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Magnetism of the Acapulco Primitive Achondrite and Implications for the Evolution of Partially Differentiated Bodies
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  • Elias N. Mansbach,
  • Benjamin P Weiss,
  • Neesha Regmi Schnepf,
  • Eduardo Andrade Lima,
  • Caue Borlina,
  • Nilanjan Chatterjee,
  • J. Gattacceca,
  • Minoru Uehara,
  • Huapei Wang
Elias N. Mansbach
Massachusetts Institute of Technology

Corresponding Author:mansbach@mit.edu

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Benjamin P Weiss
Massachusetts Institute of Technology
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Neesha Regmi Schnepf
Laboratory for Atmospheric & Space Physics, CU Boulder
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Eduardo Andrade Lima
Massachusetts Institute of Technology
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Caue Borlina
Johns Hopkins University
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Nilanjan Chatterjee
Massachusetts Institute of Technology
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J. Gattacceca
CEREGE UM 34 (CNRS, Aix-Marseille University)
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Minoru Uehara
Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE
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Huapei Wang
China University of Geosciences
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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 magnetic 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 located 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 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 x 103 °C Ma-1) of the AL parent body at low temperatures (~320°C). Its presence means that the AL parent body is unlikely to have been catastrophically disrupted at AL peak temperatures (~1200°C) without subsequent reaccretion.
31 Aug 2023Submitted to ESS Open Archive
11 Sep 2023Published in ESS Open Archive