Radiometric (K-Ar) dating of a reconnaissance nature conservatively brackets late Tertiary deformation throughout Peru between about 20 and 5 m.y. ago. Folding appears to have begun about 15 to 17 m.y. ago. If the timing for Huancavelica Department, central Peru, is applicable to other parts of the country, then deformation and considerable uplift and erosion had taken place by 10.5 m.y. ago.

Intense deformation and uplift in Peru is one of many major igneous and tectonic events that affected the western parts of North, Central, and South America and other parts of the globe during middle Miocene time. These events appear to be associated with first-order changes in the movement patterns of lithospheric plates and thus may reflect a major perturbation of the lithosphere-asthenosphere system.

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