Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p41a1352b&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P41A-1352
Other
1034 Hydrothermal Systems (0450, 3017, 3616, 4832, 8135, 8424), 5419 Hydrology And Fluvial Processes, 5420 Impact Phenomena, Cratering (6022, 8136), 6225 Mars
Scientific paper
A km-scale bolide delivers enough energy to heat subsurface water, and drive hydrothermal circulation (Abramov and Kring, 2005). This post-impact hydrothermal (PIH) circulation can lead to surface discharge of water, and chemical alteration - both are potentially detectable. We present the effects that permeability and freezing have on discharge and water:rock (W/R) ratios. We simulate the evolution of PIH systems using MAGHNUM (detailed in Travis et al., 2003). MAGHNUM solves the time-dependent transport of water and heat through a porous medium, incorporating phase transitions between ice (applicable to Mars), vapor and water. PIH evolution depends on heat sources and permeability (k); these, in turn, control discharge and chemical alteration which depends on both the peak temperatures and the W/R ratio (Schwenzer and Kring, 2008). Recently, CRISM detected phyllosilicate-rich material within ~45 km craters (Mustard et al., 2008) and the HiRISE camera imaged gullies, some emanating from central peaks, within many high latitude craters. We model a 45 km crater created by a 3.9 km dia., 7 km/s impactor. Simulations run for 100,000 yrs in a 2D axisymmetric domain with a heat flux of 32.5 mW m-2. Thus far we have tested systems with a range of surface k's (10-4 to 1 darcys) that decay exponentially with depth and are exposed to two surface temperatures (5°C and -53°C). In general W/R ratios increase with increased k. Focusing in on the upper 200 m at the center of the crater, fluid temperatures remain > 100°C for 9000 yrs and flow yields W/R ratios of 10 when exposed to a surface temperature of 5°C. Dropping the surface temperature below freezing to a Mars-like - 53°C maintains upper 200 m temperatures > 100°C for only 600 yrs and W/R ratios are reduced to 1. Higher permeabilities yield higher W/R ratios but reduced time exposure to high temperatures. When surface temperatures are below freezing total system discharge is roughly independent of k for modest permeabilities but the time until the surface freezes increases with lower k. Freezing reduces both W/R ratios and discharge because ice closes pores and restricts flow.
Barnhart Charles J.
Nimmo Francis
Travis Bryan J.
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