The regional significance of Cretaceous magmatism and metamorphism in Fiordland, New Zealand, from U–Pb zircon geochronology

Abstract

The western Fiordland Orthogneiss (WFO) is an extensive composite metagabbroic to dioritic arc batholith that was emplaced at c. 20-25 km crustal depth into Palaeozoic and Mesozoic gneiss during collision and accretion of the arc with the Mesozoic Pacific Gondwana margin. Sensitive high-resolution ion microprobe U-Pb zircon data from central and northern Fiordland indicate that WFO plutons were emplaced throughout the early Cretaceous (123.6 ± 3.0, 121.8 ± 1.7, 120.0 ± 2.6 and 115.6 ± 2.4 Ma). Emplacement of the WFO synchronous with regional deformation and collisionalstyle orogenesis is illustrated by (i) coeval ages of a post-D1 dyke (123.6 ± 3.0 Ma) and its host pluton (121.8 ± 1.7 Ma) at Mt Daniel and (ii) coeval ages of pluton emplacement and metamorphism/ deformation of proximal paragneiss in George and Doubtful Sounds. The coincidence emplacement and metamorphic ages indicate that the WFO was regionally significant as a heat source for amphibolite to granulite facies metamorphism. The age spectra of detrital zircon populations were characterized for four paragneiss samples. A paragneiss from Doubtful Sound shows a similar age spectrum to other central Fiordland and Westland paragneiss and SE Australian Ordovician sedimentary rocks, with age peaks at 600-500 and 1100-900 Ma, a smaller peak at c. 1400 Ma, and a minor Archean component. Similarly, one sample of the George Sound paragneiss has a significant Palaeozoic to Archean age spectrum, however zircon populations from the George Sound paragneiss are dominated by PermoTriassic components and thus are markedly different from any of those previously studied in Fiordland.

Tectonics of the West Antarctic rift system: new light on the history and dynamics of distributed intracontinental extension

“…The timing of HT metamorphism in NZ is determined by U-Pb ages on metamorphic zircon or titanite sampled from gneisses at sites distributed along the convergent margin. These include the Paparoa range at 119-109 Ma Ireland and Gibson, 1998;Spell et al, 2000); and Fiordland at 126-110 Ma (Ireland and Gibson, 1998;Hollis et al, 2004;Scott and Cooper, 2006). Granulite metamorphism documented in Fiordland at 108 ± 3 Ma (Gibson and Ireland, 1995) gives an indication that elevated and compressed crustal isotherms developed during convergent tectonism ( Figure 5).…”

“…Pankhurst et al (1998) introduced the term "Ross Province" for the Swanson-Ford association in western MBL (Figure 2). Correlatives of the Ross Province exist throughout the former Gondwana margin, including a number of culminations of HT metamorphic rocks derived from Paleozoic protoliths Morand, 1990;Ireland and Gibson, 1998;Vernon and Johnson, 2000;Richards and Collins, 2002;Hollis et al, 2004) (Figure 4). It is probable that Ross-Delamerian orogenic sediments and the intermediate plutonic rocks that intrude them constitute the majority of the crust within the Ross Sea sector of the WARS (Bradshaw, 2007), its continuation into New Zealand (e.g., Cook et al, 1999), and into the submerged extended continental crust bordering the Tasman Sea.…”

“…Comparison of U-Pb SHRIMP frequency distribution for Fosdick Mountains leucogranites, with New Zealand data including from the Fiordland Orthogneiss (Hollis et al, 2004), Median Batholith (Tulloch and Kimbrough, 2003), and Buckland Granite (Ireland and Gibson, 1998). Fosdick Mountains data were acquired on SHRIMP II at Australian National University under the direction of C. M. Fanning.…”

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

“…A whole rock chemical analysis shows that it has high A1 2 O 3 , CaO, Cr and Sr and distinctly low Zr, Th, Pb, Y, La and Ce (Table 1). The high A1 2 O 3 and Sr but low rare earth element (REE) concentrations are similar to the nearby 126-116 Ma Western Fiordland Orthogneiss (Mattinson et al 1986;Muir et al 1998;Tulloch & Kimbrough 2003;Hollis et al 2004) and also a granite dike that cuts across the Marguerite Amphibolite (Table 1). The chemical properties of the granite dike are similar to 108 Ma Separation Point Suite granitoids reported by Scott & Cooper (2006) from nearby Mt Irene (Fig.…”

“…Most interpretations favour formation between 126 and 113 Ma during convergent orogenesis at and after emplacement of the voluminous Western Fiordland Orthogneiss (Mattinson etal. 1986;Hollis et al 2004;Daczko & Halpin 2009). However, high-grade assemblages have also been identified as having formed at c. 108 Ma during extensional tectonics (Gibson & Ireland 1995;Scott & Cooper 2006).…”