Abstract: Mesozoic Breakup of SW Gondwana: Implications for Regional Hydrocarbon Potential

MacDonald, D.; Gomez-Perez*, I. CASP - University of Cambridge; Franzese, J.; Spalletti, L. - Centro de Investgaciones Geologicas, Argentina; Hole, M.; Trewin, N. - University of Aberdeen; Dalziel, I.; Gahagan, L.; Lawver, L. - The University of Texas at Austin

In SW Gondwana reconstructions there are good fits of major continents and poorly constrained fits of microcontinents (e.g., West Antarctica). The Falkland/Malvinas Plateau was assumed to be a rigid fragment of pre-Permian South American crust, in the former group. However, there is evidence for rotation of the Falkland/Malvinas Islands by ~180° after 190 Ma, making it unlikely that the plateau behaved as a rigid structure during breakup. To test this hypothesis, we have compiled 13 new palaeogeographic maps for the Permian-Cretaceous of the southern Atlantic area and carried out fieldwork on the islands.

Our work suggests: 1.) The rotation hypothesis is correct. In the Late Paleozoic, the islands lay east of Africa, the plateau was ~33% shorter and Patagonia was displaced east with respect to the rest of South America along the line of the Gastre Fault System (GFS). 2.) Break-up was driven by a mantle plume, emplaced at c.18OMa. 3.) The microcontinents moved as discrete terranes, the Falkland/ Malvinas block rotating clockwise during 190-165 Ma dextral slip on the GFS-Agulhas fracture system.

There are four main implications for the hydrocarbon potential: 1.) there was major crustal reorganization during early stages of breakup; 2.) Jurassic-Cretaceous basins north and east of the islands probably opened in a manner analogous to the late Mesozoic basins on the South African shelf; 3.) intermittent physical barriers controlled deposition of Upper Jurassic-Cretaceous anoxic sediments; 4.) during breakup, clastic sediments changed from a uniform volcaniclastic provenance to local derivation, with variable reservoir quality.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil