HR: 13:55h
AN: T13F-02    [Abstracts]
TI: Deriving and Testing Predictions from the Model of the Andean Orogeny
AU: * Sobolev, S V
EM: stephan@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, D-14473 Germany
AB: The high Andes were generated by the Cenozoic tectonic shortening of the South America plate margin overriding the subducting Nazca plate. Recently Sobolev and Babeyko (Geology, 33, 617, 2005) presented a numerical model of dynamic interaction between subducting and overriding plates focused at the Andean orogeny. The model suggests that the most important factor controlling magnitude of the tectonic shortening was fast and accelerating westward drift of the South America plate. Another important factor is shear coupling at the plates interface. The model with relatively high friction coefficient (0.05) at the Nazca-South America interface generates more than 300 km of tectonic shortening and replicates well crustal structure and evolution of the high central Andes. The model with the lower friction coefficient (0.01) and initially thinner crust results in less than 40 km of the South America plate shortening, replicating situation in the southern Andes. Here I derive two predictions from the Sobolev and Babeyko model and test them versus observations. (1) The consequence of about 5 times lower interplate friction in the southern Andes than in the central Andes is that down-dip limit of the frictional coupling domain between Nazca and South America plates should be by 10-20 km deeper in the southern Andes (south of 28°S) than in the high central Andes. The expected result of that is corresponding deepening of the down-dip limit of seismogenic zone and of locking zone of the interseismic deformation. This model prediction is consistent with seismological data and GPS observations. (2) The model predicts delamination of the mantle lithosphere of the shortening South America plate. It suggests that relatively cool delaminating material may move towards the trench by the corner flow in the mantle wedge. At some point the delaminating material blocks the corner flow, reducing the temperature in the mantle wedge and impeding the slab rollback. The consequence of these processes is simultaneous reduction of the magmatic arc activity and increase of tectonic shortening rate in the overriding plate during time of few to several Myr, depending on the volume of the delaminating material. Using the geological data on the tectonic shortening and statistics of the dated arc volcanoes at 19-22°S I show that the model-predicted sequence of signatures may have indeed show-up at the latitude of the Altiplano.
DE: 0560 Numerical solutions (4255)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8164 Stresses: crust and lithosphere
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005