Nanophase Iron Particles Derived From Fayalitic Olivine Decomposition in Chang'E‐5 Lunar Soil: Implications for Thermal Effects During Impacts. Issue 5 (1st March 2022)

• Record Type: Journal Article
• Authors: Guo, Zhuang; Li, Chen; Li, Yang; Wen, Yuanyun; Tai, Kairui; Li, Xiongyao; Liu, Jianzhong; Ouyang, Ziyuan
• Is Part Of: Geophysical research letters. Volume 49:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-01
• Subjects: space weathering -- nanophase iron particles -- Chang'E‐5 lunar soils; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL097323
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Surface‐correlated nanophase iron particles (npFe 0 ) alter the reflectance spectrum characteristics of airless bodies, thus making it an essential aspect of studying space weathering. Vapor deposition has been the only strongly proven npFe 0 formation mechanism owing to the long exposure time of Apollo samples, whereas other formation mechanisms remain questioned. Newly returned younger Chang'E‐5 samples provide an opportunity to study the incipient formation mechanism of npFe 0 . Here, we combined transmission electron microscopy and electron energy loss spectroscopy to characterize the microscopic features of Chang'E‐5 olivine rims. The uppermost layer of these grains exhibits the simultaneous coexistence of npFe 0 with Si‐rich material overlying an Mg‐rich layer, as well as numerous irregular vesicles containing oxygen‐rich (SiO and O2 ) components embedded in the npFe 0 . These microscopic features collectively suggest subsolidus olivine decomposition during (micro)impact‐induced fragmentation or local heating processes, which may be the essential agent to alter the reflectance spectrum of airless bodies. Plain Language Summary: Airless bodies experienced a space weathering modification to form the nanophase iron particles (npFe 0 ) that would alter the reflectance spectrum. However, the formation mechanism of npFe 0 remains controversial due to the lack of less‐exposed lunar samples to study the incipient information about npFe 0 formation, except for the widely accepted vapor deposition origin. Our study is based on the younger Chang'E‐5 samples and report the first strong evidence of unique vesicular npFe 0 produced by olivine decomposition under subsolidus conditions, which may be the first effect contributing to npFe 0 formation on the lunar surface. This formation mechanism will shed light on the npFe 0 production and further broaden the perspective of impact effects beyond the Moon and deepen the current understanding of unexplored celestial bodies using remote sensing. Key Points: Subsolidus fayalitic olivine decomposition forming unique vesicular nanophase iron particles in Chang'E‐5 soils was confirmed Nanophase iron particles in the uppermost olivine layer are embedded with numerous vesicles containing possible O2 or SiO component Unique microstructural features on fayalitic olivine rims shed light on the diversity of space weathering effects on the lunar surface