Volcanism and tectonism in the southern Central Andes: Tempo, styles, and relationships

An important objective of volcanic research is to establish a cause-and-effect relationship between the age of fault kinematics and volcanic arc evolution based on structural and stratigraphic evidence. The predominant hyperarid climate in the Central Andes since Miocene times makes it a world-class area for investigating the evolution of a volcanic arc. This region records the complete development of the late Cenozoic Andean volcanic arc. This study focuses on the interpretation of volcanism in the context of recently dated tectonic structures along the southern Central Andes Volcanic Zone between 24.5 degrees and 27 degrees S. This segment of the arc has had a complex evolution and consists of hundreds of volcanoes, including constructional (monogenetic and polygenetic) and caldera volcanoes. By reviewing and reevaluating the geological maps in the literature, we are able to better constrain the temporal evolution of the central Chilean volcanic arc, including timing and kinematics of regional faults. Recognition of 15 Oligocene to Pleistocene ignimbrites and their sources has allowed us to define 11 caldera systems contemporaneous with effusive constructional volcanoes. The extent of the ignimbrite deposits allows them to be correlated between isolated outcrops that preserve different stratigraphic sequences, enabling the construction of a more complete and accurate volcanic stratigraphy. Two main NE-SW-and N-S-oriented thrust systems dominate the structural architecture of this segment of the arc. The first, located in the Precordillera, was active between 25 and 14 Ma and extends over 200 km to the northeast through the Pedernales-Arizaro thrust fault. Parallel to this thrust, the east-vergent Antofalla thrust fault system developed during Oligocene-Miocene times. The second system, located within the volcanic arc, includes sinuous N-S contractional structures that developed in pulses between the middle and late Miocene. There appears to be a cause-and-effect relationship between tectonic pulses and the development of volcanism, whereby changes in the upper crustal stress field lead to the generation of extensional domains. These conditions favor magma storage at upper crustal levels, thus promoting a suction-pump effect. The coexistence of both dominantly effusive constructional volcanism and explosive caldera volcanism results from the same tectonic conditions that produced shortening, as a consequence of the maximum compressive stress and conjugated extensions. In this paper, we suggest a new model that integrates the coexistence and contemporaneity of compressive structures and the widespread development of effusive constructional volcanism and explosive caldera volcanism along the Andean Oligo-Miocene volcanic arc.