Plate driving forces

Abstract

Much progress has been achieved in our understanding of how mantle convection drives the surface plate motions since the earliest parametric force models were published over 3 decades ago. This progress would not have been possible without the information on 3-D mantle structure that has been obtained through seismic tomography. The interpretation of the seismic tomography models is however nonunique, owing to the imperfect sampling of the mantle by seismic waves, and also because there are other effects, in addition to lateral temperature variations, that may give rise to mantle heterogeneity. This complexity has led to the emergence of two different views on how thermal convection in the mantle drives the tectonic plate motions. The most long held and commonly accepted view is that the buoyancy forces due to subducted slabs are the primary drivers of surface plate motions (e.g., Richter, 1973; Conrad and Lithgow-Bertelloni, 2004). According to this view the thermal evolution of the mantle is controlled almost entirely by cooling from above (i.e., subducting lithosphere), and this would arise if the mantle is almost entirely heated internally, with little or no heat entering the mantle across the core–mantle boundary. The second view, supported by the earliest mantle convection models (e.g., Turcotte and Oxburgh, 1967) and some subsequent models (e.g., Jarvis and Peltier, 1982; Forte et al., 2009), is that a combination of active hot upwellings (“plumes”) and subducted slabs is required to explain the surface plate motions. The existence of such active hot plumes requires a significant heat flux across the core-mantle boundary and it would be compatible with a mainly thermal origin for the seismic anomalies evident in the tomography models (e.g., Forte et al., 2009). The current debate on which of these two contrasting views of mantle dynamics is most compatible with the available data is not yet settled, but a resolution will be possible once the magnitude of the heat flux across the core-mantle boundary becomes more clear.