J.W., 1977, Impact melt on lunar crater rims: In: Impact and Explosion Cratering, p. 815-841.
Osinski Gordon
Veillette Dan
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