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Anatomy, structural evolution, and slip rate of a plate-boundary thrust: The Alpine at Gaunt Creek, Westland, New Zealand

ALAN F. COOPER RICHARD J. NORRIS j- Department, University of Otago, P.O. Box 56, Dunedin, New Zealand

ABSTRACT South Island, New Zealand, is one of Earth's ture over a 40-km section southwest of Gaunt major transpressional structures. It has a Creek, and we have found a similar pattern of Minimum slip rates calculated for plate-vec- documented dextral strike-slip displacement alternating thrust and strike-slip sections in tor-parallel trends in on of480 km (Wellman, 1955), and as much as 70 the zone 85 km farther south, the sole of the Alpine fault at Gaunt Creek, km of convergence by reverse oblique slip north of Haast River. Westland, New Zealand, range from 18 to 24 (Walcott, 1979; Allis, 1986). Transpression The best exposure of the Alpine fault in mm/yr. Between half and two-thirds of the to- has resulted in the exhumation of amphibo- Westland is at Gaunt Creek, Waitangi-taona tal relative motion between the Pacific and Aus- lite-facies rocks from depths of 20-25 km River, which lies on the longest thrust seg- tralian plates is being accommodated by move- (Wellman, 1979; Cooper, 1980), most of ment mapped to date (Fig. 1). This paper de- ment on a single structure, the Alpine fault. which has occurred in the past 7 m.y. (Kamp scribes details of this outcrop and discusses During the past 14 ka, the leading edge of and others, 1989). Physiographically, the Al- the implications of the inferred tectonic his- the Alpine fault has changed from a moder- pine fault is best expressed in central West- tory on the mechanics of thrusting, the gen- ately southeast-dipping, oblique reverse fault land, where it separates the 3-km-high moun- eration of overthrusts, and the geomorphic to a shallowly dipping thrust. The hanging wall tains of the Southern Alps in the east from the evolution of the Alpine fault plate boundary. (Pacific plate) is composed of a gradational se- topographically subdued terrain of the quence from basal gouge, through pseudo- coastal apron to the west. On satellite REGIONAL GEOLOGY tachylite-bearing cataclasite, to progressively imagery, the is remarkably linear, more coherent schist-derived , which striking northeastward (055°). In central The regional geologic history and tectonic has been faulted against subhorizontally bed- Westland, however, the linearity of the fault development of the Alpine fault plate ded, fluvio-glacial gravel in the footwall (Aus- trace is illusory, and mylonitized schist from boundary were reviewed recently by Norris tralian plate). During uplift the hanging-wall the Southern Alps has been transported west- and others (1990). The rocks exposed to the sequence has been internally sheared and im- ward in a series of napplets over the West northwest of the Alpine fault in the Waitangi- bricated, producing duplex structures, and Coast sequence for distances of up to 2.5 km taona River area are composed of foliated retrogressively veined and altered by pervasive from the Alpine front (Bowen, 1954). These granitoid and quartzofeldspathic gneiss of hydrothermal fluid flow. overthrusts have been attributed to gravity probable Mesozoic age (Kimbrough and oth- Erosion of the exhumed fault zone produced collapse of the range front (Wellman, 1955; ers, 1994; Rattenbury, 1991) overlain by Qua- angular, cataclasite- and mylonite-derived, ta- Suggate, 1963) or tectonic shortening (Norris ternary moraine and fluvio-glacial gravel lus-fan breccias, building a west-dipping apron and others, 1990). (Fig. 1). Southeast of the Alpine fault, the beneath the . Wood fragments from Recent detailed field mapping between the Southern Alps are made up of the Haast near the base of the talus breccias have been Fox and Whataroa rivers has shown that the Schist, which reaches a metamorphic grade 14C dated at 12,650 ± 90 yr B.P. Progressive fault zone is far from simple, comprising al- of amphibolite facies in the zone of maximum tectonic shortening resulted in 180 m of over- ternating segments that have average strikes uplift adjacent to the fault. thrusting of a schist-derived across an ranging from 010° to 050° and 070° to 090°, irregular talus fan surface composed of its own respectively (Norris and others, 1990). East- GAUNT CREEK SECTION erosional debris. The structural history of the trending fault segments dip steeply but con- Alpine fault at Gaunt Creek illustrates the im- tain gently plunging and - On the south bank of Gaunt Creek, the Al- portance of the interaction between fault-in- sense indicators that suggest predominantly pine fault is exposed in an outcrop almost 700 duced topography and erosion, and the control dextral strike-slip displacement. In contrast, m long and >100 m high (Figs. 2, 3). The these processes exert on the continued tectonic, the more northward-striking segments are fault, marked by a zone of cataclasite in the geometric, and geomorphic evolution of the characterized by thick zones of cataclasite hanging wall, dips 40° southeast at creek fault zone. overlying a gently to moderately east-dipping level, but, 200-300 m northwest, isolated fault surface. Slickenside lineations indicate patches of cataclasite in the middle sections INTRODUCTION oblique thrusting. Fault segments range from of the face define a shallow, south-dipping hundreds of meters to several kilometers in thrust. In the southeastern part of the expo- The Alpine fault, forming the boundary be- length (Norris and others, 1990, Fig. 2). Seg- sure, cataclasite overlies fluvial gravel com- tween the Pacific and Australian plates in the mentation dominates the Alpine fault struc- posed of rounded schist clasts, but farther

Geologica) Society of America Bulletta, v. 106, p. 627-633, 5 figs., 1 table, May 1994.

627

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Figure 1. Locality maps. A. Plate boundary structures in the South Island, New Zealand, with localities referred to in the text. Heavy arrow represents the direction of motion of the Pacific plate, determined from the pole of rotation given by DeMets and others (1990). B. Geology of the Waitangi-taona River catchment, Westland, illustrating the segmented nature of the Alpine fault trace. Outcrop of the Alpine fault described in Figures 2 and 3 is labeled as Gaunt Creek Slip. The shading shown on the Waitangi-taona River thrust segment of the Alpine fault indicates, somewhat diagrammatically, the distribution of cataclasite.

northwest, the thrust has ridden over angular melt structures, suggests that deposition oc- cross-beds, developed between individual mylonite debris. Structurally above the fault, curred during a glacial period, probably the units of breccia. A large wood fragment, in- a varied sequence of cataclasite passes gra- last glaciation. In a zone as much as 2 m wide corporated in fine-grained sediments near the dationally into cataclastic mylonite and ulti- beneath the fault surface, platy schist tablets base of the sequence (Fig. 2), has yielded a mately into intact or coherent mylonite. in the gravel have been rotated into a subver- 14C age of 12,650 ± 90 yr B.P. (Table 1). In- tical orientation by fault drag. cluded in the debris are blocks of the pale Fluvio-glacial Gravel green, basal cataclasite, which—based on Mylonite-Derived Gravel observed present-day erosional behavior— In the southeast part of the Alpine fault survives fluvial transport for distances of only outcrop, the footwall is a sequence of crudely Subhorizontal bedding in the fluvial gravel a few or, at most, tens of meters. The largest bedded gravel composed of rounded, schist- is truncated to the northwest by a west-dip- blocks of mylonite rest on top of the dipping derived clasts. Coarse schist plates are com- ping erosional surface marking the base of a sequence and have an internal that monly imbricated with an inferred flow direc- younger sequence of lenticular breccias and dips eastward. Gravel units likewise have tion similar to that of the present-day creek. gravels. In contrast to the fluvial sequence, crude layering that also is back-tilted due to Sag structures in bedding may have origi- these younger sediments predominantly rotational slumping. nated by collapse of the creek bed following composed of angular and unsorted clasts of The predominantly mylonite-derived melting of underlying "dead" ice. The age of mylonite. Grain size is highly varied, ranging gravel passes abruptly up section into a thick the gravels is unknown, but the absence of from blocks many meters in diameter, to fine unit of subhorizontal to shallow west-dip- wood material, together with possible ice- sandy or silty seams, exhibiting fine-scale ping, poorly imbricated and cross-bedded

628 Geological Society of America Bulletin, May 1994

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SE NW 140° 320°

QUARTZOFELDSPATHIC AND AMPHIBOLITIC MYLONITE CUT BY GOUGE-FILLED SHEARS FLUVIAL OUTWASH/FAN GRAVEL WITH AND VEINS OF PSEUDOTACHYLITE. DUPLEX MIXED SCHIST-MYLONITE PROVENANCE. STRUCTURES COMMON.

BLACK ULTRACATACLASITE AND WOOD: 10,300 yrs B. P. WHISPY PSEUDOTACHYLITE. LENSES OF MYLONITE-DERIVED, TALUS FAN PALE GREEN CATACLASITE COMPOSED OF BRECCIA. LOCALLY LARGE. COMMONLY BACK-TILTED, FRAGMENTS OF CHLORITIZED MYLONITE SLUMP BLOCKS. AND QUARTZ.

SCHIST-DERIVED, FLUVIO-GLACIAL GRAVEL WITH SUBHORIZONTAL BEDDING AND STRONG PEBBLE IMBRICATION. 100m

Figure 2. Map of the Gaunt Creek slip face, compiled from horizontal photographs corrected for scale variations by radial-line methods (Ailum, 1966).

gravel, containing both mylonite and schist Lithologically, the most coherent material Mylonite debris. Fossil wood material collected from a within the cataclasite is an intensely crushed locality near the base of this sequence (Fig. 2) quartzofeldspathic mylonite invaded by veins Farther up section in the hanging wall, the yielded a 14C age of 10,300 ± 150 yr B.P. of ultracataclasite and pseudotachylite. Al- degree of cataclasis decreases gradually, and (Table 1). though strongly chloritized, relict biotite per- the rocks pass into foliated mylonite derived sists as inclusions in feldspars, and lenticular from both quartzofeldspathic and amphib- Basal Cataclasite trails of finely comminuted, granular garnet olitic rocks of the Haast Schist. Some of the are parallel to the foliation. Electron micro- types have been described as "curly" The Alpine fault surface is marked by a 50- probe analysis of the garnets yields compo- schist (Bowen, 1954; Reed, 1964), based on to 70-cm zone of moderately indurated gray sitions that are diagnostic of a Haast Schist the wavy nature of the foliation and the gouge, commonly exhibiting prominent slick- protolith (Mason, 1981). The basal cataclasite coarse grain size of relict muscovite flakes. In enside lineations. The mean orientation of the thins up dip and abruptly disappears at a modern terminology, the rocks would be S-C fault surface dips 39° southeast (150°), with height corresponding to the top of the fluvial (Lister and Snoke, 1984), in which slickensides plunging 24° almost due east gravel sequence. Here the orientation of the the mylonitic foliation, partly inherited from (086°) (Fig. 4a). Shear-sense indicators (S-C Alpine fault surface changes markedly, dip- the regional metamorphic schistosity, is fabrics and asymmetric tails to porphyro- ping 30° toward 210°. Isolated patches of cat- overprinted by zones of high shear strain. clasts) suggest dextral, reverse, oblique-slip aclasite reappear at distances of 120-180 m The mylonite, as with the underlying cata- displacement. farther west along the fault plane. clasite zones, is cut by numerous gouge-filled Structurally above the basal gouge, there is shears, representing planes of generally mi- a 30-m-thick zone of pale green cataclasite, nor, late-stage movement. Drag features in- composed of resistant chips of green mylo- Black Ultra-Cataclasite dicate that the shears are dominantly reverse nite and crushed vein quartz, enclosed in a dip-slip, although some with a normal dip-slip white to pale-green matrix of clay-rich gouge. Structurally overlying the pale green cata- character are also present. West-dipping Generally, the cataclasite is structurally ho- clasite is a rather heterogeneous unit of shears with normal slip are prominent in the mogeneous, although the clasts locally define similar thickness, which contains bands of hanging-wall section above the gravel and a crude streaky banding subparallel to the ultracataclasite alternating with lenticular may represent antithetic reverse faults reac- fault surface. In places this internal banding zones of cataclastic mylonite, in which a tivated during the change in slope of the basal dips more steeply than the cataclasite itself, schist protolith is obvious in hand specimen. thrust. Offset features in the mylonite indi- suggesting that some form of tectonic thick- Pétrographie observation indicates that len- cate displacements of no more than a few ening by stacking of duplex units is probably ticular and anastomosing black, flinty shear meters. Schist margins to some of the shear responsible (see mylonite section for more zones are composed of fresh pseudotachylite zones are noticeably bleached where mylo- detailed description). glass. nitically reciystallized biotite has been locally

Geological Society of America Bulletin, May 1994 629

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/106/5/627/3381983/i0016-7606-106-5-627.pdf by guest on 01 October 2021 Figure 3. Oblique aerial photograph of the Gaunt Creek slip face, with a view toward the southwest. Hills in the right background are the western, forested slopes of the Southern Alps, composed of recently uplifted amphibolite facies Haast Schist. The light-toned unit dipping southeast in the middle-left part of the photo is the pale green cataclasite unit of Figure 2, which directly overlies the Alpine fault surface.

chloritized. Some shear zones contain films pseudotachylite, are now exclusively devitri- tures, pseudotachylite, and gouge-filled of calcite and sparse grains of sulfide miner- fied to a sericite-rich aggregate. shears decreases, and the mylonitic foliation als. Clearly the shear zones have acted as ac- Structurally the mylonitic foliation dips becomes more regular, dipping 40°-50° to the cess channels for the movement of late-stage, about 42° to ;the southeast (129°), although southeast. The regional regularity of the dip heated hydrothermal fluids (compare Craw there is considerable scatter resulting from in- of the foliation also was recorded by Sibson and Koons, 1989). Black, flinty veins (up to 4 ternal imbrication (Fig. 4b). Between subsid- and others (1979, p. 61), and interpreted to cm wide), that originally formed both parallel iary shear zones subparallel to the basal reflect the dip of the Alpine fault at depth. and oblique to the mylonitic foliation as thrust, parts of the mylonite have been ro- tated so that the foliation has a steep, but of- HISTORY OF THE ALPINE FAULT AT ten sigmoidal, internal orientation. The GAUNT CREEK bounding shears to the duplex units intersect along a plunging 10° toward 218° TABLE 1. RADIOCARBON DATES, GAUNT CREEK The oldest, but undated, gravel of the (Fig. 4c), which is compatible with a subhor- Gaunt Creek section was deposited in a flu- Laboratory no. Host sediment 813C (%o) Radiometric age izontal shear direction trending 128°. Such vial, near-glacial environment >13 ka (yr B.P.)* duplex structures are an integral part of both (Fig. 5). As no mylonite or cataclasite debris cataclasite and mylonite units and clearly re- WK 2465* Mylonite-derived -27.7 12,650 + 90 has been recognized as detritus in the gravel, talus breccia quire essential tectonic shortening, rather either the site of deposition must have been INS 8244s Fluvial gravel -28.3 10,300 ± 130 than the simple gravity collapse suggested by upstream of the fault trace, or the fault was

•Age based on T1/2 = 5,568 yr. Wellman (1955) and Suggate (1963) for the unexposed, buried beneath older fluvio-gla- * Analysis at Radiocarbon Dating Laboratory, University of Waikato, Hamilton, New Zealand. origin of Alpine fault napplets. cial sediments. A similar situation exists cur- 'Analysis at Institute of Nuclear Sciences, Wellington, New Farther up section in the hanging wall, the rently in the flood plain of Gaunt Creek and Zealand. frequency of development of duplex struc- many Westland rivers, where the rate of

630 Geological Society of America Bulletin, May 1994

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Alpine fault basal shear (•) mean orientation (•): 060°/39°SE C1 shears (•) mean orientation (o): 049°/39°SE Mylonitic foliation; Mean orientation: 039742°SE Slickenside lineations (+) mean orientation (*): 24°/086° C2 shears (+) mean orientation (•): 070°/18°SE

Figure 4. Stereograms of structural features in rocks of the Alpine fault zone. All plots are equal-area, lower-hemisphere projections. A. Stereogram of poles to the Alpine fault basal shear surface above the oldest fluvio-glacial gravel at the east end of the exposure. Also plotted are slickenside striatums in the basal gouge. B. Plot of poles to the mylonitic foliation. C. Plot of steep (CI) and shallow (C2) shears in the hanging-wall mylonite. These shears tend to occur in sets and are responsible for the imbrication and duplex formation within the mylonite. The intersection of the mean planes to the two sets of shears is 107218°.

aggradation exceeds the uplift rate on the or a series of coalescing fans, and, hence, the tively. Although normal faulting and associ- fault. At some later stage, migration of the basal fault surface would need to change ori- ated gravity-driven, rotational slumping in active trace of the fault, acceleration of uplift entation as the thrust advanced. Some of the the overlying thrust sheet have probably con- to exceed depositional rate, or a slowing of gouge-filled normal faults in the overlying tributed to this displacement, we believe that depositional rate (or a combination of the mylonite sequence probably formed at this the dominant mechanism is tectonic conver- three) resulted in the fault cutting up through stage, in response to the flexure, rotation, and gence. These displacements correspond to the gravel. The basal cataclasite, derived subsidence of the thrust as it advanced over rates of shortening of —14 mm/yr and 11 from the hanging-wall Haast Schist se- the irregular surface topography of the talus mm/yr in a northwest direction, similar to the quence, exhibits duplex structures, suggest- fans. Normal faults are parallel to, and prob- plate-tectonic prediction of 11 mm/yr calcu- ing that it has been imbricated and tectoni- ably formed by reactivation of, antithetic lated perpendicular to the regional trend of cally thickened as the fault rocks ramped up thrusts produced at an earlier stage of uplift. the Alpine fault (DeMets and others, 1990). through the gravel sequence. Ultimately, Thus, structural complexity in the overthrust The average rate for the period from 10,300 fault-related cataclasite and mylonite became is a near-surface effect, reflecting interaction yr B.P. is a minimum, because the dated exposed at the ground surface. By this stage, between the fault and the landscape. wood sample came from near the base of the degradation of the gravel sequence had pro- On the distal edge of the talus fans, an ag- gravel, —45 m below the thrust (Fig. 2). duced a west-facing erosion surface. As the grading fluvial system mixed schist debris Minimum slip rates calculated along plate- fault scarp evolved, erosional products from the rising Southern Alps with mylonite vector-parallel slickenside trends (086°) in formed a talus fan at the Alpine front that was derived from erosion of the toe of the thrust. the basal cataclasite range from 18 to 24 mm/ derived almost exclusively from newly ex- Wood fragments from the schist-mylonite yr. If we accept a relative plate velocity of humed mylonite and cataclasite. Large gravels have yielded a 14C age of 10,300 ± 38.5 mm/yr at the latitude of nearby Franz blocks of mylonite, or even poorly consoli- 130 yr B.P. Ultimately the talus fans and flu- Josef, computed from DeMets and others dated cataclasite, perhaps dislodged by fault vial outwash gravels at Gaunt Creek were (1990), then at least half to two-thirds of the movement, earthquakes, or heavy rain, were overridden by the advancing Alpine fault total relative plate motion is being accommo- transported downslope by debris flows and thrust sheet. The evolving fluvial system sub- dated by movement along the Alpine fault it- became incorporated into the talus breccias sequently eroded and buried the toe of the self. The total slip rate calculated is very sen- as back-tilted slump blocks. During periods thrust. In the ongoing interplay between ero- sitive to the exact slip direction taken. For of stability in parts of the fan, small ephem- sion and tectonism, however, bedding traces instance, for a slip direction of 080°, the val- eral streams deposited comparatively well- in the upper gravel are disrupted, and faint, ues would be 29 and 22 mm/yr, respectively. sorted, cross-bedded sand and silt as thin shallowly dipping traces of the basal thrust These rates represent minimum values for partings between units of coarse breccia. Re- appear to propagate through gravel to the the whole fault zone, because no account is forestation of the Southern Alps, which ac- western edge of the slip. taken of any displacement farther to the east companied climatic warming following the within the hanging-wall mylonite. The bal- last glaciation, had clearly begun by 12,650 yr Rates of Movement ance of the motion between the Pacific and B.P., as shown by rare fossil wood incorpo- Australian plates is distributed over a zone rated in the talus fan sequence. As the fan In a northwest-striking section through the which extends the width of the South Island deposits built up, continued rapid uplift on Gaunt Creek area (Fig. 2), the 14C-dated, my- of New Zealand (Walcott, 1978; Norris and the fault caused thrusting of the fault rocks lonite-derived talus fans and fluvial gravels others, 1990), but clearly, as required by the out over their own erosional debris. The have been overthrust —180 m and —110 m evidence above, deformation must decrease ground surface probably consisted of a fan, during the past 12,650 and 10,300 yr, respec- away from the Alpine fault.

Geological Society of America Bulletin, May 1994 631

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Figure 5. Sketches illustrating the sequential structural development of the Alpine fault zone A. n fluvio-glacial gravel from the last glaciation (A), to the present day (E).

IMPLICATIONS FOR SEISMIC HISTORY

In the Gaunt Creek area, and in other areas that we have mapped south to Haast River, the Alpine fault is a relatively simple struc- ture with a clear sequence of fault rocks in the hanging wall and little evidence of major movement on parallel structures across a wide zone. In this sense it contrasts with some other large continental transform zones such as the , which has a broad zone of anastomosing slip planes (Sylvester, 1988). Between 80 and 250 km far- ther north, the Alpine fault branches into at least four major strands (Fig. 1A), where its structure has been compared with that of the Transverse Ranges in California (Scholz, 1977; Yeats and Benyman, 1987). The large amount of convergence along the central sec- tion of the Alpine fault has uplifted high-grade schists very rapidly, leading to hot rocks close to the surface (Allis and others, 1979; Koons, 1987) and a localization of the major zone of movement. The estimated displacement rates are sub- stantial for a single structure and indicate that the Alpine fault surface itself is the locus of a high proportion of the interplate slip. There is no evidence along the Alpine fault for fault creep (at Gaunt Creek, this would be difficult to detect, but elsewhere the fault trace crosses suitable markers such as roads and fence lines). We may conclude that the sub- stantial rate of slip on the fault must be ac- commodated by intermittent, earthquake-re- lated events (compare Adams, 1980). The shear strain rate over the past 100 yr, as cal- E. culated from geodetic retriangulation, is also high in the vicinity of the Alpine fault (Wal- cott, 1978), reaching 1.4 ± 0.4 ^rad/yr (Wood and Blick, 1986). There have been no surface- displacing earthquakes for at least the past 150 yr. The last major event at the southern end of the fault took place —300 yr ago (Coo- per and Norris, 1990), resulting in an 8-m dex- tral offset (Hull and Benyman, 1986). At the slip rate of 20-25 mm/yr suggested for Gaunt Creek, 8 m of slip would require 320-400 yr to accumulate.

632 Geological Society of America Bulletin, May 1994

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ACKNOWLEDGMENTS fault: Contributions to Mineralogy and Petrology, v. 75, Scholz, C. H„ 1977, systems of California and New p. 153-164. Zealand: Similarities in their tectonic and seismic styles: Ge- Cooper, A. F., and Nonis, R. J., 1990, Estimates for the timing of ological Society of London Journal, v. 133, p. 215-229. the last coseismic displacement on the Alpine fault, northern Sibson, R. H., White, S. H., and Atkinson, B. K., 1979, Fault rock We thank Rupert Sutherland, who col- Fiordland, New Zealand: New Zealand Journal of Geology distribution and structure within the Alpine fault zone: A pre- and Geophysics, v. 33, p. 303-307. liminary account, in Walcott, R. I., and Cresswell, M. M„ lected one of the wood samples from Gaunt Craw, D., and Koons, P. O., 1989, Tectonically induced hydrother- eds., The origin of the Southern Alps: Royal Society of New Creek, and co-workers D. Craw, P. O. mal activity and gold mineralisation adjacent to major fault Zealand Bulletin, v. 18, p. 55-65. zones: Economic Geology, Monograph 6, p. 471-478. Suggate, R. P., 1963, The Alpine fault: Royal Society of New Koons, and R. H. Sibson for continued dis- DeMets, C., Gordon, R. G., Angus, D. F., and Stein, S., 1990, Zealand Transactions, Geology, v. 2, p. 105-129. Current plate motions: Geophysics Journal International, Sylvester, A. G., 1988, Strike-slip faults: Geological Society of cussion on Alpine fault-related problems. v. 101, p. 425-478. America Bulletin, v. 100, p. 1666-1703. Rick Sibson kindly made suggestions on an Hull, A. G., and Benyman, K. R., 1986, Holocene tectonism in the Walcott, R. I., 1978, Present and late Cenozoic evolution region of the Alpine fault at Lake McKerrow, Fiordland, New of New Zealand: Royal Astronomical Society Geophysical earlier draft, and the final manuscript has Zealand, in Reilly, W. I., and Harford, B. E., eds., Recent Journal, v. 52, p. 137-164. crustal movements of the Pacific region: Royal Society of Walcott, R. I., 1979, Plate motion and shear strata rates in the vi- benefitted from the reviews of Bulletin refer- New Zealand Bulletin, v. 24, p. 317-331. cinity of the Southern Alps, in Walcott, R. I., and Cresswell, ees S. Cashman, J. Dolan, K. Meisling, and Kamp, P.J.J., Green, P. F., and White, S. H., 1989, Fission track M. M., eds., The origin of the Southern Alps: Royal Society analysis reveals character of collision tectonics in New of New Zealand Bulletin, v. 18, p. 5-12. A. Sylvester. Field work has been supported Zealand: Tectonics, v. 8, p. 169-195. Wellman, H. W., 1955, New Zealand Quaternary tectonics: Geo- Kimbrough, D. L., Rattenbury, M. S., and Tulloch, A. J., 1994, logisches Rundschau, v. 43, p. 248-257. by grants from the University of Otago Re- Late Jurassic/Early Cretaceous metamorphic age of Fraser Wellman, H. W., 1979, An uplift map for the South Island of New search Committee. Complex migmatite, Westland, New Zealand: New Zealand Zealand and a model for uplift of the Southern Alps, in Wal- Journal of Geology and Geophysics, v. 37 (in press). cott, R. I„ and Cresswell, M. M., eds., The origin of the Koons, P. O., 1987, Some thermal and mechanical consequences of Southern Alps: Royal Society of New Zealand Bulletin, v. 18, rapid uplift: An example from the Southern Alps, New p. 13-20. REFERENCES CITED Zealand: Earth and Planetary Science Letters, v. 86, Wood, P. R„ and Blick, G. H., 1986, Some results of geodetic fault p. 307-319. monitoring in South Island, New Zealand, in Reilly, W. I., Adams, J., 1980, Paleoseismicity of the Alpine fault seismic gap, Lister, G. S., and Snoke, A. W., 1984, S-C mylonites: Journal of and Harford, B. E„ eds., Recent crustal movements of the New Zealand: Geology, v. 8, p. 72-76. , v. 6, p. 617-638. 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J., 1964, Mylonites, , and associated rocks MANUSCRIPT RECEIVED BY THE SOCIETY DECEMBER 18,1992 metachert and amphibolite whiteschist from the Southern along the Alpine fault, South Island, New Zealand: New REVISED MANUSCRIPT RECEIVED SEPTEMBER 13,1993 Alps, New Zealand, with implications for uplift on the Alpine Zealand Journal of Geology and Geophysics, v. 7, p. 645-684. MANUSCRIPT ACCEPTED SEPTEMBER 22,1993

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