Measuring dynamic topography in South America

DAVILA, FEDERICO; AVILA, PILAR; MARTINA, FEDERICO; CANELO, H.; NÓBILE, JULIETA; COLLO, G.; SANCHEZ NASSIF, F.; EZPELETA, MIGUEL

Andean Tectonics

Springer

Año: 2018;

The understanding of the modern observed topography, as well as basin andlandscape evolution, requires of a good comprehension of isostatic and dynamicforces (in addition paleoclimate changes) acting at different time and space scales.Here we revisited different topographic problems of South America using the residualtopography concept at regional and local scales. Residual topography is theremaining value that results from the balance between modelled isostatic elevationsand measured elevations. This is considered the best measurement of dynamictopography. We incorporate local geological observation to test the dynamictopography from modern and ancient examples using local subsidence analyses aswell as paleo-elevations calculations from previous studies and from paleolithosphericthicknesses estimations based on geochemical studies on basalts. Threetransects across the northern-central, southern-central and southern Andes(Peruvian Andes-Solimoes-Amazonas, Precordillera-Pampas and Patagonian areas,respectively) were inspected, particularly in areas affected by the subduction ofoceanic ridges, where subsidence and/or uplifting might been influenced by dynamicforces. Our results show contradictory results and conflicts from north to southamong models and with respect to previous studies. While the pericratonic andcratonic areas of Peru and Brazil, further east from the leading edge of the Nazcaridge influence, show positive residual topographies (dynamic uplift), localsubsidence studies evidence a residual subsidence driven by sublithospheric forces.The opposite occurs in Patagonia. Most geological interpretations and oursubsidence models suggest the need of dynamic subsidence, which does notaccount for the negative residual topography models. The southern-Central Andesestimations, in turn, show relatively good matching between subsidence models andresidual topographies approaches in the pericratonic areas (in the Pampas), whichsupport dynamic subsidence likewise the dynamic topography modelling. But strongdisagreements arise along the flat-slab segment, where dynamic uplifting areexpected from dynamic topography models. We suggest that the regional elevationstate is mainly rule by the lithospheric and crustal structure and composition,supported by dynamic forces that can laterally change and generate local2morphological features like isolated basins or promontories. Future and ongoing studies will allow giving answers to the apparent contradictions.