Zealandia: the SW Pacific’s hidden continentstar.gsd.spc.int/meeting_docs/presentations/Session2a-3_Zealandia... · Zealandia 500 km Aoraki/Mt Cook 3724m Fiji W&F Samoa Niue Tonga

GNS Science

Zealandia: the SW Pacific’s hidden continent

Nick MortimerGNS Science, Dunedin

n.mortimer@gns.cri.nz

• Zealandia• Fiji• NZJGG

GNS Science

Continental crustOceanic crust

Mantle

0

20

40

150

300

kmLithosphere

AsthenosphereMesosphere

coast

• high elevation• varied geology• thick crust• large area

Geological continents

foot ofcontinental slope

Geographic continents

large, continuous landmasses

Geological continents

include continental shelves

GNS Science

Chathams

Bounty

Antipodes

Campbell

Auckland

Three Kings

Norfolk

Lord Howe

Elizabeth Reef

Bellona Reef

Chesterfield

P

OL

M

B

H

GrandTerre

Where’s the continent?

500 km

Fiji

Samoa

Niue

Tonga

KermadecsAustralia

Tasmania

North

Oceania?

Australasia?Snares

Stewart

Macquarie

Solander

W&F

Vanuatu

180160°E

50°S

30°

Mercator projection

South

GNS Science

Chathams

Bounty

Antipodes

Campbell

Auckland

Snares

Three Kings

Norfolk

Lord Howe

Elizabeth Reef

Bellona Reef

Chesterfield

P

OL

M

B

H

GrandTerre

NI

SI

Stewart

Zealandia

Zealandia:High Elevation

94% submerged

Elevated wrt ocean crust

500 km

Aoraki/Mt Cook3724m

Fiji

W&F Samoa

Niue

Tonga

Kermadecs

Macquarie

Australia

Tasmania

AustralianPlate

PacificPlate

Vanuatu

North

South

GNS Science

Granite, diorite, gabbro

Greywacke, schist

Zealandia:Varied Geology

CONTINENTAL ROCKS

Rhyolite, dacite

500 km

Zealandia basement = Pz-Mz batholiths, terranes

Vanuatu, Fiji, KermadecsThree Kings Ridge?

granites

Mortimer & Campbell (2014)

GNS ScienceSegev et al. (2012)

Zealandia:Thick Crust

At least 10-30 km throughout

Not oceanic crust

Zealandia

GNS Science

3

Zealandia: Large Area

Zealandia belongs with continents rather than islands and oceanic plateaus

Modified from Cogley (1984)

80a

rea

of

fea

ture

ab

ov

e s

ea

le

ve

l (%

)

100

60

40

20

0

GNS Science

Gondwana whakapapa

GondwanaGondwana

AntarcticaAntarctica

AustraliaAustralia

WWEE

GNS Science

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)

Good scientific uptake

GNS Science

Chathams

Bounty

Antipodes

Campbell

Auckland

Snares

Three Kings

Norfolk

Lord Howe

Elizabeth Reef

Bellona Reef

Chesterfield

P

OL

M

B

H

GrandTerre

Stewart

Zealandia

500 km

Aoraki/Mt Cook3724m

Fiji

W&F Samoa

Niue

Tonga

Kermadecs

Macquarie

Australia

Tasmania

AustralianPlate

PacificPlate

Vanuatu

Earth’s most submerged, youngest, thinnest, smallest continent

• high elevation

• varied geology <500 Ma

• 10-35 km thick crust

• 4.9 Mkm2 in area

granites

Age of crust under Fiji, Vanuatu, Kermadecs

and Three Kings Ridge?

A new and more accurate way to describe SW

Pacific geology

South

ZealandiaNorth

GNS Science

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

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

• Granites, schists, 19-24 km thick crust

• Has previously been suggested as continental crust:

Fiji

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

Fiji

NorthFiji

Basin

LauBasin

SouthFiji

Basin

GNS Science

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!

Zircon ZrSiO 4U-Pb dating

Mortimer et al. (2010), Rickard & Williams (2013), Buys et al. (2014)

✘

✘

GNS Science

P84135 P84136 P84137

P84138

P84138P84137P84136

P84135

1 mm

Fiji 2016

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

?

GNS Science

Zealandia: the SW Pacific’s Hidden Continent

A more correct and informative context for SW Pacific natural science

GNS Science

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