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.

Impact of volcanism on the sedimentary record of the Neuquén rift basin, Argentina: towards a cause and effect model

“…The hanging‐wall blocks are defined by mainly NE‐ and ENE‐oriented extensional and partially inverted normal faults. These normal faults are spaced 0.1–3 km apart, ranging from 3 to 8 km in length, and show a predominant dip‐slip sense of movement and a displacement ranging from tens to several hundred metres (Figs and ; D'Elia et al ., ; D'Elia & Martí, ). The syn‐kinematic sequence of the Sañicó depocentre is the Sañicó Formation.…”

“…Based on the intra‐depocentre discontinuity surfaces and stacking patterns of the Sañicó syn‐rift, this syn‐kinematic sequence was separated into three sections, which in turn correspond to three accumulation stages: the lower, middle and upper stages (Fig. ; D'Elia et al ., ; D'Elia & Martí, ). Volcanic rocks are volumetrically the most important units in the lower and middle stages, while they are less abundant in the upper stage of the syn‐rift sequence (Fig.…”

“…(a) Detailed geological map of the Sañicó depocentre and location of stratigraphic logs shown in b (Modified from D'Elia & Martí, ; D'Elia et al ., ). (b) Stratigraphic logs of the syn‐rift succession of the Sañicó depocentre.…”

“…Detailed geochemical, petrographic, petrologic data, as well as a tectono‐stratigraphic model of this basin can be found in D'Elia et al . (, b); D'Elia & Martí (); and D'Elia et al . ().…”

“…However, most tectono‐stratigraphic works on extensional basins that addressed high‐resolution sedimentary models, were performed on successions with null concomitant volcanism (e.g., Leeder & Gawthorpe, ; Schlische, , ; Leeder et al ., ; Schlische & Anders, ; Ravnås & Steel, ; Gawthorpe & Leeder, ). The mainstreams of research that took into account volcanic rift successions were focused on stratigraphic and chronostratigraphic schemes (e.g., Baker & Mitchell, ; Baker, ; Ebinger et al ., ; Skilling, ; Moore & Kokelaar, ; D'Elia & Martí, ; Chambefort et al ., ; Downs et al ., ) or the relationships between tectonic, magmatic and volcanic processes, such as the relation between tectonic structures and the magmatic system, the types and rate of subsidence (i.e., tectonic or volcano‐tectonic subsidence), and what controls the development of different volcanic edifices (e.g., composite volcanoes and calderas) and their magmatic plumbing systems (e.g., Ebinger et al ., ; Martí, ; Skilling, ; Moore & Kokelaar, , ; Ebinger & Casey, ; Spinks et al ., ; Wolfenden et al ., ; Aguirre‐Díaz et al ., ; Ferguson et al ., ; Rowland et al ., ; Ebinger & Scholz, ; Acocella, ). Together, these studies illustrate fundamental feedbacks between tectonic, magmatic and volcanic process in rift basins, and show how related basin subsidence affects sedimentary processes.…”