Onset of Plate Tectonics and Thermochemical Evolution of the Early Earth

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Plate tectonics represents the surface expression of the underlying mantle convection system and with regard to our solar system is unique to the Earth but its onset still remains an open question. For example, it is speculated that plate motion initiated during the Archaean, maybe due to subduction processes at the edges of continents, by crustal delamination or due to a dense basal layer. Therefore, the interaction of plates (continents) and dense material in the Archaean, and also later, is of interest. Today’s seismologically observed large low shear velocity provinces (LLSVPs) at the core-mantle boundary are also regarded as thermochemical reservoirs (piles) formed from a dense basal layer that possible originates from a basal magma ocean. The presence of chemically dense material is, however, not just a passive feature. The dense material rather recouples with the thermal convection and acts as restoring force. Therefore it has profound impact on the convective flow itself. Upwellings have less buoyancy and might not be able to break up the plates which could lead to a late onset of plate tectonics. The aim of this proposal is to study the mechanisms of plate initiation and pile formation and to give constraints on the onset time of plate motion and formation of dense reservoirs as well as the survival time of these reservoirs. Therefore an extensive parameter study with numerical thermochemical mantle convection models featuring plates is planned. In particular, the effect of rheological parameters and initial conditions on the early coupled plate-mantle system shall be investigated.