Subsolidus physical and chemical mixing of granite and gabbro during mylonitization, South Victoria Land, Antarctica

At Dromedary Massif, Southern Victoria Land, Antarctica, a suite of coarse-grained granite dykes cross-cuts a gabbro pluton which has been partially metamorphosed at amphibolite facies. During regional deformation, strain has been inhomogeneously distributed through the gabbro pluton and has been concentrated in granite dykes. In zones of relatively high strain, the granite dykes have developed a mylonitic fabric. A high strain gradient between granitic mylonite and metagabbroic host rock has induced isochemical mylonitization of the margin of the host. This grain size reduction allowed chemical diffusion between granitic and metagabbroic mylonites, resulting in a marginal zone of biotite-rich mylonite with intermediate composition. Biotite-rich mylonite decoupled from metagabbroic mylonite and flowed with granitic mylonite. Continued folding and transposition of granitic mylonite and biotite-rich mylonite has produced compositionally banded mylonite zones through thorough and irreversible mixing of the two lithologies.