A younger age constraint on high‐grade metamorphism near George Sound in Fiordland, New Zealand

Scott, James M.; Palin, J. Michael; Cooper, Alan F.

doi:10.1080/00288300909509879

Cited by 5 publications

(4 citation statements)

References 19 publications

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“…The emplacement pressure of 1.1 GPa corresponds to a depth of ~41 km, assuming 0.1 GPa = 3.7 km. By comparison, the SABT formed within the Irene Complex, whose correlatives in central Fiordland record Cretaceous pressures estimated between ~0.42 and 0.88 GPa (Scott and Cooper, 2006;Scott et al, 2009a;Scott et al, 2009b). Using the same pressure-depth relationship, these pressures correspond to depths up to ~33 km.…”

Section: ■ Discussion Misty Shear Zone and South Adams Burn Thrustmentioning

confidence: 94%

Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

et al. 2020

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Recovering the time-evolving relationship between arc magmatism and deformation, and the influence of anisotropies (inherited foliations, crustal-scale features, and thermal gradients), is critical for interpreting the location, timing, and geometry of transpressional structures in continental arcs. We investigated these themes of magma-deformation interactions and preexisting anisotropies within a middle- and lower-crustal section of Cretaceous arc crust coinciding with a Paleozoic boundary in central Fiordland, New Zealand. We present new structural mapping and results of Zr-in-titanite thermometry and U-Pb zircon and titanite geochronology from an Early Cretaceous batholith and its host rock. The data reveal how the expression of transpression in the middle and lower crust of a continental magmatic arc evolved during emplacement and crystallization of the ~2300 km2 lower-crustal Western Fiordland Orthogneiss (WFO) batholith. Two structures within Fiordland’s architecture of transpressional shear zones are identified. The gently dipping Misty shear zone records syn-magmatic oblique-sinistral thrust motion between ca. 123 and ca. 118 Ma, along the lower-crustal WFO Misty Pluton margin. The subhorizontal South Adams Burn thrust records mid-crustal arc-normal shortening between ca. 114 and ca. 111 Ma. Both structures are localized within and reactivate a recently described >10 km-wide Paleozoic crustal boundary, and show that deformation migrated upwards between ca. 118 and ca. 114 Ma. WFO emplacement and crystallization (mainly 118–115 Ma) coincided with elevated (>750 °C) middle- and lower-crustal Zr-in-titanite temperatures and the onset of mid-crustal cooling at 5.9 ± 2.0 °C Ma−1 between ca. 118 and ca. 95 Ma. We suggest that reduced strength contrasts across lower-crustal pluton margins during crystallization caused deformation to migrate upwards into thermally weakened rocks of the mid-crust. The migration was accompanied by partitioning of deformation into domains of arc-normal shortening in Paleozoic metasedimentary rocks and domains that combined shortening and strike-slip deformation in crustal-scale subvertical, transpressional shear zones previously documented in Fiordland. U-Pb titanite dates indicate Carboniferous–Cretaceous (re)crystallization, consistent with reactivation of the inherited boundary. Our results show that spatio-temporal patterns of transpression are influenced by magma emplacement and crystallization and by the thermal structure of a reactivated boundary.

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Section: ■ Discussion Misty Shear Zone and South Adams Burn Thrustmentioning

confidence: 94%

Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

et al. 2020

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“…There was then a period of general tectonic quiescence until Early Cretaceous intrusion of circa 140–120 Ma plutons in southwest and northern Fiordland [ Hollis et al , 2003; Gollan , 2006; Allibone et al , 2007], and emplacement of the batholithic Western Fiordland Orthogneiss (126–114 Ma) [ Allibone et al , 2009a; Bradshaw , 1990; Gibson et al , 1988; Mattinson et al , 1986; Tulloch and Kimbrough , 2003]. Western Fiordland Orthogneiss intrusion was accompanied by amphibolite to garnet granulite facies metamorphism [ Allibone et al , 2009a; Bradshaw , 1989; Brown , 1996; Clarke et al , 2000; Daczko et al , 2001a, 2001b, 2002; Daczko and Halpin , 2009; Gibson et al , 1988; Hollis et al , 2004; Scott et al , 2009a, 2009c], and followed regionally by extensional exhumation on detachment faults between 111 and 80 Ma [ Gibson et al , 1988; Klepeis et al , 2007; King et al , 2008; Kula et al , 2007; Scott and Cooper , 2006; Spell et al , 2000; Tulloch and Kimbrough , 1989].…”

Section: Geological Frameworkmentioning

confidence: 99%

Tracking the influence of a continental margin on growth of a magmatic arc, Fiordland, New Zealand, using thermobarometry, thermochronology, and zircon U‐Pb and Hf isotopes

Scott¹,

Cooper

Palin

et al. 2009

Tectonics

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Geothermobarometric, radiogenic isotopic and thermochronologic data are used to track the influence of an ancient continental margin (Western Province) on development of an adjacent Carboniferous‐Cretaceous magmatic arc (Outboard Median Batholith) in Fiordland, New Zealand. The data show a record of complicated Mesozoic Gondwana margin growth. Paragneiss within the Outboard Median Batholith is of Carboniferous to Jurassic age and records burial to middle crustal depths in Late Jurassic–Early Cretaceous during subduction‐related plutonism and arc thickening. In contrast, Western Province metasedimentary rocks in the area of study immediately west of the Outboard Median Batholith are Late Cambrian–Early Ordovician in age, recrystallized at the amphibolite facies in the Late Devonian–Early Carboniferous and exhibit no evidence for Mesozoic textural or isotopic reequilibration. A phase of deformation, between 128 and 116 Ma deformed, exhumed, and cooled the Outboard Median Batholith to greenschist facies temperatures, while large parts of the Western Province underwent ≥9 kbar metamorphic conditions. Zircon grains from Mesozoic inboard plutons are isotopically more evolved (ɛHf(t) = +2.3 to +4.0) than those in the Outboard Median Batholith (ɛHf(t) = +9.4 to +11.1). The contrasting zircon Hf isotope ratios, absence of S‐type plutons or Proterozoic–Early Paleozoic inherited zircon, and the apparent absence of Early Paleozoic metasedimentary rocks indicates that the Outboard Median Batholith is unlikely to be underlain by the Western Province continental lithosphere. The new data are consistent with the Outboard Median Batholith representing an allochthonous (although not necessarily exotic) arc that was juxtaposed onto the Gondwana continental margin along the intervening Grebe Mylonite Zone.

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“…Small patches of garnetiferous pelitic, semi‐pelitic, amphibolitic and calc‐silicate gneiss occur as xenoliths within the layered amphibolite and represent the country rock to which the amphibolite was intruded. Massive hornblende gabbro sills cut the Mt Murrell xenolith and granitic pegmatite dykes intrude all xenoliths (Scott et al , in press).…”

Section: Field Relationshipsmentioning

confidence: 99%

“…First, an upper age limit to M2 is given by the formation of Stage 4 zircon growth (between 118.8 and 111.2 Ma, with consideration of 2σ errors) because it would be highly unlikely to recrystallize zircon and not affect the metamorphic assemblage in the same rock. The lower age bracket is given by the emplacement of a 118.5 ± 1.2 Ma unmetamorphosed hornblende gabbro sill that intrudes M2‐bearing rocks (Scott, et al , in press). Therefore, M2 occurred at or after the age + 2σ error of Stage 4 zircon (118.8 Ma) but before the age + 2σ error of the hornblende gabbro sill (117.3 Ma).…”

Section: Relationship Of Mineral Assemblages To Zircon Overgrowthsmentioning

confidence: 99%

Polymetamorphism, zircon growth and retention of early assemblages through the dynamic evolution of a continental arc in Fiordland, New Zealand

Scott¹,

Palin²,

Cooper³

et al. 2009

Journal Metamorphic Geology

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The Marguerite Amphibolite and associated rocks in northern Fiordland, New Zealand, contain evidence for retention of Carboniferous metamorphic assemblages through Cretaceous collision of an arc, emplacement of large volumes of mafic magma, high-P metamorphism and then extensional exhumation. The amphibolite occurs as five dismembered aluminous meta-gabbroic xenoliths up to 2 km wide that are enclosed within meta-leucotonalite of the Lake Hankinson Complex. A first metamorphic event (M1) is manifest in the amphibolite as a pervasively lineated pargasite-anorthite-kyanite or corundum ± rutile assemblage, and as diffusion-zoned garnet in pelitic schist xenoliths within the amphibolite. Thin zones of metasomatically Al-enriched leucotonalite directly at the margins of each amphibolite xenolith indicate element redistribution during M1 and equilibration at 6.6 ± 0.8 kbar and 618 ± 25°C. A second phase of recrystallization (M2) formed patchy and static margarite ± kyanitestaurolite-chlorite-plagioclase-epidote assemblages in the amphibolite, pseudomorphs of coronas in gabbronorite, and thin high-grossular garnet rims in the pelitic schists. Conditions of M2, 8.8 ± 0.6 kbar and 643 ± 27°C, are recorded from the rims of garnet in the pelitic schists. Cathodoluminescence imaging and simultaneous acquisition of U-Th-Pb isotopes and trace elements by depth-profiling zircon grains from one pelitic schist reveals four stages of growth, two of which are metamorphic. The first metamorphic stage, dated as 340.2 ± 2.2 Ma, is correlated with M1 on the basis that the unusual zircon trace element compositions indicate growth from a metasomatic fluid derived from the surrounding amphibolite during penetrative deformation. A second phase of zircon overgrowth coupled with crosscutting relationships date M2 to between 119 and 117 Ma. The Early Carboniferous event has not previously been recognized in northern Fiordland, whereas the latter event, which has been identified in Early Cretaceous batholiths, their xenoliths, and rocks directly at batholith margins, is here shown to have also affected the country rock. However, the effects of M2 are fragmentary due to limited element mobility, lack of deformation, distance from a heat source and short residence time in the lower crust during peak P and T. It is possible that many parts of the Fiordland continental arc achieved high-P conditions in the Early Cretaceous but retain earlier metamorphic or igneous assemblages.

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A younger age constraint on high‐grade metamorphism near George Sound in Fiordland, New Zealand

Cited by 5 publications

References 19 publications

Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

Tracking the influence of a continental margin on growth of a magmatic arc, Fiordland, New Zealand, using thermobarometry, thermochronology, and zircon U‐Pb and Hf isotopes

Polymetamorphism, zircon growth and retention of early assemblages through the dynamic evolution of a continental arc in Fiordland, New Zealand

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