Caldera events in a rift depocentre: an example from the Jurassic Neuquén basin, Argentina

Abstract

We analyse the volcanic stratigraphy of the Lower Jurassic synrift sequence of the Sañicó depocentre, which is a sub-basin of one of the most important hydrocarbon basins in South America, the Neuquén rift basin. The Sañicó depocentre comprises a complex multicyclic volcano-sedimentary succession. The oldest part of the succession preserves a volcano-sedimentary sequence interpreted as the record of a stratovolcano. The middle part of the succession is characterized by the emplacement of two thick ignimbrites that completely filled the depocentre. Finally, the uppermost part of the succession records subordinate volcanism characterized by andesitic lavas associated with epiclastic sediments. The Sañicó depocentre shows a complex subsidence history that involves an interplay between tectonics and volcanism. During the early and late synrift phases, subsidence was relatively slow and permitted the accumulation of thick sequences of volcanic and sedimentary deposits throughout a long period of time. During the middle synrift phase, subsidence was very rapid and allowed the accumulation of a thick ignimbrite sequence in a very short time interval. In this study, this middle episode is interpreted as corresponding to a caldera-like event in which rapid subsidence occurred along the same normal faults that controlled tectonic subsidence during the previous and subsequent episodes.