MESOZOIC PERTURBATIONS OF THE EARTH SYSTEM: THE 80 MILLION YEAR OPENING HISTORY OF THE SOUTH ATLANTIC

We will present a series of Mesozoic time-slice maps of the South Atlantic documenting the complex history of strike slip faulting and oblique extension, which began about 80 Ma before final continental separation at 130 Ma. These reconstructions demonstrate that the primary control on the position of Atlantic opening was the age and structure of Precambrian blocks. They also show that early oblique extension was controlled mainly by the boundaries of Palaeozoic terranes, which were re-activated from the Late Triassic onwards. Recognition of this early extensional history explains both the clustering of failed rifts around the southern end of the South Atlantic and the basins on the Argentine shelf that sit at a high angle to the ocean margin. These reconstructions require that at the end of the period of oblique extension, the whole of the South Atlantic rift must have opened simultaneously. Improved understanding of the South Atlantic opening history allows us to address three important issues of Earth System science: 1. What is the record of the two extensive phases of plume-related volcanism (180 and 130 Ma)? Neither the plume-related topographic expression nor the erosional products of basalt volcanism have been identified. 2. How did the marine transgression into the evolving rift proceed? The "Walvis Ridge" model purports to explain the genesis of evaporites in the South Atlantic, but is a poor predictor of their distribution in southern and central parts of the ocean. 3. How were pre-existing sediment routing systems disrupted during breakup? In particular, it is possible that much of the sediment on the South American side of the rift was derived from large antecedent rivers draining Africa.