Implications for the origin of Hawaiian volcanism from a converted wave analysis of the mantle transition zone

Double layering of a thermochemical plume in the upper mantle beneath Hawaii

“…Abundance of deep eclogitic melts, stabilized at depths of 150-250 km, would increase the travel-time residuals and expand the apparent thickness of the predicted low-velocity body. Independent seismic evidence for a widespread thermal anomaly much like that of the predicted DEP has come from a recent receiver-function study that images a broad depression of the 410 km discontinuity beneath the Hawaiian swell (Huckfeldt et al, 2013).…”

Multiscale Seismic Tomography

“…In the uppermost mantle, an excess temperature of 250 K can cause P-and S-wave velocity reductions of 2.25 and 2.75 %, respectively (Nataf and Ricard 1996). Their Clapeyron slopes could be such that the 410-km discontinuity is depressed in the plume, whereas the 660-km discontinuity is elevated, resulting in a thinner mantle transition zone (MTZ) (e.g., Li et al 2000Huckfeldt et al 2013). The radial temperature distribution in the plume can be approximated as Gaussian.…”

“…A narrow low-V zone appears at depths of 670-1500 km under Hawaii, and it is connected with a large low-V zone from 2000 km depth to the CMB north of Hawaii, which looks like a tilting plume feeding the Hawaiian hotspot. Significant thinning of the MTZ also suggests a lower-mantle origin of the Hawaiian plume (e.g., Li et al 2000;Wolbern et al 2006;Huckfeldt et al 2013). The Hawaiian plume is better imaged as a whole-mantle plume using both the mantle and core phase data (Fig.…”

Hotspots and Mantle Plumes

“…High-resolution local tomography using teleseismic data recorded by a large aperture network of ocean bottom seismome-P-wave velocity ters (OBSs) deployed around the Hawaiian Islands has imaged the Hawaiian plume more clearly down to a depth of 1800 km (Wolfe et al 2009(Wolfe et al , 2011. Significant thinning of the MTZ also suggests a lower-mantle origin of the Hawaiian plume (e.g., Li et al 2000;Wolbern et al 2006;Huckfeldt et al 2013). Receiver functions have been used to image the base of a melt-rich zone located 110-155 km beneath Hawaii, and it is found that this melt-rich zone is deepest 100 km west of Hawaii, implying that the plume impinges on the Pacific plate there and causes melting at greater depths in the mantle, rather than directly beneath the island (Rychert et al 2013).…”

“…A lower-mantle plume passes through two major seismic discontinuities at 410-and 660-km depths, which correspond to phase transitions of mantle minerals (e.g., Ito and Takahashi 1989;Bina and Helffrich 1994;Helffrich 2000). Their Clapeyron slopes could be such that the 410-km discontinuity is depressed in the plume, whereas the 660-km discontinuity is elevated, resulting in a thinner mantle transition zone (MTZ) (e.g., Li et al 2000Li et al , 2003Shen et al 2002;Huckfeldt et al 2013). Ponding may occur beneath the 660-km discontinuity (dotted line in Fig.…”