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
JSS017 Oral Presentation 2373
The influence of deformations on the P-T-t conditions in continental
collisional structures
Dr. Olga Parphenuk
Physical processes of the Earth's interiors Institute of Pfysics of the Earth Russ. Ac. Sci.
Extensive development of horizontal and oblique motions of crustal plates and blocks leads to
nonstationary disturbances in the thermal regime, the heat flow and the surface and Moho topography.
Thermal-mechanical models of continental collision including horizontal shortening and brittle
overthrusting in the upper crust and lower crustal viscous flow are applied to the simulation of the
thermal and tectonic evolution of the overthrusted structures. Finite-element 2-D modeling was used to
examine the conditions under which ductile flow of the rheologically layered lower crust and upper
mantle can produce the structure with crustal roots and surface uplift as a result of shortening, loading
and erosion. The thermal effects of collisional process and postorogenic stage are studied. Thermal
calculations show that the main temperature increase is observed at depths of the middle and lower
crust and is fairly significant (up to 250K). In other words, the temperature characteristic of depths of
40-60 km is attained at depths of 20-40 km, creating there conditions for the partial melting. At the
deeper mantle levels the collisional geotherms mainly follow the deformation. Since the collisional model
is predominantly two-dimensional, it can provide insights into the variety of metamorphic conditions in a
region that experiences deformations in a horizontal compression setting. Different P-T histories and the
variety of metamorphic conditions at the surface are obtained as a result of the upward movement
along the fault, the additional loading redistribution due to erosion, and the viscous compensation at the
level of the lower crust. The final and postcollisional stages are caracterized by the significant heat flow
increase because of the thickening of the heat producing upper crust layer. The sedimentary basins are
formed at the edges of the collisional uplift by the rocks denudated from the surface elavation. At the
frontal edge of the thrust sheet the basin depth reaches the value of ~ 4 km with the maximum erosion
level of ~9 km. At the postcollisional stage the compressional regime is changed by extension but under
the stresses of an order of magnitude less. The research is supported by the Russian Foundation for the
Basic Research (grant 06-05-65221).
Keywords: overthrusting, collision, evolution