• Energy Research

The Nectarian-aged Crisium basin exhibits an extremely thin crust and complicated lunar geological history. This large multi-ring impact basin is characterized by prolonged lunar volcanism ranging from the Imbrian age to the Eratosthenian period, forming the high-Ti mare unit, low-Ti mare basalts, and very low-Ti mare unit. We produced an updated geological map of the Crisium basin and defined four mare units (Im1: 3.74 Ga; Im2: 3.49 Ga; Im3: 3.56 Ga; EIm: 2.49 Ga) in terms of distinct composition and mineralogy. Olivine was widely determined in the Ti-rich Im1, implying the hybridization source in the lunar mantle with the occurrence of small-scale convective overturn. The major phase of low-Ti basaltic volcanism occurred c.a. 3.5 Ga, forming Im2 and Im3 in the western area. The youngest mare unit (EIm) has slight variations of pyroxene compositions, implying a decrease of calcic content of basaltic volcanisms with time. Later, distal material transports from large impact events in highlands could complicate the mixing of local mare basalts in the Copernicus age, especially the Im3 unit. The identified olivine-bearing outcrops and widely Mg-rich materials (Mg# > 70, where Mg# = molar 100 × Mg/(Mg + Fe)) in the western highlands, assumed to be the occurrence of the Mg-suite candidates, require future lunar exploration missions to validate.

AbstractOrdinary γ‐CaSO4 is a metastable calcium sulfate, while γ‐CaSO4 from the hyperarid region on Earth and from Mars has been found with abnormally high stability. In this study, we used multiple microanalyses to characterize the chemical and structural properties of two such γ‐CaSO4: one from Atacama soil (#10‐d30) and the other from Martian meteorite MIL03346,168. Silicon was determined to be quasi‐homogeneously distributed in Atacama γ‐CaSO4, while both silicon and phosphorus were detected in Martian γ‐CaSO4. We found the abnormally high stability of those γ‐CaSO4 from hyperarid environments was due to the chemical impurities which filled their structural tunnels and blocked the entrance of atmospheric H2O, with non‐detectable structural distortion. We propose that the γ‐CaSO4 with Si or Si and P impurities could have igneous origin or evaporative origin. Due to the extreme similarity in the structures of bassanite and γ‐CaSO4, their XRD patterns are almost non‐distinguishable; thus some martian “bassanite” minerals identified by Curiosity's CheMin instrument at Gale crater can actually be γ‐CaSO4. The structural tunnels in γ‐CaSO4 would allow ions and ionic groups to fill, thus providing meaningful insights about the geological and geochemical processes experienced by it during the formation and transformation. The Raman spectrometer carried by the Perseverance and by ExoMars rovers will help the selection of samples enriched in γ‐CaSO4 at Jezero Crater and Oxia Planum, which should be sampled for in‐depth analysis on Mars and back to Earth.