3:15 PM - 3:30 PM
[MIS35-19] 3-D electrical conductivity image of the upper mantle beneath the Society hotspot
Keywords:hotspot, marine magnetotellurics, electrical conductivity, three-dimensional inversion, the French Polynesia
Then, we carried out the TIARES project that composed of multi-sensor stations that include broadband ocean bottom seismometers, ocean bottom electromagnetometers (OBEMs), and differential pressure gauges from 2009 to 2010. To obtain three-dimensional (3-D) image of the upwelling of the Society hotspot in terms of electrical conductivity, we newly settled eleven OBEMs and obtained MT responses at 20 sites totally. A 3-D marine MT inversion program, which can treat topographic change distorting EM data, was applied to these MT responses to estimate 3-D electrical conductivity image. The result detected a conductive anomaly elongating from the mantle transition zone to the uppermost upper mantle just below the Society hotspot. This feature is consistent with the slow velocity anomaly obtained from the surface wave tomography (Suetsugu et al., 2009). We calculated differences in temperature between the conductive anomaly and the surrounding mantle using conductivity-temperature relationship for dry olivine based on laboratory measurements. The resultant temperature difference is about 400 K at the depth of around 100 km, which is much larger than that estimated from a past seismic study. These results might imply that the effects of partial melt and/or volatiles are necessary in order to explain the high electrical conductivity anomaly beneath the hotspot.