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| Titel |
Evidence of Partial Differentiation and a Metallic Core on the CV Chondrite Parent Planetesimal |
| VerfasserIn |
Laurent Carporzen, Benjamin P. Weiss, Denton S. Ebel, Jerome Gattacceca, David L. Shuster |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044010
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| Zusammenfassung |
| We have conducted a new paleomagnetic study on the Allende CV carbonaceous chondrites,
one of the best paleomagnetically studied rocks in history. It has long been known that
the meteorite Allende and other CV carbonaceous chondrites contain a natural
remanent magnetization. This record has been difficult to interpret because the age
and setting of magnetization acquisition were poorly understood. Carbonaceous
chondrites have traditionally been thought to samples bodies that have not undergone
large-scale differentiation. The bulk chemical composition and aggregational texture of
chondrites demonstrate that they are not the products of planetary melting processes.
Thus, we need to determine the nature and acquisition time for the magnetization
in Allende in order to distinguish between the possible magnetic field sources.
Therefore, we conducted high resolution demagnetization analyses compared to
shock remanent magnetization acquisition, absolute paleointensities, and a variety of
rock magnetic measurements. We also investigated magnetostatic interactions and
viscous demagnetization. Using recent geochemical, petrologic, and isotopic datasets,
we demonstrate that the unidirectional magnetization in Allende must have been
acquired following accretion of the parent body, likely over several million years (Ma)
during metasomatism on the CV parent planetesimal ~8-10 Ma after solar system
formation. Therefore, the magnetization in Allende is apparently too young and
was acquired over too long a time period to have been produced by early external
protoplanetary disk or solar magnetic fields. Moreover, our determinations of Allende’s
paleointensities are in the range expected for core dynamos in early planetesimals. A simple
interpretation of Allende’s paleomagnetic record is therefore that CV chondrites are
derived from the outer, unmelted layer of a differentiated body with a convecting,
liquid metallic core and core dynamo. Thermal modeling of early planetesimals
heated by 26Al decay indicates that dynamos were likely generated in convecting
metallic cores lasting for -¥11 Ma after solar system formation. Because such bodies
melt from the inside out, some may preserve an unmelted, relict chondritic surface
which could be magnetized during metasomatism in the presence of a core dynamo. |
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