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Les microstructures de deformation des serpentines et la partition sismique-asismique: exemple de la Californie

Abstract : Geophysic studies have identified a seismic-aseismic partitioning along california active faults. Mapped serpentinites have been proposed to be a potential cause of aseismic creep. In order to better understand the deformation mechanisms of serpentinites in this context, we have studied, at different scale of observations, the deformation microstructures of serpentines collected in the San Andreas fault system (California). The use of several techniques of observation (petrographic microscope, SEM, TEM) and analysis (electron microprobe, EDS-SEM and TEM) was required in order to preserve information during scale shifts. Outside fault zones, serpentinites show markers of their deformation history before active faulting. Vein study allowed a good characterization of optical textures within these rocks and a better comprehension of the growth mechanisms of serpentine in interstices and open-fractures. Capillary effects could help crystrallisation in micrometer-range interstices by creating and maintenaing a diffusionnal transfer (in aqueous phase) of elements from the matrix to the vein. This continuous or incremental process, has been proposed to explain formation of fibrous veins. In opposition, open-fractures would be fed by an advectif transfer of solutes. Precipitation could occur thanks to a drop of the solute solubility due to a difference of temperature between the matrix (colder) and the fluid (hotter). Growth kinetic appears as a main factor in controlling the relative occurence of the different serpentine types encountered in this study (lizardite and chysotile), compared to classical thermodynamic parameters (pressure and température). Inside natural faults, deformation is very localized on a gouge zone or on a shiny fault plane. It is accommodated, respectively, by a pressure solution creep (stable slip) and by unstable cataclasatic events (low magnitude events, M<0). This leeds to an aseismic behaviour of serpentines at the global scale in faults.
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https://tel.archives-ouvertes.fr/tel-00006458
Contributor : Muriel Andreani <>
Submitted on : Tuesday, July 13, 2004 - 3:56:06 PM
Last modification on : Thursday, November 19, 2020 - 3:54:28 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:26:01 PM

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Muriel Andreani. Les microstructures de deformation des serpentines et la partition sismique-asismique: exemple de la Californie. Géologie appliquée. Université Joseph-Fourier - Grenoble I, 2003. Français. ⟨tel-00006458⟩

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