1. Coseismic magnetization of fault pseudotachylytes: 1. Thermal demagnetization experiments
- Author
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Eric C. Ferré, John W. Geissman, Mimi J. Hill, François Demory, M. S. Zechmeister, J. Gattacceca, Department of Geology [Carbondale] (geology), Southern Illinois University [Carbondale] (SIU), University of Texas at Dallas [Richardson] (UT Dallas), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Liverpool Hope University, Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Collège de France (CdF)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Institut National de la Recherche Agronomique (INRA), and Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Collège de France (CdF (institution))-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA)
- Subjects
Paleomagnetism ,geography ,geography.geographical_feature_category ,Natural remanent magnetization ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,Demagnetizing field ,Geophysics ,Fault (geology) ,Silicate ,chemistry.chemical_compound ,Magnetization ,chemistry ,Space and Planetary Science ,Geochemistry and Petrology ,Remanence ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,[SDE]Environmental Sciences ,Earth and Planetary Sciences (miscellaneous) ,Petrology ,Geology ,ComputingMilieux_MISCELLANEOUS ,Magnetite - Abstract
Fault pseudotachylytes form by quenching of silicate liquids produced through coseismic frictional melting. Here we show that in natural pseudotachylytes the main carrier of magnetic remanence blocked in during cooling of the frictional melt is fine-grained magnetite. This confirms previous studies on friction melt experiments. Stoichiometric magnetite, produced during earthquakes by the breakdown of ferromagnesian silicates, records the ambient magnetic field during seismic slip. We find that most fault pseudotachylytes exposed in the Santa Rosa Mountains, southern California, a classic pseudotachylyte locality, acquired their natural remanent magnetization (NRM) upon cooling of the frictional melt through the range of magnetization blocking temperatures of the magnetite grains and this primarily constitutes a thermal remanent magnetization. NRM intensities typical of most pseudotachylyte veins range from 1 to 60·10−4 Am2/kg. A few specimens, however, contain magnetizations significantly higher than that caused by the Earth's field as well as magnetization directions that are highly variable over short distances. Other magnetization processes, possibly related to coseismic electric currents, may be involved during the seismogenic process to control NRM acquisition.
- Published
- 2014
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