Wed 26th August @ 12:00 nn via Webex (WATCH RECORDING HERE)

Abstract:

The Earth’s mantle is currently divided into the African and Pacific domains, separated by the circum-Pacific subduction girdle and each domain features a large low shear-wave velocity provinces (LLSVPs) in the lower mantle. However, it remains controversial as to whether the LLSVPs have been stationary through time or dynamic, changing in response to changes in global subduction geometry. Here we compile radiogenic isotope data on plume-induced basalts from ocean islands and oceanic plateaus above the two LLSVPs which show distinct Pb, Nd and Sr isotopic compositions for the two mantle domains. The African domain shows enrichment by subducted continental material during the assembly and breakup of the supercontinent Pangaea, whereas no such feature is found in the Pacific domain. This deep-mantle geochemical dichotomy reflects the different evolutionary histories of the two domains during the Rodinia and Pangaea supercontinent cycles and thus supports a dynamic relationship between plate tectonics and deep mantle structures.

Short bio:

Luc Doucet got his Ph.D. in St Etienne, France (2012), after a short time as Lecturer in St Etienne, he got a three years fellowship from the Belgium Fund for Scientific Research. Luc moved to Brussels to apply the “non-traditional” stable-isotope systematics on the mantle and crustal rocks to study the formation of both oceanic and continental lithosphere. After an academic career break, he moved to Curtin University, Perth in March 2018 to join Professor Li and the Earth Dynamics Research Group to work on the Oceanic Large Igneous Provinces project to decipher the present-day and past connections between Earth’s mantle, supercontinent and superocean cycles. His tools are fieldwork, clean lab, various instruments and data mining to obtain petrological, geochemical and isotopic data on mafic and ultramafic rocks. He is currently co-supervising two PhD students (one in Brussels and one in Perth), teaches mineralogy and geochemistry at Curtin University, and he proudly serves as a guinea pig for the first seminar in the online seminar series.