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1 Laboratoire de Géophysique et d’Hydrodynamique en Forage, ODP-NEB, ISTEEM, cc 056, Université de Montpellier II, 34095 Montpellier, Cedex 05, France einaudi{at}dstu.univ-montp2.fr
2 Laboratoire de Pétrologie Magnatique, Université d’Aix Marseille III, Faculté des Sciences de Saint Jérôme, 13397 Marseille Cedex 20, France
3 Laboratoire de Tectonophysique, ISTEEM, CNRS UMR5568, Université de Montpellier II, 34095 Montpellier, Cedex 5, France
4 Département de géologie et de génie géologique, Faculté des sciences et de génie, Université Laval, Sainte-Foy, G1K 7P4, Québec, Canada
Physical properties of gabbroic samples from Ocean Drilling Program Hole 1105A were measured in the laboratory, with a particular emphasis on the analysis of electrical properties. This data-set includes the major lithologies sampled in ODP Hole 1105A: gabbros, olivine gabbros, oxide-rich gabbros, and, for all rock types, different ranges of alteration were sampled: from fresh to highly altered. All these lithologies correspond to the seismic Layer 3 layer of the oceanic crust, and large-scale geophysical data interpretation requires a complete understanding of the physical properties of rocks in this section. Electrical conductivities measured on brine-saturated gabbros reveal strong excess conductivity for samples rich in oxide minerals and, to a lesser extent, for altered samples. However, the classical models do not explain the excess conductivity reported in the oxide-rich samples when saturated with brine. The electrical conduction via electronic processes in metallic minerals has been taken into account in our analysis of the electrical properties. The oxide minerals’ contribution has been independently estimated through measuring dry electrical resistivity. These measurements allowed quantification of the electronic conduction, which can reach 80% of the full conductivity for the most oxide-rich gabbros.
