The central Andes of northern Chile and northwestern Argentina developed in a largely autochthonous, intracontinental setting during Proterozoic and Paleozoic time through a recurrent sequence of extensional and compressional tectonic regimes. The exposed pre-Andean crust consists of tectonically isolated outcrops of: (1) metamorphosed basement, (2) plutonio bodies, and (3) slightly metamorphosed volcanic and sedimentary strata resting upon and intruded by multiple plutonic units. U-Pb and Nd-Sm geochronology indicates the existence of a Precambrian foundation for the central Andes dating from at least middle Proterozoic time. Three episodes of Precambrian/Paleozoic deformation/magmatism are recognized: (1) the Panamerican at the Precambrian/Cambrian transition, (2) the Caledonian at the Ordovician/Silurian boundary, and (3) the Variscan during the Carboniferous. Intrusive units can be grouped into synorogenic (S-type) and anorogenic (A-type) rocks based on structural, petrographic, and geochemical relations. Mafic lavas of middle Proterozoic to lowerCarboniferous age likely were generated during episodes of crustal dilatation.

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The tectonic evolution of the proto-Andean

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