Temperature heterogeneity in the mantle transition zone beneath the North Atlantic region and the highly tilted Iceland Plume: Evidence from receiver functions

The Iceland Plume, a hot upwelling from the Earth's deep mantle, is thought to have caused high mantle temperatures beneath Iceland and its surroundings resulting in voluminous volcanism, from the North Atlantic Igneous Province at 60 Ma to the present. Tomographic models display strong low-velocity anomalies in the asthenosphere around Iceland, but the deeper structure is unclear, with recent models showing complex structure and no agreement on where the plume may be crossing the mantle transition zone (MTZ) on its way from the lower mantle upward. Plume temperatures would affect the depths of the MTZ-bounding phase transitions, which we target by detecting P-to-S conversions from the resulting seismic discontinuities. We calculate receiver functions using seismograph data from across the North Atlantic region, including new ocean-bottom data, and measure P410s and P660s arrival times to determine MTZ thickness. We find evidence for widespread lateral heterogeneity in MTZ temperature across the region with a typical 100–150 K amplitude, probably indicating complex mantle flow patterns accommodating hot upwellings from the lower mantle. A warm anomaly with this amplitude is mapped beneath southern and central Iceland, in agreement with previous studies. The thinnest MTZ, however—up to 40 km thinner and, thus, 300 K hotter than average—is below southeast Greenland and the Jan Mayen area. High MTZ temperatures below these locations are corroborated by recent waveform tomography, showing the lowest seismic velocities there. These results are consistent with a tilted plume ascending from the southeast Greenland MTZ to Iceland while flowing ~800 km southeastward.