Chemical zoning and crystal size distribution of garnet in a quartzo-feldspathic gneiss from the Lützow-Holm Complex at Skallen, East Antarctica: Implication for geothermometry

Studies of chemical compositions and grain size garnet in a quartzo-feldspathic gneiss from the Lützow-Holm Complex at Skallen, East Antarctica, form basis an interpretation timing homogenization. The contains only as mafic minerals except sporadic biotite inclusions garnet. represents approximately constant Mg/(Fe+Mg) within grain. values small grains are higher than those large grains, while grossular content their periphery is similar. shows lognormal distribution. These features indicate that were mutually not equilibrium poorly annealed, which implies insufficient grain-boundary diffusion. consideration based on qualitative phase diagram suggests homogenized before after cessation diffusion, respectively. preserve composition was with biotite. In contrast, represent bulk zoning profiles formed during fractional growth. homogeneous interior is, therefore, always appropriate for geothermometry. highest among would be suitable when diffusion ceased erroneous use causes depression estimated temperature by 60 to 80 oC, even though compositional difference corresponds ca.10 oC diagram.