Miocene crustal deformation in Southern Patagonian Andes and the rain-shadow effect – Argentina and Chile Javier Quinteros (
[email protected] ) Lab. de Tectónica Andina, Dto. de Cs. Geológicas, FCEN, UBA, Argentina Víctor A. Ramos (
[email protected] ) Lab. de Tectónica Andina, Dto. de Cs. Geológicas, FCEN, UBA, Argentina Pablo M. Jacovkis (
[email protected] ) Dto. de Computación e Instituto de Cálculo, FCEN, UBA, Argentina Abstract The development of Patagonian Andes is the result of uplift related to continous subduction climaxed by a ridge collision. One of the main features of this segment is the Southern Patagonian Batholith (SPB), a body that runs continously along all the segment in NNW direction with an average width of 120 km. The SPB, as it is fully positioned in the forearc, indicates an extreme denudation process that is explained by the establishment of an orographic rain shadow. The latter has produced drastic climatic changes during middle Miocene and some authors interpret it as a direct consecuence of a more than 1 km surface uplift. In this paper, we present a model designed to investigate the large-scale topography evolution from early to middle Miocene in a transect at around 47ºS taking into account tectonic deformation and surface erosion. The upper crustal deformation resulting from the eastward subduction of the Nazca oceanic plate, the convergence velocity and the geometry of the Bennioff zone (among other factors) were modeled through a strain-rate dependent visco-plastic rheology. The model numerically solves Stokes equations to compute the deformation. The problem is treated in a 2-D plane-strain state. Finite element methods are used for solving the equations. The erosion model is based on the one proposed by Beaumont and the stream power erosion law used by Willett. Our model takes care of slope, precipitation, elevation and wind direction and was calibrated using present-day precipitations. Experiments show that the orogenic uplift acted as a climatic stop to wet winds concentrating the erosion effects only on the west side in coincidence with isotope data recently presented by Blisniuk and paleontologic evidence on mammals fauna changes widely known in the region.
