Subduction collapse and the isolation of southwest Gondwana basins from the Panthalassa Ocean

Late Paleozoic seaways in southwestern Gondwana intermittently connected the Panthalassa Ocean with the continental interior, shaping sedimentation, climate, and biogeography across forearc to intraplate basins. While the closure of southern marine inlets feeding intraplate regions is well explained by crustal thickening during the Gondwanide orogeny, the latest Permian–Early Triassic disconnection of western seaways supplying forearc and back-arc basins along the proto-Andean active margin remains enigmatic. This disconnection coincided with global deglaciation and with mid-Permian extensional collapse following proto-Andean mountain building (San Rafael orogeny), which is paradoxical. Here we test whether a large-scale interruption of subduction associated with the Choiyoi magmatic province could have generated margin-wide uplift sufficient to disrupt marine connections at this time. First-order dynamic topography models indicate that shutdown of subduction between ∼275 and 250 Ma would have reversed dynamic subsidence and produced broad surface uplift of the Choiyoi magmatic belt. We propose that this uplift severed marine connections between the Panthalassa Ocean and western basins, forming an orographic barrier that, together with global climatic trends, promoted aridification across the continental interior.