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    Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization

    Access Status
    Open access via publisher
    Authors
    Muxworthy, A.
    Bland, Phil
    Davison, T.
    Moore, J.
    Collins, G.
    Ciesla, F.
    Date
    2017
    Type
    Journal Article
    
    Metadata
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    Citation
    Muxworthy, A. and Bland, P. and Davison, T. and Moore, J. and Collins, G. and Ciesla, F. 2017. Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization. Meteoritics and Planetary Science. 52 (10): pp. 2132-2146.
    Source Title
    Meteoritics and Planetary Science
    DOI
    10.1111/maps.12918
    ISSN
    1086-9379
    School
    Department of Applied Geology
    URI
    http://hdl.handle.net/20.500.11937/58840
    Collection
    • Curtin Research Publications
    Abstract

    © 2017 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals, Inc. on behalf of The Meteoritical Society. We conducted a paleomagnetic study of the matrix of Allende CV3 chondritic meteorite, isolating the matrix's primary remanent magnetization, measuring its magnetic fabric and estimating the ancient magnetic field intensity. A strong planar magnetic fabric was identified; the remanent magnetization of the matrix was aligned within this plane, suggesting a mechanism relating the magnetic fabric and remanence. The intensity of the matrix's remanent magnetization was found to be consistent and low (~6 µT). The primary magnetic mineral was found to be pyrrhotite. Given the thermal history of Allende, we conclude that the remanent magnetization was formed during or after an impact event. Recent mesoscale impact modeling, where chondrules and matrix are resolved, has shown that low-velocity collisions can generate significant matrix temperatures, as pore-space compaction attenuates shock energy and dramatically increases the amount of heating. Nonporous chondrules are unaffected, and act as heat-sinks, so matrix temperature excursions are brief. We extend this work to model Allende, and show that a 1 km/s planar impact generates bulk porosity, matrix porosity, and fabric in our target that match the observed values. Bimodal mixtures of a highly porous matrix and nominally zero-porosity chondrules make chondrites uniquely capable of recording transient or unstable fields. Targets that have uniform porosity, e.g., terrestrial impact craters, will not record transient or unstable fields. Rather than a core dynamo, it is therefore possible that the origin of the magnetic field in Allende was the impact itself, or a nebula field recorded during transient impact heating.

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