Global stresses in the Western Europe lithosphere and the collision forces in the Africa-Eurasia convergence zone
Sh. A. Mukhamediev
Schmidt United Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
Abstract
[1] The experimentally determined directions of the maximum horizontal compressive
stress
SH, max in the western European stress province (WESP) of the West European
platform are mostly oriented northwest with an average azimuth of 325o 26o. The
traditional approach to the mathematical modeling of the stress field in the
Western Europe lithosphere (as well as in other stable lithospheric blocks) is
based on an elastic model of the medium and boundary conditions that specify
stresses and/or displacements at the entire perimeter of the region studied. In
the particular case of Western Europe, poorly constrained boundary conditions
should be set at the southern (in the collision zone of the African and Eurasian
plates) and eastern boundaries of the region. For this purpose, experimental
directions of
S H, max are used as constraints on the sought-for solution. However,
even if the experimental directions of
S H, max agree well with their theoretical
estimates, model stress magnitudes are still sensitive to the choice of model
boundary conditions.A basically different approach proposed and implemented in this
work for determining the field of tectonic stresses uses the
experimental directions of
SH, max as input
information rather than constraints on the sought-for solution.
The spatially persisting strike of the
SH, max axis
makes it possible to construct the field of straight trajectories
of principal stresses on the WESP territory. The problem of stress
determination is then reduced to the hyperbolic-type problem of
integrating the equilibrium equations that does not require
postulating constitutive relations, and the boundary conditions
are only specified on some part of the boundary of the model
region. The lithosphere material can be mechanically anisotropic
and inhomogeneous. Stresses
tR produced by the
ridge push were specified in this work on a segment of the
Mid-Atlantic Ridge, and stresses
tC due to the
Africa-Europe collision were specified in the convergence zone. No
boundary conditions are required at the eastern boundary of the
region studied. Supposedly, straight trajectories of stresses can
be extended into oceanic lithosphere areas adjacent to the
continent. The formulation of the problem presented in the paper
provides substantial constraints on the collision stresses
tC. These constraints directly result from the equilibrium conditions
of the Western Europe lithosphere rather than from the plate
convergence kinematics in the collision zone. A simple analytical
expression obtained for the tensor of global tectonic stresses in
the study region indicates that the
SH, max magnitude
decreases in the NW direction. The minimum horizontal stress in
the WESP region is shown to be sensitive to the direction of the
collision stresses
tC. This stress whose modulus
increases in the SE direction is compressive, zero or tensile
depending on whether the vector of collision stresses
tC deviates westward from the
SH, max direction, coincide with it or deviates eastward from it. The
modification of the inferred solution incorporating stresses
applied at the base of the lithospheric plate is discussed.
Citation: Mukhamediev, Sh. A. (2002), Global stresses in the Western Europe lithosphere and the collision forces in the Africa-Eurasia convergence zone, Russ. J. Earth Sci., 4, No.1, 1-17, doi:10.2205/2002ES000083.