Formation and Alteration History of the Olivine-Carbonate Lithology at Jezero Crater

Abstract:

Background. The outcrop of the olivine-clay-carbonate lithology at Jezero crater is one of the key reasons for the selection of this location as the landing site for the Mars2020 rover. First discovered by Hoefen et al. (2003), we have continued to unravel further details regarding the characteristics of the lithology. The unit was discovered to be carbonate-bearing using CRISM data (Ehlmann et al. 2008) and extends over the rim of Jezero crater, and therefore must have been emplaced after the crater formed (Goudge et al. 2015). Figure 1 shows a map of the olivine unit as mapped by Kremer et al. (2019), and the delta at Jezero, as mapped by Goudge et al. (2015) .

Population zero olivines. The olivine unit in the Nili Fossae region displays large grain sizes (>500 microns) and is medium Fo# (45-65) (Brown et al., 2020). We use the term “population zero” for these olivines, since they show zero clay, hydration or carbonate bands. They are, however, closely associated with the serpentinised or carbonatised olivine-carbonate lithology that outcrops at Jezero and elsewhere in the broader Nili Fossae region (e.g., Ehlmann et al., 2008; Kremer et al., 2019).

What can we learn from Mars2020? In this contribution, we will discuss the possible relationship between the population zero olivine and the -carbonate altered olivine available at Jezero. We will discuss further a suite of hypotheses about the population zero olivines that may be tested in situ at Jezero crater by the Mars 2020 mission. The potential hypothesis that the clay-carbonate is carbonated population zero type olivine will be further discussed.

Figure 1 – (left) Nili Fossae and olivine carbonate from Kremer et al. 2019 (right) Jezero crater delta and map units of Goudge et al. (2015). “+Ol” means olivine band is present. “-Ol” means weak olivine band present.