field characteristics, petrography, and...

Sew Zealand Journal of Geology and Geophysics, 1997, Vol. 40: 1—170028-8306/97/4001—0001 $2.50/0 © The Royal Society of New Zealand 1997

Field characteristics, petrography, and geochronology of theHohonu Batholith and the adjacent Granite Hill Complex,North Westland, New Zealand

T. E. WAIGHT1*S. D. WEAVER1

T. R. IRELAND2

R.. MAAS3

R. J. MUIR4

D. SHELLEY1

'Department of Geological SciencesUniversity of CanterburyPrivate Bag 4800Christchurch, New Zealand

2Research School of Earth SciencesAustralian National UniversityA.C.T. 0200, Canberra, Australia

3 Victorian Institute of Earth and Planetary SciencesSchool of Earth SciencesLa Trobe UniversityBundoora, Victoria 3083, Australia

4Isotope Geology UnitScottish Universities Research and Reactor CentreEast KilbrideGlasgow, G75 OQU, United Kingdom

'Present address: Victorian Institute of Earth and PlanetarySciences, School of Earth Sciences, La Trobe University,Bundoora, Victoria 3083, Australia.

are (from north to south): Pah Point Granite; Jays CreekGranodiorite (new); Uncle Bay Tonalite; Te KingaMonzogranite; Deutgam Granodiorite; Turiwhate Granod-iorite (new); and Arahura Granite (new). Mid-Cretaceousplutonism in the Western Province is considered to be theresult of crustal thinning and extension followingoverthickening during collision of the Early CretaceousMedian Tectonic Zone volcanic arc.

Late Cretaceous alkaline activity is represented by theemplacement of the A-type French Creek Granite at 81.7 ±1.8 Ma, contemporaneous with intrusion of a major swarmof doleritic-lamprophyric dikes—the Hohonu Dike Swarm.These events correlate with the first appearance of oceaniccrust in the Tasman Sea.

The Granite Hill Complex is a suite of amphibolite faciesgneisses occurring as an uplifted wedge between the AlpineFault and the Hohonu Batholith. These gneisses areconsidered to represent an extension of the Fraser Complexto the south. A detailed understanding of their geologicalaffinities and history is yet to be established.

Keywords granitoids; geochronology; Hohonu Batholith;Jays Creek Granodiorite; Pah Point Granite; Uncle BayTonalite; Te Kinga Monzogranite; Deutgam Granodiorite;French Creek Granite; Turiwhate Granodiorite; SummitGranite; Arahura Granite; Mt Graham Granite; Rahu Suite;U-Pb zircon dating; Rb-Sr isotope data; Hohonu DikeSwarm; Granite Hill Complex; Fraser Complex; newstratigraphic names

Abstract Detailed geological mapping, petrography,geochemistry, and geochronological studies in the HohonuBatholith, North Westland, have identified 10 granitoidplutons emplaced during three intrusive episodes. Theearliest episode is represented by a single dated Paleozoicpluton, Summit Granite (new) (381.2 ± 7.3 Ma), which iscorrelated with a discrete pulse of Mid-Late Devonianplutonism recognised in the Karamea Batholith. The undatedMount Graham Granite (new) is also likely to bePaleozoic, based on chemical and petrographic character-istics.

The bulk of the batholith (seven plutons) was emplacedin the mid Cretaceous (114—109 Ma) and comprises tworelated, yet distinct, geochemical suites, which correlate withthe previously defined Rahu Suite. The plutons identified

G95077Received 22 December 1995; accepted 12 September 1996

INTRODUCTION

There have been few detailed mapping, geochemical, andgeochronological studies of granitoids in New Zealand, yetsuch work is necessary to facilitate a fuller understandingof the tectonic setting and evolution of the New Zealandcontinental crust. The Hohonu Batholith (Tulloch 1988) issituated adjacent to the Alpine Fault and inland fromGreymouth and Hokitika on the West Coast of the SouthIsland of New Zealand (Fig. 1). Previous reconnaissancestudies (Tulloch & Brathwaite 1986; Tulloch 1988) indicatedthat the granitoids of the Hohonu Batholith belong to theRahu Suite, defined as Cretaceous granitoids of transitionalI/S-type character (Tulloch 1988). Earlier workers (Wellman& Cooper 1971; Hamill 1972; Tulloch & Brathwaite 1986)also identified an area of mafic dike concentration in theHohonu Batholith, here termed the Hohonu Dike Swarm.Apart from a few K-Ar determinations interpreted as upliftages (Seward 1989), and relatively abundant fission trackdata (White & Green 1986; Seward 1989; Kamp et al. 1992;Spanninga 1993), no geochronological data on crystallisationages have been published from the granitoids of the HohonuBatholith.

New Zealand Journal of Geology and Geophysics, 1997, Vol. 40

Fig. 1 Distribution of the HohonuBatholith, South Westland.

Systematic geological mapping of the batholith byWaight (1995a) led to the identification of 10 distinctplutonic phases. Accompanying geochronological studieshave identified three discrete episodes of magmatismresponsible for the batholith. In this study we present ageological map, a general description of the plutons and otherrock types in the Hohonu area, and new geochronologicaldata.

REGIONAL GEOLOGY

The pre-Cenozoic rocks of the South Island of New Zealandare separated into the Western and Eastern Provinces (Landis& Coombs 1967), divided by a complex belt of dismemberedmagmatic arcs known as the Median Tectonic Zone(Bradshaw 1993; Kimbrough et al. 1993, 1994a) (Fig. 2,inset). The Western Province represents a fragment of theGondwanaland margin and consists of mainly earlyPaleozoic metasedimentary rocks cut by Paleozoic andMesozoic granitoids. Two tectonostratigraphic terranes—theBuller and Takaka Terranes (Cooper 1979, 1989) separatedby the Anatoki Thrust (Fig. 2)—are recognised in theWestern Province. The two terranes are now exposed in thewest and north of the South Island and in Fiordland. TheBuller Terrane (Cooper 1989) comprises a relatively uniformsuite of quartz-rich turbidites (Greenland Group) cut byPaleozoic and Cretaceous plutons (Cooper & Tulloch 1992)(Fig. 2). Paragneiss and orthogneiss of the CharlestonMetamorphic Group were previously considered to representeither Precambrian basement to the Greenland Group(Adams 1975; Mason & Taylor 1987) or metamorphosedGreenland Group (Shelley 1970). Recent U-Pb dating ofparagneiss has yielded typical Greenland Group signatures

(Ireland 1992), confirming the ideas of Shelley (1970), butsome orthogneiss components are Early Cretaceous in age(Kimbrough & Tulloch 1989).

The Hohonu Batholith intrudes Greenland Group of theBuller Terrane in the Western Province and forms an upliftedbasement block adjacent to the Alpine Fault. A belt ofamphibolite facies gneisses lies between the HohonuBatholith and the Alpine schists of the Eastern Province,separated from Greenland Group and granitoids of the BullerTerrane by steeply dipping reverse faults (Rattenbury 1987a,b; Waight 1995a). In the north, these rocks are known as theGranite Hill Complex (Mason 1990; Waight 1995a) and tcthe south as the Fraser Complex (Rattenbury 1987a; 1991)(see Fig. 3) and have previously been correlated with theCharleston Metamorphic Group (Mason & Taylor 1987:Kimbrough & Tulloch 1989; Mason 1990). Field mappingby Waight (1995a) indicates that Hthologies in the GraniteHill Complex (paragneiss, orthogneiss and metabasite) aresimilar to those of the Fraser Complex, and the two regionsare correlated.

GEOLOGICAL UNITS AND THEIR FIELDRELATIONSHIPS

Greenland Group metasediments and granitoids of theHohonu Batholith are described below in order of occurrencefrom northeast to southwest, followed by a brief descriptionand discussion of the Granite Hill Complex and HohonuDike Swarm. More detailed descriptions of the units can befound in Waight (1995a). A simplified geological map ofthe batholith is presented in Fig. 3. Granitoid nomenclaturefollows that recommended by Le Maitre et al. (1989), andgrid references and localities in the text refer to the metric

Waight et al.—Geochronology of Hohonu Batholith

NELSON-WESTLAND BLOCK

I Mesozoic-Cenozoic cover rocksI Charleston Metamorphic Group and undifferentiated gneissI Rahu Suite ~|1 Cretaceous granitesI Separation Point Suite JI Karamea Suite - Paleozoic granitesI Riwaka Complex - DevonianI Buller Terrane ~~|ITakakaTerraneJI Anatoki thrust

50 100km

L. Paleozoic metasediments

South Island

Wesland

Fiordand

MTZ

BuckjandGranite

PaparoaBatholith

Easterq Province\

Western Province

MTZ

FIORDLAND BLOCKWestern Fiordland OrthogneissCentral Fiordland metased and gneissEastern Fiordland Igneous BeltSouthwest Fiordland Block

Olympus Granite

SeparationPointBatholith

Nelson

Greymouthl

HohonuBatholith

HokitikaC.V.".TMilford Sound

Fig. 2 Summary regional geology of the Western Province, modified from Muir et al. (1994) and Warren (1967). PMCC = PaparoaMetamorphic Core Complex.

NZMS 260 Infomap 1:50 000 sheets. UOC numbers referto samples lodged in the Department of Geological Sciences,University of Canterbury.

GREENLAND GROUP

A detailed description of the Greenland Group is beyondthe scope of this paper, and readers are referred to Laird(1972), Nathan (1976), Cooper & Tulloch (1992), and Roseret al. (1996) for a more comprehensive discussion. TheGreenland Group is a uniform series of lower greenschistfades, green to grey turbidites, which have been correlatedwith similar deposits in Antarctica (Nathan 1976; Adams etal. 1995) and Australia (Cooper & Tulloch 1992). A Rb/Srisochron of 495 ± 11 Ma (Adams 1975) is believed to date

the lower greenschist facies metamorphic event and providesa minimum age for the unit. Excluding outcrops on Bell Hilland Mount Graham, most Greenland Group in the HohonuBatholith occurs as slivers adjacent to the northwesternmargins of several plutons (see Fig. 3). Greenland Groupsediments are metamorphosed to a brown-black biotitehornfels immediately adjacent to granitoid contacts.

JAYS CREEK GRANODIORITE (new name)

TYPE AREA: Midland railway bridge over Jays Creek (grid,ref. K32/883413).

This pluton is poorly exposed and crops out only in the lowerreaches of Jays Creek, Mt Te Kinga, and on a low hill east


Greymouth

Christchurch

South Island

New Zealand

s• • ••Mi

—

s

Iin

Geological Legend

L.Cretaceous, Tertiary and Quaternary deposits

^ French Creek Granite

Te Kinga Monzogranite -

•/.'•, Pah Point Granite

TT Jays Creek Granodiorite

88 Arahura Granite

S Turiwhate Granodiorite

V Deutgam Granodiorite

K?o Uncle Bay Tonalite2 i

= Summit Granite - ,m.'.'. Mount Graham Granite —'

S Granite Hill Complex _

w Fraser Complex —

I I I Alpine Schist

1 Greenland Group

0 1 2 3 4 5 6 7 8 9I t J I 1 I 1 1 1 1

L. Cretaceous

mid-Cretaceous

Devonian

?pre-Cretaceous

Triassic-Jurassic

Ordovician

10 kmI

Fig. 3 Simplified geological map and cross-section of the Hohonu Batholith. J32, J33, K33, and K32 refer to the boundaries of theappropriate NZMS 260 1:50 000 topographic maps.


of Kangaroo Lake (K32/892428). The pluton is a massive,mesocratic, medium grained biotite-granodiorite tomonzogranite containing sparse phenocrysts of whitealkali feldspar (20 mm). Plagioclase is mostly calcicoligoclase (c. An2s), and other phases include yellow-brownbiotite, secondary muscovite, and accessory allanite. Theextent of the unit beneath the Quaternary gravels is unknown,and no contacts are observed with any other basement unit.Jays Creek Granodiorite is assumed to be intrusive intoGreenland Group, which outcrops 2 km to the east atKangaroo Lake.

PAH POINT GRANITE(after Pah Point Granodiorite of Mason 1990)

TYPE AREA: Pah Point (K32/845428).

Pah Point Granite is exposed on Pah Point and the RefugeIslands in Lake Brunner, and in Rocky Creek, Mt Te Kinga,in contact with Uncle Bay Tonalite along a steep, easterlydipping reverse fault. No intrusive relationships with othergranitoids are observed. The granitoid is an orange-brown,massive, mesocratic, coarse grained biotite-monzogranite,characterised by numerous, large (30 mm) alkali feldsparmegacrysts. Plagioclase (Anis-46)1S mostly calcic oligo-clase (c. An3o). Biotite displays distinctive straw-yellow tobrown pleochroism. Accessory phases include titanite andallanite.

TE KINGA MONZOGRANITE(after Te Kinga Adamellite; Mason 1990)

TYPE AREA: Quarry near Hodgkinson Rd (K32/899380).

Te Kinga Monzogranite crops out over c. 45 km2 and makesup most of Mt Te Kinga. The granitoid is a white, leucocraticto mesocratic, predominantly coarse grained biotite-muscovite monzogranite. Although most of the pluton isequigranular, several exposures on the summit of Mt TeKinga are porphyritic, containing euhedral phenocrysts ofalkali feldspar up to 30 mm long and subhedral quartz,indicating rapid crystallisation near the roof of a relativelyshallow pluton. Both magmatic and tectonic fabrics arerecognised in Te Kinga Monzogranite. A fine-grained variantof the granitoid is well exposed near Rotomanu (K32/913394) and displays a strong magmatic foliation cut byseveral undeformed tourmaline and garnet-bearingpegmatites. In contrast, the southeast margin of the Te KingaMonzogranite displays a strong mylonitic fabric character-ised by sheared mica, ribbon quartz, and brittle deformationof feldspar. This fabric is considered to have been generatedduring movement on the nearby Alpine Fault. These rockswere originally mapped as mylonitised Uncle Bay Tonaliteby Mason (1990) but most are petrographically andgeochemically identical to Te Kinga Monzogranite.Plagioclase in Te Kinga Monzogranite is generally weaklyzoned and ranges Ani3_28, mostly being calcic oligoclase(c. An24). Mafic minerals present are muscovite and yellow-brown to brown or slightly red-brown pleochroic biotite.Minor tourmaline is observed at Rotomanu Quarry. Severalsheets of Te Kinga Monzogranite cut mafic biotite-hornblende microtonalitic variants of Uncle Bay Tonalitein Wallace Creek on the northeastern side of Mt Te Kinga(K32/875398), which suggests Te Kinga Monzogranitepostdates Uncle Bay Tonalite.

UNCLE BAY TONALITE (Mason 1990).

TYPE AREA: Unnamed stream, northwest side of Mt Te Kinga(K32/845386).

Uncle Bay Tonalite forms a wedge along the northwest edgeof Mt Te Kinga and is particularly well exposed on the shoresof Lake Brunner. The granitoid is a grey, massive, mediumto coarse grained, equigranular biotite-tonalite. Plagioclaseis subhedral and has compositions of An3o_5O. Mafic mineralsinclude yellow-brown to green-brown biotite, resorbedtitanite, and brown to green magnesio-hornblende. Accessoryphases include epidote as both a secondary and primaryigneous phase, allanite, and rare tourmaline.

DEUTGAM GRANODIORITE(after Deutgam Granite of Hamill (1972) and Waight (1995a))

TYPE AREA: Granite Point, Lake Brunner (K32/815383).

Deutgam Granodiorite is the largest and most complex ofthe plutons in the Hohonu Batholith. It makes up the bulkof the Hohonu Range and also extends to southeast MtTuriwhate, outcropping over a total of c. 120 km2. Thedominant variety is an alkali feldspar megacrystic, coarsegrained biotite-granodiorite, and other less common varietiesrange from relatively mafic megacrystic hornblende-biotite-tonalite through to leucocratic aplitic monzogranite.Plagioclase in the dominant variety is relatively restrictedin composition (An32-^3), and alkali feldspar forms pinkmegacrysts up to 70 mm long. Yellow-brown to green-brownor brown biotite and titanite are the dominant mafic minerals.Green to brown magnesio-hornblende is sparsely present,but becomes more abundant in mafic varieties, particularlytowards the presumed core of the pluton in the DeutgamPeak — Mt Treacey area. Accessory phases include allaniteand epidote (both primary and secondary).

Although the bulk of the pluton displays no fabric,Deutgam Granodiorite has developed a strong myloniticfoliation along its southeast margin as a result of movementand uplift on the Alpine Fault. This foliation overprints anearlier magmatic foliation, defined by aligned euhedral,undeformed alkali feldspar megacrysts and cut byundeformed pegmatites, visible in many exposures alongthe Taramakau and Big Wainihinihi Rivers (e.g., quarry atK33/726262). A small sheet of Deutgam Granodiorite cutsUncle Bay Tonalite in Strauchon Creek, Mt Te Kinga (K32/849393), and Deutgam Granodiorite also intrudes SummitGranite on Mt Turiwhate (K33/704252).

FRENCH CREEK GRANITE(Tulloch et al. 1994, previously Brunner Granite of Hamill 1972)

TYPE AREA: Eastern Hohonu River (K32/751383-756378).

French Creek Granite occurs along the northwest margin ofthe Hohonu Range and has many petrographical andgeochemical characteristics considered typical of A-typegranitoids (e.g., Eby 1990). The granitoid intrudes DeutgamGranodiorite, and hypabyssal rhyolitic dikes geochemicallyidentical to French Creek Granite (Waight 1995a) also cutDeutgam Granodiorite and members of the Hohonu DikeSwarm on the Hohonu Range. Dikes of the Hohonu swarmintrude French Creek Granite, yet may also be observed tobe cut by French Creek aplite dikes. Additionally, several


composite dikes consisting of mafic and rhyolitic materialcut French Creek Granite and indicate a complex temporaland genetic relationship between the Hohonu Dike Swarmand French Creek Granite.

French Creek Granite is a compositionally complexpluton generated during the intrusion and crystallisation ofseveral distinct magma pulses. The dominant variety is amassive, brick red, medium to coarse grained equigranularbiotite-syenogranite, dominated by granophyric intergrowthsof quartz and pink perthitic alkali feldspar. Other mineralsinclude minor plagioclase (Ano__2o> mostly c. An9), yellowto yellow-brown Fe-rich, Al-poor biotite, minor amphibole(ferroedenite), allanite, and aenigmatite. Co-existingplagioclase and alkali feldspar indicate a subsolvus history,although late-stage perthitic alkali feldspar and abundantgranophyric intergrowths indicate the final stages ofcrystallisation were rapid and occurred at hypersolvusconditions.

A completely hypersolvus variety of French CreekGranite is exposed in the Eastern Hohonu River (K32/755380) near its contact with Deutgam Granodiorite. It is amassive, pink to brown or blue-green, medium to coarsegrained, equigranular monzogranite dominated by poorlydeveloped granophyric intergrowths between mesoperthiteand quartz. The mafic assemblage is dominated by yellow-brown to intense blue-green to dark green sodic amphibole,with rarer brown to dark-brown biotite and aenigmatite.

Isolated outcrops of altered red-brown to grey-green,equigranular, medium grained quartz alkali feldspar syeniteoccur near the contact between French Creek Granite andDeutgam Granodiorite. This rock type is dominated by alkalifeldspar, although rare plagioclase indicates an at leastpartially subsolvus crystallisation history. Quartz isinterstitial or forms small amounts of granophyricintergrowth with alkali feldspar. Mafic minerals consist ofhighly altered green pleochroic amphibole and relativelyfresh straw-yellow to yellow-brown or red biotite.

Blue to cream, fine-grained rhyolitic dikes are commonon the Hohonu Range, intruding Deutgam Granodiorite(Hamill 1972), and are considered to represent hypabyssalequivalents to French Creek Granite (Tulloch et al. 1994;Waight 1995a). The rhyolites consist of a very fine grainedfelsitic matrix of quartz and alkali feldspar containing floworientated, acicular dark green to blue-black amphibole(riebeckite or arfvedsonite). Many of the dikes arespherulitic; the spherulites border phenocrysts of alkalifeldspar and/or embayed subhedral to euhedral quartz.Astrophyllite is present as an accessory mineral.

TURIWHATE GRANODIORITE (new name)

TYPE AREA: Mt Upright (J33/123559).

Turiwhate Granodiorite is a white to green, massive, mediumgrained, equigranular titanite-hornblende-biotite grano-diorite. Adjacent to intrusive contacts with Greenland Groupon Mt Tuhua (e.g., J33/601173, J33/605190), the grano-diorite may be somewhat more mafic than typical TuriwhateGranodiorite, and country rock is metamorphosed to afoliated biotite hornfels. Turiwhate Granodiorite intrudesSummit Granite near the summit of Mt Turiwhate (J33/688271) and is in fault contact with Deutgam Granodioritein Grahams Creek (J33/700273). The relationships betweenTuriwhate Granodiorite and Deutgam Granodiorite along the

southeast side of Mt Turiwhate remain unclear due to thickbush cover and difficult access.

Turiwhate Granodiorite contains common titanite andabundant brown-green to green pleochroic magnesio-hornblende with rare relict cores of pyroxene, features typicalof I-type granitoids (Chappell & White 1992). Plagioclase(Anig_5o) is mostly andesine (An3o^4O)- Yellow-brown todark brown biotite often contains abundant secondaryprehnite, epidote, titanite, and alkali feldspar, developedparallel to cleavage as low-grade deuteric alteration productsas described in detail by Tulloch (1979b). Allanite is presentas a rare accessory phase.

SUMMIT GRANITE (new name)

TYPE AREA: Mt Turiwhate (J33/699259).

Summit Granite is a leucocratic, equigranular, mediumgrained biotite-muscovite granodiorite to monzograniteoutcropping above the bushline on the Turiwhate Range.Metasedimentary inclusions are common and are generallyorientated parallel to a pervasive foliation throughout theunit. Summit Granite is intruded by Turiwhate Granodioriteto the northeast and by Deutgam Granodiorite to thesouthwest and occurs as an isolated cap, or roof pendant, ontop of the Cretaceous granitoids. Plagioclase (An7_2o) isdominantly sodic oligoclase (An)5). Both yellow-brown tored-brown biotite and subhedral platy muscovite are presentand rare garnet also occurs. Primary opaque phases arenotably absent.

ARAHURA GRANITE (new name)

TYPE AREA: Arahura Gorge (J33/629235).

Arahura Granite is a large pluton (c. 100 km2) of homo-geneous, white, medium to coarse grained, mesocratic toleucocratic megacrystic muscovite-biotite-monzogranite.Arahura Granite intrudes Turiwhate Granodiorite, with acontact between the two units exposed on the southern shoresof Lake Kaniere (J33/592137). Along its southeast margin,Arahura Granite is faulted against the Fraser Complex andis strongly cataclastically deformed. White to pink perthiticalkali feldspar forming megacrysts up to 50 mm long, andzoned plagioclase (An]3_33), dominate the rock. Yellow-brown to brown pleochroic biotite (generally altered tochlorite) is dominant over muscovite. Accessory phasesinclude rare titanite and allanite. Specimens of ArahuraGranite collected from near the summit of Mt Tuhua arehighly porphyritic, containing large (up to 8 mm) pheno-crysts of subhedral quartz and alkali feldspar in a fine-medium grained matrix, suggestive of emplacement andrapid cooling at relatively shallow depths.

MOUNT GRAHAM GRANITE (new name)

Mt Graham Granite is, strictly speaking, not part of theHohonu Batholith as it is separated from the granitoids onMt Tuhua by several kilometres of Greenland Group. Thepluton is poorly exposed and the best exposures were foundnear the head of Kent Creek (J33/557175). Mt GrahamGranite is a massive, leucocratic, equigranular, mediumgrained biotite-muscovite monzogranite, similar inappearance to Summit Granite. Plagioclase is albite(c. Anio), a n d yellow-brown to red-brown biotite is


subordinate to platy muscovite. Allanite-epidote is presentas a rare accessory phase.

GRANITE HILL COMPLEX (Mason 1990)

Granite Hill and several low-lying hills near Rotomanu aremade up of a complex association of paragneiss (biotite ±garnet ± sillimanite), metabasite (hornblende ± garnet), andgranodioritic orthogneiss, most varieties being well exposedin the Crooked River Gorge (K32/966392-949409). Thegneisses are intruded at Rotomanu, Crooked River, and inRough and Tumble Creek on Granite Hill by a post-metamorphic melanocratic, equigranular, medium grainedpyroxene hornblende norite (Thirsty Creek Norite of Mason1990). The metamorphic sequence most likely represents asequence of pelites and psammites, intruded by megacrysticgranitoids then metamorphosed to an amphibolite faciesassemblage, the metabasites representing either volcanic ortuffaceous units interbedded with the sedimentary sequence,or basaltic dikes emplaced into the sequence beforemetamorphism. A similar suite of amphibolite facies gneisseshas been identified in the Fraser Complex to the south(Rattenbury 1987a, 1991; Waight 1995a), and the GraniteHill Complex is considered to represent a northerly extensionof this. Particularly distinctive is a suite of foliated,megacrystic biotite granodioritic orthogneisses whichoutcrop over a wide area from the Doughboy in the south toAhaura north of the study area. Despite the lithologicalsimilarities of the Granite Hill and Fraser Complexes, theyrecord different tectonic histories. The Fraser Complex ischaracterised by anastomosing zones of mylonites relatedto movement on the Alpine Fault, disrupting both gneissesand younger mafic dikes (Rattenbury 1987b). In contrast,the Granite Hill Complex lacks any pervasive mylonitisation,and appears to have been largely unaffected by Alpine Faultmovement. Scant apatite fission track data from the GraniteHill Complex range in age from 6 to 10 Ma, older than the2 Ma ages obtained in the Fraser Complex (Kamp et al.1992), suggesting an increase in uplift age from south tonorth. The consequent lack of pervasive mylonitisation inthe Granite Hill Complex may be a consequence of upliftabove ductile deformation conditions before strike-slipmovement on the Alpine Fault.

The age and affinities of the Fraser and Granite HillComplexes remain unknown. The Fraser and Granite HillComplex gneisses have previously been associated with theCharleston Metamorphic Group of Nathan (1975) and theVictoria Paragneiss of the northern Victoria Range of Tulloch(1979a) (Young 1968; Mason & Taylor 1987; Kimbrough& Tulloch 1989; Mason 1990). Several observations makethis correlation unlikely. Firstly, the abundant metabasalticmaterial in the Fraser and Granite Hill Complexes is notpresent in either the Charleston Metamorphic Group or itsmetasedimentary precursor, the Greenland Group. Addi-tionally, preliminary isotopic data indicate the Granite HillComplex and Fraser Complex paragneisses are unlikely torepresent metamorphosed Greenland Group (Waight 1995a),the preferred interpretation for paragneisses of the CharlestonMetamorphic Group (Tulloch & Kimbrough 1989).Preliminary SHRIMP studies (Ireland 1992) also suggestthat the sedimentary precursor to the Granite Hill paragneissmay be slightly younger than the Greenland Group and theprecursor of the Victoria Paragneiss, suggesting that a simplecorrelation between Greenland Group/Charleston Meta-

morphic Group and the Granite Hill/Fraser Complexes isunlikely. The age and precursors of the Granite Hill Complexand Fraser Complex remain unclear.

Kimbrough et al. (1994b) presented a conventional U-Pb zircon age of 157 + 21 Ma for a Fraser Complexmigmatitic leucosome in the Hokitika Gorge. This age isinterpreted as representing the crystallisation age of theleucosome and a period of peak metamorphism andmigmatisation in the Late Jurassic - Early Cretaceous. Asingle zircon from a Granite Hill Complex garnet-sillimanitegneiss yielded a SHRIMP age of 115 ± 6 Ma and is alsointerpreted to represent a high-grade metamorphic-anatexisevent (Ireland 1992). This age overlaps with the bulk ofmagmatism in the Hohonu Batholith (110 Ma) and theSeparation Point Batholith (125-117 Ma) (Muir et al. 1994).Rattenbury (1987b) presented widely variable K-Ar datafrom mylonites and gneisses of the Fraser Complex,reflecting regional temperature changes. A clustering of K-Ar biotite ages at 44 Ma gives a maximum age formylonitisation, considerably older than the 25 Ma generallyconsidered as the age of inception of the Alpine Fault (Kamp1986; Cooper et al. 1987), and have been ascribed to excessargon contamination (Rattenbury 1987b).

Hohonu Dike SwarmMafic dikes occur throughout the Hohonu Batholith andGranite Hill Complex, but are primarily concentrated withinthe Hohonu Range and on Mt Te Kinga (Hamill 1972;Waight 1994, 1995a). The swarm consists of doleritic,lamprophyric, and rare phonolitic dikes displaying a verystrong WNW-ESE preferred orientation. The complextemporal and probably genetic relationships between FrenchCreek Granite and Hohonu Dike Swarm suggest the HohonuDike Swarm is the same age as French Creek Granite at82 Ma. This age is in broad agreement with K-Ar ages fromthe Lake Brunner region presented by Wellman & Cooper(1971) and also with K-Ar ages for a similar swarm in theBuller Gorge (Adams & Nathan 1978). The inferred age ofthe Hohonu Dike Swarm, the WNW-ESE preferredorientation, and chemical characteristics typical of rift-related, within-plate environments are indicative ofgeneration during NNE—SSW crustal extension in the BullerTerrane (Waight 1994, 1995a). This extension occurredcontemporaneous with the generation of the oldest knownoceanic crust in the Tasman Sea (Weissel & Hayes 1977;Stock &Molnar 1982).

EMPLACEMENT DEPTHS

It is often difficult to estimate the conditions and styles ofemplacement of granitoid plutons, and the Hohonu Batholithis no exception. Where contacts are observed with countryrock (Greenland Group) they are sharp and vertical, andGreenland Group sediments are contact metamorphosed tobiotite hornfels, indicating mesozonal depths of emplace-ment. The Al-in-hornblende geobarometer of Schmidt (1992)gives an indication of pressure of crystallisation (± 0.6 kbar)and was applied to those plutons containing the appropriateassemblage (hbl + biot + plag + qtz + kspar + titanite +ilmenite or magnetite ± epidote). Both Uncle Bay Tonaliteand Deutgam Granodiorite give similar average estimatesof pressure of hornblende crystallisation at 4.2 and 4.0 kbar.,respectively, with a total range of calculated pressures of


3.9-4.4 kbar, and indicate emplacement at c. 12 km depth.A sample of Turiwhate Granodiorite from Styx Riverprovided pressure estimates of between 3.3 and 3.5 kbar,within error of the Deutgam and Uncle Bay estimates. Twosamples from the northeast end of Mt Turiwhate gavepressure estimates of 1.4-2.2 kbar and 1.9-2.5 kbar,suggesting shallower levels of the pluton are exposed at MtTuriwhate than to the south at Styx River, although errorlimits overlap. It is difficult to estimate depths ofemplacement of the remaining plutons. Arahura Granite andTe Kinga Monzogranite display porphyritic textures at higherlevels of exposure, suggesting they were emplaced atsomewhat shallower crustal levels than the other mid-Cretaceous plutons. The presence of abundant granophyrictextures, miarolitic cavities, and associated hypabyssal dikesof French Creek Granite indicate it was emplaced at shallow,subvolcanic crustal levels, possibly around 1 kbar (3 km).

GEOCHRONOLOGY OF THE HOHONUBATHOLITH GRANITOIDS

Analytical methodsSHRIMP (Sensitive High Resolution Ion Microprobe) U-Pb zircon ages were determined at Australian NationalUniversity on SHRIMP-I using the standard techniques ofWilliams & Claesson (1987) and methods described in detailby Muir et al. (1996). Zircons were separated using standardcrushing and heavy liquid techniques, mounted in epoxy thenpolished to expose their mid-sections. Spots for analysiswere specifically selected to avoid obviously cracked ordamaged crystals, inherited cores, and any overlap withcompositional zoning within individual zircon crystals. A30 urn diameter area of the crystal to be dated was sputteredusing a mass filtered C>2~ primary beam, and selected massesranging from 196 (90Zr2

16O+) to 254 (238U16O+) weremonitored. As such small areas of crystals are analysed, theeffects of Pb loss and inheritance are easily identifiable. Nocorrection for Pb isotopic mass fractionation is applied tothe data, as all ages are determined from the 238U/206Pb ratio,which is largely unaffected by fractionation. Common Pb(taken as Broken Hill Pb isotopic composition) wasmonitored using the 207Pb/206Pb method, which assumes thatall analyses are a mixture of common and radiogenic Pb.Radiogenic 238U/206Pb is then taken as the extrapolationfrom common Pb through the measured value to theconcordia. The 238U/206Pb ages were collated and examinedusing standard statistical procedures, discussed in detail byMuir et al. (1996). The %2 statistic gives an overall indicatorof the reliability of the mean and should not exceed valuesgiven in standard statistical tables. If y} is too large, outliersare searched for and rejected, if such rejection is valid. Mostoutliers are immediately obvious from the dataset andrepresent either inherited grains or Pb loss. Final errors onthe 238U/206Pb ages are the combined systematic error(summed as variance), from analyses of the standard plusthe variance of the unknown cluster, and are presented astwo standard errors of the mean.

Rb and Sr isotope determinations were carried out on aFinnigan MAT262 thermal ionisation multi-collector massspectrometer at La Trobe University. Isotope dilution andmeasurement methods were similar to those of Maas &McCulloch (1991). Approximately 100 mg of sample wasprocessed over a period of 48 h using HF-HC1 dissolution

at 150°C in pressurised teflon bombs. Most whole-rocksamples were analysed unspiked, using Rb and Srdeterminations analysed on a Philips PW 1400 XRF at theUniversity of Canterbury. Samples with high Rb/Sr (e.g..French Creek Granite, Summit Granite, and mica separates)were spiked with 87Rb—84Sr and analysed by isotope dilutionProcedural blanks were negligible relative to sample sizeused and no blank corrections were applied to the dataAnalytical errors for 87Sr/86Sr for samples with Rb/Sr < 1are 0.01% (2 SD) (using an error of+0.5 (2 SD) for XRFRb/Sr). 87Rb/86Sr was determined by isotope dilution to±0.5% for samples with Rb/Sr > 1. Rb-Sr isochroncalculations (with errors quoted at the 2 SD level) andMSWDs (mean squared weighted deviates, a measure of datascatter) were calculated using standard two-error regressionanalysis. Absolute errors for mica whole-rock ages have beenestimated by propagation of maximum analytical errors andare estimated at < ±2 Ma (2 SD) using a reproducibility for87Sr/86Sr<±0.01%(2SD).

RESULTS

U-Pb zircon SHRIMP studies on six plutons of the HohonuBatholith (Tables 1,2; Fig. 4) identify three discrete periodsof granitoid plutonism. The oldest pluton is the SummitGranite, which yields a Mid—Late Devonian SHRIMP ageof 381.2 ± 7.3 Ma, and the youngest is French Creek Granite-giving a SHRIMP age of 81.7 + 1.8 Ma, in agreement witha previous conventional U-Pb zircon age reported by Tullochet al. (1994). The remaining plutons define a restricted mid-Cretaceous pulse of magmatism at c. 110 Ma (113.5 ::1.9 Ma, Uncle Bay Tonalite, to 108.7 ± 3.0 Ma, Te KingiiMonzogranite).

Several whole-rock and mineral samples were analysedin an attempt to construct Rb-Sr whole-rock isochrons forthe Deutgam Granodiorite and French Creek Granite(Table 3). A Rb-Sr errorchron for Deutgam Granodiorite(Fig. 5) gives an age of 110.9 ± 2.8 Ma (Sr(initiai) = 0.70808± 19 (2 SD)), remarkably close to the SHRIMP age of 110.4± 2.2 Ma. Little variation in measured whole-rock 87Rb/86Srand 87Sr/86Sr makes the errorchron far from ideal, beinglargely defined by a single aplitic sample. Furthermore, theMSWD of 20.7 is beyond acceptable limits for an idealisochron (an MSWD of >2.5 is generally considered toindicate the presence of geological scatter in the data, e.g.,the magma was initially heterogeneous in Sr isotopiccomposition, or underwent heterogeneous contaminationduring crystallisation; Rollinson 1993). The coincidencebetween the Rb-Sr whole-rock age and the SHRIMP agemay therefore be fortuitous. A biotite separate from DeutgamGranodiorite does not fall on the whole-rock errorchron andwas not used in the age calculation (Fig. 5). Similarly, whole-rock Rb-Sr errorchrons for French Creek Granite (Fig. 6)are similar to the SHRIMP age, at 88.0 ± 8.6 Ma (Sr(initial) =0.7063 ± 25 (2 SD)), yet calculated errors and MSWDs arelarge and vary considerably depending on which samplesare used in the age calculations (Fig. 6). French CreekGranite has low Sr contents and displays isotopic evidencefor open system behaviour of Sr (Waight 1995a), andtherefore the failure to yield an acceptable isochron is notsurprising.

Mica whole-rock ages were calculated for single samplesof all units of the Hohonu Batholith (excluding Mt Graham


Granite for which no age control exists) (Table 1).Throughout the batholith, biotite whole-rock ages areconsistently younger than muscovite whole-rock ages, whichare in turn younger than SHRIMP ages, reflecting the lowerclosure temperatures for the differing minerals and isotopesystems. In the absence of geological control and other moreaccurate geochronological data, the biotite whole-rockisochrons for Jays Creek Granodiorite, Pah Point Granite,and Turiwhate Granodiorite are taken to represent minimumestimates of their crystallisation ages, and are within errorof the other mid-Cretaceous plutons of the Hohonu Batholith.The biotite whole-rock age of 106.4 ± 2.0 Ma for TuriwhateGranodiorite is similar to a conventional U-Pb zircon ageon this unit of 111+2 Ma (A. J. Tulloch pers. comm. 1994).An advantage of SHRIMP dating over conventional U-Pbdating is that it is possible to identify and exclude inheritedcomponents from the age calculation. The I-type, relativelymafic nature of the Turiwhate Granodiorite suggests zirconinheritance should be minor, as in the other relatively maficplutons of the batholith, and the conventional U-Pb zirconage is therefore probably an accurate reflection ofcrystallisation age. Considerably younger Cretaceous micawhole-rock ages (67.1 + 2.0 Ma and 99.7 ± 2.0 Ma) for thePaleozoic Summit Granite are likely to represent resettingduring emplacement of the mid-Cretaceous DeutgamGranodiorite and Turiwhate Granodiorite. Similarly, theyoung biotite whole-rock age of 73.6 ± 2.0 Ma from amylonitised sample of Te Kinga Monzogranite near theAlpine Fault indicates partial resetting, probably as aconsequence of protomylonitic deformation duringmovement on the Alpine Fault. A similar biotite K-Ar ageof 72 ± 4 Ma* was presented by Hurley et al. (1962) and islikely to reflect argon loss and partial resetting associatedwith this deformation. Temperatures reached duringmylonitic deformation were obviously not high enough toreset the muscovite Rb-Sr system, which yields an agesimilar to that generated by SHRIMP analysis.

•Recalculated to conventional decay constants using tables inHarlandetal. (1990).

DISCUSSION

Geochronological data confirm field and geochemicalrelationships (Waight 1995a) and indicate three discreteepisodes of granitic magmatism in the Hohonu Batholith.The age of the oldest pluton, Summit Granite, is the samewithin error as the restricted range of ages (375 + 5 Ma)obtained for the Karamea Batholith and related plutons inWestland and northwest Nelson (Muir et al. 1996). The two-mica, peraluminous S-type nature of Summit Granite(Waight 1995a) also correlates strongly with the PaleozoicS-type Karamea Suite of Tulloch (1983a, 1988). NewZealand Devonian granitoids are part of a more widespreadepisode of plutonism recognised throughout the Gond-wanaland margin in Australia (the Lachlan Fold Belt andnortheast Tasmania) and West Antarctica (Ford Granodioriteof Marie Byrd Land and the Admiralty Intrusives of NorthernVictoria Land) (Muir et al. 1996). Summit Granite hassubsequently been intruded by Cretaceous plutons of theHohonu Batholith. No geochronological data wereobtained for the poorly exposed Mt Graham Granite, butisotopic, petrographic, and geochemical similaritiessuggest this pluton also belongs within the PaleozoicKaramea Suite.

French Creek Granite represents the only known LateCretaceous felsic plutonism in the Western Province. LateCretaceous alkaline, mafic to felsic extensional magmatismis relatively widespread in the Eastern Province and probablyrelated to New Zealand -Antarctica breakup (e.g., Weaver&Pankhurst 1991). The81.7± 1.8 Ma age for French CreekGranite has important tectonic implications, as discussed byTulloch et al. (1994). Geological evidence demonstrates thatFrench Creek Granite is contemporaneous with late membersof the Hohonu Dike Swarm. Orientation data from the dikeswarm indicate the dikes were emplaced in a strongly NNE—SSW extensional environment (Waight 1994, 1995a). Thisextension direction is approximately perpendicular to theline of opening of the Tasman Sea, and the Late Cretaceousage of the French Creek Granite also coincides remarkablywell with the oldest known oceanic crust in the Tasman Sea

Table 1 Summary of geochronological data for Hohonu Batholith granitoids. Errors on SHRIMP dataare 2 standard errors of the mean and on Rb-Sr data are 2 SD. Methods: Bt-WR and Mv-WR = micawhole-rock 2 point Rb-Sr isochron, SHRIMP = SHRIMP U-Pb zircon age.

Unit

Jays Creek GranodioritePah Point GraniteUncle Bay Tonalite

Te Kinga Monzogranite

Deutgam Granodiorite

French Creek Granite

Summit Granite

Turiwhate GranodioriteArahura Granite

Sample

UOC 14932UOC 14940UOC 14969UOC 14969UOC 14948UOC 14948UOC 14948Rb-Sr wholeUOC 15003UOC 15003Rb-Sr wholeUOC 14881UOC 14874UOC 14834UOC 14834UOC 14841UOC 14849UOC 14910UOC 14921

Grid reference

K32 883143K32 846422K32 833371K32 833371K32 849337K32 849337K32 849337

rock errorchronK32 815383K32 815383

rock errorchronK32717353K32 751838K33 709255K33 709255K33 702253J33 123559J33 646264J33 639200

Method

Bt-WRBt-WRBt-WRSHRIMPBt-WRMv-WRSHRIMP

Bt-WrSHRIMP

Bt-WRSHRIMPBt-WRMv-WRSHRIMPBt-WRBt-WRSHRIMP

Age ± 2 SD (Ma)

109.2 ±2.0110.1 ±2.095.7 + 2.0

113.5 ± 1.973.6 ±2.0

104.0 ± 2.0108.7 ±3.0110.9 ±2.8101.6 ±2.0110.4 ±2.2

88 ±8.670.3 ±2.081.7 ± 1.867.1 ±2.099.7 ± 2.0

381.2 ±7.3106.4 ±2.0104.1 ±2.0109.0 ±2.2

10 New Zealand Journal of Geology and Geophysics, 1997, Vol. 40

(Chron 33 at c. 82 Ma) (Weissel & Hayes 1977; Stock &Molnar 1982; Tulloch et al. 1994). The geochemistry of boththe Hohonu Dike Swarm and French Creek Granite is alsoconsistent with generation in an extensional, within-plate,anorogenic environment (Waight 1994,1995a) typical of thatlikely to characterise the final stages of breakup of a crustalblock such as New Zealand - Australia. Chron 33 is somedistance from the edge of the continental crust, andseparation must have occurred some time before 82 Ma,possibly as early as 90 Ma (e.g., Lawver & Gahagan 1994).It is therefore improbable that French Creek Granite

represents the actual initiation of continental rifting, and itmay represent OIB-like extensional magmatism postdatingcontinental separation of Australia and New Zealand. Tullocli(1988) suggested that A-type granitoids in the HohonuBatholith represent a distinct suite, and the term FrenchCreek Suite is proposed (Waight 1995a).

The remaining plutons of the Hohonu Batholith reflecta chronologically restricted pulse of mid-Cretaceou;«magmatism at c. 110 Ma. Similar ages have been determinedfor plutons belonging to the Rahu Suite of Tulloch (1988).with which the Hohonu Batholith has previously been

Table 2 U-Pb analyses of zircons: Hohonu Batholith.

Sample U (ppm) Th (ppm)

Uncle Bay Tonalite (UOC 14969)1.12.13.14.15.16.17.18.19.110.111.112.113.114.115.116.117.1Summit1.12.13.14.15.16.17.18.19.110.111.112.113.114.115.116.117.118.1Arahura1.12.13.14.15.16.17.18.19.110.111.112.113.114.115.1

13154301210257433538972663436306122693013151336144611901009

Granite681196260143

2413151660821511122822939422801576728405980331

Granite402359199762052441633126176927213981398588222251391

683216594162154281495420230182834169421758335198492

(UOC 14834)13595134658628884851667022215917177488382343220

(UOC 14910)249226153697615975773016983467750443447303

204pb/206pb

<0.000070.00023 ± 0.00013

O.000100.00126 ± 0.00056

<0.000340.00108 ± 0.000330.00006 + 0.000070.00037+ 0.00017

<0.000380.00077 ± 0.000310.00015 ± 0.000080.00060 + 0.000200.00029 ± 0.00012

<0.000640.00017+ 0.000120.00029+ 0.00011

<0.00012

0.00013 + 0.000030.00008 ± 0.000030.00002 ± 0.00001

<0.00002<0.000020.00011 ± 0.00003

<0.000040.00020 + 0.000060.00005 ± 0.000010.00008 ± 0.000030.00008 + 0.00003

<0.000020.00020 ± 0.000180.00004 + 0.00002

O.000020.00002 ± 0.000020.00003 + 0.000030.00023 + 0.00019

0.00043 1 0.000150.00091 ± 0.000390.00057 ± 0.000220.00029+ 0.00015

<0.000360.00026 ± 0.000080.00001 ± 0.00002

<0.00003O.000020.00024 ± 0.000080.00011 + 0.000040.00004 ± 0.000010.00001 ± 0.00001

<0.000020.00005 ± 0.00003

207pb/206pb

0.0487 + 0.00100.0524 + 0.00140.0485 ± 0.00080.0556 + 0.00200.0523 ±0.00130.0523+0.00130.0486 ± 0.00090.0463 ± 0.00120.0494 ±0.00210.0547 ±0.00170.0490 + 0.00100.0488 ±0.00100.0491 ±0.00100.0496 + 0.00080.0481 ±0.00080.0498 + 0.00140.0478 ±0.0011

0.0562 ± 0.00080.0539 ± 0.00080.0575+0.00100.0542 + 0.00080.0540 ± 0.00080.0520 ± 0.00070.0537 ± 0.00080.0551 ±0.00070.0546 ± 0.00050.0713 ±0.00080.0588 ± 0.00080.1199 ±0.00120.0549 ± 0.00070.0536 ± 0.00050.0555 ± 0.00040.0557 + 0.00050.0539 + 0.00100.0540 ± 0.0006

0.0493 ± 0.00090.0494 ± 0.00090.0527 ± 0.00200.0524 ± 0.00200.0521 ±0.00120.0497 + 0.00120.0485 ± 0.00040.0483 ± 0.00050.0749 ± 0.00050.0475+0.00190.0496 ± 0.00040.0477 ± 0.00040.0542 ± 0.00020.0480 ± 0.00070.0487 ± 0.0007

238TJ/206pb

57.46 ± 1.3957.69 ± 1.5155.24 ± 1.2059.54 ± 1.6156.06 + 1.3555.47 ± 1.2754.06 ±1.4255.87 ± 1.3256.71 ± 1.5455.81 ± 1.6154.75 ±1.2057.54 ± 1.3454.66 ±1.2156.12 + 1.7855.77 ±1.2258.84 ±2.1756.42 ±1.76

18.18 ±0.4116.20 ± 0.3511.90 ±0.2616.29 ±0.3915.16 ±0.3337.35 ±0.9119.67 ±0.4216.78 ±0.3616.40 ± 0.346.77 ±0.1712.03 ± 0.332.87 ±0.0615.88 ±0.3417.06 ±0.3516.06 ±0.3316.36 ±0.3416.29 ±0.3516.65 ±0.36

58.53 ±1.2558.04 ± 1.3859.40 ± 1.4955.56 ±1.4859.57 ± 1.4558.32 ± 1.2756.83 ±1.1557.43 ±1.216.02 ±0.1261.32 + 1.4759.04 ± 1.4258.73 + 1.2017.48 ±0.3759.50 + 1.2658.83 ± 1.22

Age (Ma)1

111.2 ±2.7110.3 ±2.9115.6 ±2.5106.5 ±2.9113.5 ±2.7114.7+2.6118.1 ±3.1114.6 ±2.7112.5 ±3.0113.7 ±3.3116.6 ±2.5111.0 ±2.6116.8 ±2.6113.7 ± 3.6114.6 ±2.5108.4 ±4.0113.3 ±3.5

344.3 ± 7.52

386.2 ± 8.0518.4+ 10.'7:

384.1 ±8.9411.8 ±8.72

170.7 ±4.12

319.8 ±6.72

372.7 ±7.8381.4 ±7.6872.8 ± 20.92

512.2 ± 13.5:;

1806.2 ±33.6:'393.4 ±8.1367.4 ± 7.3388.8 ±7.7381.9 ±7.8384.1 ±8.0376.0 ± 7.8

109.1 ±2.3110.0 ±2.6107.1 ±2.7114.5 + 3106.9 ±2.6109.4 ±2.4112.4 ±2.3111.3 ± 2.3963.5 ± 18.5:

104.4 ± 2.5108.1 ±2.6108.9 ±2.2356.3 ± 7.42

107.5 ±2.3108.6 ±2.3

(continued)

Waight et al.—Geochronology of Hohonu Batholith 11

correlated, namely Buckland Granite (109.6 ±1 .7 Ma(SHRIMP); Muir et al. 1994) in the Paparoa Batholith,several plutons in the Victoria Range (106-96 Ma (K-Ar);Tulloch 1979a), and the Berlins Quartz Porphyry (111.0 ±2.0 Ma (SHRIMP); Muir et al. unpubl. data 1994) (seeFig. 2). Although the Hohonu plutons postdate emplacementof the bulk of the Separation Point Batholith (Muir et al.1994, 1995), the age of the Olympus Granite (111.4 ±2.0 Ma; Muir et al. 1994) (Fig. 2) indicates that magmatismof Separation Point Suite composition was also occurringcontemporaneously with Hohonu Batholith magmatism.

Geochemical and petrological data indicate the mid-Cretaceous plutons of the Hohonu Batholith can be groupedinto two related suites (Waight 1995a, b; Waight et al. inpress). The Te Kinga Suite includes the Te KingaMonzogranite and Arahura Granite and comprises weaklyperaluminous, muscovite-biotite, HREE depleted monzo-granites that are ambiguous in terms of I-S-type criteria. TheDeutgam Suite (Jays Creek Granodiorite, Pah Point Granite,Uncle Bay Tonalite, Deutgam Granodiorite, TuriwhateGranodiorite) is characterised by metaluminous, hornblende-biotite tonalitic to granodioritic I-type granitoids with flat

Table 2 (continued)

Sample U (ppm)

Te Kinga1.12.13.14.15.16.17.18.19.110.111.112.113.114.115.116.11.7.118.119.120.1Deutgam1.12.13.14.15.16.17.18.19.110.111.112.113.114.1

Th (ppm)

Monzogranite (UOC 14948)21795342811957237028440668716214157213494

167634224616381294229712

182732583284031157733473483184355236941381036316

Granodiorite (UOC 15003)5812573543423555705411413372693557419553484

2261601461311534442751015261402328282159263

French Creek Granite (UOC 14874)1.12.13.14.15.16.17.18.19.110.111.112.113.114.115.1

14110297977004431066523608861633128762410814941096

71516664320193549231237545323545276504195252

204pb/206pb

0.00012 + 0.000080.00121 ± 0.000700.00012 ± 0.00009

>0.000700.00036 ± 0.000170.00178 ± 0.001130.00060 ± 0.000350.00034 ± 0.000310.00004 ± 0.000030.00020 ± 0.000100.00019+ 0.00015

<0.003820.00339 ± 0.002440.00002 ± 0.000020.00080 ± 0.00052

O.001380.00016 ± 0.00007

<0.000270.00232 ± 0.001830.00023 ± 0.00016

0.00074 ± 0.000240.00060 ± 0.000250.00055 ± 0.000420.00048 ± 0.000370.00070 ± 0.000290.00003 + 0.000030.00053 ± 0.00021

O.00010<0.000700.00013 1 0.000070.00022 ± 0.00018

O.003620.00001 + 0.000010.00004 ± 0.00003

0.00797 ± 0.002090.00059 ± 0.000160.00071 ± 0.000180.00035 ± 0.000130.00412 ± 0.000820.00099 ± 0.000210.00056 ± 0.000200.00043+ 0.000110.00098 ± 0.000210.00133 ± 0.000390.00142 ± 0.000430.00131 ± 0.000380.00126 + 0.000380.00048 ± 0.000170.00161 + 0.00026

207pb/206pb

0.0597 ±0.00130.0518 + 0.00250.0712 + 0.00210.0496 ±0.00150.0496 ±0.00120.0531 ±0.00230.0572 + 0.00300.0673 ± 0.00350.0580 ± 0.00060.0739 ±0.00160.0634 + 0.00260.0582 + 0.00330.0630 ± 0.00430.0493 ±0.00120.0500 ± 0.00200.0506 ± 0.00230.0536 ± 0.00070.0523 ±0.00130.0527 ± 0.00250.0592 ± 0.0009

0.0503 ± 0.00190.0509 ± 0.00170.0482 ± 0.00220.0501 ±0.00150.0497 ± 0.00200.0505 ± 0.00200.0522 ± 0.00190.0480 ± 0.00090.0489 ±0.00210.0496 ±0.00160.0510 + 0.00120.0474 ± 0.00220.0540 ± 0.00090.0526 ±0.0014

0.1214 ±0.00440.0590 ±0.00100.0637 + 0.00120.0593 ±0.00170.0986 ± 0.00320.0585 ± 0.00100.0700 ± 0.00250.0614 ±0.00160.0604 ± 0.00120.0586 ± 0.00150.0663 ±0.00110.0738 ± 0.00220.0656 ±0.00120.0653 ± 0.00220.0618 ±0.0012

238TJ/206pb

33.52 ± 1.2959.66 ±1.686.54 ± 0.2061.25 ± 1.5657.80 ± 1.3657.62 ±1.6325.30 ±0.808.53 ±0.2612.23 ± 0.266.78 + 0.1710.42 ± 0.3258.24 ±2.1658.96 ±2.856.42 ± 1.3556.20 + 1.5957.08 + 1.6516.72 ±0.3641.07 ± 1.0463.17 ± 1.8814.34 ± 0.47

59.04 ± 1.4958.94 ± 1.5259.44 ± 1.9657.24 ± 1.6757.57 ± 1.5158.19 ±2.1558.89 ±2.1656.4 ± 1.7154.52 ± 1.5157.55 ± 1.4758.73 ± 1.3457.19 ± 1.6034.84 ± 0.7650.58 ± 1.39

72.05 + 2.2078.18 ± 1.9777.53 ± 1.9580.40+ 1.9171.88 ± 1.9176.38 ± 1.6876.66 ± 2.0581.72 ±2.1576.87 ±1.8573.48 ± 1.7280.25 ± 1.9373.80+ 1.9674.52 ± 1.6574.88 ±2.0178.81 ±2.11

Age (Ma)1

187.1 +7.12

106.8 ±3.0985.4 ±25.72

104.2 ±2.6110.4 ±2.6110.3 ±3.1247.5 + 7.72

700.5 ± 20.2501.4 ± 10.32

863.8 ±20.22

581.5 ±17.42

108.6 + 4.0106.7 ±5.1113.1 +2.7113.5 ±3.2111.7 ± 3.2372.4 ± 7.92

154.4 ± 3.92

100.8 ±3.0429.5 ± 13.62

108.0 + 2.7108.1 ±2.8107.5 ±3.5111.4 ±3.2110.8 ±2.9109.6 ±4.0108.1 ±4.0114.0 + 3.5117.1 +3.2110.9 ±2.8108.5 ±2.5111.8 ± 3.1181.3 ±3.92

125.6 ±3.42

81.7 ±2.580.9 ± 2.081.2 ±2.078.7 ± 1.984.1 ±2.282.9 ± 1.881.5 ±2.277.2 + 2.082.2 ±2.086.1 ±2.078.2 ± 1.984.3 ± 2.284.3 ± 1.983.9 ±2.280.0 ±2.1

1 206pb/238Tj a g e b a s e d o n 207Pb/206pb c o m m o n p b correction.2 Age not used in age calculation due to lead loss or inherited grain.


HREE patterns. A detailed account of the geochemistry andpetrogenesis of these two granitoid suites is beyond the scopeof this paper and is presented elsewhere (Waight et al. inpress). The Deutgam and Te Kinga Suites are isotopicallyand chronologically identical, and the limited published dataavailable suggest correlation with the Rahu Suite of Tulloch(1988). Chemical and isotopic compositions of the mid-Cretaceous granitoids of the Hohonu Batholith are consistentwith mixing of a depleted mantle component similar incomposition to the Separation Point Batholith and GreenlandGroup sediments (Waight et al. in press). The identificationof two distinct suites or subsuites within the Rahu Suiteindicate that the current terminology for mid-Cretaceousgranitoids in the Western Province of New Zealand needsrefinement. If the term Rahu Suite is to be retained it musteither become a supersuite, or be subdivided into a numberof subsuites. The type granitoids of the Rahu Suite from theVictoria Range (Tulloch 1979a) lack the detailed isotopic,geochemical, and geochronological control which haveenabled the recognition of two distinct mid-Cretaceous suitesin the Hohonu Batholith. Further work is therefore requiredto establish the nature and affinities of the Rahu Suite plutonsof the Victoria Range and Paparoa Range.

A detailed discussion of the tectonic setting of the mid-Cretaceous Hohonu Batholith is presented in Waight et al.(in press) and only a brief discussion is given here. Previousstudies have suggested that mid-Cretaceous plutonism in theBuller Terrane represents typical calc-alkaline granitoid

melts generated above a westward-dipping subduction zone(Tulloch 1983a, 1988). However, the recognised Mesozoicsubduction systems in New Zealand are either too old (e.g.,MTZ subduction zone) or too distant (e.g., Pacific-Phoenixplate subduction zone) to be directly involved in productionof the Hohonu Batholith. The mid-Cretaceous granitoids ofthe Hohonu Batholith and the Rahu Suite overlap spatiallvand temporally with other geological features, indicative ofa major change in tectonic environment in the WesternProvince, from a convergent tectonic setting to anextensional setting, which ultimately culminated in theseparation of Australia and New Zealand (Laird 1994). TheBuckland Granite is intimately associated with the mid-Cretaceous Paparoa Metamorphic Core Complex (Tulloch& Kimbrough 1989) and extensional basins of the PororanGroup (Laird 1988; Tulloch & Palmer 1990). A model ispresented by Waight et al. (in press) in which the mid-Cretaceous plutons of the Hohonu Batholith and Rahu Suitewere generated during a major change from continentalthickening to crustal extension in the Western Province, aconcept previously considered briefly by Tulloch (1983b).Before mid-Cretaceous plutonism the continental crust ofthe Western Province was overthickened during collision ofthe Median Tectonic Zone, resulting in generation of theNa-rich "adakitic" compositions of the Separation PointBatholith (Muir et al. 1995). Extension in the WesternProvince was initiated during thermal relaxation of thepreviously overthickened continental crust and its rapid uplift

Table 3 Rb-Sr data used in the calculation of Rb-Sr whole-rock errorchrons and whole-rock mica Rb-Sr ages. Bt = biotite separate, Mv = muscovite separate, dup = duplicate analysis of a separate powdersplit.

Unit

Jays Creek Granodiorite

Pah Point Granite

Uncle Bay Tonalite

Te Kinga Monzogranite


Turiwhate Granodiorite

Arahura Granite

French Creek Granite

Summit Granite

Sample

UOC 14932(bt)UOC 14932UOC 14940(bt)UOC 14940UOC 14969(bt)UOC 14969UOC 14948(mv)UOC 14948(bt)UOC 14948UOC 15003(bt)UOC 15003UOC 15003(dup)UOC 15011UOC 15015UOC 15018UOC 14995UOC 15006UOC 14849(bt)UOC 14849UOC 14910(bt)UOC 14910UOC 14881(bt)UOC 14881UOC 14874UOC 14874(dup)UOC 14872UOC 14884UOC 14878UOC 14879UOC 14834(bt)UOC 14834(mv)UOC 14834

Rb (ppm)

791.6172

1000206

570.5143

387.8686.5

109619.8

137137114112106161197

693.1180

688.1192

29.47213218210158244228198

1435632229

Sr (ppm)

20.651474

10.55293

28.95537

69.7137.42

78717.15

53653663551926821245

71.72548

50.82556

15.2243.1

3331.410.545.935.779.12.276.7061.4

87Rb/86Sr

112.541.050

285.752.034

57.320.7706

16.09553.2340.4007

105.890.73960.73960.51950.62451.0362.198

12.69128.0020.9505

39.3060.99925.595

14.28119.15919.34943.47915.39118.4657.243

2214.1284.3

10.858

87Sr/86Sr

0.882000.709071.155380.711320.786050.709130.729990.762030.706790.860930.709060.709140.709070.709090.709910.711410.728100.749640.708760.765600.708910.713890.722560.732450.732560.760560.724580.728320.715262.873031.160440.77315


0.10

0.09

P 0.08

13

£j 0.07.QQ_ 0.06

w 0.05

0.04

0.03

Uncle Bay Tonalite113.5 ±1.9 Ma (2aJ(17 points; x 2 = 1.1)

S

0.10

0.04

Summit Granite381.2 ±7.3 Ma (2a J(10 points; x2 = 1-0)

30 40 50 60

70 80 15 17 19 21 23 25

.aQ.

Q.

CO

JOQ.tooJBQ.oCM

0.10

0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.10

0.09

0.08

0.07

0.06

0.05

DeutgamGranite110.4 ±2.2 Ma (2a J

(12 points; x2 = 0.8)

0.15

0.13

0.11

0.09

0.07

0.05

30 40 50 60 70 800.03

\ French Creek GraniteV 81.711.8 Ma (2<y

\(15 points; x 2 = 1-6)

:S oo

40 60 80 100 120 140

0.04

0.03

Te Kinga Monzogranite108.7 ±3.0 Ma (2am)(10 points; X2= 1.9)\

8.CM

0.10

0.09

0.08

0.07

0.06

0.05

0.04

0.03

ArahuraGranite ,'109.0 ±2.2 Ma (2a „) \(13 points; x 2 = 1.0)

8LCM

s 8

30 40 50 60

238U/206Pb

70 80 30 40 50 60

238 U/206 Pb70 80

Fig. 4 Tera-Wasserburg U-Pb zircon concordia diagrams for Hohonu Batholith granitoids. The dashed line represents a mixing linebetween Broken Hill common Pb and the calculated 238U/206Pb age; all analyses should lie close to this line. Outliers not used in theage calculation (shown as open circles) which lie to the left of the mixing line (e.g., Te Kinga Monzogranite) are considered to representinherited grains, whereas those which lie to the right (e.g., Summit Granite) are considered to have undergone Pb loss. All data areplotted using uncorrected Pb compositions.

and extension, possibly associated with the removal ofcompressive forces following cessation of subduction alongthe Pacific margin of Gondwanaland at c. 105 + 5 Ma(Bradshaw 1989). Rapid uplift resulted in adiabatic meltingof the lower crust and underlying mantle to produce thegranitic melts which formed the main phase of magmatismin the Hohonu Batholith at c. 110 Ma (Waight 1995a, b;Waight et al. in press).

Given the conclusions on emplacement depth providedby textural and Al-in hornblende geobarometry, and thecooling history derived from Rb-Sr and fission track data, itis possible to make some comments regarding the uplift/cooling history of the Hohonu Batholith (Fig. 7). Geo-barometric studies indicate at least some of the mid-Cretaceous plutons of the Hohonu Batholith were emplacedat 4 kbar (12 km). Intrusion of French Creek Granite at

14 New Zealand Journal of Geology and Geophysics, 1997, Vol 40

0.74

0.73 -

cj)_0.72

0.71 -

0.70


Age = 110.9 ±2.8Initial = 0.70808 ±MSWD = 20.7

: n = 7

•

Ma (2SD)19(2SD)

0.9

0.8

0.7

0.6D 50 100 150

5 1087Rb/86Sr ( rT l )

15

Fig. 5 Rb-Sr whole-rock errorchron for Deutgam Granodiorite.Data from a biotite separate from sample HRS12 (UOC 15003)do not fit on the errorchron and were not used in the age calculation(inset).

1000n

800-

oo

3re

: 400-

200

O Upl

ift a

t

•a3

"5.

Alp

i

I U-Pb zircon

Zircon fission track

Apatite fission track

120 100 80 60 40

Age (Ma)20

Fig. 7 Schematic diagram indicating uplift/cooling history of theHohonu Batholith as constrained by closure temperatures ofvarious geochronological systems.

French Creek Granite0.78

0.77

0.76

0.75

E 0.74

COCD 0.73

0.72

0.69

0.68

All analyses. Age = 88 ± 8.6 Ma (2SD)

Initial = 0.7063 ± 25 (2SD)MSWD = 547

. n = 8Excluding EHR17Age = 88 ± 5.8 Ma (2SD)Initial = 0.7058 ± 18 (2SD)MSWD = 230n = 6

10 20 30

87R b /86sr ( m )

40 50

Fig. 6 Rb-Sr whole-rock errorchron for French Creek Granite.The first age includes all available data, the second excludesreplicate analyses of EHR17 (UOC 14874) and gives a smaller,yet still unacceptable MSWD.

relatively shallow, subcrustal conditions (1 kbar, c. 3 km)at 82 Ma indicates the region had undergone c. 9 km of upliftover a period of 30 Ma, probably associated with extensionalevents during generation of the mid-Cretaceous granitoidsand the opening of the Tasman Sea. Biotite and muscoviteRb-Sr ages consistently younger than U-Pb crystallisationages are also compatible with uplift and cooling between110 and 82 Ma. Whether the batholith was actually exposedby erosion during this time is debatable, although Pororari

Group conglomerates and Paparoa Coal Measures containingabundant granitoid and Greenland Group clasts are foundimmediately to the west of the Hohonu Batholith (Nathanet al. 1986). Zircon fission track ages from granitoids of theHohonu Batholith mostly range from 57.3 ± 5.8 Ma to 9 3+ 1.5 Ma and are interpreted to represent burial and partialto complete annealing in the middle to lower parts of thezircon annealing zone before late Cenozoic uplift (Kamp etal. 1992). Granitoid massifs unconformably overlain byTertiary sediments to the south (e.g., Mt Rangitoto; Warren1967) indicate that once-exposed granitoids were reburiedduring the ensuing Tertiary marine transgression. Evidencefor reburial of the Hohonu Batholith plutons is also givenby the variable textures observed in the Te KingaMonzogranite. Porphyritic textures on the summit of Mt TeKinga suggest rapid crystallisation and emplacement atrelatively shallow depths in the crust. This is in contrast tothe strong mylonitic fabrics present along the southwestmargin of Mt Te Kinga, which indicate deformation at mid-crustal conditions, and suggest reburial before Cenozoicuplift along the Alpine Fault. Apatite fission track ages fromthe Hohonu Batholith (White & Green 1986; Seward 1989;Kamp et al. 1992; Spanninga 1993) range in age from 10.8± 11 Ma to 1.6 + 0.9 Ma. As has been shown in the WesternProvince in general, ages decrease towards the Alpine Faultand are consistent with burial in the Cenozoic and recentuplift through the apatite annealing zone in association withlate Cenozoic compression across the Alpine Fault (Kampetal. 1992).

SUMMARY AND CONCLUSIONS

Geological mapping in the Hohonu Batholith has identified10 distinct plutonic phases intruding Ordovician GreenlandGroup metasedimentary rocks. Three magmatic episodes


have been recognised using ion-microprobe (SHRIMP) massspectrometry and Rb-Sr geochronology. The Summit Graniterepresents the oldest igneous activity in the batholith,emplaced at 381.2 ± 7.2 Ma, contemporaneous with a majorpulse of granitoid magmatism in the Karamea Batholith(Muir et al. 1996). The Late Devonian age and S-typecharacter of Summit Granite indicate affinities with theKaramea Suite of Tulloch (1988). The as yet undated MtGraham Granite is chemically and lithologically similar toSummit Granite and is probably also Paleozoic in age andrelated to the Karamea Suite.

The main episode of magmatism in the Hohonu Batholithoccurred between 114 and 109 Ma and is represented byseven plutons. Emplacement of these granitoids follows amajor crustal thickening event and occurred pene-contemporaneously with the onset of a major extensionalevent in the Western Province of New Zealand, marked bythe formation of the Paparoa Metamorphic Core Complexand extensional basins of the Pororari Group. Extension isbelieved to be due to rapid thinning of thermally relaxedcontinental crust (Waight 1995a, b; Waight et al. in press)previously overthickened during collision of the MedianTectonic Zone with the Western Province and consequentgeneration of the Separation Point Suite (Muir et al. 1995).Recognition of two distinct, yet related, I-type suites (Waightet al. in press) within granitoids previously considered tobelong to the Rahu Suite (Tulloch 1988) indicates that theterm Rahu Suite needs to be used with caution, pending morecomprehensive isotopic and geochronological data from thetype plutons of the Rahu Suite in the Victoria Range andPaparoa Batholith. Potential modifications to the nomen-clature include: elevating the Rahu Suite to supersuite status;renaming the Hohonu Batholith suites as subsuites; ordropping the term Rahu Suite entirely.

The name French Creek Suite is proposed for the LateCretaceous (82 Ma) French Creek Granite, a typical A-typegranitoid. Field evidence indicates that the intrusion of thispluton was coeval with at least part of the Hohonu DikeSwarm, a predominantly doleritic to lamprophyric swarmconcentrated on the Hohonu Range and Mt Te Kinga. Thepredominant orientation of the Hohonu Dike Swarm suggestscrustal extension orientations consistent with those generatedduring opening of the Tasman Sea. Furthermore, thegeochemistry of both the French Creek Granite and theHohonu Dike Swarm is consistent with generation inanorogenic rifting environments. The Late Cretaceous ageof French Creek Granite (and by inference the Hohonu DikeSwarm) coincides with the oldest known oceanic crust inthe Tasman Sea, and indicates that the Late Cretaceousmagmatism preserved in the Hohonu Batholith can beconfidently linked to tectonic conditions present followingthe opening of the Tasman Sea.

Textural features of the French Creek Granite indicate itintruded the mid-Cretaceous plutons at relatively shallowlevels in the crust. Consequently, the Hohonu Batholith musthave been uplifted from initial emplacement depths ofc. 12 km for the mid-Cretaceous plutons to c. 3 km over theintervening 30 Ma. Such an uplift history is compatible withthe cooling indicated by Rb-Sr mica ages. It is probable thatthe whole region then underwent subsidence during thefollowing Tertiary marine transgression before recentrapid uplift during late Cenozoic movement on the AlpineFault.

ACKNOWLEDGMENTS

This paper represents part of a Ph.D. thesis by the principal authorfunded by a NZVCC scholarship at the University of Canterbury.The costs of field and laboratory work were partially funded bythe Mason Trust and a University of Canterbury research grant.Andy Tulloch is thanked for access to his unpublished field sheetsand U-Pb ages, and for constructive discussions while this studyprogressed. TEW would like to thank S. Waight, S. Baldwin, A.Dean, and R. Gerstenberger for field assistance and M. Meatesfor helicopter support. Y. Kawachi, Otago University, is thankedfor assistance with microprobe analyses. SDW, RJM, and DSgratefully acknowledge the funding of the "New Zealand Granitesand Crustal Evolution" programme by the Foundation for ResearchScience and Technology under contract UOC313. J. Bradshaw, A.Tulloch, S. Ward, S. Claus, and an anonymous reviewer are thankedfor helpful comments on the paper.

REFERENCES

Adams, C. J. 1975: Discovery of Precambrian rocks in NewZealand: age relations of the Greenland Group andConstant Gneiss, Westland. Earth and planetary scienceletters 28: 98-104.

Adams, C. J.; Nathan, S. 1978: Cretaceous chronology of theLower Buller Valley, South Island, New Zealand. NewZealand journal of geology and geophysics 18: 39-48.

Adams, C. J.; Seward, D.; Weaver, S. D. 1995: Geochronology ofCretaceous granites and metasedimentary basement onEdward Vll Peninsula, Marie Byrd Land, West Antarctica.Antarctic science 7: 265-277.

Bradshaw, J. D. 1989: Cretaceous geotectonic patterns in NewZealand. Tectonics 8: 803-820.

Bradshaw, J. D. 1993: A review of the Median Tectonic Zone:terrane boundaries and terrane amalgamation near theMedian Tectonic Line. New Zealand journal of geologyand geophysics 36: 117—125.

Chappell, B. W.; White, A. J. R. 1992: I- and S-type granites inthe Lachlan Fold Belt. Transactions of the Royal Societyof Edinburgh earth sciences 83: 1—26.

Cooper, A. F.; Barreiro, B. A.; Kimbrough, D. L.; Martinson, J.M. 1987: Lamprophyre dike intrusion and the age of theAlpine Fault, New Zealand. Geology 15: 941—944.

Cooper, R. A. 1979: Lower Paleozoic rocks of New Zealand.Journal of The Royal Society of New Zealand 9: 29—84.

Cooper, R. A. 1989: Early Paleozoic terranes of New Zealand.Journal of The Royal Society of New Zealand 19: 73—112.

Cooper, R. A.; Tulloch, A. J. 1992: Early Paleozoic terranes inNew Zealand and their relationship to the Lachlan FoldBelt. Tectonophysics 214: 129-144.

Eby, G. N. 1990: The A-type granitoids: a review of theiroccurrence and chemical characteristics and speculationson their petrogenesis. Lithos 26: 115-134.

Hamill, L. J. 1972: The geology of the western Hohonu Ranges,North Westland, New Zealand. Unpublished B.Sc. (Hons)project, lodged in the Library, University of Otago,Dunedin, New Zealand.

Harland, W. B.; Armstrong, R. L.; Cox, A. V.; Craig, L. E.; Smith,A. G.; Smith, D. G. 1990: A geologic time scale 1989.Cambridge, Melbourne, Cambridge University Press.263 p.

Hurley, P. M.; Hughes, H.; Pinson, W. H.; Fairbairn, H. W. 1962:Radiogenic argon and strontium diffusion parameters inbiotite at low temperatures obtained from Alpine Faultuplift in New Zealand. Geochimica et cosmochimica acta26: 67-80.


Ireland, T. R. 1992: Crustal evolution of New Zealand: evidencefrom age distributions of detrital zircons in WesternProvince paragneisses and Torlesse greywacke.Geochimica et cosmochimica acta 56: 911—920.

Kamp, P. J. J. 1986: Late Cretaceous-Cenozoic tectonicdevelopment of the southwest Pacific region. Tectono-physics 121:225-251.

Kamp, P. J. J.; Green, P. R; Tippet, J. M. 1992: Tectonic architectureof the mountain front-foreland basin transition, SouthIsland, New Zealand, assessed by fission track analysis.Tectonics 11: 98-113.

Kimbrough, D. L.; Tulloch, A. J. 1989: Early Cretaceous age oforthogneiss from the Charleston Metamorphic Group, NewZealand. Earth and planetary science letters 95: 130-140.

Kimbrough, D. L.; Tulloch, A. J.; Geary, E.; Coombs, D. S.; Landis,C. A. 1993: Isotopic ages from the Nelson region of theSouth Island, New Zealand: crustal structure and definitionof the Median Tectonic Zone. Tectonophysics 225:433-448.

Kimbrough, D. L.; Tulloch, A. J.; Coombs, D. S.; Landis, C. A.;Johnston, M. R.; Mattinson, J. M. 1994a: Uranium-leadzircon ages from the Median Tectonic Zone, South Island,New Zealand. New Zealand journal of geology andgeophysics 37: 393^119.

Kimbrough, D. L.; Tulloch, A. J.; Rattenbury, M. S. 1994b: LateJurassic—Early Cretaceous metamorphic age of FraserComplex migmatite, Westland, New Zealand. New Zealandjournal of geology and geophysics 37: 137—142.

Laird, M. G. 1972: Sedimentology of the Greenland Group in thePaparoa Range, West Coast, South Island. New Zealandjournal of geology and geophysics 15: 372—393.

Laird, M. G. 1988: Sheet S37—Punakaiki. Geological map ofNewZealand 1:63,360. Wellington, New Zealand. Departmentof Scientific and Industrial Research.

Laird, M. G. 1994: Geological aspects of the opening of the TasmanSea. In: van der Lingen, G. J.; Swanson, K. M.; Muir, R.J. ed. Evolution of the Tasman Sea Basin: Proceedings ofthe Tasman Sea Conference, Christchurch, New Zealand,27-30 November 1992. Rotterdam, A. A. Balkema.Pp. 1-17.

Landis, C. A.; Coombs, D. S. 1967: Metamorphic belts andorogenesis in southern New Zealand. Tectonophysics 4:501-518.

Lawver, L. A.; Gahagan, L. M. 1994: Constraints on timing ofextension in the Ross Sea region. Terra Antarctica 1 (3):545-552.

Le Maitre, R. W.; Bateman, P.; Dudek, A.; Keller, J.; Lameyre, J.;LeBas, M. J.; Sabine, P. A.; Schmid, R.; Sorenson, H.;Streckeisen, A.; Woolley, A. R.; Zanettin, B. ed. 1989: Aclassification of igneous rocks and glossary of terms.Recommendations of the IUGS Subcommision on theSystematics of Igneous Rocks. Oxford, BlackwellScientific Publications. 193 p.

Maas, R.; McCulloch, M. T. 1991: The provenance of Archeanclastic metasediments in the Narryer Gneiss Complex,Western Australia: trace element geochemistry, Ndisotopes, and U-Pb ages for detrital zircons. Geochimicaet cosmochimica acta 55: 1915—1932.

Mason, B. 1990: The geology of the Rotomanu district, NorthWestland. Records of the Canterbury Museum 10: 55-68.

Mason, B.; Taylor, S. R. 1987: High grade basement gneisses andgranitoids in Westland, New Zealand. Journal of The RoyalSociety of New Zealand 17 (2): 115-138.

Muir, R. J.; Ireland, T. R.; Weaver, S. D.; Bradshaw, J. D. 1994:Ion microprobe U-Pb zircon geochronology of graniticmagmatism in the Western Province of the South Island,New Zealand. Chemical geology (isotope geosciencesection) 113: 171-189.

Muir, R. J.; Weaver, S. D.; Bradshaw, J. D.; Eby, G. N.; Evans, J.A. 1995: Geochemistry of the Cretaceous Separation PointBatholith, New Zealand: granitoid magmas formed bymelting of mafic lithosphere. Journal of the GeologicalSociety of London 152: 689-701.

Muir, R. J.; Ireland, T. R.; Weaver, S. D.; Bradshaw, J. D. 1996:Ion microprobe dating of Paleozoic granitoids: Devonianmagmatism in New Zealand and correlations with Austral iaand Antarctica. Chemical geology 127: 191-210.

Nathan, S. 1975: Sheets S23 and S30—Foulwind and Charleston.Geological map of New Zealand 1:63,360. Wellington,New Zealand. Department of Scientific and IndustrialResearch.

Nathan, S. 1976: Geochemistry of the Greenland Group (earlyOrdovician), New Zealand. New Zealand journal ofgeology and geophysics 19: 683—706.

Nathan, S.; Anderson, H. J.; Cook, R. A.; Herzer, R. H.; Hoskins,R. H.; Raine, J. I.; Smale, D. 1986: Cretaceous aridCenozoic sedimentary basins of the West Coast region,South Island, New Zealand. New Zealand GeologicalSurvey basin studies 1. 90 p. Wellington, New Zealand.Department of Scientific and Industrial Research

Rattenbury, M. S. 1987a: Fraser Complex and Alpine Faulttectonics, Central Westland, New Zealand. UnpublishedPh.D. thesis, lodged in the Library, University of Otago.Dunedin, New Zealand.

Rattenbury, M. S. 1987b: Timing of mylonitisation west of theAlpine Fault, central Westland, New Zealand. New Zealandjournal of geology and geophysics 30: 123—169.

Rattenbury, M. S. 1991: The Fraser Complex: high grademetamorphic and igneous and mylonitic rocks in centralWestland, New Zealand. New Zealand journal of geologyand geophysics 34: 23—34.

Rollinson, H. 1993: Using geochemical data: evaluation,presentation, interpretation. United Kingdom, LongmanGroup. 352 p.

Roser, B. P.; Cooper, R. A.; Nathan, S.; Tulloch, A. J. 1996:Reconnaissance sandstone geochemistry, provenance, andtectonic setting of the lower Paleozoic terranes of the WestCoast and Nelson, New Zealand. New Zealand journal ofgeology and geophysics 39: 1—16.

Schmidt, M. W. 1992: Amphibole composition in tonalite as afunction of pressure: an experimental calibration of the Al-in-hornblende barometer. Contributions to mineralogy andpetrology 110: 304-310.

Shelley, D. 1970: The structure and petrography of the ConstantGneiss near Charleston, south-west Nelson. New Zealandjournal of geology and geophysics 13: 370-391.

Seward, D. 1989: Cenozoic basin histories determined by fission-track dating of basement gneisses, South Island, NewZealand. Chemical geology 79: 31-48.

Spanninga, G. A. 1993: Evolution of the Grey Valley Trough.Unpublished M.Sc. thesis, lodged in the Library, Universityof Waikato, Hamilton, New Zealand.

Stock, J.; Molnar, P. 1982: Uncertainties in the relative positionof the Australia, Antarctica, Lord Howe and Pacific platessince the late Cretaceous. Journal of geophysical research87: 4697-^717.

Tulloch, A. J. 1979a: Plutonic and metamorphic rocks in theVictoria Range segment of the Karamea BatholithUnpublished Ph.D. thesis, lodged in the Library, Universit,of Otago, Dunedin, New Zealand.

Tulloch, A. J. 1979b: Secondary Ca-Al silicates as low-gradealteration products of granitoid biotite. Contributions tomineralogy and petrology 69: 105—117.

Tulloch, A. J. 1983a: Granitoid rocks of New Zealand—a briefreview. Geological Society of America memoir 159: 5—20.


Tulloch, A. J. 1983b: Tectonic settings and source rocks forPaleozoic and Mesozoic granitoid rocks of New Zealand.Geological Society of New Zealand miscellaneouspublication 30A: 13.

Tulloch, A. J. 1988: Batholiths, plutons and suites: nomenclaturefor the granitoid rocks of Westland-Nelson. New Zealandjournal of geology and geophysics 31: 505—509.

Tulloch, A. J.; Brathwaite, R. L. 1986: C7: Granitoid rocks andassociated mineralisation of Westland—West Nelson. In:Houghton, B. R; Weaver, S. D. ed. South Island igneousrocks: tour guides A3, C2 and C7. New Zealand GeologicalSurvey record 13: 65—92.

Tulloch, A. J.; Kimbrough, D. L. 1989: The Paparoa MetamorphicCore Complex: Cretaceous extension associated withfragmentation of the Pacific margin of Gondwana.Tectonics 8 (6): 1217-1234.

Tulloch, A. J.; Palmer, K. 1990: Tectonic implications of granitecobbles from the mid-Cretaceous Pororari Group,southwest Nelson, New Zealand. New Zealand journal ofgeology and geophysics 33: 205—217.

Tulloch, A. J.; Kimbrough, D. L.; Waight, T. E. 1994: The FrenchCreek Granite, North Westland, New Zealand—LateCretaceous A-type plutonism on the Tasman passivemargin (extended abstract). In: van der Lingen, G. J.;Swanson, K. M.; Muir, R. J. ed. Evolution of the TasmanSea Basin: Proceedings of the Tasman Sea Conference,Christchurch, New Zealand, 27-30 November 1992.Rotterdam, A.A. Balkema. Pp. 65-67.

Waight, T. E. 1994: The Hohonu Dike Swarm: Late Cretaceouscrustal extension in the Buller Terrane. Geological Societyof New Zealand miscellaneous publication 80A: 183.

Waight, T. E. 1995a: The geology and geochemistry of the HohonuBatholith and adjacent rocks, North Westland, NewZealand. Unpublished Ph.D. thesis, lodged in the Library,University of Canterbury, Christchurch, New Zealand.

Waight, T. E. 1995b: Mid-Cretaceous plutonism associated withcrustal extension: the Hohonu Batholith, New Zealand. In:Brown, M.; Piccoli, P. M. ed. The origin of granites andrelated rocks. Third Hutton Symposium abstracts. U.S.Geological Survey circular 1129: 156.

Waight, T. E.; Weaver, S. D.; Muir, R.; Maas, R.; Eby, N. in press:The mid-Cretaceous Hohonu Batholith of North Westland,New Zealand: granitoids generated during post-subductionextension and under variable water conditions. Contri-butions to mineralogy and petrology.

Warren, G. 1967: Sheet 17—Hokitika. Geological map of NewZealand 1:250,000. Wellington, New Zealand. Departmentof Scientific and Industrial Research.

Weaver, S. D.; Pankhurst, R. J. 1991: Aprecise Rb-Sr age for theMandamus Igneous Complex, North Canterbury, andregional tectonic implications. New Zealand journal ofgeology and geophysics 34: 341-345.

Weissel, J. K.; Hayes, D. E. 1977: Evolution of the Tasman Seareappraised. Earth and planetary science letters 36: 77—84.

Wellman, P.; Cooper, A. 1971: Potassium-argon ages of some NewZealand lamprophyre dikes near the Alpine Fault. NewZealand journal of geology and geophysics 14: 341—350.

White, S. H.; Green, P. F. 1986: Tectonic development of the AlpineFault zone, New Zealand: a fission-track study. Geology14: 124-127.

Williams, I. S.; Claesson, S. 1987: Isotopic evidence for thePrecambrian provenance and Caledonian metamorphismof high grade paragneisses from the Seve Nappes,Scandinavian Caledonides, II. Ion microprobe zircon U-Th-Pb. Contributions to mineralogy and petrology 97:205-217.

Young, D. J. 1968: The Fraser Fault in central Westland, NewZealand, and its associated rocks. New Zealand journal ofgeology and geophysics 11: 291—310.

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