Neogene erosion surfaces and the Andean uplift in northern Peru

The Andean flank in central Peru is characterized by stepped profiles involving up to 20 surfaces and pediments resulting from multiple episodes of uplift and erosion. The study area exhibits the same sequence of surfaces and pediments. The erosional features are also recognized in the Eastern Cordillera in northern Peru. This paper focuses on the seven highest features in the range c. 2800-4700 m. Remnants of the four surfaces higher than 3800 m, which were formed during the interval c. 18-12 Ma, are only found south of latitude 6-6.5 degrees S. The Miocene metallogenic belt associated with the Western Cordillera terminates abruptly at that same latitude. The area north of c. 6 degrees S does not have any features higher than c. 3500 m, which is interpreted as indicating a later initiation of uplift. It also lacks any sign of magmatic activity. On the basis of these factors, the Central Andes are considered to terminate at c. 6 degrees S, the ranges to the north being assigned to the Northern Andes. Once episodic uplift was initiated in the area north of 6 degrees S, it continued at the same rhythm as in the region to the south. There was no apparent change in the pattern of episodic uplift when the normal subduction regime changed to a flat-slab regime at c. 11 Ma, probably as a result of the subduction of the Inca Plateau. The distribution of the erosion surfaces indicates that episodic uplift affected the whole of the Andean Block in northern Peru. It appears that the individual episodes occurred simultaneously and produced the same amount of uplift over the whole width of the cordilleras. There is no sign of any interruption in the process, implying a continuous orogeny from the Mid-Miocene onwards.