Mathematics – Logic
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p62a0362l&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P62A-0362
Mathematics
Logic
5415 Erosion And Weathering, 5480 Volcanism (8450), 6225 Mars
Scientific paper
Based on calculations of volatile release from estimated total volumes of Cerberus Plains (CP) volcanics and estimated water content of martian basalts, Plescia [1] proposed that water vapor released by CP volcanism may have precipitated over the plains and produced fluvial systems. Since refined measurements of the dimensions of individual lava flows based on MOLA data is now possible, the dimensions of the youngest flows are easy to measure and lower bounds on the dimensions of older, embayed flows can be determined. If magmatically derived water vapor from individual volcanic events precipitated over the plains and provided the water for outflow events, then the mass of dissolved water should equal or exceed the mass of flood waters. Lava flows embaying Marte Valles (MV) extend for at least 1200 km, are roughly 40 km in width within the MV outflow channel, and have flow fronts approximately 25m high. The total volume for these flows is 1.2e3 km3. Assuming a bulk density of 2000 kg/m3 and 0.5 wt% H2O content, this equates to 1.2e13 kg H2O. Burr et al. [2] estimated a discharge of 5e6 m3/s for MV. If all the erupted water vapor were instantly condensed at the vent, it could provide the MV discharge rate for only about an hour. These values may overestimate the quantities of water released if the lavas were not devolatilized completely. It is also unlikely that all the H2O in the lava would contribute to MV flood waters as some of the water would likely be precipitated regionally and result in widespread networks of dendritic channels; networks of small dendritic channels are noted in the vicinity of MV [2], but they are confined to just a few locales. Additionally, it may be unlikely that all the volatiles were released simultaneously as the eruption duration of CP lavas was likely on the order of years [3]. For these reasons, we conclude that condensation from the eruption plume could not form the major erosional flood channels seen in the CP. If the lavas are allowed to devolatilize at depth, water may be allowed to collect over time. Lentz et al. [4] show petrologic evidence for water exsolution for Shergottite parent magmas at depths between 4 and 6 km. Burr et al. [2] calculated that, from the lack of observed topographic subsidence, water for hours-long duration floods may have originated as shallow as a few kilometers deep, consistent with depths at which H2O may begin to exsolve from magmas. However, it is difficult for water vapor to condense and collect close to the magma body. If water that carved the fluvial systems of the CP were exsolved from CP magmas, then water would have to exsolve at depth, possibly due to pressure induced exsolution or co-exsolution with CO2, and migrate away from the magma body until it condenses in a cooler location. While special processes may occur at depth to generate liquid water from CP magmas, it seems more probable that the bulk of water that carved the fluvial systems of the CP is not derived from those magmas. [1] Plescia, J.B., Icarus 104, 20-32, 1993. [2] Burr, D.M. et al., Icarus 159, 53-73, 2002. [3] Keszthelyi et al., JGR 105, 15027-15050. [4] Lentz, R.F.C.et al., Geochim. Cosmochim. Acta 65,4551-4565,2001.
Burr Devon M.
Keszthelyi Laszlo P.
Lanagan Peter D.
McEwen Alfred S.
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