HR: 08:45h
AN: P11E-04 INVITED    [Abstracts]
TI: Deep Hydrothermal Circulation and Implications for the Early Crustal Compositional and Thermal Evolution of Mars
AU: * Parmentier, E M
EM: em_parmentier@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AU: Mustard, J F
EM: john_mustard@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AU: Ehlmann, B L
EM: bethany_ehlmann@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AU: Roach, L H
EM: leah_roach@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AB: Both orbital remote sensing and geophysical observations indicate an important role for hydrothermal crustal cooling during the Noachian epoch. Orbital remote sensing shows that phyllosilicate minerals are common in Noachian-aged terrains but have not been observed in younger terrains (<3.8 Ga). Throughout the Noachian highlands, phyllosilicates are observed in deeply eroded terrains as well as in association with impact craters, in their walls, rims, ejecta, and in central peaks of craters as large as 45 km, corresponding to excavation depths of 4-5 km. CRISM and OMEGA mapping typically show phyllosilicate-bearing rocks occupy the lowest observable stratigraphic unit, and the most common alteration minerals are iron magnesium smectites which typically form at low pressures and temperatures <200^oC. Widespread occurrences of phyllosilicates to depths of at least 4-5 km may provide evidence for deep crustal hydrothermal circulation during the Noachian. Geophysical evidence from surface deformation associated with faulting and from the analysis of the relationship of gravity and topography suggest elastic lithosphere thicknesses a large as ~30 km near the end of the Noachian, corresponding to surface heatflux of 20-40 mW/m². Relaxation of elastic stresses due to thermally activated creep results in elastic lithosphere thicknesses sensitive to crustal temperatures. Plausible planetary thermal evolution models with chondritic abundances of heat producing elements predict a surface heat flux of 50-60 mW/m² near the end of the Noachian. The difference in the heat flux required for planetary cooling and that inferred from elastic lithospheric thickness, suggests that a significant fraction of heatflow reaching the surface may be transported by hydrothermal convection rather than by conduction alone. Relaxation of crustal thickness variations due to lower crustal flow is sensitive to both the temperature and geothermal gradient at the crust-mantle boundary. In the presence of a low thermal conductivity regolith, thermal evolution models also indicate that crustal thickness variations created during the Noachian would not be preserved, even with a creep-resistant dry diabase rheology. Thus, a mechanism enhancing heat flux in the Noachian Martian crust is indicated. The studies to be reported will summarize these individual constraints on thermal structure and explore their combined implications for the depth and vigor of hydrothermal circulation during the early crustal evolution of Mars.
DE: 5418 Heat flow
DE: 5455 Origin and evolution
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting