Paleozoic volcanic events in the Central Andes

Abstract

Paleozoic volcanic rocks of northern Chile (21–27°S) can be subdivided into Early Ordovician, Early Carboniferous, and Late Carboniferous to Triassic episodes. At the western and eastern margin of the Alta Cordillera and in the Chilean Precordillera, isolated outcrops of Early Ordovician submarine basic lavas and siliceous volcanic apron deposits occur (submarine deposition level <500 m). The basaltic-andesitic lavas and the calc-alkaline dacitic-rhyolitic volcaniclastic rocks probably formed in an active continental margin setting. South of 26°S in the Cordillera de la Costa, submarine (ultra-)basic lavas and subordinate siliceous volcaniclastic rocks are locally intercalated with Devonian/Carboniferous flysch. The alkaline and tholeiitic (picro-)basalts are assumed to have been formed in a continental tensional regime originating from partial melts of a garnet-bearing mantle source. The magmas of the associated siliceous volcaniclastic deposits possibly evolved from the tholeiitic melts. Extensive outcrops of thick Late Carboniferous to Triassic volcanosedimentary units are known from the Pre- and Alta Cordillera. The terrestrial volcanic rocks consist predominantly of different types of siliceous tuffs with subordinate basic lavas. The calc-alkaline spectrum of basaltic andesites to rhyolites displays geochemical features of an evolved active continental margin magmatism with a pronounced within-plate tendency. The Early Ordovician volcanic deposits are assumed to form part of the active continental margin of Gondwana. The Early Carboniferous volcanic rocks are seen as having formed during a tensional stage of the flysch basin development. An active continental margin setting, which is well established as a geotectonic model for the Southern Andes in Late Carboniferous to Triassic time, might have extended northward into the southern Central Andes.