U-Th-Pb zircon and monazite geochronology of Western Province gneissic rocks, central-south Westland, New Zealand

Abstract

Ion-microprobe (Sensitive High Resolution Ion MicroProbe or SHRIMP) zircon and monazite U-Th-Pb geochronology of amphibolite-facies orthogneiss and paragneiss units, mostly from the Fraser and Granite Hill Complexes of Westland, New Zealand, has constrained the ages of protolith rocks and metamorphic overprints. Paragneiss zircon (6 samples, 175 analyses) comprise detrital grains of Paleozoic to Archean age and match patterns from metasedimentary (Ordovician) Greenland Group rocks of the Western Province, which are characteristic of early Paleozoic flysch units around the southwest Pacific margin of Gondwana. Orthogneiss zircon (9 samples, 138 analyses) reflect intense Devonian and Cretaceous magmatism associated with emplacement of the Karamea-Paparoa and Hohonu Batholiths within the Western Province. Both paragneiss and orthogneiss monazite analyses (10 samples, 116 analyses) are dominated by Devonian and Cretaceous ages, reflecting thermal pulses related to regional and localised granitoid intrusions. These results indicate that the Fraser and Granite Hill Complex gneisses are metamorphosed parts of the Western Province Buller Terrane with Karamea-Paparoa and Hohonu Batholith intrusive components.

Keywords:

• Fraser Complex
• Granite Hill Complex
• monazite
• orthogneiss
• paragneiss
• SHRIMP
• U-Th-Pb
• West Coast
• zircon

Introduction

The southwest Pacific margin of Gondwana (Eastern Australia, Western Antarctica and New Zealand regions) is characterised by extensive Paleozoic and Mesozoic sedimentary and igneous rocks that record a long period of predominantly east-migrating subduction-related sedimentation, volcanism and pluton intrusion (Gray & Foster 2004; Tulloch et al. 2009). The opening of the Tasman Sea and the Antarctic Ocean in the late Cretaceous has dispersed these originally contiguous regional elements (Kula et al. 2007). In New Zealand, these rocks form outcropping basement in the South Island of New Zealand and collectively form the Western Province and parts of the Median Batholith (Mortimer 2004). These rocks have been variably affected by intrusion-related metamorphic events in the Devonian-Carboniferous and Cretaceous, resulting in extensive metamorphic belts and gneisses in Westland and Fiordland (Ireland & Gibson 1998; Daczko et al. 2009). Also in Westland are high-grade paragneiss and orthogneiss rocks immediately west of the present Australian-Pacific plate boundary that have not been conclusively linked to pre-metamorphic protolith rocks (Rattenbury 1987 , 1991). These rocks have possibly been emplaced and deformed by one of various extensional (Tulloch & Kimbrough 1989; Spell et al. 2000; Kula et al. 2007), strike-slip and oblique convergent (Klepeis et al. 2004; Marcotte et al. 2005; Allibone & Tulloch 2008) plate boundary tectonic events that have affected the Western Province in the Phanerozoic. The gneisses could be up-faulted, high-grade metamorphic equivalents of nearby known rocks, faulted slices of other known terranes in the South Island or an exotic accreted terrane (Rattenbury 1991; Kimbrough et al. 1994). This paper reports on a geochronological study of these gneisses using high resolution U-Th-Pb in situ Sensitive High Resolution Ion MicroProbe (SHRIMP) dating of single zircon and monazite crystals to ascertain (1) their protolith ages and (2) the timing of metamorphism of the gneisses, to better constrain their origin and tectonostratigraphic context. This work was initiated in part to provide geochronology for a new geological map of central Westland (Nathan et al. 2002).

Geological setting

The western part of the South Island of New Zealand has a long Phanerozoic history of sedimentation, deformation and igneous and metamorphic activity. The area includes the Buller and Takaka basement terranes that form the Western Province. The oldest known rocks are metamorphosed Cambrian volcanogenic arc-related rocks that occur in a small area around Springs Junction (Nathan et al. 2002; Rattenbury et al. 2006) and more widely further north in northwest Nelson (Rattenbury et al. 1998). These predominantly mafic volcanic rocks form the older part of Takaka Terrane and the younger part is dominated by siliceous and calcareous Ordovician to early Devonian platform sedimentary rocks. Most of the basement of western South Island is Buller Terrane (Cooper & Tulloch 1992) and is dominated by the quartzo-feldspathic metasedimentary rocks of the Greenland Group of Ordovician age (Cooper 1975 , 1989). These sandstone and mudstone turbidites are generally weakly metamorphosed (lower-greenschist facies).

While plutonism has occurred intermittently through much of the Paleozoic and Mesozoic in the western South Island, there have been two well-documented periods of significant igneous intrusion. Late Devonian to early Carboniferous activity is recorded in many parts of the area (Allibone et al. 2007 , 2009a , b; Tulloch et al. 2009), particularly in the north associated with emplacement of the Karamea Batholith (Tulloch 1983 , 1988; Muir et al. 1994 , 1996a; Rattenbury et al. 1998; Tulloch et al. 2009). Most of these granite and granodiorite-dominated rocks are grouped into the S-type Karamea Suite with volumetrically minor contributions from the Tobin, Ridge and Paringa Suites (Tulloch 1983 , 1988; Tulloch et al. 2009). Early Cretaceous plutonism has contributed significant volumes of granitic rock in parts of the West Coast, notably in the Paparoa, Victoria and Hohonu Ranges. Most of these are grouped into two geochemically defined suites: the I-type Separation Point Suite and the generally slighter younger I-S type Rahu Suite (Tulloch 1983 , 1988; Waight et al. 1997). Many of these Cretaceous plutons form parts of the Karamea-Paparoa, Hohonu and Median Batholiths (Mortimer 2004).

From the early Cretaceous to Recent there has been semi-continuous deposition of clastic sediment, commonly in tectonically active, fault-controlled basins (Nathan et al. 1986 , 2002). The lower elevation parts of the West Coast area are typically blanketed with late Neogene fluvio-glacial deposits largely derived from the rapidly uplifting Southern Alps (Suggate & Waight 1999). Significant periods of tectonism in the Silurian, Devonian, Cretaceous and Neogene in western New Zealand have also contributed to complex structural geometries of the basement and older cover rocks (Tulloch & Kimbrough 1989; Allibone & Tulloch 2008). Convergent deformation in the Neogene has resulted in uplift of some ranges exposing the crustal basement rocks (Kamp et al. 1992; Batt et al. 2000 , 2004; Little et al. 2005).

High-grade gneisses occur in two main areas on the West Coast of the South Island: in the Paparoa Range and along the Alpine Fault (Nathan et al. 2002; Cox & Barrell 2007). The Paparoa Range gneisses have been attributed to a metamorphic core complex that emerged during early rifting stages that ultimately led to the opening of the Tasman Sea in the late Cretaceous (Tulloch & Kimbrough 1989). The gneisses of the Paparoa Range include both metasedimentary and plutonic protoliths (Nathan et al. 2002). The paragneisses have geochemical and geochronological similarities to the Greenland Group metasedimentary rocks that form some of the cover rocks in the upper plate of the core complex. The other main area of gneiss exposure, and the focus of this study, mostly occurs between the Alpine and Fraser Faults where gneissic rocks crop out in up-faulted ranges south of Hokitika (Rattenbury 1991; Jongens 2006) and in the southern Victoria Range (Fig. 1).

Fig. 1  Geological map of Western Province basement granitic, gneissic and metasedimentary rocks and key faults in central Westland (modified after Nathan et al. 2002; Cox & Barrell 2007) showing sample locations. The 10 km grid is in NZTM2000 coordinates. The inset map shows the New Zealand basement terranes in the central South Island (after Mortimer 2004).

Amphibolite-facies gneisses, associated granitic plutons and enveloping mylonitic rocks south of Hokitika are known as the Fraser Complex (Rattenbury 1991). These gneisses include garnet-biotite±kyanite±sillimanite metapelite, migmatitic quartzofeldspathic metasandstone and hornblende±epidote±garnet amphibolite. To the northeast a similar association is known as the Granite Hill Complex (Suggate & Waight 1999). The position of the Fraser and Granite Hill Complexes along the current plate boundary has meant a number of potential protoliths can be considered including quartz-rich clastic Buller Terrane (Rattenbury 1991), a remnant of the Cambrian-Devonian volcanosedimentary Takaka Terrane, a remnant of the Carboniferous-Cretaceous Median Batholith/Tectonic Zone (Kimbrough et al. 1994) or even a completely exotic accreted terrane. The tectonic exhumation of the gneissic rocks could potentially involve localised Cenozoic reverse fault uplift (White & Green 1986; Rattenbury 1991), major extensional unroofing (Kimbrough et al. 1994; Jongens 2006) or large-scale strike-slip fault juxtaposition.

Previous geochronology

In situ single grain SHRIMP U-Pb zircon dating of a Victoria Range paragneiss and two Granite Hill Complex paragneisses by Ireland (1992) yielded a range of concordant ages mostly between 1219 and 115 Ma that were interpreted to record Silurian and early Cretaceous metamorphism of an Ordovician sedimentary protolith derived from Archean, Proterozoic and Cambrian rocks. Further work on a Victoria Range paragneiss yielded an ion microprobe monazite U-Pb age of 377±7 Ma and Th-Pb age of 374±7 Ma (Ireland & Gibson 1998) that was interpreted to indicate widespread Devonian thermal metamorphism associated with Karamea granite batholith emplacement. A Fraser Complex migmatite U-Pb zircon lower intercept age of 157±21 Ma has been interpreted to date peak metamorphism and the upper intercept of 735±100 Ma, suggesting inheritance of Proterozoic zircon (Kimbrough et al. 1994). K-Ar dating of biotite, hornblende and whole rock Fraser Complex gneisses yielded results suggesting some excess argon contamination, but constraining cooling through the biotite K-Ar closure temperature after 44 Ma (Rattenbury 1987). Fission track dating of minerals separated from the Fraser Complex indicate ages of c. 9 Ma (zircon) and c. 2 Ma (apatite), reflecting current uplift associated with compression between the Alpine and Fraser Faults (White & Green 1986; Kamp et al. 1992).

Adjacent late Devonian to early Carboniferous plutonism has been constrained by zircon geochronology. Muir et al. (1996a) documented a cluster of c. 375 Ma ion microprobe ages as well as two younger dates around 330 Ma. Tulloch et al. (2009) obtained ages between 371 and 305 Ma, mostly concentrated around 370 Ma, from ID-TIMS analyses. Early Cretaceous plutonism is also well constrained by ages between 129 and 109 Ma for the Separation Point Suite and 115 and 105 Ma for the Rahu Suite (Muir et al. 1994 , 1997; Waight et al. 1997).

Samples

This study has concentrated on gneissic rocks located close to the Alpine Fault, particularly within the Fraser Complex (Fig. 1). The fifteen samples analysed were collected between the southern Victoria Range and Whataroa, falling into two main categories: six garnet-biotite paragneisses and nine biotite orthogneisses (Table 1). The paragneisses contain sillimanite and/or kyanite in places and are inferred to be upper amphibolite facies metapelites. Monazites from two additional samples, one paragneiss and one orthogneiss of the Charleston Metamorphic Complex previously reported by Ireland & Gibson (1998), were analysed to compare our analytical methods and results with previous geochronology on similar samples.

Table 1  Sample locations and lithological descriptions.

Sample	Location	Latitude (°S)	Longitude (°E)	Elevation (m)	Zircon	Monazite	Description
A546	Mikonui River paragneiss	43.03058	170.89978	329	Y	Y	Typical garnet-biotite paragneiss
A550	Clarke River paragneiss	42.39943	171.87749	302	Y	Y	Typical garnet-biotite paragneiss
A552	Crooked River paragneiss	42.65130	171.61800	174	Y	Y	Typical garnet-biotite paragneiss
A553	Crooked River paragneiss	42.64860	171.61440	171	Y	Y	Typical garnet-biotite paragneiss
A559	Waitangitaona River paragniess	43.29240	170.31170	96	Y	–	Typical garnet-biotite paragneiss
A560	Mt Elliot paragneiss	42.52570	171.82040	200	Y	Y	Typical garnet-biotite paragneiss
A547	Mikonui River orthogneiss	43.02812	170.89981	193	Y	Y	Typical biotite orthogneiss
A548	Solitude Creek orthogneiss	42.99129	170.94165	470	Y	–	Biotite granite derived mylonite
A549	Clarke River orthogneiss	42.39921	171.85563	200	Y	Y	Representative biotite orthogneiss with cross-cutting dike sliver
A551	Mt Elliot orthogneiss	42.52570	171.82040	200	Y	–	Typical biotite orthogneiss
A554	Hokitika Gorge orthogneiss	42.95660	171.01540	78	Y	–	Biotite granite melt derived from metasedimentary migmatite
A555	Mikonui River orthogneiss	43.03090	170.89150	300	Y	–	Biotite orthogneiss occuring with paragneiss
A556	Tuke River orthogneiss	43.02700	170.87450	155	Y	–	Biotite orthogneiss variably mylonitised and cut by mafic and felsic dikes
A557	Bonar Creek orthogneiss	43.08450	170.63910	450	Y	Y	Biotite orthogneiss within 50m of hornfelsed Greenland Group
A558	Whataroa Quarry orthogneiss	43.28460	170.36140	125	Y	–	Strongly lineated biotite orthogneiss

Analytical methods

Clean rock crushing and heavy-liquid mineral separation was undertaken at GNS Science, followed by magnetic extraction of zircon and monazite at the Research School of Earth Sciences (RSES) of The Australian National University (ANU). Approximately 100 grains from each sample were transferred onto double-sided adhesive tape under a binocular microscope without attempting to bias the sample selection. Zircon and monazite samples were mounted close to their respective reference materials, SL13 zircon, FC1 zircon and Maffra monazite. All grains were cast in epoxy and polished with a rotary pad and 1 µm diamond paste to expose crystal midsections. Before analysis, the zircon and monazite were characterised with reflected light and transmitted light imaging followed by either Hitachi S-2250N SEM cathodoluminesence (zircon) or Cambridge S360 SEM back-scattered electron (monazite) imaging. This allowed identification of cracks and mineral inclusions, as well as providing images of two-dimensional (2D) growth and recrystallisation textures to guide spot placement. The major growth domains of clean grains from all morphologies were analysed to provide representative age spectra from each sample. Before each SHRIMP analytical session, polished (analytical) surfaces were sequentially cleaned in an ultrasonic bath with petroleum spirit, ethanol, diluted laboratory detergent, 1M HCl (1×quartz distilled) and deionised (18 Mω) H₂O before being dried in a 60°C oven. A 100Å Au conductive layer was then evaporated onto the analytical surface and electrically checked for uniform and adequate conductivity before loading into the instrument.

U-Th-Pb ages were determined using the SHRIMP Reverse Geometry (RG) ion microprobe at RSES, ANU. The methods employed here are similar to those described in detail by Muir et al. (1996a), Williams (1998) and Ireland & Gibson (1998) and are summarised as follows. For zircon analysis, a 3 nA mass filtered O₂ ⁻ primary beam was focused to a c. 30 µm (long axis) elliptical spot and the beam rastered for 120 s to clean the mount surface prior to data acquisition. The magnet was stepped through positive secondary ion peaks of ⁹⁰Zr₂ ¹⁶O, ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb, ²³⁸U, ²³²Th¹⁶O and ²³⁸U¹⁶O, analysed by a single electron multiplier. For monazite analysis the primary beam current was reduced to 1 nA to prevent the ThO⁺ signal damaging the ion counter, energy filtering was employed to minimise a multi-element isobaric interference on ²⁰⁴Pb and the Zr₂O species was replaced with ¹⁴⁰Ce³¹P¹⁶O₂. Isotope ratios were recorded as measured, without applying any correction for hydride interferences or isotopic mass fractionation. Mass resolution was c. 5500 at the 1% peak height.

Zircon reference material SL13 (Claoué-Long et al. 1995; U=238 ppm) was used to calculate U abundances. FC1 zircon (Paces & Miller 1993; 1099±1 Ma) and Maffra monazite (Ireland & Gibson 1998; 421±1 Ma) reference materials were analysed once every three unknowns and were used for determining empirical quadratic calibrations based on the form ²⁰⁶Pb/U=a(UO/U)² and ²⁰⁸Pb/Th=a(ThO/Th)². Decay constants and atomic ratios recommended by the IUGS Subcommission on Geochronology (Steiger & Jäger 1977) were used to calculate ages. Analyses with ²⁰⁶Pb/²³⁸U ages <800 Ma were corrected for common Pb based on the measured ²⁰⁷Pb/²⁰⁶Pb ratio (²⁰⁷Pb correction method). Analyses were assumed to be a mixture between a concordant radiogenic datum and surface contamination common Pb with a Broken Hill isotopic composition (²⁰⁴Pb/²⁰⁶Pb=0.0625, ²⁰⁷Pb/²⁰⁶Pb=0.962, ²⁰⁸Pb/²⁰⁶Pb=2.23). Most measured data points record a high level of concordance so the common Pb correction was insensitive to the choice of isotopic composition used. Zircon analyses that recorded ²⁰⁶Pb/²³⁸U ages >800 Ma are instead listed as ²⁰⁷Pb/²⁰⁶Pb ages corrected for common Pb based on measured ²⁰⁴Pb/²⁰⁶Pb (²⁰⁴Pb correction method).

Analytical uncertainties for individual spots are reported as 1 σ within-spot errors. To condense a weighted mean ²⁰⁶Pb/²³⁸U or ²⁰⁸Pb/²³²Th age for selected samples, analyses were culled to selectively remove outliers. Outliers were statistically and/or geologically identified based on U-Th-Pb ages that were products of inheritance, local recrystallisation or Pb disturbance (e.g., around cracks and inclusions). A population of acceptable analyses from each sample was then pooled to calculate crystallisation ages using the Excel^TM macro Isoplot (Ludwig 2003). Weighted mean 95% confidence limit uncertainties were calculated from the inverse square of the assigned within-spot errors summed in quadrature with the 2 σ external reproducibility of the U/Pb or Th/Pb calibration standard that ranged from ±0.66% to ±0.76% for zircon and ±0.94% to ±1.05% for monazite.

Results

Summaries of U-Th-Pb results from individual spot analyses of paragneiss zircon (6 samples, 175 analyses), orthogneiss zircon (9 samples, 138 analyses) and combined paragneiss and orthogneiss monazite (10 samples, 116 analyses) can be found in Table 2, 3 and 4, respectively. Spot analyses used for weighted mean ²⁰⁶Pb/²³⁸U or ²⁰⁸Pb/²³²Th age calculations of selected samples are marked in bold. Uncorrected ²³⁸U/²⁰⁶Pb – ²⁰⁷Pb/²⁰⁶Pb ratios are presented as Tera-Wasserberg Concordia diagrams for all zircon analyses in Fig. 2 and all monazite analyses in Fig. 3A–J. Comparisons between monazite ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ages are presented in Fig. 3K–T. Probability density plots of sample age distributions are presented in Fig. 4. Representative grain images and summary histograms depicting paragneiss zircon, orthogneiss zircon and combined paragneiss and orthogneiss monazite age structures are presented in Fig. 5 and 6.

Fig. 2  Tera-Wasserberg concordia diagrams presenting uncorrected ²³⁸U/²⁰⁶Pb–²⁰⁷Pb/²⁰⁶Pb ratios of all zircon analyses.

Fig. 3  Tera-Wasserberg concordia diagrams presenting uncorrected ²³⁸U/²⁰⁶Pb–²⁰⁷Pb/²⁰⁶Pb ratios of all monazite analyses (A–J). Correlations between ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ages for all monazite analyses (K–T).

Fig. 4  Probability density plots for all samples. Orthogneiss ages >600 Ma omitted for clarity. For all plots ²³⁸U/²⁰⁶Pb ages <800 Ma are corrected for common Pb based on ²⁰⁷Pb. ²⁰⁷Pb/²⁰⁶Pb ages >800 Ma are corrected for common Pb based on ²⁰⁴Pb.

Fig. 5  Zircon cathodoluminesence (CL) and monazite back-scattered electron (BSE) grain images and SHRIMP analytical spot ages for representative (A) paragneiss A546; (C) orthogneiss A551; and (E) orthogneiss A552. Excellent agreement exists between monazite ²⁰⁶Pb/²³⁸U (*) and ²⁰⁸Pb/²³²Th (‘) ages. Cumulative histogram of (B) paragneiss zircon, (D) orthogneiss zircon and (F) combined paragneiss and orthogneiss monazite age structures. For all histograms ²³⁸U/²⁰⁶Pb ages <800 Ma are corrected for common Pb based on ²⁰⁷Pb. ²⁰⁷Pb/²⁰⁶Pb ages >800 Ma are corrected for common Pb based on ²⁰⁴Pb.

Table 2  U-Th-Pb geochronology results from analysis of paragneiss zircon. f₂₀₆ = fraction of common ²⁰⁶Pb of the total measured Pb. Total ratios are given as measured and are uncorrected for common Pb. Correction method 1 is based on ²⁰⁷Pb (with ²³⁸U/²⁰⁶Pb ages <800 Ma). Correction method 2 is based on ²⁰⁴Pb (with ²⁰⁷Pb/²⁰⁶Pb ages >800 Ma).

	U	Th		f206	Total	err	Total	err	Corr.	Age	err
Label	(ppm)	(ppm)	Th/U	(%)	^238U/^206Pb	(1σ)	^207Pb/^206Pb	(1σ)	meth.	(Ma)	(1σ)
Mikonui River paragneiss A546 (43.03058°S, 170.89978°E, 329m)
1.1	1237	66	0.05	0.066	16.650	0.363	0.0546	0.0014	1	375.7	8.1
2.1	858	104	0.13	0.164	10.496	0.229	0.0608	0.0005	1	585.8	12.5
3.1	289	64	0.23	−0.222	5.252	0.117	0.0753	0.0007	2	1054.0	19.9
4.1	96	45	0.48	0.371	17.486	0.461	0.0567	0.0028	1	357.2	9.3
5.1	596	22	0.04	1.172	5.769	0.128	0.0830	0.0007	2	1283.0	17.6
6.1	198	60	0.31	0.330	12.001	0.349	0.0603	0.0010	1	514.3	14.6
7.1	283	151	0.55	0.339	10.153	0.232	0.0628	0.0009	1	603.6	13.4
8.1	467	268	0.59	0.852	2.864	0.063	0.1248	0.0006	2	2022.5	9.0
9.1	1146	222	0.20	−0.288	10.522	0.381	0.0572	0.0008	1	586.9	20.7
10.1	573	253	0.46	0.399	15.532	0.348	0.0579	0.0016	1	400.7	8.8
10.1B	595	236	0.41	0.120	15.231	0.513	0.0559	0.0012	1	409.4	13.5
11.1	177	111	0.65	1.292	6.496	0.152	0.0802	0.0019	2	1165.1	50.0
11.1B	170	104	0.63	−0.182	5.632	0.132	0.0730	0.0010	2	1000.8	28.7
12.1	1122	77	0.07	2.030	19.682	0.441	0.0690	0.0032	1	313.2	7.1
12.1B	1174	75	0.07	0.670	14.188	0.351	0.0610	0.0010	1	436.2	10.6
13.1	223	98	0.45	2.948	9.728	0.238	0.0844	0.0024	1	613.0	14.9
13.1B	204	106	0.54	0.114	6.279	0.143	0.0718	0.0009	2	1016.5	26.7
14.1	518	159	0.32	0.705	7.785	0.173	0.0708	0.0015	1	773.8	16.7
15.1	101	41	0.41	0.545	6.798	0.164	0.0729	0.0020	2	835.0	101.6
16.1	90	30	0.35	0.410	5.829	0.142	0.0765	0.0015	2	1045.9	51.4
17.1	393	106	0.28	1.288	15.884	0.358	0.0648	0.0015	1	388.7	8.7
18.1	54	12	0.23	0.856	5.789	0.199	0.0804	0.0028	2	738.0	213.0
19.1	468	110	0.24	0.028	12.088	0.273	0.0578	0.0008	1	512.2	11.3
20.1	495	113	0.23	0.898	7.010	0.158	0.0749	0.0029	2	1029.0	81.6
21.1	1280	1486	1.20	−0.054	10.441	0.228	0.0592	0.0005	1	589.9	12.6
A−1.1	1301	347	0.28	5.355	2.875	0.086	0.1589	0.0003	2	2442.8	3.5
A–2.1	765	87	0.12	0.396	10.160	0.304	0.0632	0.0010	1	602.9	17.6
A–3.1	310	70	0.23	0.115	9.325	0.296	0.0624	0.0017	1	655.9	20.3
A–4.1	352	187	0.55	0.661	5.527	0.166	0.0804	0.0010	2	1187.1	25.9
A–5.1	2141	1860	0.90	0.492	12.766	0.378	0.0608	0.0008	1	483.8	14.0
n										30
Clarke River paragneiss A550 (42.39943°S, 171.87749°E, 302m)
1.1	877	774	0.91	−0.043	5.500	0.119	0.0750	0.0004	2	1064.7	9.5
2.1	158	77	0.50	−0.008	5.389	0.121	0.0760	0.0008	2	1051.3	29.4
3.1	351	49	0.15	−0.008	7.791	0.171	0.0651	0.0008	1	778.6	16.6
4.1	205	24	0.12	0.340	11.366	0.260	0.0611	0.0009	1	541.8	12.1
5.1	294	87	0.31	0.452	9.475	0.217	0.0648	0.0009	1	644.0	14.4
6.1	301	285	0.98	0.101	10.737	0.253	0.0600	0.0010	1	573.5	13.2
7.1	296	541	1.89	0.266	4.119	0.091	0.0910	0.0006	2	1440.3	13.3
8.1	484	46	0.10	0.699	8.319	0.183	0.0693	0.0018	1	726.9	15.6
9.1	324	169	0.54	0.252	17.323	0.393	0.0558	0.0009	1	360.9	8.1
10.1	295	157	0.55	0.026	12.889	0.288	0.0570	0.0009	1	481.6	10.5
11.1	399	249	0.65	0.216	11.963	0.197	0.0594	0.0010	1	516.4	8.3
12.1	139	38	0.29	0.173	5.979	0.183	0.0738	0.0023	2	918.2	81.2
13.1	612	83	0.14	−0.210	7.737	0.111	0.0636	0.0006	1	785.1	10.9
14.1	139	43	0.32	0.078	6.335	0.104	0.0712	0.0013	2	977.5	39.1
15.1	1419	265	0.19	−0.184	8.926	0.124	0.0608	0.0004	1	685.7	9.3
16.1	127	30	0.24	−0.263	4.994	0.079	0.0771	0.0012	2	1041.7	51.3
17.1	187	171	0.95	−0.903	2.898	0.052	0.1101	0.0010	2	1793.9	16.7
18.1	1189	6	0.01	−0.073	17.642	0.252	0.0530	0.0007	1	355.7	5.0
19.1	610	129	0.22	−0.044	10.558	0.151	0.0591	0.0007	1	583.6	8.2
20.1	80	1	0.01	0.077	9.363	0.166	0.0620	0.0019	1	653.7	11.3
21.1	274	71	0.27	−0.010	10.825	0.164	0.0590	0.0011	1	569.6	8.4
22.1	1523	63	0.04	−0.007	13.738	0.340	0.0560	0.0010	1	453.0	11.0
23.1	420	107	0.26	0.142	12.803	0.189	0.0580	0.0010	1	484.2	7.0
24.1	374	75	0.21	0.157	9.184	0.135	0.0630	0.0009	1	665.3	9.5
25.1	204	51	0.26	−0.075	9.331	0.157	0.0609	0.0012	1	656.7	10.8
A–1.1	1485	318	0.22	0.160	5.584	0.165	0.0760	0.0003	2	1092.5	8.2
A–2.1	846	42	0.05	0.515	7.894	0.235	0.0690	0.0011	1	765.1	22.1
A–3.1	1427	158	0.11	0.808	7.182	0.364	0.0736	0.0023	2	1024.7	62.3
A–4.1	164	201	1.26	0.084	5.814	0.178	0.0740	0.0011	2	1021.7	33.6
A–5.1	167	93	0.58	0.619	12.365	0.399	0.0622	0.0012	1	498.4	15.8
n										30
Crooked River paragneiss A552 (42.65130°S, 171.61800°E, 174m)
1.1	392	30	0.08	0.929	12.412	0.283	0.0646	0.0018	1	495.1	11.1
1.1B	396	29	0.08	−0.459	11.055	0.245	0.0551	0.0006	1	560.7	12.1
2.1	80	29	0.38	8.707	2.163	0.050	0.2205	0.0018	2	2987.0	13.2
2.1B	85	26	0.31	10.446	2.472	0.058	0.2142	0.0014	2	2922.5	11.8
3.1	409	89	0.23	0.419	17.111	0.383	0.0572	0.0009	1	364.6	8.0
3.1B	408	110	0.28	0.629	15.749	0.353	0.0596	0.0008	1	394.4	8.7
4.1	12	1	0.06	20.898	2.354	0.077	0.2966	0.0053	2	3348.0	46.9
4.1B	12	1	0.06	18.604	2.344	0.072	0.2804	0.0046	2	3315.0	38.1
5.1B	193	157	0.84	0.461	3.761	0.087	0.0982	0.0069	2	1518.7	140.1
6.1	438	185	0.44	0.167	14.414	0.318	0.0568	0.0009	1	431.7	9.4
7.1	649	280	0.45	0.019	11.009	0.242	0.0590	0.0005	1	560.4	12.0
8.1	368	3	0.01	0.160	17.289	0.458	0.0551	0.0014	1	361.9	9.4
9.1	347	69	0.21	0.323	6.113	0.136	0.0743	0.0007	2	1039.0	18.3
10.1	270	84	0.32	0.692	6.628	0.148	0.0748	0.0008	2	1023.4	28.0
11.1	417	13	0.03	0.120	18.463	0.278	0.0542	0.0011	1	339.6	5.0
12.1	171	39	0.24	11.246	5.338	0.119	0.1663	0.0019	2	2458.4	27.7
13.1	68	56	0.84	−0.975	4.998	0.089	0.0713	0.0023	2	717.4	148.9
14.1	152	106	0.72	0.118	13.027	0.223	0.0576	0.0016	1	476.2	8.0
15.1	535	101	0.20	−0.089	2.871	0.041	0.1173	0.0006	2	1912.4	9.4
16.1	128	58	0.47	−0.304	5.455	0.090	0.0732	0.0013	2	976.2	40.6
17.1	487	38	0.08	0.528	11.244	0.188	0.0627	0.0009	1	546.5	9.0
18.1	222	43	0.20	0.776	6.876	0.107	0.0745	0.0032	2	1015.1	88.9
19.1	536	221	0.43	2.486	11.409	0.311	0.0782	0.0086	1	528.7	15.2
20.1	107	49	0.47	0.145	3.318	0.063	0.1052	0.0013	2	1658.7	26.1
21.1	661	21	0.03	0.286	19.158	0.282	0.0553	0.0009	1	327.1	4.7
22.1	1187	174	0.15	−0.023	11.043	0.156	0.0586	0.0005	1	559.0	7.7
23.1	542	54	0.10	1.355	9.625	0.291	0.0718	0.0015	1	628.9	18.6
24.1	804	6	0.01	1.316	17.745	0.262	0.0641	0.0078	1	348.9	6.1
25.1	81	40	0.51	13.247	7.206	0.157	0.1729	0.0080	1	732.8	21.8
A–1.1	965	133	0.14	−0.676	3.125	0.106	0.1042	0.0009	2	1696.1	16.9
A–2.1	66	44	0.69	0.560	13.049	0.449	0.0611	0.0022	1	473.4	16.0
A–3.1	1057	19	0.02	−0.126	12.998	0.389	0.0556	0.0011	1	478.4	14.0
A–4.1	201	74	0.38	0.136	8.052	0.244	0.0655	0.0009	1	753.7	22.1
A–5.1	776	204	0.27	−0.032	14.433	0.460	0.0552	0.0008	1	432.0	13.5
n										34
Crooked River paragneiss A553 (42.64860°S, 171.61440°E, 171m)
1.1	205	106	0.53	3.073	24.594	0.620	0.0758	0.0060	1	249.2	6.6
2.1	307	88	0.30	0.267	6.068	0.136	0.0741	0.0010	2	1010.7	31.1
3.1	179	39	0.23	0.880	25.683	0.623	0.0581	0.0018	1	244.1	5.9
4.1	691	122	0.18	0.278	14.540	0.321	0.0576	0.0006	1	427.6	9.3
5.1	325	14	0.04	0.458	58.359	1.411	0.0518	0.0018	1	109.0	2.6
6.1	485	53	0.11	0.313	54.902	0.866	0.0508	0.0016	1	116.0	1.8
7.1	646	186	0.30	−0.014	8.586	0.122	0.0629	0.0006	1	710.3	9.8
8.1	130	26	0.21	1.640	52.315	1.076	0.0615	0.0035	1	120.1	2.5
9.1	517	240	0.48	−0.405	5.765	0.083	0.0704	0.0008	2	927.6	23.2
10.1	113	19	0.18	1.736	52.045	1.123	0.0622	0.0038	1	120.6	2.7
11.1	201	130	0.67	−0.308	5.355	0.082	0.0739	0.0020	2	983.2	63.8
12.1	680	17	0.03	0.720	18.205	0.502	0.0591	0.0009	1	342.3	9.3
13.1	225	18	0.08	3.565	52.186	0.932	0.0767	0.0029	1	118.0	2.2
14.1	569	132	0.24	−0.584	4.980	0.071	0.0746	0.0006	2	1031.6	19.5
15.1	1887	110	0.06	0.179	50.896	0.729	0.0500	0.0008	1	125.2	1.8
16.1	134	10	0.07	0.546	11.497	0.191	0.0626	0.0017	1	534.8	8.7
17.1	938	522	0.57	0.021	10.855	0.210	0.0592	0.0006	1	568.0	10.7
18.1	276	130	0.49	2.862	3.154	0.091	0.1308	0.0033	2	2101.9	44.1
19.1	586	290	0.51	0.471	5.090	0.090	0.0821	0.0006	2	1233.6	15.6
20.1	503	11	0.02	0.684	55.151	0.869	0.0538	0.0017	1	115.1	1.8
21.1	43	32	0.76	1.525	17.444	0.413	0.0659	0.0039	1	354.0	8.4
22.1	458	95	0.22	0.440	50.417	0.810	0.0520	0.0017	1	126.1	2.0
23.1	386	19	0.05	0.539	54.595	0.911	0.0526	0.0020	1	116.4	2.0
24.1	770	126	0.17	0.139	6.459	0.103	0.0711	0.0007	2	948.6	22.0
25.1	412	9	0.02	0.131	52.980	0.869	0.0495	0.0018	1	120.4	2.0
A–1.1	347	44	0.13	−0.034	19.072	0.581	0.0527	0.0020	1	329.6	9.9
A–2.1	630	237	0.39	0.161	58.864	1.858	0.0495	0.0012	1	108.4	3.4
A–3.1	312	186	0.61	−0.377	5.407	0.163	0.0729	0.0019	2	992.8	54.9
A–4.1	166	35	0.22	0.269	60.237	1.963	0.0503	0.0022	1	105.9	3.4
A–5.1	491	20	0.04	0.232	61.719	1.913	0.0499	0.0024	1	103.4	3.2
n										30
Waitangitaona River paragniess A559 (43.29240°S, 170.31170°E, 96m)
1.1	129	130	1.04	0.110	11.517	0.267	0.0591	0.0017	1	536.2	12.2
2.1	420	49	0.12	0.970	11.334	0.252	0.0662	0.0016	1	540.0	11.8
3.1	520	322	0.64	0.015	12.383	0.272	0.0574	0.0006	1	500.6	10.7
4.1	292	199	0.71	0.217	6.051	0.134	0.0737	0.0015	2	1016.6	43.1
5.1	44	15	0.36	−0.448	5.787	0.157	0.0699	0.0022	2	923.0	93.0
6.1	210	160	0.79	1.390	6.409	0.145	0.0814	0.0022	2	1251.9	51.4
7.1	669	507	0.78	−0.078	10.685	0.237	0.0586	0.0005	1	577.2	12.5
8.1	267	48	0.18	0.055	16.438	0.371	0.0547	0.0010	1	380.5	8.5
9.1	800	237	0.31	0.191	12.593	0.274	0.0586	0.0005	1	491.7	10.5
10.1	222	49	0.23	0.690	8.238	0.196	0.0694	0.0011	1	733.7	17.0
11.1	310	130	0.43	0.177	9.792	0.217	0.0621	0.0007	1	625.8	13.5
12.1	641	444	0.72	0.036	13.263	0.292	0.0567	0.0006	1	468.4	10.1
13.1	446	112	0.26	0.548	6.885	0.152	0.0726	0.0006	2	1011.1	16.4
14.1	318	158	0.51	−0.116	9.679	0.223	0.0599	0.0008	1	634.5	14.2
15.1	513	232	0.47	0.479	6.665	0.146	0.0729	0.0007	2	1016.6	20.0
16.1	568	7	0.01	−0.106	16.350	0.360	0.0534	0.0007	1	383.1	8.3
17.1	142	84	0.61	−0.139	9.055	0.212	0.0609	0.0010	1	676.1	15.4
18.1	1138	341	0.31	0.117	12.430	0.269	0.0581	0.0005	1	498.3	10.6
19.1	700	238	0.35	−0.170	10.120	0.280	0.0587	0.0005	1	608.4	16.4
20.1	1314	533	0.42	0.195	9.480	0.205	0.0628	0.0004	1	645.3	13.6
A–1.1	166	112	0.70	0.272	5.557	0.178	0.0771	0.0011	2	1078.2	42.1
A–2.1	154	83	0.56	−0.157	13.277	0.421	0.0551	0.0026	1	468.8	14.6
A–3.1	300	29	0.10	0.472	17.196	0.524	0.0576	0.0011	1	362.7	10.9
A–4.1	293	142	0.50	0.990	14.028	0.440	0.0637	0.0015	1	439.7	13.5
A–5.1	796	175	0.23	−0.115	13.232	0.400	0.0555	0.0019	1	470.2	13.9
n										25
Mt Elliot paragneiss A560 (42.52570°S, 171.82040°E, 200m)
1.1	1491	9	0.01	0.040	17.164	0.314	0.0542	0.0004	1	364.9	6.6
1.2	76	64	0.87	0.442	8.687	0.174	0.0664	0.0013	1	699.4	13.7
2.1	254	86	0.35	0.842	7.354	0.137	0.0732	0.0007	2	974.8	29.0
3.1	268	83	0.32	8.737	3.026	0.056	0.1799	0.0009	2	2648.7	8.4
4.1	1202	5	0.00	0.012	11.533	0.213	0.0583	0.0003	1	536.0	9.7
5.1	106	141	1.37	0.108	10.381	0.204	0.0606	0.0011	1	592.3	11.4
6.1	2017	87	0.04	0.532	9.524	0.193	0.0654	0.0005	1	640.3	12.6
7.1	1037	75	0.07	0.763	11.623	0.215	0.0642	0.0004	1	528.2	9.6
8.1	259	186	0.74	0.535	6.136	0.115	0.0758	0.0006	2	1051.1	29.7
9.1	494	30	0.06	−0.045	13.948	0.259	0.0555	0.0007	1	446.5	8.1
10.1	1647	8	0.01	0.019	18.227	0.333	0.0535	0.0003	1	344.2	6.2
11.1	3181	493	0.16	−0.173	10.259	0.188	0.0585	0.0002	1	600.6	10.7
12.1	2794	26	0.01	−0.016	16.009	0.338	0.0543	0.0003	1	390.7	8.1
13.1	706	162	0.24	−0.127	8.881	0.164	0.0614	0.0008	1	688.7	12.3
14.1	395	342	0.90	0.151	5.580	0.103	0.0760	0.0005	2	1082.7	16.3
15.1	4943	488	0.10	−0.076	11.671	0.245	0.0574	0.0002	1	530.3	10.9
16.1	164	46	0.29	−0.073	5.619	0.115	0.0739	0.0007	2	1013.2	32.7
17.1	717	15	0.02	0.509	13.328	0.256	0.0604	0.0005	1	464.1	8.7
18.1	109	80	0.76	0.227	11.558	0.228	0.0600	0.0012	1	533.8	10.3
19.1	1642	867	0.55	0.469	6.741	0.123	0.0725	0.0003	2	987.0	8.3
20.1	1043	65	0.06	1.610	11.160	0.206	0.0715	0.0008	1	544.7	9.9
A–1.1	404	50	0.13	0.487	4.941	0.149	0.0835	0.0008	2	1261.1	21.1
A–2.1	527	224	0.44	0.927	4.810	0.144	0.0883	0.0005	2	1379.9	13.6
A–3.1	890	47	0.05	0.449	13.174	0.401	0.0601	0.0005	1	469.6	14.0
A–4.1	1632	104	0.07	0.156	18.406	0.550	0.0545	0.0005	1	340.5	10.0
A–5.1	402	180	0.46	0.481	5.170	0.156	0.0816	0.0006	2	1193.4	21.0
n										26

Table 3  U-Th-Pb geochronology results from analysis of orthogneiss zircon. f₂₀₆ = fraction of common ²⁰⁶Pb of the total measured Pb. Total ratios are given as measured and are uncorrected for common Pb. Correction method 1 is based on ²⁰⁷Pb (with ²³⁸U/²⁰⁶Pb ages <800 Ma). Correction method 2 is based on ²⁰⁴Pb (with ²⁰⁷Pb/²⁰⁶Pb ages >800 Ma). Spot analyses used for weighted mean ²⁰⁶Pb/²³⁸U age calculations of selected samples are marked in bold.

	U	Th	Th/U	f206	Total	Error	Total	Error	Corr.	Age	Error
Label	(ppm)	(ppm)		(%)	^238U/^206Pb	(1σ)	^207Pb/^206Pb	(1σ)	meth.	(Ma)	(1σ)
Mikonui River orthogneiss A547 (43.02812°S, 170.89981°E, 193m)
1.1	553	413	0.77	0.003	17.357	0.319	0.0538	0.0005	1	361.1	6.5
2.1	325	79	0.25	0.053	18.242	0.972	0.0538	0.0011	1	343.9	18.0
3.1	2121	375	0.18	−0.034	15.937	0.298	0.0542	0.0002	1	392.4	7.2
4.1	384	49	0.13	0.183	16.711	0.350	0.0555	0.0016	1	374.0	7.7
5.1	280	86	0.32	0.179	17.629	0.339	0.0551	0.0008	1	355.1	6.7
6.1	519	217	0.43	0.035	16.299	0.316	0.0546	0.0006	1	383.7	7.3
7.1	574	404	0.73	0.152	15.404	0.285	0.0560	0.0006	1	404.9	7.4
8.1	247	142	0.59	0.089	16.454	0.311	0.0549	0.0008	1	380.0	7.1
9.1	295	135	0.47	0.203	16.011	0.301	0.0561	0.0007	1	389.8	7.2
10.1	760	52	0.07	−0.200	16.339	0.326	0.0527	0.0005	1	383.7	7.5
11.1	628	116	0.19	−0.007	15.896	0.294	0.0545	0.0007	1	393.3	7.2
A–1.1	988	28	0.03	−0.125	16.698	0.497	0.0531	0.0014	1	375.4	11.0
A–2.1	201	30	0.16	−0.157	16.221	0.509	0.0531	0.0024	1	386.2	12.0
A–3.1	229	76	0.34	0.174	16.186	0.497	0.0558	0.0021	1	385.8	11.7
A–4.1	1073	240	0.23	−0.014	13.073	0.388	0.0565	0.0010	1	475.2	13.8
A–5.1	2434	879	0.37	−0.029	17.915	0.549	0.0533	0.0008	1	350.2	10.6
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										387.1	6.8
n										11/16
MSWD										1.3
Solitude Creek orthogneiss A548 (42.99129°S, 170.94165°E, 470m)
1.1	250	184	0.76	0.547	54.347	1.086	0.0527	0.0015	1	116.9	2.3
2.1	596	186	0.32	0.280	59.669	1.131	0.0504	0.0010	1	106.8	2.0
3.1	703	354	0.52	0.158	54.835	1.040	0.0496	0.0009	1	116.3	2.2
4.1	239	222	0.96	0.305	54.250	1.086	0.0508	0.0015	1	117.4	2.3
5.1	452	445	1.02	0.266	57.715	1.108	0.0503	0.0011	1	110.4	2.1
6.1	534	531	1.03	0.318	57.764	1.102	0.0507	0.0010	1	110.3	2.1
7.1	626	362	0.60	0.152	54.891	1.034	0.0496	0.0009	1	116.2	2.2
8.1	488	312	0.66	0.103	52.912	1.014	0.0493	0.0012	1	120.6	2.3
9.1	503	387	0.80	0.065	55.358	1.051	0.0488	0.0010	1	115.3	2.2
10.1	331	288	0.90	−0.089	58.614	1.168	0.0475	0.0012	1	109.1	2.2
A–1.1	591	449	0.78	0.306	59.255	1.803	0.0506	0.0012	1	107.6	3.3
A–2.1	340	320	0.97	0.398	55.522	1.717	0.0515	0.0015	1	114.6	3.5
A–3.1	340	292	0.89	0.505	55.990	1.859	0.0523	0.0015	1	113.5	3.8
A–4.1	969	867	0.93	0.074	55.454	1.664	0.0489	0.0009	1	115.1	3.4
A–5.1	373	324	0.90	0.230	55.625	1.716	0.0501	0.0014	1	114.6	3.5
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										114.5	2.0
n										11/15
MSWD										1.2
Clarke River orthogneiss A549 (42.39921°S, 171.85563°E, 253m)
1.1	193	77	0.41	0.060	16.509	0.390	0.0547	0.0014	1	378.9	8.8
2.1	517	249	0.50	0.022	15.910	0.355	0.0547	0.0008	1	392.9	8.6
3.1	215	72	0.34	0.349	16.915	0.400	0.0568	0.0014	1	369.0	8.6
4.1	194	99	0.53	0.713	16.674	0.395	0.0598	0.0015	1	372.9	8.7
5.1	258	116	0.46	0.242	16.252	0.375	0.0563	0.0012	1	384.0	8.7
6.1	720	274	0.39	0.153	16.773	0.374	0.0553	0.0007	1	372.7	8.2
7.1	127	52	0.42	0.844	18.106	0.451	0.0601	0.0026	1	343.7	8.5
8.1	766	197	0.27	5.881	16.557	0.366	0.1011	0.0043	1	356.4	8.4
9.1	1175	351	0.31	3.608	13.180	0.287	0.0853	0.0012	1	455.0	9.9
10.1	678	316	0.48	0.182	13.266	0.293	0.0579	0.0008	1	467.7	10.1
11.1	1469	209	0.15	0.050	16.041	0.349	0.0549	0.0005	1	389.6	8.3
A–1.1	593	245	0.43	−0.135	16.661	0.499	0.0530	0.0007	1	376.2	11.1
A–2.1	963	121	0.13	−0.066	16.337	0.486	0.0538	0.0007	1	383.2	11.2
A–3.1	260	79	0.32	−0.069	16.447	0.500	0.0537	0.0010	1	380.8	11.4
A–4.1	457	145	0.33	0.078	16.466	0.495	0.0548	0.0008	1	379.8	11.2
A–5.1	263	167	0.65	0.204	16.128	0.491	0.0560	0.0010	1	387.0	11.6
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										378.1	6.8
n										13/16
MSWD										1.2
Mt Elliot orthogneiss A551 (42.52570°S, 171.82040°E, 200m)
1.1	472	49	0.11	0.431	17.405	0.390	0.0572	0.0009	1	358.6	7.9
2.1	2325	110	0.05	0.017	46.343	1.011	0.0489	0.0006	1	137.6	3.0
3.1	940	266	0.29	5.468	11.814	0.258	0.1016	0.0008	1	496.2	11.2
4.1	281	57	0.21	2.022	14.844	0.349	0.0713	0.0018	1	412.0	9.6
5.1	659	33	0.05	0.222	19.149	0.425	0.0548	0.0008	1	327.4	7.2
6.1	1718	128	0.08	0.403	15.443	0.335	0.0580	0.0008	1	402.9	8.6
7.1	1320	160	0.13	0.258	43.079	0.951	0.0510	0.0008	1	147.6	3.2
8.1	492	100	0.21	1.220	17.768	0.404	0.0633	0.0010	1	348.8	7.8
9.1	2085	418	0.21	0.136	48.172	1.056	0.0498	0.0007	1	132.3	2.9
10.1	444	155	0.36	0.227	54.224	1.285	0.0502	0.0016	1	117.5	2.8
A–1.1	2629	791	0.31	0.048	52.064	1.550	0.0489	0.0006	1	122.6	3.6
A–1.2	466	290	0.64	0.313	51.089	1.565	0.0510	0.0013	1	124.6	3.8
A–2.1	2531	630	0.26	0.019	49.552	1.471	0.0488	0.0007	1	128.8	3.8
A–3.1	2892	621	0.22	0.202	51.340	1.527	0.0501	0.0005	1	124.1	3.7
A–4.1	136	201	1.52	−0.202	16.972	0.532	0.0523	0.0014	1	369.8	11.4
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										127.0	6.9
n										7/15
MSWD										5.1
Hokitika Gorge orthogneiss A554 (42.95660°S, 171.01540°E, 78m)
1.1	957	464	0.50	0.603	57.511	1.281	0.0530	0.0012	1	110.5	2.5
2.1	1184	708	0.62	0.177	52.481	1.154	0.0499	0.0007	1	121.5	2.7
3.1	2577	854	0.34	−0.004	55.934	1.216	0.0483	0.0005	1	114.2	2.5
4.1	1390	415	0.31	0.070	56.223	1.235	0.0488	0.0007	1	113.6	2.5
5.1	813	289	0.37	0.070	16.916	0.369	0.0545	0.0005	1	370.0	7.9
6.1	3992	783	0.20	0.211	54.030	1.169	0.0501	0.0004	1	118.0	2.5
7.1	775	503	0.67	0.217	55.649	1.271	0.0500	0.0010	1	114.6	2.6
8.1	1360	869	0.66	−0.132	55.470	1.225	0.0473	0.0008	1	115.3	2.5
9.1	3334	843	0.26	0.199	55.517	1.204	0.0499	0.0005	1	114.9	2.5
10.1	2268	913	0.42	0.029	53.018	1.162	0.0487	0.0006	1	120.4	2.6
A–1.1	2899	976	0.35	−0.086	54.877	1.637	0.0477	0.0007	1	116.5	3.5
A–2.1	2487	837	0.35	−0.064	54.632	1.628	0.0479	0.0007	1	117.0	3.5
A–3.1	615	38	0.06	0.074	57.866	1.758	0.0488	0.0016	1	110.4	3.3
A–4.1	2794	887	0.33	0.199	51.120	1.539	0.0501	0.0012	1	124.6	3.7
A–5.1	3411	936	0.28	−0.001	54.318	1.611	0.0484	0.0004	1	117.6	3.5
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										116.0	2.3
n										14/15
MSWD										1.8
Mikonui River orthogneiss A555 (43.03090°S, 170.89150°E, 300m)
1.1	518	293	0.59	0.227	57.003	1.318	0.0501	0.0013	1	111.9	2.6
2.1	634	186	0.30	0.566	20.053	0.450	0.0572	0.0022	1	312.0	7.0
3.1	385	305	0.82	0.641	57.523	1.330	0.0533	0.0014	1	110.4	2.5
4.1	444	241	0.56	0.193	56.532	1.294	0.0498	0.0012	1	112.8	2.6
5.1	356	263	0.76	0.453	52.272	1.207	0.0521	0.0013	1	121.6	2.8
6.1	480	238	0.51	0.557	56.403	1.280	0.0527	0.0012	1	112.7	2.5
7.1	256	154	0.62	0.416	55.019	1.304	0.0516	0.0016	1	115.6	2.7
8.1	232	171	0.76	0.566	56.092	1.349	0.0528	0.0017	1	113.3	2.7
A–1.1	2323	1121	0.50	0.053	5.555	0.165	0.0754	0.0004	2	1077.8	10.5
A–2.1	476	216	0.47	0.367	55.516	1.718	0.0512	0.0015	1	114.7	3.5
A–3.1	331	186	0.58	0.392	55.128	1.707	0.0514	0.0015	1	115.4	3.6
A–4.1	846	616	0.75	0.211	56.780	1.767	0.0499	0.0013	1	112.3	3.5
A–5.1	2647	1975	0.77	0.014	53.503	1.586	0.0485	0.0005	1	119.4	3.5
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										114.2	2.4
n										11/13
MSWD										1.4
Tuke River orthogneiss A556 (43.02700°S, 170.87450°E, 155m)
1.1	438	150	0.35	0.066	16.397	0.322	0.0548	0.0008	1	381.4	7.4
2.1	300	130	0.45	0.141	16.652	0.313	0.0552	0.0008	1	375.4	6.9
3.1	692	197	0.29	0.029	16.503	0.305	0.0544	0.0005	1	379.1	6.9
4.1	361	119	0.34	0.131	16.560	0.337	0.0552	0.0007	1	377.5	7.6
5.1	1130	315	0.29	0.011	17.370	0.317	0.0538	0.0004	1	360.8	6.5
6.1	979	386	0.41	0.098	17.737	0.326	0.0544	0.0006	1	353.2	6.4
7.1	918	203	0.23	0.091	17.858	0.329	0.0543	0.0006	1	350.9	6.4
8.1	462	100	0.22	2.614	2.718	0.050	0.1442	0.0051	2	2267.3	61.9
9.1	317	85	0.28	0.709	13.587	0.256	0.0618	0.0007	1	454.7	8.4
10.1	610	439	0.74	0.175	16.046	0.301	0.0558	0.0007	1	389.1	7.2
A–1.1	1189	347	0.30	0.045	17.833	0.540	0.0539	0.0005	1	351.6	10.5
A–2.1	151	45	0.31	0.218	19.016	0.588	0.0548	0.0020	1	329.7	10.1
A–3.1	285	133	0.48	−0.058	16.351	0.528	0.0538	0.0009	1	382.9	12.1
A–4.1	509	172	0.35	−0.120	15.776	0.471	0.0536	0.0007	1	396.7	11.6
A–5.1	560	196	0.36	0.005	16.437	0.492	0.0543	0.0009	1	380.7	11.2
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										370.6	9.9
n										12/15
MSWD										3.7
Bonar Creek orthogneiss A557 (43.08450°S, 170.63910°E, 450m)
1.1	356	153	0.44	−0.054	15.978	0.356	0.0541	0.0008	1	391.5	8.6
2.1	491	138	0.29	0.401	12.278	0.270	0.0606	0.0007	1	502.8	10.8
3.1	301	149	0.51	−0.044	17.115	0.387	0.0535	0.0010	1	366.2	8.1
4.1	297	126	0.44	0.127	15.978	0.359	0.0555	0.0009	1	390.9	8.6
5.1	168	50	0.31	0.165	15.668	0.375	0.0560	0.0013	1	398.2	9.4
6.1	768	319	0.43	0.021	15.910	0.347	0.0547	0.0006	1	392.9	8.4
7.1	207	63	0.32	0.296	15.236	0.347	0.0573	0.0013	1	408.6	9.1
8.1	624	434	0.72	−0.049	16.284	0.357	0.0539	0.0006	1	384.4	8.3
9.1	488	185	0.39	0.032	16.405	0.362	0.0545	0.0007	1	381.3	8.3
10.1	493	192	0.40	0.425	16.260	0.359	0.0577	0.0008	1	383.1	8.3
A–1.1	296	119	0.41	0.020	17.088	0.516	0.0541	0.0009	1	366.6	10.9
A–2.1	271	54	0.21	−0.016	16.355	0.498	0.0541	0.0012	1	382.6	11.5
A–3.1	455	234	0.53	−0.059	16.245	0.486	0.0539	0.0007	1	385.3	11.3
A–4.1	159	38	0.25	0.747	6.662	0.203	0.0751	0.0016	2	987.9	52.6
A–5.1	6908	1756	0.26	−0.097	15.875	0.468	0.0538	0.0002	1	394.2	11.4
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										386.5	7.5
n										13/15
MSWD										1.6
Whataroa Quarry orthogneiss A558 (43.28460°S, 170.36140°E, 125m)
1.1	2317	1579	0.70	0.026	74.935	1.376	0.0479	0.0006	1	85.4	1.6
3.1	603	407	0.70	0.087	67.959	1.297	0.0486	0.0010	1	94.1	1.8
4.1	929	31	0.03	0.053	15.870	0.493	0.0550	0.0010	1	393.7	12.0
11.1	216	162	0.77	8.399	68.082	2.326	0.0921	0.0051	1	89.5	3.1
12.1	116	88	0.78	0.000	70.841	3.028	0.0696	0.0054	1	88.2	3.8
13.1	211	230	1.13	5.130	65.216	2.160	0.0614	0.0036	1	96.7	3.2
14.1	130	96	0.76	7.896	64.464	2.250	0.0701	0.0046	1	96.8	3.4
15.1	1472	803	0.56	0.699	72.376	2.160	0.0488	0.0012	1	88.4	2.6
16.1	814	409	0.52	1.125	62.951	1.908	0.0510	0.0017	1	101.3	3.1
17.1	260	193	0.77	1.965	69.402	2.503	0.0593	0.0047	1	91.1	3.3
18.1	115	86	0.78	4.618	67.654	2.448	0.0736	0.0054	1	91.9	3.4
19.1	407	348	0.88	1.924	66.786	2.077	0.0563	0.0033	1	94.9	3.0
20.1	1553	1214	0.81	0.700	67.913	2.029	0.0509	0.0011	1	93.9	2.8
A–1.1	347	397	1.18	0.098	73.954	2.321	0.0485	0.0017	1	86.5	2.7
A–2.1	1668	1178	0.73	−0.032	69.960	2.088	0.0476	0.0007	1	91.5	2.7
A–3.1	93	72	0.79	−0.018	72.188	2.564	0.0476	0.0031	1	88.7	3.2
A–4.1	3271	3055	0.97	0.039	68.781	2.045	0.0482	0.0005	1	93.0	2.8
A–5.1	464	138	0.31	−0.314	12.026	0.360	0.0551	0.0011	1	516.5	15.1
Weighted mean ^206Pb/^238U age ± 95% c.l. (Ma)										92.0	1.9
n										14/18
MSWD										1.2

Table 4  U-Th-Pb geochronology results from analysis of paragneiss and orthogneiss monazite. f₂₀₆ or f₂₀₈ = fraction of common ²⁰⁶Pb or ²⁰⁸Pb of the total measured Pb. Total ratios are given as measured and are uncorrected for common Pb. Correction is based on ²⁰⁷Pb. Spot analyses used for weighted mean ²⁰⁶Pb/²³⁸U or ²⁰⁸Pb/²³²Th age calculations of selected samples are marked in bold.

	U	Th	Th/U	f206	f208	Total	Error	Total	Error	Total	Error	Total	Error	^206Pb/^238U	Error	^208Pb/^232Th	Error
Label	(ppm)	(ppm)		(%)	(%)	^208Pb/^206Pb	(1σ)	^238U/^206Pb	(1σ)	^207Pb/^206Pb	(1σ)	^208Pb/^232Th	(1σ)	Age (Ma)	(1σ)	Age (Ma)	(1σ)
Mikonui River paragneiss A546 (43.03058°S, 170.89978°E, 329m)
1.1	232	5048	21.74	−0.056	−0.020	6.256	0.027	14.592	0.271	0.0549	0.0004	0.02036	0.00023	427.5	7.7	407.4	4.5
2.1	169	3902	23.15	2.310	1.059	4.860	0.039	32.716	0.447	0.0711	0.0011	0.00698	0.00010	189.7	2.6	139.1	2.0
3.1	205	3062	14.95	0.096	0.049	4.313	0.019	17.020	0.222	0.0548	0.0003	0.01856	0.00022	367.7	4.7	371.5	4.4
4.1	194	2667	13.73	0.083	0.046	4.040	0.012	17.259	0.252	0.0546	0.0003	0.01902	0.00022	362.8	5.2	380.6	4.3
5.1	213	2531	11.90	0.073	0.047	3.438	0.012	17.541	0.245	0.0543	0.0003	0.01828	0.00022	357.2	4.9	365.9	4.3
6.1	150	1553	10.35	0.139	0.102	3.030	0.010	17.145	0.199	0.0551	0.0003	0.01894	0.00022	364.9	4.1	378.9	4.4
7.1	175	5484	31.32	0.576	0.142	9.056	0.042	57.373	0.916	0.0535	0.0006	0.00548	0.00009	110.8	1.8	110.3	1.9
8.1	189	3169	16.75	0.309	0.168	4.105	0.022	26.559	0.335	0.0538	0.0004	0.01009	0.00013	237.5	2.9	202.7	2.7
9.1	186	5206	28.03	0.501	0.139	8.056	0.076	56.841	0.921	0.0529	0.0011	0.00552	0.00008	111.9	1.8	111.2	1.6
10.1	183	3028	16.54	0.951	0.514	4.119	0.021	26.093	0.436	0.0597	0.0005	0.01070	0.00013	240.2	3.9	214.1	2.6
n														10		10
Clarke River paragneiss A550 (42.39943°S, 171.87749°E, 302m)
1.1	204	1510	7.39	0.313	0.369	1.891	0.013	34.718	0.477	0.0526	0.0004	0.00836	0.00010	182.5	2.5	167.6	2.1
2.1	25	5	0.20	0.445	15.702	0.063	0.001	30.902	0.367	0.0543	0.0005	0.01523	0.00037	204.4	2.4	257.8	8.0
3.1	28	5	0.18	0.441	17.586	0.056	0.001	31.150	0.386	0.0542	0.0003	0.01560	0.00031	202.8	2.5	258.2	5.9
4.1	227	824	3.63	0.182	0.362	1.122	0.006	54.342	0.720	0.0500	0.0003	0.00640	0.00008	117.3	1.5	128.5	1.5
5.1	667	72	0.11	0.464	29.308	0.035	0.001	30.752	0.364	0.0545	0.0004	0.01482	0.00065	205.4	2.4	210.6	11.0
6.1	183	1674	9.16	0.372	0.317	2.612	0.013	28.638	0.482	0.0540	0.0005	0.01125	0.00021	220.5	3.7	225.3	4.1
7.1	202	1602	7.93	0.115	0.108	2.373	0.010	20.210	0.226	0.0536	0.0002	0.01649	0.00019	311.0	3.4	330.3	3.8
8.1	215	1410	6.57	0.414	0.412	2.240	0.011	29.381	0.363	0.0542	0.0006	0.01310	0.00014	214.9	2.6	262.0	2.9
9.1	208	2259	10.88	0.154	0.109	3.138	0.012	19.968	0.264	0.0541	0.0003	0.01668	0.00018	314.6	4.1	333.9	3.5
10.1	29	4	0.14	0.416	20.483	0.045	0.001	30.772	0.411	0.0540	0.0003	0.01545	0.00036	205.3	2.7	246.8	6.9
A–1.1	203	1559	7.70	−0.512	−0.457	2.369	0.020	14.456	0.235	0.0550	0.0003	0.01890	0.00033	433.3	6.8	380.1	6.6
A–2.1	178	845	4.74	−0.420	−0.520	1.706	0.010	52.497	0.960	0.0557	0.0005	0.00628	0.00010	122.2	2.2	127.2	2.1
A–3.1	180	1508	8.36	−0.538	−0.444	2.565	0.015	15.749	0.249	0.0547	0.0005	0.01744	0.00032	398.9	6.1	351.1	6.4
A–4.1	201	1056	5.26	−0.906	−1.112	1.721	0.015	50.454	1.086	0.0517	0.0004	0.00572	0.00015	127.7	2.7	116.6	3.0
n														14		14
Crooked River paragneiss A552 (42.65130°S, 171.61800°E, 174m)
1.1	214	8832	41.24	0.767	0.147	11.606	0.093	58.619	1.099	0.0552	0.0010	0.00541	0.00008	108.2	2.0	108.9	1.6
2.1	198	10144	51.17	0.861	0.133	14.469	0.127	60.260	1.076	0.0560	0.0013	0.00521	0.00007	105.2	1.9	104.9	1.5
3.1	182	5057	27.72	0.678	0.194	7.789	0.133	58.812	0.810	0.0544	0.0006	0.00533	0.00011	108.0	1.5	107.3	2.1
4.1	209	25666	122.65	6.627	0.456	32.377	0.381	52.802	1.175	0.1090	0.0031	0.00544	0.00007	113.0	2.5	109.2	1.3
5.1	203	6677	32.93	0.678	0.159	9.486	0.062	58.352	0.800	0.0544	0.0012	0.00552	0.00007	108.8	1.5	111.1	1.3
6.1	218	5565	25.48	0.579	0.175	7.373	0.056	59.805	0.981	0.0534	0.0009	0.00549	0.00007	106.3	1.7	110.4	1.3
6.2	229	4930	21.57	0.558	0.200	6.207	0.051	59.470	0.978	0.0533	0.0006	0.00543	0.00007	106.9	1.7	109.3	1.4
7.1	191	9845	51.48	0.990	0.153	14.455	0.103	58.798	1.320	0.0572	0.0009	0.00536	0.00007	107.7	2.4	107.9	1.5
8.1	179	9244	51.68	1.033	0.158	14.574	0.113	59.739	1.058	0.0576	0.0017	0.00524	0.00007	105.9	1.9	105.5	1.3
9.1	175	16216	92.46	1.642	0.141	25.970	0.218	58.910	1.465	0.0632	0.0012	0.00535	0.00007	106.7	2.6	107.8	1.3
A–2.1	252	29513	117.00	2.199	0.128	36.436	0.515	51.730	1.510	0.0771	0.0031	0.00525	0.00007	120.7	3.5	105.8	1.5
A–5.1	221	36729	166.41	1.484	0.081	38.614	0.860	27.870	1.041	0.0712	0.0034	0.00556	0.00009	223.9	8.3	112.0	1.7
Weighted mean age ± 95% c.l. (Ma)														107.5	1.6	108.3	1.7
n														10/12		12/12
MSWD													1.0		2.4
Crooked River paragneiss A553 (42.64860°S, 171.61440°E, 171m)
1.1	349	17705	50.80	1.374	0.211	14.544	0.195	54.916	1.440	0.0609	0.0014	0.00592	0.00008	114.8	3.0	119.1	1.7
1.2	251	12943	51.59	0.843	0.125	15.040	0.123	56.209	1.363	0.0560	0.0010	0.00579	0.00008	112.7	2.7	116.6	1.6
2.1	234	5247	22.39	0.470	0.162	6.461	0.033	58.950	0.826	0.0525	0.0006	0.00553	0.00006	107.9	1.5	111.4	1.2
3.1	290	17171	59.20	1.210	0.158	17.082	0.126	55.962	1.044	0.0594	0.0012	0.00580	0.00008	112.8	2.1	116.6	1.6
4.1	200	4159	20.76	0.445	0.165	5.986	0.058	58.436	1.005	0.0523	0.0007	0.00556	0.00009	108.9	1.9	111.8	1.9
5.1	326	14873	45.60	1.386	0.236	13.108	0.184	57.064	1.547	0.0609	0.0019	0.00562	0.00008	110.5	3.0	112.9	1.7
5.2	345	19215	55.63	2.215	0.326	15.142	0.124	54.881	1.121	0.0686	0.0026	0.00542	0.00006	113.9	2.3	108.9	1.3
6.1	267	17538	65.71	0.978	0.115	18.958	0.179	60.739	1.409	0.0571	0.0013	0.00532	0.00006	104.3	2.4	107.1	1.3
7.1	249	20672	82.98	1.985	0.194	22.797	0.336	58.286	1.389	0.0664	0.0015	0.00522	0.00007	107.5	2.6	105.0	1.4
8.1	226	24252	107.40	1.358	0.103	29.321	0.289	55.958	1.425	0.0607	0.0015	0.00543	0.00007	112.7	2.9	109.2	1.4
A–4.1	233	32033	137.31	1.936	0.112	36.446	0.558	39.062	1.335	0.0749	0.0038	0.00541	0.00010	159.8	5.5	108.8	2.1
A–5.1	187	28979	155.37	1.981	0.084	49.687	0.971	57.014	2.418	0.0753	0.0038	0.00509	0.00010	109.9	4.7	102.5	1.9
Weighted mean age ± 95% c.l. (Ma)														110.0	2.4	110.5	2.7
n														11/12		8/12
MSWD													1.8		4.0
Mt Elliot paragneiss A560 (42.52570°S, 171.82040°E, 200m)
1.1	160	1898	11.89	0.350	0.227	3.425	0.018	34.184	0.510	0.0530	0.0003	0.00969	0.00011	185.2	2.7	194.5	2.2
3.1	194	1272	6.56	0.063	0.078	1.811	0.009	18.111	0.236	0.0540	0.0003	0.01783	0.00023	346.2	4.4	357.0	4.6
4.1	237	1575	6.64	0.204	0.237	1.914	0.019	56.869	0.832	0.0501	0.0004	0.00585	0.00008	112.1	1.6	117.6	1.7
5.1	209	1755	8.38	0.241	0.287	1.869	0.012	27.086	0.401	0.0530	0.0004	0.00961	0.00013	233.2	3.4	192.9	2.6
6.1	233	1435	6.16	0.503	0.650	1.724	0.011	50.348	0.781	0.0532	0.0007	0.00654	0.00011	126.2	1.9	130.8	2.3
7.1	242	2147	8.87	0.961	0.922	2.324	0.025	51.293	0.951	0.0573	0.0011	0.00524	0.00007	123.3	2.3	104.7	1.4
8.1	240	1475	6.14	0.179	0.230	1.728	0.007	18.155	0.235	0.0550	0.0003	0.01797	0.00021	345.0	4.4	359.1	4.2
8.2	211	1452	6.88	0.129	0.149	1.938	0.011	18.960	0.263	0.0542	0.0003	0.01727	0.00020	330.9	4.5	345.5	4.0
9.1	210	2631	12.53	0.223	0.141	3.514	0.033	60.835	0.763	0.0502	0.0005	0.00530	0.00007	104.9	1.3	106.8	1.4
n														9		9
Mikonui River orthogneiss A547 (43.02812°S, 170.89981°E, 193m)
1.1	188	4483	23.87	0.554	0.178	6.950	0.043	53.345	0.708	0.0535	0.0006	0.00605	0.00008	119.1	1.6	121.7	1.5
1.1B	191	9170	48.10	0.525	0.110	10.654	0.047	24.931	0.420	0.0561	0.0006	0.00976	0.00013	252.2	4.2	196.1	2.6
2.1	196	4010	20.41	0.623	0.231	6.022	0.054	57.426	0.844	0.0539	0.0005	0.00564	0.00008	110.6	1.6	113.5	1.5
4.1	190	4107	21.57	0.109	0.049	4.934	0.023	18.366	0.264	0.0543	0.0003	0.01406	0.00017	341.4	4.8	282.1	3.4
5.1	251	14122	56.16	0.754	0.153	11.006	0.123	33.150	0.741	0.0568	0.0011	0.00646	0.00009	190.2	4.2	129.9	1.8
6.1	322	3197	9.93	0.043	0.033	2.914	0.015	17.150	0.255	0.0543	0.0003	0.01891	0.00024	365.2	5.3	378.5	4.7
6.2	118	1875	15.93	0.129	0.062	4.645	0.009	17.901	0.210	0.0547	0.0003	0.01828	0.00025	350.0	4.0	365.9	4.9
7.1	177	42043	237.75	2.911	0.107	60.539	1.066	51.047	1.672	0.0751	0.0024	0.00533	0.00007	121.5	4.0	107.4	1.4
7.2	173	27805	160.84	1.177	0.090	29.193	0.265	27.711	0.716	0.0615	0.0024	0.00723	0.00009	225.9	5.8	145.5	1.9
8.1	326	2286	7.01	0.051	0.057	2.009	0.007	17.387	0.267	0.0542	0.0003	0.01826	0.00020	360.3	5.4	365.4	3.9
A–1.1	195	55217	283.81	4.410	0.117	79.467	1.732	47.060	1.918	0.0951	0.0042	0.00513	0.00007	129.6	5.3	103.3	1.5
A–2.1	170	3571	20.98	−0.674	−0.222	6.413	0.053	48.620	0.674	0.0536	0.0013	0.00554	0.00007	132.1	1.8	111.8	1.3
A–3.1	198	4092	20.71	−0.454	−0.149	6.431	0.021	14.653	0.225	0.0554	0.0004	0.01882	0.00021	427.4	6.4	377.5	4.2
A–4.1	205	15600	75.97	0.082	0.009	19.102	0.262	35.363	0.931	0.0598	0.0014	0.00613	0.00008	179.6	4.7	123.5	1.6
A–5.1	229	58674	255.96	3.338	0.093	75.570	1.393	45.614	1.696	0.0864	0.0035	0.00562	0.00006	135.2	5.0	113.2	1.3
n														15		15
Clarke River orthogneiss A549 (42.39921°S, 171.85563°E, 253m)
1.1	186	2125	11.40	0.044	0.030	3.322	0.016	17.162	0.247	0.0543	0.0003	0.01931	0.00025	364.9	5.1	386.5	5.0
2.1	259	1475	5.70	0.938	1.129	1.852	0.015	10.592	0.140	0.0679	0.0010	0.01997	0.00028	576.4	7.3	395.2	5.5
3.1	240	2222	9.25	0.055	0.044	2.783	0.011	17.884	0.249	0.0540	0.0004	0.01872	0.00025	350.6	4.8	374.8	4.9
4.1	12	3	0.26	1.781	44.368	0.089	0.002	40.003	0.521	0.0655	0.0006	0.01203	0.00043	156.4	2.0	134.9	5.3
5.1	185	85	0.46	0.421	6.425	0.146	0.001	30.559	0.370	0.0541	0.0003	0.01542	0.00027	206.7	2.5	289.5	5.3
6.1	199	5103	25.70	0.673	0.186	8.085	0.041	19.418	0.303	0.0590	0.0006	0.01624	0.00018	321.6	4.9	325.0	3.5
7.1	189	1977	10.44	0.023	0.017	3.063	0.012	16.948	0.219	0.0542	0.0005	0.02025	0.00023	369.5	4.7	405.1	4.6
8.1	245	2012	8.22	1.056	0.807	2.917	0.027	41.704	0.595	0.0587	0.0005	0.00947	0.00014	151.2	2.1	189.0	2.7
9.1	13	2	0.17	0.363	14.858	0.054	0.000	28.808	0.307	0.0539	0.0004	0.01569	0.00031	219.2	2.3	268.2	7.0
10.1	187	5121	27.45	0.107	0.030	7.876	0.118	17.179	0.402	0.0548	0.0011	0.01789	0.00022	364.4	8.3	358.3	4.3
A–1.1	174	1292	7.43	−0.635	−0.578	2.326	0.011	18.421	0.487	0.0540	0.0005	0.01547	0.00022	342.9	8.8	312.2	4.5
A–4.1	168	923	5.50	−0.538	−0.674	1.688	0.012	15.658	0.265	0.0547	0.0003	0.01755	0.00026	401.2	6.6	354.0	5.2
A–5.1	148	3969	26.88	−0.348	−0.085	8.660	0.037	17.003	0.233	0.0563	0.0005	0.01681	0.00021	369.6	4.9	337.3	4.1
A–6.1	202	34	0.17	−0.512	−19.496	0.056	0.002	23.895	1.238	0.0550	0.0012	0.01692	0.00085	265.6	13.5	404.6	29.8
A–8.1	166	5205	31.37	−0.457	−0.099	9.723	0.087	14.293	0.420	0.0554	0.0010	0.01897	0.00057	437.9	12.5	380.1	11.2
n														15		15
Bonar Creek orthogneiss A557 (43.08450°S, 170.63910°E, 450m)
1.1	173	2488	14.37	0.034	0.019	4.075	0.019	18.161	0.267	0.0537	0.0003	0.01795	0.00020	345.4	4.9	359.5	4.0
2.1	199	2879	14.47	0.087	0.046	4.254	0.017	17.560	0.277	0.0545	0.0003	0.01887	0.00023	356.7	5.5	377.6	4.5
3.1	178	2327	13.07	0.124	0.076	3.645	0.018	17.143	0.218	0.0550	0.0005	0.01830	0.00023	365.0	4.5	366.3	4.5
4.1	131	2267	17.28	0.099	0.045	4.936	0.014	18.226	0.255	0.0543	0.0004	0.01784	0.00019	344.0	4.7	357.3	3.9
5.1	184	2527	13.77	0.036	0.020	3.990	0.026	17.171	0.215	0.0542	0.0003	0.01868	0.00023	364.8	4.5	374.0	4.5
6.1	168	1645	9.77	−0.012	−0.010	2.734	0.011	19.173	0.220	0.0529	0.0002	0.01678	0.00019	327.8	3.7	336.3	3.8
7.1	158	2636	16.66	0.142	0.067	4.702	0.024	18.189	0.249	0.0547	0.0003	0.01753	0.00020	344.5	4.6	351.0	4.0
8.1	250	3625	14.50	0.116	0.059	4.343	0.024	14.316	0.266	0.0566	0.0006	0.02141	0.00026	434.8	7.8	428.0	5.2
9.1	121	2102	17.37	0.110	0.050	4.906	0.024	18.534	0.219	0.0542	0.0003	0.01749	0.00020	338.4	3.9	350.3	3.9
10.1	211	3906	18.47	1.095	0.498	4.900	0.026	17.647	0.253	0.0636	0.0006	0.01687	0.00022	351.5	4.9	336.4	4.4
n														10		10
Nile River Charleston paragneiss 90–427 (Ireland and Gibson, 1998)
1.1	179	2296	12.80	0.183	0.108	3.762	0.011	17.120	0.232	0.0555	0.0002	0.01905	0.00021	365.3	4.8	381.0	4.2
2.1	465	1450	3.12	0.049	0.120	0.904	0.004	17.176	0.231	0.0543	0.0002	0.01921	0.00028	364.6	4.8	384.2	5.5
3.1	198	1744	8.80	0.061	0.054	2.545	0.010	17.558	0.238	0.0542	0.0003	0.01848	0.00024	356.9	4.7	369.9	4.7
4.1	196	2355	12.01	0.078	0.050	3.473	0.009	17.160	0.259	0.0546	0.0002	0.01867	0.00020	364.9	5.4	373.8	4.1
5.1	205	1979	9.68	0.095	0.076	2.784	0.009	17.493	0.235	0.0546	0.0003	0.01849	0.00020	358.0	4.7	370.0	3.9
6.1	207	2555	12.35	0.051	0.032	3.578	0.009	17.567	0.201	0.0541	0.0004	0.01871	0.00021	356.7	4.0	374.6	4.1
7.1	247	2446	9.91	0.098	0.076	2.892	0.015	17.546	0.301	0.0546	0.0004	0.01889	0.00026	357.0	6.0	378.0	5.2
8.1	336	2944	8.77	0.103	0.085	2.679	0.014	16.778	0.233	0.0550	0.0004	0.01881	0.00025	372.8	5.0	376.3	5.0
9.1	280	4534	16.19	−0.050	−0.023	4.777	0.022	13.898	0.194	0.0554	0.0005	0.02062	0.00025	448.1	6.0	412.7	4.9
Weighted mean age ± 95% c.l. (Ma)														361.7	6.1	375.4	5.0
n														8/9		8/9
MSWD													1.4		1.2
Constant Bay Charleston orthogneiss 90–428 (Ireland and Gibson, 1998)
2.1	231	2981	12.93	0.492	0.291	3.765	0.023	58.161	0.927	0.0527	0.0004	0.00552	0.00007	109.4	1.7	110.9	1.4
3.1	231	2717	11.77	0.348	0.228	3.401	0.022	54.733	0.816	0.0515	0.0005	0.00589	0.00007	116.3	1.7	118.5	1.4
4.1	1	9	13.61	0.544	0.300	4.037	0.026	60.279	0.919	0.0531	0.0006	0.00542	0.00006	105.5	1.6	108.9	1.3
6.1	54	1617	30.15	0.198	0.053	8.349	0.043	61.635	0.765	0.0499	0.0006	0.00515	0.00006	103.6	1.3	103.8	1.1
7.1	175	2796	15.98	0.477	0.230	4.624	0.027	59.797	0.891	0.0525	0.0010	0.00550	0.00007	106.4	1.6	110.5	1.5
8.1	202	2413	11.94	0.236	0.153	3.438	0.023	59.654	0.983	0.0503	0.0005	0.00544	0.00008	106.9	1.8	109.5	1.5
9.1	194	2710	14.00	0.412	0.229	4.000	0.038	61.212	1.108	0.0519	0.0006	0.00533	0.00007	104.0	1.9	107.2	1.5
10.1	211	2661	12.59	0.213	0.139	3.418	0.026	58.205	1.085	0.0502	0.0008	0.00544	0.00007	109.6	2.0	109.5	1.3
13.1	284	3972	13.98	2.340	1.202	4.337	0.075	42.627	1.090	0.0704	0.0038	0.00836	0.00017	146.0	3.7	166.3	3.4
15.1	265	3224	12.16	3.273	1.872	3.897	0.067	35.651	0.963	0.0795	0.0038	0.00947	0.00019	172.6	4.7	187.0	3.7
Weighted mean age ± 95% c.l. (Ma)														106.1	2.5	108.3	2.7
n														7/10		7/10
MSWD													2.0		3.9

There is good agreement between the monazite age determination of Charleston Metamorphic Complex samples from this study (Table 4) and those made by Ireland & Gibson (1998). Nile River paragneiss sample 90-427 records well-defined late Devonian weighted mean ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ages of 361.7±6.1 Ma (n=8/9, MSWD=1.4) and 375.4±5.0 Ma (n=8/9, MSWD=1.2; Fig. 3I,S). These are identical or slightly older than respective published ages of 361±6 Ma and 367±6 Ma for this sample. The Constant Bay orthogneiss sample 90-428 records poorly defined middle Cretaceous weighed mean ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ages of 106.1±2.5 Ma (n=7/10, MSWD=2.0) and 108.3±2.7 Ma (n=7/10, MSWD=3.9; Fig. 3J,T) that are marginally younger than previously reported ages of 111±2 and 112±2 Ma.

Paragneiss zircon grain morphologies are similar among all samples. Crystals are typically anhedral, rounded and 100–300 µm in length (e.g., sample A546, Fig. 5A). The majority of zircon domains consist of either magmatic oscillatory growth structures or metamorphic recrystallisation textures, or occasionally as mixtures of both. Inherited cores and thin overgrowth rims are abundant, while particular zonation patterns cannot typically be correlated with specific age populations. Composite detrital age structures are similar across all six samples (Fig. 2A–F, 4A–F) and all data are combined as a histogram in Fig. 5B. The youngest ²⁰⁶Pb/²³⁸U ages for most samples are Carboniferous to Devonian (313.2±7.1 Ma, A546-12.1; 327.1±4.7 Ma, 552-21.1; 340.5±10.0 Ma, A560-A4.1A; 355.7±5.0 Ma, A550-18.1; 362.7±10.9 Ma, A559-A3.1) while A553 from Crooked River has 13 Cretaceous ages between 103.4±3.2 Ma (A553-A5.1) and 126.1±2.0 Ma (A553-22.1) as well as two apparently Triassic ages (Fig. 2D, 4D). Over the six samples, a total of 37 analyses provide ages<400 Ma and are mostly from grains with metamorphic recrystallisation textures and low Th/U ratios (Th/U<0.1, n=20; Th/U=0.1–0.3, n=12; Th/U<0.3, n=5). Across all paragneiss samples, large numbers of ²⁰⁶Pb/²³⁸U age components are consistently recognised between 300–500 Ma (n=46 or 26.3% of all analyses), 500–600 Ma (n=27 or 15.4%) and 60–800 Ma (n=30 or 17.1%). Following a distinctive gap in ages between 800 and 900 Ma a major spike in ²⁰⁷Pb/²⁰⁶Pb ages occurs between 900 and 1100 Ma (n=33 or 18.9%) followed by scattered data through the rest of the Proterozoic 1100–2500 Ma (n=18 or 10.3%) and into the Archean as old as 3348.0±46.9 Ma (A552-4.1; n=5 or 2.9%).

Orthogneiss zircon grain morphologies are also similar among all samples. Crystals are typically euhedral with prismatic habits, 100–350 µm in length (e.g., sample A551, Fig. 5C). Most crystals preserve large domains displaying clear igneous oscillatory growth patterns. Metamorphic recrystallisation textures are common but typically exist as a replacement to oscillatory growth structures. Inherited cores are relatively uncommon and overgrowth rims are typically confined to growth terminations. Zircon crystallisation ages across all samples are generally characterised as part of either major Devonian or Cretaceous peaks (Fig. 5D). Three well-spread samples from Mikonui River, Bonar Creek and Clarke River have relatively well defined middle–late Devonian ages: A547 (387.1±6.8 Ma, n=11/16, MSWD=1.3, Fig. 2G, 4G), A557 (386.5±7.5 Ma, n=13/15, MSWD=1.6, Fig. 2N, 4N) and A549 (378.1±6.8 Ma, n=13/16, MSWD=1.2, Fig. 2I, 4I). The slightly younger late Devonian A556 from Tuke River (370.6±9.9 Ma, n=12/15, Fig. 2M, 4M) records a high MSWD of 3.7. Three closely spaced samples between Hokitika Gorge and Mikonui River have well-defined middle Cretaceous ages that agree within error: A554 (116.0±2.3 Ma, n=14/15, MSWD=1.8, Fig. 2K, 4K), A548 (114.5±2.0 Ma, n=11/15, MSWD=1.2, Fig. 2H, 4H) and A555 (114.2±2.4 Ma, n=11/13, MSWD=1.4, Fig. 2L, 4L). The notably younger sample A558 from Whataroa Quarry has a well-defined late Cretaceous age of 92.0±1.9 Ma (n=14/18, MSWD=1.2, Fig. 2O, 4O).

From the total 138 analyses of these nine orthogneiss samples, 24 were culled for pooling of weighted mean ages making an average rejection count of less than three data per sample. The variability displayed by these analyses within individual samples probably represents some combination of unaccounted analytical scatter and real geological age heterogeneity. The latter is clearly demonstrated by the five analyses of inherited zircon with ages>500 Ma in four separate samples between Whataroa Quarry and Mikonui River: 502.8±10.8 Ma, A557-2.1; 516.5±15.1 Ma, A558-A-5.1; 987.9±52.6 Ma, A557-A-4.1; 1077.8±10.5 Ma, A555-A-1.1; and 2267.3±61.9 Ma, A556-8.1. Minor spot overlap onto these zones could produce variability around the main peaks. Zircon age variability within a single orthogneiss sample is well demonstrated by sample A551 from Mt Elliot, which contains a mix of Paleozoic and Mesozoic ages (Fig. 2J, 4J, 6) that can be clearly related to the texture of zircon analysed. For example, in Fig. 5C inherited cores record late Cambrian (496.2±11.2 Ma, A551-3.1) and early Devonian ages (412.0±9.6 Ma, A551-4.1), magmatic oscillatory growth domains record early Carboniferous ages (358.6±7.9 Ma, 551-1.1; 327.4±7.2 Ma, 551-5.1) and a zone of metamorphic recrystallisation records an early Cretaceous age (137.6±3.0 Ma, A551-2.1). A total of seven early Cretaceous analyses in A551 represent a relatively poorly defined population with a weighted mean age of 127.0±6.9 Ma (MSWD=5.1).

Paragneiss and orthogneiss monazite share similar age distributions so have been combined in Table 4. Grains sourced from both paragneiss and orthogneiss samples are typically 100–400 µm in length, lack any zoning growth structure and range from rounded to wedge-shaped but are rarely prismatic (e.g., sample A552, Fig. 5E). ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ages from individual analyses and sample-weighted means typically agree (Table 4, Fig. 3K–T). Across all samples monazite crystallisation ages are mainly Devonian or Cretaceous (Fig. 5F). The two paragneiss samples from Crooked River have four combined middle Cretaceous ages that all lie within error: A553 (²⁰⁶Pb/²³⁸U=110.0±2.4 Ma, n=11/12, MSWD=1.8; ²⁰⁸Pb/²³²Th=110.5±2.7 Ma, n=8/12, MSWD=4.0; Figs 3D, 3N, 4D) and A552 (²⁰⁶Pb/²³⁸U=107.5±1.6 Ma, n=10/12, MSWD=1.0; ²⁰⁸Pb/²³²Th=108.3±1.7 Ma, n=12/12, MSWD=2.4; Fig. 3C, 3M, 4C). Three paragneiss samples (A546, Fig. 3A, 3K, 4A; A550, Fig. 3B, 3L, 4B; A560, Fig. 3E, 3O, 4F) and three orthogneiss samples (A547, Fig. 3F, 3P, 4G; A549, Fig. 3G, 3Q, 4I; A557, Fig. 3H, 3R, 4N) all have highly mixed ²⁰⁶Pb/²³⁸U monazite ages (n=73 analyses) with Cretaceous (n=15), Triassic (n=12), Jurassic (n=7), Permian (n=2), Carboniferous (n=18), Devonian (n=13), Silurian (n=5) and Neoproterozoic (n=1) age components. It is likely that mixtures of Devonian and Cretaceous zone s have caused Triassic and Jurassic ages because they do not combine to yield statistically defined ages.

Discussion

Paragneiss protoliths and metamorphism

Previous studies have recognised the strong similarity between detrital zircon ion microprobe U-Pb age spectra derived from Western Province paragneisses and Greenland Group metasediment (Ireland 1992; Ireland & Gibson 1998). Both spectra are characterised by major peaks at 500–600 Ma (Delamerian-Ross orogen) and 1000–1200 Ma (Grenville orogen) with other minor contributions from Proterozoic and Archean protoliths. An Ordovician deposition age has been suggested for the Greenland Group metasedimentary rock (Cooper 1975 , 1989). The results of this study are consistent with that scenario given the large numbers of Cambrian (n=17) and Ordovician (n=13) detrital zircons obtained from samples A546, A550, A552, A559 and A560. The small number of Silurian analyses (n=4) may simply be associated with Pb loss during the younger metamorphic events. The common detrital zircon U-Pb age spectra present in the Fraser and Granite Hill Complex paragneisses indicate the Greenland Group is a suitable protolith for these Western Province paragneisses (Ireland 1992; Ireland & Gibson 1998). This interpretation supports earlier suggestions that Western Province paragneisses are derived from the Greenland Group, based on field relationships (Laird 1967), and whole-rock Sm-Nd isotopic compositions (Pickett & Wasserburg 1989). The Greenland Group origin for the gneisses was further supported by recognition of intervening major extensional detachment faults in the Paparoa Range that have juxtaposed the contrasting metamorphic grade rocks (Tulloch & Kimbrough 1989). The results of zircon geochronology from all six paragneiss samples in this study are similar to these earlier results. Additionally, each paragneiss sample locality is within 10 km of sub-greenschist facies Ordovician Greenland Group rocks (Fig. 1), indicating the close proximity of the metasedimentary protolith in all cases.

Clear similarities have also been previously recognised between Greenland Group detrital zircon age patterns and those of other sedimentary rocks and inherited zircon age spectra in granites from the Lachlan Fold Belt in southeast Australia (Chen & Williams 1990; Ireland 1992) and the Kanmantoo group of South Australia (Gibson & Ireland 1996; Ireland et al. 1998). These rocks were possibly derived from a provenance of similar source terrains along the Paleozoic Gondwana margin. No Precambrian rocks are recognised in New Zealand (Kimbrough & Tulloch 1989). However, the consistency of detrital zircon age patterns across all samples analysed indicates that the source terranes must have included a component of Cambrian, Proterozoic and Archaean material. Potential source rocks of these ages exist in Australia and Antarctica (Ireland 1992). Alternatively, the ancient zircons may be sourced from eroding granites derived from remelting of older, lower crustal rocks (Ireland 1992) or may have been sourced from some completely different reservoir, now eroded or concealed by younger rocks.

Over all six paragneiss samples, the 37 zircon analyses with U-Pb ages<400 Ma have consistently low Th/U (< 0.3). These grains are interpreted as products of metamorphic recrystallisation and minor igneous zircon growth in response to Devonian, Carboniferous and Cretaceous metamorphism and localised melting. Thermobarometry of paragneiss samples from the Charleston Metamorphic Group near Charleston (Kimbrough & Tulloch 1989) and in the Paparoa Range (White 1994) indicate peak temperatures of 600–700°C and pressures of 4±1 kbar. Monazite ion probe geochronology on Victoria Range and Charleston paragneisses (Ireland & Gibson 1998) indicate this upper amphibolite facies metamorphism occurred during or slightly after the intrusion of Devonian granitoids (Tulloch et al. 2009). Analysis of the Charleston orthogneiss monazite demonstrated that this pervasive, regional, Devonian metamorphism was followed by more localised metamorphism during emplacement of Cretaceous granitoids (Ireland & Gibson 1998).

Paragneiss sample A553 from Crooked River contains metamorphic Cretaceous zircons (n=13) with ages ranging from 103.4±3.2 to 126.1±2.0 Ma and low Th/U ratios (from 0.02 to 0.36). The zircon age is anomalous compared to other samples, including A552 less than 500 m away. The timing of this metamorphism is better defined by weighted mean monazite ages (²⁰⁶Pb/²³⁸U=110.0±2.4 Ma, ²⁰⁸Pb/²³²Th=110.5±2.7 Ma) and is within error of the emplacement ages of Rahu Suite granitoids from the nearby Hohonu Batholith (Fig. 1; Waight et al. 1997). Paragneiss sample A552 contains slightly younger Cretaceous monazite weighted mean ages of ²⁰⁶Pb/²³⁸U=107.5±1.6 Ma and ²⁰⁸Pb/²³²Th=108.3±1.7 Ma. However, in this sample, Cretaceous metamorphism was probably less intense as monazite ages are not accompanied by Cretaceous zircon growth and recrystallisation. Metamorphic zircon ages in paragneiss samples A546, A550, A559 and 560 are Silurian (n=2), Devonian (n=9) or Carboniferous (n=5), whereas monazite ages for samples A546, A550 and A560 vary widely between the Silurian and Cretaceous. This indicates that these samples contain a mixed sample of zoned crystals. No monazite ages older than Silurian were obtained from any paragneiss sample indicating that, if present, any older detrital monazite grains were reset during later metamorphism. It is noteworthy that a detrital monazite pattern similar to the Gondwana zircon signature was found by Ireland & Gibson (1998) in a sillimanite-grade paragneiss in Fiordland.

Permian or Triassic detrital zircons are absent from all paragneiss U-Pb age spectra, ruling out a Rakaia Terrane greywacke Eastern Province protolith (Ireland 1992; Wysoczanski et al. 1997; Cawood et al. 1999; Pickard et al. 2000; Wandres et al. 2004 , 2005; Adams et al. 2007), whose metamorphosed equivalents – the Alpine Schist – occur southeast of the Alpine Fault (Fig. 1).

Orthogneiss protoliths and metamorphism

Four widely spaced orthogneiss samples A547, A557, A549 and A556 have middle–late Devonian U-Pb zircon ages of 387.1±6.8, 386.5±7.5, 378.1±6.8 and 370.6±9.9 Ma, respectively. These are interpreted as intrusion ages that are slightly older than, or contemporaneous with, the ~370 Ma emplacement of the Karamea Batholith (Muir et al. 1994 , 1996a; Tulloch et al. 2009). Karamea or other Devonian granitoids are mapped within several kilometres of each of these samples (Fig. 1). Petrogenesis of the Karamea Batholith has previously been demonstrated to be the result of mixing between primitive primary magmas and Greenland Group metasediments in varying proportions (Muir et al. 1996b). This interpretation is supported here by the presence of a minor component of inherited zircon in each sample, with ages that correspond to those identified in Greenland Group detrital zircon age spectra during the Ordovician (455.0±9.9 Ma, A549-9.1; 467.7±10.1 Ma, A549-10.1; 475.2±13.8 Ma, A547-A-4.1), Cambrian (502.8±10.8 Ma, A557-2.1), Neoproterozoic (987.9±52.6 Ma, A557-A-4.1) and Paleoproterozoic (2267.3±61.9 Ma, A556-8.1).

Orthogneiss sample A557 from Bonar Creek has an intrusive U-Pb zircon age of 386.5±7.5 Ma. Subsequent metamorphism is recorded by nine monazites with Devonian and Carboniferous U-Pb and Th-Pb ages. This rock intrudes more strongly foliated orthogneiss nearby (Jongens 2006), indicating older gneissic plutons are present in this area. One Silurian monazite (A557-8.1) probably represents an inherited monazite from a Greenland Group source that was not reset during igneous emplacement or metamorphic overprinting of the orthogneiss granitoid protolith. U-Pb zircon ages of 387.1±6.8 and 378.1±6.8 Ma were obtained from orthogneiss samples A547 and A549 respectively, interpreted to date the time of intrusion. Both samples also contain a minor component of inherited zircon. Thirty monazite analyses from these rocks yield highly mixed U-Pb and Th-Pb ages. Fifty-two monazite analyses are equal to or younger than the inferred intrusive ages. These are as young as Cretaceous and are interpreted to date subsequent metamorphism. Eight monazite ages are older than the inferred timing of intrusion and possibly represent a component of inherited monazite. Monazite inheritance is rare in granitic systems (Rapp et al. 1987); it has however been documented in leucogranites as well as high-grade metamorphic rocks (e.g., Copeland et al. 1988; Parrish 1990; Kingsbury et al. 1993; Harrison et al. 1995; Vry et al. 1996; Simpson et al. 2000). The Charleston Orthogneiss sample 90-427 records weighted mean monazite U-Pb and Th-Pb ages of 361.7±6.1 and 375.4±5.0 Ma, respectively, that are clearly associated with intrusion of Devonian granitoids (Ireland & Gibson 1998).

Three orthogneiss samples A554, A548 and A555 have well-defined middle Cretaceous U-Pb zircon intrusive ages of 116.0±2.3, 114.5±2.0 and 114.2±2.4 Ma that overlap the age ranges of Separation Point and Rahu Suites. The nearest mapped Cretaceous plutons are in the Hohonu Batholith, c. 10 km to the northeast (Nathan et al. 2002). Samples A554 and A555 also contain minor amounts of inherited Carboniferous, Devonian and Mesoproterozoic zircon, indicating their protolith incorporated some older crust such as Paleozoic granitoids or Greenland Group metasediments. The Charleston Orthogneiss sample 90-428 has weighted mean monazite U-Pb and Th-Pb ages of 106.1±2.5 and 108.3±2.7 Ma that are probably associated with intrusion of the Separation Point or Rahu Suites (Ireland & Gibson 1998). The younger sample A558 has a well-defined but previously unrecognised late Cretaceous age of 92.0±1.9 Ma (n=14/18, MSWD=1.2, Fig. 2O, 4O) that falls between intrusive ages of the Rahu Suite and the younger Hohonu Batholith A-type French Creek Granite at c. 82 Ma (Waight et al. 1997).

The ages of the orthogneiss samples are generally similar to the emplacement ages of known igneous intrusions in the region. Of interest is the lack of ages in the range 160–130 Ma. The late Jurassic to early Cretaceous age of metamorphism inferred for a Fraser Complex migmatite (Kimbrough et al. 1994) would appear to be the result of combining multiple components of Cretaceous and Devonian age with a mixed population of detrital zircons. The lack of zircons in this age range is noteworthy because rocks of this age are a major component of the Median Batholith (Muir et al. 1998; Allibone & Tulloch 2004; Allibone et al. 2007 , 2009a). However, although these older Mesozoic ages are not associated with the Fraser Complex, Separation Point and Rahu Suite ages are common.

Regional trends

The influence of Cretaceous plutonism and metamorphism is widespread throughout the area sampled (Fig. 6). The more northern paragneiss and orthogneiss samples occur close to large areas of mapped Cretaceous plutonism in the Hohonu Batholith (Waight et al. 1997) and the southern Victoria Range (Nathan et al. 2002). The more southern samples are typically located close to the Alpine and/or Fraser Faults, where Cretaceous plutonism is not well documented. Only the Bonar Creek sample A557 appears to lack Cretaceous monazites. Samples with Cretaceous zircons generally contain inherited Devonian and older zircons also, suggesting thermal metamorphism was localised and intense.

Fig. 6  Map showing histograms of zircon (black) and monazite (grey) age structures for paragneisses (left) and orthogneisses (right). For all histograms, ²³⁸U/²⁰⁶Pb ages <800 Ma are corrected for common Pb based on ²⁰⁷Pb and all ²⁰⁷Pb/²⁰⁶Pb ages >800 Ma are corrected for common Pb based on ²⁰⁴Pb.

Summary and conclusions

SHRIMP zircon U-Pb and monazite U-Pb and Th-Pb ages have been obtained from 15 gneiss samples of the Fraser Complex and similar rocks in the region between the southern Victoria Range and Whataroa. Ages are similar to those previously obtained from metamorphic rocks of the Western Province. Paragneiss samples have patterns of Paleozoic, Proterozoic and Archean detrital zircons ages, indicating that they are likely to be metamorphosed Greenland Group of Ordovician depositional age. The similar detrital zircon age spectra in the paragneisses and Greenland Group metasedimentary rocks indicate a Gondwana margin provenance. Orthogneiss samples are dominated by Devonian and Cretaceous emplacement zircon ages that are associated with recognised episodes of intensive plutonism within the Western Province. Metamorphism during the Devonian and Cretaceous is indicated by monazite geochronology.

Detrital zircon age spectra and periods of magmatism and metamorphism correspond closely to events previously defined in the Western Province. There is no evidence the Fraser Complex is an exotic terrane, nor any strong evidence of either plutonism or metamorphism between the Carboniferous (c. 310 Ma) and early Cretaceous (c. 130 Ma). There is no indication of the presence of Eastern Province protoliths in these rocks. Similarly, the absence of ages between 160 and 130 Ma suggests Median Batholith material of this age is absent. Results of this study indicate that the metasedimentary components of the Fraser and Granite Hill Complexes are part of the Buller Terrane and are intruded by middle Paleozoic and early Cretaceous plutons that dominate the Karamea-Paparoa and Hohonu Batholiths.

Acknowledgements

The field assistance of Marilyn Vogel and Cal Rattenbury is gratefully acknowledged. Marilyn Vogel undertook much of the mineral separation and preliminary electron microprobe analysis. Preliminary SHRIMP analysis was undertaken by Rattenbury and Ireland in 2001 and later by Hiess between 2003 and 2006 as a Summer Research Scholar and PhD student at RSES, ANU. Andy Tulloch and Andrew Allibone are thanked for their helpful reviews that improved the manuscript.