IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Oral Presentation 2120
Geodynamic development of the European lithosphere imprinted in its
structure and topography of the lithosphere-asthenosphere boundary
Dr. Jaroslava Plomerova
Seismology Geophysical Institute, Czech Acad. Sci. IASPEI
Vladislav Babuska
Topography of the lithosphere-asthenosphere boundary and structure of the continental lithosphere
record the geodynamic development of outer parts of the Earth. Though driving mechanisms of plate
tectonics throughout the planet history are enigmatic, architecture of the continental plates can help to
answer questions how and when the plates were assembled and to what extent they were later
deformed. We model the lithosphere thickness and anisotropic structure of European continent, in
tectonic provinces of different ages and of various settings. We observe noticeable differences in the
lithosphere thickness varying from ~60km beneath some basins (e.g., the Pannonian Basin, the Po
Plain), parts of Variscan Massifs (e.g., the southern French Massif Central, the Rhenish Massif) or the
Phanerozoic North-German Platform, to about 200-220 km in the orogenic roots (e.g., the Western and
Eastern Alps) and beneath large parts of the Precambrian Baltic Shield, with one of the oldest
continental cratons on the planet. Our models, based on array travel-time deviations, consider seismic
anisotropy, and are in good agreement with estimates of lithosphere thickness based on surface waves,
magnetotelluric soundings, or xenolith studies. At scale lengths of a few hundred kilometres, domains
with a consistent large-scale orientation of seismic anisotropy can be recognized in the continental
lithosphere. We invert and interpret jointly anisotropic parameters of body waves (P residual spheres
and shear-wave splitting) for 3D self-consistent anisotropic models of the mantle lithosphere. Velocity
anisotropy of lithosphere domains is approximated by hexagonal or orthorhombic symmetry of fossil
olivine fabrics with generally plunging symmetry axes, while mostly sub-horizontal anisotropy due to the
present-day flow is generally modelled in the asthenosphere below the continental plates. Due to
different orientations of seismic anisotropy within the lithosphere and asthenosphere, the velocity
contrast at the lithosphere-asthenosphere boundary can be larger than it could be produced by
compositional variations and by a thermal state. We interpret the anisotropic domains as fragments of
mantle lithosphere retaining an old fossil olivine fabric, which was created before these micro-continents
assembled. Dynamic forces acting in young orogenic regions with active tectonics could deform the
mantle part of the lithosphere. However, unlevelled relief of the LAB and variable fabrics even in the
Precambrian lithosphere support an idea that lithospheric roots have been formed during an early form
of plate tectonics, i.e., by systems of successive paleosubductions (Babuka and Plomerov, 1989), or
other subduction-related processes, like a thrust stacking of oceanic (proto-cratonic) lithospheres and
accretion of magmatic arcs, acting since Archean (Flowers et al., 2004; Condie et al., 2006).
Keywords: lithosphere thickness, mantle fabric, geodynamic development