THE LATE PERMIAN PEINE AND CAS FORMATIONS AT THE EASTERN MARGIN OF THE SALAR-DE-ATACAMA, NORTHERN CHILE - STRATIGRAPHY, VOLCANIC FACIES ANDTECTONICS

late Permian 2 km thick volcaniclastic succession is well exposed in t he area between the Cerros de Cas and Cerro Lanquir at the eastern mar gin of the Salar de Atacama in northern Chile. From base to top it con sists of the three members of the Peine Formation and the three member s of the Cas Formation. The terrestrial succession is dominated by pro ducts of andesitic to myodacitic effusive and explosive volcanism. Onl y in the Middle Member of the Peine Formation sedimentary deposits are predominant. Here, acustrian, flood and braid plain facies interlinge r laterally in a basin-basin margin setting. Deposition was accompanie d by extensional tectonics. From sedimentary and volcanic paleocurrent indicators of the Peine and Cas Formations, and geochemical data of m agmatic rocks of the region, it is inferred that the succession was fo rmed at the eastern margin of an extensional intra-arc basin. Volcanic facies analyses reveal that, at least, some of the basic and silica-r ich volcanic centres were located close to or even within the field ar ea, The thick ignimbrites and proximal fall out deposits of the Middle Member of the Cas Formation are supposed to belong, together with rin g dyke and central intrusions, to a late Permian caldera complex, whic h is located in the Cerro Lanquir area (Lanquir Caldera Complex).