basement geology of taranaki and wanganui basins, new...

New Zealand Journal of Geology and Geophysics, 1997, Vol. 40: 223-2360028-8306/97/4002-0223 $7.00/0 © The Royal Society of New Zealand 1997

223

Basement geology of Taranaki and Wanganui Basins, New Zealand

N. MORTIMER

A. J. TULLOCHInstitute of Geological & Nuclear SciencesPrivate Bag 1930Dunedin, New Zealand

T. R. IRELANDResearch School of Earth SciencesAustralian National UniversityCanberra ACT 0200, Australia

Abstract We present a revised interpretation of thebasement geology beneath Late Cretaceous to CenozoicTaranaki and Wanganui Basins of central New Zealand,based on new petrographic, geochemical, and geo-chronological data from 30 oil exploration wells. Recentlypublished structural and magnetic interpretations of the areaassist in the interpolation and extrapolation of geologicalboundaries. Torlesse and Waipapa Terranes have beenidentified in Wanganui Basin, and Murihiku Terrane ineastern Taranaki Basin, but Maitai and Brook Street Terranerocks have not been recognised. Separation Point Suite,Karamea Suite, and Median Tectonic Zone igneous rocksare all identified on the basis of characteristic petrography,geochemistry, and/or age. SHRIMP U-Pb zircon measure-ments on igneous samples from western Taranaki wells donot give precise ages but do provide useful constraints:Motueka-1 granite is latest Devonian - earliest Carbon-iferous; Tangaroa-1 and Toropuihi-1 are Carboniferous; andSurville-1 is Cretaceous (cf. Separation Point Suite). Ourinterpretation of sub-basin geology is compatible withpreviously observed onland relationships in the North andSouth Islands.

Keywords North Island; Taranaki; Wanganui; EasternProvince; Western Province; Median Tectonic Zone;terranes; granitoids; petrology; petrography; geochemistry;U-Pb dating; zircon

INTRODUCTION

Taranaki and Wanganui Basins (Fig. 1) are two major, LateCretaceous—Cenozoic sedimentary basins in central NewZealand, that are, respectively, hydrocarbon-producing andhydrocarbon-prospective. The clastic sedimentary rocks ofthe basins were all ultimately derived from erosion of the

underlying and adjacent pre-Late Cretaceous crystallinebasement, units of which are exposed in the North and SouthIslands.

The distribution of geological units beneath and adjacentto these two basins has important implications for thePaleozoic and Mesozoic tectonic evolution of New Zealand.The area straddles the North and South Islands, regionswhich are commonly treated separately in tectonic analyses(e.g., see comments by Black 1994). It is valuable to knowif recognised terranes and igneous suites continue betweenthe two islands and to the north and west of New Zealand.A knowledge of sub-basin geology also helps with studiesof the provenance and paleogeography of basin strata andin the reconstruction of reservoir sandstone depositionalsystems.

The onland basement rocks of New Zealand are wellcharacterised on a regional (i.e. 1:1 000 000) scale and canbe most simply divided into Eastern and Western Provincesthat are separated by the Median Tectonic Zone (MTZ). TheEastern Province is dominated by Late Paleozoic—Mesozoicindurated sandstone and mudstone with subordinate maficvolcanics and chert, in part overprinted by the Haast Schist.The Western Province consists of early Paleozoic siliciclasticand carbonate rock, intruded and metamorphosed by mid-Paleozoic and Cretaceous granitoids. The MTZ is character-ised by a zone of Carboniferous and Early Triassic to EarlyCretaceous volcanic, plutonic, and sedimentary rocks, whose

long 170°E

200km

North Island

180c

STUDYAREA

lat 35°S ~

PacificOcean

South Island

Wellington

Chatham Islands

V45°S-

Stewart IslandI

G95075Received 20 December 1995; accepted 12 September 1996

Fig. 1 Location of the study area in the New Zealand region. T,Taranaki Basin; W, Wanganui Basin.

224

38

New Zealand Journal of Geology and Geophysics, 1997, Vol. 41 *

tangaroa-1Ariki-t» • • '

, - KH

Te Ranga-1»

Wainui-1»# M o a . 1 B

Pukearuhe-1

McKee-1 & \ToeToe-1

Tane-1»Taranga-1 i

Witiora-1

lnglewood-1

Mt. TaranakW ; ™"=-' « pUniwhakau-1;' Rotokare-1.

EASTERN PROVINCE& MEDIAN TECTONIC:ZONE

| . r 1 Torlesse TerraneL, ,_J Rakaia (r), Pahau (p)

Caples Terrane (c)Waipapa Terrane (w)

Maitai Terrane

Murihiku Terrane

C X X j Rotoroa Complext l (MTZ)

WESTERN PROVINCE,*+*+*' Mainly Separation•*^^ Point Suite

r > + Mainly Karamear + + I Suite

| S ; 7 ] Buller Terrane (b)f.;./*'/*j Takaka Terrane (t)

STRUCTURESMajor Cenozoic

—""" faults

Esk Head Melange

Haast Schist

SAMPLE SITES

• well penetrates basement

o well penetrates cover only

• other subsurface sampling

POSITIVEMAGNETIC ANOMALIES

•-- >+100 gamma42°S

172°E 174° 176°

Fig. 2 Geology in the vicinity of Taranaki and Wanganui Basins. Location of oil exploration wells referred to in the text, and selectedmagnetic anomalies (from Hunt 1978) are also shown. KH, Kawhia Harbour; PP, Pio Pio; FR, Fishermans Rock; MT, Mt Tongariro:RT, Rangipo hydro tunnel; WT, Whakapapa—Tawhitikuri hydro tunnel; LT, Lake Taupo; KR, Kaimanawa Range; PU, Port UnderwoodUnshaded areas are water and Late Cretaceous to Quaternary cover. Geology from Sporli (1978), Cooper & Tulloch (1992), and Mortimer(1993, 1995).

nature and contacts with the flanking Eastern and WesternProvinces are the topic of ongoing research (Kimbrough etal. 1994). The rocks of the Eastern and Western Provinceshave been divided into a number of petrographically andgeochemically distinct tectonostratigraphic terranes andigneous suites (Fig. 2). Details of these divisions are beyondthe scope of this paper, but recent summaries have beenprovided by Roser & Korsch (1988), Tulloch (1988),Bradshaw (1989), Cooper & Tulloch (1992), Mortimer(1993, 1995), Black (1994), Kimbrough et al. (1994), andMuiretal. (1994).

PREVIOUS WORK AND SCOPE OF STUDY

Cope & Reed (1967) examined material from 10 onshoreNorth Island oil exploration wells and proposed correlationsof the indurated sandstone and schist in the wells withvarious facies of the New Zealand geosyncline (EasternProvince). Wodzicki (1974) examined basement materialfrom four offshore oil exploration wells in the area of Fig. 2and showed that various Western Province igneous andmetamorphic rocks were represented. The provenance ofCretaceous—Cenozoic sandstones in western and eastern

Mortimer et al.—Taranaki & Wanganui Basin basement 225

Taranaki Basin broadly reflects derivation from Western andEastern Province sources, respectively (e.g., Smale 1992).

In this paper we present a revised and updatedinterpretation of the distribution of basement geological unitsbeneath Taranaki and Wanganui Basins (area of Fig. 2). Sincethe above studies were completed, much new informationhas become available. In particular, our interpretations arebased on:

(1) petrographic and/or geochemical analyses of basementmaterial from a total of 30 offshore and onshore oilexploration wells, including re-examination of materialfrom the earlier studies (Tables 1, 2);

(2) U-Pb SHRIMP dates on zircons from igneous rocks infour wells (Table 3);

(3) interpretations of offshore magnetic anomalies (Hunt1978; Davy 1992);

(4) recent maps of basin and sub-basin structure from seismicreflection studies (Anderton 1981; Thrasher & Cahill1990);

(5) contemporary subdivisions of onland geology intoterranes, metamorphic facies, and igneous suites withwhich to correlate the exploration well material (e.g.,Tulloch 1988; Mortimer 1993, 1995; Black 1994;Kimbrough et al. 1994; Muir et al. 1994, 1996); and

(6) supplementary subsurface information from xenoliths,dredge hauls, and tunnels (Beetham & Watters 1985;Graham 1985, 1987; Carter et al. 1988; Gamble et al.1994).

Onland geological units are, of course, defined not juston the basis of their petrological content but also by usingfossil, stratigraphic, lithofacies, and structural data. Despitethe fact that the oil exploration well core and cuttings donot provide this extra information, we are confident that ourpetrological-geochronological approach yields validinterpretations.

PETROLOGICAL RESULTS

As expected from the studies of Cope & Reed (1967) andWodzicki (1974), samples from wells in the eastern half ofFig. 2 (east of long. 174°E) have the features of EasternProvince metasedimentary rocks, and those in the westernhalf of Fig. 1 (west of long. 174°E) have the features ofWestern Province and/or Median Tectonic Zone plutonic andmetamorphic rocks. For convenience, we describe the wellsamples in these eastern and western groups. A summary ofthe principal petrographic features of all well samples usedin this study is given in Table 1.

Eastern wellsWanganui Basin

Whole rock geochemical analyses of samples fromWanganui Basin wells are given in Table 2 and Palmer etal. (1995). As noted by Cope & Reed (1967), Kaitieke-1,Young-1, Stantiall-1, and Santoft-1A penetrated induratedclastic sedimentary rocks, and Parikino-1 penetrated schist.All sandstones are unfoliated except in Santoft-1 A (too finegrained to be classified using Bishop's (1972) textural zonescheme—it might be IIA) and in Parikino-1 (textural zoneIIA-B).

The Kaitieke-1 sandstone is a volcanic litharenite andcontrasts with the other sandstones which are feldspathiclitharenites and lithic feldsarenites (Folk et al. 1970) (Fig. 3).The well is located only 8 km along-strike from surfaceoutcrops of the volcanic litharenite-dominated WaipapaTerrane (Sporli 1978; Beetham & Watters 1985; Black 1994).On the basis of detrital modes and geographic location, wetherefore correlate Kaitieke-1 basement with the WaipapaTerrane. The closest basement outcrops to Stantiall-1,Young-1, Santoft-1 A, and Parikino-1 wells are RakaiaTorlesse sandstones exposed in the North Island axial ranges(Sporli 1978; Beetham & Watters 1985). The detrital modesand the Ti/Zr and La/Sc ratios of these samples fall withinthe range of Rakaia Torlesse sandstones (Fig. 3,4A; see alsoMortimer 1995 for other chemical similarities), and outsidethe range of the more volcaniclastic Eastern Provinceterranes which lie west of the Torlesse. The lower La/Scratio of the Parikino-1 pelite as compared to the psammite(Fig. 4A) is highly distinctive of Torlesse rather than Caplesand Waipapa volcaniclastic terranes (Roser et al. 1993;Mortimer 1993 and references therein).

All Wanganui Basin basement samples contain authi-genic pumpellyite, prehnite, or epidote, but zeolites areconspicuously absent (Table 1); the rocks have thusexperienced at least prehnite-pumpellyite facies meta-morphism. Although regional metamorphic gradients arepresent in all New Zealand terranes (e.g., Bishop 1972; Boles1974; Black et al. 1993; Mortimer 1993), grade ofmetamorphism generally varies within known limits and,we believe, can be used to supplement terrane correlationsmade on the basis of detrital petrographic and geochemicalcriteria. The prehnite-pumpellyite to greenschist facies rocksof Young-1, Stantiall-1, Santoft-IA, Parikino-1, andKaitieke-1 are similar to the observed metamorphic gradeof the Rakaia Torlesse and Waipapa Terranes with whichwe correlate them, and distinctly different from the zeolitefacies Murihiku Terrane and Pahau Torlesse Terranes (cf.Boles 1974; Black et al. 1993; Black 1994).

Subsurface basement rocks in and near Wanganui Basinhave also been sampled by means other than oil explorationwells. Fishermans Rock in Cook Strait (P51016) is aweathered tzIIA psammitic schist (Mortimer pers. obs.) ofRakaia Torlesse affinity (B. P. Roser in Carter et al. 1988,see their table 1 for chemical analysis). Graham (1985) andBeetham & Watters (1985) noted Waipapa Terrane volcaniclitharenites in the Whakapapa-Tawhitikuri tunnel butTorlesse Terrane feldsarenites in the Rangipo tunnel of theTongariro Power Development project. Graham (1987)described contact-metamorphosed Torlesse sandstonexenoliths from Mt Tongariro, thus narrowing the positionof the Torlesse—Waipapa boundary south of Lake Taupo towithin c. 10 km.

Taranaki BasinThe detrital modes of sandstones from onshore TaranakiBasin wells Kiore-1, Pukearuhe-1, Rotokare-1, Tatu-1, andUruti-1 are distinctly less quartz and lithic rich than theWanganui Basin sandstones mentioned above, and aresimilar to compositions reported from the Murihiku Terrane(Fig. 3). The abundance of tuffaceous and calcareousmaterial in the sandstones is also typical of Murihikusandstones (e.g., Boles 1974) and atypical of other EasternProvince terranes. The geochemical composition ofsandstones from the above five wells and from

Table 1 Summary of petrographic data and preferred correlation of basement samples from Taranaki and Wanganui oil exploration wells.

Well Depth (m) Lat. (S) Long. (E) Type P no. Lithology Notes Correlation

Eastern wellsKaitieke-1Kiore-1Kiore-1Manutahi-1Parikino-1Pukearuhe-1Puniwhakau-1Puniwhakau-1Rotokare-1Santoft-IAStantiall-1Tatu-1Tatu-1Te Ranga-1Uruti-1Uruti-2Young-1Young-1

Western wellsAriki-1Kiwa-1Kongahu-1Maui-2Maui-4Moa-IBMotueka-1North Tasman-Ruby Bay-1Surville-1Tane-1Tane-1Tangaroa-1Tangaroa-1Taranga-1Toropuihi-1Wainui-IWitiora-1

(Wanganui, onshore Taranaki,393.2-393.8

534.3534.9

1389.52312.2

3132-31382146.12146.13232.7

2627.4-2630.52085.5-2087.0

857.1857.7

3877-3882.5341.3-342.9

1546.3-1549.31025.7-1028.41031.5-1034.8

39°03.20'39°13.43'39°13.43'39°41.12'39°48.07'38°53.65'39°19.10'39°19.10'39°24.85'40°12.32'40°05.02'38°55.12'38°55.12'38°12.15'38°56.37'38°57.67'40° 17.63'40° 17.63'

and Te Ranga-1)175°17.83' Cuttings 33377 Medium ss Q5, F20, L75. Quartz—prehnite veins, intermediate volcanic clasts174°33.73' Core 30651 Fine-medium ss Ql 1, F41, L48. Volcanic lithics, chloritised glass fragments. Calcic plagioclase174°33.73' Core 51395 Fine ss-siltstone Quartz rich, heulandite patches, detrital muscovite174°25.02' Core 51396 Fine ss Quartz rich, detrital biotite, zeolitised glass shards, much sericite175°08.83' Core 30501 Schist tzIIB-IHA, quartz, ab., muse, chlorite, titanite, epidote. Strain-slip cleavage174°30.58' Cuttings 51393 Medium ss Q9, F37, L54. Acid volcanic and plutonic lithics. Heulandite and laumontite174°42.42' Core 30850 Fine ss Quartz rich, detrital biotite174°30.58' Core 51394 Fine ss Quartz rich. Pink zeolitised patches174°24.17' Core 51390 Medium ss Q7, F37, L56. Volcanic lithic, zeolites (including heulandite). Albitised feldspar175° 12.41' Core 29822 Fine ss-siltstone Microfaulted and incipient pressure solution cleavage. Pumpellyite175°20.03' Core 16573 Medium ss Q30, F32, L38. Detrital muscovite, biotite, epidote. Pumpellyitised feldspar174°55.02' Core 30608 Medium ss Q15, F38, L47. Volcanic lithics. Heulanditised glass shards. Calcic plagioclase174°55.02' Core 51391 Fine ss Quartz and feldspar rich, volcanic lithics, authigenic zeolites. Calcic plagioclase174°37.90' Cuttings 51397 Calc. siltstone Calcareous matrix, calcite veins, detrital quartz, biotite prominent174°34.77' Core 16570 Calc. medium ss Q10, F50, L40. Detrital biotite. Zeolite (phillipsite?) veins. Albitised feldspar174°30.75' Core 16572 Calc. siltstone Quartz rich, detrital epidote, biotite, muscovite, authigenic chlorite, zeolite175°30.00' Core 30502 Medium ss Q29, F33, L38. Detrital biotite, muscovite. Incipient pressure solution cleavage175°30.00' Core 30503 Medium ss Q44, F27, L29. Detrital biotite. Matrix sericite prominent. Pumpellyite.

Wai papaMurihikuMurihikuMurihikuTorlesseMurihikuMurihikuMurihikuMurihikuTorlesseTorlesseMurihikuMurihikuMurihikuMurihikuMurihikuTorlesse

(offshore Taranaki and offshore South Island)4814 38°12.09' 173°41.85' Cuttings 11826 Various Basalt-andesite, and volcaniclastic ss. Secondary ab, chlorite, calcite, hematite

3850-3853 39°48.65' 172°41.88' Cuttings 50886 Granitoid Fine-grained kaolinised ?biotite granite. Biotite now pale brown micaceous clay2015-2016 41°14.85' 171°52.47' Core 44741 Granitoid Coarse-grained biotite granite; brown biotite altered to chlorite and muscovite3469-3563 39°36.77' 173°26.97' Cuttings 39790 Granitoid Medium-grained hornblende diorite. Brown/green hornblende, access magnetite3850-3905 40°02.40' 173°14.45' Cuttings 39792 Granitoid Sodic leucogranite (Wodzicki 1974)3523-3546 38°29.72' 173°21.18' Cuttings 39787 Schist Biotite, hornblende, pyroxene-bearing schist (Wodzicki 1974)

1564 40°31.43' 173c29.02' Cuttings 51535 Granitoid Fine-medium grained biotite granite; c. 5% green biotite; magnetite, titanite1 2722-2725 40° 12.01' 173° 16.33' Cuttings 11828 Granitoid Fine-grained chloritised biotite granite. Pink K-feldspar. Contaminated with Cz ss

268-281 41°14.15' 173°05.28' Core 39887 Granitoid Medium-grained biotite hornblende diorite with 2-3% quartz and K-feldspar2199 40°43.33' 173°26.83' Cuttings 50890 Granitoid Fine-medium grained biotite granite; c. 2% green biotite, trace opaque4471 38°56.33' 172°38.33' Cuttings 50888 Granitoid Medium-grained biotite granodiorite; c. 3% green biotite, trace titanite4471 38°56.33' 172°38.33' Cuttings 50889 Granitoid Medium-grained biotite granodiorite; c. 3% green biotite, trace titanite

3984.5-3984.7 38°10.78' 173°52.32' Core 51291 Silicified rhyolite Feldspar phenocrysts, spherulitic groundmass. Sec. quartz, ep, chlorite, sericite3985.8 38°10.78' 173°52.32' Core 51295 Basalt Basalt. Rare clinopyroxene phenocrysts to 1 mm. Secondary epidote and chlorite

4197 38°58' 173°15' Core 54827 Granitoid Medium-grained biotite quartz-monzodiorite. Trace magnetite, titanite2192 40°51.25' 171°56.73' Cuttings 50892 Granitoid Fine-grained biotite granite; trace olive-green biotite, trace fluorite

3892-3894 38°27.87' 173°18.51' Cuttings 11827 Matrix-rich ss Single cutting (c. I % of sample) of recryt. siliceous metasandstone4222-4229 39°06.80' 173°28.50' Cuttings 50895 Granitoid Medium-grained granite, trace green biotite. Ilmenite/hematite

Torlesse

MTZSeparation PointKaramea SuiteMTZSeparation PointTakaka TerranePz I-type graniteKaramea SuiteMTZSeparation PointSeparation PointSeparation PointMTZ basementMTZ basementSeparation PointPz A-type graniteTakaka TerraneSeparation Point

z;3<N

eal

3&

sE.oOaQo*

(TO

»

oo*&E T>-<;o '

All "P no." samples are catalogued in the National Petrology Reference Collection, Institute of Geological & Nuclear Sciences. Pz, Paleozoic; MTZ, Median Tectonic Zone; ss, sandstone; calc,calcareous; Q, F, L, framework quartz, feldspar and lithic grains as a percentage of total framework grains. Percentages are visual estimates only and are probably accurate to + 25% of theamount present.

4-.

2o

ap

Table 2 X-ray fluorescence (XRF) analyses of basement core and cuttings material from Taranaki and Wanganui wells.

Well

Eastern iK.iore-1

Manutahi-1

Puni-1

Rotokare-1

Tatu-1

Uruti-1

WesternK.iwa-1

Kongahu-1

Maui-2

Motueka-1

Motueka-1

N Tasman-1

Ruby Bay

Surville-1

Surville-1

Tane-1

Tane-1

Tangaroa-1

Tangaroa-1

Taranga-1

Toropuihi-1

Witiora-1

Pno.

wells51395

51396

51394

51390

51391

16570

wells50886

44741

39790

51535i

51535ii

11828

39887

50890i

50890M

50888

50889

51291

51295

54827

50892

50895

Rock type

fine ss

fine ss

fine ss

med ss

fine ss

calc ss

granite*

granite

diorite*

granite*

granite*

granite*

diorite

granite*

granite*

granite*

granite*

rhyolite

basalt

granite

granite*

granite*

SiO2

59.52

64.24

59.44

64.60

62.72

53.68

76.25

73.29

46.51

70.29

72.01

72.87

57.38

70.34

70.53

67.90

67.67

73.33

49.15

68.15

75.61

77 58

TiO2

0.86

0.70

0.89

0.70

0.72

0.74

0.10

0.24

1.51

0.23

0.14

0.22

0.94

0.16

0.21

0.25

0.20

0.35

1.23

0.38

0.04

0.06

AI2O3

16.82

16.12

16.65

16.01

16.19

16.69

11.99

14.00

17.46

15.84

15.29

14.50

17.23

15.81

15.54

16.94

16.94

14.75

16.26

15.66

12.73

12.11

Fe2O3T

6.73

5.11

6.36

4.75

5.95

8.23

0.47

2.08

11.60

2.28

1.34

1.40

7.49

1.12

1.25

1.31

0.94

1.30

11.61

3.01

1.04

0.37

MnO

0.07

0.07

0.09

0.06

0.08

0.10

0.05

0.04

0.20

0.05

0.02

<0.01

0.13

0.03

0.03

0.02

0.02

0.05

0.18

0.03

0.01

0.01

MgO

2.46

1.98

2.84

1.91

1.95

2.17

0.23

0.47

6.17

0.47

0.17

<0.01

3.20

0.49

0.39

0.32

0.21

1.07

5.55

1.22

0.05

0.08

CaO

2.05

1.51

3.05

1.53

2.41

4.76

1.51

0.29

8.28

1.03

0.82

0.81

6.22

1.68

1.72

2.63

2.13

4.25

7.99

1.17

0.55

0.54

Na2O

3.83

3.73

3.76

3.66

3.01

4.03

2.87

2.95

3.18

4.82

4.73

3.55

3.81

4.64

4.77

5.70

6.19

3.39

3.38

5.33

3.82

3.82

K2O

2.87

3.59

2.74

3.56

3.41

1.79

4.24

5.56

1.00

4.14

4.37

4.95

2.11

4.24

4.06

2.36

2.45

0.44

0.73

2.60

4.70

4.12

P2O5

0.21

0.16

0.20

0.16

0.12

0.18

0.01

0.16

0.38

0.07

0.03

0.17

0.31

0.06

0.07

0.08

0.08

0.08

0.17

0.18

0.01

0.01

LOI

4.55

2.99

4.03

3.14

3.49

7.00

1.55

1.06

3.23

0.70

0.79

0.73

0.82

0.80

1.33

1.87

2.58

1.04

4.03

1.81

0.65

0.60

TOTAL

99.97

100.20

100.05

100.08

100.05

99.37

99.27

100.14

99.52

99.92

98.92

99.20

99.64

99.37

99.90

99.38

99.41

100.05

100.28

99.54

99.21

99.30

Ba

464

421

498

418

477

520

1055

360

458

985

922

760

566

735

689

1171

1193

137

201

741

204

907

Ce

52

54

48

51

44

55

15

47

40

53

41

42

57

14

25

35

43

21

16

37

47

14

Cr

76

35

54

34

32

35

8

5

29

2

3

16

23

<2

5

3

3

2

46

2

<2

<2

Cu

36

20

37

20

24

24

1

4

71

5

6

26

32

6

8

5

6

22

108

4

2

1

Ga

18

22

20

21

23

20

15

19

23

22

18

<1

20

19

19

18

15

14

18

21

35

13

La

20

25

18

23

19

23

11

21

12

25

18

25

24

11

11

19

24

9

4

17

20

8

Nb

7

8

9

9

10

8

3

9

4

13

9

21

9

4

5

5

4

3

<2

4

50

3

Ni

25

15

24

13

12

15

<1

5

20

3

4

35

14

2

3

1

1

1

17

2

10

0

Pb

19

17

19

19

18

18

20

33

7

15

14

<1

15

20

23

19

9

19

12

14

47

7

Rb

95

139

115

139

142

52

87

297

21

160

151

183

70

163

150

52

54

11

17

62

512

79

Sc

15

14

16

13

13

15

<1

3

33

3

2

25

23

1

2

1

2

6

40

4

1

0

Sr

210

160

595

161

430

647

348

61

947

164

155

83

609

671

634

1038

772

440

288

577

15

73

Th

8

11

11

12

8

8

4

15

2

16

13

14

10

7

12

4

4

7

2

7

37

7

U

1.9

3.5

2.8

2.7

2.0

1.9

1.0

5.0

<1.0

6.0

4.8

9.0

2.0

1.0

1.7

1.0

1.0

2.0

1.0

1.1

13.0

1.0

V

160

119

151

113

124

149

8

22

257

12

11

20

140

15

17

20

19

39

373

47

5

7

Y

28

33

31

32

29

25

2

50

25

40

22

19

37

3

1

3

2

13

21

4

129

3

Zn

90

86

104

80

97

99

63

30

134

36

21

156

84

36

34

50

30

52

97

49

92

9

Zr

171

207

194

204

204

160

60

96

76

227

151

118

234

64

78

136

127

189

61

120

121

53

Major elements wt%, trace elements ppm. * indicates cuttings, not core, analysed;Santo ft-1 A, Young-1, Kaitieke-1, and Parikino-1 well samples are given in Palmer et al.analysed by John Hunt, Spectrachem Analytical.

, total iron as Fe2C>3; LOI, loss on ignition. Analytical methods, along(1995). Analyst Ken Palmer, Victoria University, except for North Tasman-

with analyses of Stantiall-1,•1 granite PI 1828 which was

3P

p

crqp3C

03

to

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

Table 3 U-Pb analyses of zircon from Toropuihi-1, Tangaroa-1, Motueka-1, and Surville-1 rocks.

Analysis U

Toropuihi-11.1 26741.22.12.22.33.14.15.15.26.17.18.1

71893680415770737662337

24241211433944734779

Tangaroa-i1.1 42591.22.12.23.13.23.33.44.14.25.15.26.16.27.17.28.18.29.19.29.3

415025282317988983625744397108074956490480537574530

365435889074120

Motueka-11.12.13.14.15.16.17.18.19.110.111.112.113.114.1

3057538

2314335393754515290563292495696933686

Surville-11.12.23.14.15.16.17.18.19.110.111.112.113.114.115.1

1292121182

1012637303107835983718110141270756149

Th

71135799031382287527586091225426211214892284

18691481990916450443270327299786

34202277252285182169

10901070554570

23203701018172220555318142370243313106576323

86472737164722627332815421729935148512108

Th/U

0.270.500.250.330.410.361.810.510.350.490.330.48

0.440.360.390.400.460.450.430.440.750.730.460.350.530.530.320.320.300.300.620.610.59

0.760.690.440.510.560.740.620.490.660.830.630.150.620.47

0.670.590.400.710.740.860.680.780.650.950.970.860.550.680.73

204pb/206pb

0.00004 ± 0.000030.00015 ±0.000030.00015 ±0.000040.00044 ± 0.000070.00102 ± 0.000080.00116 ±0.000070.00018 ±0.000410.00010 + 0.000060.00018 ±0.000120.00331 ±0.000170.00202 + 0.000140.00153 ±0.00013

0.00286 ± 0.003060.00302 + 0.003240.00543 ± 0.005650.00278 ±0.003100.00066 ±0.001010.00065 ±0.001140.00066 ±0.001070.00063 ±0.001700.00412 ±0.005040.00757 ± 0.008070.00078 + 0.000810.00098 ±0.001030.00158 ±0.002540.00241 ±0.003550.00243 ± 0.003200.00133 + 0.001410.00044 ± 0.000530.00050 ± 0.000660.01794 + 0.025190.01321 ±0.018390.00940 + 0.01094

0.00012 ±0.000040.00115 ±0.000310.00017 + 0.000060.00091 ±0.000630.00162 ±0.000470.00056 ± 0.000360.00106 + 0.000240.00042 + 0.000370.00095 + 0.000380.00175 + 0.000440.00098 ± 0.000520.00043 ± 0.000710.00001 ±0.000010.00090 ± 0.00086

0.00104 ±0.000590.00787 ± 0.002600.00387 ± 0.003400.00180 + 0.000550.00162 ±0.000830.00623 ±0.001590.00163 + 0.000450.00811 ±0.001480.00094 ± 0.000580.00473 ± 0.002070.08576 + 0.031680.02463 ±0.019810.00221 ±0.002710.00596 + 0.002760.00001 ±0.00001

207pb/206pb

0.05386 ±0.001050.05608 + 0.000440.05380 + 0.000400.05737 + 0.000590.06614 + 0.000530.06761 ± 0.000480.05584 ±0.001730.05393 + 0.000600.05331 ±0.001110.10286 ±0.000630.08356 ± 0.000690.07445 ± 0.00087

0.08744 + 0.002180.09235 ± 0.000470.11915 ±0.001240.08932 ±0.001770.05382 ± 0.000960.05548 + 0.000530.05496 ±0.001540.05557 ± 0.000990.08480 + 0.001920.15702 ±0.025520.06072 + 0.002030.06250 + 0.001420.05613 ±0.000950.05913 ±0.001230.06660 + 0.000420.06243 ± 0.000870.05643 ± 0.000400.05605 + 0.000380.11567 + 0.001630.11906 ±0.004320.08728 + 0.00239

0.05401 ±0.000420.05945 ±0.001560.05248 ±0.000710.06749 + 0.001470.06636 ±0.001980.05872 ±0.001720.06135 ±0.001850.06864 ±0.001590.05742 ±0.001360.07096 ±0.002130.06127 + 0.001540.05590 + 0.001100.05591 ± 0.000780.05795 ± 0.00086

0.05444 ±0.002170.07712 ±0.004210.08580 ± 0.007010.06271 ±0.001550.07817 ±0.002200.08800 ± 0.003370.06121 ±0.001520.10042 ±0.005330.07353 ± 0.001920.09043 + 0.004510.44765 + 0.028370.22505 ±0.018680.07851 ±0.003130.06824 ± 0.002420.08070 ±0.01019

238Tj/206pb

19.91 ±0.4520.09 + 0.4119.99 ±0.4220.43 + 0.4322.29 + 0.4621.51 ±0.4728.18 ±0.7320.28 + 0.4420.10 ±0.4622.19 ±0.4820.44 ± 0.4227.58 ±0.59

25.46 + 0.7725.58 ± 0.6919.40 ± 0.4921.68 ±0.5519.08 ± 0.4819.15 ±0.4821.33 ±0.9920.54 ± 0.5322.00 ± 0.8521.78 ±0.5519.56 ±0.9422.96 + 0.8919.68 ±0.5119.68 + 0.5221.01 +0.5321.88 + 0.5621.85 ±0.5521.74 + 0.5416.09 + 0.4318.19 ±0.5519.64 ±0.59

17.02 ±0.1917.72 + 0.2817.71 ±0.2019.23 + 0.3118.88 + 0.3617.78 + 0.3017.68 ±0.2618.37 ±0.4019.01 ±0.3018.29 ±0.3219.41 ±0.4718.01 ±0.3017.55 ±0.2716.81 +0.31

53.96 ± 0.9649.90+ 1.4454.35 ±1.8955.74 + 0.7956.18 ± 1.2155.24 ± 1.3655.78 ±0.8151.81 + 1.0757.62 ± 1.3455.44 ± 1.7328.84 ± 1.9443.83 ± 3.0358.21 ± 1.7148.54 ± 0.9349.49 ± 2.49

Age (Ma)

315.6 ± 7.0312.1 ± 6.2314.4 ± 6.5306.5 ± 6.4278.9 ± 5.6288.3 ± 6.1224.1 + 5.7310.0 ± 6.6312.9 ± 7.0268.9+ 5.7297.8 ± 6.0224.2 ± 4.7

239.0 ± 7.2235.4 ± 6.3299.4 ± 7.6277.8+ 7.0327.3 ± 8.2325.5 ± 8.2293.1 ± 13.6303.9 ± 7.8275.2 ± 10.6255.4 ± 6.4317.1 ± 15.3270.5 ± 10.5316.8 ± 8.2315.7 + 8.4293.7 ± 7.4283.6 ± 7.2285.8 ± 7.2287.4 ± 7.2360.6 ± 9.7318.7+ 9.6306.6 ± 9.3

370.1 ± 4.0353.8 ± 5.5356.7 ± 3.9323.8 ± 5.2330.2 ± 6.1352.8 ± 5.7353.8 ± 5.0338.2 ± 7.2331.1 ± 5.1338.8 ± 5.8320.9 ± 7.5347.5+ 5.7356.5+ 5.3370.9+ 6.6

119.0 ± 2.1125.4+ 3.6114.1 ± 4.0114.2 ± 1.6111.4 ± 2.4112.0 ± 2.8114.3 ± 1.7117.7+ 2.5109.2 ± 2.5111.3 ± 3.5124.6 ± 10.7117.6 ± 8.6106.2 ± 3.1128.7 ± 2.5124.4 ± 6.4

Analyst T. R. Ireland. Analytical methods and operating conditions are similar to those described in Muir et al. (1994).


El Kaitieke-1

o Kiore-1O Pukearuhe-1• Rotokare-1

Tatu-1

Uruti-1

Stantiall-1+ Young-1

Fig. 3 Petrographic plot of visually estimated modes of medium-and coarse-grained sandstones from eastern wells of Taranaki andWanganui Basins, and of point-counted populations from selectedNew Zealand terranes. Q, F, L, total quartz, feldspar, lithic grains,respectively. North Island Torlesse (« = 19) and southern WaipapaO = 25) data from Finlow-Bates (1970), Beetham & Watters(1985), and Mortimer (1995); Murihiku data (n = 21) fromMacKinnon (1983). Hexagons indicate one standard deviationabout the mean.

60-

40-

2fJ.Puni-1Tatu-'

• Manutahi-f

Kiore-1 Kaitieke-1Uruti-1

Rotokare-1

D Taranaki Basin• Wanganui Basin

Parikino-1SantofMAStantiall-1Young-1

La/Sc

1200

a.3

400

i Maui-'2-.

Ruby Bay-1

50

MEDIAN TECTONICZONE ROCKS Kiwa-1

SiO2 (wt%)Toropuihi-1 80

Puniwhakau-1 and Manutahi-1 are permissibly Murihiku,but cannot be uniquely distinguished from Caples-Waipapasandstones using chemical criteria alone (Fig. 4A).

The presence of zeolites in Uruti-1 and 2, Tatu-1, Kiore-1,Puniwhakau-1, Rotokare-1, Pukearuhe-1, and Manutahi-1further suggests a correlation with the Murihiku Terrane (cf.descriptions by Boles 1974; Black et al. 1993). The lack ofprehnite-, pumpellyite-, or epidote-bearing assemblages rulesout a correlation with Maitai, Caples, Waipapa, and RakaiaTorlesse Terranes.

Western wells

Wells for which only petrographic data could be used forinterpretation include Ariki-1, Moa- IB, Tasman-1, andWainui-1. Ariki-1 cuttings were of altered basalt, andesite,?dacite, and volcaniclastic sandstone, all with abundantmetamorphic chlorite, hematite, and sericite. The igneousrocks in Ariki-1 are not dissimilar to those in nearbyTangaroa-1, for which core was available and which westudied in greater detail (see below). We concur withWodzicki's (1974) correlation of quartzofeldspathic andcalcareous schist in Moa- IB with the Onekaka Schist(Takaka Terrane of Cooper & Tulioch 1992); such rock typesare essentially absent from the Buller Terrane and are, asyet, unknown from the MTZ. The presence of a single cuttingof recrystallised siliceous sandstone in the nearby Wainui-1is also compatible with a Takaka Terrane correlation.

We can add little to Wodzick i ' s (1974) detai leddescription of the indurated ignimbrite-rich breccia-conglomerate in Tasman-1 (Fig. 2). Wodzicki (1974)tentatively favoured a correlation with the late EarlyCretaceous Hawks Crag Breccia but noted that the Tasman-1

100O

100

BJ

« 10•5

S ,o

s0.1

Tangaroa-1o rhyolite• basalt

Lord Howe Rise• rhyolites

Lake Roxburghtonalites

Rb Ba Th U Nb K La Ce Sr P Zr Ti Y

Fig. 4 Geochemical plots of well samples. A, Sandstones andschists from eastern wells plotted on La/Sc versus Ti/Zr binarydiagram. Murihiku, Caples-Waipapa, and Torlesse fields fromRoser et al. (1993). Arrow for Parikino-1 links analyses ofpsammitic (psam) and pelitic (pel) portions of core (pelitic at arrowtip). High metamorphic grade of Wanganui Basin samples suggestsCaples-Waipapa and Torlesse correlations; low metamorphic gradeof Taranaki samples suggests a Murihiku correlation (see text).B, Granitoids from western wells plotted on SiC>2 versus Srdiagram, comparing compositions of granitoid samples withrespect to onland reference suites. Fields from Tulioch (unpubl.data). C, Basalt and rhyolite from Tangaroa-1 plotted onprimitive mantle-normalised multi-element diagram (of Sun &McDonough 1989). Both samples have calc-alkaline andsubduction-related character. Nb concentration of basalt is plottedat practical detection limit (2 ppm). Other data from McDougall& van der Lingen (1974) and Tulioch (unpubl. data).


clasts were dominated by ignimbrite and soda granite insteadof potassium-rich granite. We note that the early LateCretaceous Beebys Conglomerate near Nelson is also areddish colour, and contains a clast assemblage more likethe Tasman-1 breccia (e.g., P43602; Johnston 1990). Thus,there may be closer onland analogues of the Tasman-1breccia than realised by Wodzicki (1974).

Geochemical data are presented for 12 wells whichpenetrate igneous basement of the MTZ or Western Province(Table 2, Fig. 4B-C). Similar results for replicate samplesof two wells, in which cuttings were hand picked by differentoperators, supports the validity of whole rock analysis usingrelatively small (c. 15 g) samples of cuttings. Only 1.5 g ofcuttings were available for XRF analysis of the NorthTasman-1 sample.

Basement in Tane-1, Surville-1, Kiwa-1, Witiora-1, andTaranga-1 can be confidently assigned to the CretaceousSeparation Point Suite (SPS); in addition to high Sr (Fig. 4B),all except Witiora-1 have high Sr/Y ratios (144-634)characteristic of the SPS (Tulloch & Rabone 1993; Muir etal. 1995). Witiora-1 rock has low Y and Rb and is stillconsidered to belong to the SPS despite K20>Na20 anddepleted Sr because these values probably result fromextreme fractionation. Surville-1 has unusually high K2Oand Rb for SPS, but low Y, Nb, and apparent lack of zirconinheritance render correlation with Rahu Suite (Tulloch1983) unlikely.

Toropuihi-1 bottomed in biotite granite with high Ga, Y,and Nb indicative of an A-type affinity, similar to granitesimmediately onshore at Whakapoi Point and at CapeFoulwind c. 100 km to the southwest (Cooper & Tulloch1992). Such granites are rare elsewhere in New Zealand.

Kongahu-1 and, less confidently, North Tasman-1 andMotueka-1 are both correlated with the S-type granites ofthe Karamea Suite, most abundantly exposed onshore in theKaramea Batholith (Fig. 2) (Tulloch 1988). Motueka-1 (andNorth Tasman-1) has somewhat high Na for typical KarameaSuite, but the zircon data discussed below confirm a mid-Paleozoic age. Although the Motueka-1 rock contains a traceof magnetite, Na and Sr are not high enough to suggestcorrelation with I-type granites of the Paleozoic ParingaSuite (Cooper & Tulloch 1992); correlation with MTZ-associated Carboniferous granites is a possibility.

Wodzicki (1974), using only petrographic criteria,correlated basement in Maui-2 and Ruby Bay-1 with theRotoroa Complex (part of the Median Tectonic Zone;Kimbrough et al. 1993, 1994). The chemical data presentedin this study (e.g., moderate Sr values, high Y compared toSPS; Fig. 4B) confirm these earlier correlations.

Tangaroa-1 intersected interbedded rhyolite and basalt.Both are considerably altered and the rhyolite is stronglysilicified. The rhyolite analysis is characterised by very lowK and Rb. A mantle-normalised multi-element plot of theanalyses (Fig. 4C) exhibits enrichments in Rb, Ba, and Srand Nb-depletion, characteristic of calc-alkaline, subduction-related suites. We know of no obvious onshore correlativesof this basalt-rhyolite basement, although a possible plutoniccorrelative of the rhyolite is the Lake Roxburgh Tonalite onthe western edge of the MTZ in Fiordland (Kimbrough etal. 1994), which has similar chemistry (Fig. 4C). Tangaroa-1 rhyolite is clearly chemically dissimilar from Cretaceousrhyolites on the Lord Howe Rise (McDougall & van derLingen 1974) (Fig. 4C). At least some foliated amphiboliteand diorite xenoliths from Mt Taranaki are not cognate and

were probably derived from Rotoroa Complex-likecorrelatives (R. B. Stewart pers. comm. 1992; Gamble et al1994).

ION PROBE ZIRCON U-Pb ANALYSES

MethodsZircon was separated and analysed on the ion probe(SHRIMP) at the Australian National University in anattempt to better constrain the affinities of rocks from fourof the wells. Isotopic data are presented in Table 3 and Fig. 5Except for Tangaroa-1, for which core of rhyolite wasavailable, all zircon samples were separated from the samehand-picked cuttings of granite used for geochemicalanalysis. The clearest, most prismatic grains were selectedfor analysis, but there is a possibility that cuttings andsubsequent zircon separates were derived from more thanone basement component.

The zircon data are normalised to 206Pb/238U of 0.0928for the 572 Ma SL13 standard. The data plotted in Fig. 5have not been corrected for common Pb contributions. ForPhanerozoic zircons, the estimation of common Pb by wavof the 204Pb/206Pb results in large uncertainties of theradiogenic 207Pb abundance. For these zircons, common Pbis determined by a lever rule between common Pb on theabscissa and radiogenic Pb on the concordia curve, and theages are derived from the 2°6pb*/238U ratios. All zirconanalyses should lie on a line connecting the radiogenic ageto common Pb (dashed lines in Fig. 5) if they are consisten*with a single magmatic age and variable contributions of acommon Pb component. Large common Pb contributionsare apparent by discordant analyses in Fig. 5, and those withlarge common Pb contributions often appear to have lost Pbas well, when compared with more concordant zircons.Discordant zircons are apparent in all four rocks, anddetermining a crystallisation age for such zircon populationscan be subjective. For this work, we adopt the simpleapproach that a concordant population that has the highestU-Pb age defines the magmatic age. A spread of data awayfrom the best-fit line indicates either: (1) the presence ofboth magmatic and inherited grains; (2) beam spotsoverlapping magmatic rim and inherited core; (3) Pb-loss;or (4) some combination of 1, 2 and 3.

ResultsApproximately half of the Toropuihi-1 zircons (Fig. 5 A)form a tight cluster around concordia at 312 + 7 Ma, withthe remaining zircons being younger, with higher commonPb, and scattered. No older inherited grains are apparent andthe scatter is probably due to Pb loss. The tight clusterindicates the Carboniferous age is almost certainlymagmatic. Strontium isotope analysis of the whole rockyields Sr = 15.39 ± 0.01 ppm and 8 7Sr/8 6Sr =1.1619 ±0.0001. Rb concentration from duplicate XRFanalysis is 512 ± 2 ppm. Model ages based on assumed Sr-initial ratios of 0.705 and 0.715 range from 314 to 318 Ma.These ages overlap with, and thus are consistent with, thezircon age of 312 ± 7 Ma. Conversely, the high 87Rb/86Srratio (100-101), together with the error on the zircon age,do not allow a precise calculation of the Sr initial ratio.

Tangaroa-1 zircons (Fig. 5B), separated from rhyolite,are scattered over the concordia plot, making a uniqueinterpretation very subjective. The oldest, most concordant

Mortimer et al.—Taranaki & Wanganui Basin basement

0.15

231

CM

0.15

20 25238(J/206pb

20 25238(J/206pb

0.15 0.15

0.00.15 20 25 30 30 40 50 60 70

238(J/206pb

Fig. 5 Tera-Wasserburg U-Pb zircon concordia diagrams for Tangaroa-1 rhyolite and Toropuihi-1, Motueka-1, and Surville-1 granites.A single magmatic population with different contributions from common Pb would lie on a line (dashed) between the inferred radiogeniccomposition and the common Pb composition on the abscissa. However, all these samples appear to have been affected by Pb loss asindicated by the scattered analyses with younger ages and/or high common Pb. Toropuihi-1 gives a relatively well constrainedCarboniferous age, and although Tangaroa-1 shows more scatter, it too is likely Carboniferous. Motueka-1 is distinctly older (possiblyDevonian), similar to the Karamea Suite (Muir et al. 1994, 1996). Surville-1 is Early Cretaceous, but there is considerable scatterbetween 110 and 125 Ma.

cluster of six grains gives a mean 238U/206Pb age of 321 Ma,although one grain with high common Pb is significantlyolder than this at c. 361 Ma. Cretaceous zircons areconspicuously absent; because of the large scatter, we canonly assign a Carboniferous magmatic age to the rock.

Motueka-1 zircons (Fig. 5C) cluster quite closely in anage range of 330-370 Ma, although the scatter exceedsanalytical error for a single statistical population. A goodcluster at c. 350 Ma is suggestive of an igneous crystal-lisation age, in which case two 370 Ma zircons are inherited.Alternatively, if 370 Ma is a magmatic age, most of thezircons have lost Pb. The low degree of scatter covering allthe zircons suggests a latest Devonian or earliest Carbon-iferous magmatic age.

Surville-1 zircons (Fig. 5D) cluster in a restricted agerange c. 110-125 Ma but with excessive scatter for this tobe a single population. The data could be interpreted eitheras representing a 125 Ma crystallisation age with Pb-lossaffecting many grains, or as a 110 Ma granite containinginherited 125 Ma grains. Either interpretation would bedifficult to justify on the basis of the Surville-1 zircon U-Pb

data alone, although in either case the magmatic age is EarlyCretaceous, and the data are consistent with the assignmentof Surville-1 to the Separation Point Suite on the basis ofchemical affinities and age (Fig. 4B) (Kimbrough et al.1994).

Although interpretation of the U-Pb data from these fourrocks is problematical when it comes to assigning amagmatic age and associated error, it is apparent that thebasement in Toropuihi-1, Tangaroa-1, and Motueka-1 isCarboniferous-Devonian in age, whereas Surville-1basement is Cretaceous. The former three samples thereforehave affinities with Paleozoic Western Province or MTZgranitoids, whereas Surville-1 is likely to correlate with theSeparation Point Suite.

MAGNETIC ANOMALIES

The short wavelength and linear nature of the JunctionMagnetic Anomaly (JMA—between Pio Pio and near Tahi-1 in Fig. 2) and its correspondence with the Dun MountainOphiolite Belt of the Maitai Terrane throughout New Zealand


has been summarised by Hunt (1978). A prominent longwavelength, high amplitude anomaly, west of the JMA, alsoextends south from Mt Taranaki to near Tahi-1 (Fig. 2;equivalent to anomaly "R" of Davy 1992). From near Tahi-1 to D'Urville Island, magnetic anomalies become indistinct,but between D'Urville Island and the Rotoroa Complex, theJMA and the western anomaly merge into a single, broad,very strong magnetic anomaly (Fig. 2). This single stronganomaly is caused by the close and parallel disposition ofthe highly magnetic rocks of the Maitai Terrane, Brook StreetTerrane, and Median Tectonic Zone; at a local scale,individual anomalies are still resolvable (Hunt 1978). Eastof the JMA, Davy (1992) has emphasised a magneticallyquiet region corresponding to the sandstone and schist ofthe Caples, Torlesse, and Waipapa Terranes.

Non-basement magnetic signatures in the area of Fig. 2include those generated by: (1) the Quaternary andesiticstratovolcano of Mt Taranaki, which has a separate, shortwavelength anomaly, slightly offset from the broad westernanomaly (Davy 1992); (2) buried Miocene andesitevolcanoes in offshore Taranaki, north of about latitude 39°S(Herzer 1995); and (3) a Late Cretaceous igneous complexin the Torlesse Terrane at latitude 42°S.

West of about longitude 174°E, Davy (1992, fig. 7)showed an area of high magnetic contrast, which heinterpreted in terms of linear magnetic anomalies (thiscontrast is not as obvious on Fig. 2, which is simplified fromHunt 1978). Although we do not necessarily accept that theseanomalies are all as linear as Davy claims (cf. Hunt 1978and Davy 1992), we do regard the high contrast as typicalof magnetic signatures of the Western Province, whichcontains a variety of highly magnetic plutons (Tulloch 1989).This variable magnetic character of Western Province andMTZ units means that magnetic anomalies are of limiteduse in distinguishing these units from Brook Street andMaitai Terranes. The JMA, however, is an invaluablemagnetic datum in interpreting basement geology beneathTaranaki and Wanganui Basins (see below).

BASIN AND SUB-BASIN STRUCTURE

Interpretation of seismic reflection lines in the area byAnderton (1981), Thrasher & Cahill (1990), and Lewis etal. (1994) has identified a number of major faults that offsetthe basement-cover unconformity by up to 6 km. TheTaranaki and Manaia Faults (Fig. 6) are two of the mostimportant in the area and have had a long and complexhistory (e.g., King & Thrasher 1992). Mortimer (1993) hasdrawn attention to the fact that the Picton Fault (Fig. 6) is amajor metamorphic and structural boundary within theMarlborough Schist.

From our experience in onshore South Island, boundariesof Mesozoic terranes often coincide with Cenozoic faults.Given the lack of precision in locating contacts betweenbasement geological units beneath Taranaki and WanganuiBasins, we have deliberately chosen to position them alongthese major basement-cover faults where geometry permits.

DISCUSSION

Our preferred basement map of Taranaki and WanganuiBasins is shown in Fig. 6. Although an improvement onearlier versions, it is still essentially an outline, as data are

sparse and some major issues remain unresolved. Onshore,Eastern Province units (terranes) occur as simple structuralbelts of varying width and are thus, to a large extent,amenable to simple interpolation and extrapolation beneaththe basins. However, the Western Province contains plutonsand batholiths that are commonly smaller than the spacingbetween the oil exploration wells, so our attempts to drawgeological boundaries around them are highly schematic.Below we discuss our assumptions, methods, and problemsin sequentially assembling Fig. 6 on a unit-by-unit basis.

Maitai TerraneThe starting point for the sub-basin geological interpretationof Fig. 6 is the correlation of the JMA with the Dun MountainOphiolite Belt of the Maitai Terrane (Hunt 1978). Althoughophiolitic or metasedimentary rocks of the Maitai Terranehave not been penetrated by any wells, we confidently drawMaitai Terrane as a narrow, discontinuous belt between itssurface exposures at Pio Pio and D'Urville Island (Fig. 2)The near-constant width of the Maitai Terrane shown irFig. 6 is schematic. The absence of the JMA south of Tahi-1 and north of D'Urville Island (Fig. 2) coincides with ar.area of considerable tectonic complexity in Taranaki Basir(P. R. King pers. comm. 1996) and may reflect local excisioriof the ophiolite belt (Fig. 6).

Torlesse TerraneThe western boundary of the Torlesse Terrane is well definedin the northern and southern parts of Fig. 6 (Beetham &Walters 1985; Graham 1985, 1987; Mortimer 1993, 1995)in between, it must lie to the west (we prefer just west) o:the Wanganui Basin wells and Fishermans Rock. With sucha boundary, Parikino-1 schist is sensibly SSW along-strikefrom the Torlesse schist in the Kaimanawa Range, but isc. 50 km farther northwest across-strike than a simple 1\TNEextrapolation of Torlesse schist from Port Underwood to nearKapiti Island would suggest (Fig. 2, 6).

The many NNE- and northeast-striking faults inWanganui Basin outlined by Anderton (1981) may becontinuations of the Wairau and/or Picton Faults (Fig. 6)However, the absence of north-, NNW-, or northwest-striking faults in seismic sections (Anderton 1981; Carter etal. 1988; Thrasher & Cahill 1990; Lewis et al. 1994) doesnot support a northwest-striking sinistral fault with 50 kmoffset in Cook Strait to account for the apparent displacementof the Torlesse-Waipapa boundary (cf. Cope & Reed 1967.fig. 1). Lack of basement sampling in northern Cook Straitpresently precludes solution of this geometrical problem.In Fig. 6 we have, for simplicity, drawn the western edge ofthe Torlesse Terrane with a north—south strike under muchof Wanganui Basin. The position of the Esk Head Melangein Fig. 2 and 6 is from Mortimer (1995) and reference:-therein.

Caples and Waipapa TerranesThese litharenite-dominated terranes lie in identicalstructural positions between the Rakaia Torlesse and MaitaiTerranes, with Caples Terrane exposed in the South Islandand Waipapa Terrane mainly in the North Island. Nomen-clature of the Waipapa Terrane is in a state of flux; it isprobably a composite terrane, and reliable discriminationof its various parts requires lithofacies, paleontological, andstructural data (Black 1994). Neither Caples nor Waipapa


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Taranaki Fault

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EASTERN PROVINCE& MEDIAN TECTONICZONE

Torlesse TerraneRakaia (r), Pahau (p)

Caples Terrane (c)Waipapa Terrane (w)

xx;xx;

Maitai Terrane

Murihiku Terrane

Brook St Terrane

Plutonic rocks ofMedian Tectonic Zone

WESTERN PROVINCE

Undifferentiated

SeparationPoint Suite

*"*] Paleozoic+ +_jj granitoids

j - : •:•! Buller Terrane (b)j "T " : " | Takaka Terrane (t)

^- Highly schematic-^ limits of batholiths

and MTZ rocks

STRUCTURES

_ Major Cenozoic— faults

Esk Head Melange

Haast Schist

SAMPLE SITES

• well penetrates basement

O well penetrates cover only

• other subsurface sampling

172°E 174°

Fig. 6 Interpretation of pre-Late Cretaceous basement geology beneath the Taranaki and Wanganui Basins based on interpretationsmade in this paper and data of Anderton (1981), Thrasher & Cahill (1990), Mortimer (1993, 1995), and Lewis et al. (1994). All contactsare speculative. Highly speculative units and contacts are shown by question marks. See Fig. 2 for names of wells. Open circles correspondto location of wells in which Late Cretaceous — Early Cenozoic sandstones may have an MTZ and/or combined Eastern and WesternProvince provenance (e.g., Smale 1992).

Terrane has been intersected in any exploration well in the250 km between Kaitieke-1 and the South Island; con-sequently, we show only undifferentiated Caples andWaipapa Terranes beneath western Wanganui Basin (Fig. 6).

Haast SchistThe occurrence of schist in Parikino-1 and Santoft-IA, andat Fishermans Rock and Kapiti Island, supports previousinterpretations that Haast Schist is continuous from the SouthIsland to the Kaimanawa Range (Fig. 6) (Cope & Reed 1967;Mortimer 1993). Mortimer (1993) emphasised majordifferences in the mesoscopic and macroscopic style of schistdeformation east and west of Picton Fault, and specificallyassigned schist near Port Underwood (Fig. 2) to the same

genetic belt as schist in the Kaimanawa Range. Exactly howfar under Wanganui Basin the schist west of Picton Faultextends is unknown. At present there are simply not enoughdata to reconcile the mutual geometry of the Caples,Waipapa, and Torlesse Terranes (see above), and differentparts of the Haast Schist between the North and SouthIslands, except as broadly continuous belts (Fig. 6).

Murihiku TerraneMurihiku Terrane lies west of Maitai Terrane and ispenetrated by nine holes. The position of the western edgeof the Murihiku Terrane in Fig. 6 is obtained as follows: theoldest strata on the western limb of the synclinorium inMurihiku rocks near Kawhia Harbour are Oretian (Late


Carnian — Early Norian; Kear 1960), which, by comparisonwith the Murihiku Terrane of Southland, suggests that onlyc. 2 km stratigraphic thickness of earlier Triassic strata aremissing at Kawhia Harbour. So, unless an otherwiseunobserved anticlinorium. repeats the strata, the MurihikuTerrane probably does not extend much farther west thanTe Ranga-1 (Fig. 2). Use of the Taranaki Fault as aconvenient western edge to the Murihiku Terrane requiresit to taper southwards against the Maitai Terrane (Fig. 6).This wedge shape accords with the occurrence of MurihikuTerrane near Nelson only as attenuated narrow fault slivers(Johnston 1981) that are too small to be shown at the scaleof Fig. 2 and 6.

Brook Street Terrane and edge of Eastern ProvinceIn Nelson, the Brook Street Terrane also occurs only asnarrow fault slivers (Johnston 1981, 1990), considerablynarrower than its maximum outcrop width of some 16 kmin the Takitimu Mountains of Southland. Because distinctivepyroxene-rich lavas and sandstones of the Brook StreetTerrane were not penetrated by any of the wells, and thereis no clearly definable linear magnetic anomaly to denoteits presence, the depiction of the Brook Street Terranebeneath Taranaki Basin on Fig. 6 is highly speculative.However, our reason for assuming its continuity north fromD'Urville Island is that Brook Street-like rocks have beendredged on the West Norfolk Ridge, 800 km to the northwestof Taranaki Basin (Mortimer & Herzer 1995), and possiblebroad correlatives may also occur in New Caledonia(Campbell 1984).

In Fig. 6, we give Brook Street Terrane an arbitrary(Takitimu) outcrop width of c. 15 km, and south of MtTaranaki we have selected the Manaia Fault as its obviouslikely western edge. An alternative interpretation entirelyomitting Brook Street Terrane from Fig. 6 would result inthe western edge of the Eastern Province coinciding withthe Taranaki Fault, as shown by Cope & Reed (1967) andWodzicki (1974).

Western ProvinceBuller or Takaka Terrane-like metasedimentary rocks occurin only two of the offshore western wells shown in Fig. 6.The high proportion of Separation Point Granite in six ofthe offshore wells, suggests a greater areal extent of thisunit offshore, compared to its onshore distribution in SouthIsland (Fig. 6). Because granites of the Separation Point Suiteintrude rocks of both the Western Province and the MedianTectonic Zone (Kimbrough et al. 1994), they do not constrainthe position of the Western Province/Median Tectonic Zoneboundary.

North Tasman-1 and Motueka-1 lie well to the east ofmost Paleozoic granitoid rocks, the exception being theEchinus Granite of Pepin Island (Kimbrough et al. 1993;Beresford et al. 1996). The (oxidised) green biotite andpresence of magnetite and titanite in the Motueka-1 samplesuggest an I-type affinity. The chemistry of this rock doesnot suggest a clear association with any of the recognisedPaleozoic suites, and isotopic study is required to furthercharacterise it. The chemistry of the rock is comparable tothe S-type Karamea Suite rather than the I-type Paringa Suite(Cooper & Tulloch 1992), except in its relatively high Na2Ocontent; correlation with I-type granitoid rocks associatedwith the MTZ is another possibility, although no clear

correlatives (including the relatively sodic Echinus Granite •are obvious. Correlation of the Motueka-1 granite with theKaramea Suite suggests a considerable narrowing of theTakaka Terrane because, onshore, S-type granites of theKaramea Suite appear to be restricted to the Buller Terrane(Cooper & Tulloch 1992). However, complete northwardexcision of Takaka Terrane is unlikely given its occurrencein Moa-IB. An alternative interpretation is a previouslyunrecorded intrusion of Karamea Suite granites into theTakaka Terrane.

As discussed by Cooper & Tulloch (1992), the graniteof Toropuihi-1 is similar in its A-type chemistry to theFoulwind Granite, although a distinctly older age ol327 ± 6 Ma was reported by Muir et al. (1994) for the sameunit.

Median Tectonic ZoneCorrelations with the MTZ can be made for the plutonicrocks in Ruby Bay-1 and Maui-2, and some xenoliths eruptedfrom Mt Taranaki (Gamble et al. 1994) are consistent withderivation from subjacent MTZ crust. No obviouscorrelatives for the basalt and rhyolite encountered inTangaroa-1 occur onshore, but a possible plutonic equivalentwhich overlaps in age within error, is the Echinus Granite(310 ± 5 Ma; Kimbrough et al. 1993), which appears to forrrbasement to the MTZ on Pepin Island (Fig. 2, 6) (Beresforcet al. 1996). Tangaroa-1 rhyolite is chemically similar to theslightly older (c. 340 Ma; Kimbrough et al. 1994) (Fig. 4C)Lake Roxburgh Tonalite in eastern Fiordland, which mayalso form older basement to the MTZ. Wide compositionalrange and subduction-related calc-alkaline chemistry of theTangaroa-1 rocks are thus consistent with a provisionalMedian Tectonic Zone correlation. Given the broadsimilarity between Ariki-1 cuttings and Tangaroa-1 core, wehave included Ariki-1 in the MTZ (Fig. 6). The fact that MTZigneous rocks have been recovered in dredges on the WestNorfolk Ridge (Mortimer & Herzer 1995) gives usconfidence in extending the MTZ north throughout the wholearea of Fig. 6. Although we agree with Wodzicki's (1974)tentative correlation of the red acid igneous breccia inTasman-1 with Late Cretaceous cover units, because thestratigraphic age of the unit is unknown, we cannot entirelyrule out still older correlation (e.g., with the Rainy RiverConglomerate of the Median Tectonic Zone; Johnston 1990).

CONCLUSIONS

On the basis of petrography, geochemistry, and U-Pb age,we correlate core and cuttings from 30 oil exploration wellsin Taranaki and Wanganui Basins with onshore geologicalunits (Tables 1,2,3). We have identified distinctive TorlesseTerrane, Murihiku Terrane, Median Tectonic Zone, andSeparation Point Suite lithologies in a number of wells.Maitai and Brook Street Terrane rocks have apparently notbeen intersected by wells, though the presence of the formeris indicated by the prominent Junction Magnetic Anomaly(Hunt 1978). We have used the well samples, along withinterpretations of magnetic and reflection seismic data, toconstruct a new geological map of the pre-Late Cretaceousbasement beneath west-central New Zealand (Fig. 6).

Due to low sampling density, the locations of boundariesbetween major rock units are imprecisely located and theirnature is indeterminate. Major questions left unanswered by


the study include: (1) Caples-Waipapa-Torlesse-Haast Schistgeometry between the North and South Islands; (2)continuity of the Maitai Terrane near Tahi-1; (3) extent ofthe Brook Street Terrane north of D'Urville Island; (4)correlation of Motueka-1 granite; and (5) regional geometryof MTZ and Western Province units. However, Fig. 6 is asignificant improvement on earlier efforts: it shows overallcontinuity of offshore and onshore geology and demonstratesa greater regional extent of New Zealand basement terranesand igneous suites than previously has been established.

ACKNOWLEDGMENTS

We acknowledge the following oil companies for drilling tobasement, thereby supplying material for this study: Amoco N.Z.,Anzpac Petroleum, Champlin Oil & Refining, Esso Exploration& Production, Home Energy, Marathon Petroleum, N.Z. AcquitanePetroleum, N.Z. Oil & Gas, N.Z. Petroleum, Shell BP & Todd OilServices, Superior Oil, and Tasman Petroleum. We also thankNeville Orr for thin sections, Stewart Bush for rock powders, KenPalmer and John Hunt for X-ray fluorescence analyses, BobStewart, John Gamble, and Joe McKee for information on MtTaranaki xenoliths, Ian Graham for Sr isotopic analysis ofToropuihi-1 cuttings, and Glenn Thrasher, Peter King, Mac Beggs,Alva Challis, Bill Watters, and Bryan Davy for helpful discussions.Earlier versions of the manuscript were improved by pre-submission reviews from Hamish Campbell, Peter King, and MacBeggs, and journal reviews from Tim Little and Russell Korsch.Institute of Geological & Nuclear Sciences contribution number886.

REFERENCES

Anderton, P. W. 1981: Structure and evolution of the SouthWanganui Basin, New Zealand. New Zealand journal ofgeology and geophysics 24: 39—63.

Beetham, R. D.; Watters, W. A. 1985: Geology of Torlesse andWaipapa terrane basement rocks encountered during theTongariro Power Development project, North Island, NewZealand. New Zealand journal of geology and geophysics28: 575-594.

Beresford, S. W.; Bradshaw, J. D.; Weaver, S. D.; Muir, R. J. 1996:Echinus Granite and Pepin Group of Pepin Island, northeastNelson, New Zealand: Drumduan Terrane basement orexotic fragment in the Median Tectonic Zone? NewZealand journal of geology and geophysics 39: 265—270.

Bishop, D. G. 1972: Progressive metamorphism from prehnite-pumpellyite to greenschist facies in the Dansey Pass area,Otago, New Zealand. Geological Society of Americabulletin 83: 3177-3198.

Black, P. M. 1994: The "Waipapa Terrane", North Island, NewZealand: subdivision and correlation. Geoscience reportsofShizuoka University 20: 55-62.

Black, P. M.; Clark, A. S. B.; Hawke, A. A. 1993: Diagenesis andvery low grade metamorphism of volcaniclastic sandstonesfrom contrasting geodynamic environments, North Island,New Zealand: the Murihiku and Waipapa terranes. Journalof metamorphic geology 11: 429-435.

Boles, J. R. 1974: Structure, stratigraphy, and petrology of mainlyTriassic rocks, Hokonui Hills, Southland, New Zealand.New Zealand journal of geology and geophysics 17:337-374.

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

Campbell, H. J. 1984: Petrography and metamorphism of theTeremba Group (Permian—Lower Triassic) and Baie deSt.-Vincent Group (Upper Triassic - Lower Jurassic), NewCaledonia. Journal of The Royal Society of New Zealand14: 335-348.

Carter, L.; Lewis, K. B.; Davey, F. 1988: Faults in Cook Strait andtheir bearing on the structure of central New Zealand. NewZealand journal of geology and geophysics 31: 431—446.

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

Cope, R. N.; Reed, J. J. 1967: The Cretaceous paleogeology ofthe Taranaki—Cook Strait area. Proceedings of theAustralasian Institute of Mining and Metallurgy 222:63-72.

Davy, B. 1992: Magnetic anomalies of the New Zealand basement.In: Proceedings of the 1991 New Zealand Oil ExplorationConference. Wellington, Ministry of Commerce, CrownOperations Group.

Finlow-Bates, T. 1970: Quantitative examination of immaturesandstones by point-count and X-ray modal analysis. Tane16: 163-173.

Folk, R. L.; Andrews, P. B.; Lewis, D. W. 1970: Detritalsedimentary rock classification and nomenclature for usein New Zealand. New Zealand journal of geology andgeophysics 13: 937-968.

Gamble, J.; McKee, J.; Grapes, R.; Bennett, D. 1994: The crustbeneath Taranaki Volcano imaged by xenoliths fromandesites in the Stratford lahars. Geological Society of NewZealand miscellaneous publication 80A. 70.

Graham, I. J. 1985: Rb-Sr geochronology and geochemistry ofTorlesse metasediments from the central North Island, NewZealand. Chemical geology (isotope geoscience section)52: 317-331.

Graham, I. J. 1987: Petrography and origin of metasedimentaryxenoliths in lavas from Tongariro Volcanic Centre. NewZealand journal of geology and geophysics 30: 139—157.

Herzer, R. H. 1995: Seismic stratigraphy of a buried volcanic arc,Northland, New Zealand, and implications for Neogenesubduction. Marine and petroleum geology 12: 511—531.

Hunt, T. M. 1978: Stokes Magnetic Anomaly System. New Zealandjournal of geology and geophysics 21: 595—606.

Johnston, M. R. 1981: Sheet O27AC—Dun Mountain. Geologicalmap of New Zealand 1:50 000. Map (1 sheet) and notes(40 p.). Wellington, New Zealand. Department of Scientificand Industrial Research.

Johnston, M. R. 1990: Geology of the St Arnaud district, southeastNelson (sheet N29). New Zealand Geological Surveybulletin 99.

Kear, D. S. 1960: Sheet 4—Hamilton. Geological map of NewZealand 1:250 000. Wellington, New Zealand. Departmentof Scientific and Industrial Research.

Kimbrough, D. L.; Tulloch, A. J.; Geary, S. E.; Coombs, D. S.;Landis, C. A. 1993: Isotopic ages from the Nelson regionof South Island, New Zealand: crustal structure anddefinition of the Median Tectonic Zone. Tectonophysics225: 433^148.

Kimbrough, D. L.; Tulloch, A. J.; Coombs, D. S.; Landis, C. A.;Johnston, M. R.; Martinson, J. M. 1994: Uranium-leadzircon ages from the Median Tectonic Zone, South Island,New Zealand. New Zealand journal of geology andgeophysics 37: 393-419.

King, P. R.; Thrasher, G. P. 1992: Post-Eocene development ofthe Taranaki Basin, New Zealand: convergent overprintof a passive margin. American Association of PetroleumGeologists memoir 53: 93—118.


Lewis, K. B.; Carter, L.; Davey, F. J. 1994: The opening of CookStrait: interglacial tidal scour and aligning basins at asubduction to transform plate edge. Marine geology 116:293-312.

McDougall, I.; van der Lingen, G. J. 1974: Age of the rhyolites ofthe Lord Howe Rise and the evolution of the south-west*Pacific Ocean. Earth and planetary science letters 21:117-126.

MacKinnon, T. C. 1983: Origin of the Torlesse terrane and coevalrocks, South Island, New Zealand. Geological Society ofAmerica bulletin 94: 967-985.

Mortimer, N. 1993: Metamorphic zones, terranes and Cenozoicfaults in the Marlborough Schist, New Zealand. NewZealand journal of geology and geophysics 36: 357—368.

Mortimer, N. 1995: Origin of the Torlesse Terrane and coeval rocks,North Island, New Zealand. International geology review36: 891-910.

Mortimer, N.; Herzer, R. H. 1995: New petrological results fromthe Vening Meinesz escarpment, and Norfolk and ThreeKings Ridge areas: terrane correlations and constraints onNeogene reconstructions. Geological Society of NewZealand miscellaneous publication 81 A. 148.

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 geoscience) 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 Australiaand Antarctica. Chemical geology (isotope geoscience)127: 191-210.

Palmer, K.; Mortimer, N.; Nathan, S.; Isaac, M. J.; Field, B. D.;Sircombe, K. N.; Black, P. M.; Bush, S.; Orr, N. W. 1995:Chemical and petrographic analyses of some New ZealandPaleozoic-Mesozoic metasedimentary and igneous rocks.Institute of Geological & Nuclear Sciences science report95/16.

Roser, B. P.; Korsch, R. J. 1988: Provenance signatures ofsandstone-mudstone suites determined using discriminantfunction analysis of major element data. Chemical geology67: 119-139.

Roser, B. P.; Mortimer, N.; Turnbull, I. M.; Landis, C. A. 1993:Geology and geochemistry of the Caples Terrane, Otago,New Zealand: compositional variations near a Permo-Triassic arc margin. In: Ballance, P. F. ed. South Pacificsedimentary basins. Sedimentary basins of the World, 2.Amsterdam, Elsevier. Pp. 3—19.

Smale, D. 1992: Provenance of sediments in Taranaki Basin—an assessment from heavy minerals. In: Proceedings ofthe 1991 New Zealand Oil Exploration Conference.Wellington, Ministry of Commerce, Crown OperationsGroup. Pp. 245-254.

Sporli, K. B. 1978: Mesozoic tectonics, North Island, New Zealand.Geological Society of America bulletin 89: 415-425.

Sun, S. S.; McDonough, W. F. 1989: Chemical and isotopicsystematics of oceanic basalts: implications for mantlecompositions and processes. In: Saunders, A. D.; Norry.M. J. ed. Magmatism in the ocean basins. GeologicalSociety of London special publication 42: 313—345.

Thrasher, G. P.; Cahill, J. P. 1990: Subsurface maps of the TaranakiBasin, New Zealand 1:500 000. New Zealand GeologicalSurvey report G142. Lower Hutt, New Zealand. DSIRGeology and Geophysics.

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

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

Tulloch, A. J. 1989: Magnetic susceptibilities of Westland—Nelsorplutonic rocks: discrimination of Paleozoic and Mesozoic:granitoid suites. New Zealand journal of geology andgeophysics 32: 197-203.

Tulloch, A. J.; Rabone, S. D. C. 1993: Mo-bearing granodioriteporphyry plutons of the Early Cretaceous Separation PointSuite, west Nelson, New Zealand. New Zealand journa*of geology and geophysics 36: 401^108.

Wodzicki, A. 1974: Geology of the pre-Cenozoic basement of tin:Taranaki — Cook Strait — Westland area, New Zealand,based on recent drillhole data. New Zealand journal ojgeology and geophysics 17: 1A1—151.

basement geology of taranaki and wanganui basins, new...

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