Earth’s face is continuously renewed by the process of plate tectonics. Whilst operating at the scale of centimeters per year, these motions modify the geometry of continents and oceans over millions of years. One drastic plate tectonic change was related the closure of the Neotethys Ocean, which used to separate India and Asia, during the Mesozoic (~200-100 Ma). This ocean has now almost entirely vanished into the interior of the Earth, leaving only a few hints of its existence at the surface of the Earth. Nevertheless, we now suggest that the Neotethys Ocean's closure was caused by two independent subduction zones: a first one to the north of the basin, initiated during the Late Jurassic, and a second one to the south, initiated during the late Cretaceous.
Scientists from an international collaboration between French (Ecole normale supérieure CNRS, and Institut des Sciences de la Terre d'Orléans,ISTO) and Norwegian (CEED, University of Oslo) researchers, have investigated the causes of the initiation and the history of the evolution of the South Neotethys subduction.
They reconstructed the first steps of the South Neotethys subduction by analyzing the metamorphic soles of ophiolites located along the suture zone which now marks the trace of the extinct South Neotethys Ocean (Fig. 1). These data suggest that the impingement of a hot, rising mantle plume head (the trailing tail is now located beneath Reunion Island) at the base of the lithosphere triggered the intra-oceanic subduction zone. To support this hypothesis, they used whole-mantle convection models self-generating plate tectonics. The models showed that plume-induced subduction events can occur every hundred of millions of years on average (Fig. 2), with effects on the surface similar to the geological record around the Indian Ocean basin (including plate fragmentation and rotations, fast subduction retreat and asynchronous deactivation along multiple continental margins, and a hot mantle temperature during the initiation of the subduction leading to supra-subduction zone signatures…).
When the Reunion plume head arrived at 110 Ma, the South-Neotethys subduction zones which surrounded it, would have dislocated in several branches. The zones then retreated independently until they reached the Indian and Arabic margins (Fig. 3). This scenario suggests that the Reunion plume has potentially induced a major plate reorganisation event affecting the Indian Ocean basin by initiating a subduction zone rather than having been a direct driver for the fast India-Asia convergence and collision. To validate this new scenario, important work remains to be done on the conditions of formation of the ophiolites used to constrain it, since they are still unevenly studied.
Citation: Rodriguez, M., Arnould, M., Coltice, N., and Soret, M., 2021, Long-term evolution of a plume-induced subduction in the Neotethys realm, Earth and Planetary Science Letters, Volume 561, https://doi.org/10.1016/j.epsl.2021.116798
Contact: Maëlis Arnould (formerly at CEED, now at the University of Lyon) maelis.arnould@univ-lyon1.fr
