Tectonic studies made in intraplate Europe have shown that
this area is more
active than would be expected from its location far away
from plate boundaries.
Intraplate Europe is characterized by horizontal and
vertical motions with
deformation rates of the order of 1-2 mm/yr and by diffuse
seismicity (Nocquet
and Calais, 2003, Tesauro et al., 2005). The first strength
map (Cloetingh et al.,
2005) has lead to a significant understanding of the
dynamics of intra-
lithospheric deformation processes. The results have
demonstrated that the
European lithosphere is characterized by large spatial
mechanical strength
variations, with a pronounced contrast between the strong
lithosphere of the
East-European Platform (EEP) east of the Tesseyre-Tornquist
Zone (TTZ) and
the relatively weak lithosphere of Western Europe.
In order to improve the previous results and to extend the
strength
calculations to the southern and western plate boundaries of
Eurasia, we are
going to construct a new crustal model, which is a part of a
comprehensive
lithosphere model. As the first result, we demonstrate the
new Moho map of
Europe. The Moho depth variations are reconstructed by
merging the most
recent maps compiled for the European regions (e.g. Ziegler
and Dèzes, 2002,
Kozlovskaja et al, 2003) and by ourselves using published
interpretations of
seismic profiles (e.g. in the Vøring and Lofoten basins).
Strong differences in the crustal structure are found
between the areas east
and west of the TTZ, respectively. The eastern region is
mostly characterized by
thick crust, e.g. over the Baltica region (~42-44 km) with a
maximum of over 60
km in the Baltic Shield. By contrast, crustal structure is
more heterogeneous to
the west from TTZ, being characterized by Variscan crust
with an average
thickness of 30-35 km, orogens (e.g. the Alps and the
Pyrenees), where the
crustal thickness is increased up to 45-50 km, and locally
by strong extensional
deformation, which resulted in a very thin crust in the
Pannonian Basin (~25
km) and in the Tyrrhenian Sea (~10 km). Concerning the
oceanic domain, the
crustal thickness is generally decreased towards the ridge
(up to 10 km in the
most western part), with local maxima up to 20-25 km (e.g.
in the Vøring and
Lofoten basins) and up to 35-40 km beneath the islands (e.g.
Iceland and
Faeroe islands), on account of mantle underplating.
We calculated gravity effect of the Moho variations and
density variations
within the crust (Kaban, 2001) and removed it from the
observed gravity field,
which gives the residual mantle anomalies (Fig. 4). Since
the upper mantle
density is supposed to be constant in the reference model
(3.35 g/cm3), the
residual anomalies chiefly reflect the effect of mantle
density variations (Kaban,
2001, 2002, Kaban et al., 2004). The mantle anomalies are
clearly separated
into two components possibly accounting for the effects of
different factors:
(1) A long-wavelength component reflects large-scale structural
heterogeneities of the Eurasia lithosphere, supposedly
related to its thermal
regime. In the study area the TTZ divides EEP, which is
characterized by
predominantly positive anomalies from Western Europe with
mostly negative
mantle anomalies.
(2) A regional relatively short-wavelength component (L
<2000 km) correlates
with specific tectonic structures. A chain of negative
mantle anomalies (~ -100
mGal) is found west of the TTZ (Pannonian basin; Rhine
graben and Massif
Central). A very distinctive positive anomaly (>100 mGal)
is located over the
Carpathians and the Adriatic Sea, supporting the idea about
strong lithospheric
blocks.
The results of deep seismic reflection and refraction and/or
receiver function
studies will be used to define the depth of the crustal
interfaces and P-wave
velocity distribution in order to complete the new crustal
model. Furthermore, in
the next stage, seismic tomography data will be used to get
the location of the
lithosphere-astenosphere boundary and calculate the
temperature distribution.
These results, jointly with the new crustal model, will
allow us to re-calculate a
strength state of the European lithosphere and to construct
a new density
model.
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