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Paleostress orientations fromstriations in Torlesse rocks, OtakiForks, Tararua Range, New ZealandMark S. Rattenbury a b & K.B. Spörli aa Department of Geology , University of Auckland , Private Bag,Auckland , New Zealandb Department of Geology , University of Otago , P.O. Box 56,DunedinPublished online: 06 Feb 2012.

To cite this article: Mark S. Rattenbury & K.B. Spörli (1985) Paleostress orientations fromstriations in Torlesse rocks, Otaki Forks, Tararua Range, New Zealand, New Zealand Journal ofGeology and Geophysics, 28:3, 435-442, DOI: 10.1080/00288306.1985.10421197

To link to this article: http://dx.doi.org/10.1080/00288306.1985.10421197

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New Zealand Journal of Geology and Geophysics, 1985, Vol. 28 : 435-442 4350028-8306/85/2803-0435$2.50/0 © Crown copyright 1985

Paleostress orientations from striations in Torlesse rocks,Otaki Forks, Tararua Range, New Zealand

MARK S. RATTENBURY·K. B. SPORLI

Department of GeologyUniversity of AucklandPrivate BagAuckland, New Zealand

Abstract Fibre striations in Torlesse rocks atOtaki Forks record a late, brittle deformation witha north-south subhorizontal compression. Thestriations occur on small-scale faults which aremainly reverse and strike-slip, and may be asso­ciated with a regime of folding on subhorizontal,east-west-trending axes . Fibre striations are post­dated by scratch striations.

Keywords striations; structural analysis; stress;Torlesse; Tararua Range

INTRODUCTION

Striations can be used to estimate paleostress ori­entations in brittle faulted rocks (Arthaud 1969;Angelier 1978; Sporli & Anderson 1980; Bruhn &Pa viis 1981). Such structures are common in the

.basement Torlesse terrane of New Zealand. (Coombs et al. 1976) and record important, usuallylate, stages of its deformation. We report on a studyof these structures with the hope of encouragingfurther work elsewhere, so that regional compari­sions can be made. The study area (Fig. I) is partof uplifted Mesozoic Torlesse greywacke sequencesthat form the Tararua Range. The lithologies aredominated by thick-bedded quartzofeldspathicsandstone and alternating thin sandstone and argil­lite. One sequence has Late Triassic fossils (Grant­Taylor & Waterhouse 1963, and Fig. I) ; the rest ofthe sequence is as yet undated. The rocks have beenaffected in tum by early isoclinal folding, brokenformation style deformation, solution and veining,movement on striated fault surfaces, moderateplunge open folding, sinistral and dextral steeplyplunging asymmetric folds, and recent fault brec­ciation (Rattenbury 1982). Brittiy deformed brokenformation is common throughout the area although

·Present address: Department of Geology, University ofOtago, P.O. Box 56, Dunedin.

Received 9 January 1984, accepted 7 December 1984

particularly developed in distinct zones includingthat of locality A, lower Otaki River, and theWaiotauru River (Fig. I) where the largest concen­trations of striations occur. The two localities belongto two different structural domains. At local ity A,

Fig. 1 Otaki Forks area showing major fault zones, bed­ding/broken formation fabric formlines with majoryounging direct ions, and Monotis localities (after Ratten­bury 1982). Inset shows the area in relation to the Tar­arua Torlesse terrane (shaded) and major active faults(after Kingma 1967).

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436 New Zealand Journal of Geology and Geophysics, 1985, Vol. 28

A Ov erp rint ing

qua rtz- enoree fbre striae (earler)

B Relat ion to fold s

quartz-chlorrte fbre striae

~ scratch striae

Fig. 2 A Relation of quartz­chlorite fibre striations to laterscratch striations (locality A,sketch of specimen AU35297). BRelation of quartz-chlorite fibreand scratch striations in a fold(sketch of outcrop, locality A). CStriation/vein relations in finesandstone/argitli te sequence(Waiotauru River, sketch of spec­imen AU35298). Circled numberslabel phases of veining and fault­ing. Specimen numbers refer toDepartment of Geology, Univer­sity of Auckland referencecollection.

C Relat ion to other veins

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along waftsstriae

o 2cm.~

Bedding

folds with horizontal east-west-trending axes arepredominant, whereas, in the Waiotauru River,steeply plunging folds are more dominant and thebroken formation fabric trends NNE-SSW.

STRIAnON ANALYSIS

Striations here occur in two types: scratch stria­tions and quartz-chlorite fibre striations. Scratchstriations consist of grooves and ridges mostlydeveloped in argillite and are associated with shinyslickenside surfaces. Quartz-chlorite fibre striationsare formed by the accretion of fibrous quartz, withinterstitial chlorite, into voids opened duringmovement along irregular fault surfaces, by a crack­seal mechanism (Ramsay 1980). Scratch striationspostdate the quartz-chlorite fibre striations (Fig. 2A)and could perhaps be associated with faults show­ing recent activity such as the Otaki Fault Zone(Hancox 1977), a 200 m wide zone of brecciated

rock and gouge. In one example (Fig. 2B), fibrestriations are at right angles to the fold axis arounda subhorizontal fold and are overprinted by scratchstriations parallel to the fold axis. Fibre striationsare both predated and postdated by nonfibrousquartz veins (Fig. 2C). The direction of quartz­chlorite fibre growth from step walls uniquely indi­cates the direction of fault movement. (Durney &Ramsay 1973), but steps on fault surfaces withoutfibre growth (roughness direction) do not neces­sarily represent the sense of fault movement(Paterson 1958; Tjia 1964).

For all fibre striations we have determined an m­axis (intermediate axis), at right angles to the stria­tion direction in the striated fault plane (Fig. 3A).A compression axis and extension axis can also beconstructed where the sense of fault movement isknown. The compression axis lies within the M­plane (to which the m-axis is pole) at an angle 9 tothe striation, and the extension axis is by definitionat right angles to the compression axis, within the

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Rattenbury & Sporii-c-Paleostress orientations, Otaki Forks 437

Fig. 3 A Striation geometry. B Example of clusteranalysis (from locality A, set I). C Calculation of SumVector for cluster analysis (each solid line represents acompression or extension axis of unit length).

M-plane. For a population offaults, a best-fit anglee can be determined by a cluster analysis of thecompression and extensions calculated through arange of evalues, assuming that the faults all belongto the same kinematic system (Sporli & Anderson1980).At locality A, the best-fit angle e lies between20 and 30° (Fig. 3B). We have measured 150 stria­tions at locality A and 134 striations at the Waio­tauru River.

Locality A, lower Otaki River

Shears with fibre striations can be subdivided intogroups according to the orientation of theircompression and extension axes (Fig. 4). Strike-slipshears (set 1)with a north-south-oriented compres­sion direction and an east-west-oriented extensiondirection are most common. Subordinate dip-slip(thrust) shears (set 2) have a similar north-south­oriented compression direction and a steeply eastdipping extension direction. Another set ofdip-slipshears (set 3) are partly normal and partly reverse,and have an extension direction similar to that ofthe set I strike-slip faults. There is a similar arrayof strike-slip (set 4) and dip-slip shears centred ona northeast-southwest compression system. Thepattern indicated by the striated surfaces is dupli­cated by the directions of compression and exten­sion of mesoscopic single and conjugate faults (Fig.4F).

The striation/fault pattern can be matched withthe model for fault patterns of Wilcox et al. (1973)and Harding (1974), as shown in Fig. 5. The strike­slip shears at locality A correspond to the syntheticand antithetic faults, and the dip-slip shears to thethrust/reverse faults of the tectonic model. Thenormal faults predicted by the model are not aswell defined but may be represented by set 3. Therecurrence of the same pattern centred on a north­east-southwest compression may be due to a changein the principal stress orientation or rotation of therocks. The fold hinge orientations (Fig. 4G) also fitthe Harding model. Some of the fibre striationshave been folded by these subhorizontal open folds;other striations cut across the folding, indicating asynchronous development. The close associationof the striations with folding, and the fact that thefolds do not appear to form an en echelon pattern,may indicate this Wilcox-Harding pattern of faultsdeveloped in a pure shear regime, during forma­tion of the east-west-trending folds. Such fault pat­terns are common for folds formed at relativelyhigh levels in the crust (Friedmann & Stearn 1971).Alternatively, if a simple shear origin has to beaccepted for the fault pattern, dextral movementon northwest-southeast-trending master faults orsinistral movement on northeast-southwest-trend­ing faults would be indicated. At the moment wehave no direct evidence for such simple shear. Insuch a simple shear regime, the northeast-south­west-trending faults that dominate the southern partof the North Island would not show dextral move­ment, corresponding to the expected pattern (Len­sen 1958), but would be sinistral, compatible withmovement postulated for Mesozoic slip along sev­eral faults of that direction (Sporli 1979). Scratchstriations are relatively rare and there are insuffi­cient concentrations for meaningful interpretation.

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Rattenbury & Sporli-s-Paleostress orientations, Otaki Forks 439

~

Fig.5 A Harding (1974) model of fault patterns, showing relative orientations of the strike-slip faults (I), reversefaults (2), normal faults (3), and concurrent folding, in relation to strain ellipse. B Stereonet projection of the Hardingmodel (triangles = extension axes, dots = compression axes). C Schematic fault/fold model for locality A (stippledsurface is plane of bedding/broken formation shear fabric).

A kinematic interpretation is impossible as no un­equivocal movement sense can be determined.

Waiotauru River

Three major fibre striation sets are part of a regimewith dominant subhorizontal north-southcompression (Fig. 6); sets 1 and 2 are mainly dip­slip thrusts, and set 3 is mainly strike-slip. Twoapplications of the Harding (1974) model are pos­sible. (1) The pattern can be considered to lie in asubhorizontal plane (Fig. 7A), similar to that oflocality A, with the dip-slip shears of set 1 corre­sponding to the reverse faults of the model. (2) Thepattern lies in a steeply west-dipping plane (Fig.7B) with the dip-slip shears of set 1 correspondingto the strike-slip faults of the Harding model andset 3(?) the reverse faults. The normal or exten­sional faults of the Harding model appear to besparsely represented. They should be normal dip­slip faults with east-west extension for the hori­zontal pattern (set 4, Fig. 7A), and reverse dip-slipfaults with east-west compression for the verticalpattern (set 5, Fig. 7B). Both sets of extensionalfaults are present (Fig. 6D) which may indicate thatboth models apply simultaneously. The most simpleexplanation of the strike-slip shears in the remain­der (Fig. 6D) is that they are set 3 shears rotatedby folding on steeply plunging axes (Fig. 7). Theage of the steeply plunging folds in the Waiotauru

River rocks relative to the striation shears is uncer­tain. The steep fold hinges fit the second alterna­tive better, but this may only be because horizontalfold hinges could not develop in this area of steeplydipping beddingfbroken formation fabric (Fig. 6H).An unsolved question is whether the striationsdeveloped before or after tilting of the bedding andshear fabric to steep dips. Scratch striations arepresent in small numbers and again have not beenanalysed in detail.

DISCUSSION

Fibre striations at locality A and Waiotauru Riverindicate a predominant north-south subhorizontalcompression. At locality A, strike-slip faulting ispredominant and at Waiotauru River, dip-slip(reverse) faulting is more common. In both areas,the dominant extension directions lie within themost common fabric plane (Fig. 4H, and 6F). Thiscould indicate either that the striations were formedafter strata in the areas were rotated into their pres­ent orientations, and that the bedding/broken for­mation fabric anisotropy played an important rolein fixing the direction of extension, or that theWaiotauru River bedding/broken formation fabrichas been steepened since formation of the striae.The contrasting fold styles (open, moderately sym-

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440 New Zealand Journal of Geology and Geophysics, 1985, Vol. 28

N

A. Set 1 dip-slip (reverse) shears

N

B. Set 2 dip-slip (reverse) shears

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Fig.6 Structural data from Waiotauru River (F: contours at 1%per 1%area, 283 points; dashed line = most commonplane, triangle = dominant extension direction; stereonets are all equal area and lower hemisphere).

metric at locality A; tight and asymmetric at Waio­tauru River), and the absence oflow-plunge foldingresponsible for the steepening, does not favourpoststriation tilting. In each area, the strain is takenup by at least two, if not three, sets of conjugatefaults consisting of four or six sets of fault planesrespectively. Three-dimensional strain patterns ofthe type proposed by Reches (1978) may be indi­cated. Compression directions derived at localityA and Waiotauru River are almost at right anglesto the present-day east-west-trending shorteningdirection derived from geodetic observations andmicroseismicity studies in the southern part of theNorth Island (Walcott 1978; Arabasz & Lowry1980).

Diagrams of m-axis orientations are complex. Atlocality A, striated surfaces with steps and quartz­chlorite fibres indicating a sense of movement aremostly dip-slip, while those without steps are mostly

strike-slip (Fig. 8). This may be because faults withsmall displacements have intact steps, while thosewith larger displacement have had their steps obli­terated by progressive movement. If this is true,our analysis would indicate that the dominant modeof faulting is strike-slip. A logical corollary to thetectonic model of Harding (1974) is that the m-axesshould form three mutually perpendicular clusterscorresponding to the strike-slip, reverse, and nor­mal faults. This has been independently predictedby Arthaud (1969) and demonstrated by Bruhn &Pavlis (1981), but neither locality A nor the Waio­tauru River shows this distribution well. This ispartly due to the minor role of normal faulting andthe possibility ofcontinuing folding during the for­mation of the striations.

Nothing is known about the absolute age of thestriations, although they are well bracketed withinthe locally recognised structural sequence. The his-

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Rattenbury & Sporli-i-Paleostress orientations, Otaki Forks 441

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Fig. 8 m-axis orientations from locality A (A) andWaiotauru River (B), of striations with known movementsense (dots) and without (crosses). There is no indicationof mutually perpendicular girdle patterns (stereoncts areequal area and lower hemisphere).

tory of deformation is too complex to allow specu­lation on whether the structures are syn- or post­Rangitata Orogeny. Only a careful study of occur­rence of striation-bearing clasts in basal conglom­erates of various ages will narrow down the timeinterval in which the striations may have been

formed. Similar striations in the Waipapa terraneof Auckland are postmetamorphic and pre-Mio­cene (Sporli & Anderson 1980). It is likely, but notproven, that the later scratch striations associatedwith fault-gouge and fault-breccia zones at OtakiForks are of Cenozoic origin.

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442 New Zealand Journal of Geology and Geophysics, 1985,Vol. 28

ACKNOWLEDGMENTSThe authors wish to thank R. J. Norris and an anony­mous reviewer for critical comment on the manuscript.Roy Harris is thanked for draughting some of the figures.

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since the Late Miocene. Tectonophysics 49 : 23-36.Arabasz, W. J.; Lowry, M. A. 1980: Microseismicity in

the Tararua-Wairarapa area: depth varying stressesand shallow seismicity in the southern NorthIsland, New Zealand. New Zealand journal ofgeol­ogy and geophysics 23: 141-154.

Arthaud, F. 1969: Methode de determination graphiquedes directions de raccourcissement, d'allongementet intermediaire d'une population de failles. Bul­letin de la Societe Geologique de France 7: 737­739.

Bruhn, R. L.; Pavlis, T. L. 1981: Late Cenozoic defor­mation in the Matanuska Valley, Alaska: Three­dimensional strain in a forearc region. GeologicalSociety ofAmerica bulletin 92: 282-293.

Coombs, D. S.; Landis, C. A.; Norris, R. J.; Sinton, J. M.;Borns, D. J.; Craw, D. 1976: The Dun MountainOphiolite Belt, New Zealand: its tectonic setting,constitution and origin with special reference tothe southern portion. American journal of science276: 561-603.

Durney, D. W.; Ramsay, J. G. 1973: Incremental strainsmeasured by syntectonic crystal growths. In: deJong, K. A.; Scholten, R. ed. Gravity and tectonics.Wiley. Pp. 67-96.

Friedmann, M.; Steam, D. W. 1971: Relations betweenstresses inferred from calcite twin lamellae andmacrofractures, Teton anticline, Montana. Geolog­ical Society ofAmerica bulletin 82: 3151-3162.

Grant-Taylor, T. C; Waterhouse, J. B. 1963: Monotis fromthe Tararua Range, Wellington. New Zealandjour­nal ofgeology and geophysics 6: 623-627.

Hancox, G. T. 1977:Mt Hector water utilization and con­servation scheme-interim report on reconnais­sance engineering geological investigations. NewZealand Geological Survey engineering geologyreport EG282.

Harding, T. P. 1974: Petroleum traps associated withwrench faults. American Association of PetroleumGeologists bulletin 58: 1290-1304.

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

Lensen, G. J. 1958:The Wellington Fault from Cook Straitto Manawatu Gorge. New Zealand journal ofgeol­ogy and geophysics 1: 178-196.

Paterson, M. S. 1958: Experimental deformation andfaulting in Wombeyan marble. Geological SocietyofAmerica bulletin 69: 465-476.

Ramsay, J. C. 1980: The crackseal mechanism of rockdeformation. Nature 284: 135-139.

Rattenbury, M. S. 1982: Geology of Otaki Forks, TararuaRange. Unpublished M.Sc. Hons thesis, lodged inthe Library, University of Auckland. 109 p,

Reches, Z. 1978: Analysis of faulting in three-dimen­sional strain fields. Tectonophysics 47: 109-129.

Sporli, K. B. 1979: Structure of the South Island Torlessein relation to the origin of the Southern Alps. In:Walcott, R. I.; Cresswell M. M. ed. The origin ofthe Southern Alps. Royal Society ofNew Zealandbulletin 18: 99-104.

Sporli, K. B.; Anderson, H. 1980: Paleostress axes frommineral striations in faulted Mesozoic basement,Auckland, New Zealand. New Zealand journal ofgeology and geophysics 23: 155-166.

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