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 Australia islands
Tasman 4 million people Sea New Near Australia Zealand
1000 km
GNS Science SW Pacific bathymetry
Fiji
New Based on satellite Caledonia gravity
Broad plateaus and ridges 1-2 km water depth
New Zealand
1000 km
Sandwell & Smith (1997), Stagpoole (2002) GNS Science SW Pacific 87 present day
Fiji tectonics 77 New Caledonia 67 mm/yr • Pacific and Australian plates
53 • nearby pole of PAC plate rotation
AUS plate New Zealand 38 • convergence variably oblique
• subduction polarity 30 changes
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 • now on two plates
PAC plate • Hikurangi Plateau adjacent AUS plate HP continental rock 85-55 Ma samples
Median Batholith (Cambrian-Cret)
Late Cret. MCCs
85-0 Ma Early Cret LIPs
45-0 Ma Preserved E Cret subduction zone 1000 km
GNS Science Zealandia and Gondwana
• ZLD on PAC and AUS plates
PAC plate • match piercing points AUS plate HP • track fracture zones
• rotation and translation
1000 km
Sutherland (1995, 1999) GNS Science 1000 km 14 April 84,000,000 B.P. Gondwana reconstruction
NG Just before major LP breakup episode MR QP KP Continental crust MP NewCal
Oceanic crust NLHR
AUST Hikurangi LIP
SNR SLHR <85 Ma continental breakup D ZLND lines ET Chall STR
IB HP Camp CR • Zealandia EANT WR was a ribbon continent WANT
After Gaina et al. (1998,1999), Sutherland (1999), Eagles et al. (2004) GNS Science 1000 km Gondwana geology WANT-ZLND-AUST along-strike CONVERGENT OROGENS comparisons MESOZOIC Sed-volc-met Plutonic
NEO PALEOZOIC AUST Sed-volc-met
Lachlan Plutonic
Del ZLND EXTENSIONAL OROGEN
CRETACEOUS HP pre-breakup MCCs EANT Rifting, thin crust, breakup, cooling, subsidence, WANT submergence: Zealandia
Mortimer (2008) 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 .5 mm wedge
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
6
4 2 Ferrar 0 0 50 100 150 200 250 300 350 400 450 500 Ma Cenozoic Cretaceous Jurassic Triassic Permian Carbonif Devonian Silur Ordov Camb
SUBDUCTION? Yes Maybe No
Cz VOLCANICS (K-Ar, Ar-Ar) Mz-Pz BATHOLITH SUITES (U-Pb zc) I-type S & IS-type A-type Subduction-related Low Sr/Y Low Sr/Y Intraplate High Sr/Y
Hayward et al. (1994), Mortimer et al. (1999), Tulloch et al. (2009), Hoernle et al. (2006) Timm et al. (2010) GNS Science New Zealand’s magmatic arcs
• different arcs give insights into different arc processes
• only some have associated FABs, accretionary wedges Camb • Cenozoic arcs founded on Mesozoic accretionary wedge
• ignore Pz, just talk about Mz, Cz Dev-Carb Tr-Cret subduction
GNS Science Mesozoic orogen
• Mz arc, Wedge forearc, wedge Forearc elements all in position Arc
• crustal thickness affected by Moho widespread extension
Mortimer et al. (2002) GNS Science Mesozoic orogen
• preserved long- Wedge lived, convergent margin Forearc Arc • variably exhumed, so can study shallow and deep levels
Arc Forearc Wedge
Mortimer et al. (2002) 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
6
4 2 Ferrar 0 0 50 100 150 200 250 300 350 400 450 500 Ma Cenozoic Cretaceous Jurassic Triassic Permian Carbonif Devonian Silur Ordov Camb
SUBDUCTION? Yes Maybe No
Cz VOLCANICS (K-Ar, Ar-Ar) Mz-Pz BATHOLITH SUITES (U-Pb zc) I-type S & IS-type A-type Subduction-related Low Sr/Y Low Sr/Y Intraplate High Sr/Y
Hayward et al. (1994), Mortimer et al. (1999), Tulloch et al. (2009), Hoernle et al. (2006) Timm et al. (2010) 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 non- marine fossils Monotis 205-212 Ma • zeolite facies
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
116 240 250 124
264 132
184
100 200 300 400 500 Ma 100 200 300 400 500 Ma
• detrital zircon peaks don’t match • detrital zircon peaks do match NZ NZ pluton chronology pluton chronology • northern Queensland source • 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 North vs South 12-0 Ma 5-0 Ma Zealandia
Cenozoic arcs 35-15 Ma North 85- 15? Cz allochthons Zealandia Ma with back-arc basin ophiolitic basalts
HP 12-0 Ma Age of back arc basin
South Zealandia
1000 km
GNS Science North South Zealandia Zealandia
SOUTH ZEALANDIA Subsiding, simple, passive, on Pacific Plate since 84 Ma NZL NORTH ZEALANDIA Subsiding, but complex: arcs, back-arc basins, allochthons, SZL ophiolites, (re) captured by Australian Plate
PEGI (2012) GNS Science Cenozoic volcanic record
Interpreted subduction episodes
16
14 MCCs 12 10
n 8
6
4 2 Ferrar 0 0 50 100 150 200 250 300 350 400 450 500 Ma Cenozoic Cretaceous Jurassic Triassic Permian Carbonif Devonian Silur Ordov Camb
SUBDUCTION? Yes Maybe No
Cz VOLCANICS (K-Ar, Ar-Ar) Mz-Pz BATHOLITH SUITES (U-Pb zc) I-type S & IS-type A-type Subduction-related = NORTH Low Sr/Y Low Sr/Y Intraplate = SOUTH High Sr/Y
Hayward et al. (1994), Mortimer et al. (1999), Tulloch et al. (2009), Hoernle et al. (2006) Timm et al. (2010) GNS Science Onland Cenozoic arc footprint
• volcanic levels exposed onland
Camb • migration in space and time
• age and cause of inception near NZ is speculative
Dev-Carb Tr-Cret
GNS Science 12-0 Ma 14-6 5-0 Arc Minerva Ma Plain 40 footprints offshore
0-2 Ma 6-17 Ma 17-23 Ma 30- 37 1 20 Ma MCC 18 35-18 Ma
Ma
32-20 32-20 Kupe Ophiolite allochthon arc at 23arcat Ma? Plain emplaced 25 Ma
• 23-18 Ma = rapid trench rollback to east
• pre-23Ma initiation = uncertain time and 500 km mechanism 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 PETLAB pet.gns.cri.nz FRED fred.org.nz 1:250K geol map data Rocks, analyses Fossils
GNS Science GNS Science Zealandia and its subduction history
520-100 Ma 100-0 Ma Gondwanaland Pacific Rim
Sutherland (2007) GNS Science