Garnets solid-melt partition coefficient

Compatible element An element with equilibrium solid/melt partition coefficient >1. In garnet (and zircon), heavy REE, scandium, vanadium, and yttrium are compatible. These elements are incompatible in all other rock-forming minerals involved in igneous fractionation processes discussed in this chapter. 

A key feature is that all the nuclides of interest are highly incompatible in common mantle mineral phases (Table 2). Clinopyroxene and garnet (present in normal peridotitic mantle at depths greater than —80 km) are the principal host minerals for uranium and thorium in the solid phase, although even in these phases partition coefficients do not exceed 0.05. An important consideration is the sense of uranium and thorium fractionation imparted by the presence of different minerals. This can be conveniently expressed in terms of Du/ >Th- Minerals with Du/ >Th > 1 retain uranium over thorium and contribute to 23 Th-excesses in a coexisting melt, whereas those with Du/ >Th < 1 help to create 23 3xh-deficits. The effects of different minerals are then weighted by their absolute partition coefficients and modal abundance to control the bulk partition coefficient of the mantle, and thus determine the sense of fractionation of thorium from uranium in a coexisting melt. 

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