Pallasite paleomagnetism: Quiescence of a core dynamo

Nichols, C.I.O. ; Bryson, J.F.J. ; Herrero-Albillos, J. (Universidad de Zaragoza) ; Kronast, F. ; Nimmo, F. ; Harrison, R.J.

Resumen: Recent paleomagnetic studies of two Main Group pallasites, the Imilac and Esquel, have found evidence for a strong, late-stage magnetic field on the parent body. It has been hypothesized that this magnetic field was generated by a core dynamo, driven by compositional convection during core solidification. Cooling models suggest that the onset of core solidification occurred ~200 Ma after planetary accretion. Prior to core solidification, a core dynamo may have been generated by thermal convection; however a thermal dynamo is predicted to be short-lived, with a duration of ~10 Ma to ~40 Ma after planetary accretion. These models predict, therefore, a period of quiescence between the thermally driven dynamo and the compositionally driven dynamo, when no core dynamo should be active. To test this hypothesis, we have measured the magnetic remanence recorded by the Marjalahti and Brenham pallasites, which based on cooling-rate data locked in any magnetic field signals present ~95 Ma to ~135 Ma after planetary accretion, before core solidification began. The cloudy zone, a region of nanoscale tetrataenite islands within a Fe-rich matrix was imaged using X-ray photoemission electron microscopy. The recovered distribution of magnetisation within the cloudy zone suggests that the Marjalahti and Brenham experienced a very weak magnetic field, which may have been induced by a crustal remanence, consistent with the predicted lack of an active core dynamo at this time. We show that the transition from a quiescent period to an active, compositionally driven dynamo has a distinctive paleomagnetic signature, which may be a crucial tool for constraining the time of core solidification on differentiated bodies, including Earth.

Idioma: Inglés

DOI: 10.1016/j.epsl.2016.02.037

Año: 2016

Publicado en: EARTH AND PLANETARY SCIENCE LETTERS 441 (2016), 103-112
ISSN: 0012-821X

Factor impacto JCR: 4.409 (2016)

Categ. JCR: GEOCHEMISTRY & GEOPHYSICS rank: 7 / 84 = 0.083 (2016) - Q1 - T1

Factor impacto SCIMAGO: 3.156 - Earth and Planetary Sciences (miscellaneous) (Q1) - Space and Planetary Science (Q1) - Geophysics (Q1) - Geochemistry and Petrology (Q1)

Financiación: info:eu-repo/grantAgreement/EC/FP7/312284/EU/Coordinated Access to Lightsources to Promote Standards and Optimization/CALIPSO
Financiación: info:eu-repo/grantAgreement/EC/FP7/320750/EU/Nanopaleomagnetism: a multiscale approach to paleomagnetic analysis of geological materials/NanoPaleoMag
Financiación: info:eu-repo/grantAgreement/ES/MINECO/MAT2014-53921-R

Tipo y forma: Artículo (Versión definitiva)

Área (Departamento): Área Física Materia Condensada (Dpto. Física Materia Condensa.)