Basaltic Rocks Analyzed by the Spirit Rover in Gusev Crater

Abstract

The Spirit landing site in Gusev Crater on Mars contains dark, fine-grained, vesicular rocks interpreted as lavas. Pancam and Mini-Thermal Emission Spectrometer (Mini-TES) spectra suggest that all of these rocks are similar but have variable coatings and dust mantles. Magnified images of brushed and abraded rock surfaces show alteration rinds and veins. Rock interiors contain Յ25% megacrysts. Chemical analyses of rocks by the Alpha Particle X-ray Spectrometer are consistent with picritic basalts, containing normative olivine, pyroxenes, plagioclase, and accessory FeTi oxides. Mössbauer, Pancam, and Mini-TES spectra confirm the presence of olivine, magnetite, and probably pyroxene. These basalts extend the known range of rock compositions composing the martian crust.Rocks at the Spirit landing site are finegrained with irregular vesicles and vugs, suggesting a volcanic origin. The rocks are angular and strewn across the surface, which suggests they were ejected from nearby Bonneville crater (1) by an impact event (2).Pancam and Mini-Thermal Emission Spectrometer (Mini-TES) spectra of rock surfaces indicate two end members, represented by dark-and light-toned rocks, with most rocks falling between these extremes. Three representative rocks, Adirondack, Humphrey, and Mazatzal, located several hundred meters apart, have been analyzed with the Athena instruments (3). Pancam images (4) show that Adirondack and Humphrey are partly coated and that Mazatzal is uniformly coated by light-toned material (Plates 9A, 10A, and 11A). Pancam spectra (Fig. 1) of the dark portions of Adirondack and Humphrey are consistent with the presence of olivine, which has a broad (composite) absorption band near 1000 nm. A weak band center near 930 nm suggests the presence of pyroxene or contamination by ferric oxides.The long-wavelength portion of Mini-TES spectra of dark rock surfaces resembles the Mars Global Surveyor (MGS)-TES spectra of

Spectroscopic evidence for hydrous iron sulfate in the Martian soil

“…We suggest that chemical weathering of rock to form soil destroys the chemically fragile olivine, hence, it would not survive to become a soil component. This interpretation is supported by the presence of alteration rinds on the Gusev rocks that show possible olivine casts, indicating that olivine has weathered away [McSween et al, 2004].) Additionally, HIS provides a good fit to the extended-visible soil spectra from IMP and Pancam.…”

Distribution of rocks on the Gusev Plains and on Husband Hill, Mars

“…[19] The presence of only meters of regolith across much of Husband Hill is counterintuitive considering the younger, surrounding plains [Crumpler et al, 2005;Arvidson et al, 2006] are comprised of harder rocks [McSween et al, 2004;Arvidson et al, 2006], and were described as being capped by more than 10 meters of unconsolidated debris [Grant et al, 2004;Golombek et al, 2006]. The apparently thicker regolith on the plains, however, likely reflects the occurrence of an initially rubbly and/or fractured substrate, which is commonly associated with primary volcanic surfaces [MacDonald, 1972].…”

“…[3] Gusev crater was selected as the landing site for the Spirit rover with the intention of sampling sedimentary deposits emplaced during discharge from Ma'adim Vallis, which breaches the southern rim of the crater [Cabrol et al, 1996[Cabrol et al, , 1998a[Cabrol et al, , 1998bKuzmin et al, 2000;Irwin et al, 2002;Golombek et al, 2003a;Grant et al, 2004]. The surface traversed by the Spirit rover after landing (14.5692°S, 175.4729°E), however, is characterized by impact-modified volcanic plains of late Hesperian age [Milam et al, 2003;Squyres et al, 2004;Grant et al, 2004;McSween et al, 2004;Crumpler et al, 2005;Golombek et al, 2006] and Husband Hill to the southeast that is older than the surrounding plains (at least early Hesperian [Kuzmin et al, 2000, Greeley et al, 2005, but perhaps Noachian) and of uncertain origin [Squyres et al, 2006;Arvidson et al, 2006]. We examined the rock population of the surfaces at regular intervals along the traverse of the Spirit rover ( Figure 1) to determine whether there was any significant variability among presumably different geomorphic surfaces that might reflect a fluvial/alluvial contribution to the impact-derived blocks and/or modification by weathering or alternate geomorphic processes.…”

Quantifying the amount of impact ejecta at the MER landing sites and potential paleolakes in the southern Martian highlands

“…[2] Mars, like other terrestrial planets, has been extensively modified by impacts large and small: from the heavily-cratered, presumably ancient southern highlands terrane [Strom et al, 1992] to small rocks tossed out by the tiny Bonneville crater near the Spirit landing site [McSween et al, 2004]. However, unlike the abundant impact breccias in the lunar and meteorite collections, the igneous nature of the Martian meteorites provides little information about impact mixing and comminution on Mars.…”

“…However, it is difficult to infer the total thickness of inferred fluvial or lacustrine sediment packages in these craters. For instance, Gusev crater is shallower than expected and has a clear fluvial system running into it [Cabrol et al, 1998], but numerous sediment sources beside fluvial and lacustrine have been suggested as being able to at least partially fill Gusev, including aeolian deposits, ashfall from Appolinaris Patera [Milam et al, 2003], and basaltic lava flows [Martinez-Alonso et al, 2005;McSween et al, 2004]. This paper gives constraints on the maximum thickness of ballistically-emplaced crater ejecta that might be present at several sites on Mars to examine its importance relative to the numerous other sedimentation processes operable on Mars.…”