Taranaki Basin, structural style and tectonic setting

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1 New Zealand Jurnal f Gelgy and Gephysics ISSN: (Print) (Online) Jurnal hmepage: Taranaki Basin, structural style and tectnic setting G. J. Knx T cite this article: G. J. Knx (1982) Taranaki Basin, structural style and tectnic setting, New Zealand Jurnal f Gelgy and Gephysics, 25:2, , DOI: / T link t this article: Published nline: 07 Aug Submit yur article t this jurnal Article views: 2326 Citing articles: 58 View citing articles Full Terms & Cnditins f access and use can be fund at

2 -New Zealand Jurnal f Gelgy and Gephysics, 1982, Vl. 25: Taranaki Basin, structural style and tectnic setting G. J. KNOX Shell BP and Tdd Oil Services Limited Private Bag New Plymuth, New Zealand Abstract Taranaki Basin is lcated mainly t the west f the Nrth Island f New Zealand, but als includes the Taranaki Peninsula nshre. Fllwing the Rangitata Orgeny, which welded a late Palezic-Late Jurassic apcretinary wedge t the Gndwanaland margin in the New Zealand area, peneplanatin tk place during the middle t Late Cretaceus. During Late Cretaceus time the basin was initiated n a fault-dissected peneplain. The structural and depsitinal histry extends int Recent time. The basin can be divided int 3 structural units in the west, nrth, and suth which are the cumulative results f reginal, yet time distinct, tectnic events. The Western Unit has been largely undisturbed since Late Ecene time, but the Nrthern and Suthern Units have been affected by Late Micene-Recent tectnic events. The Nrthern Unit has undergne nrmal faulting and extensin, and the Suthern Unit has undergne cmpressive defrmatin with reverse faulting and structural inversin. Examinatin f the structural style and gemetry within each unit allws a structural histry fr the whle basin t be described and related t ther tectnic phenmena. Keywrds Taranaki Basin; Cape Egmnt Fault Zne; Ck-Turi Lineament; nrmal fault; reverse fault; uplift; inversin; half graben; earthquake fcus; wrench fault; Late Cretaceus; Late Ecene; Late Micene; Plicene; Pleistcene; Recent; uncnfrmity INTRODUCTION Taranaki Basin is lcated generally t the west f the Nrth Island f New Zealand (Fig. 1) but als includes the Taranaki Peninsula. The eastern bundary is defined by the Taranaki Bundary Fault System extending frm Nelsn in the Suth Island t the area west f Kawhia Harbur, western Nrth Island. This fault system is subparallel t the Stkes Present address: Explratin Department, Thai Shell Explratin and Prductin C. Ltd., P.O. Bx 345, 10 Snthrnksa Rad, Bangkk 10110, Thailand. Received 28 Octber 1981, accepted 18 March 1982 Magnetic Anmaly (Hunt 1978) which is the magnetic expressin f ultramafic rcks which crp ut in Dun Muntain and Wairere serpentinite. This trend is parallel t the main structural strike expressed in the Triassic and Jurassic Kawhia Syncline and separates basement rck facies in the nrthern Nrth Island (Kear 1971). Thus, the Taranaki Bundary Fault System appears t fllw Rangitata Orgeny structural trends. The nrthwestern limit f the basin is unknwn as well cntrl is absent and seismic cntrl is limited beynd 500 m water depth. The suthwestern margin f the basin is defined by the Challenger Plateau. The basin has a sedimentatin histry which extends frm Late Cretaceus time t the present day. Tectnic activity has als been cntinuus since the initiatin f the basin and sme faults are still active. The basin has been influenced by the tectnic setting f New,Zealand alng an active plate margin and has therefre been affected by majr changes in directin and amplitude f stresses. Thus, the nature, spatial rientatin, and type f tectnic defrmatin has changed with time. STRUCTURE The basin tday exhibits a cmplex faulted style (Fig. 1) particularly ver its eastern part. These faults, mapped at Oligcene level, may shw nrmal, reverse, and/r lateral defrmatin styles. Older pre-oligcene structural features can be bserved t the west f the area f intense faulting. The basin has been subdivided int the Taranaki Graben and Maui Blck (McBeath 1977) r Western Platfrm (Pilaar & Wakefield 1978). The latter authrs subdivided the graben int Nrth and Suth areas. In this paper, the basin, including the Taranaki Graben, is subdivided n the prevailing defrmatin style, and 3 structural units are defined separated by tectnic lineaments (Fig. 2). These units cmplement earlier divisins f the basin. 1. Western Unit: This frms the western part f the basin and has been largely stable since Late Ecene time. It cincides with part f the Western Platfrm (see Pilaar & Wakefield 1978) and its maximum westward extent is unknwn wing t lack f seismic and well cntrl, but twards the Challenger Plateau it is abut 200 km wide. 2. Suthern Unit: This is characterised mainly by, reverse faulting and inversin. The unit includes the Suth Taranaki Graben and parts f the Western Platfrm. Sig. 1'"

3 126 New Zealand Jurnal f Gelgy and Gephysics, 1982, Vl. 25 'i-j LEGEND 38,...---,... >--< _Q- -V- _..JL_ -,,-- (:::.:' c- Nrmal Fault Reverse / Thrust Fault Anticlinal FOld}. Plunge Indicated Synclinal Fld Pre - Oligcene Swells Pre - Oligcene Trughs Igneus Intrusins Explratin Wells Crss Sectins - Fig 3 38 [ NORTH ISLAND 1..-_..._... 4,0 km 400 LOCAliTY MAP Fig. 1 Structural features within Taranaki Basin.

4 Knx-Taranaki Basin 127 N I'- LEGEND, , Nrmal Fault Reverse Fault.., I'- r;-;;" Igneus Intrusins \..."... Schematic bundary between Gndwanaland (west land Rangitata basement (east l Fig.4 Figure lcatin and number SCALE 40km.. u... 'II II.. 1' , f.... :--;.- r';) J. -3J I. '--'--"" c. Gl. \ \ \. 3- \. \ if j-i.0 /f I: 0 IV 38 WESTERN UNIT Suth Wanganui N!:::: Fig. 2 Structural subdivisin f Taranaki Basin.

5 128 New Zealand Jurnal f Gelgy and Gephysics, 1982, Vl Nrthern Unit: This is frmed by an area f cntinuus subsidence defined by numerus nrmal and/r blique dip-slip faults. It is als characterised by several intermediatelbasic intrusive bdies. The unit cincides bradly with the N9rth Taranaki Graben f Pilaar & Wakefield (1978). These 3.separate structural units are bunded and/r separated by tectnic lineaments ver which a distinct change in structural style ccurs. These lineaments are the Taranaki Bundary Fault, the Cape Egmnt Fault Zne, and the Ck-Turi Lineament (Fig. 2). The gemetry and structural style f these lineaments and structural units are described belw. Their relatinship t each ther and their setting within New Zealand are discussed. Basement Wdzicki (1974) extraplated the utcrpping gelgy f the nrthwest Suth Island int the Taranaki Basin. Since then new data are available frm the Kiwa-1, Surville-1, Tane-1 (Offshre), and Tangara-1 weits(fig. 1). Kiwa-1 penetrated intermediate intrusive rcks, and Surville-1 (NZ Aquitaine Petrleum Ltd 1976) penetrated weathered bitite micrcline granites. Tane-1 (Offshre) (Shell BP and Tdd Oil Services Ltd 1977) als penetrated' granites, and Tangara-1 penetrated basalts and rhylites f lw-grade metamrphic character. The latter have been dated (Adams pel's. cmm.) at 128±4 m.y. ag, which is regarded as a minimum recrystallisatin age representing a lw-rank thermal event. Similar ages are knwn frm Nelsn, Marlbrugh Sunds, Wellingtn, and Kaimanawa. Adams (pers. cmm.) suggests that the Tangara-1 basement may be a crrelative f Perm-Triassic Brk Street Vlcanics. The results frm these wells cnfirm the picture develped by Wdzicki (1974). Thus, Palezic (Gndwanaland) metamrphic basement and intrusive rcks ccur generally t the west, and late Palezic-Jurassic metasediments ccur beneath the eastern part f the basin and the Nrth Island. The bundary between the differing basement types (Gndwanaland and the Early c;retacemis metamrphsed Rangitata) is schematicauy shwn n Fig. 2. Western Unit The Western Unit has been little affected by pst Ecene tectnic' events. Thus, the Late Cretaceus Ecene histry is well demnsrated.fllwing the Late Iurassic-Early Cretaceus Rangitata rgenic phase, ersin, accmpanying an extensinal phase f faulting, prduced a fault-dissected peneplain with a lw t mderate relief. WU Western Unit N U Nrthern Unit 5 U Suthern Unit: ZA-Zne A ZB-Zne B ze-znee CEFZ Cape Egmnt Fault Zne CTL Ck - Turi Lineament TBF Taranaki Bundary Fault PTH P tea Tngaprutu High HO Hlcene PS Pleistcene P I Plicene M I Micene EO Eene PC Patecene K U Late Cretaceus ''1' Near base Plicene seismic hrizn 'Q' Near bse Oligcene seismic hrizn 'p' Near tp Cretaceus seismic "dzen 'R I Tp basement seismic hrizn D Late Micene intrusives U Basement (Rangitata Orgen r lder) Nte: See Figure I fr lcatin f crss sectins SCALE kilmetres '-- L' _-J''--_---'' ---'' --.J' Fig. 3 wu D CTL Ck-i -----lnverted half-grbe(ls----- Tw majr trends f nrmal faulting deyelped: nrth-suth and nrtheast-suthwest. Cncurrently, the basement was defrmed int swells and trughs. A prminent nrth-suth ridge (Ma Maui swell) runs frm the area f Ma-1B well t the Maui Field (Fig 1). Fault activity was largely synsedimentary with thrws up t m within half grabens. An example f a half graben is illustrated in Fig. 3 (B-B1), and Palecene-Ecene nrmal faulting frm the nrth f the basin is illustrated in Fig. 4. Sediments gradually.filled the hllws and half grabens and subsequently drwned the highs. Fault activity diminished during the Palecene. Twards zc

6 Krix-Taranaki Basin WU IEFZI NU I?TBF...-casl T.W.T :::==================O;===:::===-=7-+=-=r. sees Sea bed 10 'y' 2.0 '0' ==,----=::e 30 A AI 40 Obed================================,==TTrT========rs-r 'y '-=:::::::-----;---:--'--'I--I 20 ''--===-.::==-\::..::\ C ---wui--_>iee N U >'t'----- SU ----=-:----">1 CEFZ I CT L csl ZB ZA Sea bed-==============================r=#""lr-'::::;:=------'--=:::t'''''''':::t===r 00,y, ,t-- MI '0' \..-\ EO-PC 'P' ----:::;::::;=t_ 'R' KU M 1 EO-PC ? r-- 1 I 1 Prjected 10 km N CI KU I Prjected 15 km NNE Prjected 20km NW Fig. 3 Structural crss sectins thrugh Taranaki Basin. Nrmal faulting dminates in the nrth and reverse faulting becmes dminant twards the suth f the basin. the end f Palecene time, sme gentle reactivatin f the basement tk place, represented by a marked nlap/discnfrmity near base Ecene. By Oligcene time the area was quiescent. Such cnditins were maintained t the Recent, and the gradual buildup f a Micene-Hlcene sedimentary sequence has prduced the present shelf, slpe, and abyssal plain mrphlgy. Suthern Unit This unit is characterised by structural inversin, reverse andlr thrust fault phenmena. The eastern margin is frmed by the Taranaki Bundary Fault and the western margin is frmed by the Ck-Turi Lineament. The latter defines.the nrthwestern extent f reverse fault phenmena and trends nrtheast-suthwest frm Ck-1 t Turi-l (Fig. 2, 3). The area underwent a similar Late Cretaceusearly Tertiary histry as the Western Unit. Nrmal faulting n mainly nrtheast-suthwest trends defined half grabens which were filled with sediments. These trends extended suthwestwards int the west f the Suth Island. A Late Palecene warping als affzcted the area, and bistratigraphic studies indicate missing sectins in Ck"l, Fresne-1, Maui-4, and the Maui Field, crrespnding t an ersinal event at this time

7 TWT ln_. 0 0 Line HF -IIOON I.p N ;... 0 Fla. 4 Seismic sectin illustrating nrmal faulting in Western Unit. Palecene! t Ecene synsedimentary nrmal faults are verlain by the Q seismic hrizn (base Oligcene) (see Fig. 2 fr sectin lcatin and Fig. 3 fr abbreviatins).... w Z n S!. l!!- I'> t:i C... 0 c EI I!! n 0 0" OQ '< I'> t:i C "0 ::r '< '"!!'... I,C) 00 J'l -< g. N VI

8 Knx-Taranaki Basin 131 (Pilaar & Wakefield 1978). By Late Oligcene time, the area had becme the site f quiet marine depsitin and was largely stable. Sedimentary thickness increases twards the Taranaki Bundary Fault, suggesting eastward, dwnward tilting alng the fault in Micene time. At this time the fault may well have been a west-dipping synsedimentary fault. By Middle Micene time, carser siliciclastic debris entered the area frm the sutheast, suggesting uplift f surce areas in that directin. In late Middle-Late Micene time, vlcaniclastic debris arrived in the area nrth f the Kapuni Field, surced frm vlcanic/intrusive centres recgnised in the nrth f the Taranaki Basin. At the same time, but extending int Plicene-Pleistcene time, defrmatin episdes caused reverse faulting and inversin alng pre-existing nrmal faults. The effects f this allw 3 znes t be recgnised: 1. Zne A: This is subparallel t, and includes, the Taranaki Bundary Fault, extending frm the fault's intersectin with the Ck-Turi Lineament thrugh the McKee Field, Kapuni Field, and widening beynd the Kupe-l Manaia Fault area (Fig. 2). The nrth f the zne is characterised by steeply dipping splay faults assciated with the Taranaki Bundary Fault. Lw-angle thrust faults in the McKee and Kapuni Fields, and ther similar" structures alng the same trend, may steepen int splay faults at depth, althugh gravity slides cannt be excluded (Fig. 3, C-Cl). The magnitude f thrusting increases suthwards and culminates t the suth f Kupe-l where a wedge f basement, r pssibly an intrusive bdy, is trapped as a large fault slice between the Taranaki and Manaia Faults which intersect at depth. The Kupe-l well was drilled near the axis f a plunging anticline assciated with the Manaia reverse fault (Fig. 5). A basement t Upper Micene sequence has been inverted and is truncated by the Y (basal Plicene) seismic hrizn. The timing f inversin is shwn by the seismic reflectin pattern in the Micene sectin abve the Manaia Fault. This sectin exhibits thinning and nlap during Late Micene time fllwed by Plicene truncatin f the structure. Plicene Recent histry f the sectin exhibits cntinual sedimentatin assciated with minr nrmal faulting which may reflect cmpactin drape ver the anticline. The main cmpressive defrmatin was therefre f Late Micene-?Early Plicene age. 2. Zne B: This appears t lack prminent reverse faulting althugh uncertainty exists under the Taranaki Peninsula where seismic cntrl is pr, particularly t the suth f Munt Egmnt where revers!,: faults (ffshre) may cntinue nrthwards. Adjacent t the Ck-Turi Lineament, a small reverse fault f?middle Micene age has been recgnised. Reverse faulting f similar age t that' encuntered in Zne A ccurs in the Maui Field. Over much f the zne, a thick Plicene sectin has develped. Pre-Plicene uplift appears t have taken place in a general nrthwestward directin, but withut significant fault reversal. Severe channelling has affected the sectin alng the edge f the zne within the Ck-Turi Lineament (Fig. 6) suggesting uplift and/r develpment f a steep break f slpe. 3. Zne C: This frms the remaining area f the Suthern Unit suth f the Maui Field where reverse faulting and inversin is severe. The western bundary is defined by, and includes, the suthern part f the Ck-Turi Li.neament. This zne includes the Ck-I, Fresne-l, Nrth Tasman-l (Fig. 3, D-Dl) and Maui-4 wells where significant inversin accmpanied by steep reverse faulting alng earlier synsedimentary nrmal faults (as defined by Q, base Oligcene seismic hrizn) has affected Late Cretaceus-early Tertiary halfgraben depcentres. The degree f inversin increases frm nrth t suth (Maui m; Nrth Tasman-l 1350 m; Fresne-l, Tasman-I, and Ck-l at least 2000 m) culminating in the Suth Island where Upper Cretaceus sediments nw crp dut at the surface.. Further suth, greater uplift has ccurred, and vitrinite reflectance measurements frm the Grey muth and Buller calfields (Suggate & Lwery 1981) indicate marked uplift frm riginal burial depths exceeding 3000 and 5000 m respectively. A sectin thrugh the Nrth Tasman-I' well illustrates the faulting style (Fig. 7). At the well lcatin, a cnfirmed Late Cretaceus (uncnfrmably verlying basement) t Late Micene sectin (Brphy et al. 1979) has been defrmed and arched parallel t the strike f the faults. The sequence has been truncated and erded by a basal Pleistcene uncnfrmity. T the west (Fig. 7) and east (Fig. 3, D-Dl) Late Micene-Plicene sediments have been truncated by the uncnfrmity which extends acrss the Ck-l and Fresne-l wells. Thus, Zne C has undergne a Plicene uplift culminating in the Pleistcene. The zne extends int the nrthern Suth Island where numerus reverse faults ccur, including the Papara Fault Zne (Laird 1968) and the Papahaua Overfld structure (Laird & Hpe 1968) where late reversal and inversin have been recgnised. Nrthern Unit This unit frms a triangular area (Fig. 2). The western bundary is determined by the Cape Egmnt Fault Zne, and the Ck-Turi Lineament bunds it t the sutheast. T the nrth and east the unit is prly defined as numerus igneus intrusive

9 .. Line SK 7/2 s.p Line SK 711. p )I Kupe-I (prjected 1' 9km Suth) TWTI W '---'".:' _LLiLL-:J'.=u. PS-H - -=..:...,., - '- ---'-- -q '0 ;- 3 Fla 5 Seismic sectin shwing Late Micene reverse faulting and inversin f Micene t basement sectins in Zne A, Suthern Unit. Onlapping Late Micene sequence t west f structure.dates the inversin. Sequence is truncated by Y (base Plicene) hrizn (see Fig. 3 fr abbreviatins except fr OL.L-MI.U, Early Oligcene-Late Micene) W IV!. [ a!. a [ t.... -< IV Ul

10 line 8OK-2J1. p NW rr ln illl._11li SE TWT"'''CI L--L L-4--4' --4' OO Fig. /I Seismic sectin illustrating part f Ck-Turi Lineament between Nrthern and Suthern Units (interpretatin after E. van ScherpenzeeJ). I>l IJl I>l 5' '"... w

11 Line NT 1 I.p W TWT In Ilel Sea Level (}O Seabed PS- HO Nrth Tasman-I PS-HO E TWT Inll.. Sea Level i O.() Seabed ?m MI MI 1 0.-_ / _. PC-EO N N N N M N N M M N N "" M M 1 0 2, Basement KU ::-/ N M M M N M N N N N N N M N N Basement 2km I, SCALE 3'01 13'0 Fig. 7 Sectin shwing Plicene reverse faulting and inversin in Zne C, Suthern unit. Prgressively lder?plicene-late Micene sequence is truncated frm west twards Nrth Tasman-l well (see Fig. 3 fr abbreviatins).... w z (0 N (0 e:- p i:l i:l e:- - (1) 0" p i:l 0. (1) '0 i:l" '"... '" 00 JV <::: 2.. N Vi

12 Line HF-IIX l.p TWTlftOlC1l W CEF NU E TWT ln uu 0 0 -:= >. r=h-- r. (Y 0 Inl- \ ,... 'rv...,..,.i;: --; ;...:;;..!! ik '7/!".r)t.<>... I( j" "-i.. - :;;::---.J:,,,/_,.. 3 '0;,- _...:.:::2YiC:'k!....:. q,:, Fig. 8 Seismic sectin shwing late Middle-Late Micene intrusins adjacent t and within Cape Egmnt Fault Zne. A chatic appearance suggests a vlcanic pile r edifice nlapped by Late Micene-Plicene sediments. Fau!t znes exhibit activity int Recent time (see Fig. 3 fr abbreviatins except fr VE, vlcanic edifice). ::I 1 el I» t:i tl:i!}] ::r... w VI

13 136 New Zealand Jurnal f Gelgy and Gephysics, 1982, Vl. 25 bdies merge (Fig. 1) and seismic penetratin is pr. These bdies ccupy an area fllwing the apprximate strike prjectin f the Taranaki Bundary Fault which is prly defined nrth f its intersectin with the Ck-Turi Lineament (Fig. 3, A-A!). Other intrusive bdies ccur within the deeper axis f the unit and alng the Cape Egmnt Fault Zne. The lcatin f faulting and igneus intrusin is shwn in Fig. 1, and the character f the unit is illustrated in Fig. 3 (A-AI, B-B1, and C-Cl). Synsedimentary nrmal faulting ccurred alng the Cape Egmnt Fault Zne and pssibly alng the Ck - Turi Lineament during Oligcene - Early/ Middle Micene and extended int Late Micene time. Alng sme faults, mvement died during Late Micene time (Fig. 3, A-AI and C-C1) and ther faults were truncated by the basal Plicene uncnfrmity (Fig. 3, B-B1) r persisted int the Plicene. In general, activity alng the Cape Egmnt Fault Zne was restricted t single faults which persisted thrughut Plicene-Recent time and reach the seabed. The Ck-Turi Lineament (frm Cape Egmnt t Turi-1) cnsists f a cmplex zne f subparallel nrthwest and sutheast dipping faults giving ahrst and graben character at Micene-Recent levels (Fig. 6). Sutheast-dipping faults tend t intersect nrthwest-dipping faults, which gives a stepped appearance at the Q hrizn (base Oligcene) and lder levels. These faults have been active up t the present day and reach the seabed. Bth the Cape Egmnt Fault Zne and Ck-Turi Lineament have the effect f dwnstepping deeper hrizns t such an extent that the pre Ecene histry cann be defined because seisluic data des nt penetrate deep enugh t allw a certain identificatin f qasement ver much f the unit (Fig. 3, A-AI, B-B1, and C-Cl). The igneus intrusive phase can be apprximately dated within the unit. Seismic data (Fig. 8) suggest that initiatin f intrusin ccurred during Late Micene time r pssibly latest Middle Micene time. Sme bdies may have penetrated the seaflr and frmed vlcanic edifices (Fig. 8). Vlcaniclastics which have been dated in the Mangaa-1 well (Hematite Petrleum (NZ) Ltd 1970) and ther wells (Shell BP and. Tdd Oil Services Ltd unpublished data) are f Late Micene age. The Y (basal Plicene) seismic hrizn uncnfrmably verlies the vlcanic edifices and sediments which nlap their margins. The latter sediments have cmpacted t a greater extent and a thicker Plicene sectin has develped cmpared t that ver the edifices which have nt cmpacted. The effect is bservable frm 1.0 s (TWT) dwn t the Y hrizn (see Fig. 3,.C-Cl and Fig. 8). DISCUSSION The structural units in Taranaki Basin result frm a series f defrmatin events. The distributin and timing f the different defrmatin styles can be related t New Zealand's crustal structure and reginal tectnic events. Based n fault initiatin and structural develpment thrughut the whle basin, the first episde f defrmatin ccurred in Late Cretaceus-Late Ecene times when warping and nrmal faulting resulted in the develpment f lw-relief swells and trughs augmented by half grabens. The brad structural pattern was established during the Late Cretaceus, with activity dying ut ver the Western Unit by the Oligcene. Sme renewal f activity tk place near the end f the Late Palecene and re-emphasised the psitin f trughs and swells in the Western Unit; ther synsedimentary nrmal fault activity persisted thrugh Oligcene-Late Micene time alng the Cape Egmnt Fault Zne. The majr fault in the area was the Taranaki Bundary Fault where >7000 m f Upper Cretaceus-Recent sediments are estimated t have accumulated adjacent t the fault. Laird (1981) has related basins west f New Zealand t the pening f the Tasman Sea and separatin f Australia frm New Zealand during the breakup f Gndwanaland m.y. ag (Mlnar et al. 1975). The Late Palecene warping may have been a dying phase f this, r is pssibly related t adjustments f crustal blcks during the separatin f Australia, frm Antarctica which ccurred apprximately 55 m.y. ag. Fllwing this phase, faulting and tectnic activity was lw. Hwever, Late Ecene-Late Micene synsedimentary faulting is recgnisable alng the Cape Egmnt Fault Zne, which may be related t crustal events ccurring elsewhere in New Zealand. Apprximately 38 m.y. ag an active plate bundary develped in New Zealand (Mlnar et al. 1975), and dextral transfrm faulting alng the Alpine Fault fllwed m.y. ag (Carter & Nrris 1976). The latter authrs prpsed a series f transfrm basins develped n, and adjacent t, the Suth Island. Activity alng the Cape Egmnt Fault Zne cincided with this perid. Thus, the Taranaki Graben, encmpassed by the Cape Egmnt Fault Zne, frmed a pssible nrthward extensin t the Mnlight Aulacgen and ther Suth Island basins described by Carter & Nrris (1976). The drmancy in activity alng several faults f the Cape Egmnt Fault Zne in Late Micene Early Plicene times may well cincide with impedance t dextral transfrming pssibly assciated with a suthwestward-plunging plate bundary develped in Nrthland, as suggested by Brthers

14 Knx-Taranaki Basin (1974) and expressed by a series f vlcanic arcs (Ballance 1975). Certainly change in defrmatin style and reginal stress ccurred by Late Micene time and cntinued thrughut Pli-Pleistcene and Recent times. This defrmatin phase had, during Late Micene-Early Plicene times, differing respnses thrughut Taranaki Basin. The Western Unit was largely unaffected, but the Nrthern Unit underwent igneus intrusin prbably as late Middle Micene-Late Micene extensins f the activity in Crmandel (Ballance 1975). Further nrth, Ballance (1975) and Hayward (1976) recgnised Early-Middle Micene vlcanism in Nrthland which extended at least t the suth f Manukau Harbur. Well data and seismstratigraphic crrelatin and land mapping (Hathertn 1968) suggest that intrusives and extrusives in the Nrth Taranaki Basin are f late Middle-Late Micene age. Tw temprally distinct vlcanic prvinces are prbably present, as suggested by ffshre igneus-related magnetic and gravity anmalies (Hathertn et a ), which are different nrth and suth f Manukau Harbur. Meanwhile, Zne A f the Suthern Unit suffered cmpressin and develpment f reverse and/r thrust faults which inverted Late Micene and lder sedimentary sequences. The area ccupied by the adjacent Suth Wanganui Basin was a high area and was severely erded during the same perid. Zne B als underwent uplift and fault reversal, and uplift ccurred in the Maui Field where a basal Plicene uncnfrmity was develped. A tpgraphic differential develped alng the Ck-Turi Lineament, between the. Nrthern and Suthern Units, and ersinal channels frmed alng the fault line (Fig. 6). Fllwing the develpment f the basal Plicene uncnfrmity/discnfrmity and subsequent marine transgressin (Pilaar & Wakefield 1978), sedimentatin was mre r less cntinuus in much f the area and was accmpanied by sme nrmal faulting. The Suth Wanganui Basin underwent subsidence at the same time (Andertn 1981). Renewed tectnism ccurred with the Plicene-Pleistcene episde. In the Nrthern Unit, synsedimentary fault activity was limited t a few faults alng the Cape Egmnt Fault Zne, and nrmal and. nrmal-blique dip-slip activity increased alng the - rthern sectr f the Ck-Turi Lineament and has extended int Recent time. The best manifestatin f this phase, hwever, is in Zne C f the Suthern Unit, where reverse faulting alng previusly nrmal faults caused the develpment f anticlinal structures which were erded and truncated by a basal Pleistcene uncnfrmity. The basal Plicene uncnfrmity which truncates the earlier inversins can be traced 137 frm the Kupe-1 area int Zne C where it is abruptly truncated (Fig. 3, D-D1). In cntrast, the sutheastern parts f Znes A and B subsided thrughut Pli-Pleistcene time cntempraneusly with the Suth Wanganui Basin t the east. The Taranaki Bundary Fault had further steep nrmal and/r reversed mvements during this perid. A similar structural histry f inversin has been recgnised in the nrthwest f the Suth Island (Laird 1968) which is in direct structural cntinuity with the Suthern Unit f the Taranaki Basin. Crss sectins (Suggate et al. 1978, fig. 7.60) exhibit a similar structure t the latter: Vitrinite reflectance measurements (Suggate & Lwery 1981) indicate up t 5000 m f uplift. Plicene inversin als ccurred in the Nrth Wanganui Basin (Nelsn & Hume 1977). The cmpressive tectnism in the Taranaki Basin began during the Late Micene and was renewed in Pli-Pleistcene time. The initiatin f this. tectnism bradly cincides with a change in spreading gem'1try f the Pacific and Indian! Australian plates, the extinctin f the Nrthland-Crmandel v'<;anic arc, and develpment f the present Fiji Kermadec trench system with a dipping plate bundary beneath much f the Nrth Island. The dipping plate bundary is expressed by a zne f recrded earthquake fci (Hathertn 1970; Adams & Ware 1977) which deepen frm east t west (Fig. 9) suggesting the prbable psitin f the underthrust Pacific plate. The western limit f.the deepest fci (apprx. 250 km) cincides with the surface prjectin f the Ck-Turi Lineament. Even deeper fci at 600 km (Adams & Ferris 1976) are cnsidered t represent fundered lithsphere. Thus, the area f Late Micene-Recent phases f reverse faulting and inversin in Taranaki Basin is lcated abve a plunging Beniff zne and a zne f crustal cllisin. Pilaar & Wakefield (1978) applied a kinematic shear mdel, prpsed by Harding (1974), t Taranaki Basin t develp a first-rder right-lateral wrench mdel rientated in a nrth-suth directin. Such a mdel is applicable in a simple case where undefrmed sediments verlying a basement fault underg defrmatin fr the first time under a unidirectinal stress. This cnditin may well have applied during Late Ecene-Middle Micene time when nrmal synsedimentary faulting ccurred alng the Cape Egmnt Fault Zne and a graben feature frmed. Such a situatin wuld have been cntinuus t the suth n the Suth Island. I During Late Micene time, igneus intrusins in the nrth, cupled with a fading f fault activity and cmpressive defrmatin phenmena in the Suthern Unit, heralded a change in the relative mvements f crustal blcks. Instead f a nrth-

15 138 New Zealand Jurnal f Gelgy and Gephysics, 1982, Vl. 25 LEGEND Nrmal Fault... Reverse Fault -IOOkm- Isbatha f Seismic Activity 9_..., 4...1pm SCALE Western Unit N t::: Fig.9 Isbaths f seismic activity (adapted frm Adams & Ware 1977) and structural subdivisins f Taranaki Basin. The surface prjectin f the deepest activity cincides with the Ck-Turi Lineament.

16 Knx-Taranaki Basin INDO - AUSTRALIAN PLATE EDGE NI SI TBF CTL AF EZJ mnm Nr t h Island Suth Island Taranaki Bundary Fault Ck - Turi Line Alpine Fault Crustal shrtening expressed by reverse faultin\! / inversin and / r uplift. Vertical prjectin and suthward extrapatin f Ck - Turi Lineament. 139 / vr dippin\! plate bundary v vertical plate bundary Fig. 10 Schematic blck diagram illustrating the gemetrical relatinship f the Suthern Unit and the Ck-Turi Lineament t majr tectnic features in New Zealand. suth-directed shear, a nrtheast-suthwest blique shear develped., At the same time, cmpressive uplift ccurred alng the Alpine Fault (Mlnar et al. 1975; Carter & N9rris 1976). In this situatin, the Taranaki Bundary Fault acts as a satellite splay fault frm the Alpine Fault. A nrtheastward mving crustal blck n the nrthern side f the Alpine Fault wuld develp an verlap where sediments in the eastern part f Taranaki Basin are squeezed against the upthrwn basement blcks n the eastern side f the Taranaki Bundary Fault. The verlap, hwever, is nt simply cnstrained by a change in rientatin f a vertical fault. The plunging earthquake fci disappear beneath the extreme nrthwest f the Suth, Island. A change frm a dippiilg plate bundary i'll the nrth t a vertical plate bundary beneath the Suth Island is assumed (Fig. 10). The strike f the dipping plate bundary intersects the strike f th'j! Alpine Fault at an btuse angle. Thus, a nrtheastward mving plate Will be cnstrained at depth as it intersects the dipping plate and tends t ride upwards. Where the angle 'f the dipping plate bundary reaches a vertical attitude, the verriding wuld nt ccur and a stress differential at the surface culd cause a fault system t prpagate within the cntinental crust (Ck Turi Lineament) and separate a relatively dwnthrwn blck (Nrthern Unit) frm a mre psitive feature abve the dipping plate bundary (Suthern Unit). In this respect, the feature is n strike with the western edge f the Lau-Clville Ridge. The Late Plicene event is cntinuing tday in the nrthwest Suth Island and reflects present-day crustal gemetry. The Late Micene phase culd reflect the initiatin f this gemetry where a dipping plate bundary was nt s far west nr as deep as it is at present. Hence, cmpressive defrmatin may nly have acted n the mst easterly part f Taranaki Basin, and at the same time caused uplift f the area f the Suth Wanganui BasIn. The dwnwarping f the latter develped later as the dipping plate bundary frmed. Ballance (1975) has prpsed that an antic1ckwise 70 bending f the Nrthland Peninsula ccurred between 3 m.y. ag and the present. Such Sig, 2

17 140 New Zealand Jurnal f Gelgy and Gephysics, 1982, Vl. 25 a bending wuld have caused severe space prblems in the Nrth Taranaki Basin leading t cmpressive defrmatin. The structural gemetry f the Nrthern Unit is dminated by synsedimentary nrmal faulting during this perid and therefre des nt supprt the bending cncept. ACKNOWLEDGMENTS This paper is published with the permissin f Petrleum Crpratin f New Zealand (Explratin) Limited, Shell (Petrleum Mining) Cmpany Limited, BP (Oil Explratin) Cmpany f NZ Limited, and Tdd Petrleum Mining Cmpany Limited. The paper is based n data in unpublished reprts f present and previus staff f the Explratin Department f Shell BP and Tdd Oil Services Limited and als n sme pen-file data held at the New Zealand Gelgical Survey. S. Duff, G. Pearce, L. Pearce, J. Scanln, and E. van Scherpenzeel critically read the initial manuscripts, and draughting was carried ut by D. Tle and R. Whyte. REFERENCES Adams, R. D.; Ferris, B. G. 1976: A further earthquake at exceptinal depth beneath New Zealand. New Zealand jurnal f gelgy and gephysics 19: Adams, R. D.; Ware, D. E.1977: Subcrustalearthquakes beneath New Zealand lcatins determined,with a laterally inhmgeneus velcity mdel. New Zealand jurnal f gelgy and gephysics 20: Andertn, P. W. 1981: Structure and evlutin f the Suth Wanganui Basin, New Zealand. New Zealand jurnal f gelgy and gephysics 24: Ballance, P. F. 1975: Evlutin fthe Upper Cenzic arc and plate bundary in nrthern New Zealand. Earth and planetary science letters 28 : Brphy, F.; Falln, A.; Campbell, N. 1979: Nrth Tasman N.1 (NTA1) PPL New Zealand well cmpletin reprt. New Zealand Aquitaine Petrleum Limited. New Zealand Gelgical Survey unpublished pen-file petrleum reprt 736. Brthers, R. N. 1974: Kaikura Orgeny in Nrthland, New Zealand. New Zealand jurnal f gelgy and gephysics 17: Carter, R. M.; Nrris, R. J. 1976: Cainzic histry f suthern New Zealand: An accrd between gelgical bservatins and plate tectnic predictins. Earth and planetary science letters 31: Harding, T. P. 1974: Petrleum traps assciated with wrench faults. AAPG bulletin 58(7) : Hathertn, T. 1968: A surce fr vlcanic material in the Mhakatin beds. New Zealand jurnal f gelgy and gephysics 11 : : Gravity, seismicity, and tectnics f the Nrth Island, New Zealand. New Zealand jurnal f gelgy and gephysics 13 : Hathertn; T.; Davey, F; J.; Hunt, T. M. 1979: Gephysical anmalies arid igneus bdies ff the west cast, Nrth Island. Jurnal f the Ryal Sciety f New Zealand 9: Hayward, B. W. 1976: ;Lwer Micene stratigraphy and structure f the Waitakere Ranges and the Waitakere Grup (new). New Zealand jurnal f gelgy and gephysics 19: Hematite Petrleum (N) Ltd 1970: Mangaa-1 (Offshre). New Zealand GeQlgical Survey unpublished penfile petrleum reprt 554. Hunt, T. M. 1978: Stkes Magnetic Anmaly System. New Zealand jurnal f gelgy and gephysics 21 : '. Kear, D. 1971: Basement rck facies-nrthern Nrth Island. New Zealand jurnal f gelgy and gephysics 14 : Laird, M. G. 1968: Thi:: Papara Tectnic Zne. New Zealand jurnal' f gelgy and gephysics 11: : The Late Meszic fragmentatin f the New Zealand segplent f Gndwana. In: Cresswell, M. M.; Vella, P. ed. Gndwana five. Prceedings f the Fifth Internatinal Gndwana Sympsium, Wellingtn, New Zealand Feb. 1980: Laird, M. G.; Hpe, J.M. 1968: The Trea Breccia and the Papahaua Overfld. New Zealand jurnal f gelgy and gephysics 11 : MCBeath, D. M. 1977: Gas cndensate fields f the Taranaki Basin, New Zealand. New Zealand jurnal f gelgy and gephysics 20: Mlnar, P.; Atwater, T,; Mammerycx, J.; Smith, S. M. 1975: Magnetic malies, bathymetry and the tectnic evlutin f. the Suth Pacific since the Late Cretaceus..]urnal f the Ryal Astrnmical Sciety 40 : 383 ':::,420. Nelsn, C. S.; Hilme, T. M. 1977: Relative intensity f tectnic events revealed by the Tertiary sedimentary recrd in e Nrth Wanganui Basin and adjacent areas, N!:w Zealand. New Zealand jurnal f gelgy and g(lphysics 20 : NZ Aquitaine Petrleum Ltd 1976: Surville-1 well cmpletin repr);f New Zealand Gelgical Survey unpublished pefile petrleum reprt 677. Pilaar, W. F. 1:1.; Wakefield, L. L. 1978: Structural and stratigraphic evfutin f the Taranaki Basin, ffshre Nrth Islnd, New Zealand. Juma.l f the Australian PetrleUm Explratin Assciatin 18 : Shell BP and Tdd Oil Services Ltd 1977: Well resume Tane-1 (Offshre): New Zealand Gelgical Survey unpublished pen-file petrleum reprt 698. Suggate, R. P.; Lwery; J. 1981: Reflectance and cal rank. New Zealand Gelgical Survey reprt M p. Suggate, R. P.; Stevens, G. R.; Te Punga, M. T. ed. 1978: The gelgy f New Zealand. Wellingtn, Gvernment Printer, 2 Vls, 820 p. Wdzicki, A. 1974: Gelgy f the pre-cenzic basement f the Taranaki-Ck Strait-Westland area, New Zealand based n recent drill hle data. New Zealand jurnal. f gelgy and gephysics 17: