PaleomagnetismCenozoic tectonic evolutionTectonic rotationsSubductionHikurangi margin

and Cenozoic sedimentary and volcanic rocks record rotation about vertical axes of

. . . .. . .

3. Paleomagnetic analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Tectonophysics 509 (2011) 135164

Contents lists available at ScienceDirect

Tectonophysics3.1. Rock magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1414. Rotation domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

4.1. Raukumara domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1434.1.1. Paleomagnetic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

4.2. Wairoa domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1444.2.1. Paleomagnetic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1444.2.2. Anomalous localities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

4.3. Wairarapa domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1464.3.1. Paleomagnetic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

4.4. Marlborough domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

4.4.1. Paleomagnetic data . . .4.4.2. Rotation of basement stru

4.5. Western domains . . . . . . . .4.5.1. Paleomagnetic data . . .

Victoria University of Wellington, P.O. Box 600, We

0040-1951/$ see front matter 2011 Elsevier B.V. Aldoi:10.1016/j.tecto.2011.06.005. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136plate-boundary zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1372.1. Plate-boundary zone deformation2.2. Cenozoic tectonic evolution of theContents

1. Introduction . . . . . . . . . .2. New Zealand plate boundary zoneshortening, togetherwith dextral shear on arcuate strike-slip faults. The ends of the rotating part of theHikurangimargin dene hinges. In the south, this is accommodated by dextral shear in the Marlborough Fault Zone, andcrustal blocks, 150 km across, have rotated 50130clockwise, creating the eastern part of the New ZealandOrocline. In thenorth, thehinge is anonshore arcuate zoneof dextral shear, 1050 kmwide,with normal faulting.The Paleogene rotational history is poorly constrained, but the few paleomagnetic observations are consistentwith distributed shear of basement terranes in a zone of dextral simple shear, b200 km wide, running up thewestern part of theNewZealand, and linkingwith subduction farther north, creating thewestern half of theNewZealand Orocline. The overall pattern of rotation shows that the continental lithosphere in the Australian Plate isweak, so that deformation is controlledmainly by boundary forces along the plate interface, and passively followsthe change in trend of the subduction zone through time.

2011 Elsevier B.V. All rights reserved.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136. . . . . . . . . . . . . . . . . . . . . . .ctural trends . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .

llington, New Zealand.

l rights reserved.e Australian plate by along strike gradients of extension and

Keywords:New Zealand plate-boundary zonecrustal blocks along the Hikurangi margin, conforming closely with that indicated by the plate reconstructions.Since ~20 Ma, this was accommodated relative to thmeasurements in CretaceousAccepted 1 June 2011Available online 15 June 2011

plate motion since ~43 Ma, wrate of 44.5/Myr, and the sReview Article

Cenozoic tectonic evolution of the New Zealand plate-boundary zone: Apaleomagnetic perspective

Simon Lamb Department of Earth Sciences, South Parks Road, Oxford, OX1 3AN, UK

a b s t r a c ta r t i c l e i n f o

Article history:Received 17 December 2010Received in revised form 31 May 2011

New Zealand straddles the obliquely convergent boundary between the Pacic and Australian plates, withsubduction of Pacic plate along the Hikurangi margin. Finite plate reconstructions predict ~800 km of relative

ith 8090 clockwise rotation of the Hikurangi margin since ~20 Ma, at an averagehort-term deformation (b10 kyr) shows that rotation is still active. Paleomagnetic

j ourna l homepage: www.e lsev ie r.com/ locate / tecto. . . . . . . . . . . . . . . . . . . . . . . . . 147

. . . . . . . . . . . . . . . . . . . . . . . . . 148

. . . . . . . . . . . . . . . . . . . . . . . . . 150

. . . . . . . . . . . . . . . . . . . . . . . . . 150

..

.

.

.

.

.nsan.......e....

(Ranalli, 1995). Thus, at time scales that are short compared to theseismic cycle, over years to centuries, the response of the shallow

New Zealand straddles the obliquely convergent boundarybetween the Australian and Pacic plates, and the entire width of

136 S. Lamb / Tectonophysics 509 (2011) 135164parts of the lithosphere is essentially elastic, and the dynamicalproblem is the relationship between this shallow elastic deformationand ductile deformation at depth.

At time scales much longer than the seismic cycle, the elastic partof the lithosphere fails along faults, breaking up into rigid blocks. Inthis case, the dynamical problem becomes the relationship betweenthe underlying uid-like ductile ow and the motion of these blocks.At these longer time scales, and at length scales much greater than thedimensions of the rigid blocks, the important question is whether thelithosphere behaves overall as a uid, dominated by the dynamics ofthe ductile ow, or whether the details of the interaction betweennumerous jostling rigid blocks signicantly affects this ow (EnglandandMcKenzie, 1982; England andMolnar, 1997a,b; Freymueller et al.,2008; Lamb andWatts, 2010;McCaffrey, 2005; Thatcher, 2009). In theformer case, crustal blocks are essentially oating referred to as theoating block model on an underlying uid-like ow (Lamb, 1987,1994; McKenzie and Jackson, 1983a,b).

Paleomagnetism offers a powerful approach to tackling thisproblem, because it allows one to observe directly rigid body rotationsabout vertical axes. These rotations are those of individual crustalblocks, and so they place important constraints on the behaviour ofthe blocks, as well as the nature of the faults at their boundaries and

the plate-boundary zone is exposed on-land in a zone ~250 km wide(Fig. 1). The relative instantaneous motion of the plates can bedescribed by a rotation about a pole located to the south of NewZealand. In this study, the NUVEL-1a instantaneous pole of DeMetset al. (1994) is adopted, with ~38 mm/yr of convergence in a roughlyeastwest direction (261) in the central part (176E and 42S) of theplate-boundary zone (Fig. 1).

2.1. Plate-boundary zone deformation

North of New Zealand, both the Australian and Pacic plates areoceanic lithosphere, with subduction of the Pacic plate along theTongaKermedec subduction zone. Plio-Pleistocene back-arc spread-ing has resulted in the opening of the Havre Trough, with 80100 kmof back-arc extension (Stern, 1984; Wright, 1993, 1994) the widthof the Havre Trough is remarkably constant as far north as 26S(~1200 km north of New Zealand), indicating translation withnegligible rotation of the forearc, relative to the Australian plate, forthis segment of the subduction zone. In North Island, New Zealand,the Australian plate margin is a broad zone, up to 250 km wide, ofdeforming continental crust overlying subduction of the Pacic platealong the Hikurangi margin (Fig. 1b). Back-arc spreading terminates5. Active rotation in the New Zealand plate-boundary zone . . . . . .5.1. Active rotation of the Wairoa and Wairarapa domains . . . .5.2. Active rotation in the Marlborough domains . . . . . . . .

6. Cenozoic tectonic evolution of the Hikurangi margin . . . . . . . .6.1. Block reconstructions . . . . . . . . . . . . . . . . . . .6.2. Rotation hinges along the Hikurangi Margin . . . . . . . .

6.2.1. Northern boundary of the rotating Hikurangi Margin6.2.2. Boundary between the Wairoa and Wairarapa domai6.2.3. Cook Strait and the boundary between the Wairarapa6.2.4. Southern boundary of the rotating Hikurangi Margin

6.3. Paleogene evolution of the New Zealand plate-boundary zone7. Dynamical controls on rotation . . . . . . . . . . . . . . . . . .

7.1. Rotation of the trend of the subducted slab . . . . . . . . .7.1.1. Dynamical controls on the location of northern hinge

7.2. Strain and rotation . . . . . . . . . . . . . . . . . . . .7.2.1. Localised block rotation in dextral shear zones . . .7.2.2. Rotation and partitioning of relative plate convergenc7.2.3. Block stability . . . . . . . . . . . . . . . . . .

8. Discussion and conclusions . . . . . . . . . . . . . . . . . . . .Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . .References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction

The boundaries to the tectonic plates, where they pass throughoceanic lithosphere, generally form narrow zones up to a few tens ofkilometres wide. However, relative plate motion through continentallithosphere results in displacement, strain and rotation in a broadzone, up to several thousand kilometres wide (Lamb, 1987, 1994;McKenzie and Jackson, 1983a,b). Understanding this marked differ-ence in lithospheric response is a central problem in geology, withtwo fundamental aspects: rstly, kinematics, describing the evolutionof deformation on the Earth's surface, and secondly, dynamics,understanding the forces that drive this deformation.

It has been well understood for many decades, from bothexperimental work and direct observations of earthquakes, that atdepths less than a few tens of kilometres, the crust and mantle arecold enough, and at sufciently low pressure, that they behave in abrittle manner, whereas at greater depths, rocks fail by ductile owtheir long term stability. This way, paleomagnetically-determined. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157d northern Marlborough domain . . . . . . . . . . . . . . . . . 157. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

rotations provide clues to block dynamics in wide zones ofdeformation, especially in the context of the motions of boundingplates, helping to distinguish the role of edge and basal forces (Lamb,1987, 1994). In addition, rotation may result in marked re-orientationof earlier-formed geological features, making sense of their long-termgeological evolution. Finally, the wider scale pattern of rotationpotentially provides powerful constraints on the overall effect of thedeformation, yielding important insights into the long and short-termkinematics and large scale dynamics of continental lithosphere.

In this paper, I use paleomagnetic data to analyse lithosphericdeformation in the New Zealand plate-boundary zone during theCenozoic, updating previous syntheses of the tectonic evolution of thisregion based on less paleomagnetic data (King, 2000; Lamb, 1988;Nicol et al., 2007; Rowan and Roberts, 2008; Walcott, 1987, 1989).

2. New Zealand plate boundary zoneonshore in the Central Volcanic Region (Stern, 1984), and a zone of

3Ha

ite

hat

c an

137S. Lamb / Tectonophysics 509 (2011) 135164170E

170E

45S

35S

AustralianPlate

Esk Headsubterrane

StokesMagneticAnomaly

Alpine

Fault

NISB

Dun Mountain Ophiol

Puys

egur

Tren

chC

(a)

Fig. 1. Map showing the boundary between the obliquely converging (37 mm/yr) Pacidextral strike-slip faults, referred to as the North Island Shear Belt(NISB), separates the back-arc from the forearc (Beanland, 1995).Farther south, in South Island, subduction terminates, and the Pacicplate is continental lithosphere, and the plate-boundary is a zone ofdextral transpression (~100 km wide) within continental crust,comprising the Marlborough Fault Zone, Southern Alps and AlpineFault (Walcott, 1998).

The Alpine Fault is the single most important fault in New Zealand,with ~450 km of dextral strike-slip offset, and up to 100 km ofshortening (Sutherland, 1999;Walcott, 1998). It links up at its southernend with the Puysegur Trench, where Australian Plate oceaniclithosphere is being subducted beneath Pacic Plate, with the oppositepolarity to subduction along the Hikurangi Margin (Sutherland et al.,2000). Themajor structural features of theNewZealandplate-boundaryzone are shown in Fig. 1.

2.2. Cenozoic tectonic evolution of the plate-boundary zone

Cenozoic plate reconstructions of the New Zealand region require~800 km of displacement across the plate-boundary zone since~43 Ma, with profound shape change in the crust of the overlyingplate (Fig. 2, Cande and Stock, 2004; King, 2000; Nicol et al., 2007;Sutherland, 1995, 1999; Walcott, 1984a,b, 1987; Walcott et al., 1981).Stratigraphic and structural evidence, however, suggest that subduc-tion along the Hikurangi Margin began in the early Miocene or latestOligocene, between 25 and 20 Ma, with the development of foldingand thrusting and a marked change in the nature of sedimentationalong the east coast of New Zealand (Lamb and Bibby, 1989; Rait et al.,1990). At this time, there was a transition from ne-grained deep

Pacic plate is being subducted beneath Australian plate along the TongaKermadec subducPacic plate is thickened oceanic crust of the Hikurangi Plateau (Davy et al., 2007), which is bthe North Island Shear Belt (NISB). At the southern end of the subduction zone, oblique convecontinental collision along the Alpine Fault, which links with the Puysegur Trench, where AusNew Zealand continent. The orientation of prominent geological features such as the StokesEskhead subterrane dene the New Zealand Orocline. (b) Depth contours (km) to the top of tarea shows region of crust in the overlying wedge that is in contact with the subducted plaFrom crustal structure compiled by Beanland and Haines, 1998.-2000 m

180E

180E

35S

7 mm/yr

Hiku

rang

i Mar

gin

vre

Trou

gh

Pacific Plate

HikurangiPlateau

Tong

a-Ke

rmed

ecTr

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ham Rise

Hiku

rang

i Thr

ust F

ront

38S

42S

176S 178S

Plate interface contours (km)

(b)

70 5030

2010

Back

-arc

exte

nsion

Crust resting on subducted slab

d Australian plates running through the New Zealand region. (a) In the north, oceanicwater mudstones and limestones in the Paleogene, to Miocene coarsegrained facies, including thick conglomeratic sequences such as theGreat Marlborough Conglomerate, as well as regional rapid subsi-dence in the western part of North Island (Audru and Delteil, 1998;Holt and Stern, 1994; Lamb and Bibby, 1989; Rait et al., 1990; Reay,1993; Stern and Holt, 1994).

If the crust in the New Zealand region has remained contiguousacross the plate-boundary zone, then the Cenozoic plate motionsrequire large scale clockwise rotation of both the trend of the trenchand subduction zone, together with the crust of the overlyingAustralian plate (Walcott, 1984a, 1987; Walcott et al., 1981; Walcottand Mumme, 1982). Thus, if one considers a marker line spanning theplate-boundary zone, one can estimate this rotation history directlyfrom the nite platemotions (Fig. 3). Onewould anticipate about 110of rotation since ~40 Ma, at the time of the inception of the plate-boundary zone in the New Zealand region, or an average rate of ~2.8/Myr, and ~90 of rotation of Negene rotation, since ~20 Ma, of thesubduction zone itself, or an average rate of 4.5/Myr (Fig. 3) thelatter takes account 80100 km of back-arc extension in the southernend of the Havre Trough since ~4 Ma (Stern, 1984, 1987; Wright,1993, 1994).

Another important clue to the tectonic evolution of the plate-boundary zone comes from the geometry of New Zealand's Mesozoicand older basement. Both structural trends and the orientation ofdistinctive terranes show a marked swing in trend, dening the NewZealand Orocline, from a more nearly northwest or westnorthwesttrend in the Pacic Plate, to northeastsouthwest in the plate-boundary zone itself, and northwestsoutheast in the NorthlandPeninsula, on the Australian Plate (Fig. 1). Offset of these basement

tion zone with Plio-Pleistocene back-arc spreading in the Havre Trough. Farther south,eing obliquely subducted along the Hikurangi margin with onshore dextral strike-slip inrgence is transferred through the dextral strike-slip Marlborough Fault Zone to a zone oftralian plate oceanic lithosphere is being subducted beneath the southernmargin of theMagnetic Anomaly (outcropping as the Dun Mountain Ophiolite belt, Hunt, 1978) andhe subducted plate along the Hikurangi margin (afterWallace et al., 2009). Grey shadedte.

4 Ma10 Ma

20 Ma

Today

30 Ma40 Ma

Chatham Rise

Hiku

rangi

Margi

n

Dun Mountain Ophiolite Belt

100 km

NRD RD

RD

RDRD

RD

RD = Raukumara Domain

NorthlandPeninsula

?

inc40 Mnt t

138 S. Lamb / Tectonophysics 509 (2011) 135164Fig. 2. Plate reconstructions for the Australian and Pacic Plates since 40 Ma, close to the(2004) for the 4, 10, and 20 Ma reconstructions, and Sutherland (1995, 1999) for 30 andthe limits of intense Cenozoic deformation (green zone), and offset of distinctive basemeterranes is signicantly less than the total ~800 km of Cenozoicdisplacement across the New Zealand plate-boundary zone, requiringmore distributed deformation including rotation about vertical axesand bending of the basement terranes (Figs. 1, 2, Bourne et al., 1998;Molnar et al., 1999; Sutherland, 1999).

south (dashed red line); thin black dashed lines denote the northern continuation of subdu~40 Ma to a thin rectangular zone today. The limits of deformation at any stage in the evolutirestricted to the western side of plate-boundary zone, as a relatively narrow dextral shear zozone off the Northland Peninsula. Since 2025 Ma, subduction has propagated much farthpostulated position of the Raukumara domain is shown (marked RD), marking the westersubducting margin.

4 Ma10 Ma

20 Ma

Today

30 Ma

40 Ma

Chatham Rise

1210

8642

Cloc

kwise

rota

tion

()

(a)

(b)

Hiku

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i Mar

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100 km

Fig. 3. (a) Finite plate reconstructions of the Australian Plate in the New Zealand region sinrotated ~40 clockwise about a vertical axis since 40 Ma, or ~1/Myr. Lines spanning the plataround ~20 Ma. (b) Plots showing rotation against time, relative to the Pacic plate, of two linthe plate-boundary zone, from just north of Christchurch to near the Hauraki Gulf (blue linmore nearly parallel to the Hikurangi margin (red line) has rotated overall about ~10 morenorthern part of the Hikurangi margin in the last 4 Ma. The marked increase in rotation rateof the inception of subduction along the Hikurangi margin at 2025 Ma.eption of the plate-boundary zone, based on the nite rotation poles of Cande and Stocka, showing the change in shape of the plate-boundary zone, dened by points markingerranes. Solid red lines follow the Hikurangi subduction zone, with dextral shear to the3. Paleomagnetic analysis

Over the past 30 years, numerous paleomagnetic studies ofCenozoic and Cretaceous sedimentary rocks and volcanics havedocumented mainly clockwise rotations of crustal blocks in the New

ction. Plate motion has resulted in drastic shape change of a roughly triangular zone aton have been always roughly rectangular. Prior to ~20 Ma, deformation was most likelyne extending up through western North Island, linking with ~ESE-trending subductioner east, with the development and subsequent rotation of the Hikurangi margin. Then limit of the Paleogene plate-boundary zone, and the northern hinge of the Neogene

0000000

0 10 20 30 40 50Age (Ma)

4-5/Ma

Inception of Hikurangi

Margin

5-6/Ma

Hikurangi Margin

Plate Boundary Zone

Australian Platewrt Pacific Plate

~1/Ma

10

ce 40 Ma, relative to the xed Pacic Plate, as in Fig. 2. Overall, the Australian Plate hase-boundary zone showmuch more rapid rotation, with marked increase in rotation ratees spanning the plate-boundary zone. A line linking two points outside themain part ofe), has rotated ~100 clockwise since ~40 Ma, with ~80 since 20 Ma (~4/Myr). A line(~110 since 40 Ma, or ~90 since 20 Ma), as a consequence of back-arc extension in theof these marker lines around 20 Ma coincides with stratigraphic evidence for the timing

Table 1aPublished paleomagnetic data for Cenozoic sedimentary rocks used in this study for analysis of vertical axis rotations in the New Zealand plate-boundary zone, from the Raukumara,Wairoa, and Wairarapa domains (see Figs. 4 and 6 for locations).

Location N/na Dbis Ibis Beddingc Ddtc Idtc ke 95f Age Ma Age Ma Rg Rg Refh

Raukumara domainMB /38 37.9 52.4 027/18 14 52 14.5 6.3 16.8 0.8 14 8 RRMS /27 298 72 088/54 199 43 12.6 8.1 20.4 1.4 19 9 RROR /39 206.1 56.2 067/12 196 48 16.3 5.8 20.4 1.4 16 7 RRTA2 19 208 13.5 346/18 203 25 12.9 8.9 20 1 23 8 MLWTA3 27 219 29.1 016/28 201 36 29.6 5.0 17 1 21 5 MLWTA4 (N) 21 20.1 51.5 026/19 359 46 22.0 6.5 17 1 1 8 MLWTA4 R 12 223 36.8 026/20 208 40 41.5 6.3 17 1 28 7 MLWTA4 (all) 33 28.9 47.4 026/21 9 45 18.5 5.7 17 1 9 6 MLWTA6 N 42 264 82.9 103/70-41 4 42 14.6 5.7 18 1 4 6 MLWTA7 R 5 168.9 52.5 162/31 200 40 21.2 13.6 17 1 20 14 MLWTA7 N 23 329.7 52 162/32 8 48 35.6 4.9 17 1 8 6 MLWTA7all 28 332.4 52.4 162/33 10 47 30.9 4.8 17 1 10 6 MLWHK4 N 44 12.8 23.8 263/37-26 24 53 21.5 4.6 20 1 24 6 MLWHK4 R 54 198.1 3.5 263/37-27 203 32 10.4 5.9 20 1 23 6 MLWHK4 all 98 14.7 12.9 263/37-28 22 42 11.8 4.1 20 1 22 4 MLWMA1 35 169.1 31.3 205/28 189 44 34.7 4.0 17 1 9 5 MLW

Coastal Raukumara/Wairoa domainsWU (N) /19 66.8 70.2 194/23 86 50 55.5 4.5 9.9 1.1 86 6 RRWU (R) /24 163.9 59.3 194/23 207 63 18.7 7.0 9.9 1.1 27 13 RRMP /44 77.2 56 307/14 96 65 35.3 3.7 14.6 1.4 97 7 RRTH /23 73.4 44.9 038/19 53 53 30.7 5.5 8.8 2.3 53 7 RRTP /37 49.8 59.2 273/32 116 66 37.3 3.9 14.6 1.4 116 8 RRSB /22 56.9 11.7 353/47 39 51 22.1 6.7 14.6 1.4 39 9 RR

Wairoa domainMK* /26 21.8 63.8 187/30 65 49 79.6 3.2 6 1 65 4 RRNP /15 16.5 74.5 186/23 64 60 28.4 7.3 9.9 1.1 64 12 RRTF /22 15.3 65.5 199/20 54 60 80 3.5 13.1 2.1 54 6 RRNG /31 297.9 47.6 084/43 242 53 26.4 5.1 13.5 2.5 62 7 RRCH /20 313.4 27.8 072/56 258 65 35.3 5.6 14.2 1 78 11 RRMk1 /27 39.2 78.6 169/17 63 63 25.1 5.4 16 0.5 63 10 WMMk2 /6 205.1 60.9 177/17 225 50 20.8 5.4 15 0.5 45 7 WMMk3 /6 51.2 69 235/20 95 62 14.2 15.2 15 0.5 95 28 WMWk1 /16 273 59.1 048/14 250 67 6.4 13.9 12 0.5 70 30 WMHr1 /24 27.8 48.4 198/17 45 43 15.9 7.2 11 0.5 45 8 WMWW11 /31 14 53 183/26 41 42 5.2 9.4 5 0.05 41 10 WWWW12 /43 347 52.6 183/26 22 52 8.1 8.9 4 0.05 22 12 WWWW7 30/102 3.1 62.9 183/26 47 57 76.9 3.0 10 0.05 47 4 WWWW8 3/110 349.6 63.3 185/29 40 62 174 2.0 9 0.05 40 3 WWWW9 19/70 341.3 64.6 191/25 41 61 110 3.2 8 0.05 41 5 WWWW10 39/100 167.7 55.6 193/25 206 54 8.4 8.4 6 0.05 26 12 WWWW13 /31 207.6 63.6 072/09 197 57 65.1 3.1 2.3 0.1 17 5 WWPC /13 58.7 76.6 183/21 79 57 31.5 7.7 15.6 0.5 79 11 RRTC /48 44.3 58.6 203/10 58 54 54.1 2.8 7.6 1.1 58 4 RRPP /24 216.1 62.3 239/11 238 65 36.2 5.0 7.6 1.1 58 9 RRNR N /16 6.5 54.5 240/48 100 63 63.3 4.7 8.8 2.3 100 8 RRNR R /24 182.6 44.6 240/48 257 66 36.4 5.0 8.8 2.3 77 10 RR

Wairarapa domain (northern)BH /24 264.6 59.9 067/23 225 59 21.1 6.6 8.8 2.3 45 10 RRWT /5 79.2 50.1 051/38 28 53 176 5.8 8.8 2.3 28 8 RRTI /37 31.2 64.4 201/30 71 48 64.6 3.0 14.2 1 71 4 RR

Wairarapa domain (southern)BP /33 210.6 57.8 229/18 240 59 32.8 4.5 8.8 2.3 60 7 RRFP /13 214.6 44.2 223/41 251 36 36.8 6.9 19.6 2.1 71 7 RROK /37 339.7 58.5 207/50 76 57 31.2 4.3 21.9 1.6 76 6 RRHIN1 /20 15 49 250/16 30 63 48.4 4.7 9 2 30 8 WCMHIN2 /24 23 53 250/16 45 63 37.8 4.9 9 2 45 9 RLMBIR1 /44 7 40 279/22 5 62 15.5 5.7 2.5 0.5 5 10 RLMBIR2 /48 176 52 28.5 3.8 2.2 0.2 4 7 LMS 2/26 /10-15NW 186 67 171 2.1 2.3 0.2 4 5 B

Notes: MLW=Mumme et al., 1989, WW=Wright, 1986 and Wright andWalcott, 1986, WM=Walcott and Mumme, 1985, RLM= Randall, 2007 and also Randall et al. 2011-thisvolume, L = Lamb, 1988, B = Beanland, 1995.

a Number of sites/samples.b In situ (geographic) orientation.c Dip clockwise of strike.d Tilt corrected (stratigraphic) orientation.e Fisher precision parameter.f 95% cone of condence for mean.g Deviation of mean tilt corrected declination from True North, with error after Demarest, 1983 (0.8 sin1(sin(95)/cos(I)).h RR=Rowan and Roberts, 2008.

139S. Lamb / Tectonophysics 509 (2011) 135164

Table 1bPublished paleomagnetic data for Cretaceous and Cenozoic volcanic and sedimentary rocks used in this study for analysis of vertical axis rotations in the New Zealand plate-boundaryzone, from the Marlborough and Western domains (see Figs. 4 and 11 for locations).

Location N/na Dbis Ibis Beddingc Ddtc Idtc ke 95f Age Ma Age Ma Rg Rg Refh

Marlborough domainsBR1 31/ 207.1 44.3 283/14 212 58 29.2 4.9 4.8 0.5 32 7 RBR2 32/ 208.4 45.1 283/14 215 59 48.4 3.7 5.7 0.5 35 6 RBR3 36/ 202.2 40.7 273/20 212 59 65.6 3.0 6.7 0.5 32 5 RBR4 33/ 208.5 46.8 291/15 212 62 25.6 5.0 7.5 0.5 32 8 RUB1 27/ 186.7 45.5 241/14 198 56 56.5 3.7 4.8 0.5 18 5 RUB2 29/ 182 45.1 245/23 202 64 45.7 4.0 5.8 0.5 22 7 RUB3 22/ 190.7 53 233/15 211 61 55.5 4.3 5.9 0.5 31 7 RUB4 25/ 177.1 45.4 225/21 199 58 39.3 4.7 6 0.5 19 7 RUB5 30/ 188.1 45.3 243/15 200 57 76 3.0 6.1 0.5 20 4 RUB6 31/ 184.3 51.5 233/20 210 64 60.6 3.3 6.2 0.5 30 6 RUB7 31/ 186 48.8 233/20 210 61 34.2 4.5 6.3 0.5 30 7 RUB8 22/ 194.3 48.5 233/20 219 58 44.1 4.7 7 0.5 39 7 RWB 29/ 211.8 58 321/10 204 67 58.1 3.6 3.9 0.5 24 7 RSV 33/ 214.7 70.5 136/15 224 61 67.1 3.1 3.9 0.5 44 5 RRB 25/ 196.6 57.1 233/10 212 62 56.5 3.9 4.2 0.5 32 7 RNC 31/ 217.6 44.9 313/15 215 60 61.1 3.5 5.4 0.5 35 6 RBS 14/ 173.2 29.4 247/40 197 63 29.6 7.4 8 2 17 13.0 RCS 52/ 239.9 42.7 Fold plunge 175 59 50.8 2.8 3.3 0.3 5 4.3 RSW 29/ 217.3 49.6 353/25 184 62 34.8 4.6 4.2 0.6 4 7.8 RWV /42 186.5 48.7 245/15 200 61 84.6 2.4 8 1 20 4 RDS 46/ 157 59 218/55 279 59 10.5 6.4 18 2 99 10 MWCC 12/ 020/46 24 60 56.2 5.4 8 2 24 9 WMOT 36/ 055/20 354 62 6.7 9 9 3 6 14 WSS /8 118 54 048/101 122 44 37 11.0 20 4 122 12 VLHC3 /7 118 10 034/61 106 70 90 7.0 17 1 106 15 VLHC2 /26 147 21 071/95 121 69 26 17.0 17 1 121 55 VLBB2 /22 309 0 031/56 315 55 8 12.0 30 5 135 17 VLWC1 /30 235 45 292/47 310 66 67 3.2 59 5 138 6 VLWC2 /4 330 76 215/20 318 57 133 8.0 59 5 146 11 VLWD1 /15 62 32 349 55 143 3.4 4 1 11 5 VLWD2 /11 84 31 356 51 53 6.3 4 1 4 8 VLFC 6//26 167 37 235/24 180 59 40.4 10.6 5.5 0.4 0 17 LRWH /25 257 34 325/30 274 60 7.7 11.2 60 5 97 23 TWC3 /9 52 36 300/50 113 72 53.1 19.2 60 5 117 21 TCLA 12//10 117.9 61.5 055/55 352 64 34.8 8.3 54 4 10 17 HLMKAI 10//8 106.3 53.6 056/45 22 58 32 9.9 49 5 41 17 HLMPUH 14//13 7.6 12.7 250/70 61 69 34 7.2 66 2 84 19 HLMWHP /59 32 61 245/15 62 66 22.4 4.0 6 2 66 9 RLMBOU /18 9 21 233/50 30 57 7 14.0 9 2 34 21 RLMBIG /38 17 40 228/55 78 46 13.4 6.9 9 2 82 9 RLMSTR /12 14 54 214/47 73 45 28 8.4 9 2 77 10 RLMBIG* /50 016 44 220/20 37 49 14 5.6 9 1 37 8 RLMCAV /36 340 68 225/28 83 79 41.4 3.5 95 5 77 22 RLMDEE /20 1 50 224/50 76 56 18.6 7.8 53 2 88 14 RLMSEY /11 26 72 231/34-44 26 72 36.3 7.8 96 3 21 26 RLMLOT 86/ 195 30 210/69 219 62 9.9 5.1 30 4 51 10 RLMLYF 54/ 5 40 230/31 42 57 20.6 4.4 30 4 54 11 RLM

Western domainsWAN 26/ 4.7 55 6.8 3 0.5 4.7 10 T05TUR 101/ 9.7 58 2.0 3 0.5 9.7 3 T05RAN 53/ 13 60 2.6 2.8 0.5 13 4 T05RAU /30 192 51 31.8 4.5 20 3 12 6 MWTAU /22 210 50 6.75 11.4 25 3 30 14 MWBEX /8 238 70 72.1 5.8 35 3 58 14 MWBEN /26 54.5 60 32.6 4.8 30 3 55 7 MWPON /14 29 59 106 3.6 35 3 29 6 MWTAR /120 15 63 1.8 17 0.5 15 3 T07INA (N) /11 38 67 87.3 4.5 40 3 38 9 MWINA (R) /10 215 60 287 2.6 40 3 35 4 MWINA (all) /21 36 64 108 2.9 40 3 36 5 MWMAG /39 280 76 12.8 6.3 30 3 100 22 MW

Notes: MW = Mumme and Walcott, 1985, W = Walcott et al., 1981, T = Townsend, 2001, VL = Vickery and Lamb, 1995, HLM = Hall et al., 2004, RLM = Randall, 2007 and alsoRandall et al. 2011-this volume, T05 = Turner et al., 2005, T07 = Turner et al., 2007.

a Number of sites/samples.b In situ (geographic) orientation.c Dip clockwise of strike.d Tilt corrected (stratigraphic) orientation.e Fisher precision parameter.f 95% cone of condence for mean.g Deviation of mean tilt corrected declination from True North or for Pacic Plate (Marlborough), with error after Demarest, 1983 (0.8 sin1(sin(95)/cos(I)).h R=Roberts, 1990 and Roberts, 1992.

140 S. Lamb / Tectonophysics 509 (2011) 135164

Zealand region, with rotations up to ~130 (Table 1a and 1b, Fig. 4,Hall et al., 2004; Lamb, 1988; Little and Roberts, 1997; Mumme et al.,1989;Mumme andWalcott, 1985; Randall, 2007; Randall et al., 2011-this volume; Roberts, 1990, 1992; Rowan and Roberts, 2005, 2006,2008; Townsend, 2001; Turner et al., 2005, 2007; Vickery, 1994;Vickery and Lamb, 1995; Walcott et al., 1981; Walcott and Mumme,1985; Wright, 1986; Wright andWalcott, 1986, hereafter referred toas Paper 1).

3.1. Rock magnetism

The principals of the paleomagnetic technique are described byButler (1992). In New Zealand, the strength of the natural remanentmagnetism (NRM) in rocks varies by several orders of magnitude, and

is very weak in sedimentary rocks. Thus, Paleogene micriticlimestones and Neogene mudstones and siltstones along the eastcoast of New Zealand typically have magnetic intensities b1 mA/m.Late Cretaceous and Oligocene basaltic volcanics are orders ofmagnitude stronger, with intensities 252650 mA/m (Fig. 5).

Secondary magnetisations are common in sedimentary rocks inthe New Zealand region, especially Neogenemudstones and siltstones(Mumme and Walcott, 1985; Randall, 2007; Rowan and Roberts,2005, 2006, 2008; Walcott and Mumme, 1982, Paper 1), leading insome studies to an 80% failure rate in identifying any primarymagnetisation at all. A particular problem has proved to be thepresence of secondary iron sulphides such as greigite, which havehigh coercivities and break down at moderate temperatures, tendingto disguise any primarymagnetisation. However, large scale studies of

N

Wairarapa Domain

WesternDomains

AUSTRALIAN PLATE

100 km

Fig. 5

BIRHIN

CCSV

WBWV

UB

SSDS WC1

WC2

WHBBFC

CS

FPBP

WT

BH

TI

TC, PP

SBMP TP

TH

WU

MK*CH

TFNG

MB

OR, MS

WAN TURRAN

MA1

HK4

TA7

TA4TA3TA2

NR

Vertical axis rotations

WW13WW7-12

Wk1Hr1

Mk1-2

TAR

BEX

TAU

BEN

RAU

PON

MAG

Centr

al Vo

lcanic

Re

gion

North

Islan

d She

ar Be

lt

Havr

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ugh

NW Nelson

Wairarapa Fault

AT

Hiku

rang

i Thr

ust F

ront

INA CAV

SEY

WairoaDomain

g

Back-arc

extensionNORTHISLAND

SOUTHISLAND

Nelson

Cook Strait

Mt Ruapehu

Wanganui Basin

Mk1

MS

Raukumara Domain

OK

NP

DEE

BR

paw p

141S. Lamb / Tectonophysics 509 (2011) 135164PUHKAI

CLASW

HC2HC3 WC3

MOTAlp

ine Fau

lt

Marlborough Fault Zone

PACIFIC PL

LYFLOT

Fig.10

MarlborouDomains

Fig. 4.Map of the northern part of the New Zealand plate-boundary zone in the northernfeatures and rotation domains (Raukumara, Wairoa, etc.) dened in the text. Arrows sho

b10 Ma, red for 1025 Ma, green for 2595 Ma). The stippled region shows the inferred parNeogenezone ofrotation

wrt Pacific Plate0 - 10 Ma

10 - 25 Ma

25 - 95 Ma

Secondary magnetisation?E

h

rt of the South Island and eastern part of the North Island, showing the major structuralalaeomagnetic declination anomalies at sample localities, colour coded for age (blue for

ts of the plate-boundary zone that have undergone clockwise rotation in the Neogene.

et s

ra

SH

T

hianins

S

G

142 S. Lamb / Tectonophysics 509 (2011) 135164(a)

100 km

Back

-arc

ex

tens

ion

Sinistral offsof Cretaceou

on MoutohouFault

MK*

C

TF

NGNP

MB

OR

WW13

WW7-12

Wk1 Hr1

Centr

al Vo

lcanic

Regio

nNo

rth Is

land

She

ar B

elt

WAIROA DOMAIN

MaPe

Mk1

NP

Mmagnetostratigraphy, where 100s to 1000s m of continuous stratig-raphy are sampled at close intervals, involving thousands ofmeasurements, have proved a powerful way to identify convincingprimary magnetisations, with systematic reversals and, in some cases,progressive tectonic rotation through time (Roberts, 1990, 1992;Turner et al. 2005; Wright 1986; Wright and Walcott, 1986). In ad-dition, combining numerous measurements from different parts offold structures provides the basis of a fold test, demonstrating amagnetisation acquired prior to tilting.

Full details of themeasurement techniques and results are given inthe various publications listed in Table 1a and 1b. The measurementsare considered to be representative of the Earth's average magneticeld close to the time of the formation of the rock samples if they fullmost of the following criteria.

(1) Secular variation has been averaged out by sampling asufcient stratigraphic thickness at any particular locality. Ingeneral, a stratigraphic thickness representative of at least10 kyr of continuous sedimentation is required. If secularvariation is fully captured, then an angular dispersion of ~15for the spread of magnetisations would be expected at thelatitudes of New Zealand (Butler, 1992).

(2) Samples have been stepwise cleaned, either thermally orwith an alternating eld, and show a progressive unblocking

20 Ma - 4 Ma(b) (c)

RaukumaraDomain

WairoaDomain

Sinistral slip

Back

-arc

sho

rteni

ng/s

trike

-slip

Pw/rPw/r

Hiku

rang

i Thr

ust F

ront

Aust

ralia

n Pl

ate

Aust

Fig. 5. (a) Geological map of the Raukumara andWairoa domains (after Mazengarb et al., 20Miocenemudstone and siltstones (see Table 1a for paleomagnetic data for localities). The bou5070 since ~20 Ma (Fig. 6), however the structures which have accommodated this rem(c) Cartoons illustrating possible kinematics for the hinge zone separating the rotating Wa(relative to the Australian plate) before and since 4 Ma.Plio-Pleistocene

Miocene

Highly deformed

Mesozoic

Cretaceous

Localitydeclination

2 - 9 Ma

10 - 22 Ma

Overprint?

B MPTP

TH

WU

MA1

HK4

TA7TA4TA3

TA2

NR

Mk1-2C, PP

Hiku

rang

i Thr

ust

Fron

t

RAUKUMARA DOMAIN

ula

isborne

Northern hingeand/or stripping off of a secondary overprint, resulting in aconvergence to a stable direction of magnetisation with anintensity at least an order of magnitude greater than thedetection limit of the magnetometer. Most measurementswere made with a cryogenic magnetometer after thermalcleaning up to 500 C.

(3) At least some of the data have a reversed polarity relative to thepresent day eld, which is consistent with the magnetostrati-graphy for these rocks.

(4) The inclination, after correcting for the tilt of the strata, is closerthan before the tilt correction to that expected for the latitude ofthe sample at the time of its formation, and in general is within10 of this inclination. In some cases, atter inclinations forreversed samples are accepted (Raukumara domain) if thedeclinations are consistent with those for normal samples,which have the expected inclination for the sample latitudeafter the tilt correction.Most samples come fromstratawhichdipless than 30 and can be shown to be part of gently plunging(b10) fold structures.

(5) In many cases, it is also possible to show that remanencemagnetisations, either at a single locality or grouping oflocalities, have maximum clustering after a tilt correctionwith 100% unfolding (Tauxe and Watson, 1994). There is alsothe possibility of well-grouped magnetisation acquired during

4 Ma - Present

RaukumaraDomain

WairoaDomain

Back

-arc

exten

sion

Dextral slip

Pw/r

Hiku

rang

i Thr

ust F

ront

ralia

n Pl

ate

01), showing the major faults and the mean paleomagnetic declinations for localities inndary between the two domains forms a hingewhere there has been relative rotation ofain surprisingly obscure, though dening overall an arcuate zone (see text). (b) andiroa domain from both the Australian plate and the non-rotating Raukumara domain

folding (for example, in Miocene mudstones and siltstones), asfound by Rowan and Roberts (2008).

Rotation and attening anomalies are calculated by comparing thedirection of mean locality magnetisation, given its age, with thatpredicted for the Pacic plate (or Australian plate) at that time andlocation (Cande et al., 1995, 2000; DiVenere et al., 1994). A rotationanomaly is interpreted to be the result of rotation of a rigid crustalblock about a vertical axis.

The Pacic plate has undergone negligible Neogene rotation, andb15 anticlockwise in the Paleogene, and b5 clockwise since the LateCretaceous, relative to True North. The Australian plate has rotated~40 clockwise (~1/Myr) relative to Pacic Plate since the inceptionof the New Zealand plate-boundary zone at ~43 Ma. It is oftenconvenient, when discussing rotations in North Island and north-western South Island, to talk about rotations relative to the adjacentAustralian Plate. But, when discussing rotations in northeastern SouthIsland, in the Marlborough Fault Zone, it is easier to consider rotationsrelative to the adjacent Pacic Plate, which is essentially the same asTrue North for the Neogene.

4. Rotation domains

A convenientway to analyse the paleomagnetic data is by groupingresults into domains, forming regions roughly 50 km100200 km(Fig. 4, Lamb, 1988;Walcott, 1989). These domains are not necessarilysingle crustal blocks, but rather clusters of blocks which have similarrotation histories or rotation histories which can be convenientlygrouped together. Thus, domains are dened by both geographiclocation and similarity of structural style and tectonic setting.

The kinematics of deformation at the boundaries betweendomains poses signicant and intriguing structural problems, givingimportant insight into both the consequences and causes of rotation.In the following sections, the paleomagnetic data for themain rotationdomains are described in detail.

4.1. Raukumara domain

The Raukumara domain comprises the Raukumara Peninsula onthe extreme northeastern corner of North Island, with its geologicalcontinuation to the north, offshore (Figs. 46, Sutherland et al., 2009).It forms the southern end of the TongaKermedec subduction zone,bounded to the west by thinned continental lithosphere, and oceaniclithosphere, in the Havre trough (Reyners et al., 1999; Wright, 1993,1994). It is underlain by Mesozoic basement rocks in the west, butoverlain by extensively deformed marine Cretaceous to Neogenecover sequences farther east (Fig. 5a, Mazengarb et al., 2001).Cretaceous to early Miocene sequences are folded and cut by reversefaults with a predominantly NWSE trend, forming part of anextensive NW trending allochthonous terrane which extends muchfarther west, up into the Northland Peninsula. Overlying Miocene andyounger mudstones, siltstones and sandstones, up to 1000 m thick,locally rest with angular unconformity on the deformed Paleogene,but elsewhere are pervasively cut by high to moderate angle normalfaults which appear to sole into a low angle basal decollement at thebase of the Neogene, and thus the extensional deformation here maybe of limited vertical extent (b10 km, Mazengarb et al., 2001).

Walcott (1987) has suggested that regional uplift in this area maybe a consequence of underplating at the base of the crust where itrests on the subducted Pacic plate, with extension in the Neogene

80

ian

(M

rth

N

Tarakohe Quarry (TAR) , NW Nelson

con). (astralian Plate, with an average clockwise rate of rotation up to the present of ~1/Myr. Theorth5). Ds atom ebased Wclus

143S. Lamb / Tectonophysics 509 (2011) 135164**

-20

0

20

40

60

0 5 10

Austral

Extension in back arc

Age

Dec

linat

ion

devia

tion

from

No

**

*

*

Fig. 6. Plot of deviation of mean declination of magnetisation from True North (with 95%and Wairoa domains, against stratigraphic age of the localities (see Figs. 4, 5a, Table 1areverse polarities plotted separately, lying within error on the expected curve for the AuAustralian Plate curve is best dened by a well constrained ~17 Ma magnetisation in Nmagnetisations in western North Island (locality WAN, Fig. 4, Table 1b, Turner et al., 200the Australian Plate curve, either for individual means of reversed or normal componenteffects of magnetic overprints. (b) Localities from the Wairoa domain (including two frcalculated rotation of the Hikurangi Margin or a line spanning the plate-boundary zone,more weight is placed on a mid to late Miocene magnetostratigraphic study (Wright anwith asterisk), and also three mid Miocene localities that individually show maximum100

120

140

() c

lockw

ise +v

e

Northeastern

Wairoa syncline

Mahia Peninsula

East of Gisborne

Raukumara DomainWanganui (WAN) , western North Island

Local fold testMagnetostratigraphygrouping of all localities older than 10 Ma also show a maximum clustering at 100% unfoldwestern South Island (locality TAR, Fig. 4, Table 1b, Turner et al., 2007), and Plioceneened this way, the localities in the Raukumara domain show about ~10 scatter aboutlocalities, or between localities, which most likely represents incomplete removal of theast of Gisborne and two from coastal Wairoa domain) show close correlation with thed on nite plate reconstructions (see also red and blue curves in Fig. 3). In this respect,alcott, 1986), with sampling every 5 m over 2000 m of stratigraphy (localities markedtering at 100% unfolding (localities marked with crosses, Rowan and Roberts, 2008). A15 20 25

Plate

Raukumara Domain

a)

orth Island

10

Hikurangi Margin

Plate Boundary Zone

Wairoa Domain

dence limits), for localities in the northeastern part of North Island, in the Raukumara) Localities in the Raukumara domain are in the age range 1722 Ma, with normal anding, providing strong support that all magnetisations are primary (see Fig. 8b).

s,

ned

d

144 S. Lamb / Tectonophysics 509 (2011) 13516415 - 25 Ma Mudstone

10 - 16 Ma MudstoIn situ Tilt correcte

In situ Tilt correctecover forming an expression of regional slumping towards the trench(Lamb, 1988; Thornley, 1996).

4.1.1. Paleomagnetic dataFig. 6 shows declinations for 10 paleomagnetic localities in

the Raukumara domain (normal and reverse polarities shownseparately), plotted against stratigraphic age of the sampled sedi-ments, suggesting only small rotation (b20) of crustal blocks relativeto the Pacic plate in the last 25 Ma, with declinations close to thatexpected for the Australian Plate (Table 1a, Mumme et al., 1989;Rowan and Roberts, 2005, 2008; Walcott and Mumme, 1982).

A fold test on all localities in the Raukumara domain showsmaximum clustering for 100% unfolding at the 95% condence level(Fig. 7a), providing strong evidence that the magnetisations areprimary. However, in detail there is about 10 of scatter: localitieswith normal polarity are slightly steeper and less rotated (declinationand inclination is 011/47) compared to reversed localities (decli-nation and inclination is 200/39). This difference between reversedand normal polarity localities is most easily explained by incompleteremoval of a normal modern day overprint on a primary magnetisa-tion that has undergone a small amount of inclination attening,which will tend to steepen and rotate normal polarities slightlytowards north, and atten and rotate reversed polarities slightly awayfrom south.

The best estimate for rotation of the Raukumara domain since theearly Miocene is likely to be the mean of reversed and normalpolarities, which suggests a declination of 015 for an average age of18 Ma, essentially identical to that determined for the Australian Platefor 17 Ma rocks at Tarakohe Quarry in northwestern South Island(Locality TAR in Figs. 4, 6, Table 1b, Turner et al., 2007). In this case, the

Fig. 7. Fold tests for groupings of localities from the Raukumara and Wairoa domains, providwhen these sediments were laid down. Plots have been constructed by generating 10 randomdata. (a) All localities from the Raukumura domain (1525 Ma) showing maximum clustericompared to in situ co-ordinates. (b) Localities from the Wairoa domain older than 10 Mamaximum principal component (1) compared to in situ co-ordinates.1.0

0.8

0.6

0.4

0.2

0.0-20 0 20 40 60 80 100 120 140 160

1.0

0.8

0.6

0.4

0.2

0.0-20 0 20 40 60 80 100 120 140 160

Raukumara Domain

s, Wairoa Domain99 - 119% unfolding

% unfolding1

prin

cipal

com

pone

nt

97 - 121% unfolding

1 p

rincip

al c

ompo

nent

% unfoldingRaukumara domain, despite evidence for pervasive normal faulting, ispart of the TongaKermadec Ridge and has only been translatedduring the opening of the Havre Trough.

4.2. Wairoa domain

The Wairoa domain is a broad regional syncline trending NNE formore than 100 km, foldingMiocene to Pleistocenemarine mudstones,siltstones and sandstones (Fig. 5a, Mazengarb et al., 2001), bounded tothe west by the northern end of the active North Island Shear Belt,where dextral strike-slip faults swing round from a northeasterly tomore northerly trend (Figs. 1, 4 and 5a). Even farther west, there isactive back-arc extension in the Central Volcanic Region, at thesouthern end of the Havre trough this extension terminates about200 km farther south near Mt Ruapehu, resulting in a gradient ofextension which would be anticipated to result in clockwise rotationof both the Wairoa domain and the northern end of the North IslandShear Belt (Lamb, 1988). The nite deformation in theWairoa domainis small (dips generally less than 30), except on its eastern andnorthern margins, and so the domain can be treated as an essentiallyrigid block with horizontal dimensions of ~100100 km and avertical thickness of between 10 and 20 km, underlain by thesubducted Pacic plate (Fig. 1b, Reyners et al., 1999). The easternlimb of the Wairoa syncline, along the coast in the vicinity of theMahia Peninsula, is cut by reverse faults with the development ofsmaller scale fold structures.

4.2.1. Paleomagnetic dataExtensive paleomagnetic sampling of both limbs of the syncline,

including a detailed magnetostratigraphic study of a 2000 m thick

ing strong evidence that the magnetisation is primary, pre-dating folding and acquireddata points for each locality, but with the same locality mean and 95 as the observed

ng for 100% unfolding, with a ~50% increase in the maximum principal component (1), again showing maximum clustering for 100% unfolding, with a ~15% increase in the

lian

(M

n Nlou D

M

h (w, 5a,ringhe p~8nomf rebas

145S. Lamb / Tectonophysics 509 (2011) 135164-20

0

20

40

60

80

100

120

140

0 5 10

Austra

Extension in back arc

Age

NortheasterAnoma

(Wairoa

NR (N)

NR (R)

?NR corrected?MP + TP corrected

?WU corrected WU (N)

MK (N)

Dec

linat

ion

devia

tion

from

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th (

) cloc

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+ve

Fig. 8. Plot of anomalous deviations of mean declination of magnetisation from True Nortthe Raukumara andWairoa domains against stratigraphic age of the localities (see Figs. 4and Roberts (2008) to record Late Miocene or younger magnetic overprints acquired duthe rotation history of the Wairoa domain, compared to that shown by the vast bulk of tcorrected declinations and age of acquisition, dening ~70 of clockwise rotation sinceanalysis of the structure and magnetic sampling at all these localities suggests that the aeffects of secular variation, or are present-day eld overprints, as well as the possibility ofaulting (southeastern part of Raukumara domain), and do not constitute a compellingsequence of middle to Late Miocene sediments, shows that asubstantial clockwise rotation up to 80, relative to True North orthe Pacic plate, has occurred in the last 15 Ma (Table 1a, Figs. 1, 4, 5a,6, Mumme andWalcott, 1985; Rowan et al., 2005; Rowan and Roberts,2005, 2006, 2008; Walcott and Mumme, 1982; Wright, 1986; Wrightand Walcott, 1986). Undisturbed sedimentation occurred in theMiocene and Pliocene during rotation.

Overall, the paleomagnetic data are very coherent, showing aprogressive rotation since ~15 Ma at about 45/Myr relative to TrueNorth or the Pacic plate (Figs. 3, 6), and slightly faster in the last~5 Ma (56/Myr). Thus, 19 out of 21 localities followwithin error thetrend suggested by plate reconstructions for the Hikurangi marginitself (Fig. 6). If these localities are grouped according to age, then it ispossible to carry out a fold test. Thus, for the localities older than10 Ma, there is maximum clustering of locality magnetisations at100% unfolding, again strongly supporting the conclusion that theseare primary magnetisations (Fig. 7b).

4.2.2. Anomalous localitiesFive localities in all from the Wairoa domain and coastal regions

east of Gisborne (Fig. 5a), near the boundary between the Wairoa andRaukumara domains referred to here as anomalous localities suggest rotations in Miocene siltstones and mudstones that are up to~50 larger than indicated by the vast majority of the data for theWairoa domain (localities MK*, NR, MP, TP, WU, Figs. 5a, 8, Table 1a,Rowan and Roberts, 2008).

The anomalous localities form the basis of a very differentinterpretation by Rowan and Roberts (2008) for the rotation historyof the whole Hikurangi margin, in which rotation of the margin isthought to commence in the Late Miocene, around ~8 Ma, with ~70of clockwise rotation subsequently (Fig. 8). This inferred rotationhistory requires regional rotation rates of 814/Myr (Rowan andRoberts, 2008), signicantly faster than the rotation rate of the15 20 25

Plate

a)

orth Islands Dataomain)

P (N)

TP (N) Hikurangi Margin

Plate Boundary Zone

Rotation history for Hikurangi Margin proposed by Rowan and Roberts (2008)

Spread of mean rotations in Wairoa Syncline (Fig. 6)

ith 95% condence limits), for 5 localities in the northeastern part of North Island, fromTable 1a). All these localities, except Locality MK* (Table 1a), were considered by Rowanor after folding, forming the basis of a very different interpretation by these authors ofaleomagnetic data (Fig. 6, pale red zone). Thus, Rowan and Roberts (2008) determinedMa, or an average rotation rate of 814/Myr (shaded trajectory). However, a detailedalous localities are more likely to be a result of inadequate sampling to average out thecording local small block rotation (see text) at the edges of a region of pervasive normalis for a model of rapid and young regional rotation of the whole Hikurangi Margin.Hikurangi margin deduced from the plate motions (45/Myr, Fig. 8),and requiring Late Miocene shortening in the southern part of theHikurangi margin at a rate faster than the plate convergence rate. Forthis reason, it is very difcult to reconcile this tectonic interpretationwith the known geological and plate tectonic evolution, as acknowl-edged by Rowan and Roberts (2008).

Rowan and Roberts's (2008) tectonic interpretation is largelybased on the presence of normal and reversed components in eithersingle localities, or two to three localities up to a few tens ofkilometres apart, that show maximum clustering at less than 100%unfolding, interpreted as secondary magnetisations acquired duringor after folding (Rowan and Roberts, 2008). Folding in the Wairoadomain and farther north affects both Miocene and Pliocenesequences, and yet the mean declinations of magnetisation formaximum clustering of the magnetic overprints at the anomalouslocalities could be taken to infer clockwise rotation in the range of5080, implying a rapid and young rotation history (Fig. 8, Rowanand Roberts, 2008). But other aspects of the structural andpaleomagnetic data at these anomalous localities cast doubt on thistectonic interpretation:

(1) It is unclear whether secular variation is averaged adequatelyin magnetic overprints, because there is no constraint on thetimescale of acquisition of magnetisation. In addition, some ofthe overprints identied by Rowan and Roberts (2005b, 2006)are based on very few sampled horizons (for example, atlocality NR (Fig. 5a), only 3 sampled horizons for the normalcomponent, and 4 sampled horizons for the reversed locality;at WU, the sampling was over only a 7 metre stratigraphicthickness, with an angular dispersion of only ~11 for themagnetisations) suggesting again that some of the discrepancy(especially for Locality NR) could, in fact, just reect inadequatesampling to average out secular variation.

(2) The fold tests applied by Rowan and Roberts (2008) involveonly two or three localities which are widely spaced, up to10s km apart, and ignore the possibility that the magnetisa-tions are not synchronous or the effects of fold plunge or localtectonic rotation. These factors could cause maximum cluster-ing to be at less than 100% unfolding, even if themagnetisationswere acquired prior to folding (Tauxe and Watson, 1994).Simple tests show that even if the remagnetisations wereexactly synchronous, only a 10 fold plunge and/or 10 relativevertical axis rotation could have a signicant effect on theoutcome of the fold tests.

(3) Some of the anomalous rotations could record local largevertical axis rotation of small blocks, especially in the regioneast of Gisborne, which is located where there is dextral shearand at the southern edge of a region of pervasive extension(Section 6.2.1). This way, these data may show how relativerotation between the Wairoa and Raukumara domains hasbeen accommodated by local small block rotation, rather thanrecording the rotation of the whole Hikurangi margin (seeSection 6.2.1).

(4) Magnetisations for four of the ve anomalous localities (i.e.excluding the reversed component at locality NR) are normalpolarity (Rowan and Roberts, 2008) and may just reectcomplex overprints in the present day magnetic eld, unre-lated to tectonic rotation. For example, locality MK* has anuncorrected declination and inclination of magnetisation(022/64) identical to the present day eld in this part of

conict with the vast bulk of the paleomagnetic data, which givemaximum clustering at 100% unfolding, and so it seems safer to leaveopen the question of their interpretation, rather than using them asthe basis of a radically different tectonic interpretation.

4.3. Wairarapa domain

The regions to the south of the Wairoa domain, and east of theNorth Island Shear Belt, form a continuous nearly straight NENNE-trending fold and thrust belt, referred to as the Wairarapa domain(Fig. 4), which has undergone Neogene and active onshore shorteningperpendicular to the structural trend,with about 35 kmof shorteningin the last 1 Ma (Barnes et al., 1998; Barnes and Mercier de Lepinay,1997; Lamb and Vella, 1987; Lee et al., 2002; Nicol et al., 2002, 2007),though normal faulting, which may be part of a regional high-levelslump (Pettinga 1985, Hull 1986), similar to that in the Raukumaradomain, occurs at the northern end.

Deformation along and to the west of the Wairarapa Faultaccommodates a signicant proportion of the component of platemotion parallel to the plate-boundary zone on dextral strike-slipfaults in the North Island Shear Belt (Fig. 4, Barnes and Mercier deLepinay, 1997; Beanland, 1995; Lamb and Vella, 1987). TheWairarapadomain itself consists of large back-tilted blocks (515 kmwidetensof km long and up to 15 km thick) of Mesozoic basement rockscovered mainly by Cenozoic sequences up to 5 km thick, resting onthe subducted Pacic plate (Fig. 1b).

tra

or

)

(Fig

conrrelaotatthe

146 S. Lamb / Tectonophysics 509 (2011) 135164New Zealand and was only identied in a 16 m thick section;the angular dispersion here for magnetisations is low (~9),and the mean magnetisation is markedly different fromdetailed magnetostratigraphic studies involving 1000s m ofstratigraphy in exactly the same region (Wright and Walcott,1986).

Similar problems of interpretation are encountered for a fewlocalities in Miocene mudstones and siltstones from the Marlboroughdomains (see Section 4.4.1), where the origin and signicance ofpossible remagnetisations remain unclear. All these data are clearly in

Wairarapa Domain

RAN

TUR

WANBIR1

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Spread of mean rotations in Wairoa syncline

Fig. 9. Plot of deviation of mean declination of magnetisation from True North (with 95%domainsagainst stratigraphic ageof the localities (see Fig. 4, Table1a). These showa close coplate reconstructions (blue curve in Fig. 3), indicating that theWairarapadomainmayhave rred zone), also supported by evidence for ~10 less rotation for a Late Pliocene locality in

localities BIR and WW13, Table 1a). This difference is most likely because of enhanced rotation4.3.1. Paleomagnetic dataPaleomagnetic sampling in the Wairarapa domain is sparse,

conned to 9 widely spaced localities in Miocene and Pliocenemudstones and siltstones, spread over a 200 km length of theHikurangi margin. Fig. 9 shows a plot of declination against thestratigraphic age of paleomagnetic localities in theWairarapa domain,revealing a progressive rotation with age, following within error therotation history for the plate-boundary zone or Hikurangi margin(similar to that for the Wairoa domain) predicted by plate re-constructions (Figs. 3, 9).

15 20 25

lian Plate

Hikurangi Margin

th Island

Plate Boundary Zone. 6)

dence limits), for localities in the southeastern part of North Island, from the Wairarapationwith thecalculated rotationof a linespanning theplate-boundaryzone, basedonniteed clockwise since the earlyMioceneabout 10 less than theWairoadomain (see Fig. 6, paleWairarapa domain, compared to a similar aged locality in the Wairoa domain (compare

in the Wairoa domain in the last 4 Ma, associated with extension in the back-arc region.

S*

ortharlbom

9

UB

PU

BS

147S. Lamb / Tectonophysics 509 (2011) 135164S

KAIHope F

STR

BIG

WHP

SEY

LOT

DEE*CAV

NMD

Hinge of Little & Roberts (1997)

173E

42.5S

42S

~6

~6

95

54

~5030

95

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9

Wairau F.

Awatere F.

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FC

WV

Keke

rengu

F.The oldest locality in the Wairarapa domain (~24 Ma) is nearly10 Myr older than that in the Wairoa domain (~15 Ma, Fig. 6). So it isunclear whether the total nite rotation since the earlyMiocene (~80clockwise in the Wairarapa domain) is the same as that in Wairoadomain. Indeed, there is a hint that total Neogene rotation in theWairarapa domain might be 1020 less, if the rotation history in theWairoa domain, continuing back through time, closely follows that forthe Hikurangi margin from plate reconstructions (compared to theplate-boundary rotation trend for the Wairarapa domain), reaching~90 clockwise since ~25 Ma (Figs. 6, 9). Further support for thiscomes from the fact that rotation in the youngest locality in theWairarapa domain (locality BIR in Fig. 4, Table 1a, 19.8 relative toAustralian Plate) is indistinguishable from that of the Australian plateitself, whereas a signicantly higher rotation (locality WW13 inFig. 5a, Table 1a, 134.5 relative to Australian Plate) is observed inthe Wairoa domain (Figs. 5a, 6, 9).

4.4. Marlborough domains

The Marlborough fault system marks the southern end of theHikurangi subduction system, where the plate-boundary zone passesthrough continental crust (Figs. 1, 4, 10, 11). Here, the component ofplate motion parallel to the plate-boundary zone is greater than thenormal component, in contrast to the plate-boundary zone further

LYF

SouthernMarlboroughDomain

Average basement structural reference azimuth = 290 - 310(Hall et al. 2004) - See Fig. 12

173E

54

30

18

4.2

CLA

SW

MOT

290

310

Fig. 10. Detailed map of the Marlborough Fault Zone comprising the Marlborough domainsequences, white is basement), basement structural trends (thin dashed lines), and paleomaZone links the southern end of the Hikurangi subduction zone with the Alpine Fault, and consThe marked change in trend of the major Marlborough faults denes the boundary betweena change in crustal block size, from 10 km scale in the northern Marlborough domain, andbasement structural trend (after Hall et al., 2004) and hinge of Little and Roberts (1997), dSV

BB2

CC

BOU

ernorough

ain

Mio

cene

Low

erTe

rtiar

y AmuriLimestone

Alluvium

ConglomerateSiltstone

Siltst./Mudst.

Tectonic rotation

Assumingprimary

magnetisation

HC2HC3DS

174E

42S

*

*

*Volcanics

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Cenozoic stratigraphyPliocene

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WH 60WC3WC1-2

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WD1WD2CS

Hnorth. Major dextral strike-slip faults in the Marlborough Fault Zone(MFZ), extending for over 100 km and spaced 1030 km apart, havestrike-slip rates between 4 and 25 mm/a averaged over the last 10 Kyr(Wallace et al., 2007 and references therein), and accommodate 70100% of the relative platemotion. The nite offsets on individual faults(except the Wairau Fault) are less than ~35 km (Little and Jones,1998), with a cumulative offset of ~60 km (Reay, 1993; Wood et al.,1994). Towards the southwest, the Marlborough faults join thetranspressive Alpine Fault, which is the major feature of the southernpart of the New Zealand plate-boundary zone.

There is a distinct change in trend of the Marlborough faults from~070 in the southwest to ~055 in the northeast, and Lamb (1988)used this to distinguish the northern and southern Marlboroughdomains (Fig. 10). Cretaceous to Cenozoic cover sequences show aregional ~25 tilt within individual fault blocks, and are more tightlyfolded into a regional and faulted anticline (half wavelength ~20 km)at the northern ends of the Clarence and Kekerengu Faults

4.4.1. Paleomagnetic dataPaleomagnetic localities in the Marlborough domains span most of

the stratigraphy of the CretaceousCenozoic cover sequences thatunconformably overly deformedMesozoic basement. Hence, there is amuchwider spread of ages, as well as lithologies, compared to those inthe Raukumara, Wairoa, and Wairarapa domains, including a thick

trend,

Uppe

rCr

etac

eous

Shale

MesozoicBasement

42.5S

174E

* Paleomagnetic samples

*Volcanics

Ma

70

80

90

100

50 km

s, showing the general stratigraphy (see text grey shade on map represents covergnetic localities (with ages in Ma, see Table 1b for locality data). The Marlborough Faultists of 5 major dextral strike-slip faults, with slip rates of 425 mm/yr in the last 10 Kyr.the southern and northern Marlborough domains (Lamb, 1988), which also coincides in110 km scale in the southern Marlborough domain. Note the prominent swing in theening part of the New Zealand Orocline.

80

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on

n 2

witfor

148 S. Lamb / Tectonophysics 509 (2011) 135164Plate Bou

ndary Zoneee

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Verti

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ockw

ise +v

ew

rt Pa

cific

Pla

te

Regi

Regio

Hikurangi M

argin

~80

120 - 140

Elongate blocks in shear zone:

decreasing rotation rate with time

Age (Ma)

Inset (c)

10/Ma

6/Ma4/Ma

2/Ma

Inception ofHikurangi Margin

Australian P

late

Fig. 11. (a) Plot of paleomagnetically determined rotation (with 95% condence limits),domains) against stratigraphic age of the samples (see Figs. 4, 10, Table 1b). Rotationssequence of Late Cretaceous basaltic lavas, Paleogene micriticlimestones and basaltic volcanics, and Late Miocene to Pliocenemudstone, siltstones and sandstones (Table 1b, Figs. 4, 10). Thepaleomagnetism of the rocks, including new data, are described byRandall et al. (2011-this volume), Part 1 and only the mainconclusions are summarised here. All magnetisations are regardedas primary unless indicated otherwise.

Fig. 11 shows a plot of amount of rotation against age for allpaleomagnetic localities relative to the Pacic Plate. Overall, the datasuggest all rotation has occurred in the Neogene, since ~20 Ma, withrotations exceeding 120 clockwise in rocks as young as 17 Ma. Indetail, two distinct regions can be dened: Region 1 which comprisesthe southwestern part of the northern Marlborough Domain, and hasan average rotation rate ~4/Myr since 20 Ma, essentially the same asthe long term rotation rate of the Hikurangi margin (Fig. 11b); Region2 at the northern ends of the major Marlborough faults, where totalrotations are ~130 clockwise, and long term regional rotation rates arein the range of 67/Myr (Regions 1 and 2 in Fig. 11b). The availablepaleomagnetic data suggest that the rate of rotation has variedthrough time, with a decrease in the rate of rotation in Region 1 from~6/Myr in the earlymiddle Miocene (2010 Ma), to 2/Myr or lesssince then (Randall et al., 2011-this volume, Part 1). In Region 2, asimilar decrease in the rate of rotation is apparent prior to thePliocene, with 48/Myr between 20 and 10 Ma, 12/Myr rotationrate between ~10 and ~4 Ma, and rotation rate increasing to ~7/Myrsince ~4 Ma (Fig. 11a and c, Randall et al., 2011-this volume, Part 1).

The southern margin of the zone of rotation, in the southernMarlborough domain, is up to 30 km south of the Hope Fault, dened

rotations are corrected for the apparent polar wander path for the Pacic Plate. Since ~20 Mdetail, the spatial rotation pattern suggests two main regions, characterized by typical averafor Region 1, and pale red zone for Region 2) and dened in (b). Finite plate reconstructions(b) Map of the southern end of the Hikurangi margin, showing the Regions 1 and 2, dened bconned to the extreme northern end of the Marlborough Faults. In addition, the boundary bchange from rotation of small blocks (km-scale) in the south, to larger blocks (10 km-scale) f15 Ma, showing evidence for marked changes in the rate of rotation through time. In Regiorotation rate from ~6/Myr in the earlymiddleMiocene to b2/Myr today, though if little weremaining data. In Region 2, detailed paleomagnetic studies of the Late Miocene stratigrapMiocene, but with a marked increase in the last 4 Ma. These variations in rotation rate candistributed dextral shear, with a higher shear strain in Region 2 compared to Region 1 (see100 120

1

173 174 175

-41

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Paleomagneticlocalities

(b)

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~7/Ma

Small blockrotation

12

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of rotationAverage

clockwise rotation ratesince 20 Ma

-50

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Secondary magnetisations?BIGSTR

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WHP

Lower she

ar strain

Creation of N. Awatere/Clarence equidimensional fault block

~35 Rotation

Higher shear

strain

Rot

atio

n ()

(c)Region 2

Region 1

Regions

h respect to the Pacic Plate, for localities in the Marlborough Fault Zone (Marlboroughlocalities b20 Ma are dened by the mean locality declinations; for localities N20 Ma,by small to negligible declination anomalies for paleomagneticlocalities here (localities MOT, CLA, Figs. 10, 11b). During the last~3 Ma, the eastern margin of rotation in the northern Marlboroughdomain appears to be just east of the Kekerengu Fault, dened bynegligible declination anomalies in Pliocene mudstones at localitiesWD1,2 and CS (Fig. 10, Roberts, 1992; Vickery and Lamb, 1995).However these localities are structurally complex, with dips up tovertical, and it is possible that the fold plunge is incorrectly accountedfor (Table 1b).

There is evidence (Randall, 2007, Randall et al., 2011-this volume,Part 1) that three localities in the Miocene mudstones and siltstones(WHP, STR, BIG, Table 1b, Fig. 10) record pervasive remagnetisations,similar to those found in the Wairoa domain and farther north (seeSection 4.2.2, Rowan and Roberts, 2005, 2006, 2008). Paper 1 arguesfor acquisition of the magnetisation for localities BIG and STR duringthe creation of an overlying angular unconformity at ~9 Ma (shown aslocality BIG*, Table 1b, Fig. 11c).

4.4.2. Rotation of basement structural trendsThe important structural feature of the northern part of the South

Island is the geometry of the Mesozoic basement, which generallydips steeply (N60). In detail, there is marked local variability, butwhen averaged over subregions on a scale up to 10 km (Fig. 12b, Hallet al., 2004; Little and Roberts, 1997), a pronounced 8010 swing instrike becomes apparent (with subvertical average dips), from anazimuth of 30010 in the SE to ~020 farther NW, described indetail by Hall et al. (2004). The greatest curvature is in the vicinity ofthe Hope Fault (Fig. 12b). The large-scale basement structure is also

a, clockwise rotation of crustal blocks has occurred at an average rate of 510/Myr. Inge rotation histories since ~20 Ma and labelled Regions 1 and 2 (shown as solid red linesuggest that the whole Hikurangi margin has rotated at ~4.5/Myr since 20 Ma (Fig. 3).y average clockwise rotation rates since ~20 Ma. The higher rotation rates (~7/Myr) areetween the northern and southern Marlborough domains (heavy dashed line) marks aarther north. (c) More detailed plot of rotation history for Regions 1 and 2 during the lastn 1, a good t to the paleomagnetically-observed rotation data suggests a decrease inight is given to the uncertain result for Locality FC, a constant rate of ~4/Myr also ts thehy show that the rotation rate must have decreased markedly from the early to latebe easily explained as the response of elongate or equidimensional blocks in a zone oftext and Fig. 20cf).

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PaleomagneticLocality

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MOT

Fig. 12. (a) Plot of paleomagnetically determined rotation (with 95% condence limits), with respect to the Pacic Plate, for localities in the Marlborough Fault Zone (Marlboroughdomains) regardless of age (see Figs. 4, 10, Table 1b), against the local structural trend in Mesozoic basement (from Hall et al., 2004; Little and Roberts, 1997), dening part of theNew Zealand Orocline (Fig. 1). Horizontal error bars show where there is marked local variation in basement strike. Rotation of basement structural trends is with respect to thereferenceWNW (290) or NW (310) basement trend observed in Pacic plate rocks south of theMarlborough Fault Zone (Hall et al., 2004; Rattenbury et al., 2006). Localities such as

deteicalluctu

149S. Lamb / Tectonophysics 509 (2011) 135164DEE and CAV are from the interior of Marlborough Fault Zone, and paleomagneticallyTable 1b). Therefore, the close correlation between basement trends and paleomagnetZealand Orocline is Neogene, occurring since ~20 Ma. (b) Detailed map of basement strreected in the trend of the Eskhead subterrane, dening part of theeastern part of the New Zealand Orocline (Section 2.2, Fig. 1a,b, Hallet al., 2004; King, 2000; Sutherland, 1999). A pronounced kink in the

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Fig. 13. Plot of deviation ofmean declination of magnetisation from True North (with 95% conNorthwestern South Island (SI), against stratigraphic age of the localities (see Fig. 4, Table 1bRaukumara domain. Three Oligocene localities, from mudstone and siltstones deposited bet3080 more than expected for the Australian Plate (blue line), given their age. DespiteTauramanui) show rotations expected for the Australian Plate. Assuming the mean magnetirotations here must be Paleogene in age, and had ceased by the early Miocene, recording bstages of the Cenozoic development of the New Zealand plate-boundary zone. The large roOligocene bendings, as suggested by reconstructions of the plate-boundary zone (see Fig. 2rmined rotations up to 120 have been observed in rocks as young as 17 Ma (Fig. 10,y observed rotations strongly suggests that all of the bending in this part of the Newre, from Hall et al. (2004), showing location of paleomagnetic localities plotted in (a).north adds a further ~45 to the basement bending, coinciding withRegion 2 (Figs. 10, 12b, Little and Roberts, 1997), making ~130 oftotal bending in the basement structure (Fig. 10, 12b). Fig. 12a shows

30 35 40 45 50

Age (Ma)

Australian Plate(NW Nelson, South Island and Neogene in western North Island)

Magazine Point, SI

ale, NI Bexley, NI

Inangahua, SIPonganui, NI

aranui, NI

Paleogene bending of Ophiolite Belt, western North Island?

Paleogene and Neogene bending of Ophiolite Belt, near Nelson, South Island?

AU

BEX

PON INA

MAG

dence limits), for localities in theWestern domain, fromwestern North Island (NI) and). Most localities plot on the expected line for the Australian Plate, similar to that for theween 30 and 35 Ma (Magazine Point, Bexley and Bennydale) show clockwise rotationsthis, Miocene (2025 Ma) mudstones and siltstones in the same area (Raurimu andsations for Bennydale and Bexley are primary, averaging out secular variation, then theending of basement terranes such as the Dun Mountain Ophiolite belt during the earlytation recorded at Magazine Point, near Nelson, most likely reects both Neogene and2).

Figs. 4, 13, Mumme and Walcott, 1985). These basement terranes canbe traced into South Island. This continuity in structure clearlydistinguishes this region from the northern Marlborough domain,which is structurally disconnected from the North Island across CookStrait (see Section 6.2.3). Paleomagnetic measurements from Oligo-cene sediments at Magazine Point, just east of Nelson, indicate ~80clockwise rotation relative to the Australian plate in the last 30 Ma(Table 1b, Figs. 4, 13, Mumme andWalcott, 1985). As yet, the numberof studies in these older localities is too few to draw any rmconclusions, and more work is clearly needed to verify these results

Active Faulting 10 Kyrs(Beanland and Haines 1998)

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(b)

BlockPoles

Rotation rate (/Ma)wrt Australian Plate

Displacement wrt Pacific Plate

150 S. Lamb / Tectonophysics 509 (2011) 135164rotation anomalies for Late Cretaceous to Middle Miocene localities,plotted against the average local deviation in strike of the underlyingbasement from the reference direction in the south (azimuth of30010) note the uncertainty in regional basement structuraltrend/rotation where there are local marked variations.

Overall, a 1:1 correlation between the paleomagnetic andstructural measurements provides clear evidence that this part ofthe New Zealand Orocline is the result of Neogene rotation, asinferred by Hall et al. (2004) from paleomagnetic data in the coastalregions (Fig. 12a). The region of large rotations, north of the HopeFault, has effectively behaved as a zone of distributed dextral shear,~100 kmwide (described in Paper 1). This shear zone spans both thesouthern and northern Marlborough domains, and the kinematics ofrotation is controlled by the size, shape and orientation of the crustalblocks (Section 7.2). Thus, the coherent bending of the basementterranes, certainly prior to the development of the present Marlbor-ough Faults in Late Miocene and/or Pliocene (Paper 1), shows thatcrustal blocks in the southern Marlborough domain must be smallerthan the detectable curvature of the basement terrains (110 kmscale), comprising elongate blocks with margins parallel to strati-graphic boundaries. However, the coherent and continuous Cenozoiccover stratigraphy between the major faults in the northernMarlborough domain show that here large elongate blocks, withdimensions 1020 km50 km, have rotated coherently in theprocess, the bounding faults have also undergone a major change inorientation. Rotation of smaller and more equidimensional blocksoccurred at the northern ends of the Awatere and Clarence faults,where rotations up to ~130 clockwise are paleomagneticallyobserved.

4.5. Western domains

The western side of New Zealand, in both the North Island andnorthern part of the South Island, north of the Alpine and WairauFaults, is underlain by Mesozoic and older basement terranes, thatswing round from a SE-trend in the Northland Peninsula to asoutherly, then SW-trend farther south, dening the western part ofthe New Zealand Orocline (Figs. 1, 2, Sutherland, 1999). In the sameway that the eastern part of the orocline, in theMarlborough domains,is a result of Neogene deformation and rotation (Section 4.4.2), it istempting to assume bending on the western side must also haveoccurred on the same timescale. However, paleomagnetic andstructural data suggest a more complicated history (Mumme andWalcott, 1985; Sutherland, 1999).

4.5.1. Paleomagnetic dataFig. 13 shows paleomagnetic localities in the western part of the

North and South Islands. It is clear that most localities, when themeandeclinations are plotted against the stratigraphic age of the localities,lie on the curve predicted for the Australian Plate (Figs. 3, 13). Forexample, west of Nelson, paleomagnetic measurements (localitiesINA and TAR, Table 1b, Fig. 4, Mumme andWalcott, 1985; Turner et al.,2007) show that N-trending Palaeozoic belts and Cretaceous graniteshave not rotated relative to the Australian plate in the last 40 Ma. Themean declination for ~17 Ma locality TAR is based on a detailedmagnetostratigraphic study (Turner et al., 2007), and ~40 Ma localityINA captures the transition from normal to reversed polarity. This lackof rotation is despite the fact that there has been tens of kilometres ofNeogeneWNWNW shortening (Nicol et al., 2007), with a substantialamount in the Plio-Pleistocene. Shortening is actively occurring onNE-trending thrusts and N-trending folds and reverse sinistral strike-slip faults.

Two Paleogene localities (Bexley and Bennydale) in 3035 Mamudstones and siltstones, show evidence of rotation up to 30clockwise, broadly consistent with the swing in trend of basement

terranes from their SW-trend in the Northland Peninsula (Table 1b,172E 174E 176E 178E

Fig. 14. Short term velocity models for North Island, New Zealand. (a) Rigid blocksdened by Wallace et al. (2004) to model ten years of GPS measurements between1991 and 2003. There is a strong component of clockwise vorticity in the GPS velocityeld, consistent with both clockwise rotation of the Hikurangi margin and the obliquityof relative plate convergence. Note that in their model, two blocks (Rauk and AxiR) spanthe entire length of North Island, in marked contrast to the pattern of rotated indicatedby the paleomagnetic evidence (see Figs. 16, 17). (b) Velocity eld based on smoothedpattern of active faulting, averaged over the last 10 kyr, after Beanland and Haines(1998), indicating more rapid rotation relative to the Australian plate of the Wairoadomain (4.31/Myr), compared to the Wairoa domain (1.50.6/Myr), essentiallythe same as that shown in Fig. 17, and in good agreement with the rotation from

paleomagnetic data.

and determine their regional signicance. But they are consistent withPaleogene bending, prior to ~25 Ma, in western North Island, and bothPaleogene and Neogene bending in South Island east of Nelson, but noCenozoic rotation, relative to the Australian Plate, of South Islandwest

marked west to east gradient of increasing rotation is surprising,because of the lack of known deformation structures in this regionthat could accommodate this rotation the maximum amount ofclockwise rotation here is essentially the same as that observed for the

N

100 km

(a) (b)

Australian Plate fixed

Pacific Plate fixed

25

1035

Fig. 15. Displacement eld for the Hikurangi Margin over to past 4 Myr (in a present day reference frame), based on a block reconstruction at 4 Ma by Lamb (1988), constrained bynite plate motion, the displacements on the major faults, and assuming rigid body rotation of crustal blocks consistent with paleomagnetic observations: 25 clockwise for theWairoa domain, 10 clockwise for the Wairarapa domain, 2035 clockwise for parts of the northern Marlborough domain, relative to Pacic Plate. (a) Displacements relative toAustralian Plate. The marked swing in displacements is very similar to that suggested by the pattern of active faulting (see Fig. 14b), and is an inevitable consequence of back-arcextension in the northern part of the Hikurangi margin, and margin parallel dextral strike-slip with some orthogonal compression farther south. (b) Displacements relative to thePacic Plate; the swing in displacement to more nearly orthogonal to the trend of the subduction zone suggests partitioning of plate convergence to more nearly plate normalconvergence near the trench, and margin parallel dextral shear at the back of the deforming wedge, accommodated by both margin parallel dextral strike-slip and clockwise rigidbody rotation of crustal blocks resting on the subducted slab.

a D

151S. Lamb / Tectonophysics 509 (2011) 135164of Nelson (Figs. 4, 13, Section 6.3).In North Island, at the southern end of the Central Volcanic Region,

three major magnetostratigraphic studies in ~2000 m thick sectionsthrough Pliocene mudstones (2.63.6 Ma) along the Wanganui,Turakina, and Rangitikei Rivers, south of the Central Volcanic Region(Fig. 4, Turner et al., 2005; Wilson and McGuire, 1995) have revealedwell-constrained vertical axis rotations relative to the Australian platethat progressively increases towards the east, from essentially zerorelative to the Australian Plate (110) at the Wanganui River, to~5 clockwise about 20 km farther east, at the Turakina River, to ~7clockwise at the Rangitikei River, about 30 km even farther east. This

30.0Wairo-5.0

0.0

5.0

10.0

15.0

20.0

25.0

100 200 300Distance (km)

Velo

city

(mm/

yr)

A

2.5/Ma

4.7/Ma

South

Wairarapa Domain

Fig. 16. Rigid body orthogonal velocity proles (relative to Australian plate) along the Hikurarotation rates of themargin and an origin at point A. The red line shows a hypothetical velocitand Raukumara domains suggested by paleomagnetic data and active fault kinematics notFigs. 14b, 17). Blue line shows velocities forWallace et al.'s (2004) inferred single Rauk blocktrue pattern follows the red line, with 1-sigma velocity observational uncertainties of 3reduced Chi-squared t for a single block is 0.2. In other words, at this uncertainty level, it is neld, and the detailed pattern of tectonic rotation is essentially unresolvable with very shomeasurements on Pliocene sediments, is a much better guide to the pattern of active rotatisame period in the Wairarapa domain, relative to the Australian plate(see Section 6.2.2).

5. Act