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Melt segregation structures in granitic plutons

¹ School of Geosciences, Monash University, Clayton, VIC 3800, Australia

When melt fraction increases beyond a critical value, migmatites behave as magmas. Conversely, when melt fraction decreases, crystallizing magmas form solid-framework mushes and behave as solids. The richness in preserved mesoscopic melt segregation structures in migmatites is not matched by melt segregation structures in granitic bodies. This paper identifies melt segregation structures in granites and compares them to structures in migmatites. The rarity of segregation structures in granites is a consequence of the solid-framework mush allowing for cryptic melt extraction from its pores, the relatively short duration of solidification of the mush, and the fragile nature of the solid framework. Identifying segregation features in granitoids at outcrop scale provides the basis for understanding the physical processes that lead to chemical and mineralogical differentiation in granitic magmas.

Key Words: migmatites • granites • solidification • extraction • segregation • magma fractionation