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Evidence for melt migration enhancing recrystallization of metastable assemblages in mafic lower crust, Fiordland, New Zealand


Daczko, NR and Halpin, JA, Evidence for melt migration enhancing recrystallization of metastable assemblages in mafic lower crust, Fiordland, New Zealand, Journal of Metamorphic Geology, 27, (2) pp. 167-185. ISSN 0263-4929 (2009) [Refereed Article]

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DOI: doi:10.1111/j.1525-1314.2009.00811.x


A major arc batholith, the Western Fiordland Orthogneiss (WFO) in Fiordland, New Zealand, exhibits irregular, spatially restricted centimetre-scale recrystallization from two-pyroxene hornblende granulite to garnet granulite flanking felsic dykes. At Lake Grave, northern Fiordland, the composition and texture of narrow (< 10-20 mm across) felsic dykes that cut the orthogneiss are consistent with an igneous origin and injection of melt to form orthogneiss migmatite. New U-Pb geochronology suggests that the injection of dykes and migmatization occurred at c. 115 Ma, during the later stages of arc magmatism. Recrystallization to garnet granulite is promoted by volatile extraction from the host two-pyroxene hornblende granulite via adjacent dykes and the patchy development of garnet granulite is left as a marker adjacent to the melt migration path. New mineral equilibria modelling suggests that a two-pyroxene hornblende assemblage is stable at < 11 kbar, whereas a garnet granulite assemblage is stable at > 12 kbar, suggesting that garnet granulite may have formed with < 5 km crustal loading of the batholith. Although the garnet granulite assemblages signify that the WFO experienced high-P conditions, the very local nature of these textures indicates widespread metastability (> 90%) of the two-pyroxene hornblende granulite assemblages. These results indicate the strongly metastable nature of assemblages in mafic lower arc crust during deep burial and demonstrate that the degree of reaction in the case of Fiordland is related to interaction with migrating melts.

Item Details

Item Type:Refereed Article
Keywords:lower crust, Fiordland, melt migration, garnet granulite, migmatite
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and metamorphic petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Halpin, JA (Dr Jacqueline Halpin)
ID Code:62014
Year Published:2009
Web of Science® Times Cited:39
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2010-03-09
Last Modified:2012-03-07
Downloads:1 View Download Statistics

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