Geomorphic and tectonic evolution of the Ecuadorian Andes

In Early Miocene times the Cordillera did not exist and the Pacific Ocean r eached the Oriente. In the Middle Miocene, the uplift of an elongated swell , consisting of Palaeozoic and older rocks, created the Eastern Cordillera. Decollements were activated diverging away from the Eastern Cordillera. In the eastern trench, located approximately in correspondence with the prese nt day Interandean Depression, many thousands of meters of sediments were d eposited. A planation surface was created at the end of Lower Pliocene from the Costa to the Oriente graded to sea level. Later, ignimbric flows cover ed much of the plantation surface. Uplift brought the planation surface to 3500-4000 m. The Interandean Depression, bounded by normal faults, was crea ted during the Upper Pliocene, and large strato-volcanoes erupted at this t ime. The volcanic activity contributed to the fillings of an accumulation p lateau preserved today in many parts of the Interandean Depression. The cre ation of the Interandean Depression is the result of lateral spreading acti vated as a consequence of uplift of the Cordillera. In the Middle and Late Pleistocene the Cordillera and the Accumulation plateau were mostly affecte d by downcutting with minor episodes of accumulation during the cold phases . (C) 2000 Elsevier Science B.V. All rights reserved.