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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Poster presentation 2131
The evolution of mantle viscous stresses caused by supercontinental cycle:
numerical modelling
Dr. Alexander Bobrov
Theoretical Geodynamics Group Institute of Physics of the Earth, Russian Acad.Sc IASPEI
Numerical modelling are carried out of the fields of the main normal stresses values in the mantle, the
maximal shear stresses, and also their spatial orientation in each point. Calculations are fulfilled for
sequence of stages of a supercontinental cycle (Wilson cycle) on numerical two-dimensional model of
assembling and dispersing continents, driven by mantle flows; in turn, the flows themselves are forming
under thermal and mechanical influence of continents. Without such self-consistent interaction, Wilson
cycle would be impossible, and all structure of currents and stress fields would be another, qualitatively
differing from taking place in the real Earth. Our computer modeling demonstrates a number of realistic
features of the process: closing and then opening ocean; appearance of the marginal seas and inclined
subduction zones, etc. Mantle sources of radiogenic heat are also included in the model (in the
considered case they contribute one third of full thermal flow at the surface). Results of model
calculations have shown, that areas of the maximal shear stresses are located in the upper parts of
descending mantle flows, in particular, in the upper parts of inclined subduction zones. The model gives
that the sizes of such area where shear stresses are equal or exceed 35 MPa (350 bar), are
approximately 200 x 200 km. These magnitudes are about 10 times more the stress values in the bulk
of the manle model (3 - 5 MPa). At the same time the upgoing mantle flows are, with respect to
downgoing ones, more slow and wide, having significantly less stress magnitudes. Further, the area
before a leading edge of moving continent is outlined: the pair consisting of a descending and an
ascending mantle streams, close located to each other (similar to Andian subduction zone of South
America and closely located East-Pacific raising) which exists during rather long time, forming the
mantle area of essentially (approximately in 2.5 times in comparison with average value) increased
stresses. Later, in process of advance of continent, the ascending mantle flow deviates aside continent,
and the rest of a descending flow becomes more flat, comes under continent and gradually disappears;
stresses in it also gradually decrease. The picture is qualitatively similar to a situation at Pacific margin
of North America. This work was supported by the Russian Foundation for Basic Research (project 05-
05-65190).
Keywords: modelling, thermoconvection, stresses