Jurassic and Lower Cretaceous magmatic activity in the present-day CoastalCordillera and the Central Depression of northern Chile is marked by important plutonic and volcanic cycles. The Initial Basics unit of the Coloso Coastal gabbro complex contains the first intrusives into an ensialic marginal basin related to extension, probably due to strike-slip plate motion. These gabbros have affinities with continental tholeiitic basalts. The subsequent Jurassic Volcanic unit, ranging from basalt to andesite in composition, erupted onto the subsiding basin. Simultaneous with and after the eruption of the Volcanic unit, the Late Granitoids unit was intruded. The earliest intrusives of this Late Granitoid unit (GI of the Coastal Cordillera) follow the Initial Basics in time and have similar geochemical source indicators. Geochemical signatures of both the Volcanic unit and the Late Granitoid intrusives suggest that they are related to contemporaneous subduction. Some Late Granitoids (GII of the Central Depression) show evidence of significant crustal contamination much like that of modern Andean magmatism.
The Precordillera of the Cordón de Lila/Sierra Almeida area south of the Salar de Atacama (25°S68°W) was the center of continuous magmatic activity from Early Ordovician to Early Permian time. Various plutonic units form a basement that is overlain by Paleozoic to Cenozoic sedimentary and volcanic sequences. A continental tholeiitic series of komatiitic and tholeiitic pillow basalts, andesitic to plagidacitic lavas, and pyroclastic flows occurs along the north-central portion of this tectonic horst and is a key example for the early Paleozoic development of the central Andes. The lavas are intercalated with hemipelatic to very shallow marine clastic sediments. The sequence is solely affected by weak deformation and burial metamorphism of its stratigraphically lowest part. Geochemical data suggest formation of parental liquids in a lherzolitic upper-mantle source, followed by low-pressure tholeiitic differentiation through combined FC and AFC processes at two distinct crustal levels. The discharge of these lavas and the accompanying flysch-type sedimentation was triggered by crustal extension during Ordovician time, which resulted in a highly segmented, horst and graben-type geodynamic environment.
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