An early Jurassic graben caldera of Chon Aike silicic LIP at the southernmost massif of the world: The Deseado caldera, Patagonia, Argentina

Abstract

Detailed geological mapping of 900 km2, newly defined volcanic and volcaniclastic lithofacies, multiple stratigraphic profiles, and a new zircon U/Pb eruption age (178.7 ± 1.9 Ma) describe an early Jurassic extensional-related piece-meal collapsed graben caldera in the eastern sector of Deseado Massif, at southern Patagonia. This volcano-tectonic structure, here referred to as The Deseado Caldera, collapsed at least twice controlled by two major NW-striking normal faults, during which a large acidic ignimbrite (predominantly moderate to extremely high-grade) and co-ignimbrite lag breccias were extruded through multiple NW-fissure vents. During the two post-collapse periods, alluvial fans, lagoons and laharic sedimentary environments re-worked the intra-caldera volcaniclastic deposits. Finally, numerous elongated and aligned rhyolitic lava domes and dykes were emplaced during the final magmatic resurgence stage. This caldera represents the first clear evidence of the extensional tectonic regime influence, associated with the inception of Gondwana breakup, on the eruptive mechanisms of the Jurassic Chon Aike Silicic LIP in the Deseado Massif.