Geofyzikální ústav Akademie věd ČR, v.v.i.

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Structure and anisotropy of the continental lithosphere

 

We model lithosphere thickness (Fig. 1) and large-scale fabric of the mantle lithosphere from anisotropic parameters of teleseismic body waves recorded by dense networks of temporary and permanent seismic stations. We invert jointly shear-wave splitting parameters and P residual spheres based on data from several European regions ranging from the Apennines through the Variscan belt of central Europe to the Baltic Shield (Fig. 2). Changes in orientation of the large-scale anisotropy, caused by systematic preferred orientation of olivine, identify boundaries of large domains of mantle lithosphere. Individual domains, several hundred kilometers in lateral dimensions, are characterized by a consistent orientation of anisotropy approximated by hexagonal or orthorhombic symmetry with generally inclined symmetry axes. The domains are separated by mapped tectonic boundaries (sutures), which cut the entire lithosphere. The observations of consistent anisotropy within individual blocks of the mantle lithosphere reflect fossil olivine preferred orientation, most probably formed prior to the assembly of micro-plates that created the modern European landmass. Our findings support a plate-tectonic view, acting in early stage of the Earth evolution and represent the continental lithosphere as a mosaic of rigid blocks of the mantle lithosphere with complicated but relatively sharp contact zones. These contacts are blurred by the easily deformed overlying crust terranes.

The present research is focused on the deep structure of the Bohemian Massif and there especially of the Eger (Ohře) Rift, on the deep structure of the Phanerozoic and Proterozoic lithosphere around the central part of the Trans-European Suture Zone and Proterozoic-Archean contact in Fennoscandia (Sweden/Finland). Most of our investigations have been carried out within international passive seismic experiments (e.g., TOR-TESZ, SVEKALAPKO, BOHEMA, RETREAT, PASSEQ, LAPNET) and in cooperation with teams from many institutions like Institute de Physique du Globe (Strasbourg), Istituto Nazionale di Geofisica e Vulcanologia (Roma, Florence), Yale University (New Haven), Rudgers University (New York), University of Oulu and University of Uppsala.

 

Members of the team

Jaroslava Plomerová
Vladislav Babuška
Luděk Vecsey
Helena Munzarová
Hana Kampfová Exnerová
Jan Chyba
Bohuslav Růžek
Petr Jedlička

 

Figures

Fig. 1 Models of the lithosphere thickness in central (Babuška and Plomerová, 2006) and northern Europe (Plomerová et al., 2007b) bridged across the NW end of the Trans-European Suture Zone (TESZ, Plomerová et al., 2002). The lithosphere thickens in the Precambrian part of Europe, NE of the TESZ. Mountain roots of the Western and Eastern Alps, and the southern Carpathians, as well as lithosphere thinning in the Pannonian Basin (PB), Rhenish Massif (RM), Po Plain (PP), volcanic centres in the French Massif Central (MC), and the Eger Rift in the Bohemian Massif (BM) are distinct in the Phanerozoic part of Europe, SW of the TESZ.

Fig. 2 Fabrics of mantle lithosphere of the French Massif Central (MC), west of the Bohemian Massif across the Saxothuringian/Moldanubian contact, around the north-western part of the Trans-European Suture Zone, around the Protogine Zone (south-central Sweden) and around the Proterozoic-Archean contact of the Fennoscandian Shield (Finland) modelled by joint inversion of anisotropic parameters of body waves (Babuška et al., 2002; Plomerová et al., 1998; 2001; 2002;2006; Babuška and Plomerová, 2004; Vecsey et al., 2007). The mantle lithosphere anisotropy is approximated by hexagonal or orthorhombic symmetry of fossil olivine fabrics with generally plunging lineation a or foliation (a,c), while mostly sub-horizontal anisotropy due to a present-day flow is generally modelled in the asthenosphere.