The Falkland Islands and their position within Gondwana

Detailed mapping, at scales of 1:25000 and less, has been undertaken at key points across the Falkland Islands to understand the structural history of this displaced part of Gondwana. This mapping has revealed, previously undiscovered, downwardly injected diamictite dykes of Early Carboniferous age formed during the main phase of the Gondwana glaciation. Interference fold patterns on West Falkland have shown a relative chronology for the sub-orthogonal E-W (D1) and NE-SW (D2) structural trends on the Falkland Islands. D1 structures, related to Early Permian to Early Triassic N-S compression, form an E-W striking, southerly verging fold-belt across East Falkland, which changes strike to WNW-ESE on West Falkland, coincident with a marked decrease in strain. D2 structures include N-S and NE-SW folds, however these are dominated by the NE-SW Hornby Monocline, which is underlain by an oblique (reverse-dextral) basement fault causing West Falkland to be uplifted relative to East Falkland by 6-8 km. Seismic and gravity data reveal the offshore continuation of this basement fault to the SW for at least 60 km along strike. Comparison of vitrinite reflectance data, sedimentary facies and formation thicknesses between East and West Falkland has shown that this fault was active from at least Early Carboniferous times and throughout D1, and that it was reactivated during the Late Triassic-Early Jurassic E-W D2 compression.The geology of the Falkland Islands, including the stratigraphy (palaeocurrents, facies and lithologies), structure (fold vergence, thrust directions and cleavage orientations) and thermal history of the Lafonian foreland basin derived from vitrinite reflectance data is almost identical to that of the Eastern Cape of South Africa. This confirms that in Gondwana reconstructions, the Falkland Islands should be rotated by 180o and placed to the east of South African as an eastward extension and lateral termination of the South African Cape Fold Belt.