Chaines andines et chaines alpines; regard sur la geologie de la Cordillere des Andes au parallele de l'Argentine moyenne

Abstract

The tectonic evolution of the Andes was generally contemporaneous with the Alpine orogeny (Mesozoic-Tertiary). Pre-Andean tectonic cycles (Hercynian) involved Infracambrian and Paleozoic sediments. Comparison of the Andean cycle with the Alpine cycle shows a similar evolution in three major periods: a Mesozoic period characterized by strong compressional movements during which the thick sediments of the Chilean slopes were thrust over the relatively thin sediments of the Argentine slopes; an Eocene-Oligocene-Miocene period characterized by the deformation of terrigenous formations as a result of andesitic volcanism and reverse faulting; and a Plio-Quaternary period marked by basalt flows and the accumulation of thick terrigenous sediments in faulted, deformed basins. The absence of flysch deposits, ophiolites, major thrust sheets, and widespread metamorphism in the Andes, however, distinguishes them from the Alpine ranges. Thus, two main types of pericratonic mountain ranges (as opposed to intracratonic ranges) should be differentiated: precursory (or Andean) ranges developed on the periphery of continents but within their margins and geosynclinal (or Alpine) ranges part of which are extracratonic.