The evolution of the eastern Grampians granites
The Newer Granites of the Eastern Grampians form a distinctive suite of predominantly pink biotite granites, although white hornblende-bearing granites are also found. All of the plutons in the study area are composite bodies, although internal boundaries are rarely seen. They have been emplaced by stoping at crustal levels between 4.6 km, and are all currently exposed close to their roof zones. Biotite is the only mineral to show significant compositional variation, and does so in response to increasing subsolidus interaction with the fluid phase. All the pink granites are highly oxidised, and equilibrated at an fO2 of approximately 10-18 bars and temperature less than 400o C. The pink granites are highly chemically evolved, with marked enrichment in K, Si, Rb and HFS elements. The evolution of the fluid phase has played a dominant role in their geochemical evolution. The pink granites represent limited partial melts of depleted granulite, whereas the white (hornblende-bearing) granites have evolved from a melt of gabbroic lower crustal material. The granites were all emplaced between 419 and 404 Ma, and represent the transition between late, subduction-generated high-K magmas to melts generated by volatile degassing and heat focussing of a mantle source at pre-Caledonian basement lineaments.