New and previous structural, geochemical, and geochronological data allow us to propose the existence of a late Triassic-earliest early Jurassic flat-slab episode (similar to 227-190? Ma), here referred to as the South Gondwanian fiat-slab, comparable in size with the largest present and previously documented flat-slab configurations on Earth. This event would have been responsible for the inland arc migration, from a western position on the Antarctic Peninsula to central Patagonia (Central Patagonian Batholith), as well as the widespread contractional pulse registered in southwestern Gondwana. The existence of this late Triassic shallow subduction episode is reinforced by a combination of P-wave seismic tomographic data and a recent plate kinematic reconstruction that reveal an anomalous inland location for the subducted slab, presently at the base of the lower mantle. In Lower Jurassic times, a slab-detachment episode developed simultaneously with the impingement and south-westward displacement of the Karoo mantle plume, would have favored the destabilization of the flat-subduction configuration. A re-establishment of the subduction in southwestern Gondwana, associated with the Lower Jurassic magmatic arc retraction (Subcordilleran Patagonian Batholith), occurred under extensional conditions most likely associated with slab rollback and a southwestward asthenospheric return flow. This upper mantle flow may have exerted a suction effect on the Karoo mantle plume towards Patagonia, expanding its lifespan with a continuous southwestward rejuvenation of the synextensional SLIP Chon Aike's magmatism.