Reconstruction and break-out model for the Falkland Islands within Gondwana
The Falkland Islands are one segment of the Permo-Triassic Gondwanian Fold Belt that was displaced during the fragmentation of Gondwana. Palæomagnetic, structural and palæocurrent data, reviewed in this paper, provide convincing evidence that the Falkland Islands rotated from an original position off southeast Africa to their present position off South America during break-up. The rotation mechanism and trajectory are less certain but are an essential component of any plausible Gondwana break-up model.
The Falkland Islands possess two roughly orthogonal structural grains. D1 structures form a southerly verging fold belt that correlates with the main folding in the eastern part of the Cape Fold Belt following relocation of the islands. D1 folds were overprinted by the Early Mesozoic D2, northeast-southwest trending, Hornby Mountains Anticline producing localised kilometrescale Type I and III fold interference patterns. It is suggested here that the D2 structures may represent a break-out structure related to a dextral transtensional shear couple that may have existed between East and West Gondwana during the initial stages of break-up.
Clockwise rotation of the Falkland Islands Block (FIB) could have taken place along a series of east-west faults (e.g. the Gastre Fault Zone) in Patagonia as southern South America moved towards the Pacific during Middle Jurassic times. Contemporaneous Pacific-ward motion of southern South America during rotation of the FIB would have avoided collision with the Falkland Island Block as it docked. On a geological timescale, the break-out of the FIB and associated movements of other Gondwana fragments were rapid events, which appear to correlate with the major magmatic pulse at ca 183 Ma, related to a mantle plume beneath Africa and Antarctica. If this is correct, then doming above a large mantle plume in the South Atlantic region may have helped formation and rotation of Gondwana microplates, with rotation occurring above a viscously deforming, hotter-than-normal, substratum in a transtensional setting.