INTERCRATONIC OROGENS: THE CARIBBEAN AND SCOTIA ARCS

The Caribbean and Scotia arcs are two striking features of any tectonic map of the Earth and are in fact nearly identical in size. They are respectively located between North and South America, and South America and Antarctica, joining the North American Cordillera to the Andes, and the Andes to the West Antarctic continental margin orogen. Their tectonic evolutions can be related to the relative motion between the two pairs of cratons. Their evolving physiography produced critical controls, varying with time, on the movement of biota between the cratons, and between the Pacific and Atlantic Oceans.

The Caribbean arc differs from the Scotia arc with the presence of the Central American land bridge. Yet differential motion along the Shackleton Fracture Zone between Cape Horn and the tip of the Antarctic Peninsula has produced a ridge as shallow as 700 meters. This ridge with only minor changes in plate motions could develop into a subduction zone and generate an island arc. Absence of a South America-Antarctica land bridge permits a complete and vigorous wind-driven circum-Antarctic current and intense sediment scour in Drake Passage.

Cenozoic magnetic anomalies have been identified in Drake Passage and the eastern Scotia Sea where oceanic crust was formed as Antarctica separated from South America. High sedimentation rates, possible formation during the Cretaceous Normal Superchron, and a large igneous province obscure the equivalent history of the older Caribbean arc and seafloor. The nature and tectonic history of these 'fusible orogenic links' between the continental margin cordilleras of the western Americas and Antarctica are considered as are their evolutions in terms of possible 'mantle return flow' from the Pacific Ocean basin to the Atlantic Ocean basin. Possible analogs to the ancient geologic record such as a link between the Ordovician Taconic and Famatinian arcs of North and South America are also considered.