basement geology from three kings ridge to west norfolk ridge, southwest pacific ocean: evidence...

ELSEVIER Marine Geology 148 ( 1998) 135- 162

Basement geology from Three Kings Ridge to West Norfolk Ridge, southwest Pacific Ocean: evidence from petrology,

geochemistry and isotopic dating of dredge samples

N. Mortimer a,*, R.H. Herzer b, P.B. Gans ‘, D.L. Parkinson ‘, D. Seward d

a Institute of Geological and Nuclear Sciences, Private Bag 1930, Dunedin, New Zealand b Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, New Zealand

’ Department of Geological Sciences, University of California, Santa Barbara, CA 93106, USA ’ Departement fiir Erdwissenschaften, ETH Zentrum, 8092 Zurich, Switzerland

Received 20 May 1997; accepted 14 November 1997

Abstract

We present new petrographic, X-ray fluorescence, electron microprobe, Ar-Ar radiometric, fission track, and Sr, Nd and Pb isotopic data for igneous and metamorphic rocks from 18 dredges from a number of basins and ridges in the southwest Pacific Ocean. The dredge samples can be divided into four groups: (1) Permian to Cretaceous gabbroids, granitoids and hornfelses from the West Norfolk and Wanganella Ridges; (2) mainly Cretaceous mafic igneous rocks from the Reinga Ridge and Vening Meinesz escarpment; (3) subduction-related Late Oligocene and Early Miocene basalts and shoshonites from the Three Kings and southern Norfolk Ridges; and (4) back-arc basin and intraplate basalts of Early Miocene age in the South and North Norfolk Basins, respectively, and intraplate basalts of Pliocene age in the Reinga Basin. Our dredge data, combined with regional magnetic and gravity data, provide much-needed tests of earlier tectonic interpretations of the region. Correlatives of the Permian Brook Street Terrane and Mesozoic Median Tectonic Zone of onshore New Zealand clearly extend along the West Norfolk and Wanganella Ridges. The Three Kings Ridge was active at least in the 19- to 20-Ma period, and was probably generated above a west-dipping subduction zone. The Norfolk Basin was a back-arc basin to this arc, and had opened by 18-20 Ma. The oldest Cenozoic volcanic rocks in the region are 26-Ma subduction-related volcanic breccias on the southern Norfolk Ridge; they probably predate opening of the Norfolk Basin and associated eastward migration of the Three Kings Ridge. 0 1998 Elsevier Science B.V. All rights reserved.

Keywords: southwest Pacific; New Zealand; petrology; geochemistry; geochronology

1. Regional setting

The southwest Pacific Ocean consists of a number of submerged ridges and linear island

* Corresponding author. Fax: + 64 (3) 477-5232;

E-mail: [email protected]

0025-3227/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved.

PII: SOO25-3227(98)00007-3

chains, separated by a number of basins (Fig. 1). New Zealand, Challenger Plateau, Lord Howe Rise, Norfolk Ridge, West Norfolk Ridge and New Caledonia are underlain by variably thinned continental crust. Onland exposures show that this crust consists of Paleozoic-Mesozoic accreted ter- ranes and a variety of plutonic suites that collec-

136 N. Mortimer et al. J Marine Geology 148 (1998) 135-162

Fig. 1. Major tectonic features of the southwest Pacific Ocean NC= New Caledonia; Lay R = Loyalty Ridge; CFZ= Cook Fracture

Zone; VMFZ = Vening Meinesz Fracture Zone (escarpment); WNR = West Norfolk Ridge; WR = Wanganella Ridge; DR = Dampier

Ridge; NI=Norfolk Island; NINZ=North Island New Zealand; SINZ=South Island New Zealand; TB=Taranaki Basin; CK=

Colville Knolls; CI=Chatham Islands; BZ=Bounty Island; MTZ=Median Tectonic Zone. Following Launay et al. ( 1982) we use

the terms North and South Norfolk Basins instead of Kingston Basin and Norfolk or Gazelle Basin (Addicott and Richards, 1981;

Eade, 1988). We also use the term Reinga Ridge to describe the entire ridge system on the southwest side of the VMFZ between

longitude 168 and 172”E. Quadrilateral shows area of Fig. 2.

tively rifted from Australia, part of the Gondwana craton, in the Late Cretaceous. In the south of the region, active arc volcanism is occurring within North Island, New Zealand, and along the Kermadec Ridge in response to westward subduction of the Pacific Plate beneath the Australian

Plate. The Hikurangi Plateau, a Cretaceous large igneous province (Mortimer and Parkinson, 1996), is colliding with the North Island at the Hikurangi subduction zone. The Lau-Colville and Three Kings Ridges are generally interpreted to be relict island arcs, and the intervening Norfolk and South

N. Mortirner et ul. / Marine Geology 148 (1998) 135-162 137

Fig. 2. Location map of the study area. VMFZ=Vening Meinesz Fracture Zone (escarpment). Isobaths in m. Bathymetry from GEBCO ( 1982) modified with swath bathymetric data obtained by RV I’Atalante in 1993. Positive magnetic anomalies (Sutherland, 1996) south and west of VMFZ shown by wide diagonal pattern; positive gravity anomalies (Davy, 1996) associated with Three Kings Ridge shown by narrow diagonal pattern. Areal extent of Northland Allochthon (Herzer and Isaac, 1992 adjacent to NZ, and Herzer and Mascle, 1996 for the western extension) shown by cross pattern. Major faults (after Herzer and Mascle, 1996) shown by thick black lines.

Fiji Basins interpreted to be back-arc basins floored by oceanic crust of Cenozoic age (e.g. Ballance et al., 1982; Davey, 1982; Eade, 1988; Herzer and Mascle, 1996).

Almost all interpretations of the offshore part of the area of Fig. 2 have been formulated using bathymetric, seismic, gravity and magnetic data

(e.g. Summerhayes, 1969; Karig, 1970; Davey, 1982; Kroenke and Eade, 1982; Eade, 1988; Rigolot, 1989; Zhu and Symonds, 1994; Herzer and Mascle, 1996 to name but a few). In contrast, there has been no drilling and little dredging of seabed rocks to directly establish the geology of the area; and where dredging has been done

138 N. Mortimer et al. / Marine Geology 148 (1998) 135-162

(Summerhayes, 1969; Davey, 1982; Monzier and Vallot, 1983; Rigolot, 1989), full petrological study has not been forthcoming.

2. Purpose and significance of this paper

This paper is a companion study to three papers, recently published and/or in press, using data gathered on the same cruises in 1993: (1) reinter- pretation of the tectonics of the Vening Meinesz Fracture Zone based on swath bathymetry and seismic reflection profiling (Herzer and Mascle, 1996); (2) Cretaceous-Pleistocene stratigraphy, tectonism and basin evolution of the Reinga Basin (Herzer et al., 1997) and (3) properties of carbonaceous Cretaceous rocks dredged from the Norfolk and West Norfolk Ridges (Herzer et al., 1998).

The focus of the present paper is on igneous and metamorphic rocks dredged from 18 sites in/on the North and South Norfolk Basins, Three Kings Ridge, southern and West Norfolk Ridge, Reinga Ridge, Wanganella Ridge and Reinga Basin (Fig. 2). This first comprehensive description and interpretation of dredged basement material from offshore northern New Zealand (Fig. 2) provides critical compositional and age data with which to test earlier regional tectonic hypotheses formulated from geophysical data. Despite the still-sparse database of dredge samples, we are able to directly address a number of important and contentious issues of southwest Pacific regional geology, including: (1) age and nature of the Three Kings Ridge; (2) Mesozoic and Cenozoic geology of the Norfolk Ridge System; (3) age and tectonic setting of the Norfolk Basin; (4) offshore extent of the Northland Allochthon; and (5) potential onshore New Zealand correlatives of the Hikurangi Plateau.

3. Methods

Igneous and metamorphic rocks were recovered at five dredge stations on Institute of Geological and Nuclear Sciences cruise RE9302 of R/V Akademik M.A. Lavrentyev. These stations were all located along seismic reflection profiles, and are prefixed RE in this paper (Fig. 2). Start and end points of dredge stations were located by GPS

navigation. In addition, we obtained some hand specimens, thin sections and/or analyses of dredged rocks from earlier National Institute of Water and Atmospheric Research (NIWA) (E, U and S dredge sites), French Office de la Recherche Scientifique et Technique Outre-Mer (ORSTOM) (GO dredge sites) and Lamont-Doherty Geological Observatory (VE dredge site) expedi- tions in the region (Fig. 2; and unpublished). Not all the rocks from each of these cruises are described in this study and the original reports of Summerhayes ( 1969), Davey ( 1982), Monzier and Vallot (1983), Eade (1988), Rigolot (1989) and Herzer et al. (1997, 1998) should be consulted for more details of rocks recovered. Samples of some onshore North Island New Zealand rocks from the Tangihua and Houhora Complexes (Appendix A; Fig. 2) were also studied in order to assist with comparison and correlation.

All the above material was examined in hand specimen, and representative samples of each rock type from each dredge were selected for thin sectioning. These sectioned samples constitute the dataset for this study (Appendix A); subsets of this main dataset were selected for more detailed study. Methods of sample pretreatment and X-ray fluorescence (XRF), electron microprobe, Sr, Nd and Pb isotopic (including NBS standard measurement) and Ar-Ar analysis are similar to those described by Palmer et al. (1995), Mortimer and Parkinson (1996) and Faulds et al. (1996), and are not repeated here. Nb was determined by XRF using long counting times at the Victoria University laboratory yielding detection limits of ca. 2 ppm (K. Palmer, personal communication).

Glass for fission track analysis was treated according to the population subtraction method (Gleadow, 1981). After irradiation, both the spontaneous and induced glass mounts were polished, then etched for 2 min 30 s in a mixture of 2HF, 1HzS04, lHN0, and 6H,O (Storzer and Selo, 1978) at room temperature. A moldavite age standard of 15.21 f0.15 Ma (Staudacher et al., 1982) and two glass dosimeters were included in the irradiations. The age on the unknown was calculated using the zeta approach (Hurford and Green, 1983). A zeta value (moldavite and dosimeter glasses CN5) of 3 13 + 5 was used in the calculations.

N. Mortimer et ul. / Marine Geology 148 (19981 135.-162 139

All samples, sections and rock powders prefixed ‘P’ are catalogued in the National Petrology Reference Collection of the Institute of Geological and Nuclear Sciences. The New Zealand timescale of Crampton et al. (1995) is used throughout.

4. Petrography and mineralogy

For ease of description, we have divided the rocks used for this study into one onshore and four offshore groups. Although the names of these groups are partially based on geochronological and geochemical data, the groupings can mostly be made using simple petrographic criteria. A summary of location, hand specimen and petrographic data for all 49 samples is presented in Appendix A.

4.1. Onshore North Island

The Tangihua Complex is a disrupted ophiolite of probable Cretaceous (to Early Cenozoic?) age, that was emplaced onto New Zealand as the Northland-East Coast Allochthon in the earliest Miocene (Figs. 1 and 2; Malpas et al., 1992; Isaac et al., 1994 and references therein). Peridotite, gabbro, dolerite and tholeiitic basalt are all present, and the complex is exposed in several massifs throughout Northland. Two pyroxene-plagioclase-porphyritic basalts and two microgabbros from the Maungataniwha Massif were included in this study for XRF and isotopic analysis (Appendix A); all show minor alteration to chlorite and actinolite.

The Houhora Complex is an areally restricted suite of pre-100 Ma, probably Cretaceous, volcanic-hypabyssal igneous rocks and partially reworked submarine volcaniclastic rocks (Fig. 2; Isaac et al., 1994 and references therein). Weakly porphyritic basalt, andesite, dacite and rhyolite compositions are present, and sericitisation and prehnitisation are common (Challis, 1987; Isaac et al., 1994; Palmer et al., 1995). Five rocks analysed by Palmer et al. (1995) were selected for isotopic analysis and two of these, P44143 and P50288, for Ar-Ar dating (Appendix A).

4.2. Reinga Ridge and Vening Meinesz escarpment

Summerhayes ( 1969) described rocks from 48 dredge stations on the continental shelf near the tip of North Island, some of which were re-interpreted by Brook and Thrasher (1991). In addition to a variety of Cenozoic sedimentary rocks (not considered in this paper), some indurated sandstones and igneous rocks were also dredged. The indurated sandstones (greywackes) from sites E310 and E311 re-examined here (P8428, 8429) are unfoliated volcanic litharenites with detrital quartz:feldspar:lithics in the approxi- mate ratio 5:25:70. Volcanic lithics make up about 90% of the total lithic grains. Volcanic detritus is basaltic-andesitic, and detrital clinopyroxene and epidote constitute ca. 1% of the rock. Secondary (metamorphic) minerals include chlorite and pumpellyite.

Pebbles of mafic igneous rocks, partially altered to albite-, chlorite-and actinolite-bearing metamorphic assemblages were dredged from a number of stations on the southeastern Reinga Ridge by Summerhayes ( 1969). A typical pyroxene-plagioclase-phyric basalt from E3 19, and a typical metagabbro from E323 were chosen for this study from the larger set of samples.

Three dredge sites along the Veining Meinesz escarpment yielded mineralogically altered and brittly fractured igneous rocks of probable Mesozoic age. Site RE2 samples consist mainly of altered basalt and dolerite, but siliceous mudstones and barite (P57022) were also recovered. A broadly similar range of deformed and altered rocks was recovered at ORSTOM site G0350, including P57126, a large slab of dark green cataclasite, apparently formed from an aphyric basalt protolith. Other GO350 rock types included brecciated felsic igneous rocks and sedimentary rocks. Two small (< 30 mm) samples of basalt and dolerite were recovered from NIWA dredge site U855.

4.3. West Norfolk and Wanganella Ridges

Dredge RE6 from the crest of the West Norfolk Ridge (Fig. 3), recovered a large number of rounded to subangular pebbles of plutonic

140 N. Mortimer et al. J Marine Geology 148 (1998) 135-162

6-

AUS-

W E

SW NE 0

warlgane//a R t?dnga Basin

AUS- 6

W E 2 W E

NE

4

6

SW NE

L SE Reinga Ridpe

Fig. 3. Line sketches of seismic profiles across 12 of the dredge sites, Vertical scale is two-way travel time (s); reference number of

seismic profile shown in lower corners of sections. WNR = West Norfolk Ridge; WR = Wanganella Ridge; VMFZ = Vening Meinesz

Fracture Zone; WKT= Lower Three Kings Terrace; U3KT= Upper Three Kings Terrace; 3KR = Three Kings Ridge; SERR = southeast

Reinga Ridge.

rocks and of metamorphosed volcanic and feld- composition from pyroxene gabbro, through horn-

spathic litharenites (P57042-57062; Appendix A). blende diorite to biotite granite. Some rocks have

Although many of the pebbles are rounded, they a distinct foliation and could be described as

cannot have been transported more than 20 km orthogneisses.

(the distance from the dredge site to the shallowest The metavolcanic rocks contain 5-15% phe-

part of the crest). The plutonic rocks range in nocrysts (plagioclase + a pseudomorphed mafic

N. Mortimer et al. / Marine Geology 148 (1998) 135-162 141

mineral, presumably pyroxene). Feldspathic litharenites have Q:F:L approximately < 1:15:85 and the lithic clasts are basaltic. Most volcanic rocks and all the sandstones from this dredge have a hornfelsed texture of felted aggregates of randomly oriented fine grained blue-green amphibole and plagioclase. Electron microprobe analyses of RE6 sample P57054, showed the metamorphic amphibole is hornblende containing 8-l 5 wt% Al,O, and that the metamorphic plagioclase is An,,_,,, i.e. characteristic of the hornblende-hornfels facies.

ORSTOM dredge G0360D (Monzier and Vallot, 1983), from the Wanganella Ridge (Figs. 2 and 3) recovered a number of subangular and subrounded plutonic, volcanic and igneous breccia cobbles similar to those at site RE6 (Appendix A). This part of the ridge rises to a peak about 30 km northwest of the dredge site. A single piece of meta-andesite was recovered from dredge site RE7.

4.4. Three Kings and southern Norfolk Ridges

Dredge site REl was sited on the upper Three Kings Terrace on the flanks of a possible low volcanic cone or fault scarp (Fig. 3). Numerous well-rounded to subrounded, Mn-coated pebbles of grey and red highly porphyritic volcanic rocks were recovered. Although rounded, fauna1 evidence (discussed later) indicates that the pebbles have probably been derived from the immediate upslope region. All are basaltic-andesitic with phenocrysts of sector- and oscillatory-zoned greenish clinopyroxene (compositions discussed below). Additional phenocrysts in P57007 are hornblende (magnesio-hastingsite to edenitic hornblende), biotite and plagioclase (core and rim compositions ca. An,,,, Or,); groundmass potassium feldspar (Or,,) is also present.

NIWA dredge sites S573 and S574 were on separate sediment-free highs on the Three Kings Ridge. Pebbles from S573 consist of brownish, altered, fine grained, aphyric vesicular lava (Gamble, personal communication, 1995). Cob- bles from S574 consist of sparsely plagioclase- clinopyroxene-orthopyroxene-phyric basalt; groundmass is partly glassy, but dominated by plagioclase. Plagioclase phenocryst cores are as calcic as An,, (Gamble, personal communication,

1995). A dredge from the northern Three Kings Ridge obtained during R/V Vema cruise 33-14 in 1975 (site VE209, Fig. 2) consisted of an augite- plagioclase-phyric basalt with a partly glassy groundmass (Davey, 1982). The sample could not be located for further study, but a petrographic description and major element analysis was given by Watters in Davey ( 1982) and is included in Table 3.

ORSTOM dredge GO348 just west of the crest of the southern Norfolk Ridge, yielded biotite-rich volcanic breccias and sandstones. One particular breccia selected for study (P57118) contained poorly sorted angular monolithologic clasts, up to 20 mm in size, of devitrified vesiculated glass with abundant biotite and subordinate clinopyroxene (greenish), plagioclase and amphibole phenocrysts. The angular clasts indicate little to no epiclastic reworking and a depositional area within a few km of the original eruptive site is inferred.

4.5. Norfolk and Reinga Basins

Dredge RE3 on the scarp of the lower Three Kings Terrace at the edge of the Norfolk Basin abyssal plain yielded three pebbles of green volcaniclastic sandy siltstone (e.g. P57026). The siltstones contain framework grains of quartz, feldspar, zeo- litised glass shards, pyroxene, amphibole, mica and altered volcanics. The rounded nature of the pebbles may indicate some transport. Two subangular igneous cobbles, and many angular pebbles, were also recovered from site RE3. P57029 is a piece of vesicular pillow basalt with a fresh glassy rind; the glass contains microphenocrysts of olivine (Fo,,), plagioclase (An,,) and Cr spine1 (Cr no. =49-48, Mg no. =60-65). P57025 is a dolerite that is texturally and mineralogically similar to the pillow interior - and also similar in terms of having secondary clay alteration.

At ORSTOM site G0345, an angular cobble of altered olivine basalt was dredged from near the crest of a seamount. This seamount apparently rests on, or very nearly on, oceanic crust and protrudes from beneath 1 km (1 s TWT) of sediment cover on the west side of the South Norfolk Basin (Fig. 3). Basalt was also recovered from NIWA dredge station S565 in the southern North


Norfolk Basin (Gamble, personal communication). The S565 dredge haul consisted of cobbles of vesicular olivine-plagioclase-clinopyroxene- FeTi oxide phyric basalt; olivine compositions range from Fo 83 ,a; _ plagioclase phenocryst cores are as calcic as An,, (Gamble, personal communication, 1995). Pyroxene compositions are considered below.

ORSTOM dredge GO353 was made on a volcanic edifice protruding through sediment cover in the Reinga Basin (Fig. 3; Monzier and Vallot, 1983). A number of angular pieces of vesicular olivine basalt and palagonite breccia were recovered. P57143 is a fresh olivine basalt.

5. Radiometric and fossil dates

Rigolot ( 1989) reported whole rock K-Ar dates from Wanganella Ridge site GO360 of 167 & 10

Table 1

Ar-Ar age determinations

Ma on calcalkaline basalt, 207 f 8 Ma on granodiorite (both presumably whole rock dates) and 220 + 5 and 240 + 5 Ma on feldspars from another granodiorite. He also reported a whole rock K-Ar date of 9.5kO.5 Ma on a basalt from the South Norfolk Basin seamount at site G0345. For the present study, we have dated the exact same hand specimen from GO345 (our P57142), and a different granodiorite hand specimen from site G0360. Results of our Ar-Ar dating of 16 mineral/rock separates from 14 samples are sum- marised in Table 1, and a selection of 10 incremental heating spectra are presented in Fig. 4. For generally smooth spectra (all of the Cenozoic samples), our interpreted age is generally the weighted mean plateau age calculated from contiguous steps that are close to within analytical error of each other, and which include a large percentage of the gas released. For samples with disturbed spectra we have made a subjective judgement of

Dredge P no. UCSB Rock Type wt TFA WMPA Steps, % gas ISOA MSWD Interpreted

no. (mg) (Ma) (Ma) (Ma) age (Ma)

Onshore samples

Houhora P44143 SBlO-35 dolerite w/r Houhora P50288 SBlO-37 dolerite w/r Vening Meinesz escarpment

RE2 P57024 SBlO-33 dolerite plag West Norfolk and Wanganella Ridges

RE6 P57050 SBlO-38 gabb. diorite hbl

RE6 P57051 SBlO-34 granite biot

GO360 P57147 SBlO-39 granodiorite hbl

Three Kings and Norfolk Ridges

REl P57007 SB9-4 shoshonite biot

REl P57013 SB9-6 shoshonite biot

s574 P8502 SB9-11 basalt w/r s574 P8502 SB9-12 basalt w/r s574 P8502 SB9-9 basalt plag GO348 P57118 SB9-18 volt. breccia biot

Norfolk and Reinga Basins

RE3 P57025 SB9-43 dolerite plag RE3 P57029 SB9-45 basalt glass w/r

GO345 P57142 SB9-16 basalt w/r GO353 P57143 SB9-13 basalt wlr

2.5 58.0 60.2kO.2” 700-125O”C, 75% 60.1+0.4 1.2 >60

3.1 60.0 63.6kO.2” 550-7OO”C, 35% 58.7 + 2.9 0.1 Cret?

8.7 71.3 69.2 +0.3” 650-96O”C, 69% 67.1 k 1.8 39.0

4.9 145.0 146.OkO.2” 925-13Oo”C, 95% 146.4kO.5 0.8 146.OiO.2

0.3 116.8 na na na na

7.0 244.0 246.7kO.4” 940-102O”C, 36% 247.9 + 0.8 0.4 247.0k0.8

1.8 20.5 20.5*0.1 850-12OO”C, 91% 20.5+0.1 2.7

1.6 20.5 20.8fO.l 850-lOOO”C, 38% 21.4+0.1 2.3

11.1 17.8 19.7+0.1 600- 650°C 29% 23.6k2.1 47.0

8.0 20.1 21.6+0.1” 600- 650°C 35% 20.7kO.6 51.0

11.5 18.1 19.3 kO.5 800-lOOO”C, 52% 19.7* 1.8 2.4

5.5 26.3 26.3+0.1 850-1250°C 90% 26.3 _tO.l 4.1

20.5 18.1 20.0*0.2a 700-1250°C 75% 19.7+ 1.1 3.1 19.8kO.8

20.3 62.5 na na na na

10.9 16.3 18.4kO.l 550- 750°C 53% 16.7+ 1.2 1361.0 18.4kO.2

10.2 2.21 2.27 k 0.02 450- 8OO”C, 89% 2.28 +0.02 0.7 2.27 kO.02

> 1001

20.5+0.1

20.8 k 0.2

20.0 * 1 .o

20.0 +_ 1 .o

20.0* 1.0

26.3kO.l

Sieve size fractions used were 150-300 urn for minerals and 300-420 urn for whole rocks. w/r = whole rock; plag = plagioclase; hbl=

hornblende; biot = biotite; TFA = total fusion age; ISOA = isochron age; WMPA = weighted mean plateau age calculated from contigu-

ous steps that are within analytical error of each other; MSWD = mean of standard weighted deviations; Cret = Cretaceous; na = not applicable. Complete analytical data are available from the authors on request.

“WMPA estimated from steps that are nearly within analytical error of each other.

N. Mortimer et al. J Marine Geology 148 (1998) 135-162 143

P50298 whole rock dolerite sf310.37

TFA. 64.0 Ma ‘WMPA’. 83.6 f 0.2 Ma

! F’S7024 plagioclare from dolerile

120 ?

3m

PJ7147A hornMends from gnncdioriP 5610.39 _‘..

P57050 hornblende from gabbroie diorib se.ic.38

160

P5.7007 blotite from shoshonite SIB.04

.I UI I

+ TFAS lt3.i MB

WMPA. 19.3 *OS Ma

Fig. 4. Ar-Ar incremental heating spectra for 10 samples. Steps marked in black with bold, italic type and double-headed arrows

were those used to calculate plateau ages given in Table 1. TFA = total fusion age; WMPA = weighted mean plateau age calculated

from contiguous steps that are within analytical error of each other; “WMPA” = estimated WMPA from steps that are nearly within

analytical error of each other; SB= U.C. Santa Barbara laboratory number.


both the most reliable part of each spectrum, and of the uncertainty (which is greater than analytical uncertainty).

5.1. Onshore Houhora Complex

The two onshore samples of the Houhora Complex (P44143, P50288) gave results that, on the basis of pre-late Albian (pre-100 Ma) stratigraphic age of the complex (Isaac et al., 1994) must reflect secondary alteration. The apparent ages of P44143 climb quickly in low temperature steps from about 25 to 60 Ma; P50288 has a disturbed spectrum (Fig. 4) that first climbs from 35 to 64 Ma, then drops from 64 to 60 Ma, then climbs to 74 Ma at the highest temperatures. K/Ca ratios seem unreasonably high for most of the spectrum.

5.2. Vening Meinesz escarpment

Plagioclase from altered dolerite at site RE2, P57024, gave a very disturbed spectrum (Fig. 4), with very low K/Ca ratios, but reasonably large, high-precision signals. Overall, the pattern appears to be characteristic of episodic Ar loss and/or slow cooling and is not dissimilar in gross shape to P50288 (onshore Houhora Complex). Our pre- ferred interpretation is that the dolerite is at least 100 million years old and that it either cooled slowly prior to ca. 70 Ma and was rapidly cooled at ca. 70 Ma, or was reset by a latest Cretaceous (ca. 70 Ma) thermal event. Calcareous nannofossils in the infill of cracks in the same dolerite are Upper Otaian to Middle Altonian (ca. 19-17 Ma; Edwards, personal communication, 1996; Herzer et al., 1997). Mudstones from the same dredge site are of Haumurian (ca. 80-65 Ma) and Dannevirke (ca. 65-43 Ma) of age. Herzer et al. (1997) report that cataclastic argillaceous limestone from site GO350 contained late Teurian to Bortonian fossils (ca. 60-37 Ma).

5.3. West Norfolk and Wanganella Ridges

Two samples gave excellent results. Hornblende from a site GO360 granodiorite (P57147A; Fig. 4) yielded an interpreted cooling age of 247 +0.8 Ma. The apparent ages climb from 225 Ma to about

245 Ma, then are reasonably constant over the middle half of the spectrum, then rise slightly at the end. We interpret this result as a Permo- Triassic hornblende that has experienced a small amount of argon loss. Hornblende from a site RE6 gabbroic diorite (P57050; Fig. 4) yielded an excellent plateau cooling age of 146 +0.2 Ma. Biotite from a site RE6 granite (P57051, not shown in Fig. 4) yielded a spectrum too disturbed for interpretation. Early Miocene fossils have been recovered from sites RE6 and RE7 (Herzer et al., 1997) and represent Cenozoic sedimentary cover on Mesozoic basement.

5.4. Three Kings and southern Norfolk Ridges

Biotite separates from two site REl igneous pebbles on the Upper Three Kings Terrace (P57007, P57013) yielded excellent and good statis- tical plateaux, respectively, which we interpret as the 20.5 and 20.8 Ma crystallisation ages of the lavas. Two whole rock dates and one plagioclase date were obtained from site S574 basalt (P8502) on the crest of the Three Kings Rise. The plagioclase separate had very low K/Ca and a disturbed spectrum with large errors (Fig. 4). Our interpreted error for the plateau age is a conservative estimate. The whole rock separates had hump- shaped spectra, not unusual for whole rock samples, with flattish tops to the humps (Fig. 4). Our interpretation of the three age determinations is that the site S574 basalt crystallised between 19 and 22 Ma.

The biotite separate from the volcanic breccia sample at site GO348 on the southern Norfolk Ridge (P57118) gave a well-defined plateau (Fig. 4). Biotites were separated from the bulk sample, not a single clast, so the good degassing behaviour of this sample confirms the lack of epiclastic reworking of the breccia and suggests the clasts were derived from a single volcanic eruption at 26.3 Ma.

These radiometric dates of lavas from the Three Kings and southern Norfolk Ridges are consistent with fossil age ranges from associated sedimentary rocks reported in Herzer et al. (1997) in that the fossil ages are always coeval or younger than the radiometric ages. For example, site GO348 yielded Early Miocene (ca. 23-16 Ma) shallow water fos-


sils, as compared with the 26.3-Ma igneous age. Site RE 1 calcareous volcaniclastic sandstones yielded ?Waitakian to Otaian (ca. ?24-19 Ma) shoal faunas (Herzer et al., 1997), as compared with the 20-21 Ma igneous ages. Davey (1982) also reported Early Miocene to Late Pliocene (ca. 20-2 Ma) corals from latitude 31”22’S on the Three Kings Ridge, as compared with the ca. 20-Ma Three Kings igneous ages.

5.5. North Norfolk, South Norfolk and Reinga Basins

The fresh glassy rind from South Norfolk Basin site RE3 pillow basalt (P57029) gave a highly disturbed spectrum with very low K/Ca; it did not give an interpretable Ar-Ar age. However, fission- track dating of the glass gave a mean age of 12.6 +2.6 Ma (2~) (Table 2). Since glass is very prone to annealing (Seward, 1979) the long diameter of the shards was measured from both the induced and spontaneous populations. The small, but significant, size reduction (Table 2) means that the age reported here is only a minimum. It is possible to make corrections for this size reduction using the plateau annealing technique (Seward and Moore, 1987; Westgate, 1989). However, this

Table 2

Fission-track age on South Norfolk Basin basaltic glass

Sample number P57029G

Irradiation number eth-82

Standard track density x lo4 cm-’ 620

(counted) (3229)

p,x104cmm2 0.2412

(counted) (108) ~~~lO”crn-’ 31.7

(counted) (942) Mean spontaneous track length (urn) 60610.14

(counted) (105) Mean induced track length (urn) 6.55 + 0.23

(counted) (104)

D,iD, 0.93

Age+2a (Ma) 12.6k2.6

ps and pI represent sample spontaneous and induced track

densities, respectively. D,/Di is the long axis ratio of the sponta-

neous and induced tracks. Length measurement on the molda-

vite gave a D,/Di ratio of 0.97 which can be considered

insignificant. Samples were irradiated at the ANSTO facility,

Australia.

method was not attempted as the glass dated here is of very different chemistry to that reported by Westgate ( 1989).

Plagioclase from dolerite P57025, in the same RE3 dredge haul as the glassy pillow, gave a disturbed Ar-Ar spectrum with very low K/Ca and small 39Ar signals. However, the spectrum is fairly flat at high temperatures (Fig. 4) and we interpret the flat part of the spectrum to give the ca. 20-Ma crystallisation age of the igneous plagioclase. Three samples of chalky calcareous ooze from RE3 have yielded bathyal faunas of upper Lillburnian to Waiauan (ca. 15-l 1 Ma), Waiauan to lower Tongaporutuan (ca. 13-9 Ma) and ?Clifdenian to Waiauan (ca. ?16-11 Ma) age (Herzer et al., 1997). These younger biostrati- graphic ages suggest that the RE3 igneous rocks can be interpreted as Early Miocene basement to the basinal sediments.

Although fairly fresh, the site GO345 North Norfolk Basin basalt previously dated by Rigolot ( 1989) does contain some authigenic red clay in vesicles, slight alteration of olivine to clay, and some zeolites. In our sample preparation, we were very careful to eliminate secondary minerals by scrupulous handpicking of acid-rinsed sieve separates. The P57 142 Ar degassing spectrum (Fig. 4) is a flat-topped hump with evidence for extensive recoil yielding young apparent ages at high temperatures, but a statistically significant plateau at lower temperatures. We infer our 18.4-Ma date for the basalt is a robust age of crystallisation of the lava; the younger, 9-Ma K-Ar age reported by Rigolot ( 1989) may have been affected by secondary K-bearing minerals.

The site GO353 Reinga Basin seamount basalt (P57143) yielded a statistically good, but young whole-rock age of 2.3 Ma (Table 1). It was hoped that a date on this material would establish a link between uplift of the Wanganella Ridge and local volcanism. However, the Pliocene age considerably postdates the uplift which seismic and microfaunal evidence indicates took place in the Miocene (Herzer et al., 1997).

6. Pyroxene and whole rock geochemistry

Clinopyroxenes occur in all of the mafic volcanic rocks dredged, and also in the Norfolk Ridge


0.00 0 0.76 0.80 O.&i 0.90 0.96 1.00 0.70 0.75 0.80 0.85 0.80 0.85 1.00

Ca+Na Ca+Na

0.07 I n u I

SE REINGA RIWE

-0.70 0.75 0.80 0.85 0.90 0.96 1 Co

30

Fig. 5. Chemistry of clinopyroxene grains in selected samples: (a) Ca+Na vs. Ti for Mesozoic samples; (b) Ca +Na vs. Ti for Cenozoic samples; and (c) Ca vs. Ti + Cr for some Cenozoic samples. Cation concentrations calculated on the basis of 6 oxygens. Tholeiitic, alkaline, non-erogenic and erogenic fields from LeTerrier et al. (1982). Houhora and Tangihua fields from Mortimer (unpublished data).

volcanic breccia P57118 and Norfolk Basin fine grained sandstone P57026. One or two samples from each site were selected for electron microprobe analysis, in order to supplement petrographic and whole rock chemical data. In view of the alteration of many of the dredged rocks, pyroxene chemistry proved to be particularly useful in interpreting magmatic affinity and tectonic setting (LeTerrier et al., 1982) and therefore in assisting in correlation. Many volcanic pyroxenes in the dredge samples are sector and/or radially zoned. The dozen or so analyses per sample plotted in Fig. 5 include spots from cores and rims, as well as (001) and ( 110) sectors; for clarity of presenta- tion these are not differentiated and compositional spread for each sample is thus maximised.

Apart from the fresh glass rind on basalt P57029, almost all rocks contain some secondary minerals, resulting from either seafloor ‘weathering’ (red- brown smectite clays) or by low grade metamorphism (zeolites, chlorite). All whole rock analyses (Table 3) also show appreciable loss-on-ignition values. Thus silicon, alkaline-earth and alkali element concentrations probably do not reflect pri-

mary values. In terms of establishing magmatic affinity, we place more reliance on high-field strength elements, which are generally recognised to be less mobile. To reduce the effects of seafloor ‘weathering’, measurements of Sr and Nd isotopes for all dredged rocks were made on acid-leached residues as described by Mortimer and Parkinson (1996); results are reported in Table 4. Pb isotopic ratios were only measured on unleached samples.

The small numbers of samples from each site preclude a detailed assessment of such features as liquid lines of descent in igneous suites. For Mesozoic samples, which are generally metamorphosed, we illustrate chemical variation by way of binary plots, mainly using less mobile elements (Fig. 6); for the generally fresher Cenozoic lavas, we use normalised multi-element diagrams after Sun and McDonough (1989) e.g. Fig. 7.

6.1. Onshore rocks

New pyroxene analyses were made of two Tangihua Complex samples P34084 and P34124, and of Houhora Complex samples P44140, P44143

N. Mortimer et al. /Marine Geology 148 (1998) 135-162 147

and P50286. All pyroxenes have low Ti and Na, consistent with crystallisation from tholeiitic magmas (LeTerrier et al., 1982). Taken at face value (Fig. .5a), the minor element contents of the Houhora and Tangihua pyroxenes are similar to pyroxenes from tholeiitic rocks, but the distinctly higher Ti content of the Houhora pyroxenes suggests a transitional alkaline affinity and/or an intraplate setting.

In terms of bulk-rock chemical composition, our four analysed Tangihua basalts are also clearly different from Houhora Complex basalts which have distinctly higher Nb/Y and Ti/V (Fig. 6a), the latter typical of intraplate basalts (Shervais, 1982). The Ti/V ratios of the clearly tholeiitic Tangihua are MORB (mid-ocean ridge basalt)- like, but the very low Nb contents are suggestive of back-arc basin basalts. Such lavas have been reported, along with N-MORB compositions, from the correlative Matakaoa Complex of the East Coast Allochthon (Fig. 1) by Sewell (1992). Malpas et al. ( 1994) reported Tangihua basalts with mainly N-MORB-like chemistry and no anomalously low Nb, though the Tangihua dataset of Larsen and Parker ( 1989) contained mostly basalts with <2 ppm Nb. The different Nb contents in Tangihua basalts may be explained either by different types of depleted basalts (cf. Sewell, 1992) and/or by inter-laboratory analytical differences; discussion of the reasons behind the Nb differences is outside the scope of this paper.

Our four Tangihua basalts have fairly non-radio- genie Nd and Sr isotopic ratios that overlap the present-day Pacific MORB field (Fig. 8a). As expected from the pyroxene and whole rock chemistry, the Houhora rocks have consistently lower ENd values than the Tangihua rocks - the high and variable 87Sr/86Sr may be due to metasomatic effects.

6.2. Reinga Ridge and Vening Meinesz escarpment

Six pyroxene analyses from site E323 gabbro P8442 on the southeast Reinga Ridge fall well within the Tangihua reference field on Fig. 5a. Analyses from the altered dolerites at the dredge sites along the Vening Meinesz escarpment (P57018, 57024, 57068) show weak to moderate alkaline affinities on Fig. 5a, somewhat different

from Houhora and Tangihua pyroxenes. This particular interpretation is important because the highly altered nature of the dolerites renders whole rock normative compositions unreliable.

Site E319 metabasalt (P8433) has high field strength element concentrations and ratios very close to the four analysed Tangihua Complex rocks (Fig. 6a, Table 3). Nb accuracy (see above) is not an issue here. Since our four Tangihua basalts and the site E319 basalt were analysed under identical machine conditions, we are confident of their similarity.

The dolerites from site RE2 are similar to each other in composition, as are the pair of dolerites from U855 (Fig. 6a). The latter are more enriched in incompatible trace elements, and have lower ENd, and higher 87Sr/86Sri, than the former. High field strength element concentrations in all four rocks are consistent with the interpretation, based on pyroxene chemistry, of alkaline basalts. Certainly, none of the altered dolerites from sites RE2, U855 or GO350 on the Vening Meinesz escarpment correlate with Tangihua rocks or those on the southeast Reinga Ridge. Clear correlation of the northwestern Reinga Ridge dolerites with the Houhora Complex is also seemingly ruled out by differences in pyroxene chemistry and whole- rock ENd (Figs. 5 and 8).

6.3. West NorfiIk Ridge and Wanganella Ridge

The two metabasalts from site RE6 have Nb below detection limit of 2 ppm; this has been confirmed on two separate occasions with long Nb count times (K. Palmer, personal communication, 1995). Overall, element concentrations are in accord with their being subduction-related low- medium K tholeiites. Fig. 6b shows that they com- pare well, in having low Zr and Zr/Y, with Permian metabasalts from the Brook Street Terrane of New Zealand’s South Island. Hornblende-hornfels facies volcanic and volcaniclastic rocks are only found in abundance in New Zealand near the Brook Street Terrane-Median Tectonic Zone contact.

We have not interpreted the geochemistry of the plutonic rocks from sites RE6 and GO360 in any great detail, particularly as small sample sizes may

Tab

le

3 X

-ray

fl

uore

scen

ce

anal

yses

of

w

hole

ro

cks

E

P n

o.

Dre

dge

Roc

k na

me

SiO

z T

iO,

Al,O

, Fe

,O,

MnO

M

gO

CaO

N

a,O

K

,O

P,O

, L

OI

Tot

al

Ba

Ce

Cr

55.9

5 1.

02

15.2

1 9.

21

0.15

5.

48

9.40

3.

00

0.50

0.

08

2.70

10

0.08

59

11

71

51.9

4 0.

90

15.1

1 10

.17

0.19

7.

61

9.79

3.

06

1.16

0.

07

2.36

99

.92

103

7 13

3

51.0

6 1.

70

15.2

4 11

.34

0.19

6.

66

10.6

4 2.

89

0.13

0.

14

1.87

99

.74

25

14

127

51.1

0 0.

91

17.5

3 9.

21

0.16

6.

69

11.4

8 2.

69

0.17

0.

06

2.59

10

0.11

45

8

135

Ons

hore

T

angi

hua

Com

plex

3032

1 T

angi

hua

basa

ltic

ande

site

3407

5 T

angi

hua

suba

lk

basa

lt

3408

4 T

angi

hua

suba

lk

mic

roga

bbro

3412

4 T

angi

hua

suba

lk

mic

roga

bbro

Rei

nga

Rid

ge

and

Ven

ing

Mei

nesz

es

carp

men

t

0843

3 E

319

suba

lkal

ic

basa

lt

5702

3 R

E2

alka

lic

basa

lt

5702

4 R

E2

alka

lic

basa

lt

5706

7 U

855

alte

red

alka

lic

basa

lt

5706

8 U

855

alte

red

alka

lic

basa

lt

5712

6 G

O35

0 ca

t su

balk

ba

salt

Wes

t N

orfo

ik

and

Wan

gane

Na

Rid

ges

51.4

3 0.

90

16.4

7 9.

99

0.17

7.

33

9.53

3.

73

0.41

0.

06

0.68

10

0.10

47

10

49.5

3 2.

85

16.6

2 10

.33

0.19

4.

52

10.7

2 3.

59

1.23

0.

41

11.0

4 10

0.15

20

8 60

47

.89

2.44

16

.22

9.48

0.

32

5.57

12

.5

3.96

0.

83

0.79

9.

22

99.8

5 14

6 55

44.7

3 2.

46

13.6

3 12

.97

0.16

14

.41

6.28

3.

30

1.40

0.

67

9.56

10

0.18

35

9 93

45.5

5 2.

80

15.1

4 11

.10

0.21

9.

33

8.36

5.

02

1.63

0.

87

0.68

10

0.07

38

7 10

8

51.4

4 1.

25

17.9

1 10

.35

0.19

6.

27

8.56

3.

39

0.36

0.

30

4.79

10

0.13

60

36

5704

3 R

E6

alte

red

suba

lk

basa

lt 48

.47

1.31

16

.86

12.3

8 0.

20

7.95

8.

39

3.72

0.

50

0.21

5.

27

100.

14

179

10

5704

4 R

E6

gnei

ssic

di

orite

61

.04

1 .oo

17

.22

8.14

0.

25

1.71

5.

52

4.58

0.

23

0.32

0.

50

100.

16

76

15

5704

7 R

E6

bi-h

bl-p

x ga

bbro

48

.00

1.09

20

.54

12.2

3 0.

22

3.85

9.

97

3.65

0.

25

0.18

0.

76

100.

13

96

12

5704

8 R

E6

hbl

gabb

ro

46.9

8 1.

47

18.4

9 14

.47

0.33

4.

04

9.48

3.

82

0.34

0.

57

0.91

99

.92

108

26

5704

9 R

E6

px-h

bl

gabb

ro

48.6

9 1.

73

19.3

8 11

.92

0.28

3.

96

9.59

3.

76

0.21

0.

46

0.62

10

0.06

90

10

5705

0 R

E6

hbl

gabb

roic

di

orite

54

.88

0.75

19

.82

7.71

0.

14

3.40

9.

02

3.34

0.

80

0.16

0.

87

100.

11

184

12

5705

1 R

E6

biot

ite

gran

ite

72.0

7 0.

46

14.6

8 2.

73

0.04

0.

90

2.30

3.

83

2.90

0.

09

0.83

99

.99

646

25

5705

2 R

E6

biot

ite

gran

odio

rite

71

.33

0.56

15

.27

2.80

0.

07

1.16

3.

80

4.04

0.

81

0.13

0.

97

99.7

8 28

9 10

5705

3 R

E6

px-b

i gr

anod

iori

te

64.5

3 0.

70

17.0

3 5.

55

0.10

1.

25

4.96

4.

28

1.44

0.

15

0.72

10

0.19

54

8 19

5705

4 R

E6

horn

fels

ed

lithi

c ss

57

.48

1.00

16

.91

9.10

0.

20

3.21

7.

14

4.25

0.

36

0.33

0.

58

100.

25

53

31

5705

9 R

E6

horn

fels

ed

basa

lt 45

.86

1.47

20

.58

13.0

3 0.

27

4.84

9.

53

2.90

1.

34

0.18

1.

27

100.

12

411

21

5706

4 R

E7

alte

red

met

a-an

desi

te

58.6

2 0.

88

20.0

1 6.

27

0.49

2.

38

2.09

8.

37

0.69

0.

21

2.77

99

.77

105

32

5714

6 G

O36

0 bi

-hbl

gr

anod

iori

te

69.0

8 0.

52

14.9

1 3.

81

0.07

1.

41

3.31

3.

93

2.84

0.

12

0.14

99

.53

400

42

5714

7 G

O36

0 bi

-hbl

gr

anod

iori

te

68.2

4 0.

54

15.2

6 3.

81

0.05

1.

95

3.10

4.

07

2.86

0.

12

1.62

10

0.16

38

0 36

Thr

ee

Kitr

gs

Rid

ge

5700

7 R

El

5700

8 R

El

5700

9 R

EI

0850

2 ss

74

0850

3 SS

73

0850

5 V

E20

9

98

170

241

3

278

5

255

2.

88

3 ;1

29

c

2 7 $

10

$

2 Q

10

g

2 2

1 2

5 2

23

z

36

??

1

15

5

16

&

trac

hyan

desi

te

55.3

4 0.

90

18.2

0 8.

79

0.07

2.

72

4.94

3.

56

4.94

0.

51

4.50

99

.81

1577

61

10

1

basa

ltic

t-an

desi

te

53.5

9 0.

87

14.3

1 7.

27

0.63

5.

33

9.89

2.

79

4.59

0.

74

2.73

99

.62

1720

51

25

0

basa

ltic

t-an

desi

te

53.2

9 1.

06

16.5

0 7.

63

0.09

3.

27

8.54

2.

82

5.2

1.59

3.

87

99.3

9 16

27

79

85

suba

lkal

ic

basa

lt 51

.17

0.78

19

.01

10.3

2 0.

18

4.17

9.

69

3.49

0.

94

0.25

0.

68

99.3

8 25

5 9

27

alte

red

suba

lk

basa

lt 51

.70

1.50

16

.70

12.3

2 0.

63

2.69

6.

93

4.56

2.

36

0.61

2.

87

99.9

9 45

7 19

9

suba

lkal

ic

basa

lt 51

.54

1.83

15

.52

13.6

2 0.

19

4.06

8.

96

3.51

0.

78

? 7

? nd

nd

nd

N

orfb

lk

and

Rei

nga

Bas

ins

0850

4 S5

65

trac

hyba

salt

45.8

7 3.

16

17.8

4 10

.22

0.20

5702

5 R

E3

suba

lk

mic

roga

bbro

49

.70

1.61

17

.61

9.38

0.

12

5702

96

RE

3 su

balk

ba

salt,

gl

ass

52.3

1 1.

38

16.5

9 8.

21

0.13

5702

91

RE

3 su

balk

ba

salt,

in

side

51

.37

1.54

19

.16

8.17

0.

08

5714

2 G

O34

5 al

kalic

ba

salt

46.5

6 2.

54

18.9

9 10

.10

0.15

5714

3 G

O35

3 al

kalic

ba

salt

49.4

1 2.

55

15.5

2 11

.56

0.14

5.61

7.

81

5.29

2.

77

1.22

1.

39

99.2

0 36

3 11

7 44

6.55

10

.81

3.80

0.

25

0.17

3.

31

100.

14

29

16

264

7.36

9.

61

3.36

0.

84

0.21

2.

32

100.

15

241

33

377

4.29

10

.48

3.69

0.

85

0.39

6.

06

100.

13

206

37

428

3.99

11

.15

3.72

1.

16

1.63

4.

82

99.6

6 23

6 72

23

8 4.

57

10.6

8 4.

02

1.08

0.

46

0.71

10

0.17

13

6 47

14

3 -

Tab

le

3 (c

onfi

rmed

)

Ons

hore

T

angi

hua

Com

plex

30

321

Tan

gihu

a ba

salti

c an

desi

te

3407

5 T

angi

hua

suba

lk

basa

lt 34

084

‘fan

gihu

a su

balk

m

icro

gabb

ro

3412

4 T

angi

hua

suba

lk

mic

roga

bbro

R

eing

a R

idge

and

V

enin

g M

eine

sz

esca

rpm

ent

0843

3 E

319

suba

lkal

ic

basa

lt 57

023

RE

2 al

kalic

ba

salt

5702

4 R

E2

alka

lic

basa

lt 57

067

U85

5 al

tere

d al

kalic

ba

salt

5706

8 U

855

alte

red

alka

lic

basa

lt 57

126

GO

350

cat

suba

lk

basa

lt W

est

Nor

folk

and

W

anga

nell

a R

idge

s 57

043

RR

6 al

tere

d su

balk

ba

salt

5704

4 R

E6

gnei

ssic

di

orite

57

047

RE

6 bi

-hbl

-px

gabb

ro

5704

8 R

E6

hbl

gabb

ro

5704

9 R

E6

px-h

bl

gabb

ro

5705

0 R

E6

hbl

gabb

roic

di

orite

57

051

RE

6 bi

otite

gr

anite

57

052

RE

6 bi

otite

gr

anod

iori

te

5705

3 R

E6

px-b

i gr

anod

iori

te

5705

4 R

E6

horn

fels

ed

lithi

c ss

57

059

RE

6 ho

mfe

lsed

ba

salt

5706

4 R

E7

alte

red

met

a-an

desi

te

5714

6 G

O36

0 bi

-hbl

gr

anod

iori

te

5714

7 G

O36

0 bi

-hbl

gr

anod

iori

te

Thr

ee K

ings

Rid

ge

5700

7 R

EI

trac

hyan

desi

te

5700

8 R

El

basa

ltic

t-an

desi

te

5700

9 R

EI

basa

ltic

t-an

desi

te

0850

2 s5

74

suba

lkal

ic

basa

lt 08

503

S573

al

tere

d su

balk

ba

salt

0850

5 V

E20

9 su

balk

alic

ba

salt

Nor

folk

an

d R

eing

a B

asin

s

0850

4 S5

65

trac

hyba

salt

5702

5 R

E3

suba

lk

mic

roga

bbro

57

0296

R

E3

suba

lk

basa

lt,

glas

s 57

0291

R

E3

suba

lk

basa

lt,

insi

de

5714

2 G

O34

5 al

kalic

ba

salt

5714

3 G

O35

3 al

kalic

ba

salt

Cu

Ga

La

Nb

Ni

Pb

Rb

SC

83

16

4 <

2 41

1

9 33

13

7 0.

1 0.

4 29

3 26

71

61

69

15

2 2

58

2 16

37

15

5 0.

5 0.

4 30

0 22

88

50

94

20

6 3

54

3 3

40

119

1.8

0.4

349

89

109

108

61

18

4 2

54

2 5

35

135

0.9

0.3

268

21

61

51

85

16

4 <

2 63

1

8 41

15

5 1.

4 0.

7 29

4 23

79

50

II5

23

23

30

90

2 21

32

32

1 3.

7 1.

2 34

8 38

19

1 23

8

100

22

23

20

97

3 10

43

32

9 2.

1 0.

2 32

9 52

24

8 19

3

54

18

39

50

270

6 31

16

18

7 5.

8 1.

4 20

0 28

15

4 20

0

55

18

45

62

263

I 40

20

32

9 7.

3 1.

4 22

3 34

16

5 24

6

43

20

15

9 55

2

8 23

81

2 0.

3 0.

1 16

9 25

12

2 12

1

78

19

5 <

2 82

2

17

44

120

1.5

0.8

375

32

131

69

17

19

6 2

18

10

2 21

50

2 0.

9 0.

2 66

29

83

71

178

22

5 t2

9

3 7

30

675

0.8

0.1

267

I4

92

21

158

23

7 <

2 29

4

5 51

59

4 0.

9 03

19

1 46

13

2 35

41

23

5

<2

6 4

4 48

73

8 1.

6 0.

2 20

0 18

11

6 22

57

19

5 <

2 9

5 20

29

93

7 0.

4 0.

1 22

2 16

71

34

29

13

11

2 7

4 50

7

266

6.2

1.1

47

24

32

194

162

13

5 3

15

4 26

9

446

4.3

0.5

63

21

37

218

14

18

9 12

16

5

26

13

511

2.3

0.4

119

14

49

168

13

20

14

5 25

20

8

30

597

4.2

0.4

199

29

91

134

207

25

7 <

2 23

21

28

42

57

2 2.

1 0.

2 38

8 30

18

4 77

17

6 19

I4

6

272

5 6

12

183

2.6

1.1

97

59

93

283

67

14

17

6 8

7 91

11

21

8 8.

7 1.

1 67

30

42

18

9 25

I6

16

4

24

7 86

11

22

5 8.

2 0.

7 76

28

30

18

0

128

22

29

11

34

27

176

16

768

18.2

2.

4 16

9 28

88

18

7 19

6 17

28

7

268

28

199

30

856

16.5

5.

3 19

0 37

75

14

5 19

6 20

63

15

44

38

11

4 25

99

4 21

.7

4.5

194

104

124

224

122

18

6 2

29

II

8 32

34

4 4.

1 2.

1 28

4 25

92

69

32

23

12

2

37

2 47

34

30

7 4.

5 3.

5 24

7 61

19

7 91

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

nd

32

20

64

112

42

5 33

20

13

96

8.2

3.1

186

37

81

409

81

18

5 <2

11

2 3

6 25

20

5 1.

7 0.

1 21

4 30

75

11

5 46

16

I3

10

12

6 3

23

30

221

2.2

1.1

231

30

70

134

66

21

16

12

84

8 I4

37

29

4 4.

0 1.

4 24

9 40

11

6 15

3 83

19

35

53

68

4

12

29

565

4.7

07

265

43

I57

220

44

23

19

29

57

3 13

23

45

9 1.

9 0.

4 25

1 25

12

6 15

3

- S

r -

Th

U

V

Y

Zn

Zr

Maj

or

elem

ents

re

calc

ulat

ed

to

100

wt%

an

hydr

ous,

an

d tr

ace

elem

ents

re

calc

ulat

ed

usin

g th

e sa

me

norm

alis

ing

fact

or;

orig

inal

lo

ss

on

igni

tion

(LO

I)

and

anal

ytic

al

tota

ls

are

show

n.

Maj

or

elem

ent

conc

entr

atio

ns

give

n in

wt%

, tr

ace

elem

ents

in

ppm

. nd

= n

ot

dete

rmin

ed;

suba

lk

= su

balk

alin

e;

t-an

desi

te

= tr

achy

ande

site

; ca

t =

cata

clas

tic;

ss=

sand

ston

e.

Roc

k na

mes

ba

sed

on

chem

ical

cl

assi

fica

tion

of

Mid

dlem

ost

( 19

94);

w

here

pr

efix

ed

by

‘alte

red’

in

dica

tes

prob

able

m

etas

omat

ism

of

ro

ck.

Ana

lyst

K

. Pa

lmer

, V

icto

ria

Uni

vers

ity

of

Wel

lingt

on,

exce

pt

for

PO85

05

repo

rted

by

D

avey

(1

982)

fo

r w

hich

an

alys

t an

d m

etho

ds

are

unkn

own.

150

Table 4

N. Mortimer et al. 1 Marine Geology 148 (1998) 135-162

Summary of Sr, Nd, Pb isotopic ratios for selected onshore reference suites and dredged rocks

P no. Dredge Rock type T “Sr/s7Sri eNd (T) 2%pb,Z04pb 207pb,+,,, ZOL?p,,,Z04pb

(Ma) Unleached Leached Unleached Leached Unleached Unleached Unleached - -

Onshore reference suites 30321 Tangihua metabasalt 120 0.702954

34075 Tangihua metabasalt 120 0.702764

34084 Tangihua dolerite 120 0.702688

34124 Tangihua dolerite 120 0.703242

36525 Houhora granophyre 120 0.702929

44134 Houhora andesite 120 0.703834

44141 Houhora andesite 120 0.704316

44143 Houhora dolerite 120 0.703186

50288 Houhora dolerite 120 0.705013

Reinga Ridge and Vening Meinesz escarpment 57019 RE2 altered basalt 120 0.702420

57023 RE2 altered dolerite 120 0.702904

57067 U855 altered basalt 120 0.702797

57068 U855 altered basalt 120 0.702918

57126 GO350 cataclasite 120 0.703627

West Norfolk and Wanganeiia Ridges 57146 GO360 granodiorite 247 0.703112

57147 GO360 granodiorite 247 0.703295

57050 RE6 gabbroic diorite 146 0.705193

57051 RE6 granite 146 0.703323

Three Kings Ridge 08502 S574 basalt 20 0.704074

57007 REl shoshonite 20 0.704377

Norfolk and Reinga Basins 57142 GO345 basalt 18 0.702711

57143 GO353 basalt 2 0.702803

57025 RE3 dolerite 20 0.702456

57029 RE3 glassy rind 20 0.703286

nd 7.1 nd 19.241 15.613 38.66

nd 7.5 nd 19.016 15.577 38.48

nd 7.8 nd 18.972 15.525 38.40

nd 7.3 nd 18.814 15.604 38.58

nd 2.8 nd 19.252 15.638 39.12

nd 3.0 nd 19.991 15.692 39.76

nd 3.0 nd 19.985 15.676 39.95

nd 4.2 nd 19.068 15.600 38.87

nd 3.5 nd 19.312 15.629 39.04

0.702627 7.6 9.0 18.629 15.501 38.40

0.702966 5.7 7.3 19.362 15.599 39.10

0.702787 5.7 5.6 19.353 15.631 39.09

0.702865 5.7 5.7 19.313 15.617 39.04

0.703434 6.4 6.3 19.038 15.574 38.82

0.703230 6.0 8.9 19.305 15.603 38.74

0.703389 6.4 6.0 19.399 15.617 39.04

0.704101 6.0 6.1 18.668 15.585 38.35

0.703392 6.1 6.2 18.816 15.590 38.64

0.704030 5.2 5.6 18.875 15.610 38.71

0.704305 2.4 0.5 18.843 15.613 38.70

0.702681 7.2 6.9 19.492 15.585 39.03

0.702756 6.9 4.1 19.289 15.575 38.75

0.702484 8.9 9.2 18.671 15.518 38.22

0.703310” 6.1 9.4” 18.955 15.612 38.75

Pb data have not been corrected for age. Complete analytical data are available from the authors on request. nd=not determined.

“Very low Sr and Nd concentration for leached glass; unleached ratios considered more reliable.

have biased element concentrations in these some- times coarse-grained rocks. Fig. 6c shows that all 10 plutonic rocks lie close to, or within, the trend defined by the 260- to 130-Ma Median Tectonic Zone (MTZ) suite of igneous (mainly plutonic) rocks (see Kimbrough et al., 1994). All RE6 and GO360 plutonic rocks, including those that plot between the MTZ and Separation Point fields on Fig. 6c, have Na,O ~4.5 wt% and Y > 14 ppm. They are thus not correlatives of the sodic, high Sr/Y Separation Point Suite. Initial Sr and Nd isotopic ratios for four dredged plutonic rocks fall close to, but not entirely within, the range of onshore Triassic to Cretaceous MTZ rocks (Fig. 8a). MTZ plutons have the mineralogical

and chemical characteristics of a typical calc-alkaline, I-type, subduction-related igneous suite.

6.4. Three Kings Ridge and southern Norfolk Ridge

Fig. Sb,c shows that clinopyroxenes in lavas P8502, P57007 from both Three Kings Ridge sites, and site GO348 Norfolk Ridge volcanic breccia (P57118) are all very low in Ti, and an erogenic, subduction-related origin can be inferred. The clinopyroxene phenocrysts in P8502 have relatively low Ca contents, and co-exist with orthopyroxene; groundmass pigeonite is also present (Gamble, personal communication, 1995). In contrast, clinopyroxene phenocrysts in the REl and GO348


REINQA FUWE 6 VENINQ MEINES! ESCARPMENT

1. I 10 100

zrb~m) IwLl

1200

800

0 c

700

0 50 60 70 80

902 ww

Fig. 6. Whole rock chemistry of Mesozoic samples: (a) basalts

and gabbros from the southeast Reinga Ridge and Vening Meinesz escarpment compared with selected onland Cretaceous suites (data from this study, Challis, 1987; Sewell et al., 1988; Palmer et al., 1995). Alkaline,/subalkaline and intraplate/ MORB/arc divisions after Floyd and Winchester (1978) and Shervais (1982); (b) metabasalts from the West Norfolk and Wanganella Ridges compared with metabasalts of the Permian Brook Street Terrane (Houghton, 1985); and (c) plutonic rocks from the West Norfolk and Wanganella Ridges compared with compositional ranges of Phanerozoic New Zealand granitoids (Mortimer et al., 1997).

samples have high Ca and Ca+Na contents that are indicative of a shoshonitic affinity (Morrison, 1980).

On an SiO, versus K,O diagram (Fig. 7a), the

site VE209 and S574 samples, from the axis of the Three Kings Ridge, plot as medium-K basal@ whilst, in contrast, all three site REl lavas, from the upper Three Kings Terrace, plot in the shoshonite field. Site S573 lava P8503 has a high clay mineral content and its ‘absarokite’ classification must be considered suspect. The prominent negative Nb and Ti anomalies in the spidergrams (Fig. 7b) indicate a clear subduction-related geochemistry for all Three Kings Ridge lavas, and the extreme large-ion-lithophile element concentrations confirm the shoshonitic nature of the REI dredges, as also indicated by their phenocryst assemblages and pyroxene chemistry (Morrison, 1980). The two Three Kings Ridge samples are the most radiogenic of the entire Cenozoic dataset in terms of initial Nd and Sr isotopic ratios (Fig. 8b). Thus the isotopic data are entirely consistent with a subduction-related petrogenesis.

6.5. North und South Norfolk Basins

Clinopyroxenes in site S565 North Norfolk Basin basalt P8504 have extreme Ti contents, much higher than any other sample in the dataset; a strong alkaline affinity is indicated. Pyroxenes from the South Norfolk basin dolerite, P57025, at site RE3 show transitional tholeiitic-alkaline, non-oro- genie affinities. Detrital pyroxenes in the RE3 sandy siltstone P57026 have low-Ti, high-Ca and high-Ca + Na contents, i.e. different from the RE3 dolerite, but very similar to the shoshonitic pyroxenes at sites REl and GO348 (Fig. 5).

In terms of whole rock element concentrations, site RE3 glassy pillow basalt P57029 shows E-MORB to transitional alkaline affinity, with small, but distinct, negative Nb and Ti anomalies. The RE3 dolerite P57025 is more depleted in incompatible trace elements, particularly Nb, than the pillow lava and is also more radiogenic (Fig. 8b). Although little can be based on two samples, the negative Nb anomalies indicate these are not simple MORB rocks; there is an influence of subduction zone processes and/or sources in their genesis. Both the dolerite and pillow basalt have Zr > 80 ppm and V/Ti ~0.04, similar to many back-arc basin basalts and different from island arc tholeiites (Woodhead et al., 1993). The

152 N. Mortimer et al. I Muvine Geology 148 (1998) 135-162

61a THREE KINGS RIDGE

54 1 ;.mj

g 4A

5 I

0 37 y” ’

21

1 1

0 j 46 52 56 60 64 68

SiOz wt%

1000 c

j

SOUTH NORFOLK BASIN

100’

1’ I / 1 I, I I I I I I! 1’ I I I I1 I II I I I I I

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

ioooJ b THREE KINGS RIDGE

1’ I I I I! I / 1 I I I / , RbBaTh U NbK LaCeSr P Zr Ti Y

SEAMOUNTS

Fig. 7. Whole rock chemistry of Cenozoic samples: (a,b) from Three Kings Ridge; (c) from dredge site RE3 in the Norfolk Basin;

and (d) from seamount dredge sites in the North Norfolk, South Norfolk and Reinga Basins. PMN=primitive mantle-normalised

concentrations after Sun and McDonough (1989).

cNd urangi Plai~au (~3)

I onland MT2

Houhora Complex (~5)

a.7bs 0 704 o.io5 0.7b6

*7sr/%r,

cNd

;f2!!?5g~~,

0 - Kermadec-Taupe . Sho9hon,(8

subduction-related Iwas

-2 0.702 0.703 0.704 0.705 0.706

%t=sr ,

Fig. 8. Comparison of Sr and Nd isotopic ratios of the dredged rocks with those from reference suites: (a) Mesozoic; and (b) Cenozoic.

Analyses of acid-leached powders plotted except for onland suites and the RE3 glass. Initial “S$?Sr and cNd ratios calculated from

ages given in Table 4. Fields for Pacific MORB and Hikurangi Plateau from Mortimer and Parkinson (1996) and references therein,

field for modern back-arc (Havre Trough) and arc lavas from Gamble et al. ( 1996), field for MT2 from Parkinson and Tulloch

(unpublished) and for Tapuaenuku Complex from Baker et al. (1994).

Mg no. and Cr no. of spine1 microphenocrysts in P57029 are intermediate between those from East Pacific Rise MORB and back-arc basin basalts (Gamble et al., 1993 and references therein). We

provisionally suggest that the RE3 rocks are mineralogically and chemically most compatible with eruption in a back-arc basin setting, but more sampling would be required to support this.

N. Movfimer et al. / Marine Geology 148 (1998) 135-162 153

Intraplate (transitional to alkaline) basaltic suites of Miocene to Recent age are widely distrib- uted onshore and across the entire New Zealand continental shelf (e.g. Weaver and Smith, 1989). The three seamount basalts from sites GO345 (Miocene), GO353 (Pliocene) and S565 (undated) further add to this database.

7. Mesozoic continental basement

7. I. Northlund geology on the southeast Reinga Ridge

Autochthonous basement in Northland is com- posed mainly of pumpellyite-bearing volcanic litharenites of the Waipapa Terrane (Sporli, 1978). Sandstones associated with the Houhora Complex, Tangihua Complex and Late Cretaceous-Cenozoic strata are zeolite-facies feldsarenites (Palmer et al., 1995) and clearly different. The sandstones from dredge sites E310 and E311 are thus most likely to be from the Waipapa Terrane. Waipapa Terrane sandstones have also been dredged from the Colville Knolls, ca. 400 km southeast of the E310 and E311 (Fig. 1; Gamble et al., 1993).

Ophiolitic rocks of the allochthonous Tangihua Complex are widespread in onshore Northland (Fig. 2). Our correlation of igneous rocks from sites E319 and E323 with Tangihua Complex confirms the interpretation of Brook and Thrasher ( 1991) and Herzer and Mascle ( 1996) that Tangihua Complex rocks are exposed in the southeastern block of the Reinga Ridge.

7.2. ?Cretaceous basalts on the Vening Meinesz escarpment

The degree of sericitisation, fracturing and calcite veining of basalts from sites RE2, U855 and GO350 is such that, on the basis of initial thin section examination, we thought that they could be potential correlatives of the Cretaceous Houhora Complex. The occurrence of altered cataclastic granite at site GO350 (Appendix A) is compatible with a Houhora Complex correlation, as granophyres and silicic igneous rocks are fairly common onshore in Northland (Isaac et al., 1994).

Furthermore, the Ar-Ar incremental heating spectrum of the site RE2 dolerite is somewhat similar to the spectra of the dated Houhora Complex dolerites, inasmuch as all of them give indistinct Late Cretaceous plateaus, and none of them yield obviously primary ages. However, nei- ther relict pyroxene chemistry, bulk rock chemical composition, nor isotopic composition (Figs. 5, 6 and 8) support a clear petrological correlation with the Houhora Complex (assuming that our analysed database of Houhora rocks is complete enough),

Instead, the Ti-rich relict pyroxene chemistry, primitive Sr and Nd isotopic character, and generally more incompatible element-rich nature of the site RE2 and U855 basalts suggest a new discovery of rift-related mildly-alkaline volcanism of possible Late Cretaceous age on the Reinga Ridge. Such suites are unknown in North Island, but are known in several places in the South Island (e.g. Sewell et al., 1988; Weaver and Smith, 1989; Baker et al., 1994 and references therein). Speculatively, their presence at latitude 33”S, and their altered mineralogy and reset Ar-Ar ages, could be related to the ?Late Cretaceous continental rift of the New Caledonia and Reinga Basins (Uruski and Wood, 1991; Herzer et al., 1998).

7.3. Tangihua Complex is not abducted Hikurangi Plateau

The Tangihua Complex has typically been interpreted as a piece of Cretaceous oceanic crust with N-MORB chemistry that was abducted onto New Zealand in the Early Miocene (e.g. Larsen and Parker, 1989; Malpas et al., 1992, 1994; Isaac et al., 1994). Mortimer and Parkinson ( 1996) raised the possibility that instead, the Tangihua Complex could be an abducted part of the Hikurangi Plateau (Fig. 1). Their interpretation was based on a comparison of the then-existing major and trace element database for the Tangihua and correlative Matakaoa Complex. However, our new isotopic data for four Tangihua basalts (Table 4) do not support the provisional Hikurangi Plateau-Tangihua Complex correlation by Mortimer and Parkinson ( 1996).

As noted by Mortimer and Parkinson (1996),

154 N. Mortimer et al. I Marine Geology I48 (1998) 135-162

the Hikurangi Plateau basalts have MORB-like element concentrations but enriched, intraplate- like, isotopic ratios similar to several Cretaceous large igneous provinces in the Pacific Ocean. In contrast, the Tangihua isotopic data are distinctly less radiogenic than the Hikurangi Plateau (Fig. 8a). Although our datasets are admittedly small (4 Tangihua, 3 leached Hikurangi), we interpret the isotopic differences to be significant enough to support the earlier interpretations of Malpas et al. ( 1992, 1994)) that much of the Tangihua Complex does indeed consist of normal oceanic crust.

7.4. Brook Street Terrane-MTZ on the West Norfolk Ridge

The Norfolk Ridge remains very sparsely sampled but, because of striking stratigraphic sim- ilarities in Mesozoic basement between the Baie de St.-Vincent Group of New Caledonia and the Murihiku Terrane of New Zealand (e.g. Campbell, 1984), there is general agreement that the Norfolk Ridge must be underlain by continental crust (e.g. Eade, 1988).

We correlate the rocks from the three dredge hauls on the West Norfolk Ridge and Wanganella Ridges with Brook Street Terrane metavolcanics and Median Tectonic Zone (MTZ) plutons. Such a correlation fits with the southward trend of the West Norfolk Ridge magnetic anomalies towards Taranaki Basin (Figs. 1 and 2; Davy, 1992; Sutherland, 1996) where MTZ rocks have been identified in oil exploration wells (Mortimer et al., 1997). Davey ( 1982) speculatively regarded the highly magnetic nature of the West Norfolk Ridge as evidence that it was underlain by basic volcanics formed at a Cenozoic leaky transcurrent fault. Our dredge data indicate that the West Norfolk Ridge magnetic anomalies are at least in part caused by the presence of mafic Paleozoic-Mesozoic basement.

Extrapolation of the MTZ-Brook Street Terrane units beyond the West Norfolk Ridge is less clear, there being two possible options: ( 1) they may continue up one or both flanks of the New Caledonia Basin (Fig. 1) as suggested by Sutherland’s map showing positive magnetic ano-

malies on both sides of the New Caledonia Basin (Sutherland, 1996), and by Eade’s linking of magnetic anomalies on the West Norfolk Ridge with those of the Fairway Ridge (Eade, 1988); and (2) they may strike westwards under the Lord Howe Rise towards Australia as suggested by the report of Late Permian plutonic rocks from a dredge haul on the Dampier Ridge (McDougall et al., 1994; Fig. I), and by the presence of Late Permian to Triassic metaluminous I-type plutons in the New England Orogen (Clarence River and Moonbi suites of Shaw and Flood ( 198 1). The Gympie Terrane of the New England Orogen is also similar, in many respects, to the Brook Street Terrane of New Zealand (e.g. Cawood, 1984).

8. Cenozoic volcanic arcs and back-arc basins

8.1. Three Kings Ridge as an east-facing island arc

The Three Kings Ridge has previously been interpreted both as a west-facing (e.g. Kroenke and Eade, 1982) and as an east-facing (e.g. Davey, 1982; Ballance et al., 1982) remnant arc, though the only direct evidence for the ridge being a subduction-related volcanic chain was the single basaltic andesite (PSSOS) reported by Davey ( 1982). The complete absence of age information has also meant that regional tectonic models involving the Three Kings Ridge have, of necessity, been speculative.

The unequivocal subduction-related chemistry of samples at all four dredge sites on the ridge clearly confirms the volcanic arc character of the ridge. Shoshonites have been reported from a variety of island arc, continental margin, oblique convergence and collisional settings (e.g. Morrison, 1980). This, coupled with the general lack of sampling of the Three Kings Ridge, makes it difficult to properly assess the tectonic significance of the Miocene shoshonites from site REI. However, we note that: (1) the site REI rocks have the bulk rock and pyroxene parameters of low-Ti shoshonites, consistent with a back-arc rather than a fore-arc setting (Kepezhinskas, 1995); (2) site REI is some 70 km west of the main ridge axis; and (3) the lavas at sites S574 (on


the axis) and at site REl are almost identical in age. These three points lead us to provisionally interpret the Three Kings Ridge rocks in terms of a simple K-h relationship (e.g. Dickinson, 1975) such that the REl shoshonites formed above the deeper parts of a Benioff zone than the coeval S574 medium-K basalt. This interpretation sup- ports earlier hypotheses of west-dipping subduction zone polarity beneath the Three Kings Ridge (Davey, 1982; Ballance et al., 1982).

Our Ar-Ar ages of 20-21 Ma for the REl shoshonite pebbles and 19-22 Ma for the S574 basalt establish a firm Early Miocene age for igneous activity on the Three Kings Ridge, but the ages of inception and cessation of arc activity remain unknown. The satellite gravity map of Davy (1996) shows three distinct north-south trending chains of sub-circular positive anomalies along, and west of, the axis of the Three Kings Ridge (Fig. 2). These features have not previously been noted. The western chain does not show up in the GEBCO (1982) bathymetry of Fig. 2, but is visible on the latest CANZ (1996) map. We speculatively suggest that these peaks represent the extinct volcanoes of the Oligocene-Miocene Three Kings arc.

8.2. Combined Late Oligocene Three Kings- Norfolk arc

The Cenozoic igneous history of the Norfolk Ridge is poorly known; Norfolk Island consists of Late Pliocene intraplate alkaline lavas (Jones and McDougall, 1973), but elsewhere a thick sedimentary cover predominates. The volcanic breccia from dredge site GO348 is the only other sampling of igneous rocks on the southern Norfolk Ridge. The compositions of fresh clinopyroxenes in the zeolite- and clay-rich GO348 clasts are very similar in Ca and Ti content to the shoshonitic pyroxenes of site REl, and we tentatively infer a similar back-arc setting of eruption. The 26-Ma biotite age from the same sample provides an age for this volcanism.

A back-arc tectonic setting at 26 Ma near the crest of the Norfolk Ridge is most easily explained if, prior to opening of the Norfolk Basin, the Three Kings and Norfolk Ridges were formerly

united as a single and mature volcanic arc constructed above a west-dipping subduction zone (Ballance et al., 1982; Davey, 1982). The alterna- tive explanation - that of east-dipping subduction beneath the Norfolk Ridge - is not supported by the limited seismic reflection data in the region which shows rifted crust beneath the sediment fill of the New Caledonia Basin and no obvious trench (e.g. Uruski and Wood, 1991; Zhu and Symonds, 1994). Only near New Caledonia can an east- dipping underthrust geometry be demonstrated (Rigolot and Pelletier, 1988; Regnier, 1988), but this probably records the abduction of the New Caledonia ophiolite rather than true subduction (Aitchison et al., 1995). If it is accepted that the Three Kings Ridge and Norfolk Ridge were formerly united, then our 26-Ma date from site GO348 effectively extends the record of activity of the Three Kings arc back into the Late Oligocene.

8.3. Early Miocene Three Kings-Northland arc

The oldest arc-related volcanism in Northland is dated at ca. 26 Ma (Smith et al., 1995. The main phase of medium- to high-K arc activity com- menced at ca. 20 Ma and lasted until ca. 15 Ma (Ballance et al., 1982; Hayward, 1993; Herzer, 1995; Smith et al., 1995). Earlier workers, including Ballance et al. (1982) and Davey (1982) suggested that the Three Kings and Northland arcs were formed above the same subduction zone. Although shoshonites are unknown from Northland, our chemical and age data from the Three Kings and Norfolk Ridges lead us to entirely agree with these previous interpretations.

On the basis of magnetic data, Launay et al. (1982) regarded the Three Kings and Loyalty Ridges as being formerly contiguous island arcs. We regard this as a still-feasible hypothesis, made more plausible by the apparent offset of the two ridges along the Cook Fracture zone as seen on bathymetry and gravity maps (Fig. 1; Eade, 1988; Davy, 1996), but note that to date, only intraplate (not subduction-related) igneous rocks have been dredged from the Loyalty Ridge (Lafoy et al., 1996 and references therein). Further north, Middle Eocene-Early Miocene arc activity is docu- mented in the now-dispersed fragments of an arc

156 N. Mortimer et al. I Marine Geology 148 (1998) 135-162

that extended from at least Tonga to Vanuatu (Colley and Hindle, 1984; Tappin, 1993 and references therein). It still remains unclear how, or even if, the Three Kings arc linked with the Tonga-Fiji-Vanuatu system.

8.4. Norfolk Basin as an Early Miocene back-arc basin

The Norfolk Basin has variously been interpreted as a piece of trapped Cretaceous Pacific Ocean floor (Eade, 1988; Malpas et al., 1992), a Late Cretaceous back-arc basin (Launay et al., 1982), an Oligocene or younger back-arc basin (Davey, 1982) or an Early to Late Miocene back-arc basin (Ballance et al., 1982; Herzer and Mascle, 1996). The width of the Norfolk Basin between the facing flanks of the Norfolk and Three Kings Ridges is ca. 400 km measured parallel to the Vening Meinesz Fracture Zone (Fig. 2). The nature of crust in the Norfolk Basin is still poorly known, but Herzer and Mascle (1996) reported tilted and extended terraces on the Norfolk and Three Kings margins that are presumed to be underlain by thinned continental and/or arc crust. Only the deepest, flat-floored part of the basin (water depths >4000 m) is thought to be oceanic-like crust, i.e. only half of the width of the basin between the crests of the Norfolk and Three Kings Ridges (Figs. 2 and 9; Herzer and Mascle, 1996). The

identification of Late Cretaceous symmetrical magnetic anomalies in the Norfolk Basin (Launay et al., 1982) has not found acceptance with other authors (Herzer and Mascle, 1996).

As discussed above, the compositions of the two RE3 rocks from the scarp of the Lower Three Kings Terrace plausibly correspond to back-arc basin compositions. Although ‘back-arc basin’ basalts can erupt in settings that have not fully developed into true oceanic-like spreading (e.g. Gamble and Wright, 1995), the location of RE3 at the edge of the wide (4000 m deep) abyssal plain suggests that the ca. 20-Ma dolerite age may indeed date the actual time of inception of true spreading in the South Norfolk Basin. This speculative interpretation is corroborated by the bathyal Middle-Late Miocene microfauna at RE3 which suggest a deep basin well open at this site by 16 Ma and by the Early Miocene (ca. 24-19 Ma) shoal fauna at REl on the Upper Three Kings Terrace, which has since subsided to 2500 m (Herzer et al., 1997).

Previously, Herzer and Mascle (1996) used the reported 9-Ma K-Ar age of the site GO345 basalt (Rigolot, 1989) to infer that oceanic crust in this part of the Norfolk Basin could be as young as Late Miocene. However, our revised 18-Ma age for this intraplate seamount puts the minimum age in the Early Miocene. We have no radiometric constraints on when extension and spreading

26 Ma ?shoshonite time of inception of Three Kings arc

unknown

Fig. 9. Revised model of Oligocene to Miocene igneous and tectonic evolution of the southern Norfolk Ridge (SNR), South Norfolk

Basin (SNB) and Three Kings Ridge (3KR), emphasising new petrological and geochronological data. New Caledonia Basin and Northland Allochthon omitted for simplicity. PRB = location of seismically identified Oligocene and/or Early Miocene volcanic rocks

in the Reinga Basin (Fig. 1 of Herzer et al., 1997) that may connect the Three Kings and Northland arcs.


ceased in the Norfolk Basin, and no seismic reflectors drape over the Vening Meinesz escarpment. The end of tectonism on the Reinga Ridge (the continental side of the Vening Meinesz transform), is recorded by a change from deformed to unde- formed seismic reflectors at about the end of the Middle Miocene (Herzer et al., 1997); this may mark the end of spreading in the Norfolk Basin.

9. Conclusions

Igneous and metamorphic rocks have been recovered from 18 dredges from offshore northern New Zealand. We have used new petrological and isotopic analyses of these samples to critically test previous interpretations of the origin and tectonic development of the southwest Pacific Ocean, and to construct new hypotheses. Our data indicate the following: (1) correlatives of the onshore New Zealand Permian Brook Street Terrane and Mesozoic Median Tectonic Zone appear to be the foundations of the positively magnetic West Norfolk and Wanganella Ridges. This extends the mappable limits of these units at least to the major bend in the New Caledonia Basin; (2) the Tangihua Complex and Waipapa Terrane of onshore New Zealand continue at least 50 km northwestward from the Northland coast along the Reinga Ridge; (3) the Tangihua Complex is probably not a correlative of the Hikurangi Plateau; (4) a Late Cretaceous intraplate igneous province may underlie some of the Reinga Ridge; (5) the Three Kings Ridge was active at least in the 19- to 20-Ma period, was constructed above a west-dipping subduction zone, and was very likely continuous with the Northland arc; (6) the Norfolk Basin was a back-arc basin, and was open or opening by at least 18-20 Ma; and (7) 26-Ma subduction-related

volcanism on the southern Norfolk Ridge probably predates opening of the Norfolk Basin and occurred when the Three Kings arc lay alongside the Norfolk Ridge.

Major remaining questions include determining the age of inception and cessation of volcanism on the Three Kings Ridge, and of spreading in the South Norfolk Basin. The Late Mesozoic geology and thermal history of the Reinga Ridge and its relation to Northland also needs clarifying, as does the offshore extent of the allochthon northeast of Northland. These issues, and the validity of our provisional interpretations, will be tested as more dredge samples are obtained and analysed.

Acknowledgements

We thank the IGNS shipboard party, officers and crew of the R/V Akademik M.A. Lavrentyev for their help and seamanship. We are grateful to the National Institute of Water and Atmospheric Research (NIWA) for access to their dredge sample collection, and are particularly indebted to Bernard Pelletier and staff of ORSTOM, New Caledonia, who brought the GO-series of samples and thin sections to our attention and made them available to us. We also thank John Gamble and Ken Palmer for supplying rocks and analytical data on the S-series of samples. Neville Orr, Stewart Bush, Ken Palmer and Yosuke Kawachi provided technical assistance for the study. An earlier version of the manuscript was improved by comments from Mike Isaac, Fred Davey and John Gamble. Helpful journal reviews were given by Ian Wright and Steve Eggins. Funded by the NZ Foundation for Research Science and Technology, Contract CO5401. Institute of Geological and Nuclear Sciences Contribution 1282.


Appendix A

Summary location, hand specimen and petrographic data for the studied samples

Latitude and longitude are given for mid-points of dredges. Accuracy of positioning about f8 km for ‘E’ dredges (Summerhayes, 1969). ? = mineral is completely pseudomorphed (identification is by shape only); M&V 1983 = Monzier and Vallot ( 1983); px = pyroxene; cpx = clinopyroxene; opx = orthopyroxene; plag = plagioclase; phenos = phenocrysts; w = with; 01 = olivine; ab = albite; chl = chlorite; pump = pumpellyite; 2” = secondary; qtz = quartz; bi = biotite; hbl = hornblende; bldrs = boulders; subang = subangular.

P no. Petrographic summary

Onshore samples Tangihua Complex

30321 porphyritic metabasalt w plag and cpx phenos

34075 variolitic basalt w plag and cpx phenos

34084 subophitic dolerite

34124 subophitic dolerite

Houhora Complex

36525 granophyre, rare mafics altered to chlorite

44134 aphyric andesite flow with chlorite amygdules

44141 sparsely plag-porphyritic andesite w chlorite amygdules

44143 dolerite w cpx, plag, rare ?ol

50288 coarse doleritic interior of aphyric basalt flow

Reinga Ridge and Vening Meinesz escarpment ES19

08433

E323

08442

E310

08428

E3J1

08429

RE2

57019

57022

57023

57024

11855

57067

57068

GO350

57126

nla

SE Reinga Ridge, 100 m, 33”56’S, 172”17’E

holocrystalline metabasalt w sparse plag, cpx phenos

SE Reinga Ridge, 161 m. 34”OO’S, 172”15’E

metagabbro, partly chloritised, still relict cpx

SE Reinga Ridge, 95 m, 33”57.5’S, 171”463’E

volcanic litharenite, metamorphic ab, chl, pump

SE Reinga Ridge, 128 m, 33”58.7’S, 171”46.3’E

volcanic litharenite, metamorphic ab, chl, pump

Vening Meinesz escarpment, 1875-1950 m, 33”07.58’S, l70”54.X4’E

probably broken from outcrop (Summerhayes, 1969)




Hand specimen description

in place, Kangikapiti Head, 34”59.02’S, 173”31.34’E

in place, Ohenga Point, 34”56.08’S, 173”36.03’E

in place, Oruaiti, 35”00.2O’S, 173”36.72’E

in place, Okaituna, 34”55.81’S, 173”34,18’E

in place, Rangiawhia Peninsula, 34”52.99’& 173’24.77’E

in place, Three Kings Islands, 34”10,72’S, 172”03.37’E

in place, Three Kings Islands, 34”09.30’& 172”08.30’E

in place, Three Kings Islands, 34”11,12’S, 172”02.01’E

in place, Perforated Point coast, 34”47.50’$ 173”lO.OO’E

very altered subophitic dolerite; no relict px 10 x 3 x 2 cm subangular, Mn crusted

barite-fibrous veins and cement in feldsarenite 20 x 15 x 10 cm rounded, Mn crusted

very altered subophitic dolerite; no relict px 10 x 3 x 2 cm subangular, Mn crusted

as P57023 but some relict px; 2” calcite 30 x 20 x 15 cm weathered subang, Mn crusted

Vening Meinesz escarpment, 742 m, 33”lO.OO’S 169”56.00’E

altered dolerite w relict zoned cpx, ?ol subang piece 3 x 4 cm

altered dolerite w relict zoned cpx, ?ol, 2” calcite subround piece 2 x 3 cm

Vening Meinesz escarpment, 1600-3400 m, 32”21.8O’S, 169”08.50’E

prehnitised cataclastic basalt, no phenos angular dm slab (GO350 D2 or 3 of M&V, 1983)

epidotised cataclastic granite w calcite veins angular dm slab (GO350 Dl of M&V, 1983)

West Norfolk and Wanganella Ridges RE6 West Norfolk Ridge, 700-735 m, 33”54.43’S, 167”22.88’E

57043 fine grained altered basalt w sparse plag, cpx phenos

57044 qtz-plag-mica gneissic gabbroid

57046 porpyritic meta-andesite; plag and rare mafic phenos

57047 bi-hblLpx gabbroid

57048 fine grained hbl gabbroid

57049 med grained px-hbl gabbroid

57050 coarse grained hbl gabbroid

57051 pink-orange fine grained biotite granitoid

57052 fine grained grey biotite granitoid

57053 medium grained grey oliv-px-bi gabbroid

57054 hornfelsed mafic volcanic lithic sandstone

ang 5 cm

subround 6 cm

round 3 cm

flat subang 1 x 2 x 5 cm

subround 2 x 4 x 3 cm

individual sub ang fresh pebbles 2 x 3 cm

individual sub ang fresh pebbles 2 x 3 cm

rounded 5 x 4 x 3 cm

1 rounded 4 x 3 x 2 cm, plus 3 flatter pebbles

24X3x2cmrounded

5 x 5 x 2 cm rounded

N. Mortimer et al. / Marine Geology 148 (1998) 135-162 1.59

Appendix A

Summary location, hand specimen and petrographic data for the studied samples

Latitude and longitude are given for mid-points of dredges. Accuracy of positioning about +8 km for ‘E’ dredges (Summerhayes, 1969). ? =mineral is completely pseudomorphed (identification is by shape only); M&V 1983 = Monzier and Vallot ( 1983); px = pyroxene; cpx = clinopyroxene; opx = orthopyroxene; plag = plagioclase; phenos = phenocrysts; w = with; 01 = olivine; ab = albite; chl = chlorite; pump = pumpellyite; 2” = secondary; qtz = quartz; bi = biotite; hbl = hornblende; bldrs = boulders; subang = subangular.

P no. Petrographic summary Hand specimen description

57059 fine grained hornfelsed metabasalt 8 x 4 x 2 cm subangular

57055 epidosite 5 x 4 x 2 cm subrounded bored

57062 uralitised gabbro w 2” blue-green amphibole 3 x 2 x 0.5 cm subangular

RE7 Wanganella Ridge, 1050-1450 m, 33”33.&SS, 167”39.32’E

57064 plag and mafic- porphyritic meta-andesite, epidotised 1 x 1 x 1 cm subrounded, bored

GO360 Wanganella Ridge, 400-1000 m, 34”22.OO’S, 168”2660’E

57139 metabasaltic breccia, metamorphic chl, ep, act subrounded 5 x 5 x 7 cm (cf. G0360D12-13 of M&V, 1983)

57141 cataclastic metavolcanic w calcite veins subang 10 x 10 x 5 cm slab (cf. G0360D12-13 of M&V, 1983

57146 medium grained bi-hbl diorite-granodiorite rounded 10 x 10 x 5 cm pebble (cf. G0360Dl-9, M&V, 1983)

57147 medium grained bi-hbl diorite-granodiorite, chloritised rounded 10 x 10 x 5 cm pebble (cf. G0360Dl-9, M&V, 1983)

Three Kings and southern Norfolk Ridges

REl Upper Three Kings terrace, 2500-2700 m, 33”00,66’S, 171”42.42’E

57007 grey andesite w plag, greenish cpx, hbl, bi phenos individual l-3 cm well-rounded pebbles, minor Mn coatings

57008 red basaltic andesite w abund cpx phenos, 50% vesicles 4 well-rounded pebbles w Mn coatings

57009 red basaltic andesite w plag, cpx phenos, 10% vesicles individual 1-3 cm well-rounded pebbles

s574 Three Kings Ridge, 1180-1290 m, 30”50.1O’S, 172”44.40’E

08502 brown basalt w plag, cpx, opx phenos, sparse vesicles bldrs and cobbles ~30 cm diameter

s573 Three Kings Ridge, 840-975 m, 30”29.7O’S, 172”42.30’E

08503 brownish grey aphyric fine grained vesicular basalt cobbles and pebbles < 10 cm diameter

VE209 Three Kings Ridge, 1800-2200 m, 28”11.OO’S, 173”09.OO’E

08505 basalt w plag. cpx phenos, partly glassy groundmass not available (Davey, 1982)

GO348 Southern Norfolk Ridge, 900-1400 m, 30”07.2O’S, 167”29.80’E

57118 volt breccia (greenish cpx, bi phenos), 2” clay and zeolite subang 20 x 10 x 5 cm (GO348 Dl of M&V, 1983)

North Norfolk, South Norfolk and Reinga Basins

RE3

57025

57026

57029

GO345

57142

GO353

57143

S565

08504

Lower Three Kings Terrace, 3680-4160 m, 32”22.06’S, 170”52.04’E

ophitic dolerite, some ex ?ol tough, angular 10 x 6 x 4 cm

volcaniclastic sandy siltstone individual subrounded I x 1 x 1 cm pebbles

pillow basalt, altered interior, glassy rind, 10% vesicles subang20x15xlOcm

South Norfolk Basin, 2260-3200 m, 30056.00’S, 168”49.00’E

amygdaloidal olivine basalt w clays, zeolites angular 40 x 30 x 10 cm (GO345 Dl of M&V, 1983)

Reinga Basin, 1530-1870 m. 33”OO.lO’S, 167”50.90’E

variolitic basalt w purplish cpx, 10% vesicles angular 15 x 15 x 15 cm (GO353 Dl of M&V, 1983)

North Norfolk Basin, 830-1350 m, 29”18,5O’S, 169”46,70’E

vesicular basalt w 01, cpx, plag phenos bldrs and cobbles < 30 cm diameter

References Eocene arc-continent collision in New Caledonia and implications for regional southwest Pacific tectonic evolution.

Addicott, W.0, Richards, P.W. (compilers), 1981. Plate-tec-

tonic map of the circum-Pacific region, south-west quadrant.

Cicrum-Pacific Council for Energy and Mineral Resources,

Am. Assoc. Petrol. Geol., Tulsa, Oklahoma, USA.

Aitchison, J.C., Clarke, G.L., Meffre, S., Cluzel, D., 1995.

Geology 23, 161-164. Baker, J.A., Gamble, J.A., Graham, I.J., 1994. The age, geol-

ogy, and geochemistry of the Tapuaenuku Igneous Complex, Marlborough, New Zealand. N.Z. J. Geol. Geophys. 37, 249-268.

Ballance, P.F., Pettinga, J.R., Webb, C., 1982. A model of the

160 N. Mortimer et al. 1 Marine Geology 148 11998) 135-162

Cenozoic evolution of northern New Zealand and adjacent

areas of the southwest Pacific. Tectonophysics 87, 37748.

Brook, F.J, Thrasher, G.P., 1991. Cretaceous and Cenozoic

geology of northernmost New Zealand. N.Z. Geol. Surv.

Rec. 41.

Campbell, H.J., 1984. Petrography and metamorphism of the

Teremba Group (Permian-Lower Triassic) and Baie de St.-

Vincent Group (Upper Triassic-Lower Jurassic), New Cale-

donia. J. R. Sot. N.Z. 14, 3355348.

CANZ (Charting Around New Zealand Group), 1996.

Undersea New Zealand (New Zealand Region Physiogra-

phy) 1:4 000 000, 2nd ed. N.Z. Oceanogr. Inst. Chart Misc.

Ser. 74. Wellington, N.Z. National Institute of Water and

Atmospheric Research.

Cawood, P.A., 1984. The development of the southwest Pacific

margin of Gondwana: correlations between the Rangitata

and New England orogens. Tectonics 3, 5399553.

Challis, G.A., 1987. Petrography of igneous and sedimentary

rocks from the Three Kings Islands, northern New Zealand.

Rec. Auckl. Inst. Mus. 24, 233-242.

Colley, H., Hindle, W.H., 1984. Volcano-tectonic evolution of

Fiji and adjoining marginal basins. Geol. Sot. Lond. Spec.

Publ. 16, 151-162.

Crampton, J.S., Beu, A.G., Campbell, H.J., Cooper, R.A.,

Morgans, H.E.G., Raine, J.I., Scott, G.H., Stevens, G.R.,

Strong, C.P., Wilson, G.J., 1995. An Interim New Zealand

Geological Time Scale. Inst. Geol. Nucl. Sci., Sci. Rep. 95/9.

Davey, F., 1982. The structure of the South Fiji Basin. Tectono-

physics 87, 185-241.

Davy, B.W., 1992. Magnetic anomalies of the New Zealand

basement. In: N.Z. Oil Exploration Conf. Proc., 1. Ministry

of Commerce, Wellington, New Zealand, pp. 134-144.

Davy, B.W., 1996. Southern Oceans gravity anomaly map

Fiji region 1:4 000 000. Institute of Geological and Nuclear

Science Geophysical Map 8. Institute of Geological and

Nuclear Sciences Ltd., Lower Hutt, New Zealand.

Dickinson, W.R., 1975. Potash-depth (K-h) relations in conti-

nental margin and intra-oceanic magmatic arcs. Geology 3,

53-56.

Eade, J.V., 1988. The Norfolk Ridge System and its margins.

In: Nairn, A.E.M., Stehli, F.G., Uyeda, S. (Eds.), The Ocean

Basins and Margins, vol. 7B. Plenum, New York,

pp. 303-324.

Faulds, J.E., Feuerbach, D.L., Reagan, M.K., Metcalf, R.V.,

Gans, P.B., Walker, J.D., 1996. The Mount Perkins block,

northwestern Arizona: an exposed cross section of an evolv-

ing, preextensional to synextensional magmatic system.

J. Geophys. Res. 100, 15249-15266.

Floyd, P.A., Winchester, J.A., 1978. Identification and discrimi-

nation of altered and metamorphosed volcanic rocks using

immobile elements, Chem. Geol. 21, 291-306.

Gamble, J.A., Wright, I.C., Baker, J.A., 1993. SeaAoor geology

and petrology in the oceanic to continental transition zone

of the Kermadec-Havre-Taupo Volcanic Zone arc system,

New Zealand. N.Z. J. Geol. Geophys. 36, 4177435.

Gamble, J.A., Wright, I.C., 1995. The Southern Havre Trough:

geological structure and magma petrogenesis of an active

backarc rift complex. In: Taylor, B. (Ed.), Backarc Basins:

Tectonics and Magmatism. Plenum, New York, pp. 29-62.

Gamble, J.A., Woodhead, J., Wright, I.C., Smith, I.E.M., 1996.

Basalt and sediment geochemistry and magma petrogenesis

in a transect from oceanic island arc to rifted continental

margin arc: the Kermadec-Hikurangi margin, SW Pacific.

J. Petrol. 37, 152331546.

GEBCO (General Bathymetric Chart of the Oceans), 1982.

International Hydrographic Organisation (JNO) and

Intergovernmental Oceanographic Commission (IOC)

(UNESCO). Canadian Hydrographic Service, Ottawa,

Canada.

Gleadow, A.J.W., 1981. Fission-track dating methods: what are

the real alternatives? Nucl. Tracks Radiat. Measure. 5, 3-14.

Hayward, B.W., 1993. The tempestuous 10 million year life of

a double arc and intra-arc basin - New Zealand’s Northland

Basin in the Early Miocene. In: Ballance, P.F. (Ed.), South

Pacific Sedimentary Basins, Sedimentary Basins of the World

2. Elsevier, Amsterdam, pp. 113-142.

Herzer, R.N., 1995. Seismic stratigraphy of a buried volcanic

arc, Northland, New Zealand, and implications for Neogene

subduction. Mar. Pet. Geol. 12, 51 l-531.

Herzer, R.H., Isaac, M.J., 1992. The size of the Northland

Allochthon. N.Z. Geol. Surv. Rec. 44, 37-42.

Herzer, R.H., Mascle, J., 1996. Anatomy of a continent-backarc

transform ~ the Vening Meinesz Fracture Zone northwest of

New Zealand. Mar. Geophys. Res. 18, 401-427.

Herzer, R.H., Chaproniere, G.C.H., Edwards, A.R., Hollis,

C.J., Pelletier, B., Raine, J.I., Scott, G.H., Stagpoole, V.,

Strong, C.P., Symonds, P., Wilson, G.J., Zhu, H., Cobbly,

T., 1997. Seismic stratigraphy and structural history of the

Reinga Basin and its margins, southern Norfolk Ridge

system. N.Z. J. Geol. Geophys. 40, 425451.

Herzer, R.H., Sykes, R., Killops, S.D., Funnell, R.H., Burggraf,

D.R., Townend, J., Raine, J.I., Wilson, G.J., 1998. Late Cre-

taceous carbonaceous rocks from the Norfolk Ridge system,

SW Pacific, and implications for petroleum potential. N.Z.

J. Geol. Geophys., in press.

Houghton, B.F., 1985. Petrology of the calcalkaline lavas of

the Permian Takitimu Group, southern New Zealand. N.Z.

J. Geol. Geophys. 28, 649-665.

Hurford, A.J., Green, P.F., 1983. The zeta age calibration of

fission-track dating. Isotope Geosci. 1, 285-317.

Isaac, M.J., Herzer, R.H., Brook, F.J., Hayward, B.W., 1994.

Cretaceous and Cenozoic sedimentary basins of Northland,

New Zealand. Inst. Geol. Nucl. Sci. Mon. 8.

Jones, J.G., McDougall, I., 1973. Geological history of Norfolk

and Philip Islands, southwest Pacific Ocean. J. Geol. Sot.

Aust. 20, 2399254.

Karig, D.E., 1970. Ridges and basins of the Tonga-Kermadec

island arc system. J. Geophys. Res. 75, 239-254.

Kepezhinskas, P., 1995. Diverse shoshonite magma series in the

Kamchatka Arc: relationships between intra-arc extension

and composition of alkaline magmas. Geol. Sot. Lond. Spec.

Publ. 81, 249-263.

Kimbrough, D.L., Tulloch, A.J., Coombs, D.S., Landis, C.A.,

Johnston, M.R., Mattinson, J.M., 1994. Uranium-lead

N. Mortimer et al. I Marine Geology 148 (1998) 135-162 161

zircon ages from the Median Tectonic Zone, South Island,

New Zealand. N.Z. J. Geol. Geophys. 37, 393-419.

Kroenke, L.W., Eade, J.V., 1982. Three Kings Ridge: a west

facing arc. Geo-Mar. Lett. 2, 5--10.

Lafoy, Y., Missegne, F., Cluzel, D., LeSuave, R., 1996. The

Loyalty-New Hebrides arc collision: effects on the Loyalty

Ridge and Basin system, southwest Pacific (first results of

the ZoNtCo programme). Mar. Geophys. Res. 18, 337-356.

Larsen, J.M., Parker, R.J., 1989. Petrology and tectonic signifi-

cance of igneous rocks from the Ahipara Tangihua Massif,

Northland, New Zealand. R. Sot. N.Z. Bull. 26, 145-153.

Launay, J., DuPont, J., Lapouille, A., 1982. The Three Kings

Ridge and the Norfolk Basin (southwest Pacific): an attempt

at structural interpretation, South Pacific. Mar. Geol. Notes

2, 121-130.

LeTerrier, J., Maury, R.C., Thonon, P., Girard, D., Marchal,

M., 1982. Clinopyroxene composition as a method of identi-

fication of the magmatic affinities of paleo-volcanic series.

Earth Plan. Sci. Lett. 59, 139-154.

Malpas. J.. Sporli, K.B., Black, P.M., Smith, I.E.M., 1992.

Northland ophiolite, New Zealand, and implications for

plate-tectonic evolution of the southwest Pacific. Geology

20, 1499152.

Malpas, J.. Smith, I.E.M., Williams. D., 1994. Comparative

genesis and tectonic setting of ophiolitic rocks of the South

and North Islands of New Zealand. Proc. 29th Int. Geol.

Gong., part D. pp. 29-46.

McDougall. I., Maboko, M.A.H., Symonds, P.A., McCulloch,

M.T., Williams. I.S., Kudrass. H.R., 1994. Dampier Ridge,

Tasman Sea, as a stranded continental fragment. Aust.

J. Earth Sci. 41. 395406.

Middlemost, E.A.K., 1994. Naming materials in the magma/

igneous rock system. Earth-Sci. Rev. 37, 215-224.

Monzier, M., Vallot, J., 1983. Rapport preliminaire concernent

les dragages reahses lors de la campagne GEORSTOM III

SUD (1975). Office de la Recherche Scientifique et Tech-

nique Outre-Mer, Centre de Noumea Geologie-Geophysique

Rapport no. 2-83, 77 pp.

Morrison, G.W., 1980. Characteristics and tectonic setting of

the shoshonite rock association. Lithos 13, 977108.

Mortimer. N., Parkinson, D.L., 1996. Hikurangi Plateau: a Cre-

taceous large igneous province in the southwest Pacific

Ocean. J. Geophys. Res. 101, 687-696.

Mortimer. N.. Tulloch, A.J., Ireland, T.R., 1997. Basement

geology of Taranaki and Wanganui Basins, New Zealand.

N.Z. J. Geol. Geophys. 40, 217-230.

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 Zealand

Paleozoic--Mesozoic metasedimentary and igneous rocks,

Inst. Geol. Nucl. Sci., Sci. Rep. 95116.

Regnier, M.. 1988. Lateral variation of upper mantle structure

beneath New Caledonia determined from P-wave receiver

function: evidence for a fossil subduction zone. Geophys. J.

98, 561-577.

Rigolot, P., 1989. Origine et evolution du ‘systeme’ ride de

Nouvelle-CaledonieiNorfolk (sud-ouest Pacifique). These de

Doctorat de I’Univ. Bretagne Occidentale, Brest, France.

319 pp.

Rigolot, P., Pelletier, B., 1988. Tectonique compressive rtcente

le long de la marge ouest de la Nouvelle-Caledonie: resultats

de la campagne ZOE 400 du N/O Vauban (mars 1987). C.R.

Acad. Sci. Paris Ser. 2 307, 1799184.

Seward, D., 1979. Comparison of zircon and glass fission-track

ages from tephra horizons. Geology 7, 4799482.

Seward. D., Moore, P.R., 1987. New fission-track ages from

some Minden rhyolites (Whitianga Group) Eastern Coro-

mandel Peninsula. New Zealand. N.Z. Geol. Surv. Rec.

20, 1055109.

Sewell, R.J., 1992. Geochemistry of the Matakaoa Volcanics,

East Cape: Implications for age, correlation, and tectonic

setting of mid-Cretaceous (Albian) subalkaline volcanic

rocks from eastern North Island. Geol. Sot. N.Z. Misc. Publ.

63A, 137

Sewell, R.J., Nathan, S.. Adams, C.J., 1988. Geochemistry of

Late Cretaceous basaltic rocks from north Westland. N.Z.

Geol. Surv. Rec. 35, 113-l 16.

Shaw, SE., Flood, R.H., 1981. The New England Batholith,

Eastern Australia: geochemical variation in time and space.

J. Geophys. Res. 86, 10530-10544.

Shervais, J.W.. 1982. Ti-V plots and the petrogenesis of modern

and ophiohtic lavas. Earth Planet. Sci. Lett. 59, 101-l 18.

Smith, I.E.M., Black, P.M., Itaya, T., 1995. Inception and evo-

lution of Cenozoic arc-type volcanism in northern New

Zealand. In: Mauk, J.L., St. George, J.D., (Eds.), Proceed-

ings of the 1995 PACRIM Congress. Australasian Institute

of Mining and Metallurgy, Carlton, Victoria. Australia,

pp. 563-567.

Sporli, K.B., 1978. Mesozoic tectonics, North Island, New

Zealand. Geol. Sot. Am. Bull. 89, 415-425.

Staudacher, Th., Jessberger, E.K., Dominik, B., Kirsten, T.,

Schaeffer, O.A.. 1982. 40Ar-39Ar ages of rocks and glasses

from the Nordlinger Ries Crater and the temperature history

of impact glasses. J. Geophys. 51, 1-I I.

Storzer, D., Selo, M., 1978. Fission-track age of magnetic

anomaly M-zero and some aspects of sea-water weathering.

Init. Rep. Deep Sea Drilling Proj., 51-53, pp. 112991133.

Summerhayes, C.P., 1969. Submarine geology and geomorphol-

ogy off northern New Zealand. N.Z. J. Geol. Geophys. 12,

507-525.

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic sys-

tematics of oceanic basalts: implications for mantle composi-

tions and processes. Geol. Sot. Lond. Spec. Pub]. 42,

313-345.

Sutherland, R., 1996. Magnetic anomalies in the New Zealand

region, 1:4 000 000, version 1 .O. Institute of Geology and

Nuclear Sciences Geophysical Map 9. Institute of Geological

and Nuclear Sciences Ltd., Lower Hutt, New Zealand.

Tappin, D.R., 1993. The Tonga frontal-arc basin. In: Ballance,

P.F. (Ed.), South Pacific Sedimentary Basins, Sedimentary

Basins of the World 2. Elsevier, Amsterdam, pp. 157-176.

Uruski, C.I.. Wood, R.A., 1991. A new look at the New Caledo-

nia Basin. an extension of the Taranaki Basin. offshore North

Island, New Zealand. Mar. Pet. Geol. 8. 3799391.


Weaver, SD, Smith, I.E.M., 1989. New Zealand intraplate volcanism. In: Johnson, R.W., Knutson, J., Taylor, S.R. (Eds.), Intraplate Volcanism in Eastern Australia and New Zealand. Cambridge University Press, Cambridge, pp. 157-188.

Westgate, J.A., 1989. Isothermal plateau fission track ages of hydrated glass shards from silicic tephra beds. Earth Planet. Sci. Lett. 95, 226-234.

Woodhead, J., Eggins, S., Gamble, J., 1993. High field strength and transition element systematics in island arc and back-

arc basin basalts: evidence for multi-phase melt extraction and a depleted mantle wedge. Earth Planet. Sci. Lett. 114, 491-504.

Zhu, H., Symonds, P.A., 1994. Seismic interpretation, gravity modelling and petroleum potential of the southern Lord Howe Rise region. In: 1994 New Zealand Petroleum Confer- ence Proceedings. Ministry of Commerce, Wellington, New Zealand, pp. 223-230.

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