Detailed structure and plate reconstructions of the Central Indian Ocean between 83.0 and 42.5 Ma (Chrons 34 and 20)

The Central Indian Ocean, namely the Central Indian, Crozet, and Madagascar basins, formed by rifting and subsequent drifting of India (now Capricorn), Antarctica, and Africa (now Somalia). We gathered a comprehensive set of sea surface magnetic anomaly profiles over these basins and revisited location and identification of magnetic isochrons between C34ny (83.0 Ma) and C20ny (42.536 Ma) using the objective analytic signal technique. We present high-resolution magnetic isochrons for 29 periods based on similar to 1,400 magnetic anomaly picks. From the conjugate sets of picks, we derive two-plate finite rotation parameters for both the Capricorn-Antarctica and Capricorn-Somalia motions. These finite rotations are compared to three-plate reconstructions of the plate boundaries between the Capricorn, Antarctica, and Somalia plates, constrained by the closure of the Indian Ocean Triple junction. In general, the three-plate reconstructions slightly overrotate the reconstructed isochrons with respect to the Capricorn-Antarctica and Capricorn-Somalia two-plate reconstructions. Conversely, the two-plate reconstructions for Somalia-Antarctica slightly underrotate the isochrons compared to the Capricorn-Antarctica-Somalia three-plate reconstructions. We suspect that the discrepancies between the two-plate and three-plate methods result from the recent seafloor deformation in the Capricorn-India diffuse plate boundary and/or from the contrasted nature and geometry of magnetic isochrons at different spreading rates (i.e., magnetic structure of the three spreading centers). Three-plate reconstructions better constrain the closure of the triple junction but spread any misfit among all threeplate boundaries. When enough quality data are available, two-plate reconstructions may lead to more realistic plate motion estimates from which additional geological problems can be identified and solved.