HR: 0800h
AN: P11A-0951    [Abstracts]
TI: The evolution of volcanic material on Mars: Preliminary results of sand-lavas relationships from the analogy with sandy lavas in Iceland
AU: Mangold, N
EM: mangold@geol.u-psud.fr
AF: Orsay-Terre, FRE 2566, OrsayTerre, Bat 509 Universit\'e d'Orsay, Orsay, F-91405 France
AU: * Baratoux, D
EM: david.baratoux@cnes.fr
AF: Observatoire Midi-Pyr\'en\'ees, Laboratoire Dynamique Terrestre et Plan\'etaire, UMR 5562, 14 Avenue Edouard Belin, Toulouse, F-31400 France
AU: Arnalds, O
EM: oa@rala.is
AF: RALA, Keldnaholt vid Vesturlandsveg, Reykjavik, 112 Iceland
AU: Gr\'egoire, M
EM: michel.gregoire@cnes.fr
AF: Observatoire Midi-Pyr\'en\'ees, Laboratoire Dynamique Terrestre et Plan\'etaire, UMR 5562, 14 Avenue Edouard Belin, Toulouse, F-31400 France
AU: Platevo\"et, B
EM: platvoet@geol.u-psud.fr
AF: Observatoire Midi-Pyr\'en\'ees, Laboratoire Dynamique Terrestre et Plan\'etaire, UMR 5562, 14 Avenue Edouard Belin, Toulouse, F-31400 France
AU: Bardintzeff, J M
EM: bardizef@geol.u-psud.fr
AF: Observatoire Midi-Pyr\'en\'ees, Laboratoire Dynamique Terrestre et Plan\'etaire, UMR 5562, 14 Avenue Edouard Belin, Toulouse, F-31400 France
AU: Chevrier, V
AF: RALA, Keldnaholt vid Vesturlandsveg, Reykjavik, 112 Iceland
AU: Pinet, P
EM: patrick.pinet@cnes.fr
AF: Observatoire Midi-Pyr\'en\'ees, Laboratoire Dynamique Terrestre et Plan\'etaire, UMR 5562, 14 Avenue Edouard Belin, Toulouse, F-31400 France
AU: Math\'e, P E
EM: mathe@cerege.fr
AF: CEREGE, Europle M\'editerran\'een de l'Arbois - BP 80, Aix en Provence, F-13545 France
AU: Rochette, P
EM: rochette@cerege.fr
AF: CEREGE, Europle M\'editerran\'een de l'Arbois - BP 80, Aix en Provence, F-13545 France
AB: The surface of Mars is covered by volcanic rocks from few tens of millions years to 3.5 by old. The presence of water and atmosphere can strongly affect these rocks, by both chemical and mechanical erosion and transport. The interpretation of multispectral and hyperspectral data of Mars requires a better comprehension of these surface processes in order to understand if the spectral data still corresponds to the volcanic composition at the time of formation. Volcanic material in Iceland is a good analog for the studies of possible landforms resulting from the formation, transport and deposition of basaltic sand on Mars. Iceland is amongst the unique places on Earth with a cold environment, abundant basaltic rocks and sands, and the presence of palagonite, a possible typical constituent of the Martian soil. A first field campaign has been achieved in fall 2003, with the objectives of sites selection and chemical analysis of sands and lavas in order to establish the sources of sands, and the mineralogical and chemical evolution from lava to sands. The first site is close to Skjalbreidur volcano, south of Langjokull and is composed of weathered lava blocks, sands and gravels. The second sampling site is close to Eldborgir volcano, also south of Langjokull, weathered lava flows and sands are observed here. The third sampling site is around Hekla volcano. The results of the chemical analysis indicate different situations for the origin of sands. For the first two sites, major, minor and traces elements are correlated and indicate that the sands, which are basaltic in composition, are genetically related to the surrounding lava. The sands at Hekla volcano, andesitic in composition, indicate a contamination of material eroded from basaltic lava flow by a more silicic component erupted from Hekla. Sands coming from different sources, of possibly different chemical and mineralogical composition, and of different nature of eruption can easily mix each other which has implications for the interpretation of infra-red data of the surface of Mars. A second result concerns the evolution of the mineralogical composition of basaltic sand compared to the lava. We observed a higher concentration of MgO and Ni in Skjalbreidur and Eldborgir sands than in the surrounding lava taken as a reference. Together, these observations indicate a higher concentration of olivine in the sands which may be due to its higher strength (compared to feldspaths and pyroxene) and sorting by wind from different grain size. On the other hand, the contribution of weathering seems not have destructed these olivine grains. Indeed, magnetic results show that magnetic phases such as titanomagnetite are poorly weathered despite being at the surface since 9000 years. The weathering by the wet climate is likely slow down by the cold temperatures all the year long. The detection of olivine at the surface of Mars is thus not a simple tool to conclude that the weather did not involve liquid water.
DE: 5415 Erosion and weathering
DE: 5470 Surface materials and properties
DE: 5480 Volcanism (8450)
DE: 5757 Remote sensing
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting