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Mesozoic Breakup of Southwest Gondwana and Basin Formation Along the Argentinean Atlantic Margin

Abstract

The opening of the South Atlantic in the Early Cretaceous was only the final stage of a complex rifting process that SW Gondwana experienced throughout the Mesozoic. This work is a tribute to the pioneering efforts of Uliana, Biddle and Cerdán (1989), thirty years after the publication of their integration in AAPG Memoir 46. Extension initiated after the Mid-Permian and Mid-Triassic Gondwanan orogeny producing extensional reactivation of formed compressive structures in the Cape-Ventania foldbelt, and intracontinental rifts in Africa and South America. Since the Early Jurassic, rifting on Eastern Africa was triggered by the impact of the Karoo plume, which produced the breakup of Africa from Antarctica and India and the opening of the Mozambique channel and the Weddell Sea. The results of this work suggest that the Colorado and Salado basins offshore Argentina are part of the Jurassic African Karoo rift system that remained perched on continental crust on the south American conjugate margin across the South Atlantic Ocean. Throughout the Mid and Late Jurassic, retroarc extension in Patagonia and the Antarctic Peninsula is responsible for the synextensional emplacement of the Chon Aike silicic Magmatic Province. The Malvinas and Austral depocenters formed at this time as part of a larger system related to differential slab rollover and a slab tear in the south, that introduced a thermal anomaly responsible for the successive opening of the Weddell Sea. Retroarc extension reaches a maximum in the Late Jurassic, with the opening of the Rocas Verdes back-arc basin and the Rawson/Valdés-Outeniqua basins further inland. In the Early Cretaceous, extension largely oriented E-W and associated with far-field forces controlled the initiation of rifting and the opening the South Atlantic Ocean. The Paraná plume only reached the surface after oceanization had started in the southernmost segment of the South Atlantic. Four superimposed rifting settings were identified in the Argentinean offshore and are key to understanding the complex Mesozoic breakup history of SW Gondwana.