° Clarke, G.L., Daczko, N.R., Klepeis, K.A. and Rushmer, T.,  2005. Roles for fluid and/or melt advection in forming high-P mafic migmatites, Fiordland, New Zealand. Journal of Metamorphic Geology, 23, 557. doi:10.1111/j.1525-1314.2005.00594.x


A series of striking migmatitic structures occur in rectilinear networks through western Fiordland, New Zealand, involving, for the most part, narrow anorthositic dykes that cut hornblende-bearing orthogneiss. Adjacent to the dykes, host rocks show patchy, spatially restricted recrystallization and dehydration on a decimetre-scale to garnet granulite. Although there is general agreement that the migration of silicate melt has formed at least parts of the structures, there is disagreement on the role of silicate melt in dehydrating the host rock. A variety of causal processes have been inferred, including metasomatism due to the ingress of a carbonic, mantle-derived fluid; hornblende-breakdown leading to water release and limited partial melting of host rocks; and dehydration induced by volatile scavenging by a migrating silicate melt. Variability in dyke assemblage, together with the correlation between dehydration structures and host rock silica content, are inconsistent with macroscopic metasomatism, and best match open system behaviour involving volatile scavenging by a migrating trondhjemitic liquid.

  Field Photographs

Dr Nathan R. Daczko
GEMOC ARC National Key Centre
Department of Earth and Planetary Sciences
Macquarie University NSW 2109

Phone: +61 2 9850 8371
Fax: +61 2 9850 6904