THE TECTONO‐STRATIGRAPHIC DEVELOPMENT OF PATAGONIA, AND ITS RELEVANCE TO HYDROCARBON EXPLORATION

Abstract

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 stress, resulting from near‐continuous oblique Pacific subduction processes, producing pull‐apart and extensional grabens. During the Permo‐Triassic, an asymmetric passive rift developed east of an eastwardly‐dipping simple shear, following the axis of the proto‐South Atlantic, and was invaded by a shallow sea. The Falkland (Malvinas) Microplate is shown to have docked with Patagonia in the Early/Mid Jurassic. Clockwise symmetrical rotation and crustal deformation of the Falklands (Malvinas) and other microplates between east‐west trending, dextral strike‐slip faults controlled the development of the southern transverse Atlantic 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 shearing 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 Neocomian, and subsequent thermal sag of the Atlantic margin, is shown to have culminated in a major transgression in the Maastrichtian, which formed a regional seal for hydrocarbons.