The Diamantina Zone as the result of rifting between Australia and Antarctica: geophysical constraints

The Marion-Dufresne 80 cruise (May-June 1994) was devoted to the study of t he Diamantina Zone and the de Gonneville Triangle: 5 200 miles of bathymetr ic, gravimetric, magnetic and single channel seismic data were obtained. A new structural interpretation is proposed, using these data and the gravity anomaly map of the ocean deduced from altimetric measurements. The Diamant ina Zone and the de Gonneville Triangle correspond to a spreading segment f ormed at the axis of the ridge that separated India from Australia with a h alf rate of 20-30 km.My(-1). The segment age ranges from 90 to 120 My. Natu raliste Fracture Zone is a major structural feature whose shape is well exp lained by the 600 km offset between this segment and the other to the north east, 50-55 My ago, the southern part of the spreading segment was affected by a rifting episode which was followed by emplacement of the oceanic crus t generated at the axis of the Southeast Indian Ridge starting 44 My ago. T his mechanism explains the reliefs observed along the Diamantina Zone: tilt ed blocks and normal faults to the north, and volcanic structures to the so uth. (C) Academie des sciences / Elsevier, Paris.