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Evidence of Subduction‐Related Thermal and Compositional Heterogeneity Below the United States From Transition Zone Receiver Functions
Author(s) -
Maguire Ross,
Ritsema Jeroen,
Goes Saskia
Publication year - 2018
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 - 10.1029/2018gl078378
Subject(s) - subduction , geology , transition zone , mantle (geology) , basalt , receiver function , seismology , plateau (mathematics) , geophysics , tectonics , lithosphere , mathematics , mathematical analysis
The subduction of the Farallon Plate has altered the temperature and composition of the mantle transition zone (MTZ) beneath the United States. We investigate MTZ structure by mapping P ‐to‐ S conversions at mineralogical phase changes using USArray waveform data and theoretical seismic profiles based on experimental constraints of phase transition properties as a function of temperature and composition. The width of the MTZ varies by about 35 km over the study region, corresponding to a temperature variation of more than 300 K. The MTZ is coldest and thickest beneath the eastern United States where high shear velocity anomalies are tomographically resolved. We detect intermittent P ‐to‐ S conversions at depths of 520 km and 730 km. The conversions at 730‐km depth are coherent beneath the southeastern United States and are consistent with basalt enrichment of about 50%, possibly due to the emplacement of a fragment of an oceanic plateau (i.e., the Hess conjugate).