Malotas (b), a new eucrite from an old fall

SAAVEDRA M.; ROSZJÁR J.; RIEBE MY; VARELA M.E.; SHUYING YANG; HUMAYUN M.; RYOJI T.; BUSEMANN H,

Meteoritics and Planetary science

WIley

Lugar: New York; Año: 2022 vol. 57 p. 2081 - 2101

1945-5100

On the night of June 22, 1931 at 4 h 30 min, a fireball was seen in the vicinityof Malotas, Argentina. During the atmospheric trajectory (southwest to northeast), itexperienced several fragmentation events. After the fall, a piece was given to ProfessorJuan A. Olsacher (National University of Cordoba City, Argentina), who collected some further pieces. One of those samples was officially classified as an H5 ordinary chondritetermed Malotas. The present work focuses on the study of another two piecesrediscovered recently in the Museo de Mineralog ıa y Geolog ıa Dr. Alfred Stelzner inCordoba City, Argentina. The first piece turned out to be an achondritic meteorite termedMalotas (b). Petrographic features, chemical composition, and oxygen isotopes point to amonomict basaltic eucrite belonging to the Stannern-trend chemical subgroup of eucrites.The occurrence of anorthitic plagioclase veins in clinopyroxene, veinlet apatite, irregularshaped pockets of silica and troilite and porous silica signal metasomatism and thermalannealing before a late thermal event took place after brecciation. The latter was possiblyrecorded in the nominal U/Th-4He ages of 1.2–3.4 Ga detected in this work, whereasnominal K-Ar gas retention ages are within the range 3.5–4.2 Ga and may have escapedlate thermal modifications. The second piece is classified as an L5 chondrite. The differentcosmic ray exposure ages of 3, ~50, and 27 Ma determined for the H5 and L5 chondritesand the eucrite samples, respectively, might signal a common fall as a result of thebreakup of a polymict meteoroid