RIDGE–HOTSPOT INTERACTION: 65 MILLIONS YEARS OF REUNION HOTSPOT HISTORY

Although tomography may help to image plumes in the present mantle, the history of such plumes can only be deciphered through investigation of the volcanic structures formed during this history and the tectonic evolution of the plate. We illustrate the complexity of such a history by re-evaluating the Reunion hotspot history.

The Reunion hotspot is often envisioned as a typical intraplate hotspot, and its history described as the continuous building of volcanic structures from the Deccan traps to Reunion Islands as the Indian and African plates were moving northward. Conversely, geochemical and geophysical evidences from the CIR 19°S support two episodes of hotspot-ridge interaction, at 8-10 Ma with the emplacement of the Rodrigues Ridge, and since 2 Ma with volcanism on Rodrigues Island and a set of newly discovered volcanic ridges extending up to the CIR axis. Such an interaction while the CIR and Reunion Island are more than 1000 km away suggests that the Reunion hotspot had a long history of interaction with the Carlsberg Ridge (CR) and the CIR, starting as early as the hotspot inception by the Indian plate, which triggered the opening of the CR at 65-61 Ma. Between 58-43 Ma, systematic ridge propagation on the CR reflects interaction with the Reunion hotspot, whereas interaction with the CIR was blocked by the long Mauritius-Chagos FZ. As a result of the interaction between the hotspot and the CR, the Chagos, Nazareth, and Cargados Carajos Banks may have formed on the African plate, as conjugate of Maldives and southern Laccadives Banks. The saddle between Maldives and Chagos Banks, located at a bend in the general trend of the structure, would correspond to a fossil ridge dated 43 Ma. The good fit between Chagos Bank and the Mascarene Plateau suggests rifting and break up of pre-existing structures between 43 and 35 Ma, rather than a mid-ocean ridge passing over a hotspot.

Results of cruises Magofond 2, Gimnaut, and Knox 11-RR, and IFCPAR Project 1907-1 (M. Benoit, G.C. Bhattacharya, A. Briais, C. Bollinger, A.K. Chaubey, J. Day, E. Füri, Y. Gallet, P. Gente, H. Guillou, C. Hémond, D. Hilton, H. Horen, M. Kitazawa, B. Le Gall, M. Maia, B. Murton, F. Nauret. P. Patriat, M. Ravilly, J.Y. Royer, K. Srinivas, K. Tamaki, C. Tamura, R. Thibaud, & V. Yatheesh)