Zealandia: the SW Pacific’s hidden

Nick Mortimer GNS Science, Dunedin • Zealandia • [email protected] • NZJGG

GNS Science Geological

foot of coast continental slope

0 Oceanic crust 20 Lithosphere km Mantle 40

150 Asthenosphere 300 Mesosphere

Geographic continents Geological continents • high elevation • varied geology • thick crust • large area large, continuous landmasses include continental shelves GNS Science W&F Samoa Fiji Niue Where’s the Chesterfield H O B L Bellona Reef Tonga continent? Grand M Terre P

Kermadecs Norfolk 30° Lord Howe Three Kings

North

South Chathams Tasmania

Solander ? Bounty Stewart Snares Antipodes 50°S ? Auckland

Campbell

Macquarie

500 km 160°E 180 Mercator projection GNS Science W&F Samoa Vanuatu Fiji Niue Zealandia: Chesterfield H O B L Bellona Reef Tonga High Elevation Grand M Terre P

Kermadecs Australia Norfolk 94% submerged Elizabeth Reef

Lord Howe Pacific Elevated wrt ocean crust Three Kings Plate Zealandia North NI South Chathams Tasmania Aoraki/Mt Cook 3724m SI

Bounty Stewart Snares Antipodes

Auckland

Campbell

Macquarie

500 km

GNS Science Zealandia: Varied Geology

granites CONTINENTAL ROCKS

Granite, diorite, gabbro

Rhyolite, dacite

Greywacke, schist

Zealandia basement = Pz-Mz batholiths, terranes

Vanuatu, Fiji, Kermadecs Three Kings Ridge?

500 km

Mortimer & Campbell (2014) GNS Science Zealandia: Thick Crust

At least 10-30 km throughout

Not oceanic crust

Zealandia

Segev et al. (2012) GNS Science Zealandia: Large Area

100

80

60

40

20 area of feature above (%) level sea above feature of area

0 3

Zealandia belongs with continents rather than and oceanic plateaus

Modified from Cogley (1984) GNS Science whakapapa

Australia

EE WW

Gondwana

GNS Science Good scientific uptake

Luyendyk (1995), Kula et al. (2007), Graham et al. (2008), Grobys et al. (2008), Tulloch et al. (2009), Timm et al. (2010), Segev et al. (2012), Wobbe et al (2012), McCoy-West et al. (2013), Mortimer & Campbell (2014), Hiess et al. (2015)

GNS Science W&F Samoa Vanuatu Fiji Zealandia Niue Chesterfield H O B L Bellona Reef Tonga Grand M • high elevation Terre P granites • varied geology <500 Ma • 10-35 km thick crust Australia Norfolk Kermadecs Elizabeth Reef • 4.9 Mkm 2 in area Lord Howe Three Kings ’s most submerged, Zealandia North youngest, thinnest, Australian smallest continent

Plate South Chathams Tasmania Aoraki/Mt Cook 3724m A new and more accurate way to describe SW Bounty Stewart Pacific geology Snares Antipodes

Auckland

Campbell Age of crust under Fiji, Macquarie Vanuatu, Kermadecs and Three Kings Ridge? 500 km

GNS Science Fiji

• Fiji Platform = 400 x 250 km @ <500 m water depth

• <50 Ma geological history: North Fiji volcanics, 135º rotation Basin Fiji

Lau • Granites, schists, 19-24 km Basin thick crust

• Has previously been suggested as continental crust:

South Fiji Woolnough (1903), Crook (1963), Basin Rodda et al. (1967), Robertson (1967), Chase (1971), Glikson (1972), Gill et al. (2009), Drewes et al. (2009)

GNS Science Zircon ZrSiO4 U-Pb dating

Kermadecs 2010 Granite xenolith in tuff U-Pb zc 1.25 Ma ✘

Fiji 2013 Granite pluton U-Pb zc 36.4 Ma ✘

Vanuatu 2014 Calcsilicate xenoliths U-Pb zc 220-2800 Ma!

Mortimer et al. (2010), Rickard & Williams (2013), Buys et al. (2014) GNS Science P84135 P84136 P84137 Fiji 2016 P84138

U-Pb dating of zircon cores from beach and stream sands is underway at GNS Science, Dunedin

P84138 P84137 P84136 P84135

1 mm ?

GNS Science Zealandia: the SW Pacific’s Hidden Continent

A more correct and informative context for SW Pacific natural science

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