HR: 10:35h
AN: T12A-02    [Abstracts]
TI: Hydrous partial melting in the lower crust of the Oman ophiolite
AU: * Boudier, F I
EM: Boudier@dstu.univ-montp2.fr
AF: University Montpellier II, Place Eugene Bataillon, Montpellier, 34095 France
AU: Koepke, J
EM: koepke@mineralogie.uni-hannover.de
AF: Institut fuer Mineralogie der Universitaet Hannover, Callinstr. 3, Hannover, 30167 Germany
AU: Nicolas, A J
EM: Adolphe.Nicolas@dstu.univ-montp2.fr
AF: University Montpellier II, Place Eugene Bataillon, Montpellier, 34095 France
AB: Series of water-saturated melting experiments have been performed on natural gabbros between 900ø and 1000øC, at crustal pressure up to 200MPa (Koepke et al., 2004), that put new constraints on the composition of melt and residual crystals at increasing temperature and melt fraction produced. In the gabbro section of the Oman ophiolite, the development of high-T secondary parageneses is ubiquist, represented by orthopyroxene+pargasite rims within contact between olivine and plagioclase, while clinopyroxene is replaced by pargasite. The reference to the experimental results, and isotopic tracing (Bosch et al., 2004) lead to interpret these reactions as representing initiation of hydrous partial melting by fluids circulating at grain boundaries. The inferred mechanism allowing supercritical water to penetrate the deep gabbro section is a strong anisotropy of thermal compression inducing microcracking in the cooling lower gabbros (Nicolas et al., 2003). In the Oman gabbros, another important petrologic feature is the local occurrence, in the deeper section, of large amounts of orthopyroxene bearing gabbros either interlayered with olivine gabbros or intrusive as pegmatitic patches, in association with wehrlites, or mixed with pargasitic gabbros. The corresponding upper levels are rich in dioritic or trondjemitic dikes. These occurrences are restricted to localized areas that coincide with tips and segments limits as deduced from the detailed mapping along the NW-SE paleospreading axis. The origin of these parageneses as products of hydrous melting of the gabbros, at various melt fraction, is explored by reference to the experimental data. Koepke, J., Feig, S.T., Snow, J., Freise, M., 2004. Contrib. Mineral. Petrol. 146, 414-432. Bosch, D.et al., 2004, J. Petrology, 45, 1181-1208. Nicolas, A., Mainprice, D., Boudier, F., 2003, J. Geophys. Res. 108 (B8) 2371.
DE: 7220 Oceanic crust
DE: 8150 Plate boundary--general (3040)
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3035 Midocean ridge processes
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting