Mineralogy of the Nili Fossae region with OMEGA/Mars Express data: 1. Ancient impact melt in the Isidis Basin and implications for the transition from the Noachian to Hesperian

Abstract

[1] The Nili Fossae region located on the northwestern quadrant of the Isidis Basin, Mars, displays superb exposures of bedrock outcrops that reveal mineralogy and composition of the crust. Previous work has shown that this region exhibits the largest exposures of olivine-dominated rock units on Mars. Visible-infrared imaging spectrometer data acquired by OMEGA were calibrated to surface reflectance and analyzed to determine surface mineralogy. The dominant minerals identified are iron-bearing mafic silicates (low-and high-calcium pyroxene, olivine) and water-bearing phyllosilicate (iron-rich smectite clay). The strength and position of mineral absorption features were used to produce mineral indicator maps for the dominant species, and the maps were integrated with high-resolution imaging from the THEMIS, MOC, and HRSC instruments, and MOLA topography. We show that olivine and phyllosilicate occur in spatially distinct outcrops; the olivine-bearing rock unit is a meters-to tens of meters-thick cap unit resting on phyllosilicate-bearing bedrock, and the phyllosilicate units predate the Isidis basinforming event. On the basis of superposition, crosscutting, and geomorphic relationships, we interpret the emplacement of the olivine-bearing units as having been contemporaneous with the Isidis impact event. By analogy with the Orientale basin on the Moon, we propose that the olivine-bearing unit represents the surface exposure of the impact melt from the Isidis impact event. These results demonstrate that large regions of crust had been altered in the presence of water prior to the date of the Isidis basin-forming event in the Late Noachian (%3.96 Ga).

New evidence for a magmatic influence on the origin of Valles Marineris, Mars

“…In addition, the identification of Fe/ Mg-rich hydrated phyllosilicates exposed along faults using CRISM supports the hypothesis that (mafic) phyllosilicates can be observed on Mars at locations where tectonism interacts with water (e.g., Mustard et al, 2007).…”

“…OMEGA and CRISM have both identified a significant number of locations of hydrated sulfates Gendrin et al, 2005;Murchie et al, in press) and hydrated phyllosilicates Poulet et al, 2005;Milliken et al, 2008b;Bishop et al, 2007;Mustard et al, 2007;Bishop et al, 2008a,b;McKeown et al, 2008;Mustard et al, 2008) on the Martian surface, as well as other hydrated minerals, such as hydrated silica (Milliken et al, 2008a,b;Bishop et al, 2008a). One such locality is the Claritas rise.…”

Color imaging of Mars by the High Resolution Imaging Science Experiment (HiRISE)

“…15A) are more representative of ferric bearing materials (e.g., alteration products and dust). Olivine-rich units identified by multiple spectral datasets (Hamilton and Christensen, 2005;Mustard et al, 2007;Tornabene et al, 2008), are well defined in both the HiRISE IRB and color band-ratio images (cyan and blue, respectively). Olivine-poor basaltic materials as defined by TES and THEMIS specifically (Hamilton and Christensen, 2005;Tornabene et al, 2008) and described as ''spectrally neutral" by the OMEGA and CRISM spectral datasets due to their lack of distinctive absorption features (e.g., Mustard et al, 2007Mustard et al, , 2008 can be resolved in the HiRISE color products and are indeed distinctive from the olivine-rich variety of basaltic surface.…”

“…The mineral, lithologic and surface spectra used are shown in Table 3. 2007; Mustard et al, 2007Mustard et al, , 2008. A synthesis of these studies indicates the presence of basaltic materials both rich and poor in olivine, hydrous silicate-bearing materials, and terrains rich in the low Ca variety of pyroxene (e.g., enstatite, pigeonite, etc.).…”

Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument

“…The Nili Fossae region shows expansive outcrops of phyllosilicates 2,12 but also extensive spectral signatures of olivine in close proximity [15][16][17][18][19] . Several high-resolution observations across this region (Fig.…”