GEOLOGY OF THE GREYMOUTH AREA
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GREVMOUT;H AREA
Scale 1:250 000
SIMON NATHAN M. S.R:ATTENBURY R. P. SUGGATE (COMPILERS) ..
Institute of Geological & Nuclear Sciences 1:250 000 geological map 12
Institute of Geological & Nuclear Sciences Limited Lower Hutt, New Zealand
2002 BmLIOGRAPHIC REFERENCE Nathan, S.; Rattenbury, M.S.; Suggate, R.P. (compilers) 2002: Geology of the Greymouth area. Institute of . Geological & Nuclear Sciences 1:250000 geological map 12.' 1 sheet + 58 p. Lower Hutt, New Zealand. Institute ofGeological & Nuclear Sciences Limited.
Edited, designed and prepared for publication by P. J. Forsyth and P. L. Murray Printed by Graphic Press & Packaging Ltd, Levin
ISBN 0-478-09752-2
© Copyright Institute ofGeological & Nuclear Sciences Limited 2002
FRONT COVER
The town of Greymouth is situated on postglacial sediments at the mouth of the Grey River, in front of limestone bluffs that make up the Twelve Apostles Range. In past years coal from the Greymouth Coalfield was shipped out of the river port in small colliers, but it is now railed over the Southern Alps to Christchurch. Photo CN35937R: D.L Homer CONTENTS
ABSTRACT . v LATE CRETACEOUS AND TERTIARy . ..25
Keywords . . v Late Cretaceous to Paleocene sedimentary rocks 25 Eocene sedimentary rocks 25 INTRODUCTION . . I Oligocene to earliest Miocene sedimentary rocks T! Earl y to Middle Miocene sedimentary rocks 29 Late Miocene to Pliocene sedimentary rocks 30 THE QMAP SERIES ...... I Late Pli ocene to Earl y Pleistocene sedimentary rocks. 30 T he QMAP geographi c informati on system 1 QUATERNARY...... 31 Data sources 1 Reliability I Glacial deposits 31 A lluvial deposits 34 REGIONALSEITING ... .3 Alluvial fan deposits ... 34 Culture and land-use . . 3 Coastal marine deposits and dunes . .. 34 Swamp and lake deposits 34 GEOMORPHOWGY 3 Scree deposits . .. 36 Landsli de deposits 36 Southern Alps 3 Deposits of human origin . 36 Alpine Fault. . 3 Western mountains . . 5 TECTONIC HISTORy 37 Lowland areas 5 Plateau areas . 9 GEOLOGICAL RESOURCES .... . 39 Present day deformation . 9 Offshore bath ymetry. 10 Gold. . 39 Ilmenite (and associated minerals) . .. 40 STRATIGRAPHy.... II Other metalli c mjnerals 40 Clay... . 41 CAMBRIAN TO EARLY CARBONIFEROUS II Rock 41 Greenstone (nephrite. pounamu) and goodletite 42 Buller lerrane . 11 Limestone...... 42 Ordovician sedimentary rocks 11 Other non-metall ic mineral s 42 Paragneiss and associated rocks 12 Coal ...... 43 Devonian sedimentary rocks 13 Oil and gas .. .. 45 Water 45 Takaka terrane . 1. 3 Warm spri ngs . 45 Cambrian to Ordovician volcanjc and sedimentary rocks 13 GEOLOGICAL HAZARDS 46 Late Devoni an to Early Carboniferous intrusive rocks 14 Seisl1lotectoni c (earthquake) hazard . 46 PERMIAN TO EARLY CRETACEOUS . 17 Landsli di ng . 47 Tsun am.i...... 47 West ofthe Alpine FOliit . . 17 Triassic-Jurassic sedjmentary and volcanic rocks 17 ENGINEERING GEOLOGY . . 49 Early Cretaceous granitoid rocks 17 Early Cretaceous sedimentary rocks 17 Paleozoic-Mesozoic rocks west ofthe Alpine Fault 49 Cretaceous d ikes and high level intrusions. 19 Paleozoic-Mesozoic rocks east of the Alpine Fault 49 Tertiary sedimentary rocks 49 East ofthe Alpine Fault: Rakaia terrane .... 21 Quaternary sediments .. 49 Late Triassic sedimentary rocks . .. 21 AVAILABILITY OF QMAP DATA 51 Late Tri assic semischi stose and schistose rocks 21 Structure of Rakaia rocks 22 ACKNOWLEDGMENTS. . 51 Esk Head belt. . 22 Late Jurassic - Early Cretaceous melange 22 REFERENCES . . 52 ABSTRACT
The Greymouth 1:250 000 geological map covers uplift of the Southern Alps started in the Pliocene, but the 2 13 000 km , and includes the central part ofthe West Coast West Coast ranges did not start to rise and form the present region in the South Island ofNew Zealand. The map area is range-and-basin topography until the early Quaternary. bisectedby the Alpine Fault- a major strikC}-slip fault fonning Regional uplift by folding and faulting continues to the the active plate boundary between the Pacific and Australian present day. tectonic plates. Late Cenozoic movement (which continues to the present day) has led to the juxtaposition of two Glaciation during cool periods in the Quaternary resulted different geological provinces. in downstream aggradation from moraines and down-valley glacial outwash gravels. During warmer, interglacial periods Southeast of the Alpine Fault the rocks are part of the there is evidence of higher sea levels near the coast from Mesozoic Torlesse composite terrane, a thick, highly marine terraces that have been subsequently uplifted. deformed sequence of mainly submarine fan sedimentary rocks, of quartzofeldspathic, continental derivation. The Gold has been mined for over 100 years from both quartz topography is mountainous, and the Southern Alps rise from veins and alluvial deposits. Over70 000 kg ofgold has been near sea level to a maximum height ofover 2200 metres. extracted from quartz veins in the Reefton Goldfield, and planning is currently underway to open a new opencastmine. Northwest ofthe Alpine Fault the pre-Cretaceous rocks are Substantial reserves ofilmenite have been defined by drilling Paleozoic metasedinientary and plutonic rocks that represent in postglacial sands near the coast. The map area contains a fragment of the Gondwanaland supercontinent. almost all the reserves ofbituminous coal in New Zealand Gondwanaland started to break up in the Early Cretaceous, (300 million tonnes estimated as recoverable), mainly in a period of widespread· emplacement of granitoid rocks, the Buller and Greymouth coalfields, although not all of uplift, and detachment faults -resulting in the formation of this may be able to be mined. Recorded seeps and shows of metamorphic core complexes. Fanglomerates were deposited oil and gas have encouraged prospecting for hydrocarbons, around the rising mountain ranges. but no commercial finds have yet been located.
The olderrocks on both sides ofthe Alpine Fault were largely The Greymouth map area is subject to natural hazards, covered by Cenozoic sediments. Regional extension led to including a high level of seismic hazard from the Alpine submergence by the middle ofthe Oligocene,·and widespread Fault and other active faults, with potential for earthquake deposition of limestone or calcareous sedimentary rocks. shaking, landsliding, liquefaction and ground rupture. Development of the present oblique-compressional plate Several large, damaging earthquakes with epicentres within boundary started in the Early Miocene, and led to a complex the map area have occurred within the last 100 years. late Cenozoic history, with development of small fault Landsliding, rockfall, tsunami and flooding are ongoing bounded basins and widespread uplift and erosion. Rapid hazards.
Keywords
Greymouth; West Coast region; 1:250 000 geological map; geographic information system; QMAP; digital data; bathymetry; Buller terrane; Takaka terrane; Torlesse composite terrane; Rakaia terrane; Pahau terrane; Esk Head belt; metamorphism; textural zones; Karamea suite; Rahu suite; Separation Point suite; Alpine Fault; Southern Alps; Grey Valley; Paparoa Range; Victoria Range; Greenland Group; Gondwanaland; Waipounamu erosion surface; glaciation; interglacial; dredge tailings; gold; ilmenite; uranium; clay; greenstone; pounamu; . nephrite; limestone; coal; hydrocarbons; Kotuku oil seep; active fault; engineering geology; earthquake; Modified Mercalli scale; landslide; tsunami, 133, J31, J32, J33, K29, K30, K31, K32, K33, L29, L30, L31, L32, L33. v 170" E: 175" E
1 '% ~O : :>_~ : ~- -- -- __c$>~ _ ------.-.-----.·-··r -.---- -.------.. '-K"t,,;,," --.-- --..-, -. -..--. ------. --.-- ---.-- --. ---- .. ~!i:_~ 00...... 200~ : Whangar ~ i -~ v : ';S ~ i I-_ -,--!,i-.L---, '5 is'-0 ' , , I Auckland , I : f-----r+-I -L._,--_----, ; \ / /.... ~ :' , Waikato . R ~O;~~~~ II ~ 11 ! hal/enger :, ';.j i 47 ~m/y~ C Taranaki ,I. Raukumara : Plateau ; Basin ~ .' jL / j ; I, , ' " HawKes I : Tar,!~akl - B'aY i , " ) '.f< ;";4 , .~ 9:-?- - ..------~~~~-;~ ~;~~ . T'------.. --..------.- . --. --- ..-; ; j/ ~/' -.- -.-.:~~~~lf ..4Q : i~·
, ';S Plate Nelson well lnQt69! wa"a. ~rapa ~ i 1 '5 ,/;;.. / 'l>\:- ! ,/ ~ .-'" Ii ~ d~ : " QMAP : ' jf If/f"V / I V .},\, : , ---.- ~ . 1-1" l!7.'9 -/,/ ..,,? " ' , Greymouth I.... Jt./"Co' f ~ I \ ,,/:Z~oUra ...... r 41 mm/yr p , f/ ~Y.. ~ acific , /.0'-' - [if'£-! Plate I 1 '~'~ ~;i -1;"?"'- ~\' /" 38 in'1fl1 r , ~/ . \ Christchurch , Haas V~ Aor.aki " Chatham Rise ! ./ I ~ r I ,I .----i /~ "'- , , , , Wak:ati6l!J " I Waitakr ------._------. - - -"t - -.--. - _. ------.-. . .. __ .~~? ~_ ~_ .I , , , ~7 mm/ r / Bounty ! Murihiku , Dunedin Trough ! , 2000
I 0i-...."".;.;'OO~_....;;;200 Campbel/ Plateau Kilometres
170" E , 175" E 180" E'
Figure 1 Regional tectonic setting of New Zealand showing the location of the Greymouth geological map and other QMAP sheets, major offshore features (as illustrated by the 2000 metre isobath), and active faults. Arrows indicate the direction and rate of convergence of the Pacific Plate relative to the Australian Plate.
Adapted from Anderson & Webb (1994)
vi INTRODUCTION
THE QMAP SERIES resources and localities, fossil localities, active faults, and petrological samples. This geological map ofthe Greymouth area (Fig. 1) is one of the new national QMAP series (Quarter-million map; The QMAP series and database are based on detailed Nathan1993) being produced by the Institute of geological information plotted on 1:50 000 topographic Geological & Nuclear Sciences Ltd (GNS). QMAP base maps. These data record sheets are available for supersedes the current Geological Map of New Zealand consultation at GNS offices in Lower Hutt and Dunedin. 1:250 000 (''fourmiles to the inch") series. Three published The 1:50 000 data have been simplified for digitising "four mile" sheets - Buller (Bowen 1964), Hokitika during a compilation stage, with the linework smoothed, (Warren 1967), and Hurunui (Gregg 1964) - overlap with and geological units amalgamated to a standard national the Greymouth QMAP area. Since then, a considerable system based on age and lithology. Point amount of geological research has been completed, data (e.g. structural measurements) have not been including detailed geological mapping at 1:63 360or 1:50 000 simplified. All point data are stored in the GIS, but only scales (Laird 1988; Nathan 1975; Nathan 1978a; Nathan selected representative structural observations are shown 1978b; Nathan 1996; Roder & Suggate 1990; Suggate & on the map. Procedures for map compilation, and details Waight 1998), as well as industry investigations and of data storage and manipulation techniques, are given .university theses. In addition the whole sheet has been by Rattenbury & Heron (1997). part of a regional synthesis of Cretaceous and Cenozoic sedimentary basins (Nathan and others 1986). Data sources
The geology of the Greymouth QMAP area is in many The map and text have been compiled from published places so complex that it has been considerably simplified maps and papers, unpublished university theses, GNS in order to present itlegibly at 1:250 000 scale. Rock units technical and map files, mining company reports, field are mapped primarily in terms oftheir age of deposition, trip guides, the New Zealand Fossil Record file in its eruption, or intrusion. As a consequence, the colour ofthe digital form (FRED), and GNS geological resources units on the map face reflects their age, with overprints (GERM) and petrological (PET) digital databases (Fig. 2). used to differentiate some lithologies. Letter symbols (in Additional field mapping has been undertaken to resolve upper case, with a lower case prefix to indicate early, problems and to ensure a minimum level ofcoverage over middle orlate ifappropriate) indicate the predominant age the map area. Landslides were mapped from aerial photos, ofthe rock unit. The last lower case letter orletters indicate with limited field checking. Offshore data have been a formally named lithostratigraphic unit and/or the compiled from published studies ofthe West Coast region predominant lithology. Metamorphic rocks are mapped in (Nathan and others 1986). Data sources used in map terms of age of protolith (where known), with overprints compilation are summarised in Fig. 2, and are cited with indicating degree ofmetamorphism. Age subdivision is in other studies relating to the Greymouth QMAP area in terms ofthe international time scale. Correlation between the references. international and local time scales and absolute ages in millions of years (Ma), revised as necessary for QMAP Reliability (Crampton and others 1995), is shown inside the front cover. As a result ofthe compilation and simplification process, the accuracy with which geological contacts, faults, and The description of the geology accompanying the folds are shown onthe 1:250 000 map has diminished, geological map is generalised and is not intended to be an although point data are accurately located in terms ofthe exhaustive description of the various rock units mapped. NZMS 260 grid; the unpublished 1:50 000 data record For more detailed information the reader is referred to maps have a higher standard of detail and accuracy. The references cited throughout the text. 1:250 000 map is of regional scale only, and should not be used alone for land use planning, planning or design The QMAP geographic information system of engineering projects, earthquake risk assessment, or other work for which detailed site investigations are The QMAP series uses computer methods to store, necessary. Some data sets incorporated with the geological manipulate and present topographic and geological data (for example the Geological Resources Map ofNew information. The maps are drawn from data stored in the Zealand [GERM] data) have been compiled from old or QMAP geographic information system (GIS), a database unchecked information of lesser reliability (see developed and maintained by GNS. The primary software Christie 1989). used is ArcInfo®.
Digital topographic data were purchased from Land Information New Zealand and its predecessor the Department ofSurvey and Land Information. The QMAP database is complementary to, and can be used in conjunction with, other spatially referenced GNS digital data sets, e.g. gravity and magnetic surveys, mineral 1 ..
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1 Angus 1984 25 Jury 1981 49 Suggate & Waight 1998 2 Becker & Craw 2000 26 Koons 1978 50 Suggate 1957 3 Bell & Fraser 1906 27 Laird 1988 51 Suggate 1965 4 Berryman & others 1992 28 MacKinnon 1980 52 Suggate & others 1961 5 Blackmore 1998 29 Maxwell 1982 53 Tulloch 1979, 1995 6 Botsford 1983 30 McLean 1986 54 Turnbull & Forsyth 1986 7 Bowen 1964 31 Morgan 1908 55 Waight 1995 8 Bradshaw & Hegan 1983 32 Mortimer & Smale 1996 56 Warren 1967 9 Bradshaw 1995 33 Mortimer 1984 57 Wellman 1945 10 Brown 1998 34 Munden 1952 58 Wellman 1950 11 Browne 1987 35 Nathan 1975 59 We llman & others 1952 12 Cave 1982 36 Nathan 1976 60 White 1988 13 Cave 1986 37 Nathan 1977 61 Wilson 1956 14 Chinn 1973 38 Nathan 1978a 62 Wright 1998 15 Cooper 1992 39 Nathan 1978b 63 Yang 1989 16 Cutten 1976 40 Nathan 1994 64 Young 1966 17 Dixon 2001 41 Nathan 1996 65 Young 1968 18 Findlay 1979 42 Nathan & others 1986 19 Fyfe 1968 43 Parish 1998 20 Gage 1945 44 Petrie 1974 21 Gair 1962 45 Rattenbury & Stewart 2000 22 Gregg 1964 46 Rattenbury 1987 23 Inwood 1997 47 Roder & Suggate 1990 24 Ireland & others 1984 48 Suggate & Munden 1952
Figure 2 Major sources of geological data used in compiling the Greymouth geological map.
2 REGIONAL SETTING GEOMORPHOLOGY
QMAP Greymouth is bisected by the Alpine Fault - a The landscape of the Greymouth area has been moulded major active fault with predominantly dextral strike-slip by a combination of late Cenozoic uplift (with movement - that forms the active plate boundary between accompanying erosion), the effects of Quaternary the Australian Plate (to the northwest) and the Pacific glaciation, and coastal erosion. Plate (to the southeast) in the central part ofNew Zealand. Many of the other major faults within the map area also SouthernAlps reflect the wide zone of deformation associated with the plate boundary. Within the Greymouth map area the Southern Alps rise from near sea level to a maximum height of The plate boundary developed during the later part ofthe 2280 m (Mt Davie). The mountains trend northeast and Cenozoic, and approximately 480 km of strike slip form a drainage divide, the Main Divide, between movement has been demonstrated by offsetting ofterrane Canterbury rivers draining to the southeast and the boundaries across the Alpine Fault. This has led to the northwest-flowing rivers ofthe West Coast (Figs 4 & 5). juxtaposition oftwo different geological provinces within . the Greymouth map area; The northwestern range front ofthe Southern Alps is steep and high, and deflects the prevailing westerly air stream Fig. 3 shows the complex 'pattern of pre-Cretaceous upwards, resulting in periods of exceptionally heavy tectonostratigraphic terranes in the New Zealand region. rainfall. The maximum rainfall recorded exceeds 10 metres Within the Greymouth map area the pre-Cretaceous rocks per year in an area 3-5 km southeast of the range front ofthe Australian Plate are Paleozoic metasedimentary and (Griffiths & McSaveney 1983), and the rivers draining this plutonic rocks that represent a fragment of the area are often steep, deeply incised and prone to rapid Gondwanaland supercontinent. Southeast of the Alpine flooding. Rainfall decreases westwards to less than Fault, the rocks of the Pacific Plate are entirely of the 3 metres per year at the coast. Torlesse composite terrane - a thick, highly deformed sequence of mainly submarine fan sedimentary rocks, Southeast of the Main Divide rainfall also decreases predominantly quartzofeldspathic, of continental markedly. The southeastern flanks of the Southern Alps derivation. are dissected by a complex series oftributaries that coalesce downstream into relatively large, braided, shallow-gradient The pre~Cretace{>us rocks on both sides ofthe Alpine Fault rivers. were largely covered by Late Cretaceous and Cenozoic sediments, although these have been partly removed by During the colder phases ofthe Quaternary, the Southern erosion. Development of the plate boundary along the Alps were extensively glaciated, with glaciers extending Alpine Fault has led to a complex later Cenozoic history, down the main valleys. Small glaciers are now found above with uplift leading to the formation of mountains from 1900 metres on east- to south-facing slqpes. Valleys that Pliocene time onwards. During the Quaternary period there were previously glaciated typically have steep sides, and was extensive glaciation in the mountains, and the lowland landslides, alluvial fans and lakes are common as the areas are covered with a widespread veneer of late landscape readjusts to a warmer, wetter climate Quaternary gravels and glacial deposits. (Figs 6 & 7).
Culture and lan.d-use Alpine Fault
The Greymouth geological map covers the West Coast of The Alpine Fault is a clearly marked feature that effectively the South Island from Ross north to Westport and extends splits the map area into two parts (Fig. 8). It inland into northwest Canterbury and the upper Buller trends about 050", and satellite images highlight a straight, valley, aland area of approximately 13 000 km2 (Fig. 4). linear trace. The map area is sparsely populated with most people living in the coastal towns of Greymouth (population 10000), The dip of the Alpine Fault is generally about 40-50° SE Westport (4600), and Hokitika (4000), and smaller inland (Sibson and others 1979). Locally, however, surface communities of Inangahua, Reefton, Dobson and Ross. outcrops show that the dip flattens, probably partly due to The West Coast is linked to Canterbury by road and rail near-surface effects, and consequently the surface trace is via Arthur's Pass, and by road via Lewis Pass to the east sinuous in detail where there is incised topography ofSprings Junction. The lower reaches ofthe Buller, Grey, (Suggate 1963). and Hokitika rivers are extensively farmed. Plantation forestry, coal mining and alluvial gold mining are also There are many examples of streams, terrace risers and significant land uses. Most of the map area is covered in channels right-stepping in 6-13 metre multiples across the indigenous forest and the area includes Paparoa National Alpine Fault reflecting the recent and ongoing dextral Park, Victoria Conservation Park, and parts ofArthur's Pass component displacement of the fault (Wellman 1953; and Kahurangi national parks. Berryman and others 1992). Some of the larger valleys draining the Southern Alps, such as the Hokitika and 3 0 Cretaceous & Cenozoic sedimentary rocks Northland and East Coast Alloch thons Median Batholith Waipapa composite terrane Tor1esse composite •u • (western North Island) terrane (eastern NZ) Takaka terrane u - Monin~ai8HiII -> Buller terrane lcomposite"h~ -> • 0 0 undifferentiated terrane Hunua-Bayollsl9nd$ Esk Head bell ~ ~ melange 1-"Rakaia Cretaceous plutonic rocks Caples terrane - schist ~ ~ Dun Mountain - Maltai terrane 1111111 Devonian-Carboniferous plutonic rocks ·• • Murihiku terrane ~ w· - ?Silurian-?Devonian gneissic rocks Brook street terrane ~ gneiss
Figure 3 Pre-Cenozoic basement rocks of New Zealand, subdivided into tectonostratigraphic terranes; the extent of the Northland and East Coast allochthons is also shown . The map on the right shows more detail for the QMAP Greymouth area.
4 Taramakau, suggest 3- 10 Ian right lateral shifts, although The Bullerand Grey rivers have in cised deep gorges across the evidence is equivocal. For example, it is inferred that the Paparoa and Victoria ranges. The gorges are the glaciers that once filled the Kokatahi-Toaroha-Styx spectacular evidence that the rivers have maintained their catchment may have previously flowed into Lake Kani ere. westward path from the Southern Alps as the mountains have been uplifted during the Quaternary. Many smaller Western mountains streams have been deflected to flo w parallel to the ranges. Tn a detail ed analysis ofthe defonnation ofterraces within The north-trending Victoria and Brunner ranges and the the Upper BullerGorge (Fig. 9), Suggate (L 988) has shown NNE-trending Paparoa Range are separated by the Grey that uplift takes pLace by a combination of faulting and and Inangahua vall eys, with range-and-basin topography rolding, reflecting deformation of the underlying Tertiary resulting from late Cenozoic tectonic shortening. sediments that continues to the present day. Approximately The higher parts of the ranges show abundant evidence 350000 years ago th e Buller River flowed along a much for g lac iation in cluding cirques, hanging va ll eys and wider floodplain, now preserved as hi gh terraces, and has deposits of till. subsequently cut a narrow gorge.
The Paparoa Range has a maximum height of 1525 m at Lowland areas Mt Uriah, where rugged peaks and ridge tops surround glacial cirques cut in hard crystalline gneiss and granitoid Between the major ranges extensive low-lying areas rocks. The western flank of the Paparoa Range drops i!1 clude the Grey-lnangahua Depress ion and the sharply to a large low-lying dissected area underlain by Maruia vall ey. These areas are tectonic graben or Cenozoic sedimentary rocks. The eastern flank is more half-graben that have been partially filled by Middle complicated with subsidiary ranges and two major river Miocene to late Quaternary coarse-grained sand and gravel systems (Grey and lnangahua). deposits.
The Victoria Range, rising to 1749 m at Mt [vess, also has The lowland areas also have preserved a long glacial cirques and hanging valleys cut into hard crystalline hi story ofglacial and interglacial events, with deposits that rocks. The eastern flank of the Victoria Range descends record at least five glaciations and three interglacials. steeply into the Maruia River, whereas the western flank Moraines are preserved near th e coast in the southwest has an intricate pattern of deeply incised rivers with around the western fl anks of Mt Greenland, multiple branches in their headwaters. and in an arcuate lobe between Kumara and Lake Haupiri,
10 km
Tasman Sea
Figure 4 Shaded topographic relief model of the Greymouth map area derived from 20 metre contour data supplied by Land Information New Zealand (L1NZ), illuminated from the northeast. 5 Figure 5 Lake Browning lies just below Browning Pass (1400 m), a low-altitude pass on the Main Divide just west of Mt Davie. The headwaters of the Wilberforce River (foreground) give access, via a historic zig-zag miners' track, up the steep escarpment to the pass. The Arahura River, which drains Lake Browning, flows through deep gorges to the low lying land west of the Alpine Fault (distance), and thence to the sea. Photo CN10403l18: D.L Homer
Figure 6 The Southern Alps are formed of hard, greywacke-type rocks of the Rakaia terrane. Rock avalanches and alluvial fans, often triggered by earthquakes, are a feature of the landscape. The large rock avalanche in the foreground collapsed from the northwest side of Falling Mountain during an earthquake in 1929, transporting an estimated 60 million tonnes of broken rock in to the west branch of the Otehake River. Photo CN38312121: D.L. Homer Figure 7 Lake Christabel occupies a trough carved by a glacier that flowed down the Blue Grey River. The lake is dammed by terminal moraines deposited during the later part of the last glaciation (about 14 000 years ago), but the hummocky topography immediately downstream is formed by a landslide from the steep va lley walls on the southern (left) side; the head scarp of the landslide is not visible in this photograph. The Alpine Faull extends along the valley of the Upper Grey River about two-thirds of the way up the photograph, with the Victoria Range in the background and the Paparoa Range in the far distance. Photo CN3862019: D.L Homer
Figure 8 The Alpine Fault cuts obliquely across the Taramakau valley. An abrupt change in lithology on opposite sides, and surface traces cutting Holocene alluvium, allow the location of the fault to be accurately fixed as a narrow, linear zone of deformation. The Hope Fault, which appears to join the Alpine Fault at an oblique angle, is defined by the offsening of metamorphic isograds and the straightness of the Taramakau valley. Photo CN32364/ 19: Dol. Homer Figure 9 About 350 000 to 250 000 years ago the Buller River formed a wide, open vall ey, now represented by the high terrace at centre left. SUbsequent uplift has caused the Buller River to incise its present, much narrower gorge. The high terrace is crossed by the Lye ll Fault, which locally warps the terrace surface (Suggate 1988). The large landslide (upper right) formed during the 1968 Inangahua earthquake, and blocked the Buller River for several hours. Many smaller landslides also formed during the Inangahua earthquake. Photo CN779/8: D.L. Homer
Figure 10 The Denniston Plateau, northeast of Westport, is part of a widespread Late Cretaceous to early Tertiary unconformity surface (Waipounamu erosion surface) that was here buried under younger sediments in Late Eocene! Oligocene time and subsequently exhumed by Quaternary uplift. The unconformity is capped by about 30-50 metres of hard, cemented quartz sandstone (Brunner Coal Measures), which has effectively protected the underlying rock from erosion. The sandstone forms infertile soil, so that it is largely bare of trees. The surface is warped downwards towards the viewer, and the zig-zag road actually climbs across coal measures dipping 10-15' west. In the background the unconformity has been offset approximately 330 metres across the Mt William Fault, and bare sandstone is found at the top of the uplifted plateau. Photo CN32464/17: D.L. Homer indicating th at substantial glaciers covered much of the measurements repeated over several years is several wider Lake Brunner area at variou s times in th e millimetres per year greater (Beavan and others in press). middle to late Quaternary. Numerou s isolated mountains such as Mt Turiwhate, Mt Te Kinga, Island Hill and th e Longer-term estim ates of the rate ofstrike-slip movement Hohonu Range were partly glaciated nunataks that th e ice on the Alpine Fau lt south of the Taramakau River are flowed around without compl etely covering. approximately 10 mm/year (equi valent to 10 km/million years). Dip-slip movement has pro ved more difficult to Most of the maj or lakes in the Greymouth area, including quantify, but is likely to range between 3 and 6 mm/yr Kaniere, Moana, Poerua, Hochstetter and Sumner, are of (Norri s & Cooper 2000). It is clear that a significaot patt, glacial origin, and were formed in glacially-scoured valleys but not all , of the plate motion is being taken up by and/or dammed by glacial moraines (e.g. Fig. 7). movement at th e Alpine Fault. Much of the remaini ng movement is being accommodated within a zone up to 20 Plateau areas km southeast of the Alpine Fault (i. e. mainly within the nalTow belt of schi st and semischi st) (Beavan & Haines Gently east-dipping plateau areas on the ranges northeast 2001). and south of Westport are relics of the on ce-widespread Late Cretaceous to earl y Tertiary erosion surface that has The A lpine Fa ult s lip-rate red uces northeast o f th e been displaced by subsequent fau lting and largely eroded Taramakau Ri ver where the Hope Faultjoins from the east away. The erosion surface is commonl y indicated by (Norris & Cooper 2000). The process of transfer of much remnants of Late Cretaceous to Oli gocene sedimentary ofthe motion from th e Alpine Fault to the Hope Fault is so rock resting unconformabl y on granitoid, gneissic, and far poorly understood. metasedimentary basement (Fig. 10).
Between the coast and th e Paparoa Ran ge crest is an undulating , low-reli ef area at 100 to 400 m elevation form ed in Ol igocene limestone overlain by Miocene sediments. The gentl e dips ofthe limestone and high rainfall ha ve resulted in extensive karst topograph y in clud ing sinkholes, large cave systems and underground rivers.
Present day deformation
Deformation associated with the plate boundary extend s throughout the Greymouth map area. Folds and faults have been mapped as active structures (in red) on the geological map if there is positive evidence of deformation over the last 125 000 years. As th ere have been few detail ed investigations of individual structures, we expect th e number ofstructures classifi ed as active to increase as more research is undertaken.
Over the last 100 years there have been several large earthquakes (magni tude 6.0 or greater) with epicentres within the Greymouth map area, although non e has been associated with the Alpine Fault. This level ofearthquake activity is an indi cation of the o ngoin g deform ati on associated with the AustralianlPacific plate boundary, and is likely to continu e in the future.
The Alpine Fault is in felTed to have ruptured at the surface in association with large ealthquakes in 1717 AD, about 1630 AD, and around 1460 AD (Well s and others 1998). The probability of major rupture on the Alpine Fault is Figure 11 Displacement of Ihe road between Murchison estimated to be up to 20% over the next 20 years (Rhoades and Inangahua across the White Creek Fault caused by & Van Dissen 2000). movement during the 1929 Murchison earthquake (Fyfe 1929). The photographer is standing on the downthrown side, and the fi gure with bicycle (H .E. Fyfe, geologist) is The relati ve plate motion across th e A lpine Fault at standing on the upthrown side. Avertical offset of 14 It 9 in Inchbonnie is 39.5 ± 3 mmtyr along an azimuth of74 ± 3° (4.5 m) was recorded , and later investigations indicate a calcul ated using the Nuvel-l determination (DeMets and horizontal offset of 2.5 m (Berryman 1980; Suggate 1990). others 1990; Berryman and others 1992). The relative plate motion determ in ed fro m differences in GPS location Photo: M. Ongley 9 Northwest of the Alpin e Fault, the White Creek Fault Offshore bathymetry ruptured during the 1929 Murchison earthquake (Fig. II ), and small er surface ru ptures accompanied the 1968 The contin ental she lf in the Q MAPGreymouth area Inangahua earthquake (Lensen & Suggate 1969). Studies extends northwards to join the submerged continental shelf ofdefonned late Quaternary terrace surfaces (Suggate 1987, of the Challenger Plateau. The sealloor slopes gently 1988, 1992) have shown that there is evidence fo r ongoing «0.5") within 60 km of Cape Foulwind and 45 km of deformation both close to many mapped fa ulls and at fol ds Greymouth, and steepens to 2_30 and attains a maxi mum in the underlying Cenozoic rocks. depth of 700 m at the western edge of the map area. The relati vely flat seafloor is incised by the Hokitika Canyon Southeast ofthe Alpine Fault there are acti ve dextral sLrike to within 20 km west of Hoki tika. The head ofthe canyon
Q sl ip faulls such as the Hope and Poulter fau lts, whi ch have fa ll s steeply to the west with wall slopes of up to 8 • The ruptured to the surface in historic times (1888 and 1929 canyon trends northwest for 20 km and turns to the west respectively). GPS measurements through the Arthur's across the Chall enger Plateau to the abyssal plains, a total Pass area indicate marked strain accumulati on between distance exceeding 325 km .The overall smoothness of Arthur's Pass and the Alpine Fault near Inchbonnie (J . the sea fl oor probably rellects the deposition of large Beavan pers. comm. 200 I). Largeeartllquakes such as 1994 quantities ofthe bed load carried by the West Coast rivers. Arthur's Pass also indicate ongoing defonnatioll .
undifferentiated Karamea Suite Riwaka Complex' orthogneiss I I Terrane amalgamation Middle Devonian Fraser Complex (older parts) Early Reefton Group Baton Group' 4 Devonian undifferentiated paragneiss Silurian Greenland tectonic e vent ------ Ellis Group' I Pecksniff ~MetasedimentaTY. Ordovician Golden Bay Group Gneiss Mount Arthur Greenland Group Group 4'" Victoria I Paragneiss Late BULLER TERRANE Cambrian I {iQ~- •••••••••••••••••.•••_•••••••• Devil Middle River Cambrian olcanics Haupiri Group Group
TAKAKA TERRANE
Figure 12 Major rock un its of the Bulle r and Taka ka terra nes, and the major tectonic events that have affected them. ., indicates units that do not occur in the Greymouth map area.
10 STRATIGRAPHY
The rocks of the Greymouth QMAP area are described terranes show strong affinities with terranes in eastern below in terms offour time intervals A ustralia and Antarctica (Cooper & Tulloch 1992; MOnker & Cooper 1995). Cambrian to Earl y Carboniferous rocks • Permian to Early Cretaceous rocks Buller terrane Late Cretaceous and Terti ary sedimentary rocks Quaternary sediments Ordovician sedimentary rocks
CAMBRIAN TO EARLY CARBONIFEROUS A small area of un fossiliferous siltstone, quartzite and minor black shale, mapped as part of the Golden Bay Earl y Paleozoic rocks form two IlOIth-trending terranes Group (8b) occurs in a thin sli ver on the western slopes of the Buller and Takaka terranes (Fig. 3)- separated by the Baldy near Springs Junction, separated from Takaka terrane A natoki Fault (Bishop and others 1985; Cooper 1989). rocks by th e A natoki Fault. Correlation with Golden Bay Rocks of th e Bull er lerrane occur widely in the western Group in west Nelson (Rattenbury and others 1998) is pa rt of the QMAP Greymouth area and throughout based on lithological and structural similarities. Westl and. The Takaka terrane is best developed in west Nelson but also occurs near Springs Junction (Cooper 1989, To the west of th e Maruia vall ey, the widespre ad 1992). The relationships between units in the Buller and Greenland Group (eg) consists of interbedded light Takaka terranes are shown diagrammatically in Fig. 12. greenish-grey muddy sandstone (grey wacke) and shale (argillite) (Fig. 13a, b), interpreted as a proximal turbidite The Buller and Takaka terranes are the oldest structural succession deposited on a submarine fan (Laird 1972; Laird units in New Zealand and can be regarded as constituting & Shelley 1974). It has a uniform and highly quartzose "proto-New Zealand" which, together wi th eastern composition (Nathan 1976a; Roser & Nathan 1997), with Australi a and Antarctica, formed the southwest Pacific abundant detrital quartz, minor sodie plagioclase, and segment of Gondwanaland in the early PaJeozoic. These scattered volcanic and sedimentary rock fragments.
Figure 13 Typical exposures of Greenland Group on the coast north of Greymouth.
(a ) Interbedded th ick-bedded greywacke (dark brown) and argillite (grey) north of Seventeen Mile Bluff. Photo: S. Nathan
(b) Interbedded greywacke and argillite on the south side of Fourteen Mile Bluff, with bedding dipping about 70° south (ri ght). Argillite beds have a distinct, almost vertical fracture cleavage. This appears to be an axial plane cleavage associated with tight folding. An anticline axis, with a steeply dipping axial plane, is mapped a few hundred metres north (left) of the photograph (Nathan 1978a). Photo CN43288/4: D.L. Homer
II Figure 14 Gneissic rocks of the Buller terrane
(a) Orthogneiss (Okari Granite Gneiss, Dkn) interlayered with paragneiss (Pecksniff Metasedimentary Gneiss, Sgp) and intruded by a granitic dike on the coast north of Fox River. Photo: $. Nathan (b) Well-segregated Devonian blotite±muscovite±garnet orthogneiss (Dog) with locally developed mylonitisation. Base of Mt Elliot range front near the Ahaura River. Photo: M.S. Rattenbury (c) Incipiently mylonitised orthogneiss from Fraser Complex (Sf). Nearby this gneiss has been intruded by basaltic and larnprophyre dikes that have in turn been mylonitised. Doctor Creek, upstream from Smith Gorge. Photo: M.S. Rattenbury
Only a single fossil locality within the Greenland Group is Paragneiss and associated rocks known. Graptolites from the Waitahu River ind icate an Early Ordovician age (Cooper 1974). The Pecksniff Metasedimentary Gnei ss (6gp, Nathan 1978b) in the Paparoa Ra nge and the Victoria Paragneiss The Greenland Group is closely to tightly folded with a (6gv, Tulloch 1978) of the so uthern Victoria Range are well developed penetrative axial plane cleavage (Fig. 13b). quartzose metasedimentary rocks containing biotite and The strike of the beds and fold axial planes is SE at Mt some garnet. The paragneisses have psammitic and pelitic Greenland and ESE on the coast north of Greymouth, but bands typically several centimetres thick with leucosomes changes to NNW on the eastern side ofthe Paparoa Range of feldspar, rare calc-silicate bands (Fig. 14a), and locally (Nathan 1978a) and N to NEat Lyell and Reefton with migmatite textures indicative ofpartial melting (White (Gage 1948). It is not clear whether the cleavage fonnation 1994). They are geochemically similar to the Greenland and difference in orientation result from more than one Group (Roser & Nathan 1997) and are generally accepted deformation episode. as more highly metamorphosed equivalents (Laird 1988; White 1988; Ireland 1992). Metamorphism to upper Adams and others (1975) obtained K-Ar ages on Greenland amphibolite facies (sil limanite-grade) occurred around Group argillites. The oldest ages, around 440 Ma, suggest 360-370 Ma (Late Devonian), based on monazite U-Pb a Late Ordovician to Early Silurian age for a widespread geoch ronology (Ireland & Gibson 1998). Garnet-biotite low-grade (chlorite zone) metamorph ic event associated paragneiss (8pg) from the south ern Victoria Range has an with deformation and cleavage formation (Greenland un know n but pre-Devoniandepositional proto lithage, and Tecton ic Event). Younger granitoid plutons thal intrude records both Devon ian and Cretaceous metamorphism the Greenland Group are surrounded by aureoles (from 0.5 (Ireland & Rattenbury unpublished data 200 I). to 2 km wide) ofdark grey biotite hornfel s. 12 In the Paparoa Range the paragneiss (with minor associated Devonian sedimentary rocks orth ogneiss) has a tectoni c/metamorphi c foli ation that generall y strikes north . Sub-hori zontal myloniti c foli ation The Devonian Reefton Group (De) occurs as fi ve small occurs in several areas (S hell ey 1970) and is associated outliers, all with faulted contacts with the older Greenland w ith a mi d-Cretaceous detachme nt fau lt. The fault has Group. Eleven units have been differentiated withi n the displ aced a cover sequence of lower grade, upper cru stal quartzose sandstone (quartzite), limeston e and mudstone rocks, inc luding Greenland Group, from a higher grade (shale) sequence, whi ch is about 1500 m thi ck. It is inferred metamorphic core complex compri sing the gneisses and to have been deposited in shallow marine beach to shelf mid-cru stal plutoni c rocks (Tulloch & Kimbrough 1989). environments (Bradshaw & Hegan 1983; Bradshaw 1995). The geometrical re lation ships between low-grade Greenland Group and upper amphibolite facies gneisses The Reefton Group contains a shell y fauna dominated by of the southern Vi ctoria Range have been complicated by benthic organi sms that are part icularl y abundant in the Cenozoic fau lting. Thejuxtaposition oflow-grade and high limestone and mudstone units. Studies of the macrofauna grade rocks in the Grey Ri ver is further evidence for a indi cate an Early Devonian age, with some un certainty detachment faul t/metamorphic core compl ex (di scussed on about wheth er the fa un a is Pragian or Emsian (Bradshaw p. 19). 1999).
Paragneiss OCcuITi.ng fruthersouth between the Alpine Fault Sandstone boulders containing an Earl y Devonian faun a and the Fraser Fault contains a metapelitic assemblage of similar to th at at Reefton occur in g lacial outwash near sillimanite and kyanite in association with gru'net and biotite Lake Haupiri , but no outcrops have been found (Johnston (Mason & Taylor 1987; Rattenbury 199 1; Wai ght and and others 1980). others 1997). lnterl ayered wi th the metapelitic paragneiss are horn ble nd e-plag ioc la se± garn e t amphibolite Takaka terrane orthogneisses deri ved from igneous components such as mafic sill s, fl ows or tu ffaceous hori zon s. These gneisses, Cambrian to Ordovician volcanic and sedimentary with mi gmatitic gneiss, orthogneiss and grani toid rocks rocks (Sf) ha ve been variably mylonitised (Sfm) and are collecti vely named Fraser Complex (R attenbury 1991), The Paleozoic sedimentary rocks of th e Takaka terrane whi ch here in cludes ro cks described as Granite Hi ll near Sprin gs Jun ction are di vided into the Earl y to Middle Compl ex by Waight and others (1 997). The metapeliti c Cambrian volcanogenic Devi l Ri verVol cani cs Group, the g ne iss has z ircon age di stributio ns s ugge sting a sedimentary Haupiri Group, and the Late Crunbrian to Late depositional age ofearl y Paleozoic (Ireland 1992), but also Ordovician carbonate-ri ch Mount Arthur Group. A small records intense metamorphism in the Late Devonian and sli verofgreenschi st deri ved fro m gabbro, dolerite, and/or Earl y Cretaceous (Ireland & Rattenbury unpublished data volcaniclastic sedimentary rock (Fanner J967) is correlated 200J). Both Devonian and Cretaceous emplacement ages with the Devil River Volcanics Group (€d) ofnorthwest are inferred for the various components ofFraserComplex Nelson (Rattenbu ry and others 1998; Monker & Cooper orthogneisses. 1999). Dolomitic mudstone and ankeritic sand stone with
Tectonic history of the Buller and Takaka terranes prior to amalgamation
Buller terrane rocks were deposited in Ordovician time adjacent to a continental landmass inferred to have been the Australo-Antarctic segment of Gondwanaland (Cooper 1979, 1989). Cambrian rocks of the Takaka terrane formed on, and adjacent to, a volcanic island arc/back arc setting (Miinker & Cooper 1995; Roser and others 1996; Wombacher & Miinker 2000). The histories and tectonic sellings of the two terranes suggest that they were originally a considerable distance apart, perhaps hundreds ofkilometres (Cooper 1989). The Late Cambrian to Devonian passive margin part ofthe sequence was previously thought to have been deposited conformably on the arc-related part of the Takaka terrane (Grindley 1980; Coleman 1981; Cooper 1989). The recognition of the widespread Late Cambrian Balloon Melange Event in northwest Nelson, however, may indicate a significant tectonic contact. Although they are here retained as parts of the one terrane it is possible that the passive margin part of the sequence is allochthonous (Cooper 1997).
Amalgamation of the two terranes post-dates deposition of the Early Devonian Baton Formation (Cooper 1989; Bradshaw 2000), but pre-dates emplacement of the Late Devonian granitoids (Muir and others 1996b) and is therefore taken as Early to Middle Devonian.
The Anatoki Fault forms the boundary between the Takaka and Buller terranes. South of Maruia, the fault is inferred to have been offset 5 km by a later strike-slip fault. The two terranes were juxtaposed by substantiat strike-slip movement along the Anatoki Fault in the Early-Middle Devonian (Jongens 1997). In northwes(Nelson the Anatoki Fault also underwent Early Cretaceous ductile dextral strike-slip, followed by brittle deformation.
13 Figure 15 Quarry in Sluice Box Limestone (Mt Arthur Group), about two kilometres southwest of Springs Junction. Most of the outcrop is forest covered, but the limestone forms a distinctive ridge that can be traced for several kilometres. At thi s locality limestone is recrystallised to marble by the thermal effects of a nearby pluton.
Photo CN4349217: DL Homer
minor monomict conglomerate (€hr), polymict pebble Muir and others (I996b) recorded a group ofU-Pb SHRIMP granule conglomerate (€ha), and grey lamin ated do lomitic ages on Karamea suite grani tes that were statistically mudstone and sa nd stone with abundant interlayered felsic indi stinguishable at 375 ± 5 Ma, as well as two younger volcani c rocks (€hh) are cOITelated with the Haupiri Group dates at -330 Ma. Subsequent dati ng ofadditionalsamples of northwest Nelson. has ind icated a spread of ages in the range 375-315 Ma, with a concentrat ion of ages at about 370 Ma (Fig. 16a; The Mount Arthur Group in the Springs Junction area A. J. Tulloch, pers. comm. 200 I). (Bowen 1964) is represented by the Sluice Box Limestone (ems) and the Alfred Formation (emw) ofFauner (1967) The most widespread granitoid lithology is muscovite (see also Cooper 1979). The Sluice Box Limestone is the biotite granite (Dkg; Fig. 17a), which includes a variety of lateral equivalent of the Arthur Marble I and Summit textural types, some of which ha ve been mapped as Limestone in northwest Nelson and is composed ofmainly separate plutons (e.g., Roder & Suggate 1990; Tulloch recrystallised grey limestone and si li ceous lime 1978). A distinctive pluton ofleucocratic muscovite±biotite stone (Fig. 15). Conodonts, trilobites and inarticulate granite with large white tabular megacrysts of K-feldspar brachiopods indicate an age range of Late Cambrian to (Dunphy Granite, Dkm) occurs on the western side ofthe Middle Ordovician (Cooper 1989). The overlyi ng Alfred Brunner Range. Highly foliated biotite-muscovite granite Formation is the equivalent of the Wangapeka and Baldy gneiss in the Paparoa Range is mapped as Okari Granite formation s in west Nelson and consists of silt stone and Gneiss (Dkn). Although the dominant lithology in the minor quartz sandsLOne with graptolites of Late Ordovician Ne lson area is a distin ctive, coarse-grained porphyriti c (Gisbomian) age (R.A. Cooper, pers. comm . 200 I). gra nite containing large pink megacrysts ofpotash feldspar (Dkp), this lithology occurs on ly as a single small pluton The Haupiri Group rocks around Springs Junction are near the northwest edge ofthe Greymouth map .Two small separated from th e structurall y overlying and yo unger plutons, both foliated biotite granite with large K-feldspar Mount Arthur Group rocks by a detachment fault (R.A. megacrysts, have U-Pb ages less than 350 Ma, and are Cooper, pers. comm. 200 I). The whole succession has been mapped as Ckg (Fig. 17c). tightly folded into an an[ifoun and cut by later faulting. The finer grained rocks are commonly cleaved. Biotite-bearing granodiorite and tonalite (Dkt & Ckt) are subordinate to granite. A few small areas of hornblende Late Devonian to Early Carboniferous intrusive rocks diorite (Ckd; Fig. 17b) occur in the Victoria Range where they intrude granitic rocks. Voluminous potassic biotite granitoids of the Karamea Suite fonn the bulk ofthe Karamea Batholith that extends Undifferentiated orthogneiss (Dog) in the southern Victoria from west Nelson sou thwards into the Greymouth map area range (Fig 14b) is probably Late Devonian in age based alo ng the Victoria and Brunner ranges (Mu ir and others on preliminary U-Pb zi rcon and monazite geochronology I 996a). Isolated plutons of Karamea Suite granitoids al so (Ireland & Rattenbury unpub li shed data 200 I ). Some occur in the Paparoa Range and in th e southwest. orthogneiss within the Fraser Complex (Fig. 14c) is ofLate Devonian to Early Carboniferous age (Jreland & Rattenbury unpubli shed data 200 I). 14 35 ,!g Figure 16a c . ~ : . ~ C:'-I 30 e ~'2 Histogram showing VI i:l~""'" \I) ~ I U ~"',-~ distributi on of all available 25 , U-Pb ages fo r granitoid '" , .0'" , rocks, illustrating that 0,- 20 there is a clear bimodal ::::l , I distrib ution . 0 I -~ 15 \I) , .0 I E I ::l 10 Z I, 5 I, , 0 0 100 200 300 400 500 U-Pb ages (Ma)
• ..... French Creek Granite I Figure 16b o Rahu SUite Cretaceous Typical variation diagram • Separation POint SUite • (Si0 vs Sr), using 2 E ... Rocky Creek Granite chemical analyses of all the rocks shown in is: 1000 . • Karamea Suite } Devonian to • Fig. 16a. Geochemistry ~ • Carboniferous (/) • can aid the distinction between different su ites, but is not completely • unambiguous.
Distinction between granitoid rocks of different ages
The mountains northwest of the Alpine Fault are largety composed of granitoid rocks. Tulloch (1988) dislinguished three batholiths (Karamea, Paparoa and Hohonu) on geographic grounds. We consider that the granitoid rocks are essentially contiguous, with satellite intrusions into country rock, and therefore prefer to include them all in the Karamea Batholith as was done in the adjacent Nelson map (Ratlenbury and olhers 1998).
Radiometric dating indicates that granitoids in the Greymouth map area were emplaced in two distinct time periods: Late Devonian to Carboniferous and Early Cretaceous (Fig. 16a). One of the major challenges in preparing this map has been to consistently distinguish between granitoids ofdifferent age groupings. There are now approximately 50 U-Pb ages on granitoid ptutons within or immediately adjacent to the QMAP Greymouth sheel (Kimbrough & Tulloch 1989; Muir and others 1994; Muir and others 1996b; Muir and others 1997; Tulloch 1983; Waight and others 1997; AJ Tulloch, pers. comm. 2001), and these have been used as the basis for age discrimination. Most of the Late Devonian to Early Carboniferous rocks are S-type granitoids, while most of the Early Cretaceous granitoids are t-types, and it has therefore been possible to supplement the da ting by geochemical criteria (Fig. 16b; see Tulloch & Brathwaite 1986) and measurement of magnetic susceptibility (Tulloch 1989). There are, however, still uncer1ainties, and more radiometric dating is required.
The granitoids have been grouped into suites defined by age and composition. In order to generalise information at 1:250000 scale, individual mapped plutons within each suite have been combined into similargranitoid types - for example, granite, granodiorite/tonalite, and diorite (see map legend).
15 Figure 17 A selection of U-Pb dated granitoid rocks of the QMAP Greymouth area. Although most plutons have distinctive lithologies, the photographs illustrate the difficulty of distinguishing between Devonian-Carboniferous and Cretaceous granitoids without supporting geochemistry and radiometric dating.
(a) Two dated Devonian granites, mapped as Dkg. Medium-grained biotite-bearing Whale Creek Granite intruded by fine-grained phase of the O'Sullivans Granite (Roder & Suggate 1990; Muir and others 1996b). Buller River near Whale Creek. (b) Early Carboniferous biotite diorite (Ckd; Tobin Diorite of Tulloch 1978). Rahu River. (c) Foliated granite with large K-feldspar megacrysts (Ckg; Foulwind Granite of Nathan 1976b), dated as Early Carboniferous (Muir and others 1996b). Cape Foulwind, near Westport. (d) Early Cretaceous Darran Suite biotite granite (Kdg; Rocky Creek Granite of Tulloch 1978) from near Rahu Saddle. (e) Early Cretaceous Rahu Suite biotite-hornblende granodiorite (Krt) intruded by granitic dike. Upper Grey River near Robinson River confluence. (f) Megacrystic K-feldspar hornblende-biotite granodiorite (Early Cretaceous Separation Point Suite, Ksy) with well developed foliation , locally mylonitic. Snow Creek, tributary of the Upper Grey River. 16 PERMIAN10EARLYCRETACEOUS The SeparationPointSuite occurs mainly in the Separation Point Batholith in the Nelson map area (Rattenbury and West ofthe Alpine Fault others 1998) as well as forming a numberofisolated plutons in the Greymouth map area. They are distinctive Na-rich Triassic-Jurassic sedimentary and volcanic rocks alkali-calcic granitoids with high Sr and SrlY ratios, often with, visible titanite in hand specimen. The main lithology A small area of early Mesozoic rocks near Kirwans Hill, is equigranular biotite and biotite-hornblende granite northeast of Reefton, has particular significance because (Ksg), with minor granodiorite and tonalite (Kst) and ofits close similarities with Gondwanaland sequences in hornblende diorite (Ksd). A linear belt of granite Australia and Antarctica (Mortimer and others 1995; granodiorite with large K-feldspar megacrysts (Macey Mortimer & Smale 1996). Granite ofTulloch 1978) crops out along the western side ofthe Victoria Range, and is locally mylonitised (Ksy; Fig. The Topfer Formation (Top), covering an area ofonly 2 17f). U-Pb dating indicates that the Separation Point 2 km , consists of massive brown volcaniclastic sandstone, plutons were emplaced between 126 and 109 Ma (slightly with rare beds ofpebble conglomerate and coal. Although older than, but overlapping with, the Rahu Suite). relationships with older rocks have not been seen, the unit cannot be more than a few hundred metres thick. An isolated pluton ofbiotite granite in the eastern Victoria Petrographic studies suggest a continental, magmatic-arc Range, mapped by Tulloch (1978) as Rocky CreekGranite source area, possibly similar to that ofthe Murihiku terrane. (Kdg; Fig. 17d), gives a U-Pb age of132 Ma (A. J. Tulloch, Pollen indicates ages ranging from Middle to Late Triassic pers. comm. 2001). The granite has calc-alkaline I-type (Smale and others 1996). affinities more typical of the Darran Suite in northern Fiordland (Muir and others 1998), with which it is tentatively The Topfer Formationis intruded by steeply dipping sills correlated. A small area ofbiotite-hornblende diorite near oflow-Ti tholeiitic basalt and dolerite (Kirwans Dolerite, Springs Junction (Jdd) is also included in the Darran Suite. Jkd). The dolerite has very close geochemical and isotopic affinities with the Ferrar magmatic province ofAntarctica Early Cretaceous sedimentary rocks (Mortimer and others 1995). K-Arages range from 151-172 Ma, indicating a Middle Jurassic age. Mainly coarse-grained, non-marine sedimentary rocks of the Pororari Group (Ko) are preserved in partly fault Early Cretaceous granitoid rocks bounded blocks in and around the Paparoa Range. The distinctive maroon colour of many outcrops probably Early Creta<;:eous granitoid rocks make up a significant indicates a non-marine oxidising environment, but does part ofthe Karamea Batholith in the Paparoa, Victoria and not occur in all places. The basal contacts with older rocks Hohonu ranges. Although there are some differences in are mostly faulted, but locally unconformable. hand-specimen from the older Devonian/Carboniferous granitoids that crop out in the same areas, distinguishing The Pororari Group contains clasts of nearby basement plutons ofdifferent ages requires geochronology aided by lithologies, indicating local derivation. Pollen and spores geochemistry (see text box on p. 15). show itis oflate Early Cretaceous age (Albian; Raine 1984), implying that deposition was immediately afte~ granite Most ofthe Cretaceous granitoids are included in the Rahu emplacement and uplift (Adams & Nathan 1978; Tulloch Suite (Tulloch 1983; Tulloch & Brathwaite 1986), which, & Palmer 1990). as used here, incorporates the Hohonu Suite ofWaight and others (1998aj. The rocks are typically calc-alkaline I1S The dominant lithology within the Pororari Group is type granitoids. The dominant lithology is equigranular poorly-sorted, matrix-supported breccia and breccia biotite or biotite-muscovite granite (Krg), but there are conglomerate, locally with outsize clasts up to 0.3 m in also several large plutons ofleucocratic muscovite granite diameter, in a coarse-grained sandy matrix (Hawks Crag (Krm),typically with minor biotite. Biotite granodiorite Breccia, Koh; Fig. 18). and tonalite (Krt) are less common, but several small, high level plutons of these compositions are chilled against In the Lower Buller Gorge four members or facies of the country rockinthe north ofthe LowerBuller Gorge (Berlins Hawks Crag Breccia have been recognised locally (Beck Porphyry of Nathan 1974a). There are also several small and others 1958; Nathan 1978b) based on variations in areas ofhornblende diorite (Krd). clast lithology (either Greenland Group or a mixture of Greenland Group and granite). The sequence is interpreted U-Pb dating ofRahu Suite plutons (Muir and others 1994; to be a series of overlapping alluvial fans from different, Muir and others 1997; Waight and others 1997; local sources. In other areas, the breccia consists A. J. Tulloch, pers. comm. 2001) indicates that the Rahu predominantly ofclasts ofGreenland Group or granite from Suite was emplaced in a short period arouild 110 Ma (within nearby sources. limits of 115-105 Ma), at a range of depths (Tulloch & Challis 2000).
17 Figure 18 Typical lithologies of the Hawks Crag Breccia (Koh).
(a) Hawks Crag in the Lower Buller Gorge, the type locality, consists of very thick massive beds of greywacke-derived breccia, dipping about 40' west (right). The moss-covered cliff drops straight into the river, so it has been necessary to excavate a narrow cutting for the road .
(b) Hawks Crag Breccia exposed in the road cutting at Hawks Crag. The clasts here are entirely hornfels derived from the Greenland Group, and the largest is about 0.5 metres long. Rapid uplift and erosion of the hornfels occurred in Albian time.
(c) Hawks Crag Breccia at Fox Ri ver mouth is composed of th ick beds containing granite clasts in a sandy matrix. A pollen sample from this locality has been dated as late Albian , typical of other sampl es dated from the Hawks Crag Breccia (Raine 1984).
Photos: S. Nathan 18 In addition to the Hawks Crag Breccia, the Pororari Group shale (Nath an 1978b), and forms the basal 60 metres ofthe contains fluvial, sandstone-conglomerate sequences and Pororari Group. V-Pb dating gives an age of 101 -J02 Ma locaJ lacustri ne beds containi ng interbedded debris flows (Muir and others 1997). and turbidites. A number oflocal units have been named in different areas (Laird 1988; Nathan 1978b), buton th is map C retaceous dikes and high level intr usions they are mapped as und ifferentiated Pororari Group. In the Punakaiki area, Laird (1995) interpreted the sediments as a Thin dikes and si lls of lamprophyre, basalt and trachyte, fan-delta sequence which built out into a lake that occupied generall y less than I metre thick, intmde the Pororari Group a rapidly subsi ding half-graben. and older rocks, includin g mylonite withi n the Fraser Complex (Nathan 1978b; Huot & Nathan 1976; Quek (1976) desc ri bed a narrow, fault-bounded sequence Rattenbury 1987). K-At· ages range from 90-78 Ma (Adams in the Brown Grey River which is dominantly grey & Nathan 1978). sand stone with carbo naceous lenses. It in cludes local red stained lenses and is te ntati vely incl uded in the Pororari In the Hohonu range a dike swarm which c uts the Group, although it is so far undated . granitoids incl udes lamprophyre. dolerite and phonolite. It is thought to be geneticall y related to, and the same age I n the Lower Buller Gorge, Stitts Thff M ember (Kos) as, the alkaline syenogranite mapped as French Creek comprises light grey rhyolitic tuff with minor carbonaceous Granite (Kfg) (82 Ma; Waigh! and others 1998b).
Early Cretaceous structural development
Geological and geochronological evidence indicates that emplacement of granitoid rocks, uplift and erosion, took place in a short period between 115 and 95 Ma (Ada ms & Nathan 1978; Spell and others 2000). This is also the time when high-grade metamorphic and granitoid rocks were juxtaposed immedialely beneath low-grade Greenland Group and cross-cutting plutons by movement on low-angle detachment faults, forming metamorphic core complexes (Tulloch & Kimbrough 1989). Rapidly uplifted basement rocks provided source material for the Pororari Group, which is now preserved as faulted blocks around the margins of the core complex in the Paparoa Range (Fig. 19).
The geological map gives a plan view of the distribution of rocks from different structural le vels. Cross-sections A-A' and 8-8' provide an interpretation of the possible subsurface extrapolation of low-angle detachment faults.
The tectonic and magmatic events are together inferred to record the end of subduction and terrane accretion, changing abruptfy to continental extension preceding the break-up of Gondwana (Waight and others 1998a).
South North erosion ;::,.... Pororari Group
Cretaceous granitords ~ -- paragneiss LOWER PLATE
Figure 19 Diagrammatic cross seclion through th e metamorphic core complex in the Paparoa Range. The lower plate was uplifted along shallOW-dipping mylonitic detachment taulls displacing th e upper plate of early Paleozoic Greenland Group and some small granitoid intrusions. The extensional deform ation also resulted in the formation of fault bounded basins in Ihe upper plate that were rapidly filled with Pororari Group terrestrial sediments derived from the eroding lower plate. Modified after Tu lloch & Kimbrough (1989). t9 Figure 20 Typical sedimentary lithologies within the Rakaia terrane and Esk Head belt. (a) Thin-bedded alternating sandstone and mudstone, a typical turbidite association (Tt). State Highway 73, near Bealey Bridge. Photo CN43424116: D.L. Homer
(b) Thick-bedded sandstone, with an interbedded package of alternating sandstone and mudstone (Tt). East branch of the Poulter River. Photo: M.s. Raffenbury
(c) Lenticular boudinaged sandstone and mudstone, a weakly transposed precursor to broken formation (Tt) . Upper Wilberforce River near Browning Pass. Photo: K.R. Berryman
(d) Typically knobbly broken knocker topography associated with Esk Head belt melange (Tem) with purple-red coloration to right due to interlayered red mudstone and volcanogenic rocks. Looking towards Esk Head on the Puketeraki Range. Photo: M.J. Isaac
(e) Typically strongly sheared and transposed red and green mudstone and interlayered volcanogenic rocks within Esk Head belt melange (Tem). North Esk River. Photo: M.J. Isaac 20 East ofthe Alpine Fault: Rakaia terrane zones commonly change in width from several hundred metres to less than a metre along strike and are difficult to Rakaia terrane fonns part ofthe Torlesse composite terrane map over extended distances. which incorporates the fonner Torlesse Supergroup and ranges in age from ?Late Permian to Early Cretaceous. Late Triassic semischistose and schistose rocks Rakaia terrane is separated from the neighbouring Pahau terrane by the Esk Head belt, which is further described West ofthe main divide the Rakaia terrane rocks become below (p. 22). progressively metamorphosed into semischist and schist towards the Alpine Fault. The metamorphosed rocks have Late Triassic sedimentary rocks been mapped in textural zones (IIA, lIB, III, IV), using a classification that is now widely accepted in New Zealand Grey, indurated quartzo-feldspathic sandstone (greywacke) (see box on p. 22; also Fig. 21). and mudstone (argillite) (Tt) comprise much ofthe eastern Southern Alps within the Greymouth map area. The Incipiently cleaved to strongly transposed alternating sandstone is typically poorly to moderately sorted, fine sandstone and mudstone and thick sandstone semischist to medium-grained, and contains abundant lithic clasts of (Tt, textural zones IIA and lIB) comprise a zone . felsic igneous and sedimentary rocks. Sedimentary approximately 6-8 km wide in the south that thins to about lithotypes are dominated by (a) thick to very thick, poorly 2 km in the northeast. This zone is also slightly oblique to bedded sandstone, and (b) thin- to medium-bedded the Alpine Fault trend. The intensity of cleavage and alternating sandstone and mudstone (Fig. 20). The foliation development increases to the northwest and is sandstones are commonly well-graded and show gradational into schist. sedimentary structures such as cross-bedding, sole markings and ripples. Both lithotypes were fonned by Laminated and segregated t.z. III-IV schists occur in a turbidite depositionin a submarine fan environment. northeast-trending, 2-10 km wide belt immediately southeast of the Alpine Fault. Pelitic and psammitic Thick mudstone beds, with or without thin- to medium greyschist are inferred ~o be metamorphosed quartzo bedded sandstone, are less common in the map area. feldspathic sedimentary rocks dominated by alternating Conglomerate occurs sparingly, and is more obvious in sandstone-mudstone sequences. The schists grade from river boulders than in outcrop. The clasts range from sub quartz-albite-muscovite-chlorite mineral assemblages to angular to well rounded and are dominated by sandstone biotite-albite-oligoclase and garnet assemblages towards and mudstone, with lesser amounts of felsic igneous and the northwest. quartz-rich metamorphic rocks. The westernmost part of the schistose rocks includes a Coloured mudstone is a minor but significant rock type in higher proportion ofpelitic schist and mafic metavolcanic the map area. Typically, dark red to brown, or pale green greenschist layers, and is correlated with the Aspiring to grey mudstone occurs in bands with dark grey mudstone lithologic association (Ya), a subdivision of the Rakaia and sandstone up to several hundred metres thick (Ttv). terrane recognised in northwest Otago (Craw 1984; Rare occurrences of basalt and limestone are found in Turnbull 2000) and in Marlborough (Mortimer 1993b; association with the coloured mudstone. Coloured Begg & Johnston 2000). In the Greymouth map area these mudstone may have fonned by very slow, clastic-poor rocks also include the Pounamu Ultramafics (Yap) deposition (Roser & Grapes 1990) rather than by an comprising serpentinite, gabbro and metabasite in increased volcanogenic component. Bands of coloured association with pelitic schist and rare limestone and chert. mudstone are one ofthe few distinct marker horizons within These ultramafic rocks occur in lenses up to 200 m wide the Rakaia terrane that can be used to map regional and 1 km long, collectively aligned along a belt between structural trends. Coloured mudstone is commonly the Kokatahi and Maruia rivers, on a slightly oblique trend associated with zones of layer-parallel shearing which to that ofthe Alpine Fault. These metamorphosed ultramafic locally inten.sifies into broken formation (Ttm). The rocks host pods ofhighly valued greenstone (also known shearing probably results from low rock strength rather as pounamu or nephrite; see p. 42). than tectonic incorporation of "exotic" components in melange. Schist of the Aspiring lithologic association becomes increasingly mylonitised close to the Alpine Fault (YTm) Late Triassicfossils are relatively abundant in the vicinity and the mylonite zone has a maximum width of of Arthur's Pass, and include Monotis with fewer approximately 2 km near the southern map boundary. The Terebellina mackayi, and other bivalves, crinoids, mylonite zone narrows to the northeast, and is probably bryozoans, fish vertebrae and trace fossils (Campbell & truncated by the Alpine Fault near the Blue Grey River. Warren 1965; Cave 1982). Monotis is also present in the Greenschist (YTg) and ultramafic (YTv) bands are mapped Trent River area (Wellman and others 1952). within the mylonite zone.
Tectonic shearing is common throughout the Rakaia The eastern part ofthe belt ofschistose rocks is dominated terrane, and the zones are usually eitherparallel to bedding by quartzofeldspathic greyschist (Tt). Rare greenschist or have transposed bedding parallel to the shearing. The bands occur near the boundary with the Aspiring lithologic 21 association. The boun dary between the greyschi st and Esk Head belt the Aspiring lithologic association is inferred to be a fault that post-dates textural metamorphi sm. A local reversal of Late Jurassic - Early Cretaceous melange the reg ional westward increase in textural metamorphi sm is apparent at the boundary where the western pelitic and Thick to very thick, poorl y bedded, and locall y sheared mafic/ultramafi c schi st is t. z. lIB, an d the eastern greyschi st sandstone (Te) and stro ngly sheared melange (Tern) is t. z. III. comprise the Esk Head belt in the southeast of the Greymouth map area. At Esk Head at th e northern end of A Late Triassic depositi onal age fo r the semi schist (the the Puk eteraki Range, the distincti ve knocker topography same as the un metamorphosed part of the Rakaia terrane) is characteristic of melange (Fig. 20d). The knockers is ind icated by Torlessia in the lower grade rocks of the ty picall y consist of indu rated, partly sili cified massive Arahura River (Campbell & Warren 1965). sand stone and they are enveloped in a strongly sheared matrix ofbroken sand stone and mudstone. In add ition the Structure of Rakaia rocks melange contains lensoid tectonic clasts of sandstone, coloured mudstone, basalt and limestone (Fig. 20e). Many The structure of the Rakaia terrane is complex and difficult of these rock types are simi larto those found in th e Rakaja to resolve due to mu lti ple fold ing events, a general lack of terrane and therefore are not strictl y exotic components. marker horizons, lim ited age contro l and widespread Late Tri assic M anolis shell s have been found in limestone fau lting. In general, bedding trends north to northeast and blocks and clasts with in the melange (B radshaw 1973) at converges to northeast closer to the Alpine Fault. There Esk Head. Tn add ition, however, Late Jurassic belemn ites are multi ple phases of foliat ion development within the and Early to Late Jurassic radiolari a occur within the Esk semischi st and schist refl ectin g a protracted defo l111ational Head belt beyond the map sheet boundary (Silberling and and metamorphi c history. Schi st fo liation trends no rtheast, others 1988), constra ining the age of deform ation! sub-parallel to the Alpine Fault. Some macroscopi c fold s emplacement to post-Late Jurassic. are preserved in both th e schi stose and non-schistose rocks, commonJ y with one and rarely botJllimbs oveltumed. The western boundary with Rakai a terrane rocks is well Mesoscopi c folds are rare in the nOll -schi stose rocks. defined and mappabl e to within 100 m in places. The eastem
Textural zones
Textural subdivision is a useful method for mapping low grade metamorphic rocks, and has been widely applied (Bishop 1974; Turnbull 1988; Mortimer 1993a).Textural zones (t.z.) separated by "isotects" are independent of metamorphic facies boundaries, and can cut across isogra ds or foliation.
The application of the textural zonation system established by Hutton & Turner (1936) and Bishop (1974) has been revised by Turnbull and others (2001). Characteristics of these revised textural zones are summarised:
t.Z. I: Rocks retain their sedimentary (primary) appearance. Detrital grain texture is preserved, and bedding (when present) dominates outcrops. Metamorphic minerals may be present, but are very fine-grained «75 11m), and there is no foliation.
t.Z. flA: Rocks retain their primary appearance and sedimentary texture, although detrital grains are flattened. Metamorphic minerals are fine-grained «75 11 m), and impart a weak cleavage to sandstones. Mudstones have slaty cleavage. Bedding and foliation are equally dominant in outcrop. Rocks are termed semischist.
t.Z. fiB: Rocks are well foliated, although primary sedimentary structures may still be seen. Bedding is transposed or flattened. Clastic grains are flattened and metamorphic overgrowths are visible in thin section. Metamorphic mica grain size is still <75 11m and metamorphic segregation appears. Mudstone is changed to phyllite; meta sandstone is well foliated and forms parallel-sided slabs. Rocks are termed semischist.
t.Z.Iff: Planar schistosity identified by metamorphic micas is de veloped in all rocks. Bedding is barely recognisable, and is transposed and parallel to foliation. Clastic grains may still be recognisable in sandstones, but are recrystallised and overgrown, and metamorphiC segregation laminae are developed. Rocks are termed schist. Quartz veins develop parallel to foliation, or are rotated and flattened. Metamorphic micas are typically about 75-125 11m long (very fine sand size).
t.z. IV: Primary sedimentary structures and clastic grains are destroyed at a mm-cm scale, although primary sedimentary units may be discernible in outcrop. Schistosity tends to be irregular due to porphyroblast growth. Metamorphic mica grain size is 125-500 .urn . Schistosity and segregation are ubiquitous and rocks are termed schist. Quartz veins are abundant in most lithologies.
22 boundary of the melange is 110t well defined and rocks to The Esk Head belt is widely believed to represent the the east show generally less shearing in more localised tectonic su ture between the contrasting Rakaia and Pahau zones, but the melange component is up to 10 km wide. terranes and extends from Canterbury to Marlborough The melange has a steeply dipping fabric that is close to (Si lberling and olhers 1988) .The belt isoffset by the Alpine parallel to the bedding within less deformed Rakaia ten-ane Fault and reappears in the lower North Island throu gh the rocks to the west. Rimutaka, Tararua and Ruahine ranges (Begg & Johnston 2roJ).
Figure 21 Progressive development of schistosity on the western side of the Southern Alps.
(a) Subhorizontal thin-bedded alternating sandstone and mudstone (Tt), with incipient steeply dipping cleavage (1.z. II A). Northwest of Newton Saddle.
PhotO: K. R. Berryman
(b) Strongly transposed and fo liated west dipping semischist (Tt, I.z. liB) on the Newton Range west of Mt Newton.
Photo: J. Adams
(c) Strongly foliated and segregated I.z. III schist (Va) transitional to schist mylon ite (VTm). Approximately 2.5 km southeast of the Alpine Fault in Camp Creek on the northwest flanks of the Alexander Range. PhotO: M.S. Rattenbury 23 Figure 22 Gently dipping Paparoa Coal Measures (bottom half of cliff) overlain by Eocene (Brunner) coal measures and shallow marine sandstone in the Pike River Coalfield, central Paparoa Range. View looking eastwards to the Grey Valley. Both the Brunner and Paparoa Coal Measures in this section contain thi ck coal seams, which have been prospected by helicopter-supported drilling . Photo CNI0362133: D.L. Homer
Figure 23 Light-coloured Paparoa Coal Measures exposed in a cliff on the south side of Ten Mile Stream, consisting of thick-bedded conglomerate with a few sandstone interbeds. The overlying Eocene rocks (covered with vegetation) consist of shallow marine sandstone with a thin coal seam at the base. The contact represents a period of time during which the Waipounamu erosion surface developed and the underlying rocks were deeply weathered. In this view, the weathered material is the paler uppermost 10m of the Paparoa Coal Measures. Photo: S. Nathan
l LATE CRETACEOUS AND TERfiARY Basalt flows and breccia are interbedded withi.n th e lower part of the Paparoa Coal Measures at several locaJities, Late Cretaceous to earli est Pleistocene sedimentary rocks and have been dated at 68-7 1Ma (S ewell and oth ers 1988; record the formation and subsequent deformation of Nathan and others 2000). They appear to be part of an locali sed, faul t-bounded basin s in response to changing episode of latest Cretaceous basaltic volcanism th at was tectonic stresses across the developing boundary between widespread on th e West Coast (Nathan and others 1986). the Australian and Pacifi c pl ates. Most time interval s from Late Cretaceou s to Earl y Pleistocene are represented, Pollen dating, summarised by Raine (1 984), shows that although no sin gle basin has a complete sequence. The most ofthe Paparoa Coal Measures is latest Cretaceous in sedimentary succession locall y shows marked lateral fa cies age, but the uppermost part is Early Paleocene. The and thickness changes as well as abrupt changes in Cretaceous-Tertiary boundary occurs within a coal seam depocentres and changing paleo-hi ghs. Virtually the whole in the upper part of th e Rewanui Member (Raine 1994; area was submerged be neath the sea by the latest Vajda and others 2001). Oligocene, with a regression and the emergence of low hills th rough the Miocene and Pliocene. The present day Eocene sedimenta ry rocks mountain ranges are a latest Cenozoi c feature. Tectonic acti vity recommenced in the late Middle Eocene T he Southern Alps, immedi ately southeast of th e Alpine (about 38 million years ago), with regional extension Fault, did not stal1 to ri se rapidly until late Cenozoic time. leading to the fo rmation of local basins, many faul t Although onl y two small areas of Cenozoic sedimentary bounded, separated by areas of low-lying land. At the same rocks are preserved southeast of the Alpine Fault in thi s time a g radual marine transgressio n s tarted , and map area, it is inferred that much of Canterbury was progressively inundated th e whole West Coast region over submerged during the Cenozoic (Field & Browne 1989), the succeeding 15 mi llion years. By the end ofthe Eocene with maxi mum submergence during the Oligocene. th e map area had become an archipelago of low-lying islands sunounded by shallow seas (Nathan and others Late Cretaceous to Paleocene sedimentary rocks 1986).
Late Cretaceous to Paleocene rocks are restri cted to a The oldest Eocene sedimentary rocks are Brunner Coal narrow, NNE-trending basin (Paparoa Trough) in the Measures (Eb), c onsis ting o f quartz sands tone, central part of the map area (Nathan and others 1986). conglomerate, carbonaceous shale, and lensoid coal seams Paparoa Coal Measures (Kpc) consist of a non-marine locall y up to 10m thick (Flores & Sykes 1996; Titheridge assemblage of flu vial conglomerate, sandstone, lacustrine 1993). The formation is characteristically quartzose, being mudstone, and lensoid coal seams (Figs 22 & 23). Drilling largely derived from deepl y weathered, granitoid basement for coal and petroleum exploration has defined the rocks. Having been deepl y buried in some areas, the thickn ess variatio n within the formation, indicating a sandstone beds are commonly silica-cemented, and thus maximum thickness of abollt 750 metres in the axis of the form characteri sti c bluffs and plateaus (Figs 10, 24). trough. Detailed mapping within the Greymouth Coalfield (Gage 1952) showed that the Paparoa Coal Measures can The coal measures are conformably (and in most places be subdivided into seven units, now mapped as members g radationally) overlain by shallow-water sedimentary (Nath an 1978a). The key to subdi vision is th e recognition rocks. The most widespread unit is massive, dark brown of three lacustri ne mudstone marker bands separating carbonaceous mudstone of th e Ka iata Formation (Erk; thi cker un its of coal measures (predominantly quartzo Fig. 26) which locall y contains interbedded mass-flo w feldspathic sandstone. with conglomerate and coal seams). deposits near Greymouth and Westport (Nathan and others The uppermost (Dunollie) member is di stinctl y more 1986). In some areas, th e coal measures are overlain by quartzose towards the top, indicating in creased chemical shallow marine sandstone whi ch has been given a variety decomposition of less stable mineraJ s as the tempo of uplift of local names (e.g., [sland Sandstone near Greymouth), and erosion slowed in th e Early Paleocene. but which are here generali sed as a sin gle un it (Ers).
Late Paleocene - Early Eocene unconformity
Early in the Paleocene there was a general slowing in tectonic activity. Sedimentation ceased over the whole of the map area, and there is no Late Paleocene - Early Eocene stratigraphic record. This break represents a period of widespread peneplanation and a regional unconformity that affected much of the New Zealand region (Suggate and others 1978), more recently named Ihe Waipounamu erosion surface (LeMasurier & Landis 1996).
Generally the rocks immediately beneath the unconformity are deeply leached, wilh the less resistant minerals such as feldspar and biotite decomposed, leaving a residuum consisting mainlyofquartz and kaolin clay (Fig. 25). Wellman (1951) described the nature of the contact between the Paparoa Coal Measures and overlying Eocene sediments near Greymouth, providing evidence for a break in sedimentation accompanied by subaerial weathering (Fig. 23). The Waipounamu erosion surface forms a marked topographic feature in several parts of the Greymouth map area (e.g. Fig. 10). In all cases the surface has been covered by Late Eocene-Oligocene sediments, and subsequently uplifted and exhumed in the late Cenozoic. '------J 25 Figure 24 Aerial view of an opencast mine in Brunner Coal Measures (Eocene) on the top of Mt Frederick, Buller Coalfield, 1995. Approximately 20 metres of hard, cemented quartzose sandstone have been stripped off to expose the thick coal. The Stockton plateau in the background is formed of similar quartzose sandstone, but coal only occurs in local, lensoid seams. Photo CN32454116: D.L. Homer
Figure 25 Unconformity between Brunner Coal Measures (Eocene) and deeply weathered granitoid rocks exposed on State Highway 6 south of Charleston. In some places the rocks beneath the unconformity are so deeply weathered that they consist of little more than kaolin clay and quartz. Locally the clay has been quarried and processed for use in sanitary ware. Photo CN43407113: D.L. Homer Figure 26 Gently dipping Tertiary sequence exposed on the coast east of Cape Foulwind. In the fo reground light grey brown Kaiata Formation (Late Eocene to Early Oligocene) dips about 13' eastwards. Detailed micropaleontological studies show that the Eocene-Oligocene boundary occurs near the bend in the coastl ine. The cliffs in the background are composed of O'Keefe Formation (Late Miocene-Pliocene), and the whole sequence is capped by 3-4 metres of brown ilmenite-rich sand ben eath a last interglacial terrace surface.
Photo CN43418114: D.L. Homer
Within the Murchison Basin, at the northeast edge of the Oligocene reflector offshore and onshore beneath late map area, the Maruia Formation (Em) consists of Cenozoic deposits. carbonaceous mudstone containing a high proportion of thick-bedded quartzofeldspathic sandstone, with minor Nathan ( 1974b) included all thecaleareous sediments over congfomerate and rare coal seams (Fyfe 1968; Roder & much of the West Coast region in the Nile Group (On), Suggate 1990). which was divided into two major facies (Nathan and others 1986): On the so utheast side of the Alpine Fault, ves icul ar, (a) Pl atform fac ies (usually < 100m thick), co nsisting of columnar basalt and adjacent glauconitic greensand in the shallow-water bioclas ti c limes ton e and muddy Esk Ri ver near Grant Stream underli e late Tertiary micaceouslimestonefOOlled 0 11 arelatively stableshelf;and sedimentary rocks. This section is similar to that in the (b) Basinal facies (usuall y> I00 m thick), predominantly Brechin Burn 15 km farther southwest (Newman & muddy li meston e, massive calcareous mud stone and Bradshaw 198 1). There the basa lt and gree nsand are interbedded ca lcareous sa nd stone and mudstone, inferred to be Eocene (Field & Browne 1989), in the upper formed in rapid ly subsiding basins. part of the Eyre Group (Ee). The Platform fac ies, which includes numerous units that Oligocene to earliest Miocene sedimentary rocks have been distinguished in detailed mapping, is found as erosional remnants over much of the map area, mainly as Continued marine transgression from Late Eocene into the bluff-forming limestone. On the coast south of Westport, Oligocene led to the gradual drowning of the low-lying limestone blu ffs are one of the most striking features of land, and by the end of the Oligocene virtually the whole the Paparoa ationa! Park (Figs 27-29). The Basinal facies map area was submerged. The supply of terrigenous occurs mainly around Greymouth, where calcareous sediment dwindled, and as a consequence Oli gocene mudstone of the Port Elizabeth Member (Onp) at the sediments are typically ca lcareous and limestone is top of the Kaiata Formation grades upwards into muddy w idespread. A lthough it is inferred th at Ol igocene micritic limes tone of th e Cobden Limestone (One). sediments originally covered th e whole map area, th ei r Within the M urchi son Basin , at th e northeaste rn corn er of present limited di stribution isdue to subsequent upli ft and th e map area, ma ss ive ca lcareous mud ston e with erosion, and to alesser extent, burial by younger sediments. interbedded calc-flysc h is mapped as Matiri Formation Seismic exploration has shown that there is a widespread (Om). 27
L Figure 27 Panoramic view looking eastwards over the Punakaiki area, showing the gently-dipping sheet of Oligocene limestone that dominates the topography, with the Paparoa Range in the background. The small settlement in the centre foreground is Punakaiki, and Pancake Rocks are in the right foreground.
Photo CN36159: D.L. Homer
Figure 28 Punakaiki township is dominated by cliffs of Oligocene limestone. This small area of late Holocene coastal plain, between the limestone cl iffs and the sea, is one of the few flat areas around Punakaiki, but is subj ect to natural hazards. Because it is open to the Tasman Sea, coastal erosion is an ever-present problem, and the settlement could be subject to tsunami. On the landward side , rockfalls and landslides from the cliffs are likely to accompany large earthquakes. Large blocks fallen from the cliff can be seen on the right.
Photo CN4213119: D.L. Homer
Figure 29 Aerial view of the Pancake Rocks, Punakaiki, showing the walkway which is mainly on the last interglacial (oxygen isotope stage 5) marine bench. Thin-bedded Oligocene limestone has been eroded into spectacular landforms by a combination of coastal erosion and slow chemical solution along joints and caverns beneath the marine gravel. The Devil's Punchbowl in the centre was probably formed by the collapse of the roof of an underground cavern.
Photo CN9833110: D.L. Homer
28 Figure 30 An almost continuous section through the gently dipping Late Miocene to Early Pliocene O'Keefe Formation is exposed in the coastal cliffs east of Cape Foulwind. The flat surface above the cliffs is a last interglacial (oxygen isotope stage 5) marine terrace, and about 5 metres of marine sand is exposed at the top of the cliffs.
Photo CN32853/2: D. L. Homer
Early to Middle Miocene sedimentary rocks fluviatile facies, with locallensoid coal seams, mapped as Rotokohu Coal Measures, Mbr (Johnston 1988). A major change in th e pattern ofsedimentation, related to the initiation of oblique compression between the Pacific Further south , a thick sequence ofgrey-brown calcareous and Australian plates. took place in earliest Miocene time. mudstone (Inangahua Formation, Mbi) occurs in the axi s After almost complete submergence in the Late Oligocene, of the Grey vall ey trough, bUlthere is an unconformity to the Early Miocene was marked by the emergence of land. the west and the basal part of the sequence is mi ssing. Upl ift and renewed tectonic acti vity is reflected in a There is a gradational change into grey calcareous regional change from carbonate-ri ch to terrigenous muddy mudstone (Stillwater Mudstone, Mbs) near the base of sediments, locally called 'papa' . Several local formations the Middle Miocene. have been idenfified and includ ed in th e Blue Bottom Group. In th e Murchi son Basin, in the northeast corner ofth e map area, calcareous mudstone ofthe Matiri Formation passes The change in tectonic regime led to local upl ift and upwards into a deep-water turbidite seque nce of changin g depocentres. In some areas the re is an interbedded quartz- mi ca sandstone and mudstone unconformity beneath or within Early Miocene sediments (Mangles Formation, Mm). An influx ofCaples-derived (Nathan and others 1986). volcanogeni c sediment led to rapid infilling of th e basin , and deposit ion of shallow marine sandstone. Overlyin g is Early to Middle Miocene sediments are preserved in a flu vial sequence of muddy sandstone and conglomerate different structural basin s, now separated by uplifted ranges with lensoid coal seams near the base (Longford Fomlation of pre-Tertiary rocks. Because of this isolation, several - not exposed 0 11 this map). Correlative sediments in the different nomenclatural schemes have been devised for Maruia va ll ey, to the south, are mapped as th e lower part different areas, as summarised by Nathan and others of the Rappahannock Group (eMr). In a study of clast ( 1986). provenance, Cutten (1979) showed that there is an upwards increase in metamorphic grade, and the clasts in the upper West of the Paparoa Range, around Punakaiki, the part ofthe Rappahannock Group (mMr) consist largely uppermost unit ofthe Nile Group (Potikohua Limestone) of Caples-derived schi st. is overlain sharply by brown calcareous sandy mudstone (Welsh Formation, Mbw), with 1-2 metres ofglauconitic mudstone immediately above the contact. The rapid change in lithology indicates a hiatus, but micropaleontological studies do not indicate a recogni sable tjme break.
In the lnangahua valley, between the Papru'oa and Victoria ranges, the Nil e Group passes gradationally upwards into light brown calcareous mudstone, locally containing limestone bands near the base. Thick interbeds ofgranite derived sandstone in the upper part ind icate a nearby rising source area, probably to the east. With the increase in sand, th ere is a progressive shallowing in to estuarine and 29 Late Miocene to Pliocene sedimentary rocks muddy sandstone, carbonaceous sandstone and thin coal seams, overlain by Torlesse-deri ved conglomerate and Parts ofthe present mountain ranges were emergent during interbedded sand stone. The conglomerate correlates with the Late Miocene to Pliocene, although the topography is the upper p3l1 ofa similar section in the Brechin Burn, 15 inferred to have been generall y low-lyi ng. Sedim ents were km to the southwest (Newman & Bradshaw 1981) and is deposited in basins approximating to the present day assigned to theLate Miocene to PlioceneMotunau Group (1Pn). lowlands, and basin margin unconformities are common. Late Pliocene to Early Pleistocene sedimentary rocks West of the Paparoa Range there is a shallow marine sequence, predominantly blue-grey muddy sandstone, Rapid uplift ofthe Southern Alps is refl ected by a flood of which is mapped as O'Keefe Formation (Mbo) (Fig. 30). flu vial gravel and sand that extended n0l1hwest from the 1n Haku-I offshore well , the O'Keefe Formation consists Alpine Fault, and is inferred to have originally covered ofdeeper water mudstone, and thi s is assumed to be typical most of th e present anIand map area (Nathan and oth ers of the offshore succession . There is a widespread 19 86). The resulting conglomerate, containing unconformity beneath the O'Keefe Formation (Fig. 3 1), predominantly clasts of greywacke and schi st, is mapped and this is interpreted as evidence of a peri od of Middle as Old Man Group (1'0) (Fig. 32a, b) Petrological studies Miocene uplift (Nathan and others 1986; Kamp and others show that it is entirely deri ved from Rakaia terrane rocks 1996). (MOItimer and others 200 I). Locall y, glac ial beds have been recorded within the Old Man Group (Gage 1945; Bowen In th e Grey va ll ey and the lowland area to the so uth, the 1966), indicating the start of marked cooling (Fig. 32c). dominant lithologies are blue-grey muddy sandstone and yell ow-brown fine-grained sandstone (Eight Mile In the Inangahua vall ey the Old Man Group rests on a thin Formation, Mbc). A small area offluvial sandstone with un.it offlu vial sandstone and estuarine mudstone, mapped coal seams and conglomerate beds on the western side of as IPbw.ln the Grey valley near Ahaura, the Torlesse-delived the Grey Valley (Nathan 1978a) is mapped as Mbf. conglomerates rest on older Pliocene conglomerates of loeal (western) deri vation (I'oc), and funher south the Eight On the south eastern side ofthe Alpine Fault several small Mile Formation grades upwards into the Old Man Group. in-faulted blocks of late Tertiary sedimentary rocks occur in the Es k River catchment. These blocks contain basal
Figure 31 Steeply dipping unconformity between the O'Keefe Formation (Late Miocene to Early Pliocene) on the le« and Kalata Formation (Late Eocene) on the right , on the Denniston road near Waimangaroa. The figure is standing at the contact. Although the nature of the contact is not clear from the photograph, the basal part of the O'Keefe Formation contains pebbles of th e underlying Kaiata Formation. The same contact has a low dip at Cape Foulwind (Fig. 26), but here th e beds have been tilted up steeply, adjacent to the range front. Photo CN31518119: D.L. Homer 30 Figure 32 Old Man Group Co; Late Pliocene to earliest QUATERNARY Pleistocene) exposed In and near the opencast pit at Ross (see Fig. 43). These photographs were taken in late 2001, There is a gap in the stratigraphic record of about 1.5 Ma and the pit Is now partly filled. between deposition of the youngest pan of the Old Man Photos: S. Nathan Group and the oldest late Quaternary deposi ts in the Greymouth map area. Tn many places this is represented by a major unconformity, representing a period ofregional uplift (with greates t uplift along th e mountain ranges) lead ing to the erosion that began to shape the present landscape.
Much ofthe Grey and [nangahua valleys and the lowland to the south has a complex cover of late Quaternary moraine, river and alluvial fan gravel, coastal and lagoon deposits. and swamps. These surface and near-surface deposits together record a succession of ice advances and contemporary periods of low sea levels, and intervening interglac ial high sea levels (Fig. 33). DetaiJed investigations have revealed a glacial-interglacial sequence covering the last 400 000 years, which is correlated with oxygen isotope stages 1- 10 (Table I). T he strati graphic and altitud inal (a) Weathered conglomerate, composed almost enti rely of Rakaia terrane rocks. Most of the larger boulders relationships between glacial outwash gravels and are greywacke, but many of the smaller clasts are interglacial marine deposits can be seen in the Hokitika schist. area (Suggate & Waight 1998), and provide a unique link in correlating glacial and interglacial sequences in New Zealand.
The deposits of th e last (Otira) glaciation are best preserved, and provide the key to interpretation of older glacial deposits. Likewise, the shoreline deposits and processes of the present interglacial (postglacial) provide a model for older interglacial deposits.
Glacial deposits
Glacial landforms, especiall y moraine ridges and hummocky topography, can be recognised from aerial photographs, in places even under forest cover. Tn most exposures the glacial deposits consist of interbedded till (subrounded to subangular clasts up to boulder size in a (b) Selection of t.z. III-IV schist clasts picked out of the tight clayey matrix; Fig. 34) and fluvial outwash gravel. conglomerate. Clasts are predominantly greywacke from the Rakaia terrane, with lesser amounts of schi st and min or graniloid clasts, indicating that derivation was mainly from the Southern A lps.
Till deposits ofsuccessive glaciations(Qlt, Q2t, Q4t, Q6t, Q8t, QlOt, eQt) cannot be distinguished from each other on lithology, but are mapped as discrete units based on their elevation, dissection, and the relationship to nearby outwash gravels. The limits of different ice advances are shown in Fig. 33. More than one ice advance is identifi ed in some glacial periods, notably in oxygen isotope stage 2, and these can be recognised by detai led studies in most major catchme nts. Generally, older units are more weathered than younger, but the degree of weathering is variable between outcrops, and is not a reliable guide to (c) Steeply dipping till (left) ove rlying possible f1uvloglaclal distinguishing deposits ofdifferent age (Suggate & Waight gravels and lake silts. 1998).
31 Interglacial Glacial Ag. a-isotope Shoreline ice limits (Calendar yrs) stage ,...... 6000 1
195OO --- ~::": - 2 15000 .--- 66000 4 ------,'-- 123000 5 .----- 135000 6 ,...... ------220000 7 ---.--- 265000 8 --.--- 320000 9 --,.----- 350000 10
I 580 000 1__'5_--,
GREYMOUTH W~
Figure 33 Limits of late Quaternary ice advances and interglacial shorelines in the Greyrnouth area, derived from geological mapping and geomorphic interpretation. The coloured area shows the extent of ice during the last glacial maximum (oxygen isotope stage 2), approximately 19 500 years ago - upper valleys and mountainous areas were snowfields at this time. The dashed line shows the extent of ice 15 000 years ago, just before postglacial warming.
32 Oxygen Age Glaciation Map Interglacial Map Isotope (Calendar Symbol Symbol Stage years BP)
1 Present day Aranui QI to 12 000 (postglacial)
2 12 000 Q2 3 to Otira 4 74 000 Q4
5 74 000 to Kaihinu Q5 130 000
6 130 000 to Waimea Q6 190 000
7 190 000 to Karoro Q7 248 000
8 248 000 to Waimaunga Q8 300 000
9 300 000 to un-named Q9 340 000
10 c. 360 000 Nemona Ql0
Older un-named eQ un -ll,amed eQ
Table 1 Sequence and chronology of late Quaternary units in the Greymouth area, after Suggate & Waight (1998). Chronology is based on Martinson and others (1987).
Figure 34 Bouldery till overlain by clayey till in moraine deposits dating from late in the last glaciation (oxygen isotope stage 2). Arnold vall ey. 2 km south of Kaimata. Photo CN31384/24: D.L. Homer
Figure 35 Typ ical fl uvial outwash gravel downstream from last glaciation (oxygen isotope stage 2) moraines. in the Arnold valley, 3 km NN W of Kokiri. Coarser gravel in the upper part of the outc rop overlies finer gravel in the lower part.
Photo CN31384/25: D.L. Homer 33 Alluvial deposits
Alluvial and f1u vioglacial gravels are widespread and well preserved in the flood plains and aggradation surfaces of maj or river vall eys and date from both glacial and interglacial periods (Qla, Q2a, Q4a, Q5a, Q6a, Q7a, Q8a, Q9a, QIOa, eQa). Typicall y most outcrops consist of rounded boulders in a sandy matrix (Fig. 35). Clast li thologies in glacial outwash gravels are predominantly Rakaia greywacke, with minor schi st. There is a clear contrast between these and gravels derived from local sources west of the Alpine Fault, and this is sometimes useful when considering the ori gin of particular gravel deposits.
There is a close relati onship between term inal moraines, marking th e downstream extent of glaciers, and thei r associated outwash aggradation surfaces underlain by flu vial grave l. As a result of subsequent dissection, the remnants of many outwash surfaces are preserved as terraces. Although outwash surfaces may be clearl y recogni sable close to moraines. many become fragmentary down-vall ey, especiall y when they have been eroded in narrow valleys. The key to matching different surfaces has been the analysis of long profi les as they are traced downstream (S uggate 1965; Suggate & Wai ght 1998).
Fluvial gravels have al so been deposited by rivers duri ng Figure 36 Typical example of ilmenite-rich sand on the in terglacial pe ri ods. Such gravels have onl y been coast, near the mouth of the Fox River. The dark patch in the centre of the photograph shows subtle fractionation of recognised close to the coast, where they are graded to the dominant minerals ca used by current action . The black interglacial marine surfaces. Further inland. interglacial areas are dominantly ilmenite ; pinki sh ~ brown areas contain periods are inferred to be times of net down-cutting, with concentrations of garnet; dark greenish areas contain little aggradation. concentrations of epidote. Biotite is scatte red throughout. The lighter coloured sand is predominantly quartz and All uvial fan deposits fe ldspar. Photo: $. Nathan
Large alluvial fa ns, screes and collu via l deposits (Qla, A spectacular set of upli fted interglacial terraces is seen Q2a, Q6a, uQa) are prom inent at th e foot of steep streams ncar Westp0l1 (Fig. 37), where marine erosion during each draining ra nge fr onts. The fa ns genera ll y consist of interglacia l has cut wide marine platforms across soft , late modcrately to poorly sortcd pcbble- to boulder-size clasts Tertiary sediments (McPherson 1978; Suggate 1989). oflocal deri vation. usuall y in a sandy matri x. Many small er Similar terraces are seen elsewhere in the map area close to fans are included wi th mapped alluvial gravels. the coast (Figs 38 & 39). [n most pl aces there is a cover of no more than 5- 10 metres ofmarine sand and gravel resti ng Coastal marine deposits and dunes on older sediments. Close to the Paparoa Range, the oldest marine cover beds and overlying fan gravels are mapped Near the coast, the deposits of successive in terglacial together as eQb. periods (i ncluding the postglacial) consist mai nly of well sorted beach sand and nearshore gravel and sand (Qlb, A Il arrow strip of dunes (Qld) is found on the postglacial Q5b, Q7b, Q9b, eQb). Much ofthe sand is dark-coloured coastal plai n close to the sea. Some dune sand has been as a result of concentration of heavy minerals, includi ng included in older units mapped as marine deposits. ilmcnite, garnet and epidote (Fig. 36). Weathering in older sands has resulted in cementation by haematite. At each Swamp and lake deposits interglacial high-stand of sea level, the sea cut a cliff in older rocks, and the beach deposits beneath the cliffs are Swamp deposits (Q l a) consisting of poorl y consolidated often hi ghl y enriched in heavy minerals, locally including sand, mud and peat are mapped in fl at, generally low-lying gold . In some places th e thin marine beds have been areas close to the coast, commonly on the landward side overl ain by younger all uvial gravels. of sand dunes, and on hummocky morain ic topography.
34 Figure 37 A sequence of marine and fiuvial terraces on the western side of the Paparoa Range, south of Westport, labelled according to their map symbols. The highest terrace at the foot of the Paparoa Range is underlain by a marine bench, at least as old as 0 13, whose marine deposits are overlain by younger fan gravels (mapped as eOa). Below the high terrace on the left is the 09 terrace, with minor Q7 terraces. A similar, less extensive sequence is seen on the right of the photograph between the Totara and Little Totara rive rs. In the ce ntre much younger fluvial terraces were formed as the Totara River cut down through the interglacial sequence. The Little Totara River in the foreground is surrounded by Holocene river fiats which have been grassed for farming.
Photo CN32462111 : O.L. Homer
Figure 38 Uplifted interglacial terraces at the south end of Rapahoe beach , near Greymouth. The lower (postglacial) terrace, about 9.5 metres above sea level, contains a log radiocarbon dated at 4720 ± 70 years BP (Suggate 1968). The higher terrace is approximately 36-40 metres above sea level, and represents a widespread last interglacial (oxygen isotope stage 5) surface that is underlain by 3-5 metres of marine and gravel. The clills in the background are Cobden Limestone (Oligocene).
Photo CN4330712: D.L. Homer
Figure 39 Uplifted postglacial terrace east of Cape Foulwind, near Westport. Shallow marine sand rests unconformably on Pliocene O'Keefe Formation, with a layer of boulders and scattered logs (probabiy similar to the present beach) along the contact. A piece of wood has been radiocarbon dated at 6330 ± 65 years BP (Nathan 1976b). This amount of uplift is typical of postglacial terraces found close to the coast throughout the map area (compare Fig. 38).
Photo CN43419/16: O.L. Homer
35 Postglacial lake deposits of peat and unconsoli dated grey Landslide deposits lacustrine mud (Qlk) accumulated in hollows left by melting ice at the end of the last glaciation . Landslides (Qll, uQI) are com mon features in Sleeper co untry throughout the map area , although many are too Lacustrine mud, sand and gravel are found at an altitude small to be mapped separately. They vary in compositi on ofup to 290 metres above sea level in the Murchison area from largely coherent but very shattered rock to unso rted (Suggate 1984; Roder & Suggate 1990), and indicate the fragments ofrock in a silty clay matri x. presence ofa fomler large glacial lake. Their height relative to nearby terraces suggests an age intermediate between One ofthe largest areas of landsl iding, on the hillside east the flu viatile deposits of isotope stages 6 and 8, so these of Westport, resultsmainl y from bedding-plane slip within beds are mapped as Q7k. Brunner Coal Measures (Inwood 1997).
Scree deposits Many landslides have been triggered by large earthquakes. Within the 20'" century, the 1929 Murchison, 1929 Arthur's Large areas of scree (Qls) are present in areas of Rakaia Pass, and the 1968 Inangahua earthquakes each caused terrane in the higher parts ofthe Southern Alps. The screes substantial landsliding in parts of th e map area largely consist of slightly weathered, pebble to boulder (Figs 6 & 9), and locally ponded small lakes. sized, angular clasts of indurated sandstone.
A lthough di screte areas of active downslope movement Deposits ofhuman origin can be easily distinguished, most screes are relati vely stable, and rock weathering dating shows that the clasts Areas of ground disturbed by sluicing and dredging for on the surface of screes were formed between the present gold, especially around Kumara, have been mapped as day and about 3000 years BP (McSaveney & Whitehouse Qln. Some of the older dredge tailings have si mply been 1989). The buried parts of mapped screes are probably no piled up, and show a characteristi c hummocky landfonn older than Holocene. (Fig. 40). Since th e 1980s it has been mandatory to rehab ilitate mined land, and such land cannot now be easil y recogni sed by its surface morphology.
Figure 40 Tailings and ponds left by past dredging operations for gold in early postglacial terrace gravels in the lower reaches of the Arahura valley. Photo CN31356113: DL Homer TECTONIC HISTORY
Paleozoic to early Mesozoic margin ofGondwanaland Late Cretaceous - early Cenozoicextension
Rocks ofthe Buller terrane are characteristically quartzose, At about 80 million years ago (Late Cretaceous) the New and were deposited adjacent to a continental landmass Zealand continental block started to separate from during the Ordovician. In contrast, the Cambrian/ Australia, with the opening of the Tasman Sea. This was Ordovician rocks ofthe Takaka terrane were formed in or marked by a period of magmatism, with widespread adjacent to a volcanic arc. The different lithologies and emplacement oflamprophyre and associated dikes as well tectonic settings imply that the two terranes were originally as the localised A-type French Creek Granite. a considerable distance apart. Amalgamation of the two terranes on the margin of Gondwanaland took place in Extension led to the formation of small inland basins Early to Middle Devonian time, and was almost between 75-60 million years ago (latest Cretaceous to Early immediately followed by emplacement ofLate Devonian Paleocene), filled with non-marine (paparoa) coal measures. to Early Carboniferous granites. The end ofspreading in the Tasman Sea about 60 million years ago corresponds to the slowing down of tectonic There is almost no record of later Paleozoic to early activity. During the following 12-15 million years most of Mesozoic events apart from a small area ofTriassic non the region was emergent, and undergoing slow subaerial marine sediment which is intruded by sills ofJurassic low erosion approaching peneplanation, to form the widespread Ti tholeiitic dolerite. This is geochemically similar to Waipounamu erosion surface. widespread flood dolerites ofthe same age in Antarctica, Tasmania and South Africa that were erupted prior to the A period ofrenewed crustal extension which started about break-up ofGondwanaland. 45 million years ago (Eocene) led to regional subsidence, as well as the development oflocal, fault-bounded basins. Mesozoic eastern terranes By the end ofthe Oligocene, almost the whole region was submerged, with widespread deposition oflimestone. The Torlesse composite terrane is interpreted as an extensive and complex submarine fan apron, Late Cenozoic oblique compression predominantly deposited as a sequence of turbidites and mass-flow beds. The quartzo-feldspathic nature of the Renewed uplift at the end of the Oligocene reflected the sandstone indicates continental derivation, and recent change from oblique extension to oblique compression provenance studies have suggested eastern Australia as a across the Australian/Pacific plate boundary. Many late likely source. Cenozoic basins were fault-bounded, but with a sense of movement reversed compared to the early Cenozoic. Late The Rakaia terrane is a Triassic fan complex, and the Cenozoic sediments are predominantly terrigenous, derived younger Pahau terrane (Jurassic to Early Cretaceous) has from uplifted areas on both sides of the Alpine Fault. been tectonically accreted against it. The suture zone is represented by the Esk Head belt, comprising Dextral strike-slip movement started on the Alpine Fault, predominantly melange but containing blocks from both and continues to the present day. Progressive displacement terranes. on the Alpine Fault over a period of 20 million years has resulted in the juxtaposition of contrasting rock types. At deeper crustal levels, rocks ofthe Rakaia terrane have been metamorphosed to schist, which has been exposed An increasing component ofcompression across the Alpine by late Cenozoic uplift in a narrow belt immediately east Fault during the Pliocene, starting about 5 million years ofthe Alpine Fault. ago, led to uplift along the eastern side, and the formation ofa widespread alluvial gravel plain that covered most of Early Cretaceous break-up ofGondwanaland the onshore area west of the Alpine Fault. Uplift was greatest immediately east of the Alpine Fault, leading to The break-up of Gondwanaland was marked by several the exposure and erosion of schist formed by deep burial major events in the period 105-95 million years ago, in the and metamorphism ofRakaia terrane rocks. Early Cretaceous. Widespread emplacement of granitoid plutons was accompanied by uplift. Movement along Continuing compression led to uplift of the West Coast detachment faults led to the juxtaposition of high-grade ranges during the Quaternary, and resulted in the present metamorphic and granitoid rocks against low-grade day range-and-basin topography between the Alpine Fault metasediments, forming metamorphic core complexes. and the coast. Major climate changes during the Quaternary Uplifted basement rocks provided source material for the resulted in periods of glaciation in the mountains (with non-marine Pororari Group, now mainly preserved as faulted downstream aggradation) alternating with warmer blocks around the margins of the Paparoa Range. interglacial periods with higher sea levels close to the coast. The current level of tectonic activity, with continuing regional uplift ofthe land area and regular earthquakes, is probably typical of what has occurred through the Quaternary.
37 J:,..,.~~ " '~}ii;~ ': ~, ' tf[' ~ -;'1;(fA·' """IT," ~ . . ,~,•• ;"", .. " ~ Figure 41 Dredge working in the Grey valley near Ngahere. 1995. The tailings from the dredge are being piled up on the upper side of the dredge pond and then smoothed out and covered with soil. The dark,coloured mounds are soil that has not yet been spread across the surface. In the upper part of the photograph grass is growing on the restored land, and in a few years it will be difficult to tell that the land has been mined (compare with Fig. 40).
Photo CN32385122: D.L. Homer
Figure 42 Technological advances have allowed some previously un-mined areas to be worked by sma ll operations with considerable conservati on of water. This small working is in older outwash gravel (Q6a) in the upper Waimea vall ey. Gravel is loaded into the hopper at the back of the screen, and water is reticulated from holding ponds.
Photo CN31623122: D.L. Homer 38 GEOLOGICAL RESOURCES
The Greymouth map area contains a range of mineral westwards by glaciers and major rivers. Some of this commodities including almost all of New Zealand's sediment contains low-grade gold mineralisation derived reserves of bituminous coal. It is also a major gold from quartz veins. Progressive reworking, particularly by producing region, has significant hydrocarbon potential, fluvioglacial processes close to terminal moraines, has led and is one ofthe few areas in New Zealand where pounamu to the formation of areas of auriferous gravel which (greenstone) is found. The geological resources of the collectively constitute a giant placerfield (Henley & Adams Greymouth area have been described in detail by 1979; Craw and others 1999). McPherson and others (1994) and Eggers & Sewell (1990), and the following accountis largely summarised from those An especially favourable situation for gold concentration publications, with some updating. exists in the Taramakau and Hokitika valleys. A sequence of ice advances terminated at about the same area, with Gold meltwater outflows of successively younger glaciations concentrating gold nearthe terminal moraines and proximal The South Island was the scene ofone ofthe world's largest outwash ofearlier advances (Suggate & Waight 1998). gold rushes in the early l860s (Morrell 1968), and gold mining has continued to the present day, with much ofthe Alluvial placers have been worked by a variety of hand gold won within the Greymouth map area. Gold occurs in and mechanical methods (Figs 41 & 42), ofwhich dredging three distinct ~eological settings: associated with quartz has been the most profitable. The major areas that have veins (also referred to as lodes or reefs), in alluvial or been worked are shown on the geological map. Since 1975 fluvioglacial placers, and concentrated with other heavy there has been sustained production using small- to large minerals in marine beach placers (locally termed blacksand scale alluvial gold recovery plants. Total production of leads). alluvial gold in 1999 from the Greymouth map area was 1244kg. Gold associated with quartz veins. Lensoid and sheet like gold-bearing quartz veins occur within fold-related Locally rich placer deposits occur close to areas of gold shear zones in the Greenland Group. The veins, containing mineralisation in the Greenland Group. The recently closed gold and minor pyrite~ arsenopyrite and stibnite, are opencast pit at Ross (Fig. 43), working alluvial gravels inferred to have been deposited from hydrothermal fluids from the Mt Greenland block, yielded approximately 1400 generated in the later stages of a regional metamorphic kg of gold over a 10-year period (C. Douch, Crown event at about 420 Ma (Brathwaite & Pirajno 1993). The Minerals, pers. comm. 2002). host rock is also mineralised adjacent to the quartz veins. Marine placers. Detrital gold carried downstream to the The main producing area is the Reefton Goldfield and its coast by rivers is continually washed along the coast and northern extension, the Lyell Goldfield; at least 70 000 kg concentrated in the surfzone by the prevailing northwards ofgold has been extracted. Gold mines are restricted to a longshore drift. The gold, together with ilmenite, north-trending belt about 10 km wide, in a zone of tight titanomagnetite, gamet, zircon, and other heavy minerals, folding (Gage 1948; Brathwaite & Pirajno 1993; is concentrated inlenticularbeach placers which are locally Rattenbury & Stewart 2000). About halfofthis production called blacksand leads. The gold is invariably very fine came from the Blackwater Mine and the Globe-Progress grained and often difficult to recover. group of mines, both of which still contain substantial reserves. Although there is currently no hard-rock mining Placers in the present day beaches were extensively mined in the region; planning is under way by GRD Macraes Ltd in the early gold rush years by small-scale manual methods to reopen the Globe-Progress workings as an opencast pit. known as. blacksanding. A few beaches continue to be worked by these methods, which need little capital outlay. Quartz veins have been prospected and mined from other Small dredges worked some of the uplifted postglacial areas ofGreenland Group, including the southern Paparoa deposits, especially around Barrytown. Range and the area around Ross, but the overall production is less than 500 kg ofgold. Older raised interglacial deposits consist of sand and gravel, which weather rusty brown and become variably A number of weakly auriferous quartz veins occur in cemented with age due to oxidation ofmagnetite. This coats Torlesse rocks east of the Alpine Fault, notably in the the gold particles, and results in the gold being even more headwaters of the Taipo and Wilberforce rivers (Bell & difficult to recover than in the younger deposits. Although Fraser 1906; Becker and others 2000). Although there has individual deposits may have locally high grades, these been considerable prospecting, there has been no are localised along the interglacial shorelines, where the significant production from any of these veins. However gold was concentrated in blacksand leads (McPherson they are inferred to represent the source of much of the 1978). alluvial gold found west ofthe Alpine Fault (see below). Gold deposits on the continental shelf, inferred to have Fluvioglacial placers. Erosion ofthe Southern Alps over been formed during lower sea-levels associated with late the last two million years has produced a large amount of Quaternary glaciations, have been the target of several sediment from the Rakaia terrane, which has been carried offshore sampling programmes (Brathwaite & Pirajno 39 Figure 43 Deep opencast pit (centre) in Quaternary alluvial gravels, apparently derived from Donnelly Creek (left) on the edge of Ross township. Deep leads or horizons of high gold values have been known for many years, and 19" century underground gold workings extended beneath Ross township. The photograph was taken in 1995. SUbsequently the pit was enlarged, and mining ceased in 2002. Photo CN38488123: D.L. Homer
1993). Sea floor sediment sampling showed that Holocene and south of Hokitika. These deposits individually have muddy sediments cover 1110St of the shelf apal1 from an reservesin the range of 1-7 million tonnes ofilmenite, at an area 8- 14 km offshore from Hokitika, where an area ofsub average grade of 6- 13.8% ilmenite (B rathwaite & Pirajno economic gold-bearing gravel was loca ted. 1993), but to date have been regarded as sub-eco nomi c.
Ilmenite (and associated minerals) Other metallic minerals
Most of the postglacial sa nd deposits. together with late Antimony in the fann of stibnite is a minor mineral in Quaternary interglacial raised beach deposits along the some gold-bearing quartz veins within the Greenland coast, contain ilmenite, epidote, and garnet (Fig. 36) as Group in the southern Paparoa Range and the Reefton well as minor titanomagnetite, zircon, and traces of mona Goldfield. The only recorded production is from zite and gold. Langdon's reef, a gold -stibnite vein. Ten tonnes were sh ipped to England prior to 1882 (Morgan 1911) but later The heavy mineral assemblage has been derived mainly attempts to open up this reef were un success fu l. from schist immediately east ofthe Alpine Fault (Bradley and others 1979,2002). The ilmenite grains contain tiny McPherson and others ( 1994) described widespread silicate inclusions, leading to relativel y low titanium con occurrences of minor copper mineralisation in sma ll tent (45-47% TiO,). Chromium (0.2%) and vanadium quantities, associated with plutonic rocks, quartz veins and (0.02%) contents in the ilmenite are low, and well within schist. There has been no production from the Greymouth commercial specifications. The zircon content ofthe sand map area. varies from 0.1 to 0.3%. Traces of monazite, gold, rutile, cass iterite, scheelite and beryl in some deposits may be Several western tributariesofCascade Creek in the Lower recoverable as a by-product from large scale mining and Bu ll er Gorge have been prospected since copper recovery of ilmenite. molybdenum mi neral isatio n was discovered in the 19505 (Braithwaite 1959). An area of propy litic alteration, about The largest ilmen ite deposits are at Fairdown (east of 150-200 m wide and 800-1000 mlong, occurs within apluton Westport), Carters Beach. Nine Mile Beach, Barrytown. ofBedins Porphyry (Early Cretaceous) and the surrounding 40 hornfelsed Greenland Group. Sulphide phases consist of deep weathering of gneiss or granitoid rocks, locally pyrite, molybdenite, and minor chalcopyrite. The Bald Hill preserved beneath Brunner Coal Measures, contains mainly prospect (Bates 1989), in mountainous country north of kaolinite with minor quartz and mica, and has been mined Lyell, occurs in Greenland Group intruded by small, high in several places. In the 1970s and 1980s clay was quarried level granitoid plutons. Molybdenite-quartz veins in from near Charleston for the production ofwhite sanitary hornfels form a weak stockworkzone, 2.5 km long by 700 m ware in Westport. wide. Similar clay is found as beds within the Brunner Coal Silver is insignificant in both reefand alluvial deposits as Measures. The floor clay of the main Brunner seam near the gold contains less than 10% Ag. Regional prospecting Brunner was mined in conjunction with the coal seam in of small granitoid plutons in the southern Paparoa Range several mines, and used for making fire bricks (Morgan located float material with significant silver values (Price 1911; Gage 1952). 1984), although no source has been found. Some of the marine mudstone units within the Tertiary Traces ofcassiterite ("stream tin") are widespread in late succession have been locally used for the manufacture of Quaternary alluvium and beach sand throughout the area. bricks. In particular, the Stillwater Mudstone (Blue Bottom Although recognisedin all dredge concentrates examined Group, Miocene) was quarried for use in the Karoro (Hutton 1950), it is generally no more than a mineralogical Brickworks near Greymouth until the 1960s. curiosity except in the Grey valley near Blackball (Morgan 1911; Henderson 1917; Minehan 1989) where it appears Rock to be derived from the nearby Paparoa Range. Some of the highest values were found in concentrates from the Abundant supplies of aggregate are present throughout Ngahere dredge, where Nicholson (1955) estimated that the Greymouth map area, almost entirely as gravel from 40 tonnes/year ofcassiterite were being discharged. present day rivers, late Quaternary terraces, and locally from dredge tailings. Material is usually quarried close to Greisen-hosted tungsten mineralisation occurs at Doctor where it is needed rather than being transported over large Hill-Falls Creek; Ba.rry'town, Kirwans Hill and Bateman distances. The gravel commonly used consists Creek, and is associated with roof pendants ofGreenland predominantly ofgranite and Rakaia terrane- or Greenland Group in plutons of S-type Karamea·granitoids (Pirajno Group-derived greywacke, with varying amounts ofschist & Bentley 1985; Brathwaite & Pirajno 1993). The and gneiss depending on local sources. From the Grey occurrences are unusual as granite-related greisen zones River southwards the dominant lithology in river gravels elsewhere commonly develop wolframite rather than is Rakaia terrane greywacke. scheelite (Tulloch & Mackenzie 1986). In 1999 about 162000tonnes ofaggregate were produced Traces of the rare earth minerals monazite, thorite, for roading within the Greymouth map area, as well as uranothorite and xenotime are found in the ilmenite-rich 9000 tonnes for use as building aggregate. heavy mineral fraction of sand in present day coastal beaches. Rare earth minerals have also been recognised in There is a continuing need for large blocks of rock (rip the concentrates from gold workings in the Westport, rap) for use in stopbanks to prevent riverbank erosion Reefton and Grey River areas (Hutton 1950; Minehan during frequent, high-volume flooding in West Coast rivers. 1989). They could be a useful by-product of large-scale Transport is expensive, so the West Coast Regional Council workings for gold or ilmenite. tries to maintain a network of quarries that can be used when needed, often at short notice. Although there is no The Pororari Group hosts low grade, sedimentary uranium shortage ofhard rock, much ofit is too fractured to provide mineralisation in the Lower Buller Gorge, in the Pororari large blocks that do not break up on weathering. Oligocene River area, and near the mouth of Fox River (Beck and limestone is quarried for rip-rap in a number of places others 1958; Williams 1974). Since its discovery in 1955 (often using quarries opened for agricultural lime). The a number of companies have tested the mineralisation by Cobden Limestone near Greymouth has been quarried for adits and drilling. The mineralised beds are thin and many years, and provided the material for building and lenticular, resulting in erratic grades, almost everywhere extending Greymouth Harbour. One ofthe few quarries in less than 0.1 % Ups' Despite considerable prospecting in granitoid rocks was developed at Cape Foulwind, where the late 1960s and 1970s, no new areas of uranium large blocks were used to develop the Westport Harbour mineralisation or higher grades have been found. No moles. significant uranium mineralisation has been found in the granitoid rocks ofthis area, nor concentrations ofU-bearing Several rock types from the QMAP Greymouth area are minerals in thealluvium orbeach sand derived from them potentially suitable for use as building and facing stone (Nicholson 1955). (dimension stone), particularly granite, schist, limestone and serpentine. A significant limiting factor in finding new Clay resources is the almost ubiquitous presence of irregular jointing, caused by Cenozoic tectonism. At present it is Kaolin clay deposits, of varying quality, are widespread generally more economic to import stone for building on the western side of the Alpine Fault. Clay formed by purposes than to use local material. 41 Figure 44 A large lens of earliest Oligocene algal limestone is quarried near Cape Foulwind (centre right) as the feedstock for cement manufacture. The limestone is trucked for processing to the Milburn Cement works (centre left). Most of the cement is transported by ship from the port of Westport (above cement works), or is railed to other parts of the South Island.
Photo CN3236814: D.L. Homer
Marshall (1929) listed several local rock types that have Lim~tone been tested and used as facing stone in New Zealand , including the Fou lwind Granite, which contains spectacular Abundant resources of limestone and marble suitable for large K-feldspa r megacrysts. Serpentine from the Griffin agricultural and indu strial use are available in the Range has been used as facing stone and a small amoun t is Greymouth map area. In particular, the widespread still being quarried. occurrence of high-grade Oligocene limestone (platfonn facies of the ile Group, mainly algal and bryozoan Greenstone (nephrite, pounamu) and goodletite limestones), with CaCO) consistentl y greater than 90%, means that quarri es ca n be opened in many parts of the New Zea land greenstone (nephrite, loca l ly cal led area west of the A lpi ne Fault, and thu stm nsport costs can pounamu) is the common name for an amphibole group be minimi sed. Ordovic ian marble from the Mt Arthur mineral within the tremolite-actinol ite se ri es. It ha s Group is also quarried near SpringsJunction. traditionally been used by Maori for jewellery, tools and weapons and has strong cultural significance. Modern use At Cape Foulwind, near Westpon, a large lens of high is mainly for jewellery and ornaments. Ownership of grade algal limestone provides the feed stock for the pounamu has now been vested in the local Maori, Ngai Milburn Cement works , together with a smaller amount of Tahu. Kaiata Formation (Fig. 44). Most ofthe cement israiled or shipped ou tside the West Coast region. Nephrite occurs as thin lenses within the Pounamu Ultramafics (Bell & Fraser 1906; Johnston 1983). Almost Weathering and solution of limestone has al so developed all of the material recovered in recent years hascome from several karst featuresused for recreational purposes. Caves float material in Olderog Creek, a tributary ofthe Arahura and underground streams are present in most areas of Ri ver, where nephrite occurs as boulders, exceptionally limestone, with spectacular caves near the Nile Ri ver, Fox up to 25 tonnes in weight. Most ofthe larger bou lders have River and Bullock Creek. Pancake Rocks and th ei r now been removed and liule float materi al remain s. associated blowholes are a famo us tourist auraction near Punakaik i (Coates 1988). Goodletite is the local name for a rare and di stinct ive gree ni s h~gr ey ruby rock which is highly prized as an Other non-metallic minerals ornamemal rock. It is found only as boulders in rivers and fiuvio-glacial gravel s between the Taramakau River and Fluorite minerali sation has been recorded from several Ro ss, and consists of co rundum (varyi ng between ruby localities in the Lower BulierGorge, especially from Kehu and sapphire), tounnaline and greenchrome-rich mica. TIle Stream, where green fluorite veins cut the Berl insPorphyry prese nce of rare serpentine rindsindicates that the bou lders (Nathan I978b), and near Sinclair's Castle(Beck and others were derived from the Pounamu Ultramafics. They may 1958). Despite intensive prospecting in the 1970s, no have formed aspan of a reaction sequence between sch ist economic deposits have been found . and adjacent ultramafic rock (Grapes & Palmer 1996). 42 Mica occurs in pegmatites, which are common in granitoid Three groups ofcoal measures contain mineable coal: rocks throughout the map area. A small amount of mica Paparoa Coal Measures (Late Cretaceous-Paleocene), in was mined in 1911-12 from a pegmatite near Constant Bay, the Greymouth and Pike River coalfields, were deposited but the grade is low (Morgan & Bartrum 1915). Some sheet in the narrow north-south trending Paparoa Trough mica also occurs in a nearby pegmatite at Deep Creek. (Nathan and others 1986). In the Greymouth Coalfield, The demand for sheet mica is low, and these deposits are mapped in detail by Gage (1952), seven local units of not likely to be worked. alternating fluviatile sediment (sandstone, conglomerate and coal seams) and lacustrine mudstone have been Silica Sand comprising quartz-rich sand and sandstone recognised. Coal seams are lensoid, and locally up to 9 occurs in the Buller, Charleston and Greymouth coalfields metres thick. All Paparoa coals have low sulphur content, and at Cape Foulwind and Ross as well as in bands of and generally low ash. quartzite in Devonian rocks near Reefton. Young (1964) summarised the silica resources of the region, concluding Brunner Coal Measures (Middle to Late Eocene) were that in most places the silica content did not exceed 80%, deposited following a Paleocene to Early Eocene period andthatmuch ofthe material appears to be too micaceous of quiescence. Regional subsidence led to progressive and carbonaceous for ferrosilicon manufacture. inundation oftheregion, with coal measures at the base of the Tertiary sequence. Fault-controlled subsidence led to Eocene quartz .sand near Charleston (Little Totara Sand; increased thickness in local basins, especially the Buller Nathan 1975) is one of the most easily worked resources Coalfield. Apart from local conglomerates, Brunner Coal of silica sand in the area, and is generally rather higher Measures are dominated by quartzose sandstone. Coal , grade (average around 85% Si02 locally up to 95%) than seams are sporadic in distribution (Flores & Sykes 1996; other localities mentioned above. In recent years it has Titheridge 1993) and usually lensoid, but locally contain been quarried for use in cement manufacture, and a small seams up to 10 metres thick. amount has been used in glass manufacture. Rotokohu Coal Measures and Longford Formation Coal (Early Miocene) are fluviatile beds (mainly sandstone, conglomerate, and carbonaceous shale), representing an The Greymouth map area contains virtually all the reserves Early Miocene regression in the Inangahua valley and ofbituminous coal in New Zealand, as well as substantial Murchison Basin. Both units contain a few lensoid coal reserves of sub~bituminouscoal. Coal mining started in seams near the base. Although they have been mined the 1860s in the Greymouth and Buller coalfields, and has locally, the seams represent only a minor part of the total continued since then. Initially the bituminous coal was used coal resource. for steam-raising (rail, shipping and industrial boilers) and town gas supply, with associated coke production. Since The Coal Resources Survey undertook a complete re the 1950s these uses have declined, and in recent years evaluation of coal resources throughout New Zealand in most bituminous coal has been exported for specialist use the late 1970s and early 1980s, including drilling in some in the steel-making and chemicalindustries. poorly known areas (Taylor 1999). A summary of coal resources for each coalfield is presented by Barry and The higher rank Cretaceous and Tertiary bituminous coals others (1994), from which the recoverable reserves for the have low-medium ash, satisfactory fluidity characteristics, coalfields in the Greymouth QMAP area have been high swelling, and a high proportion ofreactive macerals. extracted (Table 2). Lower rank bituminous and sub-bituminous coals are marketed for domestic and industrial use, but are in lower Although the total reserves ofrecoverable coal seem large, demand because oflower specific energy (calorific value) not all this coal may be able to be mined for technical or and commonly higher sulphur content. environmental reasons. Almost all the reserves ofopencast bituminous coal occur within the Buller Coalfield, and All mining was underground until large-scale opencast some areas of indicated and inferred coal reserves are mining started in the Buller Coalfield in the 1940s, situated in ecological reserves. Much ofthe large indicated! ·providing a much more economic way ofmining shallow inferred reserves in the Greymouth Coalfield can be mined coal, with potential to recover virtually all the coal in thick only by underground technology, and past experience seams. Several areas previously worked by underground indicates that this is likely to be difficult because of methods have been re-opened as opencast mines (Fig. structural complexities and the gassy nature of the coal. 45). There is further potential for opencast mining in the Buller, Reefton, Garvey Creek and Charleston coalfields. Coal seams are deeper in the Greymouth and Pike River coalfields, and are likely to be mined only by underground methods.
43 Underground Opencast Measured Indicated Inferred Measured Indicated Inferred BITUMINOUS COAL (+ semi-anthracite) Buller 1.87 3.54 9.4 24.93 48.6 26.0 Garvey Creek om 0.37 1.8 358 0.72 0 Pike River 0 21.83 65 0 0 0 Greymouth 0.47 124.97 37.4 0.7 0 0 Murchison 0 0 0.5 0 0 0.2 Fox River 0 0 0.3 0 0 0 Total 2.37 150.71 55.9 29.21 49.32 26.2
SUB-BITUMINOUS COAL Inangahua 0 0 1.0 0. 18 2.64 2.2 Reefton 0.75 05 3.1 0.17 0.5 0 Charleston om om 0.1 0 12.8 0 Punakaiki 0 0 1.7 0 0 0 Total 0.78 0.51 5.9 0.35 15.94 2.2
Table 2 Reserves of recoverable coal (in million tonnes) from the Greymouth map area. Data has been extracted Irom Barry and others (1994).
Figure 45 Opencast mining in the Stockton No 2 Opencast, Buller Coalfield. A th ick coal seam is found below hard sandstone which has been stripped off prior to mining. Much of this area was previously mined by underground methods, which left behind most of the thick coal seam. The Mt Frederick Fault forms a natural western limit to mining on the left side of the view, and hills of granitoid rock (left) have been thrust over coal measures. The fault is exposed in the cliff at centre left, and forms the boundary between granite (white) and mudstone (brown). Photo CN313314: D.L. Homer 44 The late Cenozoic formation ofthe Brunner Anticline and related structures post-dated maximum burial of the coal measures, and therefore some hydrocarbons may have migrated out of the Paparoa Trough prior to formation of structural trap s. Discovery of hydrocarbons depends on loca ting structural or strat igraphic traps that have effectively held hydrocarbons since the Late Oligocene, or secondary traps where oil and gas have subsequently migrated. The Grey Valley Trough is probably the most prospective area because there ispotential for hydrocarbon generation in the late Cenozoic (Thrasher and others 1996; Suggate & Waight 1998). The Kotuku oil seeps indicate that oil has been generated and has migrated up-dip (Nathan and others 1986).
Water
Most of the water used in the urban areas and on farms is obtained from streams, and stored in local reservoirs. Because ofthe high rainfall, tank water from roofs is used in many rural houses, and little use is made ofgroundwater. lfneeded. large amounts ofhigh quality groundwatercould be obtained from late Quaternary alluvial gravels.
Warm springs Figure 46 Some of the largest oil seeps in New Zealand occur at Kotuku, in the Arnold valley. Pits have been dug A number of iso lated warm spring soccur in the Southern to extract the oil, which now forms a thin skin on top of Alps (Fig. 47), and have been listed by Mongillo & Cleland saline water. (1984). They are used locally for bathing. It is assumed Photo CN3137615: D.L Homer that the sp rings discharge meteoric water that has been heated beneath the mountain s, and transported to th e Oil and gas surface along faults and fractures. The spring waters are generally of Na-bicarbonate composition, with varying Prospecting for oil and gas has been encouraged by seeps amounts of mineralisa tion (Cave and others 1993). and shows, including oil seeps at Kotuku (Fig. 46), as well Hydrogen su lphide gas is often discharged, and the smell of H S is a distinctive feature of warm spri ngs in the as widespread traces ofoil and gas in prospecting drillholes 2 and within mines in the Greymouth Coalfield (Wellman mountain valleys. 197 I ; Gage & Wellman 1944; Young 1967; Suggate & Waight 1998).
Shallow wells were drilled in the Kotuku area in the e,u·ly 1900s, with recorded production of only a few hundred barrels. Modern exploration in the region began immediately before and during World War 2, with seismic su rveys(Modriniak & Marsden 1938) and detailed surface geological mapping lead ing to the drilling of four deep holes. Considerable seismic exploration was carried out from the 1960s onwards, followed by the drilling of one offshore well and eleven deep onshore wells. several with oil and gas shows. The most significant have been a gas blowout in SFL-I (west of Kumara), and subcommercial quantities of high-gravity oil recovered from Niagara-I. drilled west of Moana.
Geochemical and maturat ion properties of Paparoa and Brunner Coal Measuressuggest that they are good source rocks for hydrocarbon generation (Nathan and others Figure 47 Harold Wellman (left) and George Gri ndley t986). Sands tones of the Paparoa Coal Measures, Brunner relax in a warm spring close to the Alpine Fault in the Coal Measures and Island Sandstone (and correlative Haupiri valley. Wellman discovered the Alpine Fault and Eocene sandstones) have good reservoir potential, and undertook a large amount of mapping throughout the area overlying mudstones form an effective cap. covered by the Greymouth map in the 1940s and 1950s. 45 GEOLOGICAL HAZARDS
Seismotectonic (earthquake) hazard occur along the Alpine Fault and havea 9- 19% probability of occurrence in 20 years (Rhoades & Van Dissen 2000). Over the last 150 years, the Greymouth map area has The Greymouth QMAP area might expect an MM6 event experienced moderate to high levels of se ismi c with an average return peri od of 6 years, an MM7 event (earthquake) activity, and thi s is likely to continue. every 15 years, an MM8 event every 2 1years, and an MM9 event every 32 years (w. Sm ith, pers. comm. 200 I). Earthquakesare measured in lel111Sorlheir released energy according to the magnitude (M) scale. The effects (or fe lt The consequences of a large. shallow earthquake in or intensiti es) are assessed accord ing to the Modified Merca lli adjacent to the Greymouth map area are strong ground Intensity (MM) scale (Table 3). The followin g large, shaking, multiple aftershocks, shaking-induced slope shallow earthquakes have al l had epicentres within the map in stability, and possible surface fault rupture. Known fault area: rupture within the last 500 years has occurred on the Alpine 191 3 Westport (M6.0) Fault as well as on parts ofthe White Creek and lnangahua 1929 Arthur's Pass (M7. 1) faults. 1929 Murchison (M7.8) 1962 WestpOJ1 (M5.9) Unconso lidated, fi ne-grai ned sed im en ts such as swamp 1968 Inangahu a (M7. 1) deposi ts, es tuarine mud, marine sand and gra ve l, and 199 1 Ha wks Crag (M6.3) landfill have low strength , and are likely to show significant 1995 Arthur's Pass (M6.3) amplification of ground shaking during an e3lthquake. The towns of Westport, Greymouth, Hokitika and Reefton are A re-evaluation of seismi c hazard in ew Zealand by built on Quaternary deposits, and it is likely that parts of Stirling and others ( 1998) used models based on the likely these urban areas may show so me shaking amplification, ground acce leration at any place based on both hi storic as they did in the 1968 Inangahua earthquake (Suggate & earthquakes and the late Quaternary geological record. The Wood 1979). Landslides and rockfalls are likely in urban highest levels of Peak Ground Acceleration (PGA), areas close to steep hill s, for example around Pun akaiki correspo nding to th e most severe shakin g and dam age, (Fig. 28).
MM 2: Felt by persons at rest, on upper floors or favourably placed.
MM 3: Felt indoors; hanging objects may SWing, vibration similar to passing of light trucks.
MM 4: Generally noliced indoors but not outside. Light sleepers may be awakened. Vibration may be likened to passing of heavy traffic. Doors and windows rattle. Walls and frames of buildings may be heard to creak.
MM 5: Generally felt outside, and by almost everyone indoors. Most sleepers awakened. A few people alarmed. Some glassware and crockery may be broken. Open doors may swing.
MM 6: Felt by all. People and animals alarmed. Many run outside. Objects fall from shelves. Glassware andcrockery broken. Unstable furniture overturned. Slight damage to some types of buildings. A few cases ofchimney damage. Loose material may be dislodged from sloping ground.
MM 7: General alarm. Furniture moves on smooth floors. Un-reinforced stone and brick walls crack. Some pre earthquake code buildings damaged. Roof tiles may be dislodged. Many domestic chimneys broken. Small slides such as falls of sand and gravel banks. Some fine cracks appear in sloping ground. A few instances of liquefaction.
MM 8: Alarm may approach panic. Steering ofcars greatly affected. Some serious damage to pre-earthquake code masonry bUildings. Most un-reinforced domestic chimneys damaged, many brought down. Monuments andelevated tanks twisted or brought down. Some post-1980 brick veneer dwellings damaged. Houses not secured to foundalions may move. Cracks appear on steep slopes and in wet ground. Slides in roadside cuttings and unsupported excavations. Small earthquake fountains and other instances of liquefaction.
MM 9: Very poor quality un-reinforced masonrydestroyed. Pre-earthquake code masonrybuildings heavily damaged, some collapsing. Damage or distortion to some post-1980 buildings and bridges. Houses not secured to foundations shifted off. Brick veneers fall andexpose framing. Conspicuous cracking offlat andsloping ground. Generallandsliding on steep slopes. Liquefaction effects intensified, with large earthquake fountains and sand craters.
MM 10: Most un-reinforced masonry structure destroyed. Many pre-earthquake code buildings destroyed. Many pre-1980 buildings and bridges seriously damaged. Many post-1980 buildings and bridges moderately damaged or permanently distorted. Widespread cracking of flat and sloping ground. Widespread and severe landsliding on sloping ground. Widespread and severe liquefaction effects.
Table 3 Pan ofthe Modified Mercalli Intensity scale (MM), summari sed from Downes ( 1995). 46 Landsliding Tsunami
Shaking during the 1929 (Arthur's Pass and Murchi son) Coastal flooding and damage caused by tsunami (seismic and 1968 (lnangahua) earthquakes caused a large number sea waves) is possible along the entire coastline of the of landslides, and it is likely thal most older landslides Greymouth map area as well as the lower reachesofrivers. within the Greymouth map area are also earthquake The coastal towns of Westport, Greymouth and Hokitika initiated (Fig. 48). Hancox and others (2002) have are all at ri sk. Even small tsunami can ca use erosion and compiled maps showing the di stribution oflarge lands lides problems for sl11 all boats because of the strong cu rrents caused by these earthquakes. generated. Large tsun ami of more than 4 111 are life threatening, and can be very damaging to structure s. The effects ofearthquake-induced landsliding may last for man y years after an earthquake, wi th a marked increase in In histori cal times the coastline has bee n little affected by river aggradation , and increased ri sk of flooding. tsunami generated by distant events, outside New Zealand 's continental shelf. Locally-generated tsunami, potentially The hillsi de east of Westport is mapped as a large complex caused by near-shore fa ult rupture or submarine landslide, essentially ca used by downslope movement landsliding, pose a greater threat. along weak units in the Brunner Coal Measures which here dip 10- 15° west. Inwood ( 1997) has identified several A rise of ri ver water level of about a metre occurred at phases of movement, and shown that the landslide complex Westport and Ngakawau at the time of the magnitude 6.0 has been reactivated several times over the last 200 000 earthquake of 22 February 19 13, located offshore from years. Most parts of the lands lide complex appear to be Westport (G. L. Downes, pers. comm. 200 I). currentl y stab le. However, Lake Rochfort, dammed with in the landslide complex at an altitude of 480 metres above sea level (Fig. 49), is ofconcern because ofthe poss ibility ofa catastrophi c dam break after anearthq uake or torrential rain .
Figure 48 Landslide in the Maruia valley, one of many that formed during the 1929 Murchison earthquake. The landslide diverted the course of the river, and caused it to cut down in a new course, thus uncovering the Maruia Falls (left centre) (Suggate 1988). Photo CN4645 t/35: D.L. Homer 47 Figure 49 The hillside beneath Mt Rochfort, northeast of Westport, is a complex series of landslides formed on Brunner Coal Measures, which in the main photograph dip gently towards the observer. In the bottom of the photograph alluvial fans, formed during major flood events, spread outwards from the hills. Lake Rochfort (smaller photograph) fills a depression within the landslide complex, with the outlet artificially raised for hydroelectric generation, and contains approximately 320 000 cubic metres of water. The lake poses a long-term hazard to the area below in the event of sudden dam-burst. Photos CN3//12//4 &CN311/S/21: D.L. Homer
48 ENGINEERING GEOLOGY
This section provides generali sed background for Rocks of the Esk Head belt, in the southeast corner of the geotechnical in vestigations and hazard assessments, but map area, are di stinctly weaker than th e Rakaia terrane is not a substitute for a detailed site investigation. Potential rocks to the west. The belt is characterised by lower, more difficu lties with some rock units are highlighted. ro un ded topography. There is considerable close-spaced jointing and widespread shearing. Paleozoic-Mesozoic rocks west of the Alpine Fault Tertiary sedimentary rocks Granitoid, metamorphic and sedimentary rocks that mainly crop out in the mountain ranges west of the Alpine Fault There is enormous variation in the geotechnical properties are strong. hard, and nearl y a lways unweathered. of Tertiary rock units, both because of the ran ge of rock Excavation usually requires blasting, and steep faces types, and also because of the variation in induration generall y remain stable. The rocks are generall y (caused by depth of buri al). Bruoner Coal Measures pervasively jointed, often with a joint spacing ofO.S m or (Eocene) provides an extreme example. Near Cape Foulwiod, less, which makes it difficult to quarry large, unfractured the unit has never been buried by more than a fe w hundred blocks. metres, and is an unconsol id ated quartz sand. In contrast, in the Bu ll er Coalfield , where it is inferred that there has Adjacent to major, brittle fault zones, which may be tens been up to 6 km of burial (Kamp and others 1996), the same ofmetres wide, the rocks are intensely fractured, and locally unit is a massive, strong rock that needs to be blasted in are very weak due to the presence ofcrush zones and very mining operations (Figs 24 & 45). closely spaced joints. Oligocene limestones are usuall y hi ghl y cemented and Paleozoic-Mesozoic rocks east of the Alpine Fault hard, and can be quarried in large blocks. Most mudstones, especial ly those ofMiocene and Pliocene age, are re latively Greywacke sandstones of the Rakaia terrane are strong, soft, and may be prone to erosion and landsliding. hard, and variably jointed. Interbedded argi llites are not as strong, and often hi ghl y fractured. Slopes cut in fresh Quaternary sediments rock are usually stable, although rocks in very steep fa ces local ly coll apse, especially in areas that have been Quatern ary gravel and sand deposits in moraines, alluvial glaciated. terraces and fans are poorly consoli dated (classified as engineering soil s). However th e individual clasts in the Rock strength decreases with increasing metamorphic youn gest (Holocene and last glaciation) gravels are usuall y grade (e.g. in the 5- 15 Ian belt immediately east of the unweathered, and have local ly been quarri ed as aggregate. Alpi ne Fault) as foljation develops into a significant planar weakness. The properti es ofsome glacial deposits are hi ghly variable, and may be unpredictable on a local (e.g. 10 m) scale, The Arthur's Pass highway (SH73), ooe ofthe main alpi ne especially in localities where lake silts are interbedded with routes across the South Island, is entirely thro ugh Rakaia gravel. Till is often of low permeability, and may cause terrane rocks..Keepi ng th e hi ghway open throughout th e drainage problems. year poses di stinct engineering challenges (Figs 50-52).
Figure 50 Protection of the Ar thur's Pass highway is necessary in sections subject to s li ps and localised floodin g as shown by this section of the road near Candy's Bend.
Photo CN43256/21: D.L. Homer Figure 51 Active landslides and screes combined with very heavy rai nfall present a hazard for road construction and maintenance in the Southern Alps. Several different approaches are needed to keep State Highway 73 across Arthur's Pass open throughout the year. A winding section of the road previously skirted around the top of the unstable part of the landslide in the centre of the photograph. In 2001 this was replaced by a viaduct close to the Otira River beneath the zig-zag. Photo CN35817/25: D.L. Homer
Figure 52 The new viaduct which largely avoids the zig-zag route across the landslide (left).
Photo CN43352123: D.L. Homer AVAILABILITY OF QMAP DATA ACKNOWLEDGMENTS
The geological map accompanying this book is derived This map was compiled by S. Nathan (part orall ofNZMS from information stored in the QMAP geographic 260 sheets 133, 131, 132, 133, K29, K30, K31, K32, L29, information system (GIS) database, maintained by the DO, L31), M.S. Rattenbury (133, K33, DO, Ul, L32, Institute ofGeological & Nuclear Sciences, and from other L33), and RP. Suggate (Quaternary geology of most GIS-compatible digital databases. The data shown on the sheets). Major sources of contributing information were map are a subset ofthe available information. Customised geological maps at 1:50000, 1:63360, or other scales by single-factor and multifactor maps can be generated from Cave (1986), Laird (1988), Nathan (1975,1976b, 1978a the GIS and integrated with other data sets to produce, for & b, 1996), Roder & Suggate (1990), Tulloch (1995), example, maps showing fossil or mineral localities in Suggate (1957), Suggate & Waight (1998), Waight (1995), relation to specific rock types, or maps showing rock types and White (1988) as well as published papers, reports, in relation to the road network. Data can be presented for bulletins, and unpublished material from the files of the user-defined specific areas, for irregular areas such as local Institute of Geological & Nuclear Sciences, mineral authority territories, or in the form of strip maps showing exploration company reports and university theses. information within a specified distance oflinear features such as roads orthe coastline. The information canbe made New fieldwork during 1998-2001 concentrated on visiting available at any required scale bearing in mind the scale selected key areas and filling gaps in knowledge, especially . ofdata capture and the generalisation involved in digitising. the granitoid rocks ofthe Victoria Range (Sheets L29, L30, Maps produced at greater than 1:50 000 scale will not show L31; undertaken with considerable assistance from R accurate, detailed geological information unless they are Jongens), and the area southeast ofthe Alpine Fault (sheets basedon point data (e.g. structural information). Ifrequired U2, K32 and U3). K.R Berryman, S. Cox, MJ. Isaac, the QMAP series maps can also be made available in digital and I.M. Turnbull also assisted with the mapping. form using standard data interchange formats. Aerial photograph interpretation oflandslides by N. Perrin The digital data have been captured from data record maps and T. Coote was compiled from the Landslide Map of compiled on standard 1:50 000 NZMS 260 topographic New Zealand project. The offshore geology has been maps. These record maps are filed in GNS offices in compiled from Nathan and others (1986). We thank the Dunedin and Lower Hutt (Gracefield) and, although National Institute ofWater and Atmospheric Research for unpublished, are available fOfconsultation. They are stored permission to reproduce offshore bathymetry from their on transparent film and copies can be made. The legend digital records. and mapping philosophy used for the detailed maps are based on lithostratigraphy and may differ from those used The use ofinformation from unpublished university theses, onQMAP. notably Angus (1984), Blackmore (1988), Botsford (1983), Brown (1998), Cutten (1976), Dixon (2001), Inwood For new or additional information, for prints of this map (1997), Jury (1981), Koons (1978), McLean (1986), Parish at other scales, for selected data or combinations of data (1998), Petrie (1974), Waight (1995) and White (1988) is sets orfor derivative or single-factor maps basedon QMAP appreciated. The co-operation ofgeology department heads data, please contact: from Auckland, Victoria, Canterbury and Otago universities in allowing access to theses is gratefully QMAPLeader acknowledged. Institute ofGeological & Nuclear Sciences Ltd. P.O.Box30368 Development and maintenance of the GIS database was LowerHutt by D.W. Heron and M.S. Rattenbury. Digital capture and map production was by J. Arnst, C. Atkins, D.W. Heron, S. Nathan, M.S. Rattenbury and D. Townsend. The diagrams were prepared by P. Carthew, C. Hume and M.S. Rattenbury.
Parts or all of the map and text were reviewed by M.G. Laird, J. Campbell and D. Shelley (University of Canterbury), G. L. Downes, M.J. Isaac, A.J. Tulloch and I.M. Turnbull (Institute ofGeological & Nuclear Sciences), and M.R Johnston (Nelson).
Funding for the QMAP project was provided by the Foundation for Research, Science & Technology under contract C05X0003. The base map is sourced from Land Information New Zealand. Crown copyright reserved.
51 REFERENCES
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53 Gair, H.S. 1962: Notes on the geology ofthe EskValley, Canterbury. Johnston, M.R.; Mackinnon, D.I.; Mew, G. 1980: Early Devoniano New Zealand Journal ofGeology and Geophysics 5: 531-44. (Emsian) fossils from the Lake Haupiri area, North Westland. New Zealand Journal ofGeology and Geophysics 23: 391-394. Gradstein, EM.; Ogg, J. 1996: A Phanerozoic time scale. Episodes 19: 3-5. Jongens, R. 1997: The Anatoki Fault and the structure ofthe adjacent Buller and Takaka Terrane rocks, northwest Nelson, New Grapes, R.; Palmer, K 1996: (Ruby-Sapphire)-chromian mica Zealand. PhD thesis, University of Canterbury, Christchurch. tourmaline rocks from Westland, New Zealand. Journal of Petrology 37: 293-315. Jury, A.P. 1981: Mineralization at Mt Rangitoto and Mt Greenland, Westland. MSc thesis, University of Canterbury, Christchurch. Gregg, D.R. 1964: Sheet 18 - Hurunui. Geological Map of New Zealand 1:250 000. Wellington, New Zealand, Department of Kamp, P.J.; Webster, KS.; Nathan, S. 1996: Thermal history analysis Scientific and Industrial Research. by integrated modelling of apatite fission track and vitrinite reflectance data: application to an inverted basin (Buller Griffiths, G.A.; McSaveney, M.J. 1983: Distribution ofmean annual Coalfield, New Zealand). Basin Research 8: 383-402. precipitation across steepland regions of New Zealand. New Zealand Journal ofScience 26: 197-209. Kimbrough, D.L.; Tulloch, A.J. 1989: Early Cretaceous age of orthogneiss from the Charleston Metamorphic Group, New Grindley, G~w. 1980: Sheet Sl3 - Cobb. Geological Map of New Zealand. Earth & Planetary Science Letters 95: 130-40. Zealand 1:63 360. Wellington, New Zealand, Department of Scientific and Industrial Research. Koons, P.O. 1978: The Pounamu ultramafics: a study of metasomatism. MSc thesis, University of Otago, Dunedin. Hancox, G.T.P.; Perrin, N.D.; Dellow, G.D. in press: Recent studies of historical earthquake-induced landsliding, ground damage, Laird, M.G. 1972: Sedimentology of the Greenland Group in the and MM intensity in New Zealand. Bulletin ofthe New Zealand PaparoaRange, West Coast, South Island. New ZealandJournal Society for Earthquake Engineering. ofGeology and Geophysics 15: 372-393.
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Henley; RW.; Adains, J. 1979: On the evolution ofgiant gold placers. Laird, M.G. 1995: Coarse-grained lacustrine fan-delta deposits Transactions o/the Institution of Mining and Metallurgy 88: (Pororari Group) ofthe northwestern South Island, New Zealand: B41-50. evidence for Mid-Cretaceous rifting. International Association for Sedimentology Special Publication 22: 197-217. Hunt, T.M.; Nathan, S. 1976: Inangahua magnetic anomaly, New Zealand. New Zealand Journal ofGeology and Geophysics 19: Laird, M.G.; Shelley, D. 1974: Sedimentation and early tectonic 395-406. history of the Greenland Group, Reefton, New Zealand. New Zealand Journal ofGeology and Geophysics 17: 839-854. Hutton, C.O. 1950: Studies of heavy detrital minerals. Bulletin of the Geol?gical Society ofAmerica 61: 635-716. LeMasurier, W.E.; Landis, C.A. 1996: Mantle-plume activity recorded by low-relief erosion surfaces in west Antarctica and Hutton, e.O.; Turner, FJ. 1936: Metamorphic zones in north-west New Zealand. Bulletin of the Geological Society ofAmerica Otago. Transactions ofthe Royal Society ofNew Zealand 65: 108: 1450-66. 405-6. Lensen, G.J.; Suggate, R.P. 1969: Inangahua e,arthquake: a Inwood, K.S. 1997: Geologic setting, gravity collapse and hazard preliminary account of the geology. DSIR Bulletin 193: 17-36. assessment of the Kongahu Fault Zone, Westport. MSc thesis, University of Canterbury, Christchurch. Marshall, P. 1929: Building stones of New Zealand. DSIR Bulletin IJ. 47 p. Ireland, T.R 1992: Crustal evolution ofNew Zealand: evidence from age distributions of detrital zircons in Western Province Mason, B.; Taylor, S.R 1987: High-grade basement gneisses and paragneisses and Torlesse greywacke. Geochimica et granitoids in Westland, New Zealand. Journal of the Royal Cosmochimica Acta 56: 911-20. Society ofNew Zealand 17: 115-138.
Ireland, T.R.; Reay, A.; Cooper, A. E 1984: The Pounamu Ultramafic MacKinnon, T.C. 1980: Geology ofMonotis-bearing Torlesse rocks Belt in the Diedrich Range, Westland, New Zealand. New in Temple Basin near Arthur's Pass, South Island, New Zealand. Zealand Journal ofGeology and Geophysics 27: 247-256. New Zealand Journal ofGeology and Geophysics 23: 63-81.
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Morgan, P.G.; Bartrum, J.A. 1915: Thegeology and mineral resources Mlinker, C.; Cooper, RA. 1999: The Cambrian arc complex of the of the Buller-Mohikinui subdivision, Westport Division. New Takaka Terrane, New Zealand: an integrated stratigraphical, Zealand Geological Survey Bulletin 17. 9 maps + 210 p. paleontological and geochemical approach. New Zealand Journal ofGeology and Geophysics 42: 415-445. Morrell; WP. 1968: The Gold Rushes (2nd edition). A & C Black, London. Nathan, S. 1974a: Petrology ofthe Berlins Porphyry: a study ofthe crystallisation of granitic magma. Journal ofthe Royal Society Mortimer, G. 1984: Report onreconnaissance investigation ofCamp ofNew Zealand 4: 463-483. Creek Catchment, Alexander Range. Unpublished immediate report, file K32171, Institute ofGeological & Nuclear Sciences, Nathan, S. 1974b: Stratigraphic nomenclature for the Cretaceous Lower Hutt. lower Quaternary rocks of Buller and north Westlaqd, West Coast, New Zealand. New Zealand Journal of Geology and Mortimer, N. 1993a: Geology ofthe Otago Schist and adjacent rocks. Geophysics 17: 423-445. Institute .ofGeological & Nuclear Sciences geological map 7. Nathan, S. 1975: Sheets S23 & S30 - Foulwind and Charleston. Mortimer, N. 1993b: Metamorphic zones, terranes and Cenozoic Geological Map of New Zealand 1:63 360. Wellington, New faults in the Marlborough Schist, New Zealand. New Zealand Zealand, Department of Scientific and Industrial Research. Journal ofGeology and Geophysics 36: 357-368. Nathan, S. 1976a: Geochemistry of the Greenland Group (early Mortimer, N. 1995: Origin ofthe Torlesse terrane and coeval rocks, Ordovician), New Zealand. New Zealand Journal ofGeology North Island, New Zealand. International Geology Review 36: and Geophysics 19: 683-706. 891-910. Nathan, S. 1976b: Sheets S23/9 & S2417 - Foulwind and Westport. Mortimer, N.; Parkinson, D.; Raine, J.I.; Adams, C.J.; Graham, I.J.; Geological Map of New Zealand 1:25 000. Wellington, New Oliver, P.J.; Palmer, K. 1995: Ferrar magmatic province rocks Zealand, Department of Scientific and Industrial Research. discovered inNewZealand: implications for Mesozic Gondwana geology. Geology 23: 185-88. Nathan, S. 1977: Preliminary geological report on the Ahaura area, north Westland. New Zealand Geological Survey report M 60 Mortimer,N.; Smale, D. 1996: Petrology of the Topfer Formation: (Appendix B). 1 map + 4p. first Triassic Gondwana sequencefrom New Zealand. Australian Journal ofEarth Sciences 43: 467-477. Nathan, S. 1978a: Sheet S44 - Greymouth. Geological Map ofNew Zealand 1:63 360. Wellington, New Zealand, Department of Mortimer, N.; Sutherland, R; Nathan, S. 2001: Torlesse greywacke Scientific and Industrial Research. and Haastschistsource for Pliocene conglomerates nearReefton. New Zealand Journal ofGeology and Geophysics 44: 105-112.
55 Nathan, S. 1978b: Sheets S31 & part S32 - Buller-Lyell. Geological Rattenbury, M.S. 1991: The Fraser Complex: High-grade gneisses, Map of New Zealand 1:63 360. Wellington, New Zealand, igneous and mylonitic rocks in central Westland, New Zealand. Department of Scientific and Industrial Research. New Zealand Journal ofGeology and Geophysics 34: 23-33.
Nathan, S. 1993: Revising the 1:250000 Geological Map of New. Rattenbury, M.S.; Cooper, RA; Johnston, M.R 1998: Geology of Zealand - a discussion paper. Institute of Geological & Nuclear the Nelson area. Institute of Geological & Nuclear Sciences Sciences science report 93/26. 28 p. 1:250000 geological map 9. 1 sheet + 67 p.
Nathan, S. 1994: Geology of the Reefton Goldfield. Unpublished Rattenbury, M.S.; Heron, D.W. 1997: Revised procedures and map, file L31, Institute of Geological & Nuclear Sciences, specifications for the QMAP GIS. Institute of Geological & Lower Hutt. Nuclear Sciences science report 97/3. 52 p.
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S8 This full colour map illusrrates the geology of the Greymouth area, which covers the central part of the West Coast ofthe South Island. The map is part of a series, initiated in 1996, which will eventually cover the whole country. Onshore geology, offshore bathymetry, and major structural elements are shown, derived from published and unpublished mapping by GNS, NIWA, university and mineral exploration geologists. All geological data are held in a geographic information system (GIS), and are available in digital form, and as thematic maps at different scales. The accompanying, illustrated text summarises the regional geology, tectonic development, economic geology, engineering geology, and potential geological hazards.
The QMAP Greymourh area is bisected by the Alpine Fault a major dextral strike-slip fa ult that forms the active plate boundary between the Austral ian Plate (to the northwest) and the Pacific Plate (to the southeast). This has led to the juxtaposition of rocks of two different geological provinces. To the northwest, the pre-Cretaceous rocks are Paleozoic sedimentary and plutonic rocks that represent a fragment of the Gondwana supercontinent. On the southeast side of the Alpine Fault the rocks consist of the Torlesse composite terrane a thick, highly deformed sequence of mainly submarine fan sedimentary rocks of Permian to Jurassic age. There is a widespread cover of Cenozoic sediments, including late Quaternary glacial and interglacial deposits.
View looking eastwards from the coastline near Charleston to the Paparoa Range in the background, illustrating the variety of geology in the area. The rock in the foreground is banded paragneiss (Pecksniff Metasedimentary Gneiss). The flat surface in the centre is an uplifted last interglacial terrace (71 000 to 125 000 years), and the forest-covered cliffs are composed of Oligocene limestone.The Paparoa Range is composed of hard, granitoid rocks and paragneiss. Photo: S. Nathan T OO""
ISBN 0-478-09752-2 9 780473 097523