The structural evolution of the Falkland Plateau

The palaeogeographic reconstruction of the Falkland Plateau transform margin in a Gondwana pre-break-up configuration has been the subject of debate for years. This is mainly due to the uncertainty in the position of the Falkland Islands microplate. The islands were an extension of the south-east coast of South Africa, being either i) part of a rigid Falkland Plateau fixed to the South American plate or ii) undergoing a vertical-axis clockwise rotation of between 80° to 120° along the transform faults generated during the initial stages of fragmentation of south-western Gondwana. The absence of documented evidence of this rotation within the sedimentary infill of the basins surrounding the Falkland Islands represents an ongoing issue. Furthermore, a structural framework of the eastern continental shelf of the islands that takes into account the most recent seismic reflection surveys has not been published yet.

This study presents an updated description of the structural configuration of the Falkland Plateau Basin, focusing on the Volunteer and Fitzroy sub-basins. This structural framework, based on extensive 2D and 3D seismic reflection data and aided by seismic attribute mapping, provides new insights into the evolution of the Falkland Islands microplate and the Falkland Plateau Basin.

Three main structural trends were identified across this section of the Falkland Plateau. WNW-ESE trending half-grabens were mapped north-west of the Volunteer sub-basin; these correlate laterally with linear gravity anomalies following the same trend north of the Falkland Islands. NNE-SSW to N-S normal faults are predominant west of the Volunteer sub-basin and are believed to control the western margin of the Falkland Plateau Basin. Locally, the NNE-SSW trend is subdued by NNW-SSE striking en-échelon normal faults suggestive of left-lateral movement along a NNE-SSW direction. A similar trend is interpreted in the southern part of the Fitzroy sub-basin, supporting sinistral wrenching along the western margin of the Falkland Plateau Basin.

These results suggest intra-plate deformation that is consistent with a clockwise rotation of the Falkland Islands microplate along the transform faults that accommodated the initial fragmentation of Gondwana. The interpreted fault network allows us to understand the temporal variation in the orientation of the minimum horizontal stress across the Falkland Islands microplate. By comparing this variation with the regional stress regime in south-western Gondwana, the timing and mechanism of the rotation of the islands can be better constrained.