Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31e1738o&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31E-1738
Other
[3672] Mineralogy And Petrology / Planetary Mineralogy And Petrology
Scientific paper
An analysis of the 1μm olivine spectral signature applied to the entire and final OMEGA dataset [1] shows numerous olivine-bearing deposits in the 3 main basins of Mars (Argyre, Isidis and Hellas). These signatures are among the strongest of Mars, which suggests compositions with higher iron content and/or larger grain size and/or larger abundance than the ones of widespread olivine-bearing deposits observed on large parts of the southern highlands [1]. A spectral modeling based on a radiative transfer model [2] indicates that their compositions are still close to the forsterite one with abundance in the range of [15,40%] and grain sizes of a few hundreds of μm. These deposits are exclusively localized on Noachian terrains. Distribution of these deposits around Argyre basin clearly takes the form of discontinuous patches of olivine-bearing rocks on the basin terrace, which strongly suggest that their formation is related to the basin formation event. Recent numerical simulations of basin formation show that impact that formed the Argyre basin could have excavated upper mantle materials and emplaced discontinuous patches of melted mantle on the basin terraces [3]. The observed olivine deposits in Argyre are thus interpreted as olivine-bearing material excavated from the upper mantle during the impact. Olivine deposits distribution around the Hellas basin is not as clear as for Argyre because of young resurfacing processes that strongly affected its region. Olivine deposits are fewer and mainly localized on the northern terrace of Hellas. Most of them are detected in crater ejecta, while a few similar to Argyre olivine discontinuous patches are also observed suggesting that a mantle origin as for Argyre is possible. Olivine has been detected by several datasets in the Nili Fossae region and in the south of Isidis basin. The spectral modeling of OMEGA spectra indicates an olivine abundance of about 40% and megacrysts of several millimeters for the region of Nili Fossae [2]. Several plausible hypotheses has been discussed to explain this unusual concentration of olivine-rich outcrops in Nili Fossae assuming three possibilities for their emplacement relative to the formation of the Isidis basin : pre-impact [4,5], contemporaneous [6], or post-impact [7]. The pretty unique settings and compositions of these deposits in comparison to the two other major basins indicate a different origin, with the post-impact one as the preferred one. Other several localized exposures with strong olivine signature are also found throughout the southern highlands and the northern plains mostly associated with craters. Olivine-bearing material is found in craters floors but also in some crater ejecta implying the presence of an olivine-rich underlying layer. Of special interest are some craters totally filled by olivine-rich lava lakes, which could have erupted through local (impact-related) fractures. [1] A. Ody et al. (2011) LPSC XXXXII.[2] F. Poulet et al. (2009), Icarus 201, 84-101.[3] Stewart S. (2010) AGU, San Francisco, abstract #P43A-08. [4] Hoefen et al. (2003) Science,302,627-630.[5] Hamilton and Christensen (2005), Geology,33,433-436.[6]J.F. Mustard et al. (2007), JGR, 112, E08S03.[7] L.L Tornabene et al. (2008), JGR, 113, E10001.
Bibring J.
Carter Jennifer
Gondet Brigitte
Langevin Yves
Ody A.
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