Zealandia: the SW Pacific’s hidden continent
Nick Mortimer GNS Science, Dunedin • Zealandia • Fiji [email protected] • NZJGG
GNS Science Geological continents
foot of coast continental slope
0 Oceanic crust Continental 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 Vanuatu Fiji Niue Where’s the Chesterfield H O B L Bellona Reef Tonga continent? Grand M Terre P
Kermadecs Australia Norfolk Elizabeth Reef 30° Lord Howe Three Kings
North
South Chathams Tasmania
Solander Oceania? Bounty Stewart Snares Antipodes 50°S Australasia? 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 Australian Plate 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 sea level (%) level sea above feature of area
0 3
Zealandia belongs with continents rather than islands and oceanic plateaus
Modified from Cogley (1984) GNS Science Gondwana whakapapa
Australia
EE WW Antarctica
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 Pacific Plate Earth’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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