The Cenozoic history of the southern Atacama Desert, Chile

Abstract

Four episodes of landscape evolution are recognized, each of which has led to the development of a regional erosion surface. The first phase began upon elevation of northern Chile above sea level in the late Mesozoic, and each subsequent phase commenced with a major incision of drainage into the preceding landscape. Radiometric dating of pyroclastic flows shows that the earliest elements of the present topography already existed in the Lower Eocene, and that most landforms had developed by the Middle-Upper Miocene. Deep canyon formation characterized the latest erosional phase which commenced in the Upper Miocene and is still continuing. Tectonic elevation of the Cordillera de la Costa in relation to the longitudinal depressions seems to have occurred early in the landscape history, though later remobilization along major structures has since taken place. Erosional landforms in the high Andes are often blanketed by constructional volcanic features and the migration of eruptive centres since Miocene times has displaced the continental watershed to the east. Tectonically induced relative sea level changes have caused late Tertiary transgressive deposits in the littoral region to have been terraced during an irregular marine regression. The landscape history which spans the whole of the Tertiary indicates that Andean relief generation has been a prolonged pulsative process. Supergene enrichment of the copper deposits took place under the older erosion surfaces between the Lower Eocene and the Upper Miocene, and the economic viability of a prospective mine can be largely predicted from the overlying topography.