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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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