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High-resolution Mapping of North America's Mid-Mantle Reflectivity provides Evidence for Dehydration Melting
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  • Steve Asamoah Boamah Carr,
  • Tolulope Olugboji,
  • Jeffrey Park,
  • Shun-ichiro Karato
Steve Asamoah Boamah Carr

Corresponding Author:scarr13@ur.rochester.edu

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Tolulope Olugboji
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Jeffrey Park
Department of Earth and Planetary Sciences, Yale University
Shun-ichiro Karato
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Abstract

We investigate seismic discontinuities across the middle of Earth’s mantle beneath a large seismic array that spans the North American continent. We provide robust constraints on the depth distribution, sharpness, and spatial variation of seismic discontinuities by processing high-resolution Ps-converted seismic waves (~0.5 Hz) through a novel denoising filter called CRISP-RF (Clean Receiver function Imaging with Sparse Radon Filters). In the upper mantle, above the mantle transition zone (MTZ), we observe a sharp velocity decrease at depths that vary from ~290 km to ~390 km. In the lower mantle, below the MTZ, we observe another sharp velocity decrease at depths that vary from ~800 km to 1,200 km.  The lower-mantle discontinuities cluster at a depth of ~885 km, while deeper converters (> 1,000 km) are less likely. The spatial distribution of these seismic features appears stochastic, but we detect collocated upper-mantle and lower-mantle discontinuities only at 8% of observed locations. We interpret our results with a dehydration melting model, in which MTZ water is transported into either the upper or the lower mantle, but rarely simultaneously, during Earth’s long history of subduction and mantle upwelling.