Deformation, stirring and material transport in thermochemical plumes

[ 1] The deformation, stirring processes and transport structures for a series of numerical models of plume formation in axisymmetric spherical shell are examined to better understand the development of lateral heterogeneity in mantle plumes. In our models we find that under a wide range of conditions the surrounding material is heated and entrained. This indicates that plume sampling the ambient mantle material on its way to the base of the lithosphere cannot be ruled out. The deformation and convective stirring can be significantly enhanced in the thermochemical plumes and the dispersion of compositional heterogeneity can be much more effective than that in the purely thermal plumes. For models with episodic pulsations or with small-scale convection due to the interplay between the thermal and compositional buoyancy forces, material in the plume and the source region can undergo strong stretching and folding resulting in structures such as filaments, streaks, tendrils and well-mixed regions. Islands can be surrounded by highly deformed regions which may contribute to structures such as the coexistence of the compositional heterogeneity and relatively homogeneous matrix in Ocean Island Basalts ( OIBs). These results may have implications for the interpretation of the lateral heterogeneities of the OIBs.