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The link between subduction under South America and plumes and LIPs in the South Atlantic.

Principal Investigator: Dr. Bernhard Steinberger

SteinbergerRundeIISeafloor spreading in the South Atlantic is influenced by mantle plumes that are presently causing active hotspot volcanism and have created seamount trails, aseismic ridges and LargeIgneous Provinces (LIPs). Yet what determines the locations of hotspot plumes, and to what extent they are triggered by subducted slabs remains unsolved. Reconstructed eruption locations of most LIPs fall close to above the margins of the Large Low Shear Velocity Provinces (LLSVPs) in the lowermost mantle, yet to date no dynamic model exists that selfconsistently explains the generation of LIPs on LLSVP margins. In order to study these unresolved issues related to the interaction of subduction, plumes and LLSVPs, we plan to devise here a model of plate reconstructions and mantle dynamics that approximately matches presentday tomography. We will then use this model to address the following questions: Do slabs trigger plumes above the coremantle boundary, and if so, where? Can LLSVPs in the lowermost mantle be stable for hundreds of Myrs? To what extent is negative chemical bouyancy necessary or helpful to achieve longterm stability? To what extent do subducted slabs stabilize or destabilize LLSVPs? Can we devise a model in which plumes rise from LLSVP edges, rather than their centers, and if so, for what modeling parameters? Are slabs necessary or helpful to create plumes from the edges of LLSVPs? Where are plumes generated in our model, does it correspond with actual hotspot (and LIP) locations and what is the relation between the locations of plumes/LIPs and where the South Atlantic opened during the Cretaceous?