Project Details
Projekt
Plateau volcanism in the African-Southern Ocean gateway
Applicant
Privatdozent Dr. Jörg Geldmacher
Subject Area
Palaeontology
Term
since 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 526403289
The opening of the Southern Ocean gateways allowed for the emergence of the Antarctic Circumpolar Current (ACC), crucial to the onset of global Cenozoic cooling. South of Africa, the opening was associated with the formation of several large igneous provinces (LIPs) including the Mozambique Ridge, Agulhas Plateau and the smaller Northeast Georgia Rise and Maud Rise. Plate tectonic reconstructions imply that the latter three were once part of a much larger "Greater Agulhas Plateau" (or "super-LIP") and were separated by subsequent rifting. It is debated whether and to what extent the emplacement of these large volcanic features obstructed the exchange of water masses in the nascent seaway between the Atlantic and the Indian Oceans thereby delaying the onset of the ACC. The submarine Agulhas Plateau was drilled during recent IODP Expedition 392. Igneous rocks were recovered at two sites on the southern part of the plateau (Sites U1579, U1580) and at one site near ist northern edge (U1582). Preliminary (shipboard) data indicate that all sites sampled tholeiitic basalts, formed by low pressure (shallow magma chamber) fractionation of mainly olivine and plagioclase (as is typical for marine LIP lavas). Ongoing 40Ar/39Ar dating will help to answer questions regarding the emplacement age of the plateau and ist spatial-temporal evolution. Igneous rock samples from Northeast Georgia Rise and Maud Rise have also been cored during previous ODP expeditions (Legs 114 and 113, respectively). Geochemical investigations of the recovered rocks from all three plateaus will help to reveal the nature, tectonic setting and source of the magmatism. The proposed project will focus on the determination of radiogenic (Sr, Nd, Hf, Pb) isotope compositions to constrain the magma source composition for comparison with other regional and global LIP magmatism. In particular, we want to address the open question whether the Agulhas Plateau, Northeast Georgia Rise and Maud Rise magmatism can all be attributed to the same magma source and tectonic setting (i.e., plume-ridge interaction) to test the previous plate tectonic reconstruction models. Additional questions include whether a (deeply-sourced?) mantle plume initiated the magmatism and ist potential causal relationship to regional continental breakup, the opening of ocean basins, and the structure of the deep mantle. The isotope data in combination with the results from age dating and major/trace element geochemistry will help to constrain the origin and impact of this regional LIP magmatism on tectonic configuration, ocean circulation, and global climate during the mid to late Cretaceous.
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