Mantle influence on Andean and pre-Andean topography

Abstract

Mantle convection can drive long-wavelength and low-amplitude topography, which11 can occur synchronously and superimpose to tectonics. The discrimination between12 these two topographic components, however, is difficult to assert. This is because there13 are still several uncertainties and debates in the geodynamic community, for example14 the scales and rates of dynamic topography. Geological, geomorphological,15 geophysical measurements and/or landscape analyses might assist to validate models.16 In this contribution we provide new geological evidences along the central and17 southern Andes, which demonstrate that dynamic topography has been an important18 component on the South American landscape formation as well as in the ancient19 western Gondwana. Our examples in the Argentine Pampas show that dynamic20 topography is required to explain the whole observed topography and that the amount21 of dynamic components is much lower than proposed in previous work (average22 dynamic subsidence rates of ~0.04 mm/yr, which contrast with the ~0.1 mm/yr23 estimated in the US). We also propose two strategies to analyze ancient cases. The first24 requires of comparing a total elevation proxy, like the equilibrium lines (or ELA) in25 glaciated areas, with model topography derived from geochemical studies of mantle26 rocks. A second example was taken from the Triassic rifting evolution of western27 Argentina (post-rift sag deposits). Sag deposit thicknesses exceed 2 km, which do not28 correlate with the hundred-meter thick thermal calculated by rift subsidence modelling.