Embed Size (px)
Citation preview
GNS Science
Zealandia: the SW Pacific’s hidden continent
Nick MortimerGNS Science, Dunedin
• 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
Publishes original research papers, reviews, short communications, book reviews, letters, forum articles
On all aspects of the earth sciences relevant to New Zealand, the Pacific Rim, and Antarctica
Send us your manuscripts
New Zealand Journal of Geology & Geophysics
