ABSTRACT: Indian Ocean Plate Reconstructions and Passive Margin Formation

COFFIN, MILLARD F., University of Texas at Austin, Austin, TX, and JEAN-YVES ROYER, Laboratoire de Geodynamique Sous-Marine, Villefranche-Sur-Mer, France

Development of the Indian Ocean began in Middle Jurassic time and has continued to the present via a complex series of spreading episodes. We use crustal age and fracture zone data to produce models of plate kinematics. Oceanic crust is dated by magnetic anomalies and limited Deep Sea Drilling Project/Ocean Drilling Program core samples. Fracture zone trends indicating past spreading directions are interpreted from bathymetry, satellite (Seasat/Geosat) altimetry, and marine seismic, gravity, and magnetic data. Mesozoic magnetic anomalies and fracture zones offshore East Africa, Antarctica, and Western Australia constrain the separations of Madagascar and Africa, of Africa and Antarctica, and of Australia and an unidentified plate. Other evidence strongly suggests that India and Antarc ica separated in Mesozoic time, although the timing and direction are not precisely defined. Thus most passive continental margins of the Indian Ocean, including East Africa, Madagascar, southwest Seychelles, the Arabian Peninsula, the Indian subcontinent, Australia, and Antarctica, are Mesozoic products of the breakup of Gondwana. Only margins flanking the Gulf of Aden and northeast Seychelles are younger. Knowledge of plate kinematics increases the potential for successful hydrocarbon exploration by predicting rift geometries. Some margins formed with strong components of transform motion preceding or simultaneous with final breakup, notably most of East Africa, Madagascar, Western India, Western Australia, and the Explora Coast of Antarctica. Other margins formed along margin-parallel fault systems perpendicular to the direction of plate divergence, e.g., Eastern India, Northwest Australia, South Australia, and most of Antarctica's Indian Ocean sector.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)