Geology of Murihiku Area

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Geology of the
Murihiku Area
I. M. Turnbull
A. H. Allibone
(compilers)
ii
BIBLIOGRAPHIC REFERENCE
Turnbull, I.M.; Allibone, A.H. (compilers) 2003: Geology of the Murihiku area. Institute of Geological & Nuclear
Sciences 1:250 000 geological map 20. 1 sheet and 74 p. Lower Hutt, New Zealand. Institute of Geological &
Nuclear Sciences Limited.
FRONT COVER
The most prominent geological feature in the Murihiku area is the Southland Syncline. The north limb, seen here
looking southeast from south of Lumsden, is outlined by prominent strike ridges trending away through the Hokonui
Hills. The axis of the syncline lies to the south (right) and passes under the area of cloud in the far distance. The
syncline is formed in Permian to Jurassic Murihiku Supergroup sedimentary rocks, with these strike ridges in Early to
Middle Triassic North Range Group. The active Hillfoot Fault separates the Hokonui Hills from the extensive Quaternary
gravels of the Waimea Plains (left), underlain by Permian Maitai Group sedimentary rocks.
Photo CN43841/16: D.L. Homer
Edited, designed and prepared for publication by P.J. Forsyth, P. L. Murray, P. A. Carthew and
D.W. Heron.
Printed by Graphic Press & Packaging Ltd, Levin
ISBN 0-478-09800-6
© Copyright Institute of Geological & Nuclear Sciences Limited 2003
iii
CONTENTS
ABSTRACT .................................................................. v
Keywords ...................................................................... v
INTRODUCTION .......................................................... 1
THE QMAP SERIES ....................................................... 1
The Geographic Information System ............................. 1
Data sources .................................................................. 1
Reliability ....................................................................... 1
REGIONAL SETTING .................................................... 2
GEOMORPHOLOGY ...................................................... 6
Northern ranges and basins ........................................... 6
Southland Syncline ........................................................ 7
Te Anau and Waiau basins ............................................ 7
Southland and Waimea Plains...................................... 12
Takitimu Mountains and Longwood Range................. 12
Stewart Island .............................................................. 12
Offshore physiography ............................................... 12
STRATIGRAPHY ........................................................ 14
SILURIAN TO DEVONIAN ......................................... 14
Takaka terrane ............................................................ 14
CARBONIFEROUS TO CRETACEOUS ....................... 14
The Median Batholith ................................................. 14
Median Batholith from Longwood Range
 to Ruapuke ............................................................ 14
Permian Brook Street terrane intrusives within the
Median Batholith ................................................. 16
Triassic- Jurassic intrusives ........................................ 16
Median Batholith on Stewart Island ............................ 19
Carboniferous ............................................................. 19
Middle Jurassic ........................................................... 19
Late Jurassic to earliest Cretaceous ........................... 19
Early Cretaceous ......................................................... 22
Plutonic rocks of Fiordland and offshore islands ........ 22
PERMIAN TO JURASSIC ............................................ 23
Brook Street terrane ................................................... 23
Unassigned mélange units ........................................... 26
Murihiku terrane ......................................................... 26
Willsher Group ............................................................. 28
Dun Mountain-Maitai terrane .................................... 29
Caples terrane ............................................................. 31
Paterson Group ............................................................ 33
CRETACEOUS SEDIMENTARY ROCKS ................... 34
EOCENE TO PLIOCENE ............................................... 35
Eocene non-marine sedimentary rocks ........................ 35
Oligocene to Pliocene sedimentary rocks .................... 36
Te Anau and Waiau basins (Waiau Group) ................. 36
Winton Basin and Southland shelf .............................. 36
Late Miocene to Pliocene non-marine sediments ........ 39
QUATERNARY ............................................................ 41
Early Quaternary deposits ........................................... 41
Middle Quaternary deposits ........................................ 41
Late Quaternary deposits ............................................ 42
OFFSHORE GEOLOGY ................................................ 46
TECTONIC HISTORY ................................................ 48
Eastern and Western provinces ................................... 48
Mesozoic deformation within the Median Batholith .... 49
Late Cretaceous tectonics ............................................ 49
Cenozoic tectonics and basin development ................. 49
Quaternary tectonics ................................................... 50
ENGINEERING GEOLOGY ......................................... 51
Paleozoic to Mesozoic rocks ........................................ 51
Late Cretaceous and Tertiary sedimentary rocks ......... 51
Quaternary sediments .................................................. 51
GEOLOGICAL RESOURCES ..................................... 52
METALLIC RESOURCES............................................. 52
Hard-rock gold mineralisation ...................................... 52
Alluvial gold ................................................................ 52
Silicon and ferrosilicon ................................................ 52
Other metallic minerals ................................................. 53
NON-METALLIC RESOURCES ................................... 54
Coal .............................................................................. 54
Peat .............................................................................. 55
Hydrocarbons .............................................................. 55
Aggregate .................................................................... 55
Limestone .................................................................... 56
Silica sand .................................................................... 56
Serpentinite .................................................................. 56
Clay .............................................................................. 56
Building stone and riprap ............................................ 56
Groundwater ................................................................ 56
GEOLOGICAL HAZARDS ......................................... 57
Earthquakes (by G. L. Downes) .................................... 57
Tsunami (by G. L. Downes) .......................................... 60
Landslides .................................................................... 60
Volcanic hazard ............................................................ 62
Subsidence due to mining ............................................ 62
Groundwater contamination ......................................... 62
AVAILABILITY OF QMAP DATA ............................... 63
ACKNOWLEDGMENTS ............................................. 63
REFERENCES ............................................................. 64
APPENDIX 1
Nomenclature of units mappedon Stewart Island ....... 72
iv
Te Puka o Taakitimu - Monkey Island
This rocky knob near Orepuki, which becomes an island at high tide, has significance to Maaori as Te Puka o
Taakitimu – the anchor stone of the legendary Taakitimu waka/canoe which was wrecked in Te Waewae Bay. It is said
that the waka was turned to stone as the Taakitimu Mountains, and the bailer of Taakitimu became the Hokonui Hills.
v
Keywords
ABSTRACT
The Murihiku 1:250 000 geological map covers 18 000 km2
of south Otago and Southland, in the South Island of New
Zealand, and includes Stewart Island (Rakiura).
Topography varies from flat-topped ranges and intervening
basins in northern Southland, to prominent strike ridge
topography of the Kaihiku, Hokonui, and North ranges,
the jagged Takitimu Mountains, the lower bushclad
Longwood and Twinlaw massifs, and the extensive
Southland Plains. Stewart Island has generally subdued
bush and scrub-covered topography, with rolling hills and
the swampy Freshwater Depression in the centre.
Numerous other offshore islands dot the shallow waters
of Foveaux Strait and the fringes of Stewart Island. The
Waiau Basin lies in the far southwest, on the eastern edge
of Fiordland.
 The map area covers a wide range of Paleozoic to Mesozoic
rocks which form parts of several tectonostratigraphic
terranes. The Paleozoic to Cretaceous Median Batholith
comprises gabbroic to granitic plutonic rocks that intrude
metamorphic rocks of the Takaka terrane on Stewart Island
and the Permian oceanic volcanic island arc sequence of
the Brook Street terrane in the Takitimu and Longwood
ranges, and at Bluff.
Late Permian to Jurassic Murihiku terrane sedimentary rocks
separate Brook Street and Dun Mountain-Maitai terranes
and underlie most of the map area, thrust over Brook Street
terrane in the west and faulted against Dun Mountain -
Maitai terrane along the northeastern limb of the regional
Southland Syncline. The Dun Mountain-Maitai terrane is
in turn faulted against the Caples terrane in the
northeastern corner of the map area. Dun Mountain - Maitai
terrane rocks represent an Early Permian ophiolite complex,
overlain by metasediments of Permian to Triassic age. The
Caples terrane is probably of Permian to Triassic age in the
map area.
Except on Stewart Island, these basement terranes are
overlain by discontinuously preserved Cretaceous and
more extensive Eocene and younger sedimentary rocks of
the Ohai, Nightcaps, Waiau and East Southland groups.
The contact is the widespread Late Cretaceous to Cenozoic
Waipounamu Erosion Surface in northern Southland. The
fault-controlled Cenozoic Waiau Basin contains up to 5
km of marine and non-marine clastic sedimentary rocks;
coeval but much thinner shelf sedimentary rocks, typically
limestones, extend beneath the Winton and Eastern
Southland basins and the Waimea Plains.
Quaternary glaciation in Fiordland and northern Southland
produced large volumes of gravel which accumulated in
the Waimea and Southland Plains, the latter also influenced
by marine sedimentation during interglacial high sea levels.
Cirque glaciation affected the Takitimu and probably
Longwood ranges, and glaciers also formed on Mt Anglem
and Mt Allen on Stewart Island.
In northern Southland, at Gore and at Orepuki, Quaternary
deposits (including beach placers at Orepuki) have
produced at least 8000 kg of alluvial gold. Lode systems
are preserved in the volcanic rocks around the Longwood
Range but few have been mined. Platinum group metals
have been mined and prospected for in the Longwood
Range. Non-metallic minerals include limestone, sub-
bituminous coal at Ohai, and large reserves of lignite in the
East Southland Group.
The Murihiku map area is subject to seismic hazard from
the Alpine Fault west of Fiordland, and active faults in
Central Otago and Western Southland, with associated
earthquake shaking, landsliding, ground rupture,
liquefaction and delta collapse. Landslides and rockfalls,
both during and independent of major rainstorms, are minor
but ongoing hazards. Tsunami, mine collapse and flooding
are more localised hazards.
Murihiku; Southland; Stewart Island; Invercargill; Foveaux Strait; 1:250 000 geological map; geographic information
systems; digital data; bathymetry; Brook Street terrane; Caples terrane; Dun Mountain - Maitai terrane; Murihiku
terrane; Takaka terrane; Median Batholith; plutons; Pegasus Group; Paterson Group; Caples Group; Maitai
Group; Willsher Group; Dun Mountain Ultramafics Group; Livingstone Volcanics Group; Dun Mountain Ophiolite
Belt; Brook Street Volcanics Group; Takitimu Subgroup; Productus Creek Group; Barretts Formation; Greenhills
Group; Greenhills Ultramafic Complex; Bluff Intrusives; Pahia Intrusives; Holly Burn Intrusives; Tin Hut mélange;
Letham Ridge mélange; Murihiku Supergroup; Kuriwao Group; North Range Group; Taringatura Group; Diamond
Peak Group; Ferndale Group; Mataura Group; Park Volcanics Group; Ohai Group; Nightcaps Group; Waiau
Group; Clifden Subgroup; East Southland Group; Forest Hill Formation; marine terraces; alluvial terraces;
alluvial fans; moraines; till; outwash; landslides; peat swamps; sand dunes; oysters; Livingstone Fault; Hauroko
Fault; Blackmount Fault; Tin Hut Fault System; Letham Ridge Thrust; Gutter Shear Zone; Hillfoot Fault;
Escarpment Fault; Freshwater Fault System; Southland Syncline; Taieri - Wakatipu Synform; Quaternary
tectonics; active faulting; economic geology; alluvial gold; platinum; sub-bituminous coal; lignite; Ohai Coalfield;
Eastern Southland Coalfield; peat; limestone; groundwater; hydrocarbons; engineering geology; landslides;
regolith; natural hazards; seismotectonic hazard; volcanic eruptions; new stratigraphic names.
vi
Figure 1 Regional tectonic setting of New Zealand, showing the location of the Murihiku geological map and
other QMAP sheets, major offshore features (as illustrated by the 2000 m isobath) and active faults. The Murihiku
sheet lies on the Pacific Plate, east of the Alpine Fault which marks the Australian-Pacific plate boundary west of
Fiordland. The relative rates and directions of plate movements are shown by the arrows.
Adapted from Anderson & Webb (1994).
2000 m
2000
m
2
0
0
0
m
2000
m
Campbell Plateau
Bounty
Trough
Chatham Rise
H
ik
ur
an
gi
Tr
ou
gh
P
u
y
s
e
g
u
r
T
re
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Challenger
Plateau
New
Caledonia
Basin
Taranaki
Basin
Australian
Plate
Pacific
Plate
0 100 200
Kilometres
Al
pi
ne
Fa
ul
t
35° S
45° S
45° S45° S
175° E165° E165° E
170° E 175° E
170° E
35° S
180° E
40° S 40° S
37 mm/
yr
38 mm/yr
41 mm/yr
47 mm/yr
KaitaiaKaitaia
WhangareiWhangarei
WaikatoWaikato RotoruaRotorua
RaukumaraRaukumara
TaranakiTaranaki
NelsonNelson WellingtonWellington
GreymouthGreymouth KaikouraKaikoura
ChristchurchChristchurch
AorakiAoraki
HaastHaast
WaitakiWaitakiWakatipuWakatipu
DunedinDunedin
FiordlandFiordland
Hawkes
Bay
Hawkes
Bay
AucklandAuckland
mm/yr
WairarapaWairarapa
QMAP
Murihiku
1
INTRODUCTION
THE QMAP SERIES
This map is one of a national series known as QMAP
(Quarter-million MAP; Nathan 1993; Fig. 1), and
supersedes the previous 1:250 000 geological maps of the
Murihiku area which were published in the 1960s (Wood
1966; McKellar 1966; Watters et al. 1968). Since then,
Stewart Island has been mapped in detail for the first time
(see Appendix 1), and there have been numerous detailed
onshore and offshore geological and geophysical studies
of parts of the area by government, university and industry
geologists. The need for geological information has
increased as a result of the Resource Management Act,
demands for geological resources, a new educational
curriculum, and greater awareness of natural hazards andtheir mitigation. In the Murihiku area, changes in land use
have expanded the demand for geological information,
especially on groundwater. The increase in environment-
focused tourism, boosted by the creation of Rakiura
National Park, has also resulted in a demand for more
detailed information on local geology.
The geology shown on the map has been generalised for
presentation at 1:250 000 scale. Rock types are shown
primarily in terms of their age of deposition, eruption or
intrusion. The colour of the units on the map face thus
reflects their age, with overprints used to differentiate some
lithologies. Letter symbols (in upper case, with a lower
case prefix to indicate early, middle or late if appropriate)
indicate the predominant age of the unit. Metamorphic
rocks are mapped in terms of age of the parent rock (where
known), with overprints reflecting the degree of
metamorphism and deformation. The last lower case letter
(or letters) indicates either a formal lithostratigraphic unit
or the predominant lithology. A time scale showing the
correlation between international and local time scales, and
ages in millions of years (Ma) or thousands of years (ka)
(Cooper 2004), is inside the front cover.
This accompanying text is not an exhaustive description
or review of the various rock units mapped. Except for
some units on Stewart Island, names applied to geological
units are those already published; the nomenclature has
not been revised where anomalies are present. For more
detailed information on individual rock units, specific areas,
natural hazards or minerals, see the references cited
throughout the text.
The Geographic Information System
The QMAP series uses computer methods to store,
manipulate and present geological and topographical
information. The maps are drawn from data stored in the
QMAP Geographic Information System (GIS), a database
built and maintained by the Institute of Geological and
Nuclear Sciences (GNS). The primary software used is
ARC/INFO®. The QMAP database is complementary to
other digital data sets maintained by GNS, e.g. gravity and
magnetic surveys, mineral resources and localities, fossil
localities, active faults and petrological samples.
Background topographic data were purchased from Land
Information New Zealand.
The QMAP series is based on detailed geological
information, plotted at 1:50 000 scale on NZMS 260 series
topographic base maps. These record sheets are available
for consultation at GNS offices in Lower Hutt and Dunedin.
The detailed geology has been simplified for digitising,
with linework smoothed and geological units amalgamated
to a standard national system based on age and lithology.
Point data (e.g. dips and strikes) have not been simplified.
All point data are stored in the GIS, but only representative
structural observations are shown. The procedures for
map compilation and data storage and manipulation are
given by Rattenbury & Heron (1997).
Data sources
This geological map includes data from many sources,
including published geological maps and papers,
unpublished data from University theses, unpublished
GNS technical and map files, mining company reports, field
trip guides, the New Zealand Fossil Record File (FRED),
and GNS digital databases of geological resources and
petrological samples (GERM, PET). Field mapping of poorly
known areas, undertaken between 1999 and 2001, ensured
a more even data coverage over the map area. Landslides
were mapped from air photos, with limited field checking.
Offshore data were obtained from published and
unpublished surveys by NIWA, GNS, and the University
of Otago Geology Department. Types of data sources used
are shown in Fig. 2; data sources used for map compilation
are identified by * in the references.
Reliability
This 1:250 000 map is a regional scale map only, and should
not be used alone for land use planning, planning or design
for engineering projects, earthquake risk assessment, or
other work for which detailed site investigations are
necessary. Some of the data sets which have been
incorporated with the geological data (GERM, for example)
have been compiled from old or unchecked information of
lesser reliability (Christie 1989).
2
Figure 2 Types of geological data sources used in compiling the Murihiku map. Over 150 sources are represented;
details of individual sources can be obtained from the references, where they are indicated by an asterisk.
REGIONAL SETTING
The Murihiku geological map area extends from eastern
Fiordland to the Pacific coastline at the Catlins, and south
across Foveaux Strait to Stewart Island and its offshore
islands. The area lies entirely within the Pacific Plate, east
of the active Australian-Pacific plate boundary which in
southern New Zealand is the Alpine Fault, west of
Fiordland (Fig. 1). The Pacific Plate beneath Murihiku is
largely composed of fault-bounded terranes of regional
extent with different geological histories – the Paleozoic to
Mesozoic Takaka, Brook Street, Dun Mountain-Maitai,
58
59 57
52. Cawood 1987
53. Macpherson 1938
54
55. Bishop & Mildenhall 1994
56. Allibone 1991
. Campbell & Force 1973
57. McKellar 1966
58. Watters et al. 1968
59. Wood 1966
Published 1:250 000
map sheets
Student theses
Published papers
Published 1:250 000 map sheets
Published papers
39. Landis et al. 1999
40. Coombs 1950
41. Mortimer et al. 1999a
42. Cahill 1995
43. Price & Sinton 1978
44. Willett & Wellman 1940
45. Allibone & Allibone 1991
46. Allibone & Tulloch 1997
47. Watters 1978a
48. Cawood 1986
49. McIntosh et al. 1990
50. Campbell et al. 2001
51. Coombs et al. 1992
39
40
41
42
43
44
45
46
47
48
49
50
51
52
54
53
56
55
51
16
14. Boles 1971
15. Forsyth 1992
16. Banks 1977
17. Rombouts 1994
18. Macfarlane 1973
19. Waddell 1971
20. Allibone 1986
21. Peden 1988
22. Frewin 1987
23. Cook 1984
24. Webster 1981
25. Graham 1977
26. Elder 1994
27. Mossman 1970
28. Morton 1979
29. Griffin 1970
30. Clough 1987
31. Ryder-Turner 1977
32. Ritchie 1977
33. Holden 1993
34. Stenhouse 2002
35. Bishop 1962
36. Becker 1973
37. Simpson 2002
38. Bosel 1981
1 23
4
5
7
8
9
11
12
13
14
15
17
18
19
20
21
22
23
24,47
25
26
27
28
29
30
31
32
33
34
35
36
37
Student theses
1. Hall 1989
2. Kirby 1989
3. Pringle 1975
4. Scott 1974
5. G. Hyden 1979
6. Meder 1963
7. McOnie 1969
8. Houghton 1977
9. Griffith 1983
10. Willsman 1990
11. Begg 1981
12. Gass 1998
13. Arafin 1982
38
10
6
3
Murihiku and Caples terranes – which were amalgamated
along the margin of Gondwana during the Mesozoic
(Fig. 3). During and after terrane amalgamation, Brook
Street and Takaka terrane rocks were intruded by the
Median Batholith which is represented in the map area by
the plutonic rocks of Stewart Island and the Longwood
60
61
62
63
65
68
70
71
72
69
67
105
71
66
64
74
7575
76
77
78
79 80
77
81
82
83
84
8585
Other published maps
60. McKellar 1973
61. Mutch 1964
62. Wood 1969
63. Bowen 1964
64. Turnbull 1992
65. McKellar 1968
66. Lindqvist 1992
67. Wood 1956
68. McIntosh 1992
69. Speden 1971
70. Mortimer 1993a
71. Isaac & Lindqvist 1990
72. Marshall 1918
. Patchell 2002
Reports
73
74. Mutch 1976
75. Watters 1994
76. Ritchie 1994
77. Beanland & Berryman 1986
78. Mutch 1977
79. Bishop & Macfarlane 1984
80. Thomson & Read 1996
81. Stewart & Glassey 1993
82. Glassey et al. 1996
83. Liggett 1979
84. Liggett 1972
85. Purdie 1970
Unpublished maps
86. Carter & Norris 1980
87. Willett 1939
88. Willett 1950
89. Mutch 1960
90. Harrington & Wood 1947
91. Mutch 1967
92. Chandler 1964
93. Wood 1965b
94. Bluck 1998
95.Wood & Hitt 1964a
96. Wood & Hitt 1964b
97. Liggett 1973b
98. Healey 1938
99. Wood 1965a
100. Isaac & Lindqvist 1978
101. McPherson 1973
102. Watters 1947a
103. Watters 1947b
104. Speden 1957
105. Speden 1958
106. McKellar & Mutch 1967
107. Liggett 1973a
79
80
73
86
87
87
87
87
88
89
90
91
92
93
94
95
97
98
99
100
101
102
104
103
106106
107
Other published maps
Reports
Unpublished maps
96
Range. The terranes, and the Median Batholith, were
overlain by Cretaceous to Cenozoic sedimentary rocks
which are now thin or absent over much of the map area
but thicker within the Te Anau and Waiau basins.
Quaternary deposits are widespread and include the
extensive gravels of the Waimea and Southland Plains.
4
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. Chrystalls Beach Complex (Coombs et al. 2000) is
shown here as part of the Caples terrane. Pale yellow (inset) shows covering Cenozoic sediments.
Adapted from Mortimer 2004
Median Batholith
Karamea, Paparoa and
Hohonu batholiths
Haast Schist
Esk Head and Whakatane m langesé
Gneiss
SEDIMENTARY AND VOLCANIC ROCKS
PLUTONIC ROCKS
METAMORPHIC ROCKS AND
TECTONIC OVERPRINTS
Buller terrane
Takaka terrane
Torlesse composite
terrane (eastern NZ)
Brook Street terrane
Murihiku terrane
Dun Mountain - Maitai terrane
E
a
s
te
rn
P
ro
v
in
c
e
W
e
s
te
rn
P
ro
v
in
c
e
Caples terrane Rakaia
Hunua-Bay of Islands terrane
Morrinsville-Manaia Hill-Waioeka assemblage
(Waipa Supergroup)
Pahau
Northland and East Coast allochthons
NN
200 km
and
katane m langesé
CKS AND
INTS
e
NN
a and
s
hakatane m langesé
D VOLCANIC ROCKS
S
OCKS AND
RINTS
Torlesse composite
terrane (eastern NZ)
ne
aitai terrane
E
a
s
te
rn
P
ro
v
in
c
e
W
e
s
te
rn
P
ro
v
in
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Rakaia
nds terrane
a Hill-Waioeka assemblage
p)
Pahau
st Coast allochthons
NN
h
roa and
ths
Whakatane m langesé
KS
ROCKS AND
RPRINTS
rane
W
e
s
te
rn
P
ro
v
in
c
e
NN
edian Batholith
aramea, Paparoa and
ohonu batholiths
aast Schist
k Head and Whakatane m langesé
neiss
NIC ROCKS
ORPHIC ROCKS AND
NIC OVERPRINTS
ler terrane
kaka terrane
W
e
s
te
rn
P
ro
v
in
c
e
NN
200 km
ne m langesé
S AND
TS
W
e
s
te
rn
P
ro
v
in
c
e
NN
edian Batholith
aramea, Paparoa and
ohonu batholiths
aast Schist
k Head and Whakatane m langesé
neiss
IC ROCKS
ORPHIC ROCKS AND
IC OVERPRINTS
ler terrane
kaka terrane es
te
rn
o
v
in
c
e
NN
200 km
aast Schist
g
neiss
NN
200 km
a and
akatane m langesé
OCKS AND
RINTS
Torlesse composite
terrane (eastern NZ)
e
itai terrane
E
a
s
te
rn
P
ro
v
in
c
e
W
e
s
te
rn
P
ro
v
in
c
e
Rakaia
ds terrane
g
p)
Pahau
NN
a and
s
hakatane m langesé
S
OCKS AND
RINTS
ne
aitai terrane ov
in
c
e
W
e
s
te
rn
P
ro
v
in
c
e
NN
st Schist
Head and Whakatane m langesé
ss
RPHIC ROCKS AND
C OVERPRINTS
NN
200 km
A
L
P
I N
E
F A
U
L T
MurihikuMurihiku
5
Figure 4 Shaded topographic relief model of the Murihiku map area, derived from 20 m contour data supplied by
Land Information New Zealand, and illuminated from the northeast. North- to northeast-trending ranges and basins
in the northeast of the map area are separated from the northwest-trending strike ridges of the Southland Syncline by
the Murihiku Escarpment.
W
a
ia
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R
A
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a
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STEWART
ISLAND
STEWART
ISLAND
SOUTHLAND
PLAINS
SOUTHLAND
PLAINS
T
E
A
N
A
U
B
A
S
IN
T
E
A
N
A
U
B
A
S
IN
TAKITIMU
MOUNTAINS
WAIAU
BASIN
WAIAU
BASIN
S
O
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T
H
L
A
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D
S
O
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H
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D
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IM
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A
PLAINS
PLAINS
NORTHERN RANGES
AND BASINS
SYN
C
LIN
E
SYN
C
LIN
E
LONGWOOD
RANGE
LONGWOOD
RANGE
MURIHIKU
ESCARPMENT
MURIHIKU
ESCARPMENT
6
GEOMORPHOLOGY
The Murihiku map area includes several distinct
physiographic regions (Fig. 4), which are controlled by
underlying geology and influenced by erosion and late
Cenozoic tectonics.
Northern ranges and basins
The northern edge of the map sheet, between the Clutha
and Mataura rivers, lies at the southern limit of the Central
Otago region of tilted fault block ranges separated by fault-
angle depressions. Ranges up to 1500 m in elevation
include the Blue Mountains (Fig. 5) and the Black Umbrella
Range (Fig. 6). The ranges generally trend north to
northeast, with some trending northwest. Most range front
faults are Late Cenozoic in age, and the Blue Mountain
No 1 Fault is active (Beanland & Berryman 1986). The fault
blocks comprise massive to weakly foliated Caples Group
sandstone and semischist. The blocks become lower
southward as the northeast-trending fault systems die out
toward the Murihiku Escarpment. In the map area, large
scale landsliding typical of Central Otago range fronts
(McSaveney & Hancox 1996; Turnbull 2000) is present
only in the Black Umbrella Range.
The flat surfaces of the ranges, and the downlands beside
the Clutha River in the northeast of the map area, are
inherited from the Cretaceous to Cenozoic Otago Peneplain
or Waipounamu Erosion Surface (WES) (LeMasurier &
Landis 1996; Youngson & Landis 1997). This broadly
planar surface originally extended across much of the South
Island and beyond. It has a complex fluvio-marine origin,
and is of early to mid Cenozoic age in the map area. The
surface can be used as a structural marker for determining
Late Cenozoic deformation, such as folding and vertical
fault displacement (Fig. 6).
The southern ends of the Mataura, Black Umbrella and
Blue Mountains ranges are cut by the antecedent gorges
of the Mataura, Waikaka, and Pomahaka rivers (Fig.7),
formed during initial uplift of the ranges in Late Pliocene to
Quaternary time. Extensive high terraces lie between these
major valleys, with flights of lower terraces and fans near
the modern flood plains of these rivers. The upper eastern
slopes of the Black Umbrella Range contain small cirques
of glacial origin, strongly modified by landsliding.
Figure 5 The Blue Mountains and adjacent Tapanui depression, looking south. The range front fault (Blue
Mountain No 1 Fault) has active traces, although none are visible in this picture. The Blue Mountains form one of the
southernmost fault blocks in the northeast-trending Otago range and basin province. The Murihiku Escarpment,
parallel to the trend of the Southland Syncline, lies in the distance.
Photo CN43993/9: D.L.Homer
7
Southland Syncline
The most conspicuous and well-known geomorphic feature
within the Murihiku map area is the Southland Syncline
(see front cover). Alternating harder sandstone and softer
mudstone have been eroded to form strike ridges, which
define the north limb of the syncline from the Catlins coast
northwest through the Kaihiku, Hokonui, North and
Taringatura ranges. The syncline ends abruptly at the
Murihiku Escarpment, the geomorphic expression of the
Hillfoot Fault (Fig. 4). In the Catlins, these strike ridges,
crossed by northeast-trending faults, joints and lineaments,
form a trellised landscape.Strike ridges are a less obvious
feature of the landscape on the south limb, but form
prominent bluffs in the southwestern Hokonui Hills and
the Venlaw Forest, and define subsidiary folds (Fig. 8).
Strike ridge topography is less well-developed on the
western limb in the foothills of the Takitimu Mountains
(Fig. 9).
Te Anau and Waiau basins
The western margin of the Murihiku map area, between
Fiordland and the Takitimu Mountains and Longwood
Range, includes parts of the Te Anau and Waiau basins.
These depressions have existed since middle Cenozoic
time, and are controlled by subsidence along the northeast-
trending Moonlight Fault System. Both are infilled with
Cenozoic sedimentary rocks (Turnbull & Uruski 1993),
within which sandstone and limestone units form
prominent strike ridges. The Cenozoic sedimentary rocks
are overlain by extensive flights of Quaternary terraces,
deposited by the Waiau River draining the former Te Anau-
Manapouri piedmont glacier and other Fiordland glaciers.
Moraines are not extensively preserved within these basins
in the Murihiku map area. Extensive alluvial fans extend
west from the Takitimu Mountains into the basins.
Figure 6 Structure contours on the Waipounamu Erosion Surface (WES), north of the Hillfoot Fault in the eastern
part of the Murihiku map area. Major faults and folds in foliation are shown.
S
Y
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R
M
T
IE
A
RI
-
W
A
K
A
T
IP
U
4
0
0
WES concealed by Cenozoic sediments
WES eroded along fault scarps and in gorges
Waipounamu Erosion Surface (WES)
fault
fold in foliation
contour on WES (100 m interval)
1
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Tapanui
Waikaia
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C
lu
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ive
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9
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12
00
HILLFOOT FAULT
8
Figure 7 The Pomahaka River forms an antecedent gorge cutting through the southern Blue Mountains, seen
here looking north-northwest. The higher flat-topped surfaces in the middle distance are underlain by Gore Piedmont
Gravels of Early Quaternary age. The forested area to the right is underlain by Caples Group rocks, separated from
Livingstone Volcanics Group (centre) by the northwest-trending Livingstone Fault (arrowed).
Photo CN43913/10: D.L.Homer
Figure 8 Ridges underlain by steeply dipping Jurassic sandstone and conglomerate strike inland from the
Catlins coast near Teahimate Bay, on a subsidiary fold of the southern limb of the Southland Syncline. Gold has been
mined from the Teahimate beach sands.
Photo CN27259/18: D.L. Homer
9
Figure 9 Looking north along the Takitimu Mountains (left), which rise to 2000 m west of the upper Wairaki valley
(foreground). The mountains are formed of resistant Permian Takitimu Subgroup volcanic rocks; less resistant Late
Permian Productus Creek Group and Mesozoic Murihiku Supergroup sedimentary rocks form lower and less rugged
country. Murihiku Supergroup rocks underlie Mt Hamilton, the isolated peak on the skyline right of centre.
Photo CN43782: D.L. Homer
Figure 10 The Southland Plains, seen here looking north over the mouth of Waimatuku Stream west of Invercargill,
are underlain by Quaternary gravels of both alluvial and marine origin. An extensive 20 m marine bench (of OI stage
5 age) is truncated by a younger (6000 yr) sea cliff (arrowed) inland from the present coastline. Alluvial sediments from
the Oreti River and other streams merge imperceptibly onto the OI stage 5 marine bench from the north. Wind-blown
dunes trend diagonally across the back-beach lagoons in the foreground.
Photo CN43805/8: D.L. Homer
10
Figure 11 Mt Hamilton, at the northern end of the Takitimu Mountains, is underlain by a thick sequence of Murihiku
Supergroup sedimentary rocks. In this view to the south, bedding can be seen cutting across the west face of the
peak. Faults of the Tin Hut Fault System (right foreground) separate Mt Hamilton from the main Takitimu Mountains.
Figure 12 Port Pegasus and southern Stewart Island, looking to the west. The prominent domes of Bald Cone (B),
Gog (G) and Magog (M) rise above the drowned valley system occupied by Port Pegasus, and are formed of the
particularly quartz-rich granitic Gog Pluton. Denser vegetation grows on the adjacent granodioritic Easy Pluton.
Photo CN43767: D.L. Homer
11
Figure 13 The lower Freshwater valley on Stewart Island is filled by a sand plain which extends from Paterson Inlet
(distant), west to the Ruggedy Mountains. Longitudinal dune ridges overlie the sand plain. Thomsons Ridge (upper
left) lies along the northern side of the Freshwater Fault System; the southern edge of the fault system lies along the
hills to the south, and beyond to the south side of Paterson Inlet.
Photo CN44055/15: D.L. Homer
12
Southland and Waimea Plains
Over half the onshore part of the Murihiku map area
consists of flat to gently rolling terrain between the
Aparima, Oreti, and Mataura rivers, known as the Southland
and Waimea Plains (Figs 4, 10). The terrain comprises
Quaternary alluvial plains and terraces built of gravel
derived from the Paleozoic and Mesozoic rocks of the river
catchments. The older terraces are mantled with wind-
blown loess and have been subtly dissected. Younger
surfaces are flat with well-preserved meanders and low
terraces. Terrace and paleodrainage systems are complex,
as there has been considerable channel switching in
response to aggradation, stream capture, and local
tectonism.
Marine benches and paleoshorelines are present parallel
to the modern coast (Fig. 10; see also Figs 36, 37). The
benches formed during interglacial high sea levels, with
subsequent tectonic uplift increasing to the west. A marine
bench is also conspicuous east from Riverton, cut off from
the present coastline by a younger sea cliff (Fig. 10), and
extends intermittently eastwards. Older paleoshorelines
further inland are indistinct, being partly obscured by peat
mounds up to 10 m high and many hectares in extent.
Takitimu Mountains and Longwood Range
Dominating the landscape in the west of the Murihiku map
area are the Takitimu Mountains (Fig. 9) and Longwood
Range. The Takitimu Mountains consist of deeply eroded
Permian Brook Street terrane volcanic rocks uplifted
between the Moonlight Fault System, which follows the
Waiau valley, and the Tin Hut Fault System in the Wairaki
and upper Aparima valleys. As these bounding faults are
active, the Takitimu Mountains are probably still rising.
The range was extensively glaciated during the Quaternary,
and cirques, U-shaped valleys and down-valley outwash
plains are well developed. The volcanic rocks are jointed
and prone to frost shattering, so steep prograding fan
surfaces and active screes are extensively developed (seeFig. 38).
Mt Hamilton (Fig. 11) is a fault-controlled massif separated
from the main Takitimu Mountains by the active Tin Hut
Fault System, and is still rising, with tilted Quaternary
surfaces on its northern flank (Force et al. 1970). Mt
Hamilton is underlain by Triassic sedimentary rocks of the
Murihiku Supergroup, forming one of the thickest
continuous sections of Murihiku rocks in New Zealand.
Twinlaw and Woodlaw hills south of Ohai, and the lower
Riverton peninsula, are also fault-controlled uplifted blocks
of Permian volcanics. As they have not been glaciated
and the rocks are typically deeply weathered, their profiles
are much more rounded than the Takitimu Mountains. The
Longwood Range, underlain by deeply weathered
Paleozoic to Mesozoic plutonic rocks, may have been
glaciated, but no glacial erosional features remain.
Stewart Island
The topography of much of Stewart Island is dominated
by a gently east-sloping plateau that rises from c. 20 m
above sea level at the east coast to between 400 and 500 m
elevation midway across the island. This gently sloping
surface may be a stripped peneplain, an inference
supported by the deep weathering typical of the
underlying rocks. Isolated peaks such as Mt
Anglem (980 m), Mt Allen (750 m) and the Tin Range
(640 m) may represent remnant Cretaceous hills that have
survived Cenozoic erosion. The Freshwater and Rakeahua
river systems dissect the east-sloping surface. During
higher interglacial sea levels, inundation of the Freshwater
valley west to Mason Bay may have divided Stewart Island
into two or three separate islands.
Steep cliffs reflecting active marine erosion characterise
much of the west coast, interrupted by beaches such as
Mason Bay (see back cover). Beaches are backed by large
sand dunes that extend into the scrub- and bush-covered
hinterland, reflecting the strong prevailing westerly winds.
The east coast, in contrast, is dominated by the drowned
valleys of Paterson Inlet, Port Adventure, Lords River and
Port Pegasus (Fig. 12). The drowned valleys, the easterly
slope of the topography, and the generally eastward
drainage direction are consistent with gentle tilting of the
island towards the east, probably during the late Cenozoic.
Extensive sand plain deposits form gently east-dipping
flights of terraces throughout the Freshwater River
catchment (Fig. 13). These terraces are overlain by
longitudinal and parabolic dune fields that have modern
analogues at Mason and Doughboy bays, where dunes
are actively advancing eastward under the prevailing
westerly winds. Extensive modern and fossil peat swamps
are interbedded with the dune fields and sand terraces.
Evidence of Quaternary glaciation is preserved at Mt Allen
(Allibone & Wilson 1997), and cirques and moraines are
common features of the Mt Anglem massif (Fig. 14).
Offshore physiography
Foveaux Strait from Te Waewae Bay east to Slope Point in
the Catlins is a shallow seaway with a relatively flat floor
draped in gravel and sand and punctuated by hard rock
knobs, some of which reach the surface as islands, rocks
and intertidal reefs (Cullen 1967). Areas of sandy to
gravelly bottom host the world famous Bluff oyster banks
(Cullen 1962). At the western entrance of the strait, the sea
floor remains shallow (Fig. 4) to the head of the Solander
Trough, beyond the mapped area. The sea floor deepens
rapidly west of Stewart Island into the Solander Trough.
At the east end of the strait, there is some relief on the sea
floor to depths of 40-50 m but the slope does not steepen
until east of Ruapuke Island. Southeast of Stewart Island
the sea floor is irregular and may be a continuation of the
exhumed erosion surface studded with granite hills seen
onshore (Figs 4, 12).
13
Figure 14 The Mt Anglem massif on Stewart Island, with well-developed cirque topography, moraine ridges (dashed
lines) and a glacial tarn (foreground). Jointing in quartz monzodiorite of the North Arm Pluton dips subvertically above
the tarn.
Photo CN2715/17: D.L. Homer
14
STRATIGRAPHY
The Murihiku map area includes significant areas of many
of New Zealand’s major Paleozoic to Mesozoic “basement”
rock units and, in particular, the Permian to Jurassic clastic
sedimentary rocks. Late Cretaceous to Cenozoic “cover”
sedimentary rocks occur in the fault-controlled Te Anau
and Waiau basins and beneath the Southland Plains.
Fluvioglacial and alluvial deposits of Quaternary age are
widely preserved, mainly in basins and lowlands.
Sedimentary and volcanic basement rocks are primarily
subdivided into tectonostratigraphic terranes (Figs 3, 15;
Bradshaw 1993; Mortimer et al. 1999b). Within each terrane
the rocks are described in terms of their age and lithology,
related to traditional lithostratigraphic units at formation
or group level. Several terranes have been affected by
regional metamorphic and structural events and schistose
rocks are also subdivided in terms of their textural
development. In the west the terranes have been intruded
by, or are dominated by, plutonic rocks of the Median
Batholith. Where plutonic rocks are a minor part of a terrane
they are described under that terrane. Median Batholith
plutonic rocks are described in order of age, subdivided
into plutons and intrusive complexes but only allocated to
petrogenetic suites where these are known. Much of the
mapping and subdivision of Stewart Island basement rocks
is new and is based on work by Allibone & Tulloch (see
Appendix 1).
SILURIAN TO DEVONIAN
Takaka terrane
Metasediments of the Pegasus Group (SDp) (Watters et al.
1968; Henley & Higgins 1977) form rafts, xenolith screens
and narrow elongate belts associated with Median
Batholith plutons on Stewart Island. The group consists
of micaceous schist rich in biotite and muscovite,
quartzofeldspathic psammitic schist, laminated
metaquartzites with traces of biotite and pyrite, calcareous
psammitic schists rich in Ca-plagioclase, amphibole and
clinozoisite, and hornblende-biotite amphibolites.
Micaceous schists commonly contain minor sillimanite but
garnet and cordierite are both rare. Primary sedimentary
features have been destroyed by deformation and
metamorphism, although transposed lithologic layering is
still present (Fig. 16). In the Kopeka River catchment,
Pegasus Group rocks are pervasively intruded by dikes
from the adjacent Blaikies Pluton (shown by an overprint).
At least three phases of ductile deformation and
metamorphism have affected the Pegasus Group (Williams
1934b; Henley & Higgins 1977; Watters 1978b; Allibone
& Tulloch 1997; Tulloch 2003). The earliest predates
emplacement of granitoid rocks at 344 ± 2 Ma while later
phases occurred between c. 344-305 Ma and during
movement on the Gutter Shear Zone between c. 128-
120 Ma (Fig. 17). The youngest detrital zircons from the
Pegasus Group, dated by single-crystal U-Pb TIMS
(Walker et al. 1998), are 420 Ma, suggesting a maximum
Late Silurian to Devonian sedimentation age and
correlation with Takaka terrane.
CARBONIFEROUS TO CRETACEOUS
The Median Batholith
Plutonic rocks in Fiordland, in the Longwood Range, at
Pahia Point and Bluff, beneath Foveaux Strait, and on
Stewart Island are part of the Median Batholith (Mortimer
et al. 1999b). Eastern parts of the batholith have previously
been interpreted as a zone of dismembered fault-bounded
volcanic arc fragments with likely allochthonous
relationships to both the Eastern and Western Provinces,
and referred to as the Median Tectonic Zone (Bradshaw
1993; Kimbrough et al. 1992; Kimbrough et al. 1994; Muir
et al. 1998).
The batholith was formed between the Late Devonian
(c. 380 Ma) and mid Cretaceous (c. 100 Ma) along the paleo-
Pacific margin of Gondwana (Mortimer et al. 1999b) with
the intrusion of several distinct suites of I, S and A-type
granitoids at different times (e.g. Tulloch 1983, 1988; Muiret al. 1998). Paterson Group volcanic and sedimentary
rocks on Stewart Island are likely to be coeval with
plutonism in the Median Batholith and were regarded as
part of the Median Batholith by Mortimer et al. (1999b).
Numerous plutons have been mapped on Stewart Island
(Fig. 17) and in the Longwood Range. They are inferred to
represent single or several closely related intrusions of
magma that form contiguous mappable bodies, except where
dismembered by younger plutons. Units such as the
Bungaree, East Ruggedy and Pahia Intrusives comprise
numerous small plutons, plugs and dikes that generally
cannot be shown separately at 1:250 000 scale, or which
have not been mapped to a level where boundaries between
individual bodies have been established. Suite and source
affinities of plutons are discussed where applicable.
Median Batholith from Longwood Range to Ruapuke
Permian to Jurassic plutonic rocks on the mainland lying
west and south of the Brook Street Volcanic Group from
the Longwood Range to Bluff are included in the Median
Batholith (Mortimer et al. 1999a, 1999b; Fig. 18A). These
intrusives are divided into an older Permian to Triassic
suite of mafic to ultramafic rocks, and younger Triassic to
Jurassic mafic, intermediate and felsic plutons (Mortimer
et al. 1999b). The older intrusives represent the roots of
the adjacent Brook Street terrane volcanic arc while the
younger suite was emplaced after accretion of the Brook
Street terrane arc to the margin of Gondwana (Mortimer
et al. 1999a, 1999b).
The Longwood - Pahia Point area has been investigated
by Wood (1966), Challis & Lauder (1977), Price & Sinton
(1978), Bignall (1987), Rombouts (1994) and others.
Previous work has been summarised and supplemented
with isotopic data by Mortimer et al. (1999a), with several
new plutons and intrusive units described. The Bluff
Intrusives have been intensively studied by Service (1937),
Harrington & McKellar (1956), Watters et al. (1968),
Mossman (1970, 1973), Graham (1977), Bosel (1981),
O’Loughlin (1998) and Spandler et al. (2000).
15
Figure 15 Major fault systems, and basement tectonostratigraphic units of the Murihiku area related to their
lithostratigraphic framework. FWFS - Freshwater Fault System; E - Escarpment Fault; G - Gutter Shear Zone.
Caples Group
Maitai Group
Livingstone Volcanics Group
Dun Mountain Ultramafics Group
Murihiku Supergroup (see Fig. 23)
Productus Creek Group
Brook Street Volcanics Group
(Takitimu Subgroup)
Greenhills Group
Brook Street terrane intrusives
Many plutons (see Figs 17 and 18),
including some in Brook Street terrane
L
in
iv
g
s
to
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e
Fault
Hillfoot Fault
L
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G
Terrane boundary and
other major faults
Tectonostratigraphic unit Lithostratigraphic unit
Pegasus Group
Late Cretaceous to
Recent sediments
Caples terrane
Dun Mountain -
Maitai terrane
Murihiku terrane
Brook Street terrane
Median Batholith
Takaka terrane
N
20 km
16
Permian Brook Street terrane intrusives within the
Median Batholith
In the Longwood Range, Permian intrusives form two large
plutons: Pourakino Trondhjemite (Ybj) and Hekeia
Gabbro (YTh) (Cowden et al. 1990; Mortimer et al. 1999a).
Trondhjemite dikes and a small stock intrude adjacent
Takitimu Subgroup rocks, which are altered to hornfels.
The trondhjemite may be a composite earliest to Middle
Permian unit, intruded between 292 Ma (Mortimer et al.
1999a) and 261 Ma (Tulloch et al. 1999). Hekeia Gabbro
also intrudes Takitimu Subgroup. It includes gabbro,
olivine gabbro, norite, troctolite, and anorthosite. A dioritic
phase is differentiated in places and cumulate textures
occur locally. On the coast between Pahia Point and
Riverton, Brook Street intrusive rocks include the informal
Colac granite (eTc) and Oraka diorite (eTo) units (Bignall
1987; Mortimer et al. 1999a). Isotopic data show these
Permian intrusives to be petrologically primitive, with no
crustal contamination, and genetically related to Brook
Street terrane island arc rocks. Ar-Ar spectra from Hekeia
Gabbro suggest minimum cooling ages of 249-245 Ma
(latest Permian to earliest Triassic) (Mortimer et al. 1999a).
Figure 16 Raft of Pegasus Group
metasediments within Kaninihi Pluton quartz
monzodiorite at South West Cape, Stewart
Island, showing pervasive folding of lithologic
layering. Lithologies include quartz-muscovite
schist and amphibolite.
The Bluff Intrusives (Ybz) include the layered Greenhills
Ultramafic Complex (Mossman 1970, 1973) which intrudes
the Permian metasedimentary Greenhills Group. The
ultramafic complex has a concentrically zoned dunite-
wehrlite core more than 750 m thick, surrounded by an
upper olivine clinopyroxenite portion 650 m thick, and an
outer gabbroic ring dike system. The zoned core has well-
developed cumulate layering, modified by magma flow and
mixing. Cogenetic dunite, wehrlite, gabbro, anorthosite,
trondhjemite, and hornblende pegmatite dikes, and younger
basalt and ankaramite dikes cut the complex. Associated
gabbro and norite (Fig. 18B), and diorite, granodiorite and
quartz diorite occur at Bluff itself. Similar norite, tonalite,
and diorite with inclusions of hornfels and tonalite outcrop
on Ruapuke Island (Webster 1981). Bluff Intrusives are
dated at 265 Ma (Middle Permian) (U-Pb TIMS age;
Kimbrough et al. 1992).
Triassic- Jurassic intrusives
Mesozoic intermediate to silicic plutonic rocks are more
widespread than Brook Street intrusives, and form the
western side of the Longwood Range and much of the
17
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18
coast from Pahia Point to Colac Bay (Challis & Lauder 1977;
Price & Sinton 1978; Mortimer et al. 1999a). Mafic
intrusions along the coast are termed Pahia Intrusives
(Challis & Lauder 1977). Holly Burn Intrusives (Thb)
(Mortimer et al. 1999a) in the western Longwoods include
diorite, mela- and leuco-diorite, quartz monzodiorite,
granodiorite and rare monzogranite and syenogranite, and
the informal Austin quartz monzodiorite along the coast
(Bignall 1987; Mortimer et al. 1999a). Larger areas of diorite
and quartz diorite are differentiated. On the western margin
of the Holly Burn Intrusives, steeply west-dipping foliation
outlined by quartz, biotite and epidote defines the
Grindstone Gneiss (shown by an overprint) (Wood 1969;
Mortimer et al. 1999a).
Pahia Intrusives (Jpi) include layered gabbronorite, norite
and hornblende gabbros, and minor peridotite, with
cumulate layering (Price & Sinton 1978). Layering was
accompanied by flow and deformation and is highly
irregular. Orbicular texture is rarely developed. Centre Island
is composed of layered gabbro with numerous mafic dikes
(Bignall 1987) and although undated is included in the
Pahia Intrusives. Diorite, quartz diorite and granite are
present along the Pahia Point coast (Challis & Lauder 1977;
Price & Sinton 1978; Bignall 1987) (Fig. 18C). The informal
units Boat Harbour diorite and Ruahine granite are
differentiated (Mortimer et al. 1999a). Mesozoic intrusives
of the Median Batholith are not known at Bluff. Late
Triassic tonalite, quartz monzonite and diorite (lTq) occur
on Ruapuke Island, where they have been dated by Rb-Sr
(Devereux et al. 1968; Webster 1981).
Holly Burn Intrusives and coastal equivalents range in
age from Middle Triassic to earliest Jurassic, and the Pahia
Intrusives are slightly younger (Devereux et al. 1968;
Kimbrough et al. 1994; Mortimer et al. 1999a; Tulloch
et al. 1999) based on a variety of dating methods. These
Triassic - Jurassic Median Batholith rocks are isotopically
more evolved than the Permian Brook Street plutons they
intrude.
Figure 18
(A) Nomenclature of Brook Street terrane plutonic rocks (included in the
Median Batholith) in relation to Brook Street Volcanics, Productus Creek
and Greenhills groups in the Murihiku map area, from Bluff to the
Longwood Range. Units in italics are informal.
(B) Norite on the foreshore at Bluff. Bluff norite has been extensively used
for dimension stone, as well as for reclamation work in Bluff Harbour.
(C) Diorite of the Pahia Intrusives at Monkey Island near Pahia Point.
Mackinnon
Peak
Intrusives
Colac
granite
Productus
Creek
Group
Takitimu Subgroup
Brook Street
Volcanics Group
White Hill
Intrusives Pourakino
Trondhjemite
Hekeia
Gabbro
diorite
Greenhills
Group
Granodiorite,
quartz diorite,
diorite
Norite and
gabbro
Dunite
and other
ultramafics
BLUFF and RUAPUKE
LONGWOOD RANGE to COLAC BAY
TAKITIMU MOUNTAINS
Brook Street
intrusives
Brook Street
Volcanics Group
P
E
R
M
IA
N
T
R
IA
S
S
IC
A
Bluff Intrusives
(includes
Greenhills
Ultramafic
Complex)
Oraka
diorite
CB
19
Median Batholith on Stewart Island
The plutonic rocks that comprise c. 90% of the Stewart
Island basement were previously mapped as the granitoid-
dominated Rakeahua Granite in southern and western
Stewart Island, and the diorite-dominated Anglem Complex
in northeastern Stewart Island. Both units were inferred to
comprise numerous individual intrusions (Watters et al.
1968). Subsequent mapping has delineated many of the
plutons initially included in these (superseded) units, and
each is briefly described below in order from oldest to
youngest. Field relationships and radiometric dates have
been used to determine the ages of different plutons.
Radiometric dating indicates that the various plutons that
comprise the Median Batholith on Stewart Island were
emplaced between c. 344 and 105 Ma (Tulloch 2003). Dikes
of diorite and gabbro, whose age is unknown, are
intercalated with Pegasus Group schist and orthogneiss
within the Gutter Shear Zone. These dikes form a diffuse
swarm that extends for about 35 km along strike between
the catchments of Doughboy Creek and the Lords River.
Cretaceous deformation between c. 130 and 100 Ma resulted
in development of the Gutter Shear Zone, Escarpment Fault
and Freshwater Fault System within the Median Batholith
on Stewart Island (Allibone & Tulloch 1997; Tulloch 2003)
(Fig. 17). Cataclasis alongsome faults within the Freshwater
Fault System may have occurred during the Cenozoic.
Carboniferous
Carboniferous intrusive rocks comprise c. 12% of the
Median Batholith on Stewart Island. Individual plutons
include the Ridge Orthogneiss (eCr) (344 ± 2 Ma), Ruggedy
Granite (eCg) (342 ± 2 Ma), Table Hill Orthogneiss (eCt)
(c. 340 Ma), Knob Pluton (Cmk) (305 ± 10 Ma), the Freds
Camp (lCf) (294 ± 5 Ma), Big Glory (lCb) and Forked
(lCk) plutons (308-294 Ma) (Allibone 1991; Allibone &
Tulloch 1997; Tulloch 2003) and the Neck Granodiorite
(eCn) (c. 340 Ma; T.R. Ireland and N.J.D. Cook pers. comm.
2003). The undated Adventure South Orthogneiss (Þv)
and Kopeka South Pluton (Þk) may also be Paleozoic in
age (Tulloch 2003).
The Ridge (Fig. 19A), and Adventure South orthogneisses
comprise foliated, locally K-feldspar megacrystic biotite
granodiorite and subordinate granite, while the Table Hill
Orthogneiss comprises foliated and often lineated biotite
± muscovite-bearing granite and leucogranite. These
gneissic intrusions form tabular bodies intercalated with
each other and with Pegasus Group schist in central and
southern Stewart Island. The Ridge Orthogneiss also forms
isolated blocks within and between younger plutons south
of the Gutter Shear Zone. Massive equigranular granite
and granodiorite dominate the Ruggedy Granite and Neck
Granodiorite respectively, with deformation restricted to
those parts of both plutons within and adjacent to the
Freshwater Fault System. The Freds Camp, Big Glory and
Forked plutons comprise massive quartz monzonite,
syenogranite, granite and alkali feldspar granite with
variable amounts of biotite. Variably foliated, distinctly
peraluminous biotite ± muscovite ± garnet granodiorite
and granite comprise the Knob and Kopeka South plutons.
Aligned K-feldspar megacrysts (Fig. 19B), tabular xenoliths
of Pegasus Group schist, and zones of compositional
banding define fabrics in many parts of the Knob Pluton
which are related to both magma flow and later ductile
deformation.
Tulloch et al. (2003) assigned the Ruggedy Granite to the
dominantly I-type Tobin Suite and cited the Ridge
Orthogneiss as the type pluton of the S-type Ridge Suite.
The alkaline nature of the Freds Camp, Big Glory and Forked
Creek plutons suggests correlation with the A-type
Foulwind Suite (Tulloch et al. 2003). The c. 305 Ma U-Pb
monazite age of the Knob Pluton also suggests correlation
with the A-type Foulwind Suite, although the peraluminous
and potassic nature of this intrusion distinguishes it from
other members of that suite. Suite affinities have not been
assigned to the other Carboniferous plutons.
Middle Jurassic
Middle Jurassic rocks form about 22% of the Median
Batholith on Stewart Island and include the Rakeahua
(mJk) (c. 169-166 Ma), South West Arm (mJs) (c. 167 Ma),
and Euchre (eJe) plutons. The Euchre Pluton is assigned
a Middle Jurassic age on the basis of its geochemical
similarity to the South West Arm Pluton. The Rakeahua
Pluton (Allibone & Tulloch 1997) includes gabbro,
anorthosite, diorite, a late quartz monzodiorite phase, and
minor dolerite. A particularly large body of layered
anorthosite and gabbro within the Rakeahua Pluton forms
the prominent Mt Rakeahua. The South West Arm (Allibone
& Tulloch 1997) and Euchre plutons comprise relatively
homogenous biotite granodiorite and granite. K-feldspar
megacrysts occur locally within the South West Arm Pluton
but are absent from the finer grained Euchre Pluton.
Late Jurassic to earliest Cretaceous
Late Jurassic and earliest Cretaceous rocks emplaced
between c. 145 and 130 Ma form about 28% of the Median
Batholith on Stewart Island. Principal units include the
Codfish Granite (lJc) (c. 152 Ma), Saddle (eKx) and Deceit
(mJd) plutons (c. 145 Ma), Bungaree (eKa) and East
Ruggedy (eKy) Intrusives (c. 140-130 Ma), North Arm and
Rollers plutons (eKn, eKz) (c. 132-130 Ma), Richards Point
Porphyry (eKr) (c. 130 Ma), Tarpaulin Pluton (eKt)
(c. 125 Ma), and Freshwater Northeast (eKf) and Smoky
(eKs) plutons (less than c. 130 Ma).
North of the Freshwater Fault System a progression from
dominantly mafic (Saddle Pluton) through intermediate
(Bungaree and East Ruggedy Intrusives, North Arm and
Rollers plutons) to granitoid plutonism (Tarpaulin,
Freshwater Northeast and Smoky plutons) is apparent
during Late Jurassic to earliest Cretaceous time. The Saddle
Pluton (Frewin 1987; Tulloch 2001) comprises gabbro and
diorite, with minor dunite and norite (Fig. 19C), and includes
gabbro at Cow and Calf Point (Watters et al. 1968). These
mafic rocks form Little Mt Anglem, The Paps, and the
northeastern slopes of Mt Anglem. The Bungaree and East
20
Figure 19 Typical Median Batholith rocks on Stewart Island
(A) Foliated potassium-feldspar megacrystic Ridge Orthogneiss within the Gutter Shear Zone, cut by an Upper
Rakeahua Pluton leucogranite dike, on Adams Hill.
(B) Aligned megacrysts of potassium feldspar in the Knob Pluton at the mouth of Seal Creek, southeast coast of
Stewart Island.
(C) Steeply dipping primary igneous layering in gabbro and anorthosite of the Saddle Pluton on The Paps.
(D) Compositional banding and associated foliation (schlieren), probably related to magma flow, in the Doughboy
Pluton on the west face of Mt Allen.
(E) Rafts of coarse biotite leucogranite and smaller amphibolite xenoliths in the Mason Bay Pluton at the south end of
Little Hellfire Beach.
(F) Schematic view of field relationships in the Gutter Shear Zone. Intercalated layers of Pegasus Group, Table Hill
Orthogneiss and Ridge Orthogneiss are cut by a swarm of aplite, leucogranite and pegmatite dikes associated
with the Upper Rakeahua, Campsite and Lords plutons. Dike rocks may form up to 50% of outcrops and
dominate float within the dike swarm, giving a false impression of bedrock geology.
pegmatite dike
leucogranite
dike
Table Hill
Orthogneiss
intrusive
contact
transposed contact
Pegasus
Group
Ridge
Orthogneiss
1
0
–
1
0
0
m
1
0
–
1
0
0
m
F
A
E
D
B
C
21
Figure 20 Deformation fabrics associated with major Stewart Island faults.
(A) Strongly foliated diorite and quartz monzodiorite of the Walkers Pluton within the Gutter Shear Zone at the Ernest
Islands.
 (B) Strongly foliated granitoid rocks derived from either Southwest Arm Pluton or Tikotatahi Pluton within the
Escarpment Fault at Port Adventure.
Ruggedy Intrusives comprise numerous small plutons and
dikes of diorite, quartz monzodiorite and granodiorite with
subordinate granite, gabbro, and amphibolite (Waddell
1971; Frewin 1987). Similar diorite, quartz monzodiorite and
granodiorite form the large North Arm and smaller Rollers
(Frewin 1987) plutons. Dioritic rocks of the Bungaree
Intrusives and North Arm Pluton form the summit region
of Mt Anglem. The Tarpaulin (Cook 1987, 1988) and
Freshwater Northeast plutons comprise biotite granodiorite
and granite, while the more aluminous Smoky Pluton
comprises biotite-muscovite ± garnet granodiorite and
granite. Both the Freshwater Northeast and Smoky plutons
intrude the c. 130-132 Ma North Arm Pluton.
A widespread but not pervasive foliation is developed in
the North Arm, Tarpaulin and Saddle plutons, and in older
rocks within the Bungaree and East Ruggedy Intrusives.
This foliation is cut by younger plutons within the Bungaree
and East Ruggedy Intrusives and by the Freshwater
Northeast and Smoky plutons. The intense foliation
developed in southern parts of the North Arm and Tarpaulin
plutons, and in the East Ruggedy Intrusives on the northern
side of the Freshwater valley, marks the northern edge of
the Freshwater Fault System.
South of the Freshwater Fault System, Late Jurassic-Early
Cretaceous plutonism is represented by the Codfish
Granite, Deceit Pluton, and Richards Point Porphyry. The
Codfish Granitecomprises massive biotite granite in which
primary magmatic minerals are extensively retrogressed to
chlorite, sericite and epidote. The Deceit Pluton comprises
massive unfoliated, biotite ± muscovite granodiorite, granite
and leucogranite. The granodioritic Richards Point
Porphyry (Allibone 1991) is characterised by a prominent
chilled margin indicating emplacement at a shallow depth.
No suite affinity has been assigned to any of these rocks,
although their age is similar to rocks included in the Darran
Suite of Fiordland by Muir et al. (1998).
BA
22
Early Cretaceous
Plutons emplaced between c. 125 and 105 Ma comprise
about 38% of the Median Batholith on Stewart Island and
only occur south of the Escarpment Fault. Four generations
of intrusions are recognised within this time span; the
second and fourth generations in particular are probably
part of the Separation Point Suite. Pluton definitions are
given in the Appendix. The plutons include, from oldest to
youngest:
1. The dioritic to quartz monzodioritic Walkers Pluton
(eKw) (c. 127-120 Ma) (Peden 1988; Tulloch 2003) and
the heterogeneous quartz monzodioritic-granodioritic
Escarpment Pluton (eKv) (c. 126 Ma). Foliations in
both plutons are inferred to have formed during
movement on the adjacent Gutter Shear Zone (Fig. 20A)
and Escarpment Fault (Fig. 20B).
2. The Easy (eKe) (c. 128 Ma), Tikotatahi (eKi) and
Doughboy (eKd) (Fig. 19D) plutons comprise texturally
similar hornblende, biotite quartz monzodiorite and
granodiorite with minor granite (Peden 1988) and may
represent apophyses of a single larger body. Rafts of
diorite and gabbro occur within the Easy Pluton at Port
Pegasus (Þd). Field relationships and geochemical data
suggest the Mason Bay Pluton (eKm) (Allibone 1991)
is related to these three plutons. It includes biotite
quartz monzodiorite, biotite granodiorite and granite
plus numerous amphibolite rafts (Fig. 19E).
3. The Blaikies (eKb) (c. 116 Ma) and Upper Kopeka
(eKp) plutons largely comprise peraluminous biotite ±
muscovite ± garnet granite and granodiorite,
mineralogically distinct from other mid Cretaceous
plutons on Stewart Island (Allibone & Tulloch 1997;
Tulloch 2003). Muscovite and garnet are particularly
common in the southern part of the Blaikies Pluton
which contains numerous rafts of Pegasus Group
schist. Foliation development is inferred to reflect the
effects of both magma flow and subsequent post-
crystallisation ductile shear. Peraluminous S-type
granitoids elsewhere in New Zealand are Paleozoic in
age and these two plutons have no known correlatives.
4. The Gog (eKg) (c. 105 Ma), Lords (eKl) , Campsite
(eKc), and Upper Rakeahua (eKu) plutons comprise
fine-grained leucocratic biotite granodiorite and granite
with subordinate quartz monzodiorite, leucogranite,
pegmatite and aplite, with related dikes (Fig. 19F)
(Allibone & Tulloch 1997; Tulloch & Kimbrough in
press). No sharp contact exists between the Gog and
more mafic Kaninihi Pluton (eKk), suggesting that the
two plutons are closely related, with the former
representing the evolved core of the latter. The
extensive swarm of related aplite, leucogranite and
pegmatite dikes (outlined on the map face), and
similarities between these four plutons, imply that they
are apophyses of a major body that underlies much of
southern and central Stewart Island.
Plutonic rocks of Fiordland and offshore islands
Biotite granodiorite and biotite-hornblende tonalite (eKh)
form much of Paddock Hill at the northwest corner of the
map, and are overlain by Cenozoic sedimentary rocks along
the Hauroko Fault (Carter et al. 1982) and toward Lake
Manapouri (cf. Wood 1966). A c. 500 m2 area of massive
epidotised diorite (eKh), cut by a fine-grained amphibolite
dike, underlies Cenozoic rocks along the Blackmount Fault
(Carter & Norris 1980) and is inferred to be an outlier of
Fiordland basement rocks. These rocks are undated, and
are tentatively included in the Median Batholith.
Some of the numerous islands off Stewart Island and in
Foveaux Strait have not been visited because of access
difficulties, and are mapped as undifferentiated Median
Batholith (Þu).
23
PERMIAN TO JURASSIC
Brook Street terrane
In the Murihiku map area the Brook Street terrane forms
the Takitimu Mountains, the eastern Longwood Range,
the Riverton and Bluff peninsulas, some of the islands and
reefs in northern Foveaux Strait, and underlies much of the
southern Southland Plains. The terrane is intruded in places
by the Median Batholith, and in the eastern Takitimu
Mountains it is overthrust by the Murihiku terrane (Landis
et al. 1999).
As well as Permian plutonic rocks, described above under
the Median Batholith, the Brook Street terrane includes
several other lithostratigraphic units. The oldest is the
Brook Street Volcanics Group, which in the map area is
represented by the Early Permian Takitimu Subgroup. The
Early to Late Permian Productus Creek Group rests
conformably on the Takitimu Subgroup. Jurassic Barretts
Formation unconformably overlies both units. Permian
Greenhills Group metasediments and Bluff Intrusives
represent the Brook Street terrane at Bluff.
Figure 21
(A) Composite stratigraphic column through the Takitimu Subgroup in the Takitimu Mountains, after Houghton (1981)
and Landis et al. (1999). Formations indicated by * are not differentiated on the map.
(B) Pillow lava of the Takitimu Subgroup in a quarry on Twinlaw.
(C) Volcanic breccia cut by dikes within Takitimu Subgroup at Riverton.
Photo CN44044/10: D.L. Homer
Letham Ridge Thrust
PRODUCTUS CREEK GROUP
Caravan Formation
Elbow Formation *
Maclean Peaks Formation *
Heartbreak Formation
Chimney Peaks Formation *
Brunel Formation *
0
5
10
15
20 km
(Base not seen)
A
Breccia
Conglomerate
Sandstone
Mudstone
Pillow lava
Andesite
Basalt
Rhyodacite
Tuff
T
A
K
IT
IM
U
S
U
B
G
R
O
U
P
CC
C
B
24
In the central Takitimu Mountains the Takitimu Subgroup
(Ybt) consists of an eastward-younging homoclinal
sequence (Mutch 1964; Houghton 1981), striking N-S and
dipping vertically. To the south and north the strike
changes, although some of the central Takitimu formations
can still be recognised. Takitimu Subgroup is
predominantly volcaniclastic and includes mudstone,
sandstone, conglomerate and breccia, and subordinate
basaltic, rhyolitic, and andesitic flows and pillow lavas
(Houghton 1977, 1981, 1982, 1985; Houghton & Landis
1989; Landis et al. 1999). It is subdivided into 6 formations
(Fig. 21A). Only the predominantly volcanic Heartbreak
Formation (Ybt) (Houghton 1981) of microgabbro, basaltic
rocks, pillow lava and volcaniclastic breccia, and the
youngest Caravan Formation (Ybt) (Willsman 1990; Landis
et al. 1999) of volcanic breccia with distinctive ankaramitic
dikes and tuffs, are differentiated on the map face. The
rocks are folded about steeply to gently plunging axes in
the south (Nebel 2003) and are gently southeast-dipping
in the north (Pringle 1975; Scott 1974). The rocks contain
zeolite and prehnite-pumpellyite facies mineral assemblages
(Houghton 1982).
Undifferentiated Takitimu Subgroup, comprising flow
rocks, dikes, pillow lavas (Fig. 21B, C) and intercalated
sedimentary rocks including breccias, conglomerates,
sandstones and tuffs, forms Woodlaw and Twinlaw, the
eastern Longwood Range, and the hills west from Riverton.
Bedding in these areas strikes generally north to northwest
and is gently folded (Harrington & Wood 1947; Macfarlane
1973; Banks 1977). Takitimu Subgroup rocks at the
confluence of the Makarewa and Oreti rivers (Wood 1966)
comprise altered and veined basalt and andesite flows
(Watters 1961). The Takitimu Subgroup is interpreted to
be the remains of a calc-alkaline volcanic arc and adjacent
sedimentary basins (Houghton