Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

Stowell, Harold H.; Tulloch, A. J.; Zuluaga, Carlos A.; Koenig, Alan E.

doi:10.1016/j.chemgeo.2010.02.015

Cited by 56 publications

(80 citation statements)

References 53 publications

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“…The Pembroke Granulite, Fiordland, New Zealand (Figure ), is a relatively low‐strain portion of the Median Batholith (Figure , inset), a composite regional batholith comprising Carboniferous to Early Cretaceous plutons from the lower crust of a Cordilleran magmatic arc (Blattner, ; Mortimer et al., ). The gabbroic protolith to the Pembroke Granulite was emplaced at 136–129 Ma (Hollis, Clarke, Klepeis, Daczko, & Ireland, ; Stowell, Tulloch, Zuluaga, & Koenig, ) and had an igneous assemblage of enstatite, diopside, brown‐green pargasite, plagioclase, and ilmenite (Stuart, Piazolo, & Daczko, ). Though commonly gabbroic, the whole rock composition of the protolith varies by several weight percent for all major element oxides and has some minor grain size variations (Stuart et al., ).…”

Section: Regional Geologymentioning

confidence: 99%

“…Melt‐rock interaction dehydrated the host assemblage in layers (cm‐dm) around the dykes, transforming the partially hydrated S 1 assemblage to pale pink layers comprising the D 2 assemblage garnet, clinopyroxene, plagioclase, and rutile (Blattner, , ; Clarke, Daczko, Klepeis, & Rushmer, ; Clarke, Klepeis, & Daczko, ; Daczko, Clarke, & Klepeis, ; Daczko & Halpin, ; Schröter et al., ; Smith, Piazolo, Daczko, & Evans, ). Termed garnet reaction zones (GRZ), they represent peak metamorphism in the Pembroke Granulite, forming at conditions of 680–815°C and 11–14 kbar (Daczko & Halpin, ; Stowell et al., ).…”

Section: Regional Geologymentioning

confidence: 99%

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The recognition of former melt flux through high‐strain zones

Stuart

Piazolo

Daczko

2018

Journal Metamorphic Geology

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High‐strain zones are potential pathways of melt migration through the crust. However, the identification of melt‐present high‐strain deformation is commonly limited to cases where the interpreted volume of melt “frozen” within the high‐strain zone is high (>10%). In this contribution, we examine high‐strain zones in the Pembroke Granulite, an otherwise low‐strain outcrop of volcanic arc lower crust exposed in Fiordland, New Zealand. These high‐strain zones display compositional layering, flaser‐shaped mineral grains, and closely spaced foliation planes indicative of high‐strain deformation. Asymmetric leucosome surrounding peritectic garnet grains suggest deformation was synchronous with minor amounts of in situ partial melting. High‐strain zones lack typical mylonite microstructures and instead display typical equilibrium microstructures, such as straight grain boundaries, 120° triple junctions, and subhedral grain shapes. We identify five key microstructures indicative of the former presence of melt within the high‐strain zones: (a) small dihedral angles of interstitial phases; (b) elongate interstitial grains; (c) small aggregates of quartz grains with xenomorphic plagioclase grains connected in three dimensions; (d) fine‐grained, K‐feldspar bearing, multiphase aggregates with or without augite rims; and (e) mm‐ to cm‐scale felsic dykelets. Preservation of key microstructures indicates that deformation ceased as conditions crossed the solidus, breaking the positive feedback loop between deformation and the presence of melt. We propose that microstructures indicative of the former presence of melt, such as the five identified above, may be used as a tool for recognising rocks formed during melt‐present high‐strain deformation where low (<5%) volumes of leucosome are “frozen” within the high‐strain zone.

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Section: Regional Geologymentioning

confidence: 99%

Section: Regional Geologymentioning

confidence: 99%

The recognition of former melt flux through high‐strain zones

Stuart

Piazolo

Daczko

2018

Journal Metamorphic Geology

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“…() and discussed in Stowell et al . (). Much of the garnet in the Malaspina Pluton is closely associated with trondhjemitic veins and includes both fine‐grained intergrowths with clinopyroxene and coarse porphyroblasts that commonly form vein selvages.…”

Section: Geological Settingmentioning

confidence: 99%

Temporal links between pluton emplacement, garnet granulite metamorphism, partial melting and extensional collapse in the lower crust of a Cretaceous magmatic arc, Fiordland, New Zealand

Stowell

Parker

Gatewood

et al. 2014

Journal Metamorphic Geology

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Garnet granulite facies mid‐to lower crust in Fiordland, New Zealand, provides evidence for pulsed intrusion and deformation occurring in the mid‐to lower crust of magmatic arcs. 238U‐206Pb zircon ages constrain emplacement of the ∼595 km2 Malaspina Pluton to 116–114 Ma. Nine Sm‐Nd garnet ages (multi‐point garnet‐rock isochrons) ranging from 115.6 ± 2.6 to 110.6 ± 2.0 Ma indicate that garnet granulite facies metamorphism was synchronous or near synchronous throughout the pluton. Hence, partial melting and garnet granulite facies metamorphism lasted <5 Ma and began within 5 Ma of pluton emplacement. Garnet granulite facies L‐S tectonites in the eastern part of the Malaspina Pluton record the onset of extensional strain and arc collapse. An Sm‐Nd garnet age and thermobarometric results for these rocks directly below the amphibolite facies Doubtful Sound shear zone provide the oldest known age for extension in Fiordland at ≥112.8 ± 2.2 Ma at ∼920 °C and 14–15 kbar. Narrow high Ca rims in garnet from some of these suprasolidus rocks could reflect a ≤ 1.5 kbar pressure increase, but may be largely a result of temperature decrease based on the Ca content of garnet predicted from pseudosections. At peak metamorphic conditions >900 °C, garnet contained ∼4000 ppm Ti; subsequently, rutile inclusions grew during declining temperature with limited pressure change. Garnet granulite metamorphism of the Malaspina Pluton is c. 10 Ma younger than similar metamorphism of the Pembroke Granulite in northern Fiordland; therefore, high‐P metamorphism and partial melting must have been diachronous for this >3000 km² area of mid‐to‐lower crust. Thus, two or more pulses of intrusion shortly followed by garnet granulite metamorphism and extensional strain occurred from north to south along the axis of the lower crustal root of the Cretaceous Gondwana arc.

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“…The outboard belt preserves Jurassic (168–137 Ma) and older arc rocks that accreted onto Gondwana by ~129 Ma [ Tulloch and Kimbrough , ; Marcotte et al ., ; Scott and Cooper , ]. The inboard belt (130–105 Ma) includes 126–115 Ma mafic‐intermediate plutons of the Western Fiordland Orthogneiss (WFO) [ Bradshaw , ], which was emplaced into the middle and lower crust [ Muir et al ., ; Allibone et al ., ] and accompanied by lower crustal melting [ Daczko et al ., ; Hollis et al ., ; Stowell et al ., ].…”

Section: Geological Context and Previous Workmentioning

confidence: 99%

Three‐stage evolution of lower crustal gneiss domes at Breaksea Entrance, Fiordland, New Zealand

Betka

Klepeis

2013

Tectonics

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[1] New structural analyses reveal the presence of several kilometer-scale gneiss domes and many subdomes within an exhumed section of Cretaceous lower crust in SW Fiordland. The domes are defined by complex, nearly concentric trajectories of foliations and steep high-strain zones in migmatitic, granulite, and eclogite facies orthogneiss. Structural patterns combined with evidence of deformation that was synchronous with partial melting and high-grade metamorphism, steep mineral lineation orientations, sense of shear indicators, and near-isothermal decompression suggest that buoyancy-driven diapiric flow of hot, partially molten crust aided initial dome formation.

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Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

Cited by 56 publications

References 53 publications

The recognition of former melt flux through high‐strain zones

The recognition of former melt flux through high‐strain zones

Temporal links between pluton emplacement, garnet granulite metamorphism, partial melting and extensional collapse in the lower crust of a Cretaceous magmatic arc, Fiordland, New Zealand

Three‐stage evolution of lower crustal gneiss domes at Breaksea Entrance, Fiordland, New Zealand

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