A geodynamic model of plumes from the margins of Large Low Shear Velocity Provinces

Abstract

We present geodynamic models featuring mantle plumes that are almost exclusively created at the margins of large thermo‐chemical piles in the lowermost mantle. The models are based on subduction locations and fluxes inferred from global plate reconstructions and ocean floor paleo‐ages. Sinking subducted slabs not only push a heavy chemical layer ahead, such that dome‐shaped structures form, but also push the thermal boundary layer (TBL) toward the chemical domes. At the steep edges it is forced upwards and begins to rise — in the lower part of the mantle as sheets, which then split into individual plumes higher in the mantle. The models explain why Large Igneous Provinces – commonly assumed to be caused by plumes forming in the TBL above the core‐mantle boundary (CMB)– and kimberlites during the last few hundred Myr erupted mostly above the margins of the African and Pacific Large Low Shear Velocity Provinces (LLSVPs) of the lowermost mantle, which are probably chemically distinct from and heavier than the overlying mantle. Our models support that mantle plumes are more intimately linked to plate tectonics than commonly believed. Not only can plumes cause continental break‐up, but conversely subducted plates may trigger plumes at the margins of LLSVPs near the CMB. © 2012 American Geophysical Union