Paleoceanographic and paleogeographic reconstructions of the Mozambique Channel (Indian Ocean) : contribution of the isotopic study of Fe-Mn crusts

• Main Author: Charles, Claire
• Other Authors: Laboratoire Géosciences Océan (LGO), Université de Bretagne Sud (UBS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Unité Géosciences Marines (GM), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Université de Bretagne occidentale - Brest, Jean-Alix Barrat
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2022
• Subjects: Fe-Mn crusts; Mozambique channel; NADW; NIDW; Nd; Pb isotopes; Uplift; Canal du Mozambique; Encroûtements Fe-Mn; Isotopie Nd; Pb; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences
• Online Access: https://theses.hal.science/tel-03858288; https://theses.hal.science/tel-03858288/document; https://theses.hal.science/tel-03858288/file/These-2022-SML-Geosciences_marines-CHARLES_Claire.pdf

The Mozambique Channel, located east of the African craton and west of the Madagascar continental margin, hosts intense mixing of water masses from the Atlantic and Indian Oceans, raising questions about whether and how they have circulated over time, adapting to the geodynamics of the channel. Geochemical analysis (major and trace elements; Nd and Pb isotopes) and absolute dating (Be isotope) of 33 Fe-Mn crusts, distributed from the Agulhas Plateau in the south to the Comoros Basin in the north, will be used to establish time series to study the evolution of regional currents up to 30.7Ma. For the past 80 000 years, the NADW has been flowing as far as the Jeffrey Ridge, whereas in the Comoros Archipelago, the NIDW is in the majority. However, this oceanographic model has not always worked this way.Since its formation, the NADW has had a strong influence as far as the Glorious Islands. Between 11.7 and 3.4Ma, an uplift disturbed the geodynamics of the channel, raising the Davie Ridge. The NADW decreased in the north, until it retired from the Comoros Basin, to the benefit of the NIDW expansion. Between 5.1 and 1.6 Ma, subsidence was recorded in the centre of the channel, which modified the bathymetry and oceanography of the area. Geochemistry also reveals Tethyan and Himalayan elemental inputs into the deep currents. Thus, thanks to a high-resolution study of the deep currents of the Mozambique Channel, this PhD completes the oceanographic models of the Indian Ocean and innovates in geodynamic reconstructions using Fe-Mn encrustations in the characterisation of vertical movements. Le canal du Mozambique, localisé à l’est du craton africain et à l’ouest de la marge continentale de Madagascar, abrite d’intenses mélanges de masses d’eau des océans Atlantique et Indien qui soulèvent des interrogations, à savoir si et comment elles ont circulé au cours du temps, en s’adaptant à la géodynamique du canal. L’analyse géochimique (éléments majeurs, traces isotopie Nd, Pb) et la datation absolue (isotopie Be) de 33 ...