A NARROW PLUME CONDUIT ROOTED IN THE LOWER MANTLE BENEATH LA RÉUNION HOTSPOT

Abstract:

The arrival of some plumes and the birth of hotspots at the Earth surface have broken up the Pangea in many continents ~200 Ma ago. La Réunion hotspot is known as one of the largest on the Earth. Its birth, 65Ma ago, creating the Deccan volcanic traps in India (almost 2 million km²) and the death of more than 90% of life on the Earth including dinosaurs. So far the origin of the mantle plumes and their role in geodynamics are still controversial in Earth sciences. In that respect, we use the dataset from the French-German RHUM-RUM experiment around La Réunion hotspot (2012-2013), from IRIS data center and FDSN to investigate the deep structure of the plume along its complete track from its birth to its present stage. The use of spectral element method allows us to perform forward modelling for several thousand paths across the Indian ocean. The sensitivity matrix (first order approximation of the Hessian matrix) is built from the coupling of normal modes along and across mode branches, by using nonlinear asymptotic coupling theory. This waveform inversion approach enables us to resolve deep anomalies in the mantle beneath the Indian Ocean. We found a low velocity zone (extending from the west to the east) in the upper mantle beneath the Mascarene Basin and also in the Central Indian Ocean Basin. A plume conduit with a broad head in the upper mantle and narrow tail anchored in the lower mantle transition zone have been mapped. The connection between la Réunion hotspot and the African LLSVP (Large low-shear velocity province) is also brought to light by our model.