Water in the mantle: Results from electrical conductivity beneath the French Alps

• Published in: Geophysical research letters Vol. 31; no. 6; pp. L06612 - n/a
• Main Authors: Tarits, P., Hautot, S., Perrier, F.
• Format: Journal Article
• Language: English
• Published: American Geophysical Union 01-03-2004; Blackwell Publishing Ltd
• Subjects: Dynamics of lithosphere and mantle—general; Electrical properties; Geomagnetic induction; Geomagnetism and Paleomagnetism; Lithosphere and upper mantle; Mineral Physics; Sciences of the Universe; Seismology; Tectonophysics
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2003GL019277

A deep magnetotelluric sounding in the French Alps provided a vertical electrical conductivity profile between ∼200–1000 km. Two prominent features are observed. First, the conductivity in the depth range 400–800 km is smaller than the conductivity of a pyrolite mantle obtained from laboratory results for a normal geotherm. Second, the data do not require the conductivity to change throughout the transition zone (410–660 km). In this part of the mantle, a temperature of 350–450 C less than normal explains the magnetotelluric conductivity profile. At 200–400 km, our model favors a cold mantle with 1000–1500 ppm of water dissolved in olivine. If correct, this model suggests that the subducted slab is dehydrated before reaching the transition zone.