Mantle influence on Andean and pre-Andean topography

DÁVILA, F.M.; LITHGOW-BERTELLONI, C.; MARTINA, F.; AVILA, P.; NÓBILE, J.C.; COLLO, G.; EZPELETA, M.; CANELO, H.; SANCHEZ, F.

The Evolution of the Chilean-Argentinean Andes

Springer International Publishing

Año: 2018;

Mantle convection can drive long-wavelength and low-amplitude topography, which can occur synchronously and superimpose to tectonics. The discrimination betweenthese 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 southern Andes, which demonstrate that dynamic topography 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 the whole observed topography and that the amount of dynamic components is much lower than proposed in previous work (average dynamic subsidence rates of ~0.04 mm/yr, which contrast with the ~0.1 mm/yr estimated in the US). We also propose two strategies to analyze 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 example was taken from 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.