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ORIGINAL RESEARCH PAPER
Seismic stratigraphy and structure of the Northland Plateau
and the development of the Vening Meinesz transform margin,
SW Pacific Ocean
R. H. Herzer ÆB. W. Davy ÆN. Mortimer Æ
P. G. Quilty ÆG. C. H. Chaproniere Æ
C. M. Jones ÆA. J. Crawford ÆC. J. Hollis
Received: 21 July 2008 / Accepted: 8 April 2009 / Published online: 16 May 2009
ÓSpringer Science+Business Media B.V. 2009
Abstract The Northland Plateau and the Vening Meinesz
‘‘Fracture’’ Zone (VMFZ), separating southwest Pacific
backarc basins from New Zealand Mesozoic crust, are
investigated with new data. The 12–16 km thick Plateau
comprises a volcanic outer plateau and an inner plateau
sedimentary basin. The outer plateau has a positive magnetic
anomaly like that of the Three Kings Ridge. A rift margin
was found between the Three Kings Ridge and the South Fiji
Basin. Beneath the inner plateau basin, is a thin body inter-
preted as allochthon and parautochthon, which probably
includes basalt. The basin appears to have been created by
Early Miocene mainly transtensive faulting, which closely
followed obduction of the allochthon and was coeval with
arc volcanism. VMFZ faulting was eventually concentrated
along the edge of the continental shelf and upper slope.
Consequently arc volcanoes in a chain dividing the inner and
outer plateau are undeformed whereas volcanoes, in various
stages of burial, within the basin and along the base of the
upper slope are generally faulted. Deformed and flat-lying
Lower Miocene volcanogenic sedimentary rocks are
intimately associated with the volcanoes and the top of the
allochthon; Middle Miocene to Recent units are, respec-
tively, mildly deformed to flat-lying, calcareous and turbi-
ditic. Many parts of the inner plateau basin were at or above
sea level in the Early Miocene, apparently as isolated highs
that later subsided differentially to 500–2,000 m below sea
level. A mild, Middle Miocene compressive phase might
correlate with events of the Reinga and Wanganella ridges to
the west. Our results agree with both arc collision and arc
unzipping regional kinematic models. We present a conti-
nental margin model that begins at the end of the obduction
phase. Eastward rifting of the Norfolk Basin, orthogonal to
the strike of the Norfolk and Three Kings ridges, caused the
Northland Plateau to tear obliquely from the Reinga Ridge
portion of the margin, initiating the inner plateau basin and
the Cavalli core complex. Subsequent N115°extension and
spreading parallel with the Cook Fracture Zone completed
the southeastward translation of the Three Kings Ridge and
Northland Plateau and further opened the inner plateau basin,
leaving a complex dextral transform volcanic margin.
Keywords Northland Plateau
Southwest Pacific tectonics
Vening Meinesz Fracture Zone
New Zealand continental margin South Fiji Basin
Three Kings Ridge Transform margin
Introduction
Background
The northern continental margin of New Zealand (Fig. 1)is
bordered by the Three Kings and Colville remnant arcs and
the Norfolk and South Fiji fossil back-arc basins, and is
R. H. Herzer (&)B. W. Davy C. M. Jones C. J. Hollis
GNS Science, 1 Fairway Drive, Avalon, Lower Hutt 5040,
New Zealand
e-mail: r.herzer@gns.cri.nz
N. Mortimer
GNS Science, 764 Cumberland Street, Dunedin 9016,
New Zealand
P. G. Quilty A. J. Crawford
School of Earth Science, University of Tasmania, Hobart,
TAS 7001, Australia
G. C. H. Chaproniere
Research School of Earth Sciences, The Australian National
University, Acton, ACT 0200, Australia
123
Mar Geophys Res (2009) 30:21–60
DOI 10.1007/s11001-009-9065-1
overlain by the Northland Allochthon. The contact between
the continent and the Norfolk Basin is a complex fault
scarp—the Vening Meinesz Fracture Zone (Herzer and
Mascle 1996); the contact between continent and the South
Fiji Basin (SFB) is a plateau—the Northland Plateau (Herzer
et al. 2000)—which is the focus of this study. The Plateau
lies seaward of a series of sedimentary and ophiolitic nappes,
mapped as the Northland Allochthon (Ballance and Spo
¨rli
1979; Herzer and Isaac 1992), which contain the dismem-
bered Cretaceo-Paleogene sedimentary continental margin
as well as thrust sheets of backarc-basin mafic complexes.
The origin of these basalt-dominated ophiolites is critical to
developing a SW Pacific model and is the subject of
continuing study and debate. In particular, the presence and
role of a transform fault between the SFB and the continental
margin has been neither proven nor understood.
In the Norfolk Basin, rifting, extension and some seafloor
spreading occurred in a generally northwest–southeast
sense during the Early to Middle Miocene (Herzer et al.
1997; Mortimer et al. 1998; Sdrolias et al. 2004), although
its history might well go back to the Cretaceous (Launay
et al. 1882; Eade 1988; Bernardel et al. 2002; Crawford
et al. 2003; Sdrolias et al. 2004; DiCaprio et al. 2009). Arc-
type volcanic rocks have been recovered from ridges on
both its western and eastern sides—Upper Oligocene
(26 Ma) on the Norfolk Ridge and Upper Eocene (37 Ma)
and Lower Miocene (20 Ma) on the Three Kings Ridge
(Mortimer et al. 1998; Fraser 2002 in Bernardel et al. 2002).
Satellite gravity (Sandwell and Smith 1997) indicates that
the Three Kings Ridge was once continuous with the Loy-
alty Ridge (Fig. 1). As the Norfolk back-arc basin extended,
the Three Kings Ridge was carried 290 km southeastwards
Fig. 1 Regional setting of the study area in the SW Pacific Ocean
with geographic features identified. Many features have informal
names, taken from published papers and science reports or introduced
here for ease of writing where no formal name exists on maps.
AP =Aupouri Peninsula, BOP =Bay of Plenty, CP =Coromandel
Peninsula, CS =Cavalli Seamount, CT =Cagou Trough,
EC =East Cape, HFZ =Hunter Fracture Zone, HG =Hauraki
Graben, HT =Huia Terraces, JL =Julia Lineament, M =Mohaka-
tino volcanic belt, NC =North Cape, NFB =North Fiji Basin,
NHTR =New Hebrides Trench, NMR =North Maria Ridge,
PT =Philip Trough, RB =Reinga Basin, RR =Reinga Ridge,
SMR =South Maria Ridge, SNB =South Norfolk Basin,
SS =Sarah Seamounts, SSFB =southern South Fiji Basin,
ST =The Slab and Thrust, TB =Taranui block, TT =Tuatara
Terrace, TVZ =Taupo Volcanic Zone, K =The Knolls, VLL =van
der Linden Lineament, VMFZ =Vening Meinesz Fracture Zone,
WNR =West Norfolk Ridge, WR =Wanganella Ridge,
WT =Weta Terrace. Illumination is from the SSE
22 Mar Geophys Res (2009) 30:21–60
123
towards a postulated trench somewhere to the east (Davey
1982; Herzer and Mascle 1996; Mortimer et al. 1998). A
trench has been suggested both west of an ancestral Three
Kings Ridge (Kroenke and Eade 1982; Crawford et al.
2003; Schellart et al. 2006) and east of it (Davey 1982;
Ballance 1999), and obduction proposed at the southwest-
ern end (Kroenke and Dupont 1982). Transform faults at the
northern and southern margins of the basin, the N115°-
trending Cook and Vening Meinesz Fracture Zones (CFZ
and VMFZ), trace the main vector of extension of the basin.
While the CFZ is a well defined fault (Mauffret et al. 2001),
the VMFZ adjacent to the Norfolk Basin is neither straight
nor simple, but composed of an en echelon array of splays
and offsets (Herzer and Mascle 1996).
In the SFB there is evidence that Early Miocene, as well
as Oligocene, spreading has occurred (Herzer and Morti-
mer 1998; Herzer et al. 2000,2001; Mortimer et al. 2007).
Magnetic anomalies in the southern part of the basin near
New Zealand were interpreted alternatively as seafloor of
32–25 Ma age with a spreading centre in the west (Mal-
ahoff et al. 1982; Davey 1982) or 30.9–25.6 Ma age with a
spreading centre in the east (Sdrolias et al. 2003), but we
judge these anomalies to be too short and too variable to
conclusively date the crust. The southeastward shift of the
Three Kings Ridge in the Miocene creates major space
problems on the Northland margin, depending on where
the active trenches and transforms were, and how and in
what sequence the two back-arc basins opened. Where,
precisely was the VMFZ in this system, and how did it
function?
The presence of the Cavalli Seamount schist and granite
core complex on the Northland Plateau may be a mani-
festation of space accommodation (Fig. 1). The Cretaceous
protoliths were metamorphosed about 23–20 Ma, and
exhumed very rapidly at 19.9 Ma (Mortimer et al. 2003,
2008). The exhumation postdates the end of obduction of
the Northland Allochthon (c. 22 Ma) and coincides with
opening of the Norfolk Basin along the VMFZ.
The Northland Allochthon is divided into three geo-
graphic segments by younger tectonism and erosion—a
western one offshore on the South Maria Ridge, a central
one covering much of Northland, and an eastern segment in
the East Cape region (the northeastern corner of the North
Island) (SMR and EC, Fig. 1). The western segment faces
the Norfolk Basin, and is dissected by several strands of the
VMFZ (Herzer and Mascle 1996). The central segment
faces the SFB across the Northland Plateau, and is cut by
the VMFZ along the NW continental shelf (Isaac et al.
1994). The eastern segment faces the Kermadec forearc,
and is presumed to have been originally located close to
Northland and separated from the central segment by post-
Early Miocene back-arc rifting and eastward retreat of the
Kermadec Trench.
The Northland Allochthon was obducted from the
northeast in the latest Oligocene—earliest Miocene (*25–
22 Ma) (Hayward et al. 1989; Isaac et al. 1994; Rait
2000a). The later stages of its emplacement overlap with
the early phases of Northland Arc volcanism (Hayward
1993; Herzer 1995). The sedimentary facies of the North-
land Allochthon demonstrate the existence of a non-
accretionary, pre-obduction, terrigenous continental slope
through the Paleogene and Late Cretaceous as far back as
90–100 Ma (Isaac et al. 1994), and no sign of a nearby pre-
Miocene volcanic arc. Estimates as to how far the ophio-
lites of the Allochthon have travelled vary from hundreds
of kilometres (Cassidy 1993; Rait 2000b) to almost no
distance at all (Whattam et al. 2005).
The ophiolites, usually referred to as the Tangihua
Complex, include mid-ocean ridge basalt (MORB) and
supra-subduction basalts of Cretaceous and Late Oligocene
(25.0 ±0.8 to 29.6 ±1.0 Ma) ages, alkaline ocean island
basalts (OIB) basalts of Paleocene age (Isaac et al. 1994;
Nicholson 1999; Nicholson et al. 2000a,b; Nicholson and
Black 2004; Whattam et al. 2004,2005,2008), and minor,
faulted-in ultramafic rocks and gabbros, mainly in the
North Cape area. There is debate about the origin and age
of the basalts but the supra-subduction signature is signif-
icant in constraining their origin. Pacific Cretaceous crust
might have come from the Hikurangi/Moa plate (Suther-
land and Hollis 2001) or the Phoenix plate (Nicholson and
Black 2004) or cryptic terranes now subducted. The only
known potential source of Oligocene crust is the SFB
(Malahoff et al. 1982; Davey 1982; Whattam et al. 2004,
2005). Northwest of New Zealand the Cretaceous-Upper
Paleocene basaltic Poya Terrane (Aitchison et al. 1995;
Cluzel et al. 2001, and sources therein) was obducted from
the northeast onto New Caledonia (Cluzel et al. 2006).
Diachronous collision with the Zealandia continent by a
Loyalty/Three Kings intra-oceanic arc, consuming Poya
and other oceanic crust from New Caledonia to New
Zealand (Crawford et al. 2003; Aitchison et al. 1995;
Schellart 2007), might have been the mechanism for pro-
viding the Tangihua Cretaceous-Oligocene ophiolites.
The Poya Terrane and Tangihua Complex do not have
entirely coincident Cretaceous age ranges—as old as
Albian (112–100 Ma) (Isaac et al. 1994) for Tangihua and
as old as Campanian (84–71 Ma) for the Poya Terrane
(Cluzel et al. 2001). The Poya basalts have been interpreted
to represent a volcanic passive margin of a backarc basin
constructed on the leading edge of the rifted Australian
plate (Crawford et al. 2003), and includes basalts ranging
from typical rift tholeiites (E-MORB) to N-MORB com-
positions. If it is presumed that the backarc-like compo-
nents of the Tangihua basalts (negative Nb-Ta anomalies),
reflect upper crustal contamination during emplacement
through thinned continental crust, as for the Poya basalts, it
Mar Geophys Res (2009) 30:21–60 23
123
is possible that the Poya and Cretaceous Northland basalts
formed on the same margin and were obducted during a
common tectonic regime, as Nicholson et al. (2000b)
suggest. An origin for the Tangihua basalts from the
Hikurangi Plateau large igneous province has been dis-
proved (Mortimer et al. 1998).
Widespread Cenozoic arc volcanism affected the
northern New Zealand margin. Volcanic rocks are dated as
Late Eocene to Early Miocene on the Three Kings Ridge
(Mortimer et al. 1998,2007; Fraser 2002 in Bernardel et al.
2002), Early Miocene on and west of Northland (Herzer
1995; Hayward et al. 2001) and in the Sarah Seamounts in
the SFB (Mortimer et al. 2007), Early to Middle Miocene
on the Northland Plateau (Mortimer et al. 2007), and
Middle Miocene in the Lau Ridge, Coromandel Peninsula
and Mohakatino volcanic belts (Cole et al. 1985; Edbrooke
2001; King and Thrasher 1996) (Fig. 1). Sparse dredging
has yielded volcanic sediments as old as Early Miocene
and lavas as young as Plio-Pleistocene on and near the
Colville Ridge (Ballance et al. 1999; Mortimer et al. 2007).
In the northern North Island, there is rare, distal, Eocene
volcanic ash (Edbrooke et al. 1994).
The Early Miocene Northland Arc lies within the con-
tinent, trending NW–SE. It is composed of northeastern
and southwestern belts which straddle the Northland Pen-
insula. The arc appears to merge via a bend with the
younger NNE–SSW trending Coromandel-Mohakatino arc,
which migrated slowly eastwards in the Middle and Late
Miocene to the present Taupo Volcanic Zone (Smith et al.
1995). Considering the Northland-Coromandel-Mohaka-
tino volcanic rocks as a continuum, Brothers (1984,1986)
proposed that the Northland Arc was actually a short NE-
trending arc that migrated southeastwards, and Kamp
(1984) applied this to a model of southward propagation of
Pacific plate subduction beneath the North Island. The
Northland Plateau volcanoes could extend the length of the
Brothers postulated volcanic arc. Ballance (1999), Hay-
ward (1993), Hayward et al. (2001) Herzer (1995) and
Mortimer et al. (2007) favoured SW-dipping subduction,
fuelling a NW-trending arc of uniform Early Miocene age,
whereas Schellart (2007) proposed NE-dipping subduction
and slab foundering to generate this arc. Mortimer et al.
(2007) suggest that the volcanic chains of the Northland
Plateau and Northland began as a single NE-facing arc and
were tectonically juxtaposed by strike-slip. Crawford et al.
(2003) proposed that the Northland Plateau was part of a
colliding Three Kings arc that jammed a NE-dipping sub-
duction zone on the New Zealand margin.
In this paper we present the results of the geophysical
and stratigraphic investigations carried out in tandem with
recently published petrologic and radiometric dating stud-
ies of the Northland Plateau and SFB (Mortimer et al.
2007). These permit, for the first time, an understanding of
the geological content, evolution and significance of the
75,000 km
2
Northland Plateau with respect to Zealandia,
the SFB and the Three Kings Ridge, and the development
of a model for the tectonic evolution of the northern New
Zealand margin.
Methods
Seismic reflection, marine gravimetric, and air and sea-
borne magnetic data were compiled from all available
sources (National Geophysical Data Centre GEODAS
http://www.ngdc.noaa.gov/mgg/geodas/geodas.html,
Mobil International Oil Co 1979; Australian Gulf Oil 1973;
NZ Oceanographic Institute collections, GNS Science in-
house data bases). We undertook two research cruises on
the Northland Plateau—SF9901 ONSIDE I in 1999 and
SF0202 ONSIDE II in 2002 (Herzer et al. 2004). These
cruises followed on from the earlier seismic investigations
of Herzer and Mascle (1996) and Herzer et al. (1997).
Navigation was by differential GPS. Seismic reflection was
recorded on a 450 m, 48 channel streamer. A 210 cu in GI
airgun source, configured in 105/105 harmonic mode,
operating at 2,000 psi, was fired at *50 m intervals. For
seismic processing, a 12.5 m common depth point (CDP)
spacing provided 12-fold CDP gathers, comprising four
traces from each of three shots. A standard velocity func-
tion beneath the seafloor was used for NMO (normal move-
out) and migration. Gravity was measured with a Lacoste
and Romberg marine gravity meter—S80. Magnetics were
recorded with a proton precession magnetometer on
SF9901 and an Overhauser magnetometer on SF0202. In
addition, we provide new biostratigraphic information from
72 fossiliferous samples collected in 26 dredge hauls
(Table 1).
The principal seismic lines and all dredge stations are
shown in Fig. 2. The igneous petrology and geochemistry
from these and other recent cruises are presented elsewhere
(Mortimer et al. 2007), and are utilised in this paper. Where
a dredge station appears in Fig. 2but not in Table 1,no
useful fossiliferous rocks were found. The full suite of
rocks may be seen in the NZ Petrological Database
(PETLAB: http://pet.gns.cri.nz), and the detailed fossil
data is available in the Fossil Record Electronic Database
(FRED: http://fred.gns.cri.nz) both at www.gns.cri.nz.
Dredge samples in Table 1and the databases are identified
by cruise and dredge number (e.g. SF0202-D17). In the text
we omit the cruise numbers SF9901, SF0202 and SS237.
For foraminiferal samples in dredges D1 to D13, the
planktic biozonation (SN zone) scheme of Jenkins (1985,
1993a,b), Stott and Kennett (1990) and the larger fora-
miniferal letter stage scheme of Adams (1984) were used.
Correlation of these zones with the schemes of Blow
24 Mar Geophys Res (2009) 30:21–60
123
Table 1 Fauna, flora, ages, depositional environments and stratigraphic units of dredged fossiliferous sedimentary rocks from the Northland Plateau region
Field no. GNS
PETLAB
no.
NZ fossil
record no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ stage
Radiolaria
zone and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged feature
SF9901-
D1B-3$
63140 SE34174/
f4
-34.1005 174.1668 778–577 F lE Mio/Pl SN4, Tf1/Pl AB on
Ec
Bioclastic, algal,
bryozoan,
foraminiferal
limestone
Inner neritic
(0–20 m)
Cavalli Seamount
SF9901-
D1B-8$
63141 SE34174/
f5
-34.1005 174.1668 778–577 F E-M Pleist/
Wn-Wh
SN14/Wn-Wh A on Ec Siliceous
limonite
(replaced
limestone)
Upper bathyal
(200–500 m)
Cavalli Seamount
SF9901-
D1A-
4A$
63145 SE34174/
f2
-34.1050 174.178 1229–958 F Earliest Pli/
eWo
SN12a/eWo A on Ec Limestone with
schist clasts
Lower bathyal
(500–
2,000 m)
Cavalli Seamount
SF9901-
D2A-1
63149 SE33173/
f2
-33.6782 173.955 1609–1475 F NF likely
Neogene
Cv Palagonite
granule
breccia,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D2. No Ar–Ar date
SF9901-
D2B-2
63151 SE33173/
f1
-33.693 173.956 1260–1184 F E Mio/lLw-
Pl
SN2-SN4/lLw-
Pl
Cv Foraminiferal
limestone
Upper bathyal
(200–500 m)
Poor Knights volcano
D2. No Ar–Ar date
SF9901-
D4B-4$
63159 SE33174/
f2
-33.457 173.882 2953–2809 D, F, R Lw-Pl, Prob Po-
Pl
NF NF Cv Volcanic
sandstone
(clast?)
Upper bathyal
(200–500 m)
Volcanic outer plateau
volcano D4. Ar–Ar
dates 21.9 ±0.3 Ma
and 17.9 ±0.8 Ma
SF9901-
D4C-1A
63160 SE33174/
f3
-33.457 173.882 2953–2809 F, R lLwh-Pl, prob
Po-Pl
NF Cv Volcanic
sandstone
Upper bathyal
(200–500 m)
Volcanic outer plateau
volcano D4. Ar–Ar
dates 21.9 ±0.3 Ma
and 17.9 ±0.8 Ma
SF9910-
D5B-3
63163 SE33175/
f1
-33.573 175.494 2167–1898 F E-M Pleist/
Wn-Wh
SN14/Wn-Wh Cv Foraminiferal
sandstone
Lower bathyal
(500–
2,000 m)
Volcanic outer plateau
crater D5. No Ar–Ar
date
SF9901-
D5B-4
63221 SE33175/
f2
-33.573 175.494 2167–1898 F E-M Pleist/
Wn-Wh
SN14/Wn-Wh Cv Foraminiferal
sandstone
Lower bathyal
(500–
2,000 m)?
Volcanic outer plateau
crater D5. No Ar–Ar
date
SF9901-D6-
1A
63222 SE33176/
f1
-33.397 176.605 2200–1852 F E Mio/lLw-
Pl
SN2-SN4/lLw-
Pl
Cv Breccia matrix Lower bathyal
(500–
2,000 m)?
Poor Knights volcano
D6. Ar–Ar dates
20.1 ±1.9 Ma and
17.6 ±0.9 Ma
SF9901-D6-
1C
63224 SE33176/
f2
-33.397 176.605 2200–1852 F lL Mio/Tk SN11/Tk Cv Limestone (not
breccia
matrix)
Lower bathyal
(500–
2,000 m)?
Poor Knights volcano
D6. Ar–Ar dates
20.1 ±1.9 Ma and
17.6 ±0.9 Ma
SF9901-
D7B-5$
63181 SE33176/
f4
-33.233 176.264 2453–2122 F lE Mio/Pl SN4/Pl Cv Volcaniclastic
sandstone
Lower bathyal
(500–
2,000 m)?
Outer volcanic plateau
volcano D7. Ar–Ar
date 22 ±9Ma
SF9901-
D9A-1$
63182 SE34175/
f4
-34.433 175.415 1488–8392 F lE–eM Mio/
Pl-Sc
SN4/SN5/Pl-Sc Cv Volcaniclastic
sandstone,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D9. No Ar–Ar date
Mar Geophys Res (2009) 30:21–60 25
123
Table 1 continued
Field no. GNS
PETLAB
no.
NZ fossil
record no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged feature
SF9901-
D9A-3
part$
63184 SE34175/
f1
-34.433 175.415 1488–1392 F eE Mio/
lLw-Po
SN3/lLw-Po Cv Stiff clay,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D9. No Ar–Ar date
SF9901-
D9A-4$
63185 SE34175/
f2
-34.433 175.415 1488–1392 F eE Mio/
lLw-Po
SN3/lLw-Po Cv Sandstone,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D9. No Ar–Ar date
SF9901-
D9A-3
part$
63187 SE34175/
f6
-34.433 175.415 1488–1392 F lE–eM Mio/
Pl-Sc
SN4/SN5/Pl-Sc Cv Tuff breccia,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D9. No Ar–Ar date
SF9901-
D9A-3
part$
63188 SE34175/
f7
-34.433 175.415 1488–1392 F lE–eM Mio/
Pl-Sc
SN4/SN5/Pl-Sc Cv Volcaniclastic
sandstone,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D9. No Ar–Ar date
SF9901-
D9B-1$
63189 SE34175/
f8
-34.406 175.516 1525–1166 F lE–eM Mio/
Pl-Sc
SN4/SN5/Pl-Sc Cv Volcaniclastic
sandstone,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D9. No Ar–Ar date
SF9901-
D9B-3$
63190 SE34175/
f9
-34.406 175.516 1525–1166 F M Mio/Sl-
Sw
SN6/Sl-Sw Cv Conglomerate,
volcano-
sedimentary,
calc cement
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D9. No Ar–Ar date
SF9901-
D9B-2$
63191 SE34175/
f3
-34.406 175.516 1525–1166 F lE Mio/Pl SN4/Pl Cv Volcaniclastic
sandstone,
calcareous
Upper bathyal
(200–500 m)
Poor Knights volcano
D9. No Ar–Ar date
SF9901-
D12A-
1$
63202 SE34176/
f1
-34.818 176.782 1828–1626 F lE Mio/Pl SN4/Pl Cv Volcaniclastic
sandstone,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D12. No Ar–Ar date
SF9901-
D12A-
6$
63203 SE34176/
f2
-34.818 176.782 1828–1626 F lE Mio/Pl SN4/Pl Cv Volcaniclastic
sandstone,
calcareous
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D12. No Ar–Ar date
SF9901-
D12B-
1$
63204A SE34176/
f3
-34.8608 176.7822 1872–1607 F lE–eM Mio/
Pl-Sc
SN4/SN5/Pl-Sc Cv Limestone,
lithoclastic,
pelagic
Lower bathyal
(500–
2,000 m)
Poor Knights volcano
D12. No Ar–Ar date
SF9901-
D13-1$
63213 SE35176/
f2
-35.693 176.441 1347–1091 F Earliest
Plio/eWo
SN12a A on C,
D, E?
Mudstone,
calcareous
Lower bathyal
(500–
2,000 m)
Upper continental slope
SF9901-
D13-1$
63215 SE35176/
f1
-35.693 176.441 1347–1091 F Earliest
Plio/eWo
SN12a A on C,
D, E?
Mudstone,
calcareous
Lower bathyal
(500–
2,000 m)
Upper continental slope
SF0202-
D14B-1
P66793 SE35177/
f4
-35.0573 177.0379 1755–1400 F, N mM Mio/Sl-
eSw, L
Plio/Wm
N10/11/M Mio,
N21/Late
Plio
NN5–
NN7/M
Mio?
Cv Volcanic and
sedimentary
breccia. Ooze
in cavities
Seems to be
shallow
water,
temperate but
difficult to
ascertain
Poor Knights volcano
D14. Ar–Ar date
14.7?/1.0 Ma
26 Mar Geophys Res (2009) 30:21–60
123
Table 1 continued
Field no. GNS
PETLAB
no.
NZ fossil
record no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged feature
SF0202-
D16-1i$
P66820 SE33172/
f3
-33.5854 172.3940 1570–1392 F Latest E
Mio/late
Pl
N7/Latter half E
Mio
AB Coquina
bioclastic
limestone
grainstone,
large foams,
bryozoa,
algae,
echinoids,
molluscs
Clean, warm,
shallow
marine,
photic zone,
virtually
devoid of any
terrigenous
input
The Slab. NW end of
inner plateau
sedimentary basin
SF0202-
D16-
1ii$
P66820 SE33172/
f4
-33.5854 172.3940 1570–1392 F, N Latest E
Mio/late
Pl
N7/Latter half E
Mio
NN1–
NN4/E
Mio
AB Coquina
bioclastic
limestone
grainstone,
large foams,
bryozoa,
algae,
echinoids,
molluscs
Clean, warm,
shallow
marine,
photic zone,
virtually
devoid of any
terrigenous
input
The Slab. NW end of
inner plateau
sedimentary basin
SF0202-
D16-6$
P66823 SE33172/
f5
-33.5854 172.3940 1570–1392 F, N E Mio/Lw-
Pl
N4–N7/E Mio NF AB Algal balls
within 16-1,
enclosing
large
bryozoans
and rare pale
mudst clasts
Warm, shallow
water,
perhaps
towards the
lower part of
the photic
zone.
Virtually no
terrigenous
input
The Slab. NW end of
inner plateau
sedimentary basin
SF0202-
D17B-
3i$
P72174 SE33172/
f6
-33.2796 172.5323 1540–1425 F Latest E
Mio/lPl
N7/late E Mio B–AB Volcanic
sandstone/
breccia, clasts
of basalt and
pumice,
calcareous
Outer shelf or
deeper with
no evidence
of dissolution
The Thrust. Ridge
NW end of inner
plateau
sedimentary basin
SF0202-
D17B-
3ii$
P72175 SE33172/
f7
-33.2796 172.5323 1540–1425 F Mid E Mio/
Po-ePl
N5/N6/E Mio B Calcareous silty
sandstone,
closely
spaced
parallel joints
or bedding
planes, cross-
cutting veins
Cool water low
nutrient
environment
The Thrust. Ridge
NW end of inner
plateau
sedimentary basin
Mar Geophys Res (2009) 30:21–60 27
123
Table 1 continued
Field no. GNS
PETLAB
no.
NZ fossil
record no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged feature
SF0202-
D17B-
4$
P66810 SE33172/
f8
-33.2796 172.5323 1540–1425 F, N eM Mio/
late Pl-
Sc
N8/latest E–eM
Mio
ND AB Hard, chalky
foram
limestone,
minor volc/
terrig? detritus,
associated
volcanic
sandstone
Temperate water,
outer shelf-
slope devoid
of terrigenous
input; favours
nannoplankton
The Thrust.
Ridge
NW end
of inner
plateau
sedimentary basin
SF0202-
D17B-
8$
P66812 SE33172/
f9
-33.2796 172.5323 1540–1425 F, NEarliest
Mio/Lw
N4B/N6/Earliest
pt of E Mio
NN1/
Earliest
Mio
B Volcaniclastic
conglomcerate.
Clasts of
pumice,
sandstone
(17B-3?),
basalt. Calcite
matrix, veins
and
replacement
Shallow,
temperate
water;
probably inner
shelf
The Thrust. Ridge NW
end of inner plateau
sedimentary basin
SF0202-
D19-4$
P66804 SE32173/
f2
-32.6801 173.1766 2330–1850 F, NEarly E Mio N4B-N8/E Mio NN1-2/E
Mio
Cp Volcanic breccia
with ooze
Temperate
waters, mid-
outer shelf
Edge of upper Huia
Terrace. Ar–Ar
dates 21.1?/1.84
and 20.4 ±0.05 Ma
SF0202-
D21-14
P66834 SE33174/
f4
-33.9775 174.3827 1570–1500 F, N Prob E Mio/
Lw-Sc
N4-N8/Prob E
Mio
NF Cv Hydrothermal or
tectonic lava
breccia
Outer shelf,
upper slope
depths
Poor Knights volcano
D21. Ar–Ar date
18.5 ±4Ma
SF0202-
D22-3
P66841 SE34173/
f4
-34.2070 173.9784 1330–980 F, N E or M Mio E or M Mio ND AB? on
Ec
Muddy calc
sandstone,
schist detritus,
fsp, qz, biot,
clinopx. Like
66842 but
burrowed or
mud ball
texture
Marine, mid-
shelf depths?
West peak Cavalli
Seamount
SF0202-
D22-4
P66842 SE34173/
f5
-34.2070 173.9784 1330–980 F, N Early half
of M
Mio
Early half of M
Mio
M-L Mio AB? on
Ec
Muddy calc
sandstone,
schist detritus,
fsp, qz, biot
Within the photic
zone
West peak Cavalli
Seamount
SF0202-
D22-5
P66843 SE34173/
f6
-34.2070 173.9784 1330–980 F, NN21/Late
Plio
N21/Late Plio M-L Mio A?on Ec Chalky limestone
nanno foram
ooze
wackestone,
planktics, some
echinoids,
angular detrital
mins
Outer shelf or
continental
slope.
Planktonic
percentage
suggests the
latter
West peak Cavalli
Seamount
28 Mar Geophys Res (2009) 30:21–60
123
Table 1 continued
Field no. GNS PETLAB
no.
NZ fossil
record no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged feature
SF0202-
D22-9
P66844 SE34173/
f7
-34.2070 173.9784 1330–980 F, N Early pt of
M Mio/
Earliest
Sl
N9/early pt of M
Mio
M-L Mio AB? on
Ec
Limestone
breccia
cementing
schist/gneiss
blocks.
Micritic
foram
wackestone
matrix.
Schist,
granite and
volcanic
lithics
Mid shelf near
base of photic
zone, perhaps
slumping is
involved to
mix elements
West peak Cavalli
Seamount
SF0202-
D23-2$
P66865 SE34174/
f12
-34.2667 174.0823 1410–830 F, NEarly half of
E Mio
Mio or younger Early half
of E
Mio
B Pebbly volcanic
sandstone
Warm water,
normal
marine
salinity,
within photic
zone
South Cavalli
Seamount
SF0202-
D23-5i$
P66867 SE34174/
f13
-34.2667 174.0823 1410–830 F, NEarly half of
E Mio
Mio or younger Early half
of E
Mio
B Basaltic
volcaniclastic
sandstone
with
mudstone rip-
ups
Continental
shelf depth
South Cavalli
Seamount
SF0202-
D23-
5ii$
P66868 SE34174/
f14
-34.2667 174.0823 1410–830 F Mio or
younger
Mio or younger B Silty limestone-
polymict volc
sandstone
contact.
Much calcite
veining and
replacement
in sandstone
Marine,
probably
basically
quiet water
but with
occasional
influx of sand
and
volcanism
(active at the
time?)
South Cavalli
Seamount
SF0202-
D23-8i$
P66964 SE34174/
f15
-34.2667 174.0823 1410–830 N Early half of
E Mio
Early half
of E
Mio
B Calc
volcaniclastic
mudstone,
calcite
replacement,
veins and
geopetal
crack
South Cavalli
Seamount
Mar Geophys Res (2009) 30:21–60 29
123
Table 1 continued
Field no. GNS
PETLAB no.
NZ fossil
record no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged
feature
SF0202D-
23-9i$
P66966 SE34174/
f22
-34.2667 174.0823 1410–830 F, NEarly half of
E Mio
ND Early half
of E
Mio
B Flaggy calc fine
sandstone,
scattered
detritals
mainly felds,
biotite, many
parallel
calcite
microveins,
scattered
forams
Indeterminate South Cavalli
Seamount
SF0202-
D23-
9ii$
P66967 SE34174/
f16
-34.2667 174.0823 1410–830 F, NEarly half of
E Mio
E-M Mio
tentative
Early half
of E
Mio
B Flaggy calc
mudstone,
scattered
detritals
mainly felds,
biotite, many
parallel
calcite
microveins
?larger
cross-cutting
veins
Not
determined
South Cavalli
Seamount
SF0202-
D23-
9iii$
P66968 SE34174/
f17
-34.2667 174.0823 1410–830 F E-M Mio E-M Mio B Flaggy
calcareous
siltstone
Marine, mid-shelf,
below the photic
zone
South Cavalli
Seamount
SF0202-
D23-
10$
P66969 SE34174/
f10
-34.2667 174.0823 1410–830 F, N E or early
half of M
Mio
E or early half of
M Mio
ND B Epiclastic
volcanic
sandstone
Subtropical, shallow but
possibly below
photic zone
South Cavalli
Seamount
SF0202-
D23-
11$
P66970 SE34174/
f11
-34.2667 174.0823 1410–830 F, NEarly half of
E Mio
Prob Mio Early half
of E
Mio
B Foraminiferal
volcaniclastic
sandstone.
Multiple,
mainly
parallel drusy
calc veins as
in D23–8
Marine, continental
shelf depths
South Cavalli
Seamount
SF0202-
D24A-
1$
P66849 SE34174/
f18
-34.3602 174.1860 1275–1180 F, N E or M Mio E or M Mio NF Cv Limestone Inner shelf Cavalli Ridge,
volcano
SF0202-
D25A-
9$
P66791 SE34176/
f5
-34.4406 176.9799 2250 F E Mio (estimate) Cv Volcaniclastic
sandstone,
foraminiferal
Outer shelf depths Volcanic outer
plateau
volcano
D25. Ar–
Ar date
1.2?/
0.8 Ma
30 Mar Geophys Res (2009) 30:21–60
123
Table 1 continued
Field no. GNS
PETLAB
no.
NZ fossil
record
no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged
feature
SF0202-
D26B-1
P66845 SE34174/
f19
-34.4422 174.1852 1140–985 F M Miocene/Sl-
eSw
N9–N12/M Mio AB? Foram
lismestone
breccia.
Basaltic
clasts and
detrital plag,
clinopx
Mid shelf? planktonic
foraminifera
dominate but rock
appears fragmented
and with volcanic
clasts
Cavalli
Ridge,
upper
continental
slope
SF0202-
D26B-
6i
P66846 SE34174/
f20
-34.4422 174.1852 1140–985 F, N Late E Mio-eM
Mio/Pl-Sc
N6–N8/Latter
half E Mio
ND AB?, B? Bioclastic
bryozoan
foraminiferal
limestone
packstone,
common
echinoids,
rounded
volcanic
lithics
Shallow, inner shelf
within the photic
zone
Cavalli Ridge,
upper
continental
slope
SF0202-
D26B-
6ii
P66847 SE34174/
f21
-34.4422 174.1852 1140–985 F, N eM Mio/Latest
Pl-Sc
N8/E Mio ND AB? Foraminiferal
limestone
packstone,
?bryozoa,
echinoids,
molluscs
Outer shelf or slope
depths below photic
zone; bryozoa
suggest limitation to
outer shelf
Cavalli Ridge,
upper
continental
slope
SS237-
DR33-
A1
P69390 SE33171/
f5
-33.2911 171.3352 2445–1370 F M Miocene/Sl-
eSw
N9–N12/N13/
Mid Mio
Friable
sandstone.
Angular
terrigenous
sand grains,
diverse
benthic foram
fauna, trace
glauconite
Very shallow inner
shelf, close to a
source of freshly
weathered angular
sand
Isolated block
in VMFZ,
South
Norfolk
Basin
SS237-
DR33-
B1
P69391 SE33171/
f6
-33.2911 171.3352 2445–1370 F EMio/Po-ePl N5/N6/E Mio Cross-laminated
calc
sandstone
Inner to mid-shelf Isolated block
in VMFZ,
South
Norfolk
Basin
SS237-
DR33-
B2
P69392 SE33171/
f7
-33.2911 171.3352 2445–1370 F E Mio/Po-ePl N5/N6/E Mio Cross-laminated
calc
sandstone
Inner to mid-shelf Isolated block
in VMFZ,
South
Norfolk
Basin
SS237-
DR33-
L1
P69400 SE33171/
f8
-33.2911 171.3352 2445–1370 F E Miocene
(somewhat
tentative).
Slabby, jointed,
veined
sandstone,
angular, fresh
volcanic
grains
Isolated block
in VMFZ,
South
Norfolk
Basin
Mar Geophys Res (2009) 30:21–60 31
123
Table 1 continued
Field no. GNS
PETLAB
no.
NZ fossil
record
no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage
adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth and
environment
Dredged
feature
SS237-
DR33-
N1
P69402 SE33171/
f9
-33.2911 171.3352 2445–1370 F Early Mio/lLw-
Po
N4/N5/E
Miocene
Bryozoan
bioclastic
limestone
grainstone
Shallow marine, well
aerated, inshore
Isolated block
in VMFZ,
South
Norfolk
Basin
SS237-
DR33-
P3
P75969 SE33171/
f10
-33.2911 171.3352 2445–1370 R, DLate Cret Early
Mh
NF Dinos
Early
Mh
Limestone Isolated block
in VMFZ,
South
Norfolk
Basin
SS237-
DR33-
R2
P69406 SE33171/
f11
-33.2911 171.3352 2445–1370 F, R, D Mio (prob
middle or
Early)
Mio (prob
middle or
Early)
ND NF Conglomerate
with dirty,
sandy matrix
with
abundant
planktonic
forams
Clasts high energy,
matrix mid-shelf
approx
Isolated block
in VMFZ,
South
Norfolk
Basin
SS237-
DR34-
B1$
P69415 SE33171/
f12
-33.2217 171.7465 2700–2600 R, D Early Miocene Early
Miocene
NF B Muddy
sandstone.
Contains
reworked
eM Eocene
Dh,
Heretaungan
49.5–
56.2 Ma
Scarp of Weta
Terrace,
west Three
Kings Ridge
SS237-
DR34-
B3$
P69417 SE33171/
f13
-33.2217 171.7465 2700–2600 R, D Early Miocene Early
Miocene
NF B Muddy
sandstone
Scarp of Weta
Terrace,
west Three
Kings Ridge
SS237-
DR34-
B4$
P69418 SE33171/
f14
-33.2217 171.7465 2700–2600 R, D Early Miocene Early
Miocene
NF B Sandstone/
mudstone
Scarp of Weta
Terrace,
west Three
Kings Ridge
SS237-
DR34-
B6$
P69420 SE33171/
f15
-33.2217 171.7465 2700–2600 F Neogene Neogene B Muddy
sandstone,
angular
immature
minerals and
euhedral
volcanic
phenocrysts
Inner to mid shelf Scarp of Weta
Terrace,
west Three
Kings Ridge
SS237-
DR34-
B7$
P69421 SE33171/
f16
-33.2217 171.7465 2700–2600 R, D Early Miocene Early
Miocene
NF B Pebbly
volcanic
sandstone
Scarp of Weta
Terrace,
west Three
Kings Ridge
32 Mar Geophys Res (2009) 30:21–60
123
Table 1 continued
Field no. GNS
PETLAB
no.
NZ fossil
record
no.
FRED
Latitude
WGS84
Longitude
WGS84
Depth
(m)
Fossil
group
examined
Age and NZ
stage adopted
Foram
zone and
age/NZ
stage
Radiolaria
zone
and
age
Nanno
zone
and
age
Palyno
morph
age
Seismic
unit
dredged
Lithology Paleodepth
and environment
Dredged
feature
SS237-
DR34-
B8$
P69422 SE33171/
f17
-33.2217 171.7465 2700–2600 R, D Early Miocene Early
Miocene
NF B Siltstone-
sandstone.
Contains
reworked
eM Eocene
Dh,
Heretaungan
49.5–
56.2 Ma
Scarp of Weta
Terrace,
west Three
Kings Ridge
SS237-
DR34-
B9$
P69423 SE33171/
f18
-33.2217 171.7465 2700–2600 R, D Neogene Neogene NF B Mudstone,
calcareous
Scarp of Weta
Terrace,
west Three
Kings Ridge
SS237-
DR34-
D1$
P69435 SE33171/
f19
-33.2217 171.7465 2700–2600 R, D Plio-Pleist? NF NF B Chert breccia Scarp of Weta
Terrace,
west Three
Kings Ridge
SS237-
DR35-
A1$
P69436 SE33171/
f20
-33.3100 171.9800 1660–1574 F Prob E Mio B, Cv Lithic/crystal
sandstone,
broken
bryozoa,
molluscs,
foraminifera
(Amphiste-
gina).
Euhedral
plag, biotite,
pyroxene
Shallow marine,
wave zone,
clear water
South Three
Kings
Ridge, foot
of volcano
SS237-
DR35-
A2$
P69437 SE33171/
f21
-33.3100 171.9800 1660–1574 F Prob E Mio B, Cv Dirty limestone
with shark
tooth, solid
limestone
chips
Shallow marine,
wave zone,
clear water
South Three
Kings
Ridge, foot
of volcano
SS237-
DR35-
B29$
P69451 SE33171/
f22
-33.3100 171.9800 1660–1574 F Lw-Pl Latest Olig-E
Mio
B, Cv Veins of
nanno/foram
ooze in
volcaniclas-
tic sandstone
Shallow
marine, warm
temperate
South Three
Kings
Ridge, foot
of volcano
SS237-
DR35-
D$
P69457–
P69460
SE33171/
f23
-33.3100 171.9800 1660–1574 F Approx Lw-Po Latest Olig or
Earliest
Mio
B, Cv Volcaniclastic
sandstone,
fresh angular
volc debris
Mod high
energy, inner
to mid shelf
South Three
Kings
Ridge, foot
of volcano
D=dinoflagellates; F =foraminifers; N =nannofossils; R =radiolarians; italicised letter in ‘‘Fossil group examined’’ =diagnostic group; E =Early; M =Middle; L =Late; e =early; m =middle; l =late; e.g. eM =early
Middle; ND =no determination due to poor or insufficient material; NF =barren
=dredge station not on a seismic line; $=dredge station on or very near a seismic line
Mar Geophys Res (2009) 30:21–60 33
123
(1969) and Berggren et al. (1995) and ages of bio-events
followed Shipboard Scientific Party (2001). These zones
were correlated to the New Zealand stage scheme follow-
ing Morgans et al. (1996).
For all other foraminiferal samples, age information is
expressed in terms of the P/N zones established by Blow
(1969) and refined by Berggren et al. (1995). Planktic
foraminiferal taxonomy and age ranges followed Bolli
and Saunders (1985) and Kennett and Srinivasan (1983)
for the Neogene, and Toumarkine and Luterbacher (1985)
and especially Olsson et al. (1999) for the Paleocene. A
few species names not used by these authors followed
Blow (1969). Where possible, larger foraminiferal tax-
onomy followed that of Chaproniere (1984) while their
palaeoenvironmental interpretation followed Chaproniere
(1975).
For all nannofossil samples, the general diversity was
low, with most samples having assemblages comprising
between 10 and 20 identifiable taxa; only one sample
having over 20 taxa. The assemblages comprised mainly
common long ranging taxa. This made assignments to the
international high resolution standard zonal schemes of
Martini (1971) or Okada and Bukry (1980) impossible.
However, samples could be assigned to the broader zonal
intervals defined by Young (1998) and supplemented with
additional events identified by Perch-Nielsen (1985),
Okada and Bukry (1980) and McGonigal and Wei (2003).
For radiolarians, identifications and age assignments
were based on Campbell and Clark (1944), Nigrini and
Lombari (1984), Sanfilippo et al. (1985) and Hollis (1997).
All results were correlated with the New Zealand geo-
logical time scale of Morgans et al. (1996) in (Cooper
2004).
Regional geological, bathymetric and geopotential
trends
Continental basement, arc and back-arc trends
Mesozoic accreted terranes make up the continental Zea-
landia basement in this study (Eade 1988; Mortimer et al.
1998; Mortimer 2004; Sutherland 1999). On the eastern
side of the Northland Peninsula, the basement comprises
relatively non-magnetic Permo-Triassic greywacke of the
Waipapa Composite Terrane (Mortimer 2004). Greywacke
extends onto the continental shelf (Thrasher 1988; Gamble
et al. 1993). In the extreme north of the peninsula, the
basement is composed of the Cretaceous volcanic and
flyschoid Houhora Complex (Mount Camel Terrane),
which outcrops only as islands and promontories joined by
a large tombolo, forming the Aupouri Peninsula (AP,
Fig. 1) (Isaac et al. 1994; Toy et al. 2002). Buried and
eroded volcanoes of the Northland Arc (Herzer 1995) give
rise to isolated gravity and magnetic highs ([500 nT) off
the western coast (Figs. 3,4). Arc volcanoes and volcanic
bodies of the Northland Allochthon occur as eroded mas-
sifs on land.
The Three Kings and Colville Ridges are highlighted by
positive gravity and magnetic anomalies (Figs. 3,4). West
+
_
COLVILLE RIDGE
1000
2000m
3000m
2000m
2000m
1000m
35°S
36°S
34°S
173°E 174°E 175°E 176°E 177°E
WHANGAROAB
3000m
2000m
1000m
SOUTH FIJI BASIN
VLL
Northland Allochthon front
UN
PPER
CO
TI
NE
N
T
A
L
SLOPE
BASIN
POOR KNIGHTS SEAMOUNTS
HUIA
TERRACES
CS
OCEANIC CRUST
33°S
172°E
Northland
THREE KINGS
RIDGE
VMFZ
NORTHERN SPUR
KNIGHTS
VOLCANIC OUTER PLATEAU
INNER PLATEAU BASIN
TUATARA TERRACE
WETA TERRACE
D13
D25
D12
D5
D4
D7
D6
D11
D9
P70
D2
D1
RE1
D19
D18
D17
D16
D21
D22
D23 D24
D26
D14
D20
DR35
DR33
MO-142
SF02-6
MO-141
Fb7305
6
/
5-9
9F
S
51/
41/4-
99FS
Sf99-1/2/18
0
41-O
M
MO-139
MO-138
SF02-3
SF02-3
SF02-4
SF99-3
DR34
F10
F12
F11
F9
F13
T1046-4
TN-17
AP
SF99-8
(F14)
Fig. 2 Northland Plateau
showing geological provinces,
major structures, seismic lines,
and dredge stations (numbered
stars). The thick black line
identifies the gravity profile.
VMFZ faults are from Thrasher
(1988) and Herzer and Mascle
(1996). Red dotted line flanked
by (?) and (-) signs follows the
maximum gradient of the van
der Linden Lineament magnetic
dipole (VLL). Thick red and blue
dashed lines locate illustrated
seismic profiles identified by
Figure number, e.g. F12.
AP =Aupouri Peninsula,
CS =Cavalli Saddle (white
area) including Cavalli
Seamount, south Cavalli
Seamount and Cavalli Ridge
34 Mar Geophys Res (2009) 30:21–60
123
of the Three Kings Ridge axis, further north–south-trend-
ing gravity lineaments mark the edges of two terraces
(informally named Weta and Tuatara after the creatures
that inhabit the Three Kings Islands), descending to the
abyssal floor of the South Norfolk Basin (Fig. 1). Both
terrace edges consist of fault-block ridges and associated
volcanoes with sediment back-fill forming perched basins
(Herzer and Mascle 1996; Mortimer et al. 1998). Rising
from the centre of the lower terrace (Tuatara) is a linear
chain of horsts, which we have called ‘‘The Knolls’’ (K,
Fig. 1) marked by gravity highs approximately along lon-
gitude 171°200E (Herzer and Mascle 1996; Bernardel et al.
2002). The resulting distinctive set of three paired linear
positive and negative gravity anomalies (Fig. 3) is repeated
west of the southern Loyalty Ridge, offset by the Cook
Fracture Zone (Sandwell and Smith 1997), indicating that
these structures predate most of the activity on the CFZ.
The high relief of the Vening Meinesz Fracture Zone
(Herzer and Mascle 1996) creates a strong, linear north-
west-trending gravity dipole at the south end of the Norfolk
Basin. The anomaly interrupts the N–S gravity structures of
the terraces, some of which at their southern end appear to
bend towards the SSE. The VMFZ anomaly continues
strongly over a short distance southeast of the intersection
with the Three Kings Ridge, but is replaced by subdued
anomalies east of the Aupouri Peninsula.
In the SSFB, the regional gravity anomaly decreases
gradually by 10–15 mgal from east to west. Magnetic
anomalies form a NNE and NW chevron pattern in the
central part of the basin and may merge into anomalies on
the Northland Plateau (Fig. 4). Short, WNW to NW-
trending gravity and magnetic lineaments lie near the
eastern and western basin margins. Their orientation sug-
gests they may follow fracture zones. A large field of
volcanoes, the Sarah Seamounts (SS, Fig. 1), loosely
aligned in chains east of the Three Kings Ridge, produces
its own set of approximately E–W gravity and magnetic
trends (Figs. 3,4).
Northland Plateau and continental shelf trends
The Northland Plateau is a 110–220 km wide mid-slope
terrace lying in 1,500–2,700 m of water between the con-
tinental shelf and the abyssal plain of the SFB. It consists
Fig. 3 Satellite gravity map (Sandwell and Smith 1997) with trends
superimposed. Blue =negative, orange =positive. Cavalli Se-
amount is circled in black. The Thrust is indicated by a white arrow.
The Slab is just SW of it. Greywacke was found at the red circle
(Gamble et al. 1993). The fine dotted line encloses the Northland
Plateau. The heavy dashed line separates the domains described NW
and SE of Cavalli Saddle
Mar Geophys Res (2009) 30:21–60 35
123
mainly of two domains (Fig. 2)—a smooth sedimentary
basin adjacent to the shelf and an uneven, less sedimented,
outer plateau area that extends to the SFB (Herzer et al.
2000). Its border with the continental shelf, although
embayed, is roughly linear and NW-trending; its border
with the SFB is very irregular. The latter includes a rela-
tively smooth, arcuate step in the northwest, two large
promontories (the northern spur) containing seamounts in
the centre, and a wide, gently sloping re-entrant in the
southeast near the Colville Ridge.
A 550-km-long, prominent, linear, NW-trending mag-
netic dipole is present on the Plateau. This is the van der
Linden ‘‘Fault’’ of Sutherland (1999), which we call the
van der Linden Lineament (VLL; Figs. 2,4). It separates
the positively magnetic (\350 nT) volcanic outer plateau
from the generally negative to weakly positive sedimentary
inner plateau basin (IPB). A NW-trending linear chain of
seamounts, the Poor Knights Seamounts (Mortimer et al.
2007), is aligned along the dipole on the positive side. The
peaks coincide with short wavelength positive magnetic
anomalies, inferred to be induced and/or preserved mag-
netisation in igneous basement beneath volcanoes.
Within the inner plateau and continental slope, a linear
chain of weakly positive magnetic anomalies extends along
the base of the slope. The negative to weakly positive
magnetic zone extends northwestwards across the Three
Kings Ridge axis and beyond into the domain of terraces in
the eastern Norfolk back-arc region. Interestingly, the
western limit of this zone (170.5°E) coincides with the
western limit of the Allochthon on the Reinga Ridge.
Physiographically the inner plateau ends at the Three
Kings Ridge. The relief of the ridge at the intersection is
subdued, but just east of the axis is a broad isolated high.
The northern half of the high, which we call ‘‘The
Thrust’’ for reasons given below, coincides with a gravity
high at 172.6°E, 33.2°S (Fig. 3). The southern half,
which we have called ‘‘The Slab’’, has a distinctive
flattish top and steep sides, and, despite its relief, a
negative free-air gravity anomaly like the rest of the
sedimentary basin.
Fig. 4 Magnetic map with southwestern Allochthon front superim-
posed. The fine dotted line encloses the Northland Plateau. The heavy
dashed line separates the domains described NW and SE of Cavalli
Saddle. Cavalli Seamount is circled in white. Greywacke is found at
the red circle. Air and seaborne magnetic data from National
Geophysical Data Centre GEODAS http://www.ngdc.noaa.gov/mgg/
geodas/geodas.html, and GNS science in-house databases
36 Mar Geophys Res (2009) 30:21–60
123
The outer plateau positive magnetic belt abuts or merges
westwards with the magnetic anomaly of the main axis of
the Three Kings Ridge but meets the Colville Ridge in a
narrow negative trough (Fig. 4). Northwesterly positive
trends are restricted to the vicinity of the van der Linden
Lineament whereas NNE-trending, broad wavelength,
high-amplitude anomalies of variable area on the outer part
of the Plateau appear to line up with positive seafloor
spreading anomalies on the adjacent oceanic crust to the
north. The alignment could be coincidental or it could be
that igneous bodies related to SFB crust underlie a thick
pile of andesitic volcanic rocks on the volcanic outer
plateau.
The northwestern end of the outer plateau, the south-
western corner of the SFB, is distinguished by two thin,
arcuate gravity lineaments of 20–40 mgal amplitude
(Fig 3). They define the edges of the Huia Terraces
(Fig. 2), *2,000 and 2,600 m below sea level which trend
NNW, intersecting the Three Kings Ridge and Northland
Plateau at high angles.
The van der Linden Lineament and other NW trends,
including the continental shelf edge, are sinistrally offset
by 30 km at *174°E (Figs. 2,3,4). Within the zone of
offset is a tight cluster of seamounts that includes Cavalli
Seamount, South Cavalli Seamount and a small N-trending
ridge, named here Cavalli Ridge, which together form a
saddle that divides the inner plateau into the Whangaroa
and Knights basins. Northwest and southeast of the saddle
the geology and structure of the margin are different in
important respects.
Northwest of a line through the Cavalli Saddle the fol-
lowing is seen (Fig. 3,4). The SFB seafloor magnetic
anomalies lack a clear spreading pattern, although there is a
hint of a NNE trend and a NNW trend parallel with the
Huia Terraces, which is partly obscured by the Sarah
Seamounts. No clear spreading anomalies impinge on the
Northland Plateau. The negative gravity anomaly of
Whangaroa Basin is *30 mgal more negative than that of
Knights Basin, and the positive magnetic anomalies in the
band along the base of the continental slope are relatively
broad and strong. The bathymetric continental shelf edge is
linear, trending northwesterly (Figs. 1,2) and under the
shelf and upper slope there is gravity and seismic structural
expression of the VMFZ (Herzer and Mascle 1996). The
adjacent land area, the Aupouri Peninsula (AP, Fig. 2), is
thin and low, and the outcropping basement terrane is the
Houhora Complex.
Souththeast of the line through the Cavalli Saddle the
following is observed. The Northland Plateau projects into
the SFB, and the basin’s seafloor-spreading magnetic
anomaly highs appear to partially line up with magnetic
highs on the Plateau. The gravity anomaly on the inner half
of the Northland Plateau (Knights Basin) is not as negative
as it is to the NW. The main gravity anomaly and the
nearby van der Linden Lineament trend N125°–130°and
extend to their intersection with the Colville Ridge. The
magnetic anomalies in the band along the base of the
continental slope are small and weak. The continental shelf
edge is crenelated, though broadly linear, with the same
overall trend as that to the northwest. Under the continental
shelf there are NNW gravity and magnetic trends east of
175°E, which could arise in the geology of the pre-existing
basement, but more likely reflect a southward swing of the
volcanic arc trends and splaying of the VMFZ. The VMFZ
may branch east of 175°E: one branch taking a more
southerly N150°track east of the Coromandel Peninsula,
while another strikes N120°parallel to the continental
slope (Figs. 2,3). Smaller northeasterly trends in the
gravity appear to cut across the shelf. Together these may
account for the crenelation of the shelf edge and upper
slope. These NNW–NNE trends are parallel with those of
the Coromandel Peninsula, western Taupo Volcanic Zone
and the large eastern Bay of Plenty faults of the North
Island fault system as well as the Plio-Pleistocene Hauraki
Graben. The land area on the Northland Peninsula south-
east of the Cavalli Saddle is higher and much wider than to
the northwest, and the outcropping basement rocks are of
the Waipapa Terrane.
Stratigraphic units identified, defined and dated
Background
The stratigraphy and structure of the Northland Plateau,
like the onshore, is a complex juxtaposition of allochthon,
autochthon, syntectonic deposits, volcanoes and volcanic
deposits, pre- and post-volcanic deformation, and various
basement rocks. A thick sediment blanket allows for few
outcrops suitable for stratigraphic dredging. There are no
drill holes, no regional marker reflectors, lateral facies
changes are common, and the seismic data are too sparse
for confident regional seismic sequence mapping.
The available published reference points are: the dates
of obduction of the Allochthon, the age of Norfolk Basin
extension and related movement of the VMFZ, the defor-
mation history of Northland and the neighbouring Reinga
Basin area, the uplift history of Cavalli Seamount, and the
ages of arc-related volcanism on the Three Kings Ridge,
Northland and the Northland Plateau (Fig. 5).
Tectonism
The period of obduction of the Allochthon is considered to
be within the Waitakian (Lw, earliest Miocene) (25.2–
21.7 Ma, timescale of Cooper 2004; Isaac et al. 1994;
Mar Geophys Res (2009) 30:21–60 37
123
Fig. 5). Thus the top reflector of the Allochthon in seismic
profiles would be no older than *25 Ma or no younger
than *22 Ma (Fig. 5) unless there was a significant period
of post-allochthon erosion.
Motion on the VMFZ, accompanying southeastward
translation of the Three Kings Ridge, is bracketed approxi-
mately by the eruption of MORB at 23 Ma in the Cook
Fracture Zone (Bernardel et al. 2002) and eruption of alka-
line lavas at 16.2 and 15 Ma on two linear intraplate sea-
mounts in the SFB interpreted as mini-hotspot trails
(Mortimer et al. 2007). The interval included eruption of
MORB at 19.8 Ma on the west side of the Tuatara Terrace in
the western Three Kings fault terraces, MORB at 19.3 Ma
north of the CFZ and OIB at 15.8 Ma on a seamount on the
abyssal floor of the South Norfolk Basin (Mortimer et al.
1998,2007). It included subsidence of the East Wanganella
Sub-basin and deformation on the southern margin of the
VMFZ which led to uplift on the Reinga and northern
Wanganella Ridges (Herzer et al. 1997). The southeastern
end of the Reinga Ridge was sliced longitudinally by the
VMFZ into two parallel, flat-topped ridges—South Maria
Ridge and North Maria Ridge—that are connected to the
northwestern continental shelf of Northland. Thus trans-
current or transform-related faulting would have affected the
Northland Plateau and continental shelf during the Early and
early Middle Miocene, obliterating much of the allochthon
structure, as well as affecting the geological basement and
the deposition of volcanic rocks and sediments.
The metamorphic rocks of Cavalli Seamount in the
Cavalli Saddle complex were exhumed rapidly at c.
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Fig. 5 Correlation diagram of tectonic, volcanic and sedimentary
phases in the northwestern NZ region and the Northland Plateau
(sources cited in text). Seismic reflector horizons N6 to N1.9 are from
Herzer (1995) and Herzer et al. (1997). Horizons Top B and Top AB
(with possible age ranges) are from this study. Grey bars =tectonism
and erosion; orange bars =volcanism of mainly unit C and its
correlatives (pale orange =dated by seismic correlation only);
green,turquoise and blue bars =sedimentation of Units B, AB and
A, respectively. Use of red and blue lettering is simply to help
distinguish labels
38 Mar Geophys Res (2009) 30:21–60
123
100 mm/year at 19.9 Ma during the active phase of VMFZ
activity after Allochthon obduction. The top of the
seamount, flattened by erosion to sea level, has subsided by
500 m since 18 Ma (Mortimer et al. 2003,2008).
A late phase of compression affected the Reinga Basin,
causing more uplift and planation of the southeastern
Reinga Ridge, coinciding with a dramatic basin inversion
that completed the uplift of the Wanganella Ridge (Herzer
et al. 1997; Fig 5). The age of late uplift is poorly con-
strained, however, by an arbitrary top Middle Miocene age
for a seismic reflector (N2.5) between dated top Early
Miocene (N*) and near-top Late Miocene (N1.9) reflectors
in the Reinga Basin (Herzer et al. 1997). Tectonic quies-
cence of Northland in the Middle and Late Miocene, con-
fined to regional southwestward tilting (Isaac et al. 1994),
suggests that the SE Reinga/Wanganella Ridge events
might have been over much sooner. Nevertheless, tectonism
was increasing elsewhere in the North Island in this period.
Volcanism
Arc volcanism of the early Three Kings Ridge is repre-
sented by dredge samples obtained from scattered bits of
the dismembered ridge—boninites from several locations
down the western side of the ridge (Crawford et al. 2004),
including a 37 Ma boninite on a plateau west of the ridge
(Bernardel et al. 2002), a 32 Ma andesite on the lower Huia
Terrace east of the ridge (Mortimer et al. 2007), and a
26 Ma shoshonite breccia on the Norfolk Ridge, which
may be related to the Three Kings Ridge eruptive story
(Mortimer et al. 1998; Fig. 5).
The only well studied volcanic arc near the Northland
Plateau is the Northland Arc (Hayward et al. 2001). The
deposits of the northeastern belt of the arc, which is the
closest to the Plateau are described here from NW to SE
(Fig. 5). In the North Cape region, rocks of the Parengar-
enga Group (see Isaac et al. 1994) record volcanic activity
from 23 to 17 Ma (Hayward et al. 2001). The group
includes Waitakian (Lw) (25–22 Ma) andesitic material
deposited in piggy-back basins on the Allochthon, 22–
19 Ma conglomerate containing explosive andesitic volca-
niclastic sediments deposited on the continental slope, and
20–17 Ma mixed volcaniclastic-terrigenous rocks, depos-
ited in strike-slip fault basins and intruded by andesite
breccia dykes (Brook and Thrasher 1991; Isaac et al. 1994).
To the southeast, 22.5–17.5 Ma rocks of the Whangaroa
volcanic centre intrude allochthonous thrust sheets. Farther
southeast, in the Taurikura volcanic centre, volcanics and
intrusives that overlie and intrude the Allochthon are 21.5–
16.1 Ma in age, and ages of volcanic islands are 19.5–
15.5 Ma. Volcanic rocks of the southeasternmost group, the
Kuaotunu Volcanic Complex are somewhat younger; they
range from 18.1 to 16.3 Ma on islands north of the
Coromandel Peninsula to 18.5–11.0 on northern Coro-
mandel Peninsula itself. The youngest peninsular volcanics
may include a component of the postulated relatively young
Lau-Colville-Coromandel-Mohakatino arc (Herzer 1995).
Volcanoes of the western belt overlap in time with those of
the eastern belt and all but one appear to have started 23–
22 Ma.
The arc-type volcanoes of the Northland Plateau range
generally from 21.9 to 17.6 Ma, with younger ages of 14.7
and 1.4 Ma found close to the Colville Ridge, a pattern not
unlike that of the Northland Arc, bearing in mind that the
Plateau volcanoes are represented by only 12 radiometric
dates (Mortimer et al. 2007) and that, by its very nature, the
dredge sampling may be biased to stratigraphically
younger lavas.
Stratigraphic units
To define units, we have used seismic facies and local
superposition relationships, supported by micropaleonto-
logy (Table 1), radiometric dates (Mortimer et al. 2007)
and micro-structure of dredge samples. Sedimentary rocks
are dated less precisely by microfossils (Table 1) than
igneous rocks are by radiometric methods. On the corre-
lation diagram (Fig. 5) events or units constrained by fos-
sils may have a wider than actual age range because of the
taxa therein. This leads to overlap and some ambiguity of
reflector age.
There are six seismic units, labelled A to E from the top
down, beneath the Northland continental margin (which
includes the shelf, slope and Northland Plateau; Figs. 6,7,8).
Starting from the bottom:
Unit E
Unit E is an acoustic basement characterised by a flat-topped
or block faulted and tilted facies with a strong, unconform-
able top reflector. Age and origin vary from Tangihua vol-
canic rocks of the Northland Allochthon on the northwestern
continental shelf (Summerhayes 1969; Mortimer et al. 1998)
to Mesozoic greywacke on the southeastern extremity of the
continental shelf (Gamble et al. 1993) (Fig. 3) and Cenozoic
schist and gneiss (Unit Ec) on Cavalli Seamount in the IPB
(Mortimer et al. 2003,2008; Fig. 9).
Unit D
Unit D is a disrupted seismic unit with seismically amor-
phous to chaotic-reflector and some layered facies. Its top is
not well defined, being often at the limit of seismic pene-
tration, but may be block faulted, hummocky or relatively
smooth (Figs. 6,7,9,10,11,12). We consider it to include
the Northland Allochthon and the parautochthon which
Mar Geophys Res (2009) 30:21–60 39
123
could include Tangihua and Houhora basalts. The layered
facies might include piggy-backed Unit B or undeformed
older allochthonous strata. Its base is not seen. The allo-
chthonous part of the unit is presumed to be of earliest
Miocene tectonic emplacement age (Waitakian (Lw), 25–
22 Ma) based on onshore geology. No confirmed fossilif-
erous Unit D was sampled in this study but Tangihua vol-
canic rocks are known from the continental shelf (above).
Unit C
Volcanoes (Cv) and magnetic, acoustically opaque or
chaotic seismic facies of the volcanic outer plateau (Cp)
comprise Unit C (Figs. 9,11,13). Based mainly on six
dredged seamounts (Mortimer et al. 2007 and this paper),
Unit C is generally of earliest Miocene to late Early Mio-
cene age [25–17.6 Ma, Waitakian-Altonian (Lw-Pl)], but
may extend to the Middle Miocene [14.7 Ma, Lillburnian
(Sl)] in the east (Fig. 5).
Unit B
Unit B is a high-amplitude-reflector sedimentary unit, both
syntectonic and pre-tectonic, locally deformed by folds,
reverse, and normal faults, deposited in, or blanketing, fault
angles and synclines, and exposed rarely in structural
VEHO=8:1
VE SED = 6:1
2
0
1
2
3
4
5
Whangaroa Basin
0
1
2
3
4
5
Huia Terraces
The Slab The Thrust
MO72-142
0
1
2
3
4
5
Norfolk Basin
Three Kings Ridge
Weta Terrace
DR35 RE1, DR34 proj
SF0202-6
D16 D17B D18 D19
D20
MO72-141/SF9901-8
Andesite
21 Ma
Andesite
L Olig - E Mio
sed
E Mio volcaniclastics
32 Ma
E Mio sed
Andesite 21 Ma
E Mio shelf lst
Andesite
Continental Shelf
50 km
Unit A (M Miocene - Recent)
Unit AB (E - M Miocene)
Unit B (Oligo - E Miocene)
Units A-B (u
E Miocene - Recent)
Units Cv & Cp (volcanics)
Unit D (Allochthon)
Unit E (basement, undifferentiated.
May include allochthon)
Oceanic crust
ndifferentiated
SN
SW NE
SW NE
SFB
WB
WB
WB
Upper slope
Fig. 11
Fig. 10
Inner Plateau Basin
Continental Shelf Volcanic Outer Plateau South Fiji Basin
Sec TWT
Sec TWT
Sec TWT
PKSVMFZ
VLL
VMFZ
E?
E?
VLL
Cv
Cp
Cv
Cp
Cp
D
D
D?
Fig. 6 Line drawings of seismic profiles MO72-142, SF0202-6 and MO72-141/SF9901-8. Profile MO72-142 cuts the Weta Terrace at a shallow
angle so the scarp from which RE 1 and DR 34 were obtained is not obvious. See Fig. 2for line locations
?
MO72-138
MO72-139
0
1
2
3
4
5MO72-140
0
1
2
3
4
5
5
0
1
2
3
4
Cavalli Saddle
0
1
2
3
4
5
NW S
E
SF0202-8
D1
D22
Granite Schist
N
S
D24
E Mio shallow lst
Andesite
Cavalli
Seamount
Whangaroa Basin
Knights Basin
Continental Shelf
Unit A (M Miocene - Recent)
Unit AB (E - M Miocene)
Unit B (Oligo - E Miocene)
Units A-B (u
E Miocene - Recent)
Units Cv & Cp (volcanics)
Unit D (Allochthon)
Unit E (basement, undifferentiated.
May include allochthon)
Unit Ec (basement, core complex)
Oceanic crust
ndifferentiated
50 km
SN
SW NE
KB
Upper slope
Fig. 9
Inner Plateau Basin
TWT
ce
S
Sec TWT
TWTceS
VE H O = 8:1
VE SED = 6:1
2
WB
KB
VMFZ
VMFZ
D?
Cv
Ec
D
Cv
Fig. 7 Line drawings of seismic profiles MO72-140, MO72-139 Cavalli Saddle, MO72-138 and SF0202-8 Cavalli Seamount. See Fig. 2for line
locations
40 Mar Geophys Res (2009) 30:21–60
123
uplifts (Figs. 9,10,11,12,13). The bedding may be
bounded by faults or pass laterally into Unit C as volcanic
aprons. Its lower contact may distinctly onlap or indis-
tinctly merge with Unit D. In the deeper parts of the IPBs,
it is widespread but deeply buried and at the limit of the
seismic penetration, making recognition difficult. We
interpret Unit B to include the syntectonic S1 sequences
mapped by Brook and Thrasher (1991) on the continental
shelf, the Parengarenga Group onshore, which includes
piggy-back and infaulted basins developed coevally with
widespread arc volcanism on the Allochthon, and lateral
equivalents or analogues of the Waitemata Group (Isaac
et al. 1994). Unit B could locally include undeformed
facies of the Allochthon.
The oldest sedimentary rocks dredged were from
bathymetric highs that expose deformed sequences
(Fig. 6). Dredge D17B on the scarp slope of the Thrust
(Fig. 11) yielded volcanic sandstones and breccias as old as
Waitakian (Lw, earliest Miocene) with common calcite
veining, while Dredge DR35 sampled a faulted sedimen-
tary sequence at the base of an andesitic volcano on the
southernmost Three Kings Ridge/westernmost Northland
Plateau (Fig. 6), recovering, among other sediments, vol-
caniclastic sandstones of similar or older age. Dredge D23
on South Cavalli Seamount, which contains tilted and
faulted sedimentary rocks, recovered earliest Miocene
volcaniclastic debris-flow type sandstones interbedded with
flaggy calcareous mudstones shot through with calcite
SF9901-5/6
SF9901-4/14/15
SF9901-1/2/18
0
1
2
3
4
5
0
1
2
3
4
5
6
0
1
2
3
4
50 km
SW
NE
Andesite
E Mio
VolcaniclasticsD12
D4
D9
P70
D11 Volc congl
E Mio
Volcaniclastics
18,22Ma
20 Ma
D13 Seds undifferentiated
Unit A (M Miocene - Recent)
Unit AB (E - M Miocene)
Unit B (Oligo - E Miocene)
Units A-B (u
E Miocene - Recent)
Units Cv & Cp (volcanics)
Unit D (Allochthon)
Unit E (basement, undifferentiated.
May include allochthon)
Oceanic crust
ndifferentiated
SW
SWSW
N
E
NE
Knight Basins
KB
PKS
VE H O = 8:1
VE SED = 6:1
2
Fig. 13
Knight Basins
Inner Plateau Basin
Continental Shelf Volcanic Outer Plateau South Fiji Basin
TWTceS
TWT
ceS
TWTceS
VLL
VMFZ
Cv
Cp
Cv
Cp
Cp
Cv
Cv
Fig. 8 Line drawings of seismic profiles SF9901-5/6, SF9901-4/14/15 and SF9901-1/2/18. See Fig. 2for line locations
Fig. 9 [SF0202-8] Detail of Cavalli Seamount and its surroundings showing debris fans (B at extreme left) derived from Cavalli Seamount,
nearby volcanic bodies (Cv at right), and normal faults developed during differential subsidence
Mar Geophys Res (2009) 30:21–60 41
123
veins and parallel microveins. All these rocks, now found
at bathyal depths ranging from 830 to 1,660 m, were
deposited in shelf depths, often in the photic zone \100 m,
including the wave zone in the case of some samples in
DR35. These rocks were deposited during the emplacement
of the Northland Allochthon, and define the older part of
Unit B.
The next oldest series of fossiliferous rocks comprises
Lower Miocene volcanic sandstones, breccias and lime-
stones recovered from the Northland Plateau volcanoes
(Dredges D2, D6, D7, D9 and D12), Lower Miocene
mudstones, sandstones and volcanic sandstones from the
fault scarp of the Weta Terrace (DR34), where a tilted unit
underlying a passive fill unit is exposed (Fig. 6), and Lower
Miocene calcareous silty sandstone and volcanic sandstone
and breccia from the section exposed in the Thrust (D17B).
The ages of those on the volcanoes agree well with the lava
radiometric ages reported by Mortimer et al. (2007). In
fact, samples D2, D9 and D12 provide additional Early
Miocene minimum ages for three volcanoes for which Ar–
Ar dates were unobtainable (Table 1; Fig. 2). Hyaloclas-
tites were very common in Dredge DR34, indicating
proximity to a volcanic source (Fig. 6). Volcaniclastic
sandstones in DR34 contain angular lithic clasts and crystal
debris that include quenched glassy lavas with plagioclase,
augite, hornblende and biotite phenocrysts; these almost
certainly derive from proximal shoshonitic andesite vol-
canoes (cf. RE9302-1 in Herzer et al. 1997). Associated
rocks were deposited in outer shelf to lower bathyal depths
(100–2,000 m), and are now all at lower bathyal depth and
Fig. 10 [SF0202-6] Detail of
the upper continental slope (left)
formed by a major fault strand
of the VMFZ and the inner
plateau basin (IPB) underlain by
extensional or transtensional
faulting (right) in the Three
Kings Ridge area. The horst at
the foot of the slope coincides
with a high positive gravity
anomaly suggesting ultramafic
rock
Fig. 11 [SF0202-6] Detail of the Thrust inverted basin and the
transition to the volcanic outer plateau. The overthrust is clear in
adjacent profile SF0202-4 (inset) displayed at less vertical
exaggeration. In strike line SF0202-3 (not shown), these strata are
horizontal and the thrust is undetectable, indicating that the thrust is
towards the SW
42 Mar Geophys Res (2009) 30:21–60
123
deeper (1,200–2,500 m). They define the main volcani-
clastic part of Unit B.
Radiometric dates for the NW to central Northland
Plateau volcanoes and the adjacent Whangaroa to North
Cape volcanic centres of the Northland Arc are no younger
than 17.6 Ma—approximately the age of the N6–N7 fora-
minifer zone boundary (17.3 Ma). The younger zone, N7
(16.4–17.3 Ma), encompasses the overlap of Units B and
AB on the correlation diagram (Fig. 5) and the ages of the
Slab (D16) and Cavalli Seamount (D1 and D22) shallow-
water limestones. Reflector Top B could be assigned to
somewhere between the base and top of N7 on the basis of
a change from volcanic to non-volcanic deposition, which
would agree with the change of seismic facies. However,
the change, as demonstrated by Hayward et al. (2001) and
Mortimer et al. (2007), was not instantaneous and universal
but progressive and migratory, so the facies change would
have been somewhat time transgressive. This is evident in
the nature of the rocks of that age reported here (Table 1),
which include epiclastic volcanic sediments and clean
limestones. The depositional environment was also varied,
with coexisting volcanic highs, tectonic highs, and basins,
which would have favoured radically different facies. It is
noteworthy that on tectonic highs the older rocks have
common calcite veining and replacement, whereas N7 and
younger rocks are undeformed or not affected by such
diagenesis. There is some merit, therefore, in placing
reflector Top B, which separates high amplitude and/or
deformed units from low amplitude relatively lightly
deformed units, into the N7 zone (16.4–17.3 Ma).
Southeastwards, this age may apply to reflector Top B
past seamount D9 (Fig. 2), on which volcanic sediments
are Altonian-Clifdenian (Pl-Sc) (SN4–SN5, 19.0–
15.1 Ma), all the way to seamount D12 on the southeastern
Plateau, on which volcaniclastic sandstones are of similar
age (Table 1). East of D12, an appreciably younger age of
Fig. 12 [SF0202-4] Detail of
an interpreted flower structure
on the southwestern side of the
Slab. Lack of a positive free-air
gravity anomaly suggests that
the shallow chaotic Unit D
(allochthon/parautochthon)
under with the Slab is non-
igneous and non-metamorphic
Fig. 13 [SF9901-4] Detail of the sedimentary relationship of a Poor Knights seamount chain (PKS) volcano and the inner plateau basin (IPB),
and late stage compression that locally affected the basin
Mar Geophys Res (2009) 30:21–60 43
123
14.7 ±1.0 Ma (Ar–Ar) (Mortimer et al. 2007) and 14.8–
12.7 Ma (foram zones N10–N11) was obtained for a small
volcano D14 not far from the Colville Ridge.
Based mainly on dredge samples, Unit B is generally
dated as earliest Miocene to late Early Miocene age (25 to
approximately 17 Ma, Waitakian-Altonian; Fig. 5).
Unit AB
This unit is a largely a passive regional basin fill, but also
includes foreset deposits (Figs. 9,10,11,12,13). It is less
extensive than Unit A, and is locally gently deformed. It is
commonly of relatively low reflector amplitude and most
easily distinguished from Unit A where deformation or
slope depositional processes have created an unconformity,
causing Unit A to onlap Unit AB. It is otherwise con-
formable with Unit A, and the bounding reflector may be
indistinguishable. Unit AB may be conformable or onlap
on Unit B, and unconformable (including onlap) on Units
C, D and E. Deformation is in the form of open folds,
reverse and normal faults, and penetration by small diapirs.
Rare, high-amplitude reflectors in Unit AB may be rela-
tively young volcaniclastic sediments.
A somewhat younger suite of rocks than Unit B, with
ages clustering mainly in the late Early to early Middle
Miocene range, was obtained from this mildly deformed to
draping unit and from some high places not crossed by
seismic profiles. These rocks are mainly limestones. They
include shallow-water (photic zone) bryozoan and algal
coquina (the Slab D16, Foraminifer zone N7, ca. 17.4–
16.5 Ma), limestone conglomerates and calcareous sand-
stones cementing underlying metamorphic rocks or volca-
nic rocks (Cavalli Seamount D1, D22, and Cavalli Ridge
D26B), inner-shelf bioclastic limestones (Cavalli Ridge
D26B), and mid-shelf to upper slope foraminiferal chalky
limestones virtually devoid of terrigenous input (D22 and
the Thrust D17B). The last example (D17B) might be
either an upper layer of the exposed section in the Thrust or
a lithified pelagic coating. Together these rocks record a
submarine terrain of isolated or semi-isolated banks of
varied depths, with a much reduced volcanogenic input.
With the exception of D1 on the summit of eastern Cavalli
Seamount, the rocks are now in lower bathyal depths,
indicating that the region as a whole subsided, but blocks
subsided differentially.
Core dates for Unit AB are late Early Miocene to early
Middle Miocene [N7–N9, 17.3–14.8 Ma, late Altonian-
Clifdenian (Pl-Sc); Fig. 5]. Dates possibly extending this
range down to N6 (18.8 Ma) and up to N12 (12.1 Ma) are
from two samples dredged on Cavalli Ridge but not on a
seismic line. The older sample (D26B-6i) has a poor fauna
and could be from Unit B. The younger sample (D26B-1)
may be from the upper part of Unit AB or could include a
shelf equivalent of Unit A. There is no biostratigraphic
control for the boundary between Units AB and A.
Unit A
Unit A is a passive sedimentary basin fill and regional
sediment blanket sequence with mainly parallel, medium
amplitude turbidite reflectors and mounded, low amplitude
contourite facies (Figs. 9,10,11,12,13). It is both con-
formable and unconformable on older Unit AB, and
unconformable on Units B, C, D and E. It onlaps structural
and volcanic highs. Deformation is limited to dewatering
structures. No dredge samples of Unit A were taken. By
elimination its age should be generally mid Middle Mio-
cene to Recent (15–0 Ma).
Geophysical interpretation
The continental shelf and upper slope
The continental shelf and upper slope are underlain by
many faults (Figs. 6,7,8). NW-trending faults of the
Vening Meinesz Fracture Zone continue from the Norfolk
Basin, where they form high fault scarps and basins, along
the northwestern shelf offshore the Aupouri Peninsula,
where they define long, narrow, deep sedimentary basins
(Thrasher 1988; Brook and Thrasher 1991; Herzer and
Mascle 1996), to *150 km southeast of the Cavalli Saddle.
Beyond that, seismic reflection coverage is sparse, but
gravity trends suggest that the fault system changes strike
and swings southwards (Fig. 3). Off the Hauraki Gulf,
where seismic coverage is slightly better, the shelf is
composed of acoustic basement highs and fault-bounded
basins, which trend north and northeastwards as well as
northwestwards (Thrasher 1986).
Northwest of the line though Cavalli Saddle (Fig. 3)
much of the shelf is underlain by the Allochthon (Seismic
Unit D and some Unit E) (Figs. 6,7), described by Brook
and Thrasher (1991), Herzer and Mascle (1996) and Isaac
et al. (1994). Decollement zones, magnetic, acoustically
opaque, igneous bodies, and deep, asymmetrical sedimen-
tary basins with syntectonic infill of Unit B (S1) are seen
within it in seismic profiles. Faulting is locally intense, the
faults on the outer shelf appearing to be deep crustal
structures diverging upwards through a complex sedimen-
tary and igneous(?) sequence in what might be flower
structures. Decollements beneath the Allochthon on the
inner shelf trend towards terrestrial outcrops of basement
rocks (Unit E), probably of the nearby Houhora Complex.
Thin-skinned faulting above the decollements bounds
asymmetric sedimentary basins with listric footwalls, filled
with sediments of Unit B (S1) probably comprising the
44 Mar Geophys Res (2009) 30:21–60
123
Lower Miocene Parengarenga Group. The igneous bodies
could be either Northland Arc volcanoes or Tangihua
massifs.
The upper continental slope northwest of the Cavalli
Saddle (i.e. above the Whangaroa Basin) is underlain by
seaward-dipping reflectors of seismic Units A and AB,
beneath which lie Units B, D and E. Allochthon and
basement (Units D and E) are down-stepped in places by a
major fault at the shelf edge (MO72-140, 142 and SF0202-
6; Figs. 6,7). The step is filled with wedges of syntec-
tonically deposited Unit B (showing basin asymmetry with
depocentre shifts), passive or folded and antithetically
faulted Unit AB, and passive Unit A to form the conti-
nental slope (Fig. 10). Where not down-thrown at the shelf
edge, the Allochthon (Unit D) forms a ramp down to the
Northland Plateau from a severely faulted structural high
under the continental shelf adjacent to the basement high of
the Aupouri Peninsula (Profile MO72-141/SF9901-8;
Fig. 6) (Isaac et al. 1994). We interpret this shelf margin
fault system to be part of the VMFZ. Together the tectonic
and depositional dips and the strike of the fault define a
linear shelf edge and slope from 171.7°to 173.3°E (Fig. 1).
There is a small amount of anticlinal bending of Units D
and A.
Where the shelf and upper continental slope step sea-
wards at the Cavalli Saddle, there is a shallow acoustic
basement that includes rare coherent reflectors (Unit B?)
and at least one volcano (Cv) (Mortimer et al. 2007; Profile
MO72-139; Fig. 7).
Southeast of the line through Cavalli Saddle, extending
as far as the Colville Ridge, the upper continental slope
(above the Knights Basin) is thinly mantled by seismic
Unit A, draped over and around a shallow, faulted, locally
outcropping, acoustic basement (Figs. 7,8). Lenses of
undeformed, probable Unit AB are present in fault angles.
These translate into deep, sediment-filled basins under the
continental shelf. Both the top and base of the slope
coincide with faults with significant downthrow. The
gravity trends (Fig. 3) and seismic data indicate that
northerly and northeasterly striking fault sets are present as
well as the northwesterly fault structure, giving the slope
its crenelated morphology (Fig. 1). No allochthon-related
decollement surfaces have been discerned in the southeast.
Some of the faulting on the southeastern shelf (MO72-138
in Fig 7) could be as young as Plio-Pleistocene.
The composition of the acoustic basement is known
from only a few samples. It is likely that the Allochthon or
remnants of it are present. Thrasher (1986) inferred from
magnetic data that Waipapa Group and Miocene volcanic
rocks underlie the southeastern shelf, and noted that the
volcanic rocks mainly encircle volcanic islands and the
Coromandel Peninsula. Volcanic sandstones and basaltic to
rhyolitic boulder/cobble conglomerates were dredged from
the upper continental slope (D11) on a faulted supra-
basement volcano (Unit Cv) (Fig. 8).
The inner plateau basins and their basement
Both Whangaroa and Knights Basins contain a passive fill
of turbidite-type sediments (seismic Unit A) (Figs. 6,7,8).
The fill is channelled and scoured near areas of seafloor
relief—the upper continental slope, the mouths of sub-
marine canyons and gaps between highs in the Poor
Knights seamount chain (Mitchell and Eade 1990a).
Beneath Unit A, deformation in Units AB–E varies from
practically nil, through broad open folding, tilting, normal
and reverse faulting, low angle thrusting and small-scale
diapirism to complete loss of seismically resolvable
structure (Figs. 9,10,11,12,13). Mesoscopic deformation
in rocks from the lower units (B–E) ranges from brittle, low
temperature deformation (tension gashes and calcite veins)
in Unit B, to high temperature, ductile deformation and
migmatisation (schist and granite gneiss) in Unit Ec
(Mortimer et al. 2003,2008).
Major horsts may form seafloor prominences (Figs. 6,7,
8), including Cavalli Ridge and Cavalli Seamount, the Slab
and small knolls on the southern end of the Three Kings
Ridge. Units A and AB thin and pinch out across them. The
high amplitude reflector Unit B appears to pinch out on
some horsts and actually be part of other ones. Cenozoic
volcanoes (Unit Cv) in the basin are distinguishable by
their subsurface and seabed morphology, corroborated by
magnetic anomalies.
Units AB, B and D are displaced locally by reverse
faults and overthrusts with southwesterly or northeasterly
apparent vergences. These compressional-strain features do
not appear to extend far along strike, and, like the larger
horsts, may produce bathymetric relief.
Southern three Kings Ridge and Whangaroa Basin
Seismically chaotic and amorphous facies underlie almost
the whole of the western Whangaroa Basin and southern-
most Three Kings Ridge, often effectively forming an
acoustic basement. Most of the facies is interpreted as
allochthon and parautochthon (Unit D).
The northwestern part of Whangaroa Basin provides the
best window into the early stratigraphy of the Northland
Plateau and its structure. Three seismic dip profiles and
three seismic strike profiles of different vintages cross this
region (Fig. 2). Where the IPB crosses the southern end of
the Three Kings Ridge, Units A and AB thin radically,
branch around an outlier formed by the Thrust and the
Slab, and pinch out, which puts the lower units of the
Plateau within reach of the dredge, and a complex array of
faults within range of the shallow seismic system (Fig. 6).
Mar Geophys Res (2009) 30:21–60 45
123
Under the southwestern branch of the Whangaroa Basin,
between the upper continental slope and the outlier, there is
widespread faulting with mainly normal apparent throws
(Figs. 6,10). Block rotation of Unit D is common, and Unit
B appears to be deposited syntectonically, which gives the
impression of an extensional margin. Near the base of the
upper continental slope (Fig. 10) is a large outcropping
fault block with a very high-amplitude top reflector and
very high gravity. We suggest that the block could be of
ultramafic basement as peridotites outcrop along strike at
North Cape and were dredged on The Knolls on Tuatara
Terrace.
The structure of the outlier is complex (Fig. 6). Both
extensional and compressional components of fault throw
are present, with deep and shallow growth faulting, pop-
ups, and shifts of depocentre affecting what we interpret as
Unit B. The Slab is underlain by faulted, acoustically
amorphous Unit D, which the low gravity suggests is of
low density, non-igneous allochthon or parautochthon. The
faulting is pervasive, with rotated blocks with normal
apparent throws to both NE and SW and apparent flower
structures (Fig. 12). Unit B lies in fault basins and is itself
faulted. The Thrust appears to be an inverted basin uplifted
in an overthrust with southwestward apparent vergence
(Profile SF0202-4 and 6; Fig. 11) exposing a high ampli-
tude bedded unit identified as Unit B. The arched over-
thrust is cut by faults of normal apparent throw (possibly
extrados). A complex graben, which itself contains appar-
ent inversion structures, separates the nose of the Thrust
from compressively deformed strata in the northern part of
the Slab.
The juxtaposition of extensional and compressional-
strain structures, positive and negative relief, and inver-
sions of the same across a geologically short distance are
consistent with strike-slip fault systems. This combination
could represent a wide transtensive and transpressive zone
in which the southwestern branch of the Whangaroa Basin
is a transtensive or margin-parallel strike-slip pull-apart.
However, the extensional and compressional strain could
also be due to separate phases of deformation.
North of the Thrust, the deformation diminishes, ending
finally at the volcanic outer plateau (Unit Cp), which is
identified by its jagged acoustic basement bathymetry
(Fig. 11). In this transition zone the magnetic anomaly
changes from strongly negative to strongly positive, the
van der Linden Lineament dipole zone.
On the southernmost (non-magnetic) part of the Three
Kings Ridge (Profile MO72-142; Fig. 6), a high-amplitude,
gently drape-folded, bedded reflector series, interpreted as
Unit B, outcrops. It overlies a chaotic facies (Unit D) and
passes laterally into seismically amorphous volcanic bodies
(Unit C). These units extend westward under a perched
sedimentary basin containing Unit A on the Weta Terrace
and outcrop in a scarp facing the Norfolk Basin.
In the central part of Whangaroa Basin (Profile MO72-
141/SF9901-8; Fig. 6), up to 2.2 s TWT (c. 2.2 km) of
almost undeformed sediment with smooth even turbidite-
type reflectors (Units A and AB) lie in onlapping contact
on a seaward-sloping surface of the Allochthon (Unit D),
which is locally veneered by up to 200 ms (c. 200 m) of
undeformed, high amplitude possible Unit B. Units A and
AB are not always distinguishable from one another in the
central Whangaroa Basin, although rootless dewatering
faults are more commonly visible in the parallel reflectors
of Unit A. The combined Unit A/AB pinches out on the
Allochthon where the latter is exposed on the continental
slope. They also onlap the flank of a peak (Unit Cv) of the
Poor Knights (PKS) chain, which itself appears to rest on
the Allochthon. The relationship between this peak and the
Allochthon (Unit D) could be either depositional or a
gliding nappe, as there is no deformation.
Cavalli Saddle
At the Cavalli Saddle, deformation and uplift have brought
deeper stratigraphic units to the surface. The dominant
structural features are the main Seamount with its twin
(eastern and western) peaks, Cavalli Ridge, and an inter-
vening peak—South Cavalli Seamount. The main Cavalli
Seamount, 1,100 m high, flat topped, and composed of
schist and granite gneiss of low magnetic intensity, occu-
pies a position midway between the volcanic outer plateau
and the continental shelf. An array of four seismic lines in
the form of a cross superimposed on a diamond was shot
around and through this area (Fig. 2). Unit A pinches out
against all these bathymetric highs, and is severely restric-
ted through the saddle, thinning radically and pinching out
on outcropping outliers. Channels and contourites are
common in Unit A around the highs, giving it a pseudo-
deformed aspect. All four older seismic units are present.
The western side of the Cavalli Saddle is a horst with a
flattish eroded top cut into lenticular bodies of Units B and
Cv. These bodies downlap onto each other and onto an
acoustically amorphous facies. They are interpreted as
debris fans shed from Cavalli Seamount and formerly high
areas of the Cavalli Saddle. The eastern part of the saddle is
more intensely deformed, with relatively steeply tilted
blocks of Unit B exposed in relief at the seabed on Cavalli
Ridge and South Cavalli Seamount. Faulted volcanoes
(Unit Cv) with rugged surfaces are present in the subsur-
face and piercing the sea floor (Profiles MO-139, SF0202-
8; Figs. 7,9). The flanks of the volcanoes pass laterally into
Unit B in Knights Basin.
On the south and west sides of Cavalli Seamount
(Fig. 9), the deformed and apron units (D/B), which lie in
46 Mar Geophys Res (2009) 30:21–60
123
and west of the horst, are down-faulted into a graben,
forming a moat. The graben is largely passively infilled by
Unit AB. On the north and east side of the seamount,
deformed units (D/B) are upturned against its sides, Unit D
showing evidence of thin-skinned listric faulting on Unit E.
These units pass laterally into the typical chaotic and
amorphous seismic facies that includes Units D and Cv in
Knights Basin, and Unit D to the north. The change north
of Cavalli Seamount from allochthon to the volcanic sub-
strate (Cp) of the volcanic outer plateau is not identifiable.
Knights Basin
In Knights Basin, smooth, even, turbidite-type sedimentary
reflectors may reach more than 2.2 s (c. 2.2 km) thickness.
They are especially thick at the western and eastern ends of
the basin, which appear to have escaped unconformity-
producing uplift events since the deposition and faulting of
volcanic Unit Cv and Unit B (Figs. 7,8). Deformation of
Unit A in these areas is limited to small rootless faults and
associated buried infills (pock marks?) that are typical of
dewatering. In the easternmost part of the basin Units B
and D are just visible at the limit of seismic penetration
(2.2 s TWT), where their structure cannot be resolved,
beneath thick, undeformed sediments.
Seismically amorphous volcanic and structural highs
occur in the basin and, as previously mentioned, on the
adjacent upper continental slope. These coincide more or
less with the line of magnetic highs at the foot of the slope
and appear to be buried volcanoes of Unit Cv. They
apparently arise within Unit B, or upon Unit D or E which
may be faulted. The volcanoes have jagged or flat tops and
are themselves commonly offset by faults, both faulted
against and laterally gradational into Unit B.
Along the northern side of the basin the flanks of several
volcanoes of the Poor Knights chain (Unit Cv) sweep down
into the basin, merging with Unit B. The flanks may overlie
a faulted seismic basement, or be themselves faulted, but
faulting does not seem to have broken up these volcanic
edifices in the way that it has for those in the basin and
slope (Figs. 7,13).
Parts of central and eastern Knights Basin appear to
have undergone late and localised deformation. In Fig. 13
Units A and AB onlap both the continental slope and a
seamount of the Poor Knights chain. Unit A in turn onlaps
Unit AB, which, along with B and an underlying unit (D or
E), has been rucked up into anticlines and blind thrusts
with an apparent vergence towards the northeast. However,
these structures are of very limited lateral extent along the
basin axis as there are no traces on seismic or bathymetric
lines nearby to the NW or SE. This could mean that the
structure more likely strikes across the basin, with an
easterly or northerly vergence.
Evidence of shallow water and subsidence
Post-Early Miocene subsidence of the upper terrace (Weta)
west of the Three Kings Ridge from near sea level to
2,500 m was reported by Herzer et al. (1997, Dredge RE1;
Fig. 2). Photic-zone limestones from the 1,400 m deep
Slab, capping the extensional terrain of northwestern
Whangaroa Basin (D16; Fig. 6) are dated as late Early
Miocene. In the Cavalli Saddle, the horst containing Lower
Miocene Unit B, which was planed off and veneered by
Unit AB or A, now lies at 1,500 m below sea level. There
is also the flat top of Cavalli Seamount itself at 500 m
water depth. Other profiles show faulted flat tops now in
deep water and buried by younger units, and several dredge
sites contain shallow water fossils (see above and Table 1).
Dredge hauls from the Thrust (D17), the Slab (D16) and
three seamounts (D9, D12 and P70) contained breccias and
conglomerates (only scattered pebbles in the case of D16)
representing Lower Miocene Units B and AB. Clasts
include well rounded pebbles and cobbles of greywacke,
basalt and dolerite, and detrital garnet and biotite (Morti-
mer et al. 2007). As in the case of the eastern margin of the
Norfolk Basin (upper Three Kings terrace), where polished
shoshonite pebbles have been dredged (Mortimer et al.
1998), many parts of the inner half of the Northland Pla-
teau underwent marine planation in the Early Miocene and
have since subsided to more than 2,000 m water depth.
The volcanic outer plateau
The volcanic outer plateau consists of a rugged seismic
facies (Unit Cp), which is at least 2 s TWT (c. 2 km) thick,
with a generally very uneven top and local relief of 0.1–1 s
(not counting the large seamounts) incompletely buried by a
thin (\1 s TWT; \1 km) sediment blanket (Figs. 6,7,8).
The base of Cp is not seen, and sparse internal reflectors are
discontinuous and variably dipping, suggesting volcanic
sources but without identifiable large edifices. The overly-
ing sediments are divided into an upper, rather transparent
unit, and a generally thinner, relatively high-amplitude
lower unit. The upper unit is variably horizontal or draped,
with local channel-and-levee facies, and is probably of
mixed turbidite/hemipelagic origin, a likely lateral equiva-
lent of Units A and AB which cannot be differentiated on
the volcanic outer plateau. The lower unit is lenticular and
more discontinuous, commonly with a mounded and valley-
fill facies, and intimately associated with seismically opa-
que, triangular mounds interpreted as small volcanoes that
are part of the seismic basement (Cp). The lower unit is
interpreted as the lateral equivalent of Unit B, and like Unit
B in the basin, it is locally tilted and faulted.
The inner margin of the volcanic plateau is dominated by
the seamounts of the linear Poor Knights chain (Fig. 2). The
Mar Geophys Res (2009) 30:21–60 47
123
gravity anomaly map suggests there may be *14 of these
seamounts, a few of which have large circular or elliptical
anomalies, but the rest of which have irregular shapes. In
detail, their morphology is virtually unknown. The most
detailed bathymetric map (Mitchell and Eade 1990a) shows
three of them. These have broad, very irregular shapes and
some straight sides, suggesting multiple-vent volcanic
centres influenced by faults. No flat tops have been found.
The seismic lines show that sloping, sub-parallel, shal-
low reflectors, locally visible within the flanks of the Poor
Knights seamounts, are interstratified with each other, with
the deeper sedimentary sequence of the Knights Basin, and
with the rugged seismic facies of the volcanic massif.
Profile SF9901-3 shot along the crest of the southeastern
half of the chain (Fig. 2) showed no sequential onlaps and
downlaps that might have indicated a progressive strati-
graphic age difference from seamount to seamount. The
radiometric and palaeontological ages are too sparse to
effectively test for NW–SE diachronism, though young
Ar–Ar ages were obtained from Dredges D14 and D25 near
the Colville Ridge (Mortimer et al. 2007).
Faulting with a normal component of offset and unde-
termined strike is evident but rare in the volcanic outer
plateau. It affects Units Cp and B over areas as wide as
20 km, but not the Unit A sediment cover. This suggests
tectonic extension during or immediately after Plateau
volcanism, or possibly but less likely, caldera collapses.
The northern spur of the Plateau, which projects into the
SFB (Fig. 2) and may share some magnetic (and con-
structional volcanic?) affinity with it, comprises two mas-
sifs with high, rugged areas free of sedimentary Unit A. It
has a volcanic seismic facies similar to the rest of the
volcanic plateau, but with few internal reflectors, and thus
possibly proportionally more lava. On existing evidence
(Mortimer et al. 2007) the composition of the plateau
seismic facies (Unit Cp) like the seamounts (Unit Cv)
seems to comprise Lower Miocene, subduction-related la-
vas and volcanic breccias.
In three of the four seismic profiles across the northern
boundary of the volcanic outer plateau there is no obvious
structural break between the Plateau and the SFB floor
(Figs. 6,7,8). On these profiles (SF9901-8, 4/14/15 and
18) the Plateau volcanic facies (Cp) descends in an uneven
slope to the SFB floor where it appears to merge with rather
flat Layer 2 of the oceanic crust beneath 1–2 s TWT (c. 1–
2 km) of sediment of turbidite reflection character. Layer 2
appears as up to 0.5 s of high amplitude discontinuous
reflectors of probable intercalated lavas and sediments
overlying an indistinct basement reflector, between 6.2 and
5.8 s TWT below sea level. Unit B merges with the deepest
sedimentary reflectors on the oceanic crust of the SFB. In
Profile SF9901-4/14/15 (Fig. 8) faulting affects Layer 2
and possibly the slope break but its origin is unknown. The
overall aspect of the boundary between the Plateau and the
basin is passive and there is no evidence for a fossil trench
and subduction complex.
On Profile SF9901-5/6 (Fig. 8), a seamount (Dredge D4)
straddling the boundary has volcanic apron reflectors (Unit
Cv), which sweep down onto the oceanic crust and into the
basal sedimentary layers of the SFB on one side, and into
the Unit B reflectors within the volcanic plateau facies on
the other (Herzer et al. 2000). This seamount was therefore
dredged extensively for its important stratigraphic value, as
the relative ages of the volcanic outer plateau and the SSFB
could be tested via this key volcano. It is located near an
oceanic magnetic anomaly identified as 8 (26.6 Ma) by
Malahoff et al. (1982), and 11 (29.8 Ma) by Sdrolias et al.
(2003). Andesites dredged from the flanks of the volcano,
which perforce represent some of the youngest erupted
material on the edifice, have 22 and 17.9 Ma Ar–Ar ages
(Mortimer et al. 2007). These ages do not contradict the
Oligocene ages predicted for the SSFB crust from mag-
netics, but could be pointing to a younger age for it. Neither
do they preclude the possibility of Oligocene oceanic crust
deep under the Plateau.
East and west margins of the SFB
The structure of the SFB margins is largely obscured by
volcanoes but rift structures are evident in places on both
margins. On the eastern margin (unpublished data), seismic
profiles typically show a sediment-covered volcanic base-
ment descending from the crest of the Colville Ridge and
merging with the SFB crust. North of 28°S, where the
Colville Ridge becomes the Lau Ridge, the rift margin is
evident in the form of the Lau Terrace.
On the western margin seismic profiles show three
volcano-tectonic domains flanking the eastern Three Kings
Ridge (unpublished data). In the north, a complex volcanic
region ends at a scarp (the Julia Lineament), which has
been interpreted as either a fracture zone (Davey 1982)ora
spreading centre (Sdrolias et al. 2003). In the centre, the
Sarah Seamounts, dated from 21.8 to 19.9 Ma (Mortimer
et al. 2007), rise from the basin floor and the flank of the
ridge. In the south, the Huia Terraces, from which andesite
lavas Ar–Ar dated at 31.7 and 21.1 Ma were dredged
(Mortimer et al. 2007), are formed by basement fault
blocks with normal apparent throws (Fig. 6), which des-
cend to the oceanic crust of the SFB floor. There is no
evidence of a trench. The younger date was from a rugged
peak, probably a superimposed volcano, but the older date,
the only pre-Miocene lava found so far in the SSFB region,
was from the basement of the lower terrace, interpreted as
the southeastern rift margin of an ancestral Oligocene
Three Kings Ridge. The conjugate margin would have been
the Colville-Lau Ridge.
48 Mar Geophys Res (2009) 30:21–60
123
Lower Miocene backarc basin basalt from within the
Cook Fracture Zone (23 Ma) (Bernardel et al. 2002), from
the crust north of the Cook Fracture Zone (19 Ma), from the
Julia Lineament (22 Ma), and from Deep Sea Drilling
Project (DSDP) sites 205 and 285 (26 and 22 Ma) (Morti-
mer et al. 2007) are evidence that the SFB continued to
spread in the Early Miocene along with the Norfolk Basin,
as proposed by Mortimer and Herzer (2000) and Herzer
et al. (2001). However, comparatively little is known of the
southern South Fiji Basin (SSFB). In the SSFB, the higher
free air gravity anomaly in the east than in the west (Fig. 3),
is not reflected in the bathymetry, which is smoothed by the
presence of [1 s TWT ([1,000 m) of sediment and shows
the greatest depths in the centre. The anomaly could indi-
cate that the crust is younger in the east as suggested by
Sdrolias et al. (2003) and Mortimer et al. (2007).
Gravity/magnetic models
In our gravity models across the Plateau, oceanic crust is
assumed to consist of a basaltic upper crust (2.7 Mg/m
3
)
underlain by gabbro and metagabbro (3.0 Mg/m
3
), and
continental crust is assumed to comprise granite and gneiss
(2.7 Mg/m
3
) overlying amphibolite and granulite (3.0 Mg/m
3
)
(Meissner 1986). The models assume sediment densities of
2.1 and 2.5 Mg/m
3
, an upper crustal density of 2.7 Mg/m
3
,
a lower crustal density of 3.0 Mg/m
3
, and a mantle density
of 3.4 Mg/m
3
. As there are few constraints on the models,
alternative distributions of these crustal components
(changing the relative thicknesses of the upper and lower
crust) are possible. A constant regional anomaly was sub-
tracted from the gravity and magnetic data prior to mod-
elling. Magnetic anomaly was calculated by subtracting the
IGRF field (Maus et al. 2005).
Model FB7305 (Fig. 14) is typical of several gravity/
magnetic models constructed that traversed from the east-
ern Northland Plateau up onto the Northland continental
shelf. Although there are no seismic data or marine gravity
measurements for model FB7305 the gravity anomaly
interpolated from the satellite gravity grid of Sandwell and
Smith (1997) was used. The sedimentary thickness and
upper surface of magnetic bodies are consistent with sim-
ilar potential field models (not shown) on Profiles SF9901-
8 and SF9901-5/6 where seismic reflection data was
available. Gravity models are broadly constrained to match
observed c. 25 km crustal thickness onshore (Stern et al.
2006) and inferred oceanic crust of the SFB.
Several features are common to all models:
a. The modelled crust thickens from ca. 8–10 km (oce-
anic crust) to ca. 12–16 km crust in the Northland
Plateau region to ca. 21 km at the continental shelf
break.
b. Slight crustal thinning (1–2 km) occurs beneath the
Whangaroa and Knights Basin.
40 km
3.0
2.5
1.0
3.4
2.7
2.7
2.7 0.1
0.1
2.5
2.5
N
SLine FB7305
2.1
Modelled
Modelled
Observed
Observed
0.1
2.7
ci
tengaM
ylamonA
(nT)
ylamonAytivarG
)gk/
Nu
(
)
m
k
(h
tp
eD
600
400
400
200
200
5
10
15
20
25
-200
0
Mantle
Continental crust
Lower crust
Oceanic
VLL
Fig. 14 2-D Gravity/magnetic model across the Northland Plateau.
2D modelling was performed using ENCOM Modelvision software.
Red and yellow =sedimentary layers; blue =basaltic bodies. Square
labels =density (10
-3
Kg/m
3
), circular labels =magnetic suscep-
tibility (SI). See Fig. 2for line location
Mar Geophys Res (2009) 30:21–60 49
123
c. All the magnetic anomalies can be modelled by
plausible magnetically induced bodies. The volcanic
outer plateau can be modelled by a ca. 4–6 km thick
body of 0.1 susceptibility (c. 4.5 A/m magnetisation).
The dipole transition to a negative magnetic anomaly
across the van der Linden Lineament is best modelled
by a 3–5 km downward offset over a c. 20 km distance
of the upper surface of the above body to the southwest
of the van der Linden Lineament.
d. The central and inner Whangaroa and Knights Basins
can be fit by a similarly magnetised, but thinner (c. 1–
3 km) body which shallows and thins towards the shelf
seafloor from c. 3 km beneath the basin centres.
Although the body is likely to include a component of
Miocene volcanics, correlation with the Mobil seismic
reflection data (MO profiles; Figs. 6,7) suggests some
of this body may correspond to Northland Allochthon
ophiolite material.
A magnetisation value of 4.5 A/m is high for basaltic
crust (Bleil and Petersen 1983; Tivey 1996). Higher values
(\25 A/m) are possible for very young (\1 Ma) crust.
However such a young age was considered unlikely. Sig-
nificantly lower values would have required unrealistically
thick magnetic bodies. Such magnetisation is also charac-
teristic of ultramafic rocks. Although ultramafic rocks are
present in the onshore obducted ophiolite complexes, they
are a comparatively small component of them. There might
be ultramafic bodies offshore, for instance the high-density
fault block in seismic Profile SF0202-6, which is one of a
field of knolls at the base of the slope in westernmost
Whangaroa Basin (south end of the Three Kings Ridge)
(Mitchell and Eade 1990b). Could these knolls be ultra-
mafic bodies such as those dredged on The Knolls in the
Norfolk Basin or granitoid bodies such as Cavalli
Seamount? They were not found elsewhere in the IPB,
where the gravity models were constructed, so no shallow,
high-density bodies were put into the gravity models. The
magnetic bodies correlate well with a volcanic basement
interpreted from seismic sections, although the location of
the base of the sedimentary layer had to be interpolated
under the sedimentary basins.
Discussion
Composition of the Northland Plateau
The volcanic outer plateau has a substantially Early Mio-
cene arc-related history, but the Huia Terraces suggest
some continuity with, or superposition on, an older Three
Kings Arc, itself overprinted by Early Miocene volcanism.
Additionally, the possible continuity of SFB spreading
anomalies beneath the outer plateau, and lack of an obvious
structural boundary between the two, suggests that the
volcanic outer plateau might have an igneous basement
with SFB affinities, which has eluded the small amount of
dredging so far. Magnetic models are consistent with a
substantial amount of positively magnetised mafic rock
beneath it. The relief of the Early Miocene outer plateau
was apparently not great enough to be near sea level
(possibly excepting seamounts P70 and D9), and there is
not much visible internal structure beneath Lower Miocene
to Recent draped sediments.
The inner plateau, including the upper continental slope,
is profoundly different. This region has been modelled by a
gently inclined, relatively thin slab of material of basaltic
magnetic susceptibility and resulting induced magnetisa-
tion. The magnetic anomaly could have been equally well
modelled by including bodies with reversed remanent
magnetisation—e.g. for some of the Northland Allochthon
material. A large component of the negative anomaly
within the Whangaroa and Knights Basins results from the
dipole effect of the vertical offset of magnetic bodies
southwest of the van der Linden Lineament. Anomalies
associated with the Northland ophiolites and the Northland
Arc are commonly positive (with significant exceptions),
while Houhora Complex (Mt. Camel) anomalies are weak
(Davey 1974). Waipapa greywackes are non-magnetic to
weakly negative. The magnetic anomalies of the inner
plateau, including negative anomalies and the belt of
weakly positive anomalies at the foot of the slope, are
probably sourced in magnetised parts of the Northland
ophiolite (allochthonous and parautochthonous Tangihua
basalts), Miocene arc volcanic bodies and basement Mt.
Camel and Waipapa Terranes.
The inner plateau and upper slope reveal a complexity,
derived from the strike-slip zone and perhaps post-obduc-
tion extension, which unfortunately partly overprints the
earlier structure. Tilted flat tops on acoustic basement fault
blocks suggest that significant areas of the inner plateau
and slope might have been above sea level and planed off
during, and possibly prior to, the Early Miocene. Another
possibility is that the inner plateau had an initially flat
basaltic sea floor. Faulting, differential uplift and subsi-
dence were common in the Early Miocene. This tectonism
led to almost all the features we see today—the Whangaroa
and Knights sedimentary basins, and the high standing
continental shelf and Cavalli Seamount. However, the van
der Linden Lineament appears to have no structural
expression in the Early Miocene and younger geology,
implying that it either predates the VMFZ, or is buried by
or simply caused by volcanic rocks. Large areas of the
inner plateau nevertheless remain floored by the chaotic
facies that is most likely the Allochthon.
50 Mar Geophys Res (2009) 30:21–60
123
An emergent or shallow inner plateau helps to account
for the presence of the otherwise unexplained detrital
conglomerates, pebbles and grains found on the Slab, the
Thrust and among the Poor Knights seamounts of the outer
plateau. These rocks would have been derived from the
continent and the inner plateau when the latter was high
enough to be eroded and/or allow sediment to pass from the
continent to the south. Since experiencing Early to Middle
Miocene subsidence, the IPB has acted as a sediment trap
between the continent and the volcanic outer plateau.
Regional correlation and Miocene deformation
The depositional history and timing of tectonic and vol-
canic events of the Northland Plateau are in good agree-
ment with those in the greater region (Fig. 5), despite the
contrast between the meagrely documented Paleogene and
better documented Neogene histories. The radiometric and
paleontological data from dredge stations, in the absence of
well data, provide moderately good control for the seismic
stratigraphy and events.
The 32 Ma pre-Miocene andesite on the lower Huia
Terrace substantially pre-dates the emplacement of the
Northland Allochthon and activity along the VMFZ, and
belongs to an early Three Kings Arc. If the andesite is
indeed from the faulted terrace edge, it limits the age of
rifting of the southernmost part of the SFB to some time
post-32 Ma. The andesite post-dates by 6 My the meta-
morphism ascribed to postulated arc collision in the
northern Norfolk Basin (Meffre et al. 2006), and by 5 My
the western Three Kings boninite (Fraser 2002), but dem-
onstrates that subduction was fuelling a normal andesitic
arc in the southern Three Kings Ridge area in the Early
Oligocene. Boninites typically occur in forearc settings so,
at face value, the Three Kings Ridge boninite suggests
inception of a west-facing Three Kings Ridge arc in the
Late Eocene, behind which the South Fiji back-arc basin
could have developed. However, the location of the boni-
nite is not an infallible criterion as, given the large amount
and widespread nature of Early Miocene rifting north of the
VMFZ (Mortimer et al. 2007; this paper), the axis of the
Eocene arc need not have been the same as that of the
Oligocene or Miocene arcs.
The first Neogene tectonic event in Northland was
obduction of the Allochthon, the body that we see widely
under the inner half of the Northland Plateau. The ages of
the dredged tectonised sediments on the Northland Plateau
[nannofossil zone NN1-foram zone N6, *24–17.3 Ma)
both overlap with and post-date the Northland Allochthon
emplacement (25–22 Ma, Waitakian (Lw)]; some fall
within the span of subsequent VMFZ activity, which
includes the dramatic exhumation of the high-grade
metamorphic rocks of Cavalli Seamount.
Coeval with the period of VMFZ activity was the vol-
canism of the Northland Arc. The ages of the volcaniclastic
sediments and lavas of Units B and Cv on the Plateau
correlate well with those of the Northland Arc. This cor-
relation even extends to the indication that the far eastern
part of the Plateau, adjacent to the Colville Ridge, contains
significantly younger volcanic rocks than the main body.
There is reasonable agreement between the Top B reflector
of the Northland Plateau and the N3–N6 reflectors that
mark the main top volcanic reflectors of the Northland
Basin (Isaac et al. 1994), and the near top Early Miocene
N* reflector of the Reinga Basin (Herzer et al. 1997;
Fig. 5). Top B does not correspond to a single time horizon
but a collection of unconformities near the top of the main
Lower Miocene volcanic and frequently deformed series,
which was dated by somewhat overlapping fossil assem-
blages in dredged rock suites. Top B is well enough con-
strained in age, nevertheless, to enable comparisons with
events in these other basins to be made. It confirms that the
whole region from the Northland Plateau to the Reinga
Ridge was simultaneously affected by post-Allochthon
tectonism. This event is reasonably ascribed to the move-
ment of the VMFZ as the Norfolk Basin opened from 23 to
15 Ma and the Three Kings Ridge moved southeastwards.
The timing of events defined by Unit AB is unfortu-
nately not so precise. Although the boundary with under-
lying Unit B is located by unconformities and timed to
within 1 My (Fig. 5), the upper boundary might be as old
as 14.8 Ma (foraminifer zone N9) or as young as 12 Ma
(foraminifer zone N12), perhaps even higher. The dredge
stations used to date Unit AB were not sited on seismic
lines, except for D16, but all were located on bathymetric
highs. What is significant is that the upper boundary of Unit
AB on the seismic profiles marks the last deformation
event on the Northland Plateau, i.e. the folding and reverse
faulting seen on Profile SF9901-4, and possibly the faulting
on Profile SF0202-6 that produced The Thrust. This means
that it could correlate with a Middle Miocene regional
event. Interestingly, Middle Miocene deformation was
reported on and near the VMFZ margin well to the NW
(Herzer et al. 1997), although its age is just as poorly
constrained as that on the Northland Plateau. Three Kings-
Northland region arc volcanism had died out at the end of
the Early Miocene (except near the Colville-Coromandel
area), but notable compression in the late Early Miocene
and Middle or Late Miocene deformed the southeastern
Reinga Basin and may have uplifted the impressive
Wanganella Ridge (Herzer et al. 1997). An explanation for
this tectonism was not offered by Herzer et al. (1997)
because the N2.5 reflector critical to its timing had only an
assumed top Middle Miocene age, based on its position
between top Early Miocene (N*) and near top Miocene
(N1.9) reflectors. Now, the evidence for coeval
Mar Geophys Res (2009) 30:21–60 51
123
compressional strain on the Northland Plateau lends cre-
dence to a regional tectonic phase in the Middle or Late
Miocene, involving a continuation or renewal of activity on
the VMFZ system, with a reversal or change of the regional
stress.
Regional kinematic models
Two possible end-member regional tectonic scenarios are
considered here. These provide a SW Pacific framework in
which we later consider more detailed tectonic develop-
ment of the Northland Plateau and environs.
Arc collision
In this model, the SSFB opened mainly in the Oligocene,
becoming fully open by 23 Ma. This scenario involves
arc collision and two subduction zones, in which a Loy-
alty-Three Kings-Northland Plateau intra-oceanic arc
collided with Zealandia as originally proposed by Craw-
ford et al. (2003) and elaborated by Schellart (2007) and
Whattam et al. (2008). In our model (Fig. 15;Frames1–4),
the approaching terrane would have been somewhat
analagous to the present day New Hebrides Trench-
Hunter Fracture Zone behind which the North Fiji Basin
is growing. The portion that approached Northland might
have had a leading edge involving both trench and leaky
transform. SFB back-arc material might be brought for-
ward by tectonic erosion of the advancing arc to a
favourable position for obduction onto Northland. In this
model the open or almost open SSFB and volcanic outer
plateau would have docked against the Northland-Reinga
Ridge margin, allowing Upper Oligocene ophiolites
(Whattam et al. 2005) to be obducted, while the
Fig. 15 Regional kinematic models for the South Fiji and Norfolk
basins. The arc collision model proposed here is a variant of an earlier
model by Crawford et al. (2003). The arc unzipping model is from
Mortimer et al. (2007), only two panels of which are shown here. The
Australian plate is fixed. Radiometic ages of MORB are from
Mortimer et al. (2007)
52 Mar Geophys Res (2009) 30:21–60
123
Cretaceous component of the Tangihua ophiolites (Nich-
olson et al. 2007) would be sourced from the remnant of
basaltic crust between the Northland Plateau Arc (the
volcanic outer plateau) and the New Zealand continent.
Both the Northland Plateau and the SSFB would then
have been translated southeastwards in the Early Miocene
when SFB spreading propagated into the Loyalty-Three
Kings Ridge, opening the Norfolk Basin (Frame 4). The
Early Miocene arc-type volcanism of the Northland Pla-
teau and Northland Arc would have been initiated by
opposing subduction systems, and erupted largely after
the intervening Pacific plate had been totally consumed.
Shoshonite volcanism on both sides of the Three Kings
Ridge (Mortimer et al. 1998,2007) would have been
caused by arc rifting, as the ridge retreated southeast-
wards (Crawford et al. 2003), or slab sinking after
obduction (Schellart 2007). The andesitic volcanism per-
sisting in the Northland Plateau and Northland Arcs for 6
My after their subduction zones met, would be fuelled by
post-collisional, extension-related magmatism from sub-
duction-modified lithosphere. This model provides an
obvious obduction interface supplied by the NE-dipping
subduction zone (a parallel origin with the New Caledonia
ophiolite), and ready sources for both the Cretaceous and
Oligocene ophiolites.
Arc unzipping
In this model, the SSFB opened mainly in the Early Mio-
cene with crust formed from 26 Ma onwards. Although this
scenario (Fig. 8 in Mortimer et al. 2007), could have begun
with collision of the Three Kings Ridge with the Norfolk
Ridge when the SSFB was in its infancy, it is, in its sim-
plest form, the unzipping of a Norfolk-Three Kings conti-
nental margin arc with a single WNW-dipping Pacific slab
subduction zone. Two frames of the model are shown here
(Fig. 15a, b). In this model, only Pacific crust was ever
adjacent to Northland and the Reinga Ridge, allowing
Cretaceous ophiolites to be obducted. The SSFB expanded
by seafloor spreading from 26 Ma through the Early
Miocene, adding to the volcanic outer plateau by leaky
transform volcanism, while at the same time the Northland
Plateau was carried southeastwards by strike-slip on the
VMFZ as the Norfolk Basin opened. The Early Miocene
arc volcanism in Northland and the Three Kings Ridge was
caused by Pacific subduction only, while shoshonite vol-
canism on both sides of the ridge was caused by rifting or a
deepening Pacific slab as the trench and Colville Ridge
retreated rapidly southeastwards from 22 to 18 Ma. This
model has the simplicity of a single subduction system
plunging beneath the continent, but the origin of the Oli-
gocene ophiolites and the supra-subduction chemistry are
hard to explain.
Like every model proposed so far for the northern New
Zealand margin, neither of the above is without problems
or is a definitive solution. The answer lies in the age of the
crust of the SSFB. Did the Allochthon event signal colli-
sion of the tail end of the Loyalty-Three Kings system and
a largely Oligocene SSFB with New Zealand or herald the
beginning of strike-slip motion on the VMFZ and rapid
opening of a largely Miocene SSFB?
Evolution of the Northland Plateau and continental
margin
The above SW Pacific tectonic models provide the two
most likely but radically different scenarios governing the
Miocene evolution of the northern New Zealand margin.
Our more detailed reconstructions of the Northland Plateau
area in the Miocene, accommodating either model, are
considered below.
Published models deal with the large-scale picture only
and do not distinguish the VMFZ and van der Linden
Lineament, which are important at the scale of the conti-
nental margin. The parallelism of these two linear features
suggests that they are related in a simple-shear geometry.
Indeed left-stepping strike-slip has been invoked to move
the Early Miocene volcanic outer plateau arc segment from
a position along strike from the onland Northland Arc
(adjacent to the Reinga Ridge) to a new position across
strike from the Northland Arc on the other side of the van
der Linden Lineament (Mortimer et al. 2007). This would
explain the similar ages and lithologies of the two volcanic
provinces. In detail, the regional geopotential anomaly
pattern shows that the van der Linden Lineament is not a
simple left-step segment of the VMFZ. The Norfolk Basin,
the Weta Terrace, the Tuatara Terrace and its Knolls
extend without interruption to the Reinga Ridge, ending at
the VMFZ (Fig. 3), and there is no obvious large relay
structure at the step. So the main southeasterly offset of the
Three Kings Ridge and the volcanic Northland Plateau
against the Zealandia margin occurs at the Reinga
escarpment of the VMFZ and its southeasterly projection
(VMFZ in Fig. 1), not the van der Linden Lineament. Our
new seismic data show that the van der Linden Lineament
is not distinguished by obvious Miocene faulting as is the
VMFZ. The VMFZ, then, was most likely the main fault
system along which the Three Kings Ridge was translated
290 km southeastwards in the Miocene. Both the North-
land Plateau and the SFB had to move with the Three
Kings Ridge, with the major shearing taking place in the
VMFZ between the Plateau and the continent. Even if the
volcanic outer plateau grew in tandem with seafloor
spreading in the SSFB at this time (Mortimer et al. 2007),
there is still the geometry of the IPB to consider. Although
nett displacement must have been taken up at the
Mar Geophys Res (2009) 30:21–60 53
123
Australian-Pacific plate boundary, which included the
rolling-back proto-Kermadec Trench and the developing
North Island fault system, the proto-inner plateau basin was
affected by the extension taking place in the Norfolk Basin.
Without significant shear on the VMFZ there would have
been huge crustal shortening in the Northland Plateau.
The space problem presented by the Northland Plateau
is fundamental to understanding how the margin evolved.
Although the initial geometry of the VMFZ is unknown, in
the final geometry, the left steps resemble restraining
bends. These steps are found from the end of the South
Maria Ridge (the southeastern segment of the Reinga
Ridge) to Cavalli Seamount (Fig. 1). The Cavalli Complex
is located opposite the change from the low-lying Aupouri
tombolo to the higher-standing Northland ‘‘mainland’’. If
we were to close the Norfolk Basin without too much
attention to detail, Cavalli Seamount would be restored to a
position at the western end of the flat-topped South Maria
Ridge. It is simple to imagine that, as the Northland Plateau
moved along the continental margin, uplift would occur in
a restraining bend environment in the South and North
Maria Ridges, the Aupouri Peninsula, the surrounding
continental shelf, the Cavalli Saddle complex and many
parts of the IPB basement. The uplift would be followed by
erosional planation and eventually submergence by iso-
static adjustment.
But it is not that simple. The scarps of the VMFZ trend
N125°–130°. If the Norfolk Basin were closed along this
trend, a hole 600 km long by 70–150 km wide would
remain along the margin between the Northland Plateau
and Reinga Ridge. Shortening this crust during Norfolk
Basin opening would raise a mountain range of alpine
proportions. Dredge samples from the South Maria Ridge
to the Cavalli Saddle, the geology of Aupouri Peninsula,
and our seismic data demonstrate that, with the known
exception of the crystalline rocks of Cavalli Seamount,
there was not enough uplift to completely remove the
Allochthon or Unit B, let alone widely expose high-grade
crystalline rocks; and the gravity indicates isostatic
equilibrium.
A close look at the gravity anomaly and bathymetry
trends reveals that much of the supposed space problem is
actually accounted for by extension, for which we see
ample evidence in the Northland Plateau and southern
Three Kings Ridge seismic data. The structures that give
rise to the tripartite northerly gravity lineaments west of the
Three Kings Ridge continue north of the Cook Fracture
Zone along the Loyalty Ridge (Sandwell and Smith 1997).
They are offset by the Cook Fracture Zone, and were thus
already formed before the main southeastwards opening of
the Norfolk Basin. They are extensional features (Bernar-
del et al. 2002) (Fig. 16). The N005°strike of these
Fig. 16 Swath and gravity-derived bathymetry of the northern
Norfolk Basin and Three Kings Ridge (Mauffret et al. 2001). The
older Cagou Trough–Three Kings Ridge structure is disrupted by the
younger Philip Trough rifting and South Fiji Basin–Cook Fracture
Zone spreading structures
54 Mar Geophys Res (2009) 30:21–60
123
lineaments along the Three Kings Ridge (Cagou Trough,
The Knolls, Weta and Tuatara Terraces) implies a N95°
orthogonal extensional strain regime. The Cook Fracture
Zone is a clearly defined transform fault that strikes N115°.
Seafloor spreading and rift structures (e.g. Philip Trough)
trend N25°–30°(orthogonal to the Cook Fracture Zone)
and disrupt the N005°structures (Fig. 16). From end to
end, the Reinga-Northland shelf edge also has an average
trend of N115°(parallel with the Cook Fracture Zone),
although the outline is ragged due to N125°–130°-trending
scarps and segments and N150°-trending splays (Herzer
and Mascle 1996). The consistent superposition of different
extensional structures thus indicates at least two stages of
motion: we propose that the vectors of movement of the
Three Kings Ridge-volcanic outer plateau-SSFB micro-
plate, relative to a fixed Australian plate, were initially east
(N95°), then approximately southeast (N115°).
The southern ends of the N005°-trending western Three
Kings rift trends curve slightly southeastwards in a sub-
parallel sense with the Huia Terraces and the Wanganella
Ridge. This curvature cannot be drag folding if the VMFZ
strike-slip motion was right lateral. The Norfolk Basin
rifting could have exploited pre-extensional inherited
structures either from a colliding Oligocene arc or the
shape and inherent weakness of the Mesozoic continental
margin.
If we now close the Norfolk Basin so that the elbow
formed by the Three Kings Ridge and volcanic outer pla-
teau fits loosely in the crook of the Norfolk and Reinga
Ridges, allowing some space for crust, either the Three
Kings Ridge forearc (Fig. 17, 1A) or continental margin
(Fig. 17, 1B), which will be stretched into the western
Three Kings Ridge terraces, the IPB is significantly
reduced in size, and the Cavalli offset coincides with the
TKR
SFB 23
Ma
CR
VLL
VOP
PACIFIC
A
FUTURE CAVALLI
SEAMOUNT
95°
CAVALLI SEAMOUNT
CORE COMPLEX
UNROOFED
TKR
SFB 20
Ma
CR
VOP
PACIFIC
IPB
20 Ma
MORB
A
VLL
EAST WANGANELLA
SUB-BASIN
TKR
FUTURE CAVALLI
SEAMOUNT
23 Ma
VOP
PAC IF I C
B
TKR
SFB
VOP
IPB
20 Ma
MORB
B
20 Ma
CR
95°
PACIFIC
VLL
EAST WANGANELLA
SUB-BASIN
CAVALLI SEAMOUNT
CORE COMPLEX
UNROOFED
Uplift
TKR
SFB 11 Ma?
NB
CR
14 Ma?
MC
A+B
VOP
IPB
TKR
SFB
CAVALLI
SEAMOUNT
15 Ma
NB
115°
CR
MC
VMFZ
VOP
IPB
A+B
VLL
Uplift
2. Initial rifting 95°
3. Later
rifting and
spreading
115°
1. Convergence and obduction
4. Basin inversions
Unzipping arc
Collided arc
Subducton
Obduction
(active)
Arc volcanism
Normal faults
(active)
Reverse faults
(active)
Core complex
Inactive faults
Fig. 17 Miocene tectonic evolution of the northern New Zealand
margin, governed by Aarc collision or Barc unzipping. The modern
outline of the Northland Plateau is used in all the frames in order to
track it through the steps. VOP =volcanic outer plateau; IPB =in-
ner plateau basin; Chevrons =active volconoes; CR =Colville
Ridge arc; MC =Mohakatino-Coromandel volcanics
Mar Geophys Res (2009) 30:21–60 55
123
Reinga-South Maria Ridge offset. The van der Linden
Lineament is already present as an inherited deep crustal
fault (suture/subduction zone) in the arc-collision model
(A) but does not yet exist (as a conjugate pull-apart margin)
in the arc-unzipping model (B).
Starting from this initial geometry, moving the Three
Kings Ridge-volcanic outer plateau block in a N95°direc-
tion until the Weta and Tuatara Terraces are fully formed
(about 140 km), causes the western IPB to also expand,
obliquely, to its full width (Figs. 17, 2A and 2B). The van
der Linden Lineament might have behaved as an oblique
extensional rift shoulder, while the Cavalli offset became a
zone of N95°transfer faults. In model A, the entire Three
Kings Ridge-volcanic outer plateau-SSFB microplate
moves. In model B the van der Linden Lineament begins to
form, and possibly develops into a leaky transform that
shares oblique strain to the south and SFB back-arc
spreading to the north. There was considerable deformation
of the Zealandia crust at this time as the VMFZ plate
boundary began to form and link to the Kermadec Trench,
the Hikurangi Trench and the developing North Island fault
system (Fig. 15). The deep half-graben of the Early Miocene
East Wanganella Sub-basin, the splay faults that separate the
Taranui, Reinga and South Maria blocks of the Reinga
Ridge, the locally thick Lower Miocene deposits on the
Reinga Ridge (Herzer and Mascle 1996; Herzer et al. 1997)
and unroofing of the Cavalli Seamount core complex
(Mortimer et al. 2003,2008) were probably all conse-
quences of the strongly oblique initial extension.
Next, the motion changed to N115°, concentrating dis-
placement and attendant deformation on the VMFZ trend
(Fig. 17,3A?B). Asperities, either inherited from the old
continental margin or brought about by segmentation of the
Reinga Ridge by the splay faults (above), induce trans-
tension and transpression in transient zones, with mild local
crustal shortening (e.g. Herzer and Mascle 1996; Herzer
et al. 1997). Stress transmitted locally into the IPB during
this phase could account for local reactivation and reversal
of faults within the western IPB, such as in the Thrust and
the Slab, while extension continued in the eastern IPB. The
southeastward displacement of the IPB effected by the
N95°and N115°movements would shunt the East Cape
region towards its present location along oblique or curving
shears that connect to the Miocene North Island fault
system. There had to be decoupling of blocks, which
allowed the East Cape to migrate south-southeastwards
while the Plateau and SSFB continued to move south-
eastwards on a linear path orthogonal to the proto-Ker-
madec Trench. The final displacement of the East Cape
block was achieved by propagation of the Havre Trough
into the continental TVZ.
The structural evolution of the VMFZ is preserved in a
visible tripartite zonation: an en echelon complex of
escarpments and splays along the Reinga Ridge segment
(TB-RR-SMR in Fig 1), a linear shelf edge in the North
Cape region (NMR in Fig. 1), and a crenelated margin from
Cavalli Seamount to the Havre Trough (SHELF in Fig. 1).
The late compressive phase that affected the region in the
Middle Miocene is shown in Fig. 17,4A?B, but the
kinematics are unknown. By this time, the Norfolk and SFBs
were probably fully open and the NE-trending Mohakatino-
Colville-Lau Arc was well established as a stable, through
going linear feature. So far as is known, this arc remained in
position from 17 to 6 Ma, and there was no significant
Pacific trench retreat or backarc basin crust formation in this
time period. It could be that the Pacific lithosphere was
strongly coupled to the Australian lithosphere during Mo-
hakatino-Colville-Lau Arc times and stresses were able to
propagate well into the Reinga and Taranaki Basins.
Conclusions
Integration of new seismic interpretations, micropalaeon-
tological data and potential field modelling with published
radiometric ages has allowed us to investigate the geo-
logical constitution and depositional and tectonic history of
the Northland Plateau. The Plateau, with an intermediate
crustal thickness of 12–16 km, can be divided into a vol-
canic outer plateau (including Poor Knights Seamount
Chain) and an IPB (comprising Whangaroa and Knights
Basins separated by Cavalli Saddle).
The volcanic outer plateau consists of a 4–6 km thick
volcanic body (Unit Cp) that thins at the van der Linden
Lineament, stepping down by several kilometres to a thin
slab buried 3 km beneath the IPB, which slopes up to the
seabed at the shelf edge. Unit Cp supports seamounts (Unit
Cv) and draped sediments (Units B, and A/AB). However,
only Lower Miocene calc-alkaline rocks on the surface have
been sampled and only the top 2 s TWT are seen in seismic
records. The composition of what lies beneath them is not
known. The outer plateau has a strong (generally positive)
magnetic fabric that is continuous with that of the Three
Kings Ridge. Broad northerly trending magnetic highs on
the outer plateau, which line up approximately with SFB
anomalies, could indicate a related or coeval origin of the
outer plateau and basin. The outer plateau is cut locally by
normal faults. Structure is otherwise not evident. The
northern edge of the volcanic outer plateau bordering the
SFB is passive and apparently contiguous with the SFB
oceanic crust. Although the structure of the eastern and
western margins of the SFB is largely obscured by volca-
nism, there is local evidence of extension and no evidence
of a trench along the Three Kings Ridge. The NNW-
trending Huia fault terraces, containing 32-Ma andesite,
may be part of a Three Kings Ridge—SFB rift margin.
56 Mar Geophys Res (2009) 30:21–60
123
The IPB was affected by Early Miocene transtensive and
possibly transpressive faulting, but faulting was not per-
vasive as there are large fault-free areas. The seamount
chain, dividing the inner and outer plateau along the van
der Linden Lineament is undeformed. The IPB is floored
by allochthon and parautochthon (seismic unit D), which
probably includes an ophiolitic complex, and deformed and
flat-lying Lower Miocene volcanogenic sedimentary rocks
(Unit B) including some faulted and partly buried Lower
Miocene arc volcanoes (Unit Cv). The volcanoes are
grouped along the base of the upper slope where they are
identified by a chain of weakly positive magnetic anoma-
lies. Larger positive anomalies in the NW might include
positively magnetised basaltic or ultramafic bodies. Over-
lying units (AB and A) are, respectively, mildly deformed
to flat-lying, calcareous and turbiditic, and up to 2.2 s TWT
(c. 2.2 km) thick.
A pronounced left step approximately midway along the
Plateau’s length coincides with Cavalli Seamount, an Early
Miocene uplift of metamorphic and plutonic rocks occu-
pying a saddle that separates the Whangaroa and Knights
Basins. It coincides with a change in basement terranes and
topography in Northland, but the relationship, if any, is
unclear.
The SE-striking VMFZ fault system extending along the
northwestern continental shelf and slope, changes east of
the saddle to include SSE to S and SSW-striking, margin-
cross-cutting structures. Major SSE-trending structures,
inferred from gravity anomalies, may have linked the
VMFZ with the North Island fault system before the Taupo
Volcanic Zone opened.
Many parts of the IPB were at or above sea level in the
Early Miocene. Differential subsidence later lowered these
to 500–1,500 m or more below sea level. Angular, tilted
blocks in Unit D suggest an initial substrate of low relief
over wide areas, perhaps erosional, perhaps basaltic sea
floor. Except for possibly a few large seamounts with
flattish tops that have not been sampled, there is no evi-
dence that the volcanic outer plateau was ever at sea level.
The structure and stratigraphic history of the Plateau
record that obduction was followed closely by VMFZ
faulting, differential uplift and subsidence and (even partly
coevally) by arc volcanism in the Early Miocene, with a
late compressive phase in the Middle Miocene, and finally
regional and differential subsidence. The sequence of
events correlates well with deformational and depositional
events in Northland, the Reinga Basin, and Wanganella and
Reinga Ridges to the west.
Regional kinematic models involving either Late Oligo-
cene-Early Miocene arc collision or Late Oligocene-Early
Miocene arc unzipping provide parallel starting points to
examine the origin and evolution of the post-obduction
VMFZ and Northland Plateau-Northland continental
margin. Post-obduction rifting of the Norfolk Basin,
orthogonal to the strike of the Norfolk and Three Kings
Ridges, tore the Northland Plateau from the Reinga Ridge
margin by strongly oblique rifting, creating the IPB and the
Cavalli core complex. It was followed by N115°extension
and spreading parallel with the Cook Fracture Zone, which
completed the southeastward displacement of the Northland
Plateau, leaving the very complex dextral strike slip struc-
tural margin we have come to call the VMFZ.
Acknowledgments We thank the following people and organisa-
tions: shipboard parties of GNS cruises SF9901 (ONSIDE I) and
SF0202 (ONSIDE II), GNS technicians Kim Rose, Anya Duxfield and
scientist Dan Barker, NIWA seismic technicians Steve Wilcox and
Mike Stevens, Universite
´de Nouvelle Cale
´donie scientist Christine
Laporte-Magoni, CNRS Ge
´osciences Azur scientists Jean Mascle and
Etienne Ruellan, Captains Andrew Leachman and Roger Goodison
and crew of R/V Tangaroa, captain and crew of R/V Southern Sur-
veyor cruise SS03-01 (Norfolk’n Around), GNS scientists Graeme
Wilson, Ian Raine and Percy Strong for additional micropaleontology,
Vaughan Stagpoole for compilation of the magnetic map, Fred Davey
and Andy Nicol for constructive discussions, GNS technicians
Michelle Dow, Neville Orr, John Simes and Roger Tremain for lab-
oratory work. This work was funded by the Foundation for Research
Science and Technology (New Zealand), and travel grants from the
French Ministe
`re des Affaires Etrange
`res.
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