48375 20200221144332.0 doi 10.1016/j.epsl.2016.02.037 sideral 94071 ART-2016-94071 eng Nichols, C.I.O. Pallasite paleomagnetism: Quiescence of a core dynamo 2016 Access copy available to the general public Unrestricted 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. info:eu-repo/grantAgreement/ES/MINECO/MAT2014-53921-R info:eu-repo/grantAgreement/EC/FP7/320750/EU/Nanopaleomagnetism: a multiscale approach to paleomagnetic analysis of geological materials/NanoPaleoMag info:eu-repo/grantAgreement/EC/FP7/312284/EU/Coordinated Access to Lightsources to Promote Standards and Optimization/CALIPSO info:eu-repo/semantics/openAccess by http://creativecommons.org/licenses/by/3.0/es/ 4.409 2016 GEOCHEMISTRY & GEOPHYSICS 7 / 84 = 0.083 2016 Q1 T1 3.156 2016 Earth and Planetary Sciences (miscellaneous) 2016 Q1 Space and Planetary Science 2016 Q1 Geophysics 2016 Q1 Geochemistry and Petrology 2016 Q1 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Bryson, J.F.J. (orcid)0000-0002-0901-8341 Herrero-Albillos, J. Universidad de Zaragoza Kronast, F. Nimmo, F. Harrison, R.J. 2003 395 Universidad de Zaragoza Dpto. Física Materia Condensa. Área Física Materia Condensada 441 (2016), 103-112 Earth planet. sci. lett. EARTH AND PLANETARY SCIENCE LETTERS 0012-821X 4548337 http://zaguan.unizar.es/record/48375/files/texto_completo.pdf Versión publicada 106920 http://zaguan.unizar.es/record/48375/files/texto_completo.jpg?subformat=icon icon Versión publicada oai:zaguan.unizar.es:48375 articulos driver 2020-02-21-13:46:02 ARTICLE