RESOLVING THE FALKLANDS/MALVINAS CONTROVERSY: IMPLICATIONS FOR SUPERCONTINENT RECONSTRUCTION

There is a long-standing controversy over the fit of the Falkland Islands/Islas Malvinas into reconstructions of SW Gondwana. In general terms there are two camps: fixists argue that the present-day position of the islands relative to South America was the same in the early Mesozoic; rotationists believe that the islands were part of the east side of Africa until fragmentation, rotation, and translation began in the Toarcian (Early Jurassic). The original hypothesis was posited in 1952, based on a supposed fit of the islands to the SE corner of the Karoo Basin in Natal. The hypothesis was reborn in 1982 with publication of a paleomagnetic study supporting rotation.

The fixist argument is based on three strands. First, the supposed lack of structures relating to rotation and translation of the islands. Second, arguments based on Late Jurassic or even Cretaceous structures which formed after the proposed time of rotation; these studies are generally at a sub-basin scale. Third, a small detrital zircon study, suggesting a South American provenance for the Devonian of the Falklands. Rotation is supported by a series of large-scale studies applying various tests to the rotation hypothesis: macropaleontology, glacial sedimentology, a second paleomagnetic study, structural geology (two studies), Permian lithostratigraphy and sedimentology, igneous geochemistry, and a global plate tectonic reconstruction. The key strands of the rotationist argument are: 1. that a pre-rift fit of the South Atlantic to a fixed Africa must involve deformation of South America, and 2. that all of the geological studies point to a better fit of the islands to SE Africa than to South America.

This paper reviews the evidence for and against rotation It also:

• proposes a Triassic close-fit based on all the available geological evidence and discusses the importance of tracking continental deformation;
• refutes the argument that ‘no evidence of a mechanism’ nullifies a hypothesis, which echoes Jeffreys’ arguments against Wegener’s theory of continental drift;
• uses the Falklands example to emphasise the importance of microcontinents in plate-tectonic reconstructions.