GP Seminar - Shawn Wei "Imaging Mantle Wedge Melting of the Tonga-Lau-Fiji Subduction System"

05/13/2016 - 3:30pm

Please join us for the GP Seminar

Friday, May 13, 3:30 pm
IGPP Conference Room (Munk 303)
(Coffee and snacks at 3:00 pm in the Reading Room!)
Imaging Mantle Wedge Melting of the Tonga-Lau-Fiji Subduction System
S. Shawn Wei
Green Scholar Postdoctoral Fellow, IGPP
We conduct tomographic studies of Rayleigh wave velocity and body wave attenuation to examine the thermal variations and the distribution of partial melt in the mantle wedge, using data from local seismic array. The shear-wave velocity structure is first determined using only teleseismic data with the two-plane-wave method, and then jointly inverted from the phase velocities of teleseismic and ambient-noise Rayleigh waves obtained from noise cross-correlation. Additionally, we determine the 3-D P and S wave attenuation structure from t* measurements using local earthquakes. Tomographic results show extremely low velocity and high attenuation within the upper 80-km of the mantle beneath the Lau back-arc basin, suggesting perhaps the lowest shear-wave velocity (VSV = 3.6 km/s) and highest seismic attenuation (QP < 35 andQS < 25) known in the mantle. These anomalies require not only abnormally high temperature but also the existence of partial melt. The inferred melting regions align with the spreading centers at shallow depths of 20-70 km, but shift westwards away from the slab, indicating a passive decompression melting process governed by the mantle wedge flow rising from the west. Assuming that velocity anomalies reflect variations in mantle porosity filled with melt, the mantle porosity is reduced in areas of high mantle water content, implying that the melt segregation and extraction are significantly enhanced by the water released from the subducting slab.
For more information on this event, contact: 
Jessie Saunders
Event Calendar: 
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