USING TECTONIC GEOMORPHOLOGY TO UNDERSTAND THE TOPOGRAPHIC EVOLUTION OF THE COLOMBIAN ANDES

Testing hypotheses of biotic diversification that are linked to the uplift of the northern Andes and the evolution of the major river systems of South America, requires a clear understanding of the spatial variations in the timing of topographic growth. The timing of topographic growth is also important to understand the tectonic and geodynamic processes at work. Current models that explain the topographic growth in the northern (Colombian) Andes involve: a) initiation of shortening and progressive growth of topography since the Cretaceous-Paleogene or b) a rapid phase of surface uplift accommodated by high angle faults during the past 10 Ma. An alternative to the previous models could be a rapid phase of surface uplift associated with a flat slab subduction beneath the northern section of the Eastern and Central cordilleras, that started since ~10 Ma. Flat subduction of a thick oceanic plate north of 5° N could have resulted in strong coupling of the subducting and overriding plates, increasing convergent deformation and resulting in topographic growth. The isostatic adjustment accommodating the subduction of the plateau would have also contributed to the uplift. These models have contrasting implications for the regional paleogeography, as they imply differing times of orogenic uplift. This study will contribute to the debate over the timing, mechanisms and evolutionary consequences of topographic growth in the northern Andes by integrating new geomorphological data from the northern Andes including the analysis of incision of canyons in peneplain surfaces and geomorphic indexes (chi and ksn) on river profiles. Our preliminary results suggest that the northern Andes are undergoing uplift and this has resulted in recent drainage organization of the main inter-Andean rivers. This recent uplift is expressed north of 5 N in several low-relief high-elevation surfaces as the Altiplano Antioqueño and the Santander Mesas, which are deeply dissected by rivers.