2:30 PM - 2:45 PM
[SIT28-04] Imaging the crust and mantle beneath the equatorial Mid-Atlantic Ridge using the PI-LAB experiment
Keywords:lithosphere-asthenosphere, Mid-Atlantic Ridge, oceanic , receiver function, transition zone, surface wave
Here we present our first imaging results of the crust, mantle, and transition zone from S-to-P receiver functions, P-to-S receiver functions, and surface waves. S-to-P receiver functions image a ~7 km thick oceanic Moho across our study area. We image a negative discontinuity, likely the lithosphere-asthenosphere boundary, which deepens progressively away from the western ridge segment from 30 to 80 km beneath 0 to 40 My old lithosphere. The depths are consistent with thermally controlled thickening with age. However, the amplitude and sharpness of the phases we observe also suggest melt may be present at the base of the lithosphere. We find Rayleigh wave average phase velocities that range from ~1.5 km/s at 5 s period to 4.31 km/s at 143 s, and fundamental mode Love waves with average phase velocities of 4.00 km/s at 5 s to 4.51 at 22 s. We invert these phase velocities for 1-D average radially anisotropic shear velocity structure and find a ~60 km thick fast lid with velocities of 4.62 km/s, and x values up to 1.08 with radial anisotropy in the upper 200 km. 3D shear velocity inversions require a fast lid beneath the ridge, to ~30 km depth, with a thicker fast lid at greater age. The low velocity zone beneath the ridge has a minimum velocity of 4.1 km/s. With P-to-S receiver functions we image thinning of the transition zone by 5 to 20 km in the western part of our study region consistent with a 200 K thermal anomaly. The result suggests mid-ocean ridges have a signature deep as the transition zone, implying whole mantle convection.