Complex lithospheric structure under the central Baltic Shield from surface wave tomography.

M. Bruneton (1) , Helle A. Pedersen (1) , Véronique Farra (2) , Nicholas Arndt (3) , P. Vacher (4) , U. Achauer (5) , A. Alinaghi , J. Ansorge , G. Bock , W. Friederich , M. Grad , A. Guterch , P. Heikkinen , S. Hjelt , T. Hyvonen , J.P. Ikonen , E. Kissling , K. Komminaho , A. Korja , E. Kozlovskaya , M. Nevsky , H. Paulssen , N. Pavlenkova , J. Plomerova , T. Raita , O.Y. Riznichenko , R. Roberts , S. Sandoval , I. Sanina , N. Sharov , Z. Shomali , J. Tiikkainen , E. Wielandt , K. Wilegalla , J. Yliniemi , Y. Yurov

1 LGIT - Laboratoire de Géophysique Interne et Tectonophysique
2 IPGP - Institut de Physique du Globe de Paris
3 LGCA - Laboratoire de Géodynamique des Chaines Alpines
4 LPGN - Laboratoire de Planétologie et Géodynamique de Nantes [UMR 6112]
5 EOST - Ecole et Observatoire des sciences de la terre

[1] Regional seismic tomography provides valuable information on the structure of shields, thereby gaining insight to the formation and stabilization of old continents. Fennoscandia (known as the Baltic Shield for its exposed part) is a composite shield for which the last recorded tectonic event is the intrusion of the Rapakivi granitoids around 1.6 Ga. A seismic experiment carried out as part of the European project Svecofennian-Karelia-Lapland-Kola (SVEKALAPKO) was designed to study the upper mantle of the Finnish part of the Baltic Shield, especially the boundary between Archean and Proterozoic domains. We invert the fundamental mode Rayleigh waves to obtain a three-dimensional shear wave velocity model using a ray-based method accounting for the curvature of wave fronts. The experiment geometry allows an evaluation of lateral variations in velocities down to 150 km depth. The obtained model exhibits variations of up to ±3% in S wave velocities. As the thermal variations beneath Finland are very small, these lateral variations must be caused by different rock compositions. The lithospheres beneath the Archean and Proterozoic domains are not noticeably different in the S wave velocity maps. A classification of the velocity profiles with depth yields four main families and five intermediate regions that can be correlated with surface features. The comparison of these profiles with composition-based shear wave velocities implies both lateral and vertical variations of the mineralogy. INDEX TERMS: 7218 Seismology: Lithosphere and upper mantle; 7255 Seismology: Surface waves and free oscillations; 8180 Tectonophysics: Tomography; 9619 Information Related to Geologic Time: Precambrian; 1025 Geochemistry: Composition of the mantle; KEYWORDS: lithosphere, surface wave, Baltic Shield Citation: Bruneton, M., et al. (2004), Complex lithospheric structure under the central Baltic Shield from surface wave tomography,

Mots clés: Structures Internes et Evolution comparée des planètes

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux

M. Bruneton, Helle A. Pedersen, Véronique Farra, Nicholas Arndt, P. Vacher, et al.. Complex lithospheric structure under the central Baltic Shield from surface wave tomography.. Journal of Geophysical Research : Solid Earth, 2004, 109 (B10) (B10), pp.B10303. ⟨10.1029/2003JB002947⟩. ⟨hal-00109927⟩