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Structural analysis of a middle Cretaceous accretionarywedge, Wairarapa, New ZealandPhilip M. Barnes a b & Russell J. Korsch a ca Department of Geology , Research School of Earth Sciences Victoria University ofWellington , P.O. Box 600, Wellington , New Zealandb Department of Scientific and Industrial Research , New Zealand Oceanographic Institute,Division of Water Sciences , Private Bag, Kilbirnie , Wellingtonc Bureau of Mineral Resources , GPO Box 378, Canberra , 2601 , AustraliaPublished online: 17 Jan 2012.

To cite this article: Philip M. Barnes & Russell J. Korsch (1990) Structural analysis of a middle Cretaceousaccretionary wedge, Wairarapa, New Zealand, New Zealand Journal of Geology and Geophysics, 33:2, 355-375, DOI:10.1080/00288306.1990.10425693

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New Zealand Journal o/Geology and Geophysics. 1990. Vol. 33: 355-375 0028-8306/90/3302-0355 $2.50/0 © Crown copyright 1990

355

Structural analysis of a middle Cretaceous accretionary wedge, Wairarapa, New Zealand

PHILIP M. BARNES1

RUSSELL J. KORSCH'­

Department of Geology Research School of Earth Sciences Victoria University of Wellington P.O. Box 600 Wellington, New Zealand*

*Present addresses: lNew Zealand Oceanographic Institute, Division of Water

Sciences, Department of Scientific and Industrial Research, Private Bag, Kilbirnie, Wellington.

2Bureau of Mineral Resources, GPO Box 378, Canberra 2601, Australia.

Abstract The middle Cretaceous (Motuan) Mangapokia Formation near Te Awaiti, southeast North Island, New Zealand, is a complexly deformed, weakly metamorphosed, submarine fan turbidite sequence that represents the youngest part of the Torlesse accretionary wedge.

Two fold events, several episodes of shear fractures, and local development of melange fabric were associated with Cretaceous subduction and accretion. Fl folds occur within melange fragments and predate regional stratal disruption and melange formation. The melange fragments were rotated during formation of melange. Isoclinal to tight, predomin­antly asymmetric, overturned, meso scopic F 2 folds developed during accretion but after pervasive stratal disruption and melange formation. Fold axes trend northeast-southwest and plunge variably to the northeast or southwest.

Two later fold events are post-Torlesse, probably late Cenozoic responses to Miocene-Recent subduction at the Hikurangi Margin. Mesoscopic and macroscopic, upright, predomin-antly close to open F3 folds overprint and interfere with the Cretaceous folds and associated structural fabrics, and dominate the regional structural grain. F3 hinge planes trend northeast-southwest, axes plunging to the northeast or southwest; their trend is spread by up to 80° as a result of an F4 fold event. Mesoscopic and macroscopic, open to gentle, upright F4 folds, best developed in the east, strike pre­dominantly northwest-southeast, and plunge variably to the northwest or southeast. Dome and basin structures result from interference between F4 and F3.One macroscopic F4 fold, the Te Awaiti Syncline, has affected most of the Te Awaiti area. Late Cenozoic folds with northwest-southeast orientations have not previously been recorded in eastern Wairarapa. The folds are most likely crossfolds that formed almost simultaneously with F3 folds during a single phase of deformation. Quaternary deformation includes tilting of the region on northeast-south west-trending growing folds.

G89051 Received 28 August 1989; accepted 2 February 1990

Keywords Cretaceous; structure; subduction; accretionary wedge; Wairarapa; Torlesse; Mangapokia Formation; geometric analysis; folds; melange; New Zealand

INTRODUCTION

In eastern Wairarapa, the Early Cretaceous Pahaoa Group consists of the Mangapokia and Taipo Formations, which are complexly deformed sequences occurring almost contin­uously for a distance of 140 km within the East Coast Deformed Belt (Moore & Speden 1979, 1984). Near Te Awaiti (Fig. 1), the Mangapokia Formation consists of Motuan (middle Cretaceous) poorly fossiliferous, trench-fill, submarine fan, turbiditic, feldspatholithic sandstone, mudstone, and conglomerate of mixed volcanic and sedimentary provenance (Barnes 1990) along with minor ocean-floor material (basalt, chert, red and green mudstone, and limestone) of unknown age that is restricted to melange zones. The rocks have been interpreted as being the youngest part of the Torlesse accretionary wedge in southern North Island (Barnes 1985, 1988).

D Post-mid Cretaceous

~ Jurassic-mid Cretaceous

D Torlesse accretionary wedge

Fig. 1 Simplified geological map of southeast Wairarapa, showing the distribution of the Torlesse terrane, and location of the study area.

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- --= Bedding form line

~:::::::=~ Shea~ ~oliation in melange . contalnmg ocean· floor matenal

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-+ Numerous small scale F, folds

~ Numerous small scale F. folds

-Fault

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New Zealand Journal of Geology and Geophysics, 1990, Vo1. 33

0.5 I

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Fig.2 Form surface structural map and cross-sections oftheTe Awaiti area, Details of inset areas are presented on Fig, 4, 5, 6, 7 and 13, and are discussed in the geometric analysis,

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Barnes & Korsch-Structure of accretionary wedge, Wairarapa

PACIFIC OCEAN

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Fig. 2 (continued).

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358 New Zealand Journal of Geology and Geophysics, 1990, Vol. 33

10 Recent tilting by growing regional folds.

9 Mesoscopic faults at high-angles to bedding .

Fig. 3 Defonnational history of the Te Awaiti area, southeastNorth Island. Sketches illustrate the development of structures. S1-S4 are axial surfaces of F CF4 folds.

• F, opo.to .. ",.m",_o~dm,,_I0". _::

7 F, "."010 ,,,,,. m .. """,,o ond """"""". 10'''. ,~.

6 F 2 isoclinal to tight mesoscopic folds.

5 Regional shearing and disruption via bedding-parallel shears, and cOmpressional and extensional faults at low- and high-angles to bedding. Local development of melange fabric.

4. Extension to produce complex fracture pattems and veins.

3 F 1 isoclinal to gentle mesoscopic folds.

2 Development of extensional (transposition) fabric of unknown areal extent.

1 Syn- or post depositional slump folds (i.e., Pre-tectonic).

The structure of Mangapokia Fonnation near Te Awaiti is complex; four generations of tectonic folds (F1-F4) and several episodes of faulting have been recorded (Fig. 2). Exposure is excellent and several macroscopic folds are recognised. Bedding is variably sheared and disrupted, and melange fabric occurs locally. Bedding orientations vary from horizontal through vertical to overturned with gentle dips. Nevertheless, moderately dipping upright beds predominate. The rocks are metamorphosed to at least the zeolite facies of Coombs et al. (1959). A discussion of the mechanisms of stratal disruption and melange fonnation, of the early defonnational history of the rocks, and of a comparison of the structural history at Te Awaiti with structural histories detennined elsewhere in the Torlesse by other workers will be presented elsewhere. The aim of this paper is to undertake a structural analysis of these intensely defonned rocks, including descriptions of the geometry of the mesoscopic and macroscopic structures of Mangapokia Fonnation. Fold description follows Fleuty (1964) and Ramsay (1967). Structural nomenclature follows the standard procedures outlined by Turner & Weiss (1963). The data are plotted on equal area projections (Schmidt nets) and, for many readings, the density distribution was detennined

by contouring using the square-grid method of Stauffer (1966). S2-S4 are axial surfaces of folds, not penetrative fabrics.

DEFORMATIONAL mSTORY

The defonnational history of the Torlesse accretionary wedge near Te Awaiti is summarised in Fig. 3. An early extensional fabric is overprinted by F1 folds that were later dissected by tensional fractures and veins. These early structures were observed in melange inclusions and all predate regional stratal disruption and melange fonnation Barnes (1985). Structures associated with regional disruption include attenuated beds, boundins, "pinch and swell" structure, tectonically elongated conglomerate clasts, lozenge (transposition) fabric, and tectonic melange. The varying states of disruption represent arbitrary stages in a progressive structural continuum. The most defonned sequences reached their fabric via a combination of repeated movement on shears subparallel to bedding, thrusts and nonnal faults at low angles to bedding, and reverse and nonnal faults at high angles to bedding. The melanges are tectonic, rather than sheared, chaotic sedimentary deposits. Tectonic disruption

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Barnes & Korsch-Structure of accretionary wedge, Wairarapa 359

probably occurred through a range of consolidated to semi­indurated physical states by a combination of intergranular flow and cataclasis. Melange units containing exotic ocean­floor (basalt, chert, red and green mudstone) lithologies occur as sheet-like bodies 2-25 m thick. They are inferred to represent basal thrusts of imbricated packets of strata ranging from tens of metres to hundreds· of metres thick. Detailed descriptions of the events labelled 2-5 in Fig. 3 will be presented elsewhere.

By the end of event 5 (Fig. 3) the rocks consisted of dis­rupted sedimentary sequences and melange (Barnes 1985). The shear foliation in the melange was subparallel to the bedding in the disrupted sedimentary sequences. Thus, at that time, an essentially planar fabric existed, upon which later deformations were superimposed. This factor has enabled us to undertake a classical Turner & Weiss (1963) type structural analysis on these complexly deformed rocks.

The sixth event (Fig. 3) was the formation of isoclinal to tight, predominantly asymmetric, mesoscopic F* folds that developed after the initial pervasive disruption ot strata, but during continued accretion and imbrication of thrust-bound packets. The first six events in Fig. 3 produced structural fabrics typical of sediments deformed in accretionary wedges (Barnes 1985), and they are inferred to have occurred during middle Cretaceous subduction. Later events produced structures common in late Cenozoic sequences in eastern North Island, and they are probably Late Tertiary and Quaternary responses to the present convergent regime at the Hikurangi Margin (pacific-Australian plate boundary).

FOLDING

Pretectonic structures are rare, being represented mainly by soft-sediment slump folds within channel-fill, matrix­supported conglomerate facies. Some tight folds in sandstone layers appear to "float" within a coarse-grained sandy matrix, and small, tight folds in horizontally laminated sandstone fragments are ripped up and incorporated into pebbly mud­stone (Barnes 1988).

Mesoscopic tectonic folds are abundant and most commonly developed in thin- to medium-bedded alternating sandstone and mudstone facies and thin conglomerate beds. In contrast, thick-bedded sandstone units are rarely folded mesoscopically, and in facies with high mudstone contents, shear-related structures predominate. Four generations of tectonic folds are recognised. One generation predates formation of melange, and three postdate the melange. Photographs of the folds will be presented elsewhere, and for full descriptions of them refer to Barnes (1985). Only a brief summary will be presented here.

Rare, premelange, mesoscopic Fl folds occur within discrete melange fragments. The folds developed in bedding that displays various stages of extensional, fault-controlled disruption, ranging from attenuated but relatively coherent to thoroughly disrupted fabrics. The folds have limbs truncated by shear-foliation within the surrounding argillaceous melange, suggesting that they developed prior to the inclusions being incorporated within the melanges.

F2 folds are extremely numerous and also have been recognised only on a mesoscopic scale. They postdate the completion of regional stratal disruption and melange development (Fig. 3). The folds have variable style with interlimb angles ranging from about 85° to isoclinal. Inclined,

gently plunging folds predominate, and upright, gently to moderately plunging folds are less numerous.

F3 folds are common throughout the area, and in many exposures are the dominant mesocopic structures. Macroscopic F3 folds are common, and hinge regions can be traced for up to 1 km (Fig. 2). The folds occur in all lithologies, have variable style, and refold and overprint F2 structures. The melange zones are also folded by this phase. Generally they are more open and less asymmetric than F2, and usually differ significantly in orientation from overprinting, F4 structures. Upright to steeply inclined, subhorizontal to moderately plunging folds predominate. They are nearly coaxial with F2, and locally are developed on the overturned limbs of F 2 structures. Hence, they include synclinal antiforms and anticlinal synforms.

Mesoscopic F4 folds are best developed and most easily identified in the east where their axial traces are oriented at high angles to the regional bedding trend (Fig. 2). The folds refold and overprint F 2 and F 3 structures, and also are locally developed on the overturned limbs ofF2 folds.

GEOMETRIC ANALYSIS

Fl folds are superimposed on an early broken formation and were observed within fragments in melange produced during regional pervasive disruption. The fragments are surrounded by penetratively sheared argillaceous matrix and were probably rotated and translated significantly during the formation of the melanges. Hence the orientations ofF 1 folds and associated fractures are now meaningless in terms of a geometric analysis. The F2, F3, and F4 fold events are superimposed upon an extensional fabric (S r). They developed after regional disruption and melange formation, and their present orientations have been analysed.

Four, small coastal areas are described in detail, followed by a macroscopic geometric analysis for the whole area. Exposure in each detailed area is sufficient to allocate most mesoscopic structures to fold generations on the basis of overprinting relationships alone. Correlation of structures between areas then allows examination of the style changes between different fold generations, the variations within single generations, and the orientation patterns of different structures. Thus, the method is useful for unravelling the structural complexity of the whole Te Awaiti area. In each detailed area studied, sandstone beds are variably attenuated and fragmented, contacts between sandstone and mudstone lithologies are commonly sharp, and most mudstone units have been intensely sheared and preferentially eroded out

Area A Area A represents about 600 m2 Of coastal platform at G.R. S28B/2392651O (grid references refer to the NZMS 260 map series) (Fig. 4). Well-bedded, alternating sandstone and mudstone, with an average bed thickness of 100-150 mm have undergone at least two periods of folding (F2 and F3). The exposure is dominated by a refolded F 2 fold. F 2 axial surface traces are refolded by gentle to open F3 folds whose subvertical axial surfaces trend northeast-southwest. The F2 folds are asymmetric, tight to isoclinal, and S-shaped with overturned short limbs. Poles to axial surface of the F 2 folds (S2) define a partial great circle girdle, indicating that S2 has been folded cy lindrically about a 1t-axis (B~ ~ ) oriented 30° to 040°.

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New Zealand Journal of Geology and Geophysics, 1990, Vol. 33

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Barnes & J(orsch-Structure of accretionary wedge, Wairarapa 361

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All F3 folds plunge gently or moderately to the northeast and are mainly symmetrical, reflecting their position close to the hinge region of a macroscopic F3 fold (Fig. 2). Hence they can be distinguished from F2 on the basis of style and orientation of axial surfaces. The small spread in orientation of F3 fold axes (B ~]) and axial surfaces (S3) reflect small variations in the orie~tation of So prior to the F3 event. Poles to So defme a partial great circle girdle (Fig. 4). The 1t-axis is oriented 32° to 046°, and coincides with both the F2 and F3 fold axes. The spread of bedding is similar to that of the S2 axial surfaces and reflects the F3 event.

AreaB Area B (Fig. 5) represents a 4500 m2 segment of coastal platform 1.1 kIn east of the Oterei River mouth (Fig. 2). Here, alternating sandstone and mudstone have been deformed by at least two periods of folding (F3 and F4). Rare younging directions suggest an upright sequence. Axial traces of the predominantF3 folds trend northeast-southwest, and those of F4 trend northwest-southeast (Fig. 5). Poles to So define a great circle girdle with a 1t-axis oriented 12° to 033°.

F3 folds are slightly asymmetrical with subvertical axial surfaces, and interlimb angles ranging from 40° to 156°

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Barnes & Korsch-Structure of accretionary wedge, Wairarapa 363

(Fig. 5). The trends ofF3 are spread through 75°, reflectin¥, redistribution by F4 folding. The 1tSo-axis coincides with B s! and reflects F 3 folding. F 4 folds have interlim b angles ranging from 120° to 166° (Fig. 5). Hence, although the average F3 and F4 interlimb angles vary significantly (117° and 152°, respectively), their overlap prevents .differentiation by style alone. Although most F 4 folds were observed on the northwest­dipping limb of the dominant F3 anticline (Fig. 5), their significant variation in plunge results from folding of a nonplanar form surface (So>. The superposition ofF4 upon F3 folds has produced one mesoscopic near-symmetrical dome structure in the southeastern part of the area (Fig. 5), and an elongate, mesoscopic, double-plunging anticline, c. 15 m in length, about 30 m northeast of the sketch map (G.R. S28B/ 26306617).

AreaC Area C represents a 2300 ml segment of coastal platform exposure centred on G.R. S28B{l4oo6512 (Fig. 6). Well­bedded, alternating sandstone and mudstone have been deformed by at least three periods of folding (F l-F4). Poles to beddin!!s define a great circle girdle with the 1t-axis coinciding with B s! (Fig. 6); hence the bedding pattern on the net is controlled mainly by the F3 event.

Fl folds have a similar style to those in area A, and form an S-shaped couplet. The shared limb of this fold represents the only overturned beds in this area (Fig. 6). F3 folds, with interlimb angles ranging from 94° to 172° (av. 138°, Fig. 6) are the largest and predominant structures. Refolding ofF3 by cylindrical F4 folds has resulted in 75° variation in the strikes of S3. Poles to S3 define a partial great circle girdle with subvertical 1t-axis (B~:). F4 folds have interlimb angles ranging from 123° to 174° (av. 149°), with considerable overlap to the F3 folds (Fig. 6). B~: fold axes mainly plunge gently to the east although the data are biased because most of the F4 folds were measured on east-dipping limbs of F3 folds.

AreaD Area D represents a 6200 ml segment of coastal platform centred on G.R. S28B{l3776504 (Fig. 7). The sequence represents an overall coarsening -upward, 100m thick channel complex consisting of coarse to fine-grained, predominantly clast-supported conglomerate, and alternating sandstone and mudstone (Barnes 1988). Mesoscopic folds and faults are common, and three generations of folding (Fl' F3, F4) are inferred (Fig. 7). The area has been subdivided into two structural domains (D 1 and D2) differentiated on the basis of

S O~3 d S .. . 1t 0' ~o ,an 30nentatlons. Fl folds are rare and identified tentatively on the basis of

style and orientation of axial surfaces; no overprinting relationships were observed. The folds have interlimb angles ranging from 47° to 86° (Fig. 7), and are associated with the only overturned beds in the area. F3 folds are common, particularly in the alternating sandstone and mudstone lithologies at the base of the sequence (domain Dl, Fig. 7). The folds have interlimb angles ranging from 96° to 172° and axial traces up to 30 m in length. They die out up and down the axial plane. Bends in F 3 axial traces suggest that B ~! axes may have been redistributed by a later deformation, although it is possible that F3 could have folded a nonplanar form surface. The two 1tSo-F,:es have slightly different orientations, corresoondinl!: to B <;:~ in their resoective domains (Ph!;. 7).

This indicates that the original orientations of B~ 3 fold axes have been modified, not only within each doma'l.n but also between domains D 1 and D2, and that bedding orientations reflect mainly the F3 event. In domain Dl, poles to S3 show significant spread around a partial great circle girdle whose 1t­axis plunges very steeply to the southeF.t. This is coincident with the intersection of S3 and S 4 (i.e., Bs: ). In domain D2, the pole plunges steeply to the north.

Synopsis of areas studied in detail Synoptic, equal area projections (Fig. 8) and Table 1 summarise the data from the areas studied in detail. The 1tSo-axes plunge gently to the northeast and east coinciding broadly with both Fl and F3 fold axes. Fl poles to axial surfaces (Sl) define a partial ?!feat circle girdle whose 1t-axis coincides with F 3 fold axes (Bs!, Fig. 8). Hence the girdles in both 1tSoand 1tSl can be related to the F3 fold event. The predominant F3 folds are upright with subvertical axial surfaces; fold axes (B ~!) plunge gently or moderately to the northeast and show considerable variation in trend. Local overprinting ofF3 by F4 folds, and the subisoclinal nature of F 1 folds, indicates that the large variations in the strike of S3 and trend of B ~! axes results mainly from the F4 event, rather than F3 folding a nonplanar form surface. The superposition of F4 upon F3 folds locally produce dome structures and double-plunging anticlines. Uyright, gentle F4 folds have variably plunging fold axes (B~: ) lying in a WNW -ESE plane because they developed in a bedding surface that was nonplanar after the F3 event.

MACROSCOPIC GEOMETRIC ANALYSIS

Outside of the areas examined in detail, exposure is not everywhere sufficient to allow use of overprinting relation­ships. Hence, folds of different generations often had to be identified on the basis of style and orientation patterns. Williams (1970, 1985) and Mosher & Helper (1988) discussed the problems of correlation on the basis of style alone. Nevertheless, as discussed by Hobbs et al. (1976), in the absence of better criteria, it is necessary to use style in association with any other supporting evidence, such as orientation patterns or metamorphic assemblages, to correlate between fold generations. Overprinting relationships were observed at many localities throughout the study area and, in each case, the validity of style groups and orientation patterns were checked.

Regional bedding trends (Fig. 2) define numerous macroscopic folds and a gross change in strike from north-south in the west, to northeast-southwest in the east. The Te Awaiti area has been divided into 12 structural domains (Fig. 9 and 10) on the basis of homogeneity of 1tSq (see method in Turner & Weiss 1963). The geometry ot structures in domains 3 and 4 is discussed below. In domain 3, structures in melange differ significantly from those in the enclosing sedimentary sequence, whereas domain 4 is an example of redistribution of F 1 structures during later folding. A synopsis only is presented here for the remaining domains (for full details see Barnes 1985).

Domain 3 - melange crosscutting coherent strata Domain 3 represents a strip of coastal platform adjacent to the Waikowhai Stream mouth (Fig. 9). The upright sedimentary sequence, cut by a 5-10 m thick melange zone (section GH,

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Fig

. 7

Fon

n su

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ural

map

(A

). eq

ual

area

pro

ject

ions

of

stru

ctur

al

!!'

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5

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old

axis

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). a

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) ofF

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in a

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Fig

. 2)

. N

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n lo

wer

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s $=

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com

er o

f ste

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ets

are

the

num

ber o

f obs

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tions

; num

bers

on

low

er ri

ght a

re

z <:

'so

,ao

th

e co

ntou

r in

terv

al i

n %

per

1 %

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a. C

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pace

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60

90

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are

for

coa

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VJ

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erat

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cies

_ V

J

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Tab

le 1

S

umm

ary

of t

he g

eom

etri

c an

alys

is o

f det

aile

d ar

eas

A-D

. S

ee F

ig.

2 fo

r lo

cati

ons.

Hor

izon

tal l

ines

cor

rela

te s

truc

tura

l com

pone

nts

in d

iffe

rent

are

as. T

he S

com

pone

nt in

clud

es a

be

ddin

g-pa

rall

el s

hear

fabr

ic.

The

F, f

old

even

t is

not r

ecog

nise

d in

any

of

the

area

s. I

nt. p

att.

= I

nter

fere

nce

patt

erns

. 0

So

(Sir

)

F2

BS

2 So

S2

F3

BS

3 So

BS

] S2

S3

F4

BS

4 SO

BS

4 S2

BS

4 s]

S4

Int.

p

atl

AR

EA

A

Dip

s pr

edom

inan

tly

NE

, lo

call

y ov

ertu

rned

1tS o

= 32

° to

046

°

Tig

ht-i

socl

inal

ove

rtur

ned,

as

ymm

etri

c S

-fol

ds

Plu

nge

gent

ly N

E, s

mal

l sp

read

D

ip g

entl

y-m

od. N

NW

-NE

1t

S 1 =

30°

to 0

41 °

Gen

tle

to o

pen,

sym

met

rica

l

Plu

nge

gent

ly N

E, s

mal

l sp

read

3

0 to

041

°

Sub

vert

ical

, ~W s

trik

e m

oder

ate

spre

ad

Typ

e 3

of R

amsa

y (1

967)

R

efol

ded

F 1

fold

s

AR

EA

B

Dip

s pr

edom

inan

tly

NW

and

SE

1t

S o = 1

0° t

o 03

4°

Gen

tle

to c

lose

, as

sym

etri

cal

Plu

nge

gent

ly N

E, r

arel

y SE

, la

rge

spre

ad

Not

obs

erve

d

Subvertical,~W.~ge

spre

ad, v

erti

cal

axis

Gen

tle,

sym

met

rica

l

Plu

nge

pred

omin

antl

y N

W,

rare

ly S

E

N/A

Sub

vert

ical

Sub

vert

ical

, str

ike

NW

-SE

sl

ight

spr

ead

Dom

e st

ruct

ures

and

refo

lded

fo

lds

AR

EA

C

Dip

s pr

edom

inan

tly

gent

ly N

E

1tS o =

12°

to 0

45°

Rar

e, t

ight

, ov

ertu

rned

, S

-fol

ds

Plu

nge

gent

ly E

Str

ike

N-S

, dip

mod

erat

ely

E

Ope

n to

gen

tle,

sym

met

rica

l

Plu

nge

gent

ly N

-E,

larg

e sp

read

N

/A

Sub

vert

ical

, str

ikes

NE

-SW

, S

E s

teep

ly d

ippi

ng a

xis

Gen

tle,

sym

met

rica

l

Plu

nge

pred

omin

antl

y ge

ntly

E

, rar

ely

W.

Sli

ght s

prea

d N

/A

Plu

nges

ste

eply

SE

Sub

vert

ical

, E-W

str

ike

Ref

olde

d F

3 fol

ds

AR

EA

D

Do

mai

nD

l

Dip

s pr

edom

inan

tly

NE

1t

S o =

22°

to 0

68°

Dom

ainD

2

Dip

s ge

ntly

E,

1tS o

= 22

° to

093

°

Clo

se, s

ymm

etri

cal,

upri

ght

Clo

se o

vert

urne

d

Plu

nges

60°

to 3

56°

Plu

nge

gent

ly E

Str

ike

E-W

, di

p m

oder

atel

y N

S

trik

es p

redo

min

antl

y E

-W

Ope

n to

gen

tle

Plu

nge

pred

omin

antl

y ge

ntly

N

E, l

arge

spr

ead

N/A

Str

ikes

E-W

, sub

vert

ical

ax

is

Gen

tle,

upr

ight

N/A

N/A

Plu

nge

stee

ply

to m

oder

atel

y E

Sub

vert

ical

, str

ikes

SW

-SE

Ope

n to

gen

tle

Plu

nge

pred

omin

antl

y ge

ntly

E,

mod

erat

e sp

read

N

/A

Str

ikes

E-W

, sub

vert

ical

. 1t

S 3 =

80°

to

030°

Gen

tly

war

ped

F3 a

xial

su

rfac

es

tP 3 ('

I) '" R:c ~ n I ~ ~ g, g s. o ~ ~ i ~ ~.

.§

I\) ~

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366

N

New Zealand Journal of Geology and Geophysics, 1990, Vol. 33

partial great circle girdle with a 1t-axis (B ~D oriented 74° to 234°, whereas in a second refolded fold (Fig. llC), an inferred B ~~ axis is oriented 50° to 192° (Fig. 10, 1tS2 points labelled as "2"). Poles to all other S2 surfaces define a great circle girdle with 1t-axis oriented 40° to 081 0. This girdle has a simi~ orientation to that in S sf and thus is probably related to F3 (FIg. 10).

Ss, S,

24

180

,. .. ... ..

34

+

......

+

+

.....

;~.I •• •• ';..r", • ... :~~

;. '-"~ • ·ot"'f~ •

. :.~! .'.

." . -': ..

N

. \ .\.~ + . \

\ ... \ . '.~I, . , , . "­.. "-. ~~

+

• B~: approx.

Fig.8 Synoptic equal area projections of structural components in areas A-D. Numbers in the lower left comer of nets are the number of observations.

Fig. 2), contains numerous F3 folds (Fig. 10). The 1tSo-axis, oriented 20° to 078°, coincides with the predominant F3 axes. The F4 event is inferred to have modified the orientations of S3 and B~! axes. In the melange (G.R. S28B/23346500) the shear-foliation is complexly folded; the folds developed after formation of the melange. Poles to S~ defme a great circle girdle with a 1t-axis oriented 60° to 072 ,coinciding with both the F2 and F3 fold axes (Fig. 10). The F2 folds are isoclinal; thus Sif was essentially planar after the F2 event. Therefore, this girdle probably is related to the F3 event.

Locally, F 2 folds are refolded by F 3 and F4 folds (Fig. 11). As a consequence, B~2 is distributed along a northeast­southwest-striking girdfe. Poles to S2 from one refolded fold (Fig. llA; 1tS2 points labelled as "I" on Fig. 10) defme a

In contrast to the enclosing sedimentary sequence, F3 folds in the melange range from isoclinal to open, and hence cannot be distinguished confidently from F2 on the basis of style alone. Since F3 folded a shear-foliation that was effectively planat after the F2 event, the variable orientation of B~! fold axes in the melange must reflect a later deform-ati~n. Open to gentle F4 folds were observed in Sif and in S2 (FIg.lIC) .

The great circle for 1tS.f in the melange has an almost identical strike to the great circle for So in the enclosing sedimentary sequence. However, the 1t-axes plunge at 60° and 20° respecti vel y (Fig. 11); this indicates that, although the melange has a parallel strike to adjacent bedding, it has a steeper dip, and hence must truncate the bedding at an acute angle. B ~ 3 axes are more steeply plunging than B~! because they fomi~d in an original surface (S.) that was more steeply dipping than So.

Domain 4 - F z folds refolded by F 3 and F 4

Domain 4 (Fig. 9) is homogeneous with respect to 1tSo' B ~~ and B~: ' but five subdomains (4A-E) can be recognised on the basis of 1tS2 (Fig. 12J. The 1tSg1-axis is oriented 32° to 036°, coinciding with both B s 2 and Bs ~ axes. F3 folds are common on a macroscopic scale °(Fig. 2) and, hence, the girdle in So probably results predominantly from F . F folds occur within melange fragments at G.R. S28B/22~96545, but their orientations cannot be used in the geometric analysis because of probable rotation of the fragments. Overprinting relationships are common in the Waikowhai Stream (Fig.l3).

In each of the subdomains 4A-E (Fig. 12), poles to S2 define full or partial great circle girdles, indicating that S2 was folded cylindrically and that within individual subdomains Sz was planar but had different orientations between subdo­mains prior to the post-F 2 folding. Since F z are mostly tight to isoclinal, their axial surfaces are effectively subparallel to bedding. Hence, folds in S2 mostly should have similar orientationssto late fol~ in So. That is, the 1tS2-axes may represent Bs! and/or B s~ axes. A synoptic 1tS2 equal area projection (Fig. 12) shows that the 1tS2-axes from the subdomains define a great circle girdle with orientation 356/ E/35. The observed pattern cannot simply be a result of folding S2 during the F3 event because S2 would have been planar prior to F3, and during F3 this should result in 1tSz-axes of similar orientation in different subdomains. An F4 event must be inferred to produce the different girdles in 1tSz•

Theoretically the 1tSz-axes could represent one of the following:

(1) They could be B~ ~ fold axes within refolded Fz folds. That is, each subdomain had a similar post-F3 1tSz-axis, and their present different orientations are due to refolding by F4 (e.g., Fig. 12. inset A, areas V and U).

(2) They could be B~~ fold axes. That is, prior to F4, each subdomain represented a planar portion of Sz in an F 3 fold. Refolding by F4 produced B~~ fold axes of variable orientation (e.g., Fig 12 inset B, areas X, Y, Z).

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Barnes & Korsch-Structure of accretionary wedge, Wairarapa 367

Fig. 9 Distribution of structural domains in the Te Awaiti area, differentiated on the basis of homogeneity of nSo'

(3) The 1tS2-axes for some subdomains could represent B~~ fold axes, while those in other subdomains could be B~ 4 .

2

For cases (1) and (3), the synoptic 1tS2 girdle (Fig. 12) would simply represent a plane containing thel3, and the F3 plus F4 fold axes, respectively. In case (2), all Bs ~ axes would lie within the S 4 plane (Fig. 12, inset B) and hence the synoptic 1tS2 girdle would define the orientation of S4' Case (2) is considered unlikely because it implies that S4 would dip gently (35°) to the east. Observed mesoscopic F4 folds have northwest-southeast-striking, subvertical axial surfaces (Fig. 10) and hence could not contain the northeast and southeast gently plunging 1tS2-axes.

The 1tS2-axis in subdomain 4E (detailed area A) represents a B ~3 fold axis. In subdomain 4B at G.R. S28B/23846602, poles

2

to S2 measured around a probable F4 mesoscopic fold define a partial great circle girdle with a 1t-axis oriented 200

to 1230 (Fig. 12). This axis differs from that for the whole subdomain by a 940 trend, suggesting that 1tS2 for this subdomain is a B ~~ fold axis. In subdomain 4A, the 1tS2-axis is oriented 360 to 1340 (Fig. 12). At G.R. S28B/22636620, an F3 fold refolds a NNE-plunging isoclinal F2 fold. The north­plunging B~! axis is markedly different from the southeast­plunging 1tS2-axis for the whole subdomain. Thus the 1tS2-axis most likely represents B ~ 4 • Furthermore, the 1tS2-axis for this subdomain lies within th~ average S4 plane.

The above examples suggest that the 1tS2-axes from subdomains 4A-E have different orientations as a result of the superposition of both F 3 and F 4 folds upon F 2' The synoptic diagram (Fig. 12) includes 1tS2-axes representing both B ~~ (e.g., subdomains 4B, 4C, and 4E) and B~4 (e.g., subdomain 4A) fold axes. B~~ axes represent cylindrlcal F3 folds in S2' which now have different orientations as a result of the F4 event (Fig. 12, inset A). The B ~ 4 axis results from folding a planar segment of a nonplanar pbst-F3 S2 surface by F4 (Fig. 12, inset B), and hence lies within the average mesoscopic S 4 plane. The synoptic great circle girdle has no relationship to any S-surface, but simply represents the plane containing the 1tS2-axes.

o-s 1km '====='=' ====="

~-Domalnboundary

-----J>32-Trl!nd and plunge of ;rSo-axis

5-oomilin number

F- -~au[t

Synopsis of the Te Awaita area

Based on maps of regional trends of mesoscopic structures (Fig. 2 and 13), and structural analysis (Fig. 10), several important points arise: (1) In all structural domains, bedding (So) is folded

cylindrically about gently to moderately plunging fold axes. Departures from cylindrical patterns in some dOmains reflect the superposition of different fold events.

(2) On the basis of mesascopic (Fig. 10) and macroscopic (Fig. 2) data, the 1tSo -axis in most domains can be related to the F3 folds. A synoptic 1tSo diagram (Fig. 14) shows 1tSo-axes plunging both to the northeast and to the southwest. Domain 11 represents an area where So was effectively planar after the F3 event, with macroscopic F4 folds producing the northwest-plunging 1tSo-axis. In domain 6, the northeast-plunging 1tSo-axis reflects the F3 event, and the northwest-plunging axis reflects the F4 event.

(3) Fl folds play no role in the geometric analysis because they were identified only in melange zones and hence their relationships to the other folds are unknown. The dominant orientation of bedding after the Fl fold event is also unknown. F2 folds were only recognised on a mesoscopic scale, F3 are the most common, and both F3 and F4 developed on a macroscopic scale. When the location of each domain is considered (Fig. 9),

the geometric analysis (Fig. 10) and regional structural trends (Fig. 2) indicate that all of the domains west of the Oterei River (domains 1-5) have northeast-~lunging iSo-axes, and predominantly northeast-plunging Bs! and Bs! fold axes. However, east of the Oterei River, domains 8, 9 and 12, have southwest-plunging 1tSo-axes. This suggests that a northwest­north-trending, gentle, macroscopic F4 syncline is situated in the vicinity of, or immediately east of, the Oterei River mouth (Fig. 2). This upright, noncylindrical plane fold has a subhorizontal axis. The fold, referred to here as the Te Awaiti Syncline, affects most of the study area, has an axial trace at

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, 368 New Zealand Journal of Geology and Geophysics, 1990, Vo1. 33

Domain 2 1,--3--'1

4 5 Sedimentary Melange sequence G.R. S28IB2334 6500

377 (0.2),1.5,3,5,8 698 (0.1),1,2,10,14 43

5

79 1,5,10,17

3

1---------, I I I I I I I I I See fig. 12 I I I I I I I I L. _______ .J

Fig. 10 Equal area projeCtions of structural components from domains 1-12 in the Te Awaiti area. Numbers on the lower left comers of nets are the numbers ofobservations; numbers on the lower right are the contour interval in % per 1 % area. The Sz. S], and S4nets represent the axial surfaces ofFz• F]. and F4 folds respectively. The secondary. subsidiary girdles (dashed lines) in Szfrommelange in domain 3 are discussed in the text.

least 2 km in length, and is the largest structure recognised in the Te Awaiti area.

The best evidence for the F4 event is seen in domains where the pole 7tSo plunges to the northwest (domains 6 and 11). Also, in some domains, the strike of S] has been spread by up to 80° as a result of the F4 event. Synoptic diagrams of average S] and S4 orientations from each domain (Fig. 14) show S] is approximately normal to S4'

DISCUSSION

The eastern Gondwana continental margin was dominated by subduction from the Carboniferous to middle Cretaceous (Korsch & Wellman 1988; Spfirli & Ballance 1989). The structural style and complexity of Mangapokia Formation, together with the occurrence in melange zones of ocean-floor pelagic sediments and associated oceanic basalt, suggests

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Barnes & Korsch-Structure of accretionary wedge, Wairarapa 369

6 7 8

455 (0.15), 1, 2.5, 4, 8 20

Fig. 10 (continued)

deformation within an accretionary wedge. Near Te Awaiti, the middle Cretaceous (Motuan) rocks are complexly deformed with four generations of folding and several episodes of faulting recorded. We interpret the rocks to be the youngest part of the Torlesse terrane, whereas SporH & Ballance (1989) considered them to be Mata accretionary terrane, and related to a separate and younger (middle Cretaceous) phase of subduction than Torlesse rocks.

9 10 11 12

37 2,5,10,15 66 (1),4,10,15,19 26

The early deformational events (1-6 in Fig. 3), which will be described in detail elsewhere, occurred in a subduction! accretion setting at the Gondwana plate margin in the middle Cretaceous (Barnes 1985). Fl folds were superimposed on an early, extensional-related shear fabric. These structures were observed only within discrete melange fragments, indicating that their formation predated the fmal development of the melange fabric. The orientations of the folds are now

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-370 New Zealand Journal of Geology and Geophysics, 1990, Vol. 33

c =Z~

===_Shear- foliation (Sst)

Axial surface S2

Axial surface 53

~ Fault

Axial surface S4

Fig. 11 Mesoscopic overprinting relationships in melange in domain 3 (G.R. S28B/23346500). All folds occur within the shear­foliation and hence postdate the formation of the melange. Sketches are traced from photographs. A, Steep-plunging isoclinal Fa fold refolded by tight to isoclinal F~ folds. Orientation data for Sa is shown in Fig. 10, labelled as 'I". Hammer length = 330 mm. B, Small-scale, asymmetric-tight isoclinal Fa folds within the hinge of, and overprinted by, an isoclinal F 3 fold. Compass diameter = 70 mm. C, Isoclinal Fa folds refolded by a late, open, southwest­plunging F 4 fold Orientation data for Sa is shown in Fig. lO,labelled as ''2''. Ruler is 175 mm long.

meaningless because the fragments were rotated during development of melange. Events 1-5 are dominated by multiple episodes of shearing and disruption of strata, particularly in the incompetent units, and local development of melange. These events are inferred to have occurred during frontal accretion, possibly shortly after decoupling from the downgoing plate.

Fa folds developed after initial pervasive shearing, and they are superimposed on the melange fabric as well as on the disrupted sedimentary sequences. Because of their tight to isoclinal shape, they probably also formed during the middle Cretaceous supduction!accretion event, but in a position in the imbricated accretionary wedge landward of the site of decoupling and initial accretion where the most intense strains were located.

Because of reasons outlined below, we consider that the F3 folds are related to the Miocene-Recent subduction! accretion resulting from convergence between the Pacific and Australian plates at the Hikurangi Margin (Walcott 1984). In eastern North Island and northeast South Island, Late Cretaceous and Paleogene sedimentary sequences consist predominantly of quartzose sandstones and shales, glauconitic sandstone, calcareous sandstone and mudstone, limestone, and bentonitic mudstone (e.g., Waterhouse & Bradley 1957; Eade 1966; Kingma 1967; Pettinga 1982) deposited during nonconvergent, relatively quiescent tectonism (Korsch & Wellman 1988). Subduction at the Hikurangi Margin, relating to convergence between the Pacific and Australian plates, commenced in the Early Miocene and continued to the present day (Walcott 1984, 1987). Cenozoic sedimentary sequences were deformed by northeast-trending folds and thrusts (e.g., Pettinga 1982), and deformation is continuing today (Walcott 1987).

A clue to the timing of the later deformations in Manga­pokia Formation can be seen in the structures recorded in other Cretaceous and Tertiary rocks. In the Te Awaiti region (Fig. 15), Motuan breccia-conglomerate (Gentle Annie Formation) andMotuan-Ngaterian (middle-Late Cretaceous) sandstone and siltstone (Springhill Formation) exposed 2-8 kIn northwest of Te Awaiti is tightly folded (Moore & Speden 1984), but no detailed structural studies have been undertaken. The rocks appear less deformed than Mangapokia Formation and probably represent fault-angle half grabens or basins that developed on, and were deformed by, the accretionary wedge in the Motuan. George (1988) described a similar tectonic relationship between basement Neocomian Torlesse rocks and overlying Aptian-Albian (late Early Cretaceous) Whatarangi Formation at Cape Palliser, 25 km east of Te Awaiti. Between the Te Awaiti area and White Rock, 14 kIn to the southwest (Fig. 15), a Piripauan-Landon (Late Cretaceous-Oligocene) shelf and slope sequence (Waterhouse & Bradley 1957) is folded by a northeast­trending, macroscopic open anticline of probable late Cenozoic age, and is bound to the west by an inferred Early Miocene thrust fault that is now steeply dipping and reactivated. Similar northeast-southwest-trending macroscopic open folds occur in Tongaporutuan - Kapitean (Late Miocene) calcareous mudstone and sandstone sequences 10 kIn north ofTe Awaiti (Fig. 15).

The third generation (F3) folds in Mangapokia Formation are predominantly close to gentle, and they developed on both mesoscopic and macroscopic scales. The orientations and style of the folds are similar to other late Cenozoic structures common elsewhere in southeast North Island (Fig. 15; Kingma

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Barnes & Korsch-Structure of accretionary wedge, Wairarapa 371

Fig. 12 Distribution of five subdomains (4A-E) within domain 4, differentiated on the basis of homogeneity of1tS2 (axial surfaces of~ folds); equal area projections of 1'2 structural data; and synoptic 1tS2 net. Numbers at the lower left comer of nets are the number of observations; numbers on the lower right are the contour intervals in % per 1 % area. The secondary girdle in 1tS2 in subdomain 4B (dashed line) is discussed in the text. Inset figures show hypothetical structural relationships between F2, F3• and F4 folds, to produce the 1tS2-axes with different orientations on difference areas (subdomains 4A-E). Inset Fig. A: the 1tS -axes representB ~ ~folds withinrelolded F2 folds (areas V and U), their orientations are different now as a result of the F4 event. Inset Fig. B: the 1tS2-axes represent B~4 folds. whereby F4 folds develo~d in a nonplanar S2 surface resulting from the F3 event (areas X. Y and Z).

~I __ -+---I

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Open to gentle, upright, mesoscopic and macroscopic fourth generation (F 4) folds are late Cenozoic or Quaternary .

16"" S2 16 FA

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The orientations of F4 folds are unusual. Similarly oriented late Cenozoic structures have not been recorded previously in eastern Wairarapa, suggesting that they maybe a local feature. Their orientations differ significantly from the northeast­southwest-trending, regional Quaternary growing folds that characterise the southern North Island, as described by Singh (1971), Wellman (1971), and Ghani (1978). The F4 folds possibly represent cross folds that formed almost simultaneously with F3, during a single phase of deformation

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374 New Zealand Journal of Geology and Geophysics, 1990, Vol. 33

N

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83

Axial planes

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Fig.14 Synoptic equal area projections for domains 1-12 in the Te Awaiti area.

(e.g., Mosher & Helper 1988). Their orientations were controlled by the previously intensely deformed, irregular bedding surfaces, rather than by a different orientation of the major stress field during F4.

Thus the Torlesse accretionary wedge in the Te Awaiti area has had a complex structural history during Cretaceous subduction and accretion that has been further complicated by a later episode of convergent tectonics in the late Cenozoic.

ACKNOWLEDGMENTS _

This research was undertaken through the Research School of Earth Sciences at Victoria University of Wellington, between 1983 and 1986. We thank Dan May, Ian Wright, John Bradshaw, and Paul Williams for constructive comments on the manuscript. New Zealand Oceanographic Institute staff Fiona Berry typed the manuscript, and Karl Majorhazi drafted the figures.

REFERENCES

Barnes, P. M. 1985: Sedimentology, petrology, and structure of Mangapokia Formation (Pahaoa Group) near Te Awaiti, southeast Wairarapa, New Zealand. Unpublished M.Sc. thesis, lodged in the Library, Victoria University of Wellington. 256 p.

---1988: Submarine fan sedimentation at a convergent margin: the Cretaceous Mangapokia Formation, New Zealand. Sedimentary geology 59: 155-178.

----1990: Provenance of Cretaceous accretionary wedge sediments: the Mangapokia Formation, Wairarapa, New Zealand. New 'kaland journal of geology and geophysics 33: 125-136.

Coombs, D. S.; Ellis, A. J.; Fyfe, W. S.; Taylor, A. M. 1959: The zeolite facies with comments on the interpretation of hydrothermal syntheses. Geochimica et cosmochimica acta 17: 53-107.

Eade, J. V. 1966: Stratigraphy and structure of the Mount Adams area, eastern Wairarapa. Transactions of the Royal Society of New 'kaland geology 66: 103-117.

Fluety, M. J. 1964: The description of folds. GeologicalAssociation proceedings 75: 461-492.

George, A. D. 1988: Accretionary prism rocks of the Torlesse terrane, western Aorangi Range--Cape Palliser, New Zealand. Unpublished Ph.D thesis, lodged in the Library, Victoria University of Wellington. 184 p.

Ghani, M. A. 1978: Late Cenozoic vertical crustal movements in the southern North Island, New Zealand. New Zealand journal of geology and geophysics 21: 117-125.

Hobbs, B. E.; Means, W. D.; Williams, P. F. 1976: An outline of structural geology. New York, Wiley International. 571 p

Kingma, J. T.1967: Sheet 12-Wellington. Geological map of New Zealand 1:250000. Wellington, New Zealand. Department of Scientific and Industrial Research.

Korsch, R. J.; Wellman, H. W. 1988: The geological evolution of New Zealand and the New Zealand region. In: Nairn, A. E. M.; Stehli, F. G.; Uyeda, S. ed. The ocean basins and margins. Vol. 7B. Plenum Publishing Co. Pp. 411-482.

Moore, P. R.; Speden, I. G. 1979: Stratigraphy, structure, and inferred environments of deposition of the Early Cretaceous sequence, eastern Wairarapa, New Zealand. New 'kaland journal of geology and geophysics 22: 417-433.

----1984: The Early Cretaceous (Albian) sequence of eastern Wairarapa, New Zealand. New Zealand Geological Survey bulletin 97: 97 p.

Mosher, S.; Helper, M. 1988: Interpretation of poly-deformed terranes. In: Marshak, S.; Mitra, G. ed. Basic methods of structural geology. Part II, Special topics. New Jersey, Prentice Hall. pp. 361-384.

Pettinga, J. R. 1982: Upper Cenozoic structural history, coastal Southern Hawke's Bay, New Zealand. New Zealandjournal of geology and geophysics 25: 149-191.

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Barnes & Korsch-Structure of accretionary wedge, Wairarapa 375

Fig. 15 Simplified Cretaceous­Cenozoic structure and stratigraphy in the Te Awaiti-White Rock region, and position of this study area (Fig. 2). Lithological contacts from Moore & Speden (1984). Neocomian Torlesse terrane inferred from George (1988). Mp, PiripauanStage; L, Landon Series; Tt, Tongaporutuan Stage; Tk, Kapitean Stage; W, Wanganui Series; Wo, Opoitian Stage; Wn, Nukumaruan Stage.

TI-W

Ramsay, 1. G. 1967: Folding and fracturing of rocks. New York, McGraw Hill Co. 586 p.

Singh, L. 1. 1971: Uplift and tilting of the Oterei coast, Wairarapa, New Zealand, during the lastten thousand years. In: Collins, B. W.; Fraser, R. ed. Recent crustal movements. Royal Society of New Zealand bulletin 9: 25-30.

Sp6rli, K. B.; Ballance, P. F. 1989: Mesozoic/Cenozoic ocean floor/ continent interaction and terrane configuration, southwest Pacific area around New Zealand. In: Ben Avraham, Z. ed. Mesozoic and Cenozoic evolution of the Pacific Ocean margins. Oxford University monograms, geology and geophysics 8: 176-190.

Stauffer, M. R. 1966: An empirical-statistical study of three­dimensional fabric diagrams as used in structural analysis. Canadian journal of earth sciences 3: 473-498.

Turner, F. 1.; Weiss, L. E.1963: Structural analysis of metamorphic tectonites. New York, McGraw Hill Co. 545 p.

o I

pm

OCEAN

O Late (Calcaroous mudstona,

limastona)

Late Cretaceous-­IImI Oligocene (Limastona, 11!211 glauooni1lc sandstona,

shala, benton~a)

•

middle-Late Cretaceous (Braccia­

conglomerats, sandstonalsilt 51ona)

Early-middle

D creraceous accreticlnrurvl Torlesse terrane

(pm, Mangapokia Fmn)

Principle Late -- Cenozoic faults ~ Inferred Early

Miocene thrust

+t Late Cenozoic folds

#F, F3 folds; this study

4km I

+

1

Walcott, R. I. 1984: Reconstructions of the New Zealand region for the Neogene. Palaeogeography, paleoclimatology, palaeoecology 46: 217-231.

----1987: Geodetic strain and the deformational history of the North Island of New Zealand during the late Cainozoic. Philosophical transactions ofth£ Royal Society of London A321: 163-181.

Waterhouse, 1. B.; Bradley, 1. 1957: Redeposition and slumping in theCretaceo-TertiarystrataofS.E.Wellington.Transactions ofth£ Royal Society of New 'ZBlland 84: 519-548.

Wellman, H. W. 1971: Holocene tilting and uplift on the Glenburn coast, Wairarapa, New Zealand. In: Collins, B. W.; Fraser, R. ed. Recent crustal movements. Royal Society of New 'ZBlland bulletin 9: 221-223.

Williams, P. F. 1970: A criticism in the use of style in the study of deformed rocks. Geological Society of America bulletin 81: 3283-3296.

----1985: Multiply deformed terrains-problems of correlation. Journal of structural geology 7: 269-280.

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