Melt mixing and transport across the Whale Head Rock contact aureole of the Albany-Fraser Orogen, Western Australia

The processes that facilitate the production of granitoids are elucidated by the study of exposed lower crustal sections. The focus of this study is an exposure of the lower crustal portion of Albany-Fraser-Orogen (AFO) of Western Australia. This outcrop, located at Whale Head Rock in the western AFO, preserves the interface between an intrusive body and migmatised sedimentary rocks. Detailed mapping, petrography and thermodynamic modelling are combined to characterize the sources and distribution of melt generations in the aureole. U-Pb dating of zircon indicates that the tonalite crystallisation and migmatization of the metapelitic units were coeval at ca. 1.3 Ga. While thermodynamic modelling yields conditions of ca. 820°C and 0.5 GPa, in metapelites throughout the area. The contact zone evolves from igneous dominated textures to migmatitic sediments, dominated by concordant, internally derived leucosomes. The distribution of mineral assemblages and mineral chemistry across this section indicates that the mixing between intrusive and internally generated melt is structurally constrained. The back reaction with late stage, more evolved, melts within this mixing zone indicates that it acts as a pathway for continued melt removal and transport. This study represents and outcrop scale model for the complex processes that are involved in the production of granitoids at high temperature, medium pressure conditions. Giving further insight into the generation and extrapolation of melt from thinned crustal settings.