Upper Cenozoic volcanism and tectonism in the Andes of northern Chile

Abstract

Recent geological and radiometric information of the Upper Cenozoic volcanic sequences of northern Chile, in conjunction with previous evidences, point out the complex evolution of the Central Andes volcanism. Volcanic activity developed along the Andean Range during the last 23 m.y., appears to have been temporally and genetically related to tectonic movements that shaped the major morphostructural features of this region. Since the Middle Miocene (12 m.y.) there has been a constant overlap, both in time and space, between lavas and ignimbrites. However, ignimbrite eruptions seem to predominate up to the Upper Miocene, while lava eruptions are dominant from the Pliocene to the Quaternary. Small-scale chronological and volumetric variations of the volcanic activity in the studied areas, make difficult the correlations with volcanic episodes through long distances. Units older than Pliocene have been folded and thrusted as a result of compressive movements that occurred ca. 7-4 m.y. ago. This deformation is mostly remarkable at the borders of major faulted blocks. These blocks were structured along pre-existing fractures caused by tectonic movements during the Lower Miocene. Pliocene and Quaternary block movements developed mainly through N-S fault systems. These faults, together with NW-SE and NE-SW systems, control the spatial distribution of most volcanic vents in this region. Locally, the N-S faults may correspond to reactivations of previous fault zones. This allowed successive effusions of volcanic material, at least during the last 17 m.y.