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S U M M A R YWe present a numerical study on convection in a rotating spherical shell that explores the influence of the two possible driving sources in planetary iron cores: temperature differences exceeding the adiabatic gradient and compositional differences that arise from the rejection of light elements at the inner core freezing front. Similarly, both effects play an important role in driving convection in Earth's outer core but their individual contribution remains uncertain. Dynamically, both components significantly differ in terms of their diffusion timescales since heat diffuses much faster than chemical elements. To investigate the influence of the driving mechanisms on the convective flow pattern, we consider different scenarios including the two extreme cases of purely thermally and purely compositionally driven convection and the more likely situation of a joint action of both sources. We solely focus on implications resulting from the given difference in the thermal and chemical diffusivity. For the present, we disregard the effects that might arise from the more realistic case of distinct thermal and chemical boundary conditions. We show that the driving mechanism strongly affects the resulting flow pattern, for example, differential rotation and global quantities such as mean energy and transport efficiencies. Additionally, we use a selected case for a specific comparison of two different codes based on a pseudospectral and a finite volume formulation, respectively.