Diverse and highly differentiated lava suite in Jezero crater, Mars: Constraints on intracrustal magmatism revealed by Mars 2020 PIXL

Abstract

The Jezero crater floor features a suite of related, iron-rich lavas that were examined and sampled by the Mars 2020 rover Perseverance, and whose textures, minerals, and compositions were characterized by the Planetary Instrument for X-ray Lithochemistry (PIXL). This suite, known as the Máaz formation (fm), includes dark-toned basaltic/trachy-basaltic rocks with intergrown pyroxene, plagioclase feldspar, and altered olivine and overlying trachy-andesitic lava with reversely zoned plagioclase phenocrysts in a K-rich groundmass. Feldspar thermal disequilibrium textures indicate that they were carried from their crustal staging area. Bulk and mafic minerals have very high FeO and low MgO to FeO_total ratios, which are partially reproduced by thermodynamic models involving high-degree fractional crystallization of a gabbroic assemblage and possibly also assimilation of iron-rich basement. Together, these in situ constraints on petrogenesis provide a uniquely detailed record of intracrustal processes beneath Jezero crater during a time period not represented by Mars samples to date.

Fig. 1.. Geologic traverse map and interpretive cross section with locations of PIXL analyses.

The stratigraphic positions of Beaujeau and Guillaumes are somewhat uncertain due to complexity of the exposures along the southern part of the traverse (54). Both could represent the Nataani member. The Alfalfa abrasion is located at the Sid outcrop, a block isolated from the main mass of the Ch’al member possibly by erosional retreat of the Ch’al member margin. Units were observed to dip on the order of 5° to 10° away from the interior of Séítah. The Content member of the Séítah fm is basaltic and appears to unconformably overlie layered olivine cumulate wehrlites (89) but is not represented here due to its limited exposure. Two sets of paired core samples for MSR correspond with the Bellegarde and Alfalfa abrasions. A summary of Máaz names, including core sample names, is in table S2.

Fig. 2.. Máaz fm microscopic images and PIXL element and diffraction maps.

(A) Merged SHERLOC WATSON and PIXL MCC microscopic images of PIXL map scan areas outlined in blue for targets Montpezat 2, Guillaumes, Bellegarde, Beaujeu 2, and Alfalfa. Labeled fields in (A) indicate regions for correlation between images. (B) Decorrelation stretched images of MCC multispectral channels near-infrared–green–blue (723, 535, and 447 nm). (C) PIXL red-green-blue (RGB) maps, corrected for topography and diffraction (table S6 and Supplementary Materials). Red FeO, green Al₂O₃, and blue CaO. (D) Red TiO₂, green K₂O, ad blue P₂O₅. (E) Red FeO, green SO₃, and blue Cl. Colors are oversaturated where concentrations are greater than the color scale. (F) X-ray diffraction profiles. Diffraction patterns for each PMC are represented by hues on the color wheel where diffraction magnitude (0 to 3 natural log units relative to nondiffracting baseline) is represented by color intensity (black = no diffraction, bright colors = strong diffraction), and the different colors represent combinations of diffraction peaks observed in eight energy bins from 0.8 to 12.8 keV. Black areas are either amorphous or microcrystalline below the resolution of PIXL (<30 to 50 μm). As diffraction patterns reflect a combination of mineral identity and crystallographic orientation, detection of the same pattern (color) over multiple contiguous PIXL spots generally indicates a monomineralic crystalline domain, and single-color grains correspond to monocrystalline minerals.

Fig. 3.. Summary of regions of interest (ROIs) used for determining corrected bulk compositions in Máaz fm abrasion target scans.

ROIs include low salt, salt-rich, and Fe-silicate alteration that is also enriched in Cl and is defined in the table S4 caption. Targets are listed in order of decreasing Mg#. For each of the four abraded Máaz fm Targets, the ROI map and binary plots of SO₃ versus Cl, Na₂O versus Cl, and FeO_T versus Cl are shown. (A) Montpezat 2, binary plots also include points from Montpezat 1 line scan; (B) Guillaumes; (C) Bellegarde; and (D) Alfalfa.

Fig. 4.. Diagrams comparing PIXL corrected igneous bulk compositions and Mars igneous compositions.

(A) Total alkali versus silica diagram for Mars igneous compositions, including shergottite nakhlite chassignite (SNC) meteorites, Jezero crater Máaz and Séitáh fm PIXL abraded targets raw and corrected igneous bulk compositions and SuperCam natural surface and abrasion patch average compositions (Table 1) (, , –104). Basaltic shergottite Zagami and differentiated shergottites are also plotted (27, 43, 63, 105, 106). (B) Basaltic shergottite Zagami-normalized element abundance diagram with Máaz fm abraded targets and select evolved martian meteorites (27, 43, 63, 106).

Fig. 5.. Jezero crater floor PIXL mineral endmember compositions.

PIXL data are compiled in Table 2, table S5, and (41). Mineral compositions determined from Máaz natural surfaces and abrasion patches by SuperCam (36) as well as compositional fields for early to late-stage minerals found in select evolved martian meteorites are also plotted (43, 44). (A) Pyroxene enstatite (En)–wollastonite (Wo)–ferrosilite (Fs) ternary diagram with “1-kbar forbidden zone” (28) indicated by thick black line; (B) Olivine forsterite (Fo)–fayalite (Fa) binary plot; (C) Feldspar albite (Ab)–orthoclase (Or)–anorthite (An) ternary diagram.

Fig. 6.. Alfalfa PIXL maps and diagrams demonstrating feldspar textures and compositions.

(A) PIXL red-green-blue maps for the Alfalfa abraded target, where red is K₂O, green is Al₂O₃, and blue is SiO₂, corrected for effects of topography and diffraction. Corroded pl-1 feldspar is partially resorbed with an embayment, indicating thermal disequilibrium. A low-K reaction rim (bluish purple) surrounds larger feldspars and is distinct from K-rich groundmass (pink). (B) Map of plagioclase anorthite content (An#) determined for feldspar phenocrysts in Alfalfa. Both pl-1 and pl-2 display reverse zonation, and pl-1 also exhibits oscillatory zonation. (C) Plot of K₂O versus Al₂O₃ presents the PIXL data as a three-component mixture of high-Al feldspar, high-K groundmass, and low K, Al phases, including mafic minerals, Fe oxides, and silica that are identified on the basis of PIXL XRF compositions. SuperCam (SCAM) points are from (36). (D) CaO-FeO-Al₂O₃ (mol %) ternary plot with endmember mineral fields and feldspar reaction rim highlighted to demonstrate that the rim is composed of a fine-grained mixture of feldspar (identified by high Al and Ca with low Fe), pyroxene (identified with high Ca and Fe with low Al), Fe-silicates, and Fe oxides (identified with high Fe relative to Ca and Al).

Fig. 7.. Equilibrium and fractional crystallization of a Montpezat parental magma at 0.1 GPa.

Calculated Perple_X models (79) (version 6.9.0) liquid lines of descent (LLD) and Máaz igneous compositions presented on plots of (A) SiO₂ versus MgO, (B) FeOt versus MgO, (C) CaO versus MgO, and (D) K₂O versus MgO. Máaz igneous compositions are renormalized to 100% without P₂O₅ and MnO to be consistent with the calculated LLD since the model does not include P₂O₅ and MnO. See the Supplementary Materials for modeling details.