Roles for fluid and/or melt advection in forming high-P mafic migmatites, Fiordland, New Zealand |
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| Authors: | G L CLARKE N R DACZKO K A KLEPEIS T RUSHMER |
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| Institution: | School of Geosciences F05, University of Sydney, Sydney, NSW 2006, Australia (); GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia; Department of Geology, The University of Vermont, Burlington, VT 05405 USA |
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| Abstract: | 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. |
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| Keywords: | garnet granulite granulite formation metasomatism migmatite partial melting |
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