HR: 09:30h
AN: P11E-07    [Abstracts]
TI: Modal Mineralogy Of The Martian Phyllosilicate-rich Terrains And Implication For Their Formation
AU: * Poulet, F
EM: francois.poulet@ias.u-psud.fr
AF: Institut d'Astrophysique Spatiale, Batiment 121, Université Paris-Sud, Orsay, 91405, France
AU: Chevrier, V
EM: vchevrie@uark.edu
AF: Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701, United States
AU: Bibring, J
EM: bibring@ias.u-psud.fr
AF: Institut d'Astrophysique Spatiale, Batiment 121, Université Paris-Sud, Orsay, 91405, France
AU: Langevin, Y
EM: yves.langevin@ias.u-psud.fr
AF: Institut d'Astrophysique Spatiale, Batiment 121, Université Paris-Sud, Orsay, 91405, France
AU: Gondet, B
EM: brigitte.gondet@ias.u-psud.fr
AF: Institut d'Astrophysique Spatiale, Batiment 121, Université Paris-Sud, Orsay, 91405, France
AB: Using classical methods of spectral identification based on the absorption band depth of minerals, OMEGA has provided an unambiguous identification of phyllosilicates on the surface of Mars (Poulet et al. 2005, Nature, 438). First constraints on the conditions of their formation were derived (Chevrier et al., 2007, Nature, 448), however the complete story of their formation and their evolution will be fully understood if mineral abundances are known. The modal mineralogy of the phyllosilicate-rich terrains will be presented from the analysis of the OMEGA reflectance spectra using a nonlinear unmixing model based on the Shkuratov radiative transfer theory. Several occurences (regional deposits in Mawrth Vallis and in Nilo-Syrtis, numerous localized deposits in the two hemispheres) are studied in detail. Significant differences in mineral abundances between these regions are found. The modelling of the OMEGA spectra of the phyllosilicate-rich outcrops in Mawrth Vallis requires the largest amount of phyllosilicates (about 60% of nontronite and/or montmorillonite) mixed with hydroxides (ferrihydrite as a very likely end-member) and some non-phyllosilicate materials (plagioclase, Martian dust, pyroxenes). This suggests that the degree of alteration was stronger in Mawrth Vallis than anywhere on Mars. In the NiloSyrtis region, we observe significant spot-to-spot differences in modal mineralogy, and these differences are remarkably consistent with the geomorphology. In the second part of the paper, the modal mineralogy will be compared to kinetic-thermodynamic modeling of weathering of basalt and the implications for the formation of the phyllosilicate-rich terrains will be addressed.
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting