Understanding the pull-apart basins in the western North Patagonia region, Argentina: lessons from the Jurassic Comallo volcanic sedimentary complex in the Ingeniero Zimmerman Resta area

To understand the development of pull-apart basins in western North Patagonia, Argentina, we examine a volcanic-sedimentary sequence in the Ingeniero Zimmerman Resta area, dated between 187.4 Ma and 163.42 Ma. This sequence correlates with specific sections of the Comallo volcanic sedimentary Complex. The sequence includes three volcanic periods and two interbedded sedimentary periods. The first period features dilute and dense pyroclastic flows or surges from phreatomagmatic eruptions, along with small, shallow lakes or lagoons. The second period includes intermediate- to basic dense pyroclastic flows, effusive flows, and limestones. The third period consists of rhyolitic flows and dacitic and andesitic dikes. The rocks are subalkaline with a calc-alkaline trend, similar to those found in cold, wet, oxidized magmas in subduction zones, which are characterized by mantle flux melting. The Pliensbachian crystallization age corresponds to that of several volcanic complexes, indicating a temporary, localized volcanic episode in western North Patagonia. The geological structures, stratigraphic organization, and sedimentary and volcanic sequences in this area suggest that these deposits formed in pull-apart depocentres during the Lower Jurassic.