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Overview of Zealandia and Its Subduction Record

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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 23arc at 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 .
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