The south american subduction zone : a study of rheological parameters using 3D finite element modelling

Sharma, Rekha GND

A 3D finite element modelling is carried out to test the rheology of the South American subduction zone. Two study areas are chosen, one from the Northern Andes (20°S-25°S) and another from the Southern Andes (36°S-40°S) having different geometric features. Both models contain six homogeneous units with different rheological parameters. A frictionally coupled zone is assigned between the subducting and the overriding plate. The coefficient of friction (µ = 0.14) is found to produce the geological estimated uplift rate of 0.2 mm/yr for the Altiplano plateau region. Increase in the strength of the frictionally coupled zone amplifies the drag of the subducting plate, which in turn decreases the amount of uplift of the overriding plate. Combined mechanical effect of slab pull velocity and the gravity force is observed to create subsidence in the overriding plate for all coefficients of friction (µ = 0.1, 0.2, 0.5). The overriding plate subsidence increases with increase in coefficient of friction. Overriding plate uplift is also found to dependent on its crustal thickness. Decrease in the crustal thickness of the overriding plate implies increase in its uplift. Slab dip angle is also an important physical parameter that affects the overriding plate uplift. The Southern Andean model with shallower dip angle (β = 13.4°) is observed to produce lower uplift in the fore-arc region but higher uplift in the back-arc region as compared to the Northern Andean model having a steep slab dip angle (β = 18.4°). The oblique subduction of the subducting plate leads to subsidence in the overriding plate for all coefficients of friction (µ = 0.0, 0.1, 0.2, 0.5).


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