New Evidence for 4.32 Ga Ancient Silicic Volcanism on the Moon. Issue 13 (8th July 2021)

• Record Type: Journal Article
• Authors: Zeng, Xiaojia; Li, Xiongyao; Xia, Xiao‐Ping; Liu, Jianzhong; Cui, Zexian; Yu, Wen; Ouyang, Ziyuan
• Is Part Of: Geophysical research letters. Volume 48:Issue 13(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-08
• Subjects: lunar -- lunar granite -- silicic volcanism; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL092639
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The currently available Apollo‐returned granitic lithology is restricted to only the nearside of the Moon (e.g., Procellarum KREEP Terrane [PKT]). In contrast, lunar meteorites represent randomly ejected crustal material, and they extend our understanding of the lunar magmatic history through time and space. Here, we report a 4, 321.5 ± 5.2 Ma (2σ) granitic fragment found in lunar basaltic breccia meteorite Northwest Africa (NWA) 10, 447, which is compositionally similar to the regoliths from the Moon's Non‐PKT regions. This granitic fragment has crystallization age similar to the oldest (∼4.32 Ga) granites sampled during the Apollo 12 and 17 missions, and adds to the growing evidence of ancient silicic volcanism on the Moon. In addition, this newly identified granitic fragment in the Th‐ and TiO2 ‐ poor breccia NWA 10447 provides evidence for that lunar granite may occur outside of the PKT of the Moon (i.e., the mare region with low Th and TiO2 contents). Plain Language Summary: Lunar granite, that is, highly evolved lithologies, can provide valuable information about the magmatic evolution of the lunar crust. At present, only a few (∼20) granites have been found in the Apollo samples (i.e., Apollo 12, 14, 15, and 17) and lunar breccia meteorites (e.g., NWA 4472), and they occur as rock fragments (e.g., 12, 013) or mm‐sized clasts within breccia (e.g., 14, 321). In this paper, we report a mm‐sized granitic fragment in lunar basaltic breccia meteorite NWA 10447, which has relatively low contents of Th (0.79 ppm) and TiO2 (0.6 wt%). This fragment provides evidence for that lunar granite would occur outside of the PKT of the Moon, where the breccia meteorite NWA 10447 is ejected from. In addition, the granitic fragment has crystallization age (∼4.32 Ga) similar to the oldest granites returned by Apollo 12 and 17 missions, providing new evidence for the existence of more ancient silicic volcanism on the Moon. This study also indicates that our understanding of lunar silicic magmatism is still insufficient. The further investigation of more silicic lithologies from other lunar meteorites (e.g., Th‐poor breccias) will be helpful in filling this knowledge gap. Key Points: One rare mm‐sized granitic fragment has been identified in lunar basaltic breccia meteorite Northwest Africa 10447 This granitic fragment has a crystallization age of 4.32 Ga, which is consistent with the ages of the oldest Apollo granite samples Lunar granite may occur outside of the Procellarum KREEP Terrane of the Moon (i.e., the mare region with low Th and TiO2 contents)