Paleomagnetism of the Orgueil and Ivuna meteorites and implications for the evolution of the CI chondrite parent body
Abstract
Several chondritic meteorites contain magnetizations that have been attributed to either solar nebula fields or to core dynamos that may have operated within partially differentiated planetesimals. The field source assigned to each meteorite's paleomagnetic record largely depends on the relative age of the magnetization compared to the lifetime of the solar nebula and the estimated onset timing for planetesimal dynamos. The paleomagnetism of CI (Ivuna-type) chondrites has been less explored than that of other carbonaceous groups due to the limited amount of material available for study. We present results from a new paleomagnetic study of CI1 chondrites Orgueil and Ivuna. The dominant ferromagnetic mineral in both meteorites is magnetite that formed during long-term aqueous alteration on the CI parent body ~4564 Ma, during the estimated lifetime of the solar nebula. Upon formation, this magnetite would have acquired chemical remanent magnetization if an ambient field was present. Our alternating field demagnetization experiments revealed that Orgueil does not have a retrievable high coercivity (>15 mT) magnetic remanence. Our subsample of Ivuna was contaminated by exposure to a strong field, such as that from a hand magnet, prior to our analyses. However, a previous paleomagnetic study revealed that another Ivuna subsample contained a single remanence component that persisted up to AF levels of ~40 mT, and that remanence at higher AF levels was likely unstable [Brecher and Arrhenius, 1974]. We determined that Ivuna and Orgueil are both capable of preserving stable magnetization from weak paleofields within higher coercivity grains (>15 mT and >40 mT for Orgueil and Ivuna, respectively). The absence of high coercivity magnetization in both meteorites may place an upper limit of <~5 μT on any ambient field present at the time of magnetite formation in these meteorites.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGP43B0799T
- Keywords:
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- 1507 Core processes;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1510 Dynamo: theories and simulations;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1517 Magnetic anomalies: modeling and interpretation;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1527 Paleomagnetism applied to geologic processes;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1560 Time variations: secular and longer;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1595 Planetary magnetism: all frequencies and wavelengths;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 5440 Magnetic fields and magnetism;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS