Unique angrite-like fragments in a CH3 chondrite reveal a new basaltic planetesimal. (15th April 2020)

• Record Type: Journal Article
• Authors: Zhang, Ai-Cheng; Kawasaki, Noriyuki; Kuroda, Minami; Li, Yang; Wang, Hua-Pei; Bai, Xue-Ning; Sakamoto, Naoya; Yin, Qing-Zhu; Yurimoto, Hisayoshi
• Is Part Of: Geochimica et cosmochimica acta. Volume 275(2020)
• Page Start: 48
• Page End: 63
• Publication Date: 2020-04-15
• Subjects: Angrite-like fragment -- Angrite -- Sayh al Uhaymir 290 -- CH chondrite -- Planetesimal -- Oxygen isotope; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2020.02.014
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Most meteorites are believed to be chips from planetesimals and can provide clues to constrain the chemical evolution and dynamic history of the early Solar System. In this study, we report two unique fragments (ALF-1 and ALF-2) enclosed in the CH3 carbonaceous chondrite Sayh al Uhaymir 290. These two fragments are dominated by Ca, Fe-rich olivine with various amounts of Al, Ti-rich augite, anorthite, oxide minerals, Ca-phosphate mineral, FeNi metal, enstatite, and less Al, Ti-rich augite. The Ca-Mg-Fe systematics and Fe/Mn ratios of olivine grains in the two fragments are similar to that of the volcanic angrites. These similar features imply that the parent body of the two fragments might have bulk chemistry, oxygen fugacity, and differentiation resembling the angrite parent body. However, high-precision SIMS measurements reveal oxygen isotope compositions Δ 17 O = 0.91 ± 0.18‰ (2σ) of olivine in the two fragments are distinctly different from that of known angrite meteorites, possibly representing a new type of basaltic planetesimal. The two fragments also have a few mineralogical features distinct from angrite meteorites. They include: (1) the lack of a typical igneous texture; (2) the coexistence of two spatially associated Al, Ti-rich augites with different contents of CaO, Al2 O3, MgO, and P2 O5 ; (3) the presence of an enstatite-dominant rim in ALF-1; (4) the presence of a Cr, Mn-rich margin in ALF-1; and (5) complex microscale heterogeneity in oxide minerals. We argue that these features could be due to complex thermal histories in their parent body and/or after ejection from their parent body. Among these features, the Mn, Cr-rich margin and the enstatite-dominant rim in ALF-1 can be best explained with thermal events in nebular settings. This implies that the differentiation of the parent body of the two fragments might have taken place prior to the dissipation of the nebular gas.