Direct observation of adakite melts generated in the lower continental crust, Fiordland, New Zealand |
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| Authors: | James A. Stevenson Nathan R. Daczko Geoffrey L. Clarke Norman Pearson Keith A. Klepeis |
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| Affiliation: | School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia;;GEMOC, Macquarie University, North Ryde, NSW 2109, Australia;;Department of Geology, University of Vermont, Burlington, VT 05404, USA;;Present address: School of Earth and Planetary Sciences, Macquarie University, North Ryde, NSW 2109, Australia |
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| Abstract: | Adakites have a distinct chemistry that links them to melting of a mafic source at high pressure. They have been attributed to melting of subducted oceanic crust or melting of the mafic crustal roots of thick continental arcs, and are an important contrast to mantle wedge melting as a means of generating continental crust. We report the first direct evidence for the generation of adakitic melts in mafic lower continental crust, in an exhumed Cretaceous arc in the South Island of New Zealand. The lower crustal Pembroke Granulite has the bulk chemistry and partial melting textures involving peritectic garnet appropriate for a source region for an adakitic melt. The melt migrated from the area through a fracture network now filled with trondhjemitic veins. Emplacement of the melt was in the upper crust of the Cretaceous section, illustrated by the presence of coeval adakites in the upper crustal Nelson-Westland region. |
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