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| Titel |
The Moho and the LAB under central Fennoscandia |
| VerfasserIn |
Lev Vinnik, Elena Kozlovskaya, Sergey Oreshin, Grigoriy Kosarev, Katja Piiponen |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108647
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| Publikation (Nr.) |
 EGU/EGU2015-8410.pdf |
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| Zusammenfassung |
| P- and S-wave velocity profiles of the crust and upper mantle are obtained from P- and S-wave receiver functions (PRFs and SRFs) for 20 seismograph stations of the POLENET/LAPNET array in Lapland and a few stations in southern Finland. The lithosphere-asthenosphere boundary (LAB) beneath cratons is often described as ‘elusive’. Nevertheless, beneath Lapland we detect a clear low S-wave velocity zone with the top (LAB) at a depth of 160 km. This depth corresponds to the wet solidus of peridotite (~1100 degrees C).The bottom of the LVZ (the Lehmann discontinuity) is at a depth of 240-250 km. Seismic anisotropy within the LVZ is distinctly different from the rest of the upper mantle.
As shown previously by controlled-source experiments, the Moho in southern Finland is anomalously deep (up to ~60 km versus the normal depth of ~40 km), but the depression of ~20 km has practically no effect in the gravity field. Vp in the lower crust is high (7.3 – 7.5 km/s) and can be explained by eclogitization (Kukkonen et al. 2008). In our Vs profiles the crust/mantle boundary in this region is found at a depth of only ~47 km. The strong dependence of the estimated depth on frequency (0.1 Hz for the receiver functions and 10 Hz for controlled-source seismology) suggests that the crust/mantle boundary in this region is a transition zone rather than a sharp interface. Another possible reason for the discrepancy in the Moho depths is the difference in the wave types (P waves in the controlled source experiments and S waves in receiver functions) and the presence of a layer with a low Vp/Vs ratio: P- and S-wave velocities can be in the crust and mantle ranges, respectively. This interpretation is supported by the extremely low Vp/Vs ratio (1.65) in a depth range from 47 to 75 km in our mantle models. This ratio is the likely effect of a large fraction of orthopyroxene (enstatite). |
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