Tectonic evolution of the Southwest Indian Ocean since the Mid-Cretaceous: plate motions and stability of the pole of Antarctica/Africa for at least 80 Myr

• Published in: Geophysical Journal International
• Main Authors: Fisher, Robert L., Sclater, John G.
• Format: Text
• Language: English
• Published: Oxford University Press 1983
• Subjects: Articles; Antarctic; East Antarctica; Indian; Bouvet; Prince Edward Fracture Zone; Antarc*; Antarctica
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/73/2/553; https://doi.org/10.1111/j.1365-246X.1983.tb03330.x

The Southwest Indian Ridge is the boundary where seafloor is being created between the African and Antarctic plates. East of the newly-recognized Du Toit Fracture Zone at 27°E it trends north-easterly and is cut by a series of six deep near north-south clefts marking transform faults. This series starts with the dual Prince Edward Fracture Zone near 35°E and includes Discovery II (also dual) at 42°E, Indomed at 46°E, and Gallieni at 52°E, terminating with the spectacular Atlantis II and Melville Fracture Zones at 57°30′E and 60°0′E respectively. The trend of these fracture zones is compatible with an instantaneous pole of relative motion for Antarctica/Africa at 8.4°N, 42.4°W. Between 35°E and 55°E the development of the Southwest Indian Ridge has separated the elevated Madagascar Ridge from the discontinuous Crozet Plateau that was contiguous to it prior to Eocene time. In this entire sector the ocean floor overall is elevated with respect to ocean floor of equivalent age elsewhere. Between these features anomalies 0–22 (0–53 Ma) have been identified north and 13–26 (35–60 Ma) south of the ridge axis. These anomalies, and 0–34 (0–80 Ma) located just to the west in the Mozambique Basin, lie at the same distance from the ridge axis as a similar sequence east of the Bouvet triple junction. The similarity in distance from the ridge axis of these anomaly sequences is evidence that Africa and East Antarctica have been separated by a single plate boundary from 80 Ma to the present. The pole representing the motion of these two plates at the present has not moved in totality far from the position it occupied in the Late Cretaceous, 80 Ma. Furthermore, calculation of intermediate finite rotation poles for four intervals within this span reveals only minor (< 15°) excursions from the present pole. The spatial reconstruction of the Southwest Indian Ridge at 80 Ma (anomaly 34) places the ridge midway between Africa and Eastern Antarctica and lying at right angles to the north-trending Mozambique Ridge. The separation of ...