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Signals of 660 km topography and harzburgite enrichment in seismic images of whole‐mantle upwellings
Author(s) -
Maguire Ross,
Ritsema Jeroen,
Goes Saskia
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl073120
Subject(s) - geology , mantle (geology) , upwelling , transition zone , mantle plume , geophysics , hotspot (geology) , plume , anomaly (physics) , seismology , petrology , tectonics , lithosphere , thermodynamics , oceanography , physics , condensed matter physics
Various changes in seismic structures across the mantle transition zone (MTZ) indicate that it may hamper thermal and chemical circulation. Here we show how thermal elevation of the postspinel phase transition at 660 km depth plus harzburgite segregation below this depth can project as narrow high‐velocity anomalies in tomographic images of continuous thermochemical mantle upwellings. Model S40RTS features a narrow high‐velocity anomaly of +0.8% near 660 km depth within the broad low‐velocity structure beneath the Samoa hot spot. Our analyses indicate that elevation of the 660 phase boundary in a hot pyrolitic plume alone is insufficient to explain this anomaly. An additional effect of harzburgite enrichment is required and consistent with geodynamic simulations that predict compositional segregation in the MTZ, especially within thermochemical upwellings. The Samoa anomaly can be modeled with a 125–175°C excess temperature and a harzburgite enrichment below 660 of least 60% compared to a pyrolitic mantle.