HR: 17:45h
AN: P34A-06    [Abstracts]
TI: Hydrothermal Processes in Impact Craters on Mars: Implications From Lonar Crater, India, and Other Craters.
AU: * Newsom, H E
EM: newsom@unm.edu
AF: Institute of Meteoritics, Dept. of Earth and Planetary Sci., University of New Mexico, Albuquerque, NM 87131 United States
AU: Nelson, M J
EM: mel14@unm.edu
AF: Institute of Meteoritics, Dept. of Earth and Planetary Sci., University of New Mexico, Albuquerque, NM 87131 United States
AU: Shearer, C K
EM: cshearer@unm.edu
AF: Institute of Meteoritics, Dept. of Earth and Planetary Sci., University of New Mexico, Albuquerque, NM 87131 United States
AU: Misra, S
EM: saumitra@gg.iitkgp.ernet.in
AF: Dept. of Geology and Geophysics, Indian Institute of Technology, Kharagpur, 721 302 India
AB: Impact craters played an important role in aqueous and geochemical processes in the near-surface environment of Mars, including chemical transport and soil formation. The formation of large craters on Mars resulted in hydrothermal systems that lasted for tens to hundreds of thousands of years and probably resulted in the mobilization of salts onto the surface of Mars. We have been carrying out extensive studies of impact deposits from several terrestrial analog craters, including Mistastin, Lonar, and Chicxulub using SIMS, XRF, XRD and EMP techniques. Even small craters may have been important for surface processes on Mars based on our recent work at the Lonar, India crater. The relatively small Lonar crater (1.8 km diameter) is one of only two known terrestrial craters to be emplaced in basaltic target rock [1], and our work has led to a new model for the rock component of the martian soil involving a component of hydrothermally altered basalt [2]. Based on the work of Hagerty and Newsom [1], this crater is the smallest known crater with a substantial post-impact hydrothermal system. Our work on the nature of hydrothermal alteration in drill cores from the crater floor of Lonar and Chicxulub includes mobilization of trace elements, such as lithium, beryllium, and boron, based on our new SIMS analyses. In January of 2004 during fieldwork at the Lonar crater we discovered previously unknown alteration zones in the ejecta blanket around the rim of the crater. The ejecta blanket at Lonar extends beyond 1350 m from the rim with discontinuous patches as far as 3000 m. These consist of areas in the ejecta blanket on the order of 20 to 50 meters in extent that are moderately to highly altered. Preliminary analysis shows a depletion of K2O, Na2O and Fe2O3 in the material from the altered zones compared to the fresher basalt blocks. The recent fieldwork at the crater and examination of drill core material from the ejecta blanket suggests that the ejecta blanket is far more important for geochemical transport and hydrothermal alteration in small craters than had previously been realized. The discovery of alteration zones in the ejecta blanket is consistent with evidence for fluid flow (carbonate deposition) in a drill core north of the crater in the ejecta blanket. [1] Hagerty, J.J. and Newsom, H.E. (2003) Meteoritics and Planetary Science, 38, 365-381, [2] Nelson M.J., Newsom, H.E. and Draper D. (2004), in review.
DE: 5410 Composition
DE: 5415 Erosion and weathering
DE: 5420 Impact phenomena (includes cratering)
DE: 6225 Mars
DE: 3665 Mineral occurrences and deposits
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting