Mesozoic rifting evolution of SW Gondwana: A poly-phased, subduction-related, extensional history responsible for basin formation along the Argentinean Atlantic margin

Abstract

The opening of the South Atlantic in the Early Cretaceous was the final stage of the complex rifting history of SW Gondwana. In this contribution we reassess the chronology of Mesozoic basin formation in southern South America and Africa and integrate it in the long-term breakup history of SW Gondwana. Triassic rifting is characterized by intracontinental rifting in Africa (Karoo I phase), and retro-arc extension on the SW-margin of Gondwana. In the Early Jurassic, the impingement of the Karoo plume triggered rifting in Eastern Africa, producing the Karoo II basins (and the Colorado and Salado basins on the Argentinean shelf). East Africa rifting ultimately lead the breakup of Eastern from Western Gondwana in the Middle Jurassic. In Patagonia, the Austral, Malvinas and other related basins formed in association with the synextensional emplacement of the Chon Aike magmatic province in the Patagonian retro-arc. In the Late Jurassic the Rocas Verdes back-arc basin opened in southern Patagonia, while oblique rifting in the core of the Late Paleozoic Gondwanides orogen produced the Outeniqua and Rawson/Valdés basins. The South Atlantic Rift initiated in the Early Cretaceous associated with present-day E-W extension. Rifting occurred diachronically from south to north, initiating in the previously thinned Rawson/Valdés-Outeniqua segment. A precursor oblique rift system and a larger degree of extension in this segment could explain the lack of Seaward Dipping Reflectors (SDR) south of the Colorado-Cape fracture zones. Rifting and SDR emplacement occurred progressively to the north along different rift segments, producing strongly asymmetric conjugate margins.