WAS THE FORMATION OF THE ANDEAN HIGH-PLATEAU TRIGGERED BY DRY CLIMATE? PROPOSALS FROM PROCESS NUMERICAL MODELING

High plateaus are generally thought to result from tectonic compression interfering with pre-existing structural heterogeneities of the crust and in association with other tectonic processes such as viscous lower crustal flow. Computer modeling integrating climatic, erosional and tectonic processes suggests in this paper that a feedback effect between climate and tectonics is at least partially responsible for the formation of high-plateaus, providing an alternative to tectonically-controlled mechanisms. In the model, regardless of the structural tectonic setting, dry climatic parameters (particularly if imposed at the early stages of tectonic shortening) favor the formation of endorheic intramountain basins which transfer the accommodation of tectonic shortening towards the external parts of the orogen, eventually leading to the formation of a high plateau. This feedback operates in the following steps: 1) Dry climatic conditions at the early stages of orogenesis (later perpetuated in the highlands by orographic isolation) favor the tectonic defeat of rivers draining the orogen, promoting lake formation, intramountain sediment trapping, and the eventual formation of an internally-drained (endorheic) basin; 2) Endorheism extends the life of intramountain basins thus increasing the mass trapped within the orogen and expelling deformation towards the external parts of it; and 3) This propagation of tectonism further isolates the central parts of the orogen from incoming precipitation, reinforcing intramountain sediment trapping. This feedback phenomenon is able to predict basic topographic, drainage, and tectonic differences between orogens lacking a high-plateau such as the Alps and orogens with a well-developed high plateau such as the Andes, without invoking tectonic controls or inherited weaknesses in the crust. It also suggests that internal drainage and high-plateaus might be a natural stage of orogeneses starting under dry climatic conditions and/or rapid tectonic shortening rates, such as the Andes.