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- Title
Magnetism of the Acapulco Primitive Achondrite and Implications for the Evolution of Partially Differentiated Bodies.
- Authors
Mansbach, Elias N.; Weiss, Benjamin P.; Schnepf, Neesha R.; Lima, Eduardo A.; Borlina, Cauê S.; Chatterjee, Nilanjan; Gattacceca, Jérôme; Uehara, Minoru; Wang, Huapei
- Abstract
Primitive achondrites like the acapulcoites‐lodranites (AL) clan are meteorites that formed on bodies in the process of forming a metallic core, providing a unique window into how early solar system processes transformed unmelted material into differentiated bodies. However, the size and structure of the parent body of ALs and other primitive achondrites are largely unknown. Paleomagnetism can establish the presence or absence of a metallic core by looking for evidence of a dynamo field. We conducted a magnetic study of the Acapulco acapulcoite to determine its ferromagnetic minerals and their recording properties. This is the first detailed rock magnetic and first paleomagnetic study of a primitive achondrite group. We determined that metal inclusions inside silicate grains consist of two magnetic minerals, kamacite and tetrataenite, which have robust recording properties. However, the mechanisms and timing by which these minerals acquired any natural remanent magnetization are unknown. Despite this, Acapulco has not been substantially remagnetized since arriving on Earth and therefore should retain a record dating to 4.55 billion years ago. Future studies could characterize this record by using high‐resolution magnetometry measurements of individual populations of grains and developing an understanding of how and when they became magnetized. Our discovery of tetrataenite in ALs provides the first mineralogical evidence for slow cooling [<∼5–10 × 103°C per million years (Ma−1)] of the AL parent body at low temperatures (∼320°C). Its presence suggests the AL parent body is unlikely to have been catastrophically disrupted at AL peak temperatures (∼1,200°C) without subsequent reaccretion. Plain Language Summary: Primitive achondrites are a rare variety of meteorites that formed as the result of limited melting on their parent bodies. They therefore provide key insights into the stages of segregation of metal and rocks in early solar system bodies. However, the sizes and structures of these parent bodies remain uncertain. Here, we conduct a rock magnetic study of the Acapulco acapulcoite to identify the magnetic recorders and to determine if the meteorite could retain a ∼4.55 billion year old magnetic record. We find that sub‐micrometer sized iron‐nickel grains embedded in silicate grains should retain a stable magnetization. The presence of high‐Ni iron grains suggests acapulcoites cooled slowly at low temperatures, indicating that the parent body could not have been catastrophically disrupted without later reaccretion. Key Points: We studied the rock magnetics properties of the primitive achondrite Acapulco to pave the way for future paleomagnetic investigationsWhile bulk samples are poor recorders, silicate grains with metal inclusions may retain stable magnetizations over 4.5 billion years (Ga)The presence of tetrataenite means that Acapulco's parent body was likely not catastrophically disrupted at temperatures >320°C
- Subjects
ACAPULCO (Mexico); ACHONDRITES; REMANENCE; METAL inclusions; HYPOTHERMIA; MAGNETISM
- Publication
Journal of Geophysical Research. Planets, 2023, Vol 128, Issue 12, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2023JE008076