000048375 001__ 48375 000048375 005__ 20200221144332.0 000048375 0247_ $$2doi$$a10.1016/j.epsl.2016.02.037 000048375 0248_ $$2sideral$$a94071 000048375 037__ $$aART-2016-94071 000048375 041__ $$aeng 000048375 100__ $$aNichols, C.I.O. 000048375 245__ $$aPallasite paleomagnetism: Quiescence of a core dynamo 000048375 260__ $$c2016 000048375 5060_ $$aAccess copy available to the general public$$fUnrestricted 000048375 5203_ $$aRecent 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. 000048375 536__ $$9info:eu-repo/grantAgreement/ES/MINECO/MAT2014-53921-R$$9info:eu-repo/grantAgreement/EC/FP7/320750/EU/Nanopaleomagnetism: a multiscale approach to paleomagnetic analysis of geological materials/NanoPaleoMag$$9info:eu-repo/grantAgreement/EC/FP7/312284/EU/Coordinated Access to Lightsources to Promote Standards and Optimization/CALIPSO 000048375 540__ $$9info:eu-repo/semantics/openAccess$$aby$$uhttp://creativecommons.org/licenses/by/3.0/es/ 000048375 590__ $$a4.409$$b2016 000048375 591__ $$aGEOCHEMISTRY & GEOPHYSICS$$b7 / 84 = 0.083$$c2016$$dQ1$$eT1 000048375 592__ $$a3.156$$b2016 000048375 593__ $$aEarth and Planetary Sciences (miscellaneous)$$c2016$$dQ1 000048375 593__ $$aSpace and Planetary Science$$c2016$$dQ1 000048375 593__ $$aGeophysics$$c2016$$dQ1 000048375 593__ $$aGeochemistry and Petrology$$c2016$$dQ1 000048375 655_4 $$ainfo:eu-repo/semantics/article$$vinfo:eu-repo/semantics/publishedVersion 000048375 700__ $$aBryson, J.F.J. 000048375 700__ $$0(orcid)0000-0002-0901-8341$$aHerrero-Albillos, J.$$uUniversidad de Zaragoza 000048375 700__ $$aKronast, F. 000048375 700__ $$aNimmo, F. 000048375 700__ $$aHarrison, R.J. 000048375 7102_ $$12003$$2395$$aUniversidad de Zaragoza$$bDpto. Física Materia Condensa.$$cÁrea Física Materia Condensada 000048375 773__ $$g441 (2016), 103-112$$pEarth planet. sci. lett.$$tEARTH AND PLANETARY SCIENCE LETTERS$$x0012-821X 000048375 8564_ $$s4548337$$uhttps://zaguan.unizar.es/record/48375/files/texto_completo.pdf$$yVersión publicada 000048375 8564_ $$s106920$$uhttps://zaguan.unizar.es/record/48375/files/texto_completo.jpg?subformat=icon$$xicon$$yVersión publicada 000048375 909CO $$ooai:zaguan.unizar.es:48375$$particulos$$pdriver 000048375 951__ $$a2020-02-21-13:46:02 000048375 980__ $$aARTICLE