[S21-2] Seismic images of the upper mantle

[S21-2-03] Mantle lithosphere edges of Baltic Shield and East European Craton retrieved by seismic anisotropy

^○Jaroslava Plomerova, Helena Munzarova, Vladislav Babuska, Ludek Vecsey (Institute of Geophysics, Czech Academy of Sciences, Prague, Czech Republic)

Several passive seismic experiments provided data for detailed studies of upper mantle anisotropy, namely fabrics of the mantle lithosphere. Lateral variations of body-wave anisotropic parameters, retrieved from teleseismic P-sphere patterns, shear-wave splitting and teleseismic tomography, detected domains of mantle lithosphere with differently oriented fossil fabrics (Babuska and Plomerova, PEPI 2006) and delimited their extent in the upper mantle. The south-western edge of the Baltic Shield, adjacent to the Sorgenfrei—Tornquist Zone that separates the Precambrian and Phanerozoic parts of Europe, is characterised by a sharp change of both the lithosphere thickness and fabrics (Plomerova et al., Tectonophysics 2001). On the contrary, in the central part of the Trans-European Suture Zone, a broad transition between the East European Craton and Phanerozoic Europe, no significant change in the mantle lithosphere fabric has been detected across the Tornquist–Teisseyre Zone (Vecsey et al., SE 2014), but westward lithosphere thinning. Results of body-wave tomography (Chyba et al., PEPI 2017) suggest thrusting the Phanerozoic European lithosphere over the East European craton. Change of the lithosphere thickness around the contact of the Proterozoic and Archean parts within the Baltic Shield is insignificant (Plomerova and Babuska, Lithos 2010) and the contact appears as a broad transition in the south-central Fennoscandia, which can be modelled as an Archean wedge penetrating into the Proterozoic mantle (Vecsey et al., Tectonophysics 2007). This model is supported by xenolith ages (Peltonen and Brugmann, Lithos 2006). Further to the north, the Archean-Proterozoic boundary follows the surface trace of the Baltic-Bothnia Megashear Zone (Plomerova et al., SE 2011). Anisotropic tomography (Munzarova et al., under prep.) indicates a westward continuation of the cratonic lithosphere that retains its own fossil fabric.