The construction of the first 3D strength cube of the European lithosphere has lead
to an improved understanding of the dynamics of intra-lithospheric deformation
processes. The 3D strength model is constructed using a first order 3D geometrical
model of Europe’s lithosphere and consists of several regions, representing areas of
different composition, tectonic and/or thermal history. The depths of the different
interfaces of the layers are distinguished on the base of deep seismic reflection and
refraction or surface wave dispersion studies. The base of the crust is detected
using a recently compiled European Moho map. Further constraints on the thermal
lithospheric structure are obtained from heat flow studies and upper mantle seismic
tomography.
The first results show that the European lithosphere is characterized by major
spatial mechanical strength variations, with a pronounced contrast between the strong
lithosphere of the East-European Platform east of the Tesseyre-Tornquist line and the
relatively weak lithosphere of Western Europe. Within the Alpine foreland, pronounced
north-west-southeast trending weak zones are recognized that coincide with major
structures, such as the Rhine Rift System and the North Danish-Polish Trough, that
are separated by the high strength North German Basin.
Moreover, a broad zone of weak lithosphere characterizes the Massif Central and
surrounding areas. A pronounced contrast in strength can also be noticed between the
strong Adriatic indenter and the weak Pannonian Basin area and between the
Fennoscandia, characterized by a relatively high strength, and the North Sea rift
system corresponding to a zone of weakened lithosphere.
The next approach to realize a 3D European strength map consists of a refinement of
the previous thermal model in order to obtain more detailed temperature
distributions, which will be subsequently used as input parameter in the calculation
of the integrated strength.
The new model under development consists of one 3D block limited on the top by the
topography reconstructed using GTOPO30 data and on the bottom by the
lithosphereastenosphere boundary, defined using tomography data. This 3D block is
divided in a number of layers depending on the number of discontinuities detected in
the crust and mantle lithosphere by seismic reflection and tomography data. Two main
layers are defined in every part of the model (crust and lithospheric mantle layer),
while the others (e.g. sedimentary and lower crust layer) are only specified in the
areas where they are observed.
In order to generate the temperature distribution in our model we used the steady
state conditions to solve the heat conduction equation. In tectonically active
regions, affected by uplift and erosion, the velocity of the rocks inside the crust
with respect to top free surface is taken in account. The model is constrained at the
top by surface temperatures corrected for latitude and altitude effects and at the
bottom by temperatures obtained by the inversion of tomography data. Sensitivity
tests will be made to check the influence on the model of the approach chosen to
calculate the heat production, density and thermal conductivity variation and of the
boundary conditions used.
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