| Title | Impact melt sheet formation on Mars and its implications for hydrothermal systems and exobiology |
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| Author | Pope, K O; Keiffer, S W; Ames, D E |
| Source | Icarus vol. 183, 1, 2006 p. 1-9, https://doi.org/10.1016/j.icarus.2006.01.012 |
| Year | 2006 |
| Alt Series | Earth Sciences Sector, Contribution Series 2005494 |
| Publisher | Elsevier BV |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Area | Mars |
| Subjects | extraterrestrial geology; igneous and metamorphic petrology; metamorphism; metamorphism, shock; hydrothermal deposits; hydrothermal systems; meteorite craters; craters |
| Illustrations | tables; graphs |
| Program | Targeted Geoscience Initiative (TGI-1), 2000-2003 |
| Program | Consolidating Canada's Geoscience Knowledge |
| Abstract | Hydrothermal deposits are a prime exobiological research target on Mars and impact craters are potentially a significant source for these deposits. Key factors in the longevity of terrestrial impact
crater hydrothermal systems are the volume of shock melt produced and the degree to which this melt is quenched by mixing with un-melted clasts. Mixing occurs when the shock melt is smeared along the crater floor, and the degree of mixing is
inversely proportional to the thickness of this smeared layer. To investigate the potential development of thick melt sheets on Mars, we apply an analytical impact model to asteroid and long-period (LP) comet impacts that produces martian craters
with final diameters of 30--640 km. We combine our model shock melt volumes with estimates of the surface area of the transient cavity to estimate initial shock melt thickness, which we use as a proxy measure of the amount of mixing between shock
melt and un-melted clasts. We calculate this shock melt thickness parameter for a range terrestrial craters with and without thick melt sheets, from which we infer the melt sheet characteristics for the model Mars craters. The results demonstrate
that most asteroid impacts on Mars do not produce thick, clast-free melt sheets. Only asteroid impact craters greater-or-equal-to 580 km in diameter on previous termMarsnext term produce shock melt thicknesses comparable to Earth's 200-km-diameter
Sudbury crater, and martian craters less-than-or-equal-to 65 km in diameter produce shock melt thicknesses comparable to terrestrial craters that lack melts sheets entirely. LP comet impacts on Mars are more likely to produce thick melt sheets. LP
comet impact craters greater-or-equal-to 280 km in diameter on Mars produce shock melt thicknesses comparable to that of the Sudbury crater. Given that LP comet impacts on Mars are rare compared to asteroid impacts, we conclude that large, long-lived
impact hydrothermal systems are likewise rare on Mars. Comparisons of the Mars asteroid impact rate with the potential longevity of impact hydrothermal systems indicate that such systems were active <1% of the time in the last 3.5 Ga, which raises
questions about the exobiological importance of impact crater hydrothermal systems on Mars after the Noachian. |
| GEOSCAN ID | 221435 |
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