The distribution of radioactive heat production in I- and S-type granites and residual source regions: Implications to high heat flow areas in the Lachlan Fold Belt, Australia

An analysis of the uranium and thorium fractionation processes in various granites implies a direct dependence on processes of magmatic differentiation, the magma source materials, and residual accessory phases; suggesting that no universal, vertical heat-producing element distribution may be applied to all granite crust. Metaluminous I-type granites show evidence for downward decreases in heat-producing elements within the plutons. The heat-producing element content of I-type residual source regions is probably similar to that of the most mafic I-type granites. The fractionation trends of peraluminous S-type granite indicate that no significant change in heat-producing elements should occur with depth in the plutons. Geochemical evidence indicates that residual source regions of S-type granites will contain high concentrations of heat-producing elements and reside deep in the crust. Anomalously high heat flow in southeastern Australia corresponds to areas of S-type granites and may be largely due to deep crustal radioactivity, rather than Cainozoic mafic magmatism.