Mantle influence on Andean and pre-Andean topography

DÁVILA FEDERICO M.; LITHGOW-BERTELLONI CAROLINA ; MARTINA FEDERICO ; AVILA PILAR

The making of the Chilean-Argentinean Andes

Springer

Año: 2018; p. 363 - 385

Mantle convection can drive long-wavelength and low-amplitude topography, whichcan occur synchronously and superimposed to tectonics. The discrimination etween these two topographic components, however, is difficult to assert. This is because there are still several uncertainties and debates in the geodynamic community, for example the scales and rates of dynamic topography. Geological, geomorphological, geophysical measurements and/or landscape analyses might assist to validate models. In this contribution we provide new geological evidences along the Central and Patagonian Andes, which demonstrate that dynamictopography has been an important component on the South American landscape formation as well as in the ancient western Gondwana. Our examples in the Argentine Pampas show that dynamic topography is required to explain not only the basin subsidence but also the whole observed topography. We also suggest that the dynamic components in this region are much lower than numerical models (average dynamic subsidence rates of ~0.04 mm/yr ?-this work-, which contrast with the ~0.1 mm/yr estimated in the US). We also propose two strategies toanalyze ancient cases. The first requires of comparing a total elevation proxy, like the equilibrium lines (or ELA) in glaciated areas, with model topography derived from geochemical studies of mantle rocks. A second strategy was the analysis of the Triassic rifting evolution of western Argentina (post-rift sag deposits). Sag deposit thicknesses exceed 2 km, which do not correlate with the hundred-meter thick thermal calculated by rift subsidence modelling.