Seismic tomography of the La Réunion mantle plume

Thesis

This study aims to generate a multifrequency tomography model of the mantle beneath the Réunion hotspot, where a whole mantle conduit may be present.

From 2011 to 2016, the RHUM-RUM project (Réunion Hotspot Upper Mantle – Réunions Unterer Mantel) instrumented a 2000 km × 2000 km area of the Indian Ocean seafloor, islands and Madagascar with broadband seismometers and hydrophones. The central component was a 13-month deployment of 57 German and French Ocean Bottom Seismometers (OBS) deployed at 2300-5600 m depth. This was supplemented by deployments of 37 stations on Réunion, Mauritius, Rodrigues, the southern Seychelles, the Iles Eparses and southern Madagascar. More than 200 teleseismic events during the 13-month long deployment were recorded and additional 400 events before and after the main OBS deployment were recorded by permanent stations.

Here, I present the data yield, processing methods and P wave images based on over 55,000 multifrequency cross-correlations measurements in passbands between 30 and 2.7 seconds dominant periods. Ideally, all frequency bands that efficiently transmit body-waves would be used but this meets practical limits in the noise characteristics of ocean-bottom recordings. The multifrequency traveltime observations are embedded into a global ray theoretical inversion. This new high resolution tomographic model, which illuminates the mantle column beneath La Réunion and surrounding areas, is discussed and compared to existing global models.

The model reveals a massive upwelling rooted in the African LLVP. Branches tilting up- and outward from a central cusp at around 900 km above the CMB (∼2000 km depth), and connect to the hotspot locations of La Réunion, Afar, Kerguelen, and possibly Crozet. These mantle connections support evidence of long-standing observations of geochemical similarities across Indian Ocean hotspots.

Authors: Tsekhmistrenko, M

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Tomography; Mantle plumes
• Subjects: Seismic tomography--Data processing