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Complex ascent of mantle plumes in a phase-changing world

Phase changes in the mantle have long been known to play a major role for convection in a one-component mantle. When considering cases with depleted ambient upper mantle and upwelling mantle either chemically or mechanically enriched with basaltic crust, very complex density-difference histories are possible for a wide range of realistic temperature-composition scenarios. We explore the ascent of enriched mantle plumes in ambient mantle using combined thermodynamic and themomechanical modelling. Plumes are unlikely to feel a blocking effect from the negative Clapeyron slope of the 660 phase transition due to excessive buoyancy in the uppermost lower mantle. Hot plumes cross the phases transition at temperatures above the negative slope segment and are even promoted. Instead, they may stall and spread in the upper mantle transition zone for significant periods of time, as this depth is characterized by negative thermal expansion for mantle compositions at elevated temperatures. With time, both, the cooling plume and the heating ambient mantle experience density reduction and secondary plumes can spawn from that domain. These secondary plumes may show large lateral offsets from the deep plume stem and show complex and divers geochemical signatures.


Anders Lillevang Vesterholt, Thorsten J. Nagel
Aarhus University, Denmark
GeoKarlsruhe 2021