Architecture of the subcontinental lithospheric mantle of the Archean segment of the Fennoscandian Shield: Analysis of seismic data

Abstract

Here, Karelian seismological network data were studied to reveal the architecture of the subcontinental lithospheric mantle (SCLM). The receiver functions method was used, which is based on the identification of converted waves from teleseismic earthquakes and their joint inversion into a velocity model. Original one-dimensional (1D) velocity models for the continental lithosphere of the central Karelian Craton (KC) and the western Belomorian Mobile Belt (BMB; both part of the Archean segment of the Fennoscandian Shield) were presented, analysed and interpreted in geological and petrological terms.The obtained results reveal that the SCLM is >200 km thick both in the KC and the BMB. The mantle in both structures was shown to contain a well-defined, contrasting boundary with the crust. However, the boundary between the SCLM and the asthenosphere was not identified in this study. The SCLM was found to be stratified and divided into upper, middle and lower layers in both structures. The boundary between the upper and middle layers was identified at a depth near the upper line of the garnet stability limit in mantle peridotites; the boundary between the middle and lower layers corresponds to the graphite/diamond equilibrium line.The SCLM of the BMB was shown to exhibit a distinct lowered velocity zone in the middle layer. The 1D velocity model of the central KC was found to be in good agreement with the evidence for the SCLM stratigraphy, based on the study of mantle xenoliths and xenocrysts from kimberlites and lamproites from the area.