Petrological Traverse of the Olivine Cumulate Séítah Formation at Jezero Crater, Mars: A Perspective From SuperCam Onboard Perseverance

Abstract

Séítah is the stratigraphically lowest formation visited by Perseverance in the Jezero crater floor.We present the data obtained by SuperCam: texture by imagery, chemistry by Laser-Induced Breakdown Spectroscopy, and mineralogy by Supercam Visible and Infrared reflectance and Raman spectroscopy. The Séítah formation consists of igneous, weakly altered rocks dominated by millimeter-sized grains of olivine with the presence of low-Ca and high-Ca pyroxenes, and other primary minerals (e.g., plagioclase, Cr-Fe-Ti oxides, phosphates). Along a ∼140 m long section in Séítah, SuperCam analyses showed evidence of geochemical and mineralogical variations, from the contact with the overlying Máaz formation, going deeper in the formation. Bulk rock and olivine Mg#, grain size, olivine content increase gradually further from the contact. Along the section, olivine Mg# is not in equilibrium with the bulk rock Mg#, indicating local olivine accumulation. These observations are consistent with Séítah being the deep ultramafic member of a cumulate series derived from the fractional crystallization and slow cooling of the parent magma at depth. Possible magmatic processes and exhumation mechanisms of Séítah are discussed. Séítah rocks show some affinity with some rocks at Gusev crater, and with some Martian meteorites suggesting that such rocks are not rare on the surface of Mars.

Carbonate Detection With SuperCam in Igneous Rocks on the Floor of Jezero Crater, Mars

“…Overall, carbonates detected by SuperCam look chemically closest to carbonates reported in nakhlites. LIBS data suggest that they may have a variable Mg#, ranging between 0.42 and 0.70, which is close to the Mg# range covered by olivines detected in Seitah (Beyssac et al., 2023). By contrast, carbonate occurrences in the Máaz formation have different chemical compositions.…”

“… Comparison of the composition of the points where carbonates were detected with laser‐induced breakdown spectroscopy in Jezero, to the carbonates found in Martian meteorites (from Bridges et al., 2019), using molar compositions. The bar at the bottom represents the Mg‐Fe compositions of the olivines identified in Seitah (in both abraded patches and natural surfaces); no olivine was found in rocks of the Maaz formation or the Content member (Beyssac et al., 2023; Udry et al., 2022). …”

“…Within the Séítah fm, a distinct member, called the Content member, was identified (Horgan et al, 2022;Núñez et al, 2022); it differs from Séítah rocks by its morphologythe rocks are pitted-and its composition-less primitive than Séítah rocks and actually close to the composition of Máaz rocks (Wiens et al, 2022). Although primary mineralogy is generally well preserved (Beyssac et al, 2023;Udry et al, 2022), secondary phases are found in both Máaz and Séítah (e.g., Mandon et al, 2022;Meslin et al, 2022;Farley et al, 2022;Tice et al, 2022;Wiens et al, 2022).…”

Samples Collected From the Floor of Jezero Crater With the Mars 2020 Perseverance Rover

“…SuperCam remote micro‐imager (RMI) images of Séítah outcrops show a rock texture comprised of relatively equant 1.0–3.5 mm dark gray‐green particles separated by interstitial lighter‐toned materials. This texture is particularly evident at Bastide (see Beyssac et al., 2023; Wiens et al., 2022).…”

“…Although the SiO 2 abundance is approximately the same in the abraded sites, alkalis measured using SuperCam‐LIBS on the abraded Séítah sites (<1 wt.%) are generally lower than the natural surfaces. SuperCam‐LIBS and Raman spectra indicate olivine Fo 55–60 (Beyssac et al., 2023; Wiens et al., 2022). As shown by the oxide ternary diagram (PIXL data, Figure 10) and total alkali versus silica diagram (SuperCam‐LIBS data, Figure 11), the bulk compositions of the Séítah targets are consistent with an ultramafic rock modified by some degree of aqueous alteration.…”