Geological context of crustal anatexis and granitic magmatism in the northeastern Glenelg River Complex, western Victoria

The Cambro-Ordovician Gienelg River Complex in the Harrow district, western Victoria, consists of extensive granitic rocks associated with a migmatiti c metasedimentary envelope. Metasedimentary rocks comprise amphibolite faci es massive-laminated quartz-feldspathic schists and layered gneisses with m inor sillimanite-bearing horizons. Intercalated are stromatic and nebulitic migmatites of granitic and tonalitic character; textural evidence suggests that both varieties developed by in situ partial melting. Ranging from ada mellite to leucotonalite, granitic rocks contain abundant magmatic muscovit e, commonly with garnet and sillimanite, and exhibit generally unrecrystall ised igneous textures. Heterogeneous structurally concordant plutons transi tional to migmatites and more uniform intrusive phases ore delineated with both types hosting diverse metasedimentary enclaves, micaceous selvages and schlieren: a gneissic foliation of variable intensity is defined by the la tter. These petrographic attributes are consistent with derivation of pluto ns by anatexis of a peraluminous metasedimentary protolith. The schileric f oliation is not tectonically imposed, but rather directly inherited from th e migmatitic precursor, compositional variations within which are preserved by the layered Schofieid Adamellite. The most mafic granitic body (Tuloona Granodiorite) also has igneous microgranular enclaves indicating a more co mplex petrogenesis. Metasedimentary rocks experienced five episodes of fold ing, the latest involving macroscopic open warps. This is analogous to the structural history elucidated elsewhere in the Glenelg River Complex, by in ference a coherent tectonic entity whose present metamorphic and stratigrap hic configuration might be governed by Fg folding. Structures within migmat ites intimate that partial melting proceeded throughout the deformational h istory and peaked syn-D-4 to pre-D-5, whilst temperatures had waned to sub- biotite grade in the southwestern Glenelg River Complex, Granitic rocks wer e generated during this anatectic culmination and were therefore emplaced l ate in the orogenic history relative to other syntectonic phases of the Gle nelg River Complex.