HR: 0800h
AN: V51B-1479    [Abstracts]
TI: Microstructures and Chemistry of Serpentine Minerals in Veins: Constraints on the Hydration Processes of Oceanic Peridotites
AU: * Andreani, M
EM: andreani@ipgp.jussieu.fr
AF: IPGP, 4 Place Jussieu - Box 89, Paris, 75252 France
AU: Mevel, C
EM: mevel@ipgp.jussieu.fr
AF: IPGP, 4 Place Jussieu - Box 89, Paris, 75252 France
AU: Boullier, A
EM: Anne-Marie.Boullier@obs.ujf-grenoble.fr
AF: LGIT, BP 53, Grenoble, 38041 France
AU: Baronnet, A
EM: baronnet@crmcn.univ-mrs.fr
AF: CRMCN, Campus de Luminy, Marseille, 13288 France
AB: Serpentine minerals are hydrous sheet silicates forming in various geological settings (oceanic extension, subduction, transform faulting) by hydrothermal alteration of magnesian silicates, major components of mantle rocks. They are known to display a large variety of structural types (chrysotile, polygonal serpentine, lizardite, antigorite) whose relative stabilities are poorly constrained by P, T and chemistry. Recent experimental studies suggest that other parameters such as the water-rock ratio, crystallization kinetics, and deformation may affect formation of serpentine types. This study investigates the role of these parameters in natural settings to test if the wide range of serpentine microstructures can record environmental conditions of crystallization. Oceanic serpentinization is accompanied by abundant veining showing different generations of veins with various morphologies and internal textures corresponding to different opening and crystallization conditions. We have selected a representative and extensive set of veins from oceanic serpentinites. We present a detailed chemical, micro- and nano-structural study of the vein-filling serpentine minerals. Vein formation mechanisms are deduced from morphology and texture which then provide constraints on serpentine crystallization conditions. In addition to petrological observations, genetic relationships among the different serpentine types in veins have been identified at different scales using a wide variety of techniques (RAMAN spectroscopy, SEM, TEM, and chemical analyses). The relative importance of parameters that control microstructure stability of serpentines is compared with those obtained from laboratory experiments. These results show how the suite of serpentine microstructures observed in veins is linked to the evolution of environmental conditions (T, chemistry, W/R, mass transfer process-deformation, kinetic) during serpentinization.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1039 Alteration and weathering processes (3617)
DE: 1042 Mineral and crystal chemistry (3620)
DE: 8030 Microstructures
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005