The distribution of melt has been mapped in a granite pluton deformed whilst it contained melt. At the outcrop scale, leucomonzogranite melt was segregated from hornblende monzogranite when the rigid crystal framework was tectonically compacted. The melt collected in well-defined, structurally controlled sites that formed during dextral, non-coaxial, strike-slip shearing. The segregations are generally isolated, but locally they link to form extensive branched arrays which drained larger volumes of granite in a two-step process. First, melt drained from the compacting matrix through the array and pooled along dilatant foliation planes; later, the melt moved farther away when a single planar melt-transfer channel formed. Thin section maps show that most melt was distributed in the foliation plane and along the lineation in the crystallising matrix. The location of melt at the grain scale is primarily controlled by the feldspar-dominated shape fabric of the crystal framework, and not by tectonic stresses as at the outcrop scale. Tectonic stresses account for the relatively small proportion of melt films located in grain boundaries normal to the lineation. The distribution of melt-bearing grain boundaries outlines larger domains in the thin sections that form a linked three-dimensional network through which melt moved within the crystallising framework.

Abstract Granulite facies anatexis ( T ≈ 900 °C) in the Wuluma Hills region of the Arunta Inlier was synchronous with deformation. During D3 contractional deformation strain was partitioned into S3 shear zones, which alternate with lower strain domains containing F3 fold hinges. Subsequent D4 deformation was minor and in part extensional. Leucosomes in the S3 shear zones are principally veins oriented parallel, or subparallel, to the pervasive S3 foliation. Leucosomes in the F3 hinge domains are more complex, and occur parallel to anisotropy due to lithological layering, the pre-existing S1/2 foliation, S3 and fold axial planes (F3 and F4). Some leucosomes (generally high Na 2 O, low K 2 O and Rb/Sr) record melt migration paths, and other sites of melt accumulation. All the migmatites are residual and lost melt when deformation forced melt from matrix grain boundaries, through a network of small lensoid channelways to accumulation sites in fold hinges, there larger batches of magma developed. Leucosomes in accumulation sites develop a schlieric or diatexitic appearance because inflowing melt eroded the host rocks. Later increments of D3 contractional strain overpressured the accumulated granitic magma and it migrated again to other (more stable) low pressure sites through veins generally oriented parallel to S3. Magma/melt movement stopped when the solidus was reached, or the magma reached a structurally stable site (e.g. pluton).

To form a granite pluton, the felsic melt produced by partial melting of the middle and lower continental crust must separate from its source and residuum. This can happen in three ways: (1) simple melt segregation, where only the melt fraction moves; (2) magma mobility, in which all the melt and residuum move together; and (3) magma mobility with melt segregation, in which the melt and residuum move together as a magma, but become separated during flow. The first mechanism applies to metatexite migmatites and the other two to diatexite migmatites, but the primary driving forces for each are deviatoric stresses related to regional-scale deformation. Neither of the first two mechanisms generates parental granite magmas. In the first mechanism segregation is so effective that the resulting magmas are too depleted in FeO T , MgO, Rb, Zr, Th and the REEs, and in the second no segregation occurs. Only the third mechanism produces magmas with compositions comparable with parental granites, and occurs at a large enough scale in the highest grade parts of migmatite terranes, to be considered representative of the segregation processes occurring in the source regions of granites.