Magnetite in Muong Nong‐Type Australasian Tektites From South China

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2023-10, Vol.24 (10), p.n/a
• Main Authors: Pan, Qing, Xiao, Zhiyong, Wu, Yanxue, Wu, Yunhua, Yan, Pan
• Format: Article
• Language: English
• Subjects: Australasian strewn field; Crystallography; Detection; Earth; Extraterrestrial materials; impact cratering; impact melt; Iron; Magnetic field; Magnetic fields; Magnetic properties; Magnetic susceptibility; Magnetism; Magnetite; Magnetization; Minerals; Remanent magnetization; rock magnetism; Saturation; Sulfur; Sulphur; Tektites; troilite
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2023GC011103

South China belongs to the northern geographic branch of the Australasian strewn field (AASF) of tektites and microtektites, and this area is assumed to be part of the uprange region of the putative impactor trajectory that formed the yet undiscovered source crater. Ferromagnetic minerals in impact glass may record the magnetization process and thermal history of impact melt, but the possible identity of ferromagnetic minerals in AASF tektites from South China is elusive. Here, we perform a rock magnetism and crystallography study of iron‐sulfur spherules in Muong Nong‐type tektites from South China, revealing abundant single‐domain and pseudo single‐domain nano‐grains of magnetite within the spherules. This result is consistent with the detection of magnetic signals caused by single‐domain and pseudo single‐domain magnetite in these samples. Compared to the large value ranges of magnetic properties of tektites in the entire strewn field, individual specimens of both Muong Nong‐type and single splash‐form tektites have relatively homogeneous magnetic properties in terms of magnetic susceptibility, natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM) and NRM/SIRM ratio. The results indicate that the impact melt that formed each tektite specimen experienced similar thermal history, and most AASF tektites from South China were cooled in an ambient magnetic field that is the same order of magnitude as the Earth's magnetic field. Plain Language Summary The vast Australasian strewn field (AASF) of tektites and microtektites was formed at 0.788 million years ago by an enormous impact that may have occurred somewhere in the Indochina Peninsula. The magnetic properties of tektites may record the cooling history and post‐ejection magnetization process of the tektite‐forming melt, which could provide additional insights into the possible impact location. AASF tektites from South China are a unique portion of this strewn field regarding the hypothesized impactor trajectory, and our earlier rock magnetism study suggested that tektites in this region exhibit systematically different magnetic properties. This work performs detailed geochemical and crystallographic analyses for iron‐sulfur spherules in Muong Nong‐type tektites from South China, revealing abundant nano‐sized magnetite grains in the interior that are consistent with being single‐domain and pseudo single‐domain magnetite. This result is consistent with the detection of ma