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Accueil > Documents > Pages personnelles > Benoît ILDEFONSE > Recherche > Structures et Propriétés physiques des magmas

Structures et propriétés physiques des magmas

Experimental study of low-frequency attenuation in partially molten gabbro

Examples of experimental results

This study aimed to better characterize seismic properties of a partially cristallized/molten gabbro, by measuring attenuation in Oman gabbronorite samples at low frequencies. Experiments were realized in Frankfurt, in collaboration with Nikolai Bagdassarov. This experimental device allows shear modulus and internal friction measurements in a large range of temperature (700-1230°C) and frequency (20-0.002 Hz).

Evolution of average 1/Qs and liquid fraction with temperature

The presence of melt was documented in thin sections. the contribution of the melt phase is demonstrated by i) the presence of a molten phase of 10% in samples measured at 1165°C, ii) the weak correlation above melting temperature between our measurements and a model in which attenuation is exclusively caused by temperature, iii) the good correlation of the measured attenuation with models in which attenuation is caused by squirt flow. Whatever the orientation of the sample foliation with respect to torsion, the molten phase is always preferentially aligned in the foliation plane. Measured values of attenuation, compared to attenuation model at the East Pacific Rise are compatible with a 10% liquid fraction (maximum estimate) in the low velocity zone beneath the melt lens at the ridge axis.

References
- Fontaine, F., Ildefonse, B. and bagdassarov, N.S., 2000. Shear Attenuation in Partially Molten Gabbros : Low-Frequency, Torsion Experiments . EOS Trans. AGU, 81(48), fall Meet. Suppl., Abstract V11A-10, 2000.
- Fontaine, F. ; Ildefonse, B. ; Bagdassarov, N., 2003. Temperature dependence of internal friction of partially molten gabbronorite at seismic frequencies. EGU 2003, Nice, Geophys. Res. Abstracts, 5, 02235.
- Bagdassarov, N.S., Maumus, J., Fontaine, F., Ildefonse, B., 2003. Physikalische Eigenschaften teilgeschmolzener Gesteine an der mittelozeanischen Spreizungsachse. Mitteilunge der Deutschen Geophysikalischen Gesellschaft, 3/2003, 2-16.
- Fontaine, F.R., Ildefonse, B. and Bagdassarov, N., 2005. Temperature dependence of shear wave attenuation in partially molten gabbronorite at seismic frequencies. Geoph. J. Int. 163 : 1025-1038.
- Fontaine, F.R., Neuville, D.R., Ildefonse, B., Mainprice, D., 2008. Influence of viscosity variation of basaltic and andesitic melts on seismic attenuation in partially molten gabbronorite. Phys. Earth Planet. Inter., 167, 223-229. doi:10.1016/j.pepi.2008.04.010