The Mantle Transition Zone in Fennoscandia: Enigmatic High Topography Without Deep Mantle Thermal Anomaly

Abstract

Seismological data acquired by dense receiver networks in Fennoscandia enable imaging of Earth's upper mantle structure at unprecedented resolution and provide critical observations for resolving the ongoing debate on the cause of enigmatic high topography in Norway. Proposed mechanisms for the high topography include impact of a mantle plume, as supported by the observation of low seismic velocities in the uppermost mantle in southern Norway in contrast to high velocities in Sweden. We image the mantle transition zone (MTZ) in Fennoscandia by common conversion point stacking of 14,873 receiver functions from 14 networks including the recently deployed ScanArray. We find both MTZ discontinuities at their expected depths of 410 and 660 km within an uncertainty of 5–15 km and the thickness of the MTZ similar to the global average. These observations show that the high topography in western Scandinavia cannot be caused by thermal influence from the deep mantle.