INVESTIGADORES
DAVILA Federico Miguel
congresos y reuniones científicas
Título:
Non-isostatic contribution in the topography of the Andean broken foreland?
Autor/es:
NÓBILE, J., DÁVILA, F.M.,
Lugar:
Melbourne, Australia
Reunión:
Conferencia; Geomorphology Conference; 2009
Resumen:
The Sierras Pampeanas (SP), in the south central Andes (28°-34° SL), is the analogue for “broken forelands”. It developed during a slab flattening stage, which drove crustal refrigeration and transmission of deformation far into the foreland (>500 km from the modern Chilean trench). Although this region is considered as a homogeneous basement-thrusting province, it shows major differences along and across strike in the tectonic features, basin dynamics and also in the topography. Long-wavelength elevation models (>300 km) shows a decreasing in altitude from N to S. While the northern mountain picks are >4000 m and the modern basin levels above 700m, the southern part of the broken foreland is partly depressed (with picks <<2000 mosl and basin levels <<500 m). But, the “depressed” southern region is under high coupling due to flat subduction and where, according to the mechanical models, the higher altitudes would be expected. This expected differences has not been detected by apatite fission track thermochronology. In addition, both regions record strong differences in the crustal composition. While the northern SP shows clear evidences of overcompensation, with Bouguer anomalies much flatter than expected when compared with free-air gravity; the southern SP record an anomalous crustal thickness >55 km, associated with low elevation topographies <1500 mosl. As suggested by seismological studies, overdensification of the lower crust (eclogitization) might explain the “depression features” in the southern SP, but it does not account for the non-compensated situation to the north. We suggest that non-isostatic forces, driven by mantle flow, are contributing in the isostatic equilibrium of the Andean foreland and allow explaining the “residual topography”. A geomorphologic approach will assist to tackle these problems in the Andean broken foreland. Studies with lower temperature thermochronometer (eg. U-Th/He) are planned to test subtle exhumation differences. Studies are complemented by dynamic topography models.