Tectonic Evolution of the South Atlantic from Late Jurassic to Present (Paleoceanographic Mapping Project Progress Report No. 27-1287)
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The breakup of the continents around the South Atlantic was characterized by a stepwise, northward-propagating rift system, beginning in the southernmost South Atlantic. Fit reconstructions of South America and Africa that require rigid continental plates result in substantial misfits either in the southern South Atlantic or in the equatorial Atlantic. To achieve a fit without gaps, we assume a combination of complex rift and strike slip movements: 1. along the South American Parana-Andean Cochabamba deformation zone, 2. within marginal basins in South America (Salado, Colorado basins), and 3. along the Benue Trough/Niger Rift system in Africa. These faults are presumed to have been active before or during the breakup of the continents. Our model predicts a successive "unzipping" of rift zones starting in the southern South Atlantic. Between 150 Ma (Tithonian) and approximately 130 Ma (Hauterivian), rifting propagated to 38°S, causing tectonic movements within the Colorado and Salado basins. Subsequently, between 130 Ma and Chron M4 (126.5 Ma) the tip of the South Atlantic rift moved to 28°S, resulting in intracontinental deformation along the Parana-Andean Cochabamba line. Between Chron M4 and Chron MO (118.7 Ma) rifting propagated into the Benue Trough and Niger Rift, inducing rift and strike slip motion. After Chron MO (118.7 Ma), the equatorial Atlantic began to open, while rifting and strike slip motion still occurred in the Benue Trough and Niger Rift. Since Chron 34 (84 Ma), the opening of the South Atlantic is characterized by simple divergence of two rigid continental plates, as shown in our set of revised seafloor spreading isochrons.