THE TECTONOSTRATIGRAPHIC DEVELOPMENT OF PATAGONIA, AND ITS RELEVANCE TO HYDROCARBON EXPLORATION

The history of terrane accretion along the Pacific margin, that formed the Palaeozoic basement to Patagonia, is discussed. This pre-existing NW-trending basement fabric was periodically reactivated by shear str ess, resulting from near-continuous oblique Pacific subduction process es, producing pull-apart and extensional grabens. During the Permo-Tri assic, an asymmetric passive rift developed east of an eastwardly-dipp ing simple shear, following the axis of the proto-South Atlantic, and was invaded by a shallow sea. The Falkland (Malvinas) Microplate is sh own to have docked with Patagonia in the Early/Mid Jurassic. Clockwise symmetrical rotation and crustal deformation of the Falklands (Malvin as) and other microplates between east-west trending, dextral strike-s lip faults controlled the development of the southern transverse Atlan tic margin basins. Early restricted deposition in these basins (Early Jurassic-Neocomian) led to the deposition of proved continental source -reservoir associations. Rifting and transverse dextral strike-slip sh earing propagated northwards, up the axis of the Atlantic. As terrane collision progressed. the rift zone widened SWwards to the Pacific and NEwards to the Colorado Basin. Atlantic sea-floor spreading in the Ne ocomian, and subsequent thermal sag of the Atlantic margin, is shown t o have culminated in a major transgression in the Maastrichtian, which formed a regional seal for hydrocarbons.