The Early Stages of the Magmatic Arc in the Southern Central Andes

Abstract

A temporal and tectonic framework for the initiation of the Andean magma-tism and its most early stages are presented in this work, based on the current geological, geochemical and geochronological information available in north-ern Chile between 20º00’ and 30º00’S. This information has been collected from Triassic and Jurassic plutonic, volcanic and volcanosedimentary units cropping out mainly at the Coastal, Domeyko and Frontal Cordillerasand the Precordillera, as two roughly parallel belts that extend for more than 1000 km in the Chilean territory. The petrological and geochemical data suggest that the magmatism during the Triassic and Jurassic was dominantly in-termediate in composition and had arc or subduction affinities.. The magma sources should have had a mantle component, but the crustal influence was greater during the Triassic. The geochronological information show a significant magmatic lull near the Triassic–Jurassic boundary, associated to the migration of the arc to the present-day Coastal Cordillera. Nonetheless, there are no more evidences for a change in the tectonic setting from the Triassic to the Jurassic. Therefore, the early stages of the Andean magmatism can also be represented by the Triassic igneous units.