Formation of ferroan dacite by lunar silicic volcanism recorded in a meteorite from the Moon

Abstract

An igneous clast from the Northwest Africa 773 (NWA 773) clan of lunar meteorites formed by silicic volcanism on the Moon. The clast was identified in Northwest Africa 2727 (NWA 2727), which is included in the NWA 773 clan. Over 80 mode% of the clast consists of silica + plagioclase + K-Ba-feldspar. The silica phases cristobalite, tridymite, and quartz are all present in the clast, indicating rapid cooling at low pressure in agreement with a volcanic setting. This clast is characterized as a dacite on the basis of mineral modes and whole-rock chemical composition. Olivine and pyroxene in the clast have high Fe/Mg ratios (olivine Fe# > 99, pyroxene Fe# > 99; with Fe# = molar Fe/(Fe + Mg) × 100), suggesting crystallization from a residual liquid after fractionation of more magnesian silicates. The clast is similar in some respects to ferroan gabbro alkaline-phase-ferroan (FG/ARFe) clasts that are inferred to be comagmatic with olivine gabbro (OG) and other mafic lithologies of the NWA 773 clan. However, the high silica concentration and dominance of apatite as the main Ca-phosphate (no merrillite was identified) are distinct from the FG/ARFe clasts. Thus, the dacite clast probably crystallized in a magmatic setting that was independent of the OG and FG/ARFe lithologies. The mafic major element composition, young age, and high KREEP-content of the NWA 773 clan have been used previously to infer an origin from the Procellarum-KREEP terrane (PKT) on the nearside of the Moon. Several candidates for silicic volcanism/plutonism have been identified in the PKT (e.g., Gruithuisen Domes, Hansteen alpha, Lassell Massif). The presence of the dacite lithology provides additional support for an origin in or around PKT for meteorites of the NWA 773 clan, and for complex igneous activity in PKT region.

Petrology and geochemistry of lunar feldspathic meteorite Northwest Africa 11111: Insights into the lithology of the lunar farside highlands

“…Unlike vermicular quartz in symplectite assemblage B2, the cristobalite shows a subhedral to anhedral shape and occurs as interstitial phase or inclusion in olivine. This texture and mineral assemblage is similar to alkaline‐phase ferroan clasts in the NWA 773 clan (Fagan et al., 2014; Kayama et al., 2018; Nagaoka et al., 2020; Valencia et al., 2019). However, K‐rich feldspar/K‐rich glass and Ca‐phosphates were not found in clast E3.…”

Possible Non‐Mare Lithologies in the Regolith at the Chang’E‐5 Landing Site: Evidence From Remote Sensing Data

“…The proposed large volume of silicic materials in this region potentially indicates intrusive bodies at depth in the Aristarchus Plateau (Glotch et al., 2010; Hagerty et al., 2009; Zanetti, 2015), and the rock types may include granite/felsite and possibly monzogabbro (Jolliff, 1991; Jolliff, Floss, et al., 1999). These rock types occur in the Apollo samples as rare evolved lithologies, and usually occur as small clasts in Apollo impact breccias and some lunar meteorites (Fagan et al., 2014; Jolliff, Floss, et al., 1999; Joy et al., 2011; Nagaoka et al., 2020; Seddio et al., 2013), complicating the interpretation of their origin and petrogenesis. The CE‐5 mission probably will collect Aristarchus ejecta spread over the mare plains.…”