Overview of Zealandia
and its subduction record
Nick Mortimer, GNS Science, Dunedin, New Zealand
GNS Science
New Guinea
SW Pacific
geography
Fiji
New
Caledonia
Scattered,
remote
islands
Australia
4 million people
Tasman
Sea
Near Australia
New
Zealand
1000 km
GNS Science
SW Pacific
bathymetry
Fiji
Based on satellite
gravity
New
Caledonia
Broad plateaus
and ridges 1-2 km
water depth
New
Zealand
1000 km
Sandwell & Smith (1997), Stagpoole (2002)
GNS Science
SW Pacific
present day
tectonics
87
Fiji
77
New
Caledonia
67 mm/yr
53
PAC plate
AUS plate
New
Zealand
•  Pacific and
Australian
plates
•  nearby pole of
rotation
•  convergence
variably oblique
38
•  subduction
polarity
changes
30
1000 km
Bird (2003)
GNS Science
OJP
MP
Zealandia
•  continent that is
95% submerged
•  rifted internally
and on most
margins
45-0 Ma
120-85 Ma
PAC plate
AUS plate
85-55 Ma
HP
•  now on two
plates
•  Hikurangi
Plateau adjacent
continental rock
samples
Median Batholith
(Cambrian-Cret)
Late Cret. MCCs
85-0 Ma
45-0 Ma
1000 km
Early Cret LIPs
Preserved E Cret
subduction zone
GNS Science
Zealandia
and
Gondwana
•  ZLD on PAC and
AUS plates
PAC plate
AUS plate
HP
•  match piercing
points
•  track fracture
zones
•  rotation and
translation
1000 km
Sutherland (1995, 1999)
GNS Science
14 April 84,000,000 B.P.
1000 km
Just before major
breakup episode
LP
MR
QP
MP
Gondwana
reconstruction
KP
Continental crust
NewCal
Oceanic crust
NLHR
AUST
Hikurangi LIP
SNR
SLHR
D
<85 Ma continental breakup
lines
ZLND
ET
Chall
STR
IB
Camp
CR
EANT
HP
WR
•  Zealandia
was a ribbon
continent
WANT
After Gaina et al. (1998,1999), Sutherland (1999), Eagles et al. (2004)
GNS Science
Gondwana
geology
1000 km
WANT-ZLND-AUST
along-strike
comparisons
CONVERGENT OROGENS
MESOZOIC
Sed-volc-met
Plutonic
PALEOZOIC
NEO
AUST
Sed-volc-met
Plutonic
Lachlan
ZLND
Del
EXTENSIONAL OROGEN
HP
EANT
WANT
Mortimer (2008)
CRETACEOUS
pre-breakup
MCCs
Rifting, thin crust, breakup,
cooling, subsidence,
submergence: Zealandia
GNS Science
GNS Science
New Zealand’s
subduction history
Cambrian to Now
500 Ma Jaquiery Granite, Fiordland
White Island, August 2012
Expressions of subduction:
plate convergence, Benioff zone
EQs, magmatic arc with distinct
petrochemistry, fore-arc basin,
back-arc basin, accretionary
wedge
.5 mm
GNS Science
GEONET, Eberhart-Phillips et al. (2008), Wallace et al. (2009), Schellart & Spakman (2012)
GNS Science
Mantle
wedge
Lee et al. (2012) Hawkes Bay QMAP
GNS Science
New Zealand’s igneous rock record
Interpreted subduction episodes
16
14
MCCs
12
10
n 8
Ferrar
6
4
2
0
0
50
Cenozoic
100
Cretaceous
350
400
200
250
300
150
Triassic
Devonian
Jurassic
Permian
Carbonif
SUBDUCTION?
Cz VOLCANICS (K-Ar, Ar-Ar)
Subduction-related
Intraplate
Yes
Maybe
450
Silur
500 Ma
Ordov
Camb
No
Mz-Pz BATHOLITH SUITES (U-Pb zc)
I-type
Low Sr/Y
High Sr/Y
Hayward et al. (1994), Mortimer et al. (1999), Tulloch et al. (2009), Hoernle et al. (2006) Timm et al. (2010)
S & IS-type
Low Sr/Y
A-type
GNS Science
New Zealand’s
magmatic arcs
•  different arcs give
insights into different
arc processes
•  only some have
associated FABs,
accretionary wedges
Camb
Dev-Carb
•  Cenozoic arcs
founded on Mesozoic
accretionary wedge
Tr-Cret
•  ignore Pz, just talk
about Mz, Cz
subduction
GNS Science
Mesozoic
orogen
Wedge
Forearc
Arc
Moho
Mortimer et al. (2002)
•  Mz arc,
forearc,
wedge
elements all in
position
•  crustal
thickness
affected by
widespread
extension
GNS Science
Mesozoic
orogen
Wedge
•  preserved longlived, convergent
margin
Forearc
Arc
Arc Forearc
Mortimer et al. (2002)
•  variably exhumed,
so can study
shallow and deep
levels
Wedge
GNS Science
The Mesozoic Arc
Median Batholith = site of most NZ
Phanerozoic magmatism
GNS Science
Thermobarometry
112 Ma
105 Ma
Mortimer (2000), Flowers (2005), DePaoli et al. (2011)
GNS Science
Mesozoic plutonic record
Interpreted subduction episodes
16
14
MCCs
12
10
n 8
Ferrar
6
4
2
0
0
50
Cenozoic
100
Cretaceous
SUBDUCTION?
Cz VOLCANICS (K-Ar, Ar-Ar)
Subduction-related
Intraplate
450
350
400
200
250
300
150
Triassic
Devonian
Jurassic
Permian
Carbonif
Yes
Maybe
Silur
500 Ma
Ordov
Camb
No
Mz-Pz BATHOLITH SUITES (U-Pb zc)
I-type
Low Sr/Y
High Sr/Y
S & IS-type
Low Sr/Y
Hayward et al. (1994), Mortimer et al. (1999), Tulloch et al. (2009), Hoernle et al. (2006) Timm et al. (2010)
A-type
GNS Science
Major change in Zealandia arc at c. 130 Ma
170-130 Ma
High Sr/Y
130-110 Ma
Low Sr/Y
Mafic
underplate
Garnet-in
SW
NE
•  thickening crust in maturing arc and/or flat slab subduction
Tulloch & Kimbrough (2003)
GNS Science
Mesozoic
fore-arc
basin
• 
at least 13 km
Murihiku Terrane
strata over 120 m.y.
• 
marine and nonmarine fossils
• 
zeolite facies
Monotis
205-212 Ma
Curio Bay, 160 Ma
fossil forest
GNS Science
Mesozoic
fore-arc
basin
• 
in New
Caledonia as
well as New
Zealand
• 
structurally
simple
• 
provenance links
to Median
Batholith arc
GNS Science
Mesozoic
accretionary
wedge
Lloyd Homer, GNS
GNS Science
Mesozoic
accretionary
wedge
•  first cycle sandstones
•  different Perm-Cret
basins accreted in
wedge
•  frontal accretion and
underplating
•  polyphase Jura-Cret
schist overprint
Mackinnon (1983)
GNS Science
Exotic vs local
provenance
Older Jura-Trias wedge
Younger Cretaceous wedge
116
124
240
250
264
132
184
100
• 
• 
200
300
400
500 Ma
detrital zircon peaks don’t match
NZ pluton chronology
northern Queensland source
100
• 
• 
• 
200
300
400
500 Ma
detrital zircon peaks do match NZ
pluton chronology
local Median Batholith source
constrain time of wedge cessation
•  detrital zircon studies of Mesozoic accretionary wedge
Wandres et al. (2004), Adams et al. (2008, 2009)
GNS Science
Haast Schist:
an exhumed
accretionary
wedge
quartz veins, fluids, mass balance, Ar-Ar, thermochronology,
PTt paths, c. 135 Ma exhumation & mesothermal Au-W
GNS Science
Subduction
termination
•  130, 105, 85 Ma?
•  youngest rocks in
arc and wedge c.
110 Ma
•  oldest Zealandia
intraplate c. 97 Ma
•  reason = Hikurangi
Plateau collision.
Other models
•  BUT – did it ever
really stop to the
north?
GNS Science
OJP
MP
12-0 Ma
North
Zealandia
8515?
Ma
5-0
Ma
North vs
South
Zealandia
Cenozoic arcs
35-15 Ma
Cz allochthons
with back-arc
basin
ophiolitic basalts
HP
12-0 Ma
Age of back arc
basin
South
Zealandia
1000 km
GNS Science
North
Zealandia
SOUTH ZEALANDIA
Subsiding, simple, passive, on Pacific Plate since 84 Ma
NZL
SZL
PEGI (2012)
South
Zealandia
NORTH ZEALANDIA
Subsiding, but complex: arcs, back-arc basins, allochthons,
ophiolites, (re) captured by Australian Plate
GNS Science
Cenozoic volcanic record
Interpreted subduction episodes
16
14
MCCs
12
10
n 8
Ferrar
6
4
2
0
0
50
Cenozoic
100
Cretaceous
450
350
400
200
250
300
150
Triassic
Devonian
Jurassic
Permian
Carbonif
SUBDUCTION?
Cz VOLCANICS (K-Ar, Ar-Ar)
Subduction-related = NORTH
Intraplate = SOUTH
Yes
Maybe
Silur
500 Ma
Ordov
Camb
No
Mz-Pz BATHOLITH SUITES (U-Pb zc)
I-type
Low Sr/Y
High Sr/Y
S & IS-type
Low Sr/Y
Hayward et al. (1994), Mortimer et al. (1999), Tulloch et al. (2009), Hoernle et al. (2006) Timm et al. (2010)
A-type
GNS Science
Onland
Cenozoic
arc
footprint
•  volcanic levels
exposed onland
•  migration in space
and time
Dev-Carb
Camb
•  age and cause of
inception near NZ
is speculative
Tr-Cret
GNS Science
14-6
12-0 Ma
5-0
Ma
40
0-2 Ma
6-17 Ma
17-23 Ma
3018
Ma
37
35-18 Ma
32-20
arc at 23 Ma?
Minerva
Plain
Arc
footprints
offshore
Kupe
Plain
1
20 Ma MCC
Ophiolite allochthon
emplaced 25 Ma
•  23-18 Ma = rapid trench
rollback to east
•  pre-23Ma initiation =
uncertain time and
mechanism
500 km
85
Mortimer et al. (2007, 2010), Herzer et al. (2011)
GNS Science
Rick Herzer
GNS Science
New Zealand National Databases
QMAP data.gns.cri.nz/geology
1:250K geol map data
PETLAB pet.gns.cri.nz
Rocks, analyses
FRED fred.org.nz
Fossils
GNS Science
GNS Science
Zealandia and its
subduction history
520-100 Ma
Gondwanaland
Sutherland (2007)
100-0 Ma
Pacific Rim
GNS Science