Zealandia

GSA Today, v. 27, doi: 10.1130/GSATG321A.1
Zealandia: Earth’s Hidden Continent
ABSTRACT
A 4.9 Mkm2
region of the southwest
Pacific Ocean is made up of continental
crust. The region has elevated bathymetry
relative to surrounding oceanic crust,
diverse and silica-rich rocks, and rela-
tively thick and low-velocity crustal struc-
ture. Its isolation from Australia and large
area support its definition as a conti-
nent—Zealandia. Zealandia was formerly
part of Gondwana. Today it is 94% sub-
merged, mainly as a result of widespread
Late Cretaceous crustal thinning preced-
ing supercontinent breakup and conse-
quent isostatic balance. The identification
of Zealandia as a geological continent,
rather than a collection of continental
islands, fragments, and slices, more cor-
rectly represents the geology of this part
of Earth. Zealandia provides a fresh context
Nick Mortimer, GNS Science, Private Bag 1930, Dunedin 9054, New Zealand; Hamish J. Campbell, GNS Science, P.O. Box 30368,
Lower Hutt 5040, New Zealand; Andy J. Tulloch, GNS Science, Private Bag 1930, Dunedin 9054, New Zealand; Peter R. King, Vaughan
M. Stagpoole, Ray A. Wood, Mark S. Rattenbury, GNS Science, P.O. Box 30368, Lower Hutt 5040, New Zealand; Rupert Sutherland,
SGEES, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand; Chris J. Adams, GNS Science, Private Bag 1930,
Dunedin 9054, New Zealand; Julien Collot, Service Géologique de Nouvelle Calédonie, B.P. 465, Nouméa 98845, New Caledonia; and
Maria Seton, School of Geosciences, University of Sydney, NSW 2006, Australia
in which to investigate processes of conti-
nental rifting, thinning, and breakup.
INTRODUCTION
Earth’s surface is divided into two types
of crust, continental and oceanic, and into
14 major tectonic plates (Fig. 1; Holmes,
1965; Bird, 2003). In combination, these
divisions provide a powerful descriptive
framework in which to understand and
investigate Earth’s history and processes.
In the past 50 years there has been great
emphasis and progress in measuring and
modeling aspects of plate tectonics at
various scales (e.g., Kearey et al., 2009).
Simultaneously, there have been advances
in our understanding of continental rifting,
continent-ocean boundaries (COBs), and
the discovery of a number of micro-
continental fragments that were stranded
in the ocean basins during supercontinent
breakups (e.g., Buck, 1991; Lister et al.,
1991; Gaina et al., 2003; Franke, 2013;
Eagles et al., 2015). But what about the
major continents (Fig. 1)? Continents are
Earth’s largest surficial solid objects, and it
seems unlikely that a new one could ever
be proposed.
The Glossary of Geology defines a con-
tinent as “one of the Earth’s major land
masses, including both dry land and conti-
nental shelves” (Neuendorf et al., 2005).
It is generally agreed that continents have
all the following attributes: (1) high eleva-
tion relative to regions floored by oceanic
crust; (2) a broad range of siliceous igne-
ous, metamorphic, and sedimentary rocks;
(3) thicker crust and lower seismic velocity
Figure 1. Simplified map of Earth’s tectonic plates and continents, including Zealandia. Continental shelf areas
shown in pale colors. Large igneous province (LIP) submarine plateaus shown by blue dashed lines: AP—Agulhas
Plateau; KP—Kerguelen Plateau; OJP—Ontong Java Plateau; MP—Manihiki Plateau; HP—Hikurangi Plateau.
Selected microcontinents and continental fragments shown by black dotted lines: Md—Madagascar; Mt—Mauritia;
D—Gulden Draak; T—East Tasman; G—Gilbert; B—Bollons; O—South Orkney. Hammer equal area projection.

structure than oceanic crustal regions; and
(4) well-defined limits around a large
enough area to be considered a continent
rather than a microcontinent or continental
fragment. The first three points are defin-
ing elements of continental crust and are
explained in many geoscience textbooks
and reviews (e.g., Holmes, 1965; Christensen
and Mooney, 1995; Levander et al., 2005;
Kearey et al., 2009; Condie, 2015). To our
knowledge, the last point—how “major” a
piece of continental crust has to be to be
called a continent—is almost never dis-
cussed, Cogley (1984) being an exception.
Perhaps this is because it is assumed that
the names of the six geological continents—
Eurasia, Africa, North America, South
America, Antarctica, and Australia—
suffice to describe all major regions of
continental crust.
The progressive accumulation of bathy-
metric, geological, and geophysical data
since the nineteenth century has led many
authors to apply the adjective continental
to New Zealand and some of its nearby
submarine plateaus and rises (e.g., Hector,
1895; Hayes, 1935; Thomson and Evison,
1962; Shor et al., 1971; Suggate et al., 1978).
“New Zealand” was listed as a continent
by Cogley (1984), but he noted that its
continental limits were very sparsely
mapped. The name Zealandia was first
proposed by Luyendyk (1995) as a collec-
tive name for New Zealand, the Chatham
Rise, Campbell Plateau, and Lord Howe
Rise (Fig. 2). Implicit in Luyendyk’s paper
was that this was a large region of conti-
nental crust, although this was only men-
tioned in passing and he did not character-
ize and define Zealandia as we do here.
In this paper we summarize and reassess
a variety of geoscience data sets and show
that a substantial part of the southwest
Pacific Ocean consists of a continuous
expanse of continental crust. Furthermore,
the 4.9 Mkm2
area of continental crust is
large and separate enough to be considered
not just as a continental fragment or a
microcontinent, but as an actual conti-
nent—Zealandia. This is not a sudden
discovery but a gradual realization; as
recently as 10 years ago we would not have
had the accumulated data or confidence in
interpretation to write this paper. Since it
was first proposed by Luyendyk (1995),
the use of the name Zealandia for a south-
west Pacific continent has had moderate
uptake (e.g., Mortimer et al., 2006; Grobys
et al., 2008; Segev et al., 2012; Mortimer
and Campbell, 2014; Graham, 2015).
However, it is still not well known to the
broad international science community. A
correct accounting of Earth’s continents is
important for multiple fields of natural
science; the purpose of this paper is to for-
mally put forth the scientific case for the
continent of Zealandia (Figs. 1 and 2) and
explain why its identification is important.
ZEALANDIA AS A CONTINENT
New Zealand and New Caledonia are
large, isolated islands in the southwest
Pacific Ocean. They have never been
regarded as part of the Australian continent,
although the geographic term Australasia
often is used for the collective land and
islands of the southwest Pacific region. In
the following sections, we summarize the
four key attributes of continents and assess
how Zealandia meets these criteria.
Elevation
Continents and their continental shelves
vary in height but are always elevated rela-
tive to oceanic crust (Cogley, 1984). The
elevation is a function of many features,
fundamentally lithosphere density and
Figure 2. Spatial limits of Zealandia. Base map from Stagpoole (2002) based on data from Smith and
Sandwell (1997). Continental basement samples from Suggate et al. (1978), Beggs et al. (1990), Tull-
och et al. (1991, 2009), Gamble et al. (1993), McDougall et al. (1994), and Mortimer et al. (1997, 1998,
2006, 2008a, 2008b, 2015). NC—New Caledonia; WTP—West Torres Plateau; CT—Cato Trough; Cf—
Chesterfield Islands; L—Lord Howe Island; N—Norfolk Island; K—Kermadec Islands; Ch—Chatham
Islands; B—Bounty Islands; An—Antipodes Islands; Au—Auckland Islands; Ca—Campbell Island.
Mercator projection.

thickness, as well as plate tectonics (e.g.,
Kearey et al., 2009). The existence of
positive bathymetric features north and
south of New Zealand has been known for
more than a century (Farquhar, 1906). The
accuracy and precision of seafloor map-
ping have improved greatly over the past
decades (Brodie, 1964; Smith and
Sandwell, 1997; Stagpoole, 2002) and a
deliberately chosen color ramp on a satel-
lite gravity-derived bathymetry map pro-
vides an excellent visualization of the
extent of continental crust (Fig. 2). The
approximate edge of Zealandia can be
placed where the oceanic abyssal plains
meet the base of the continental slope, at
water depths between 2500 and 4000 m
below sea level. The precise position of the
foot of the continental slope around
Zealandia was established during numer-
ous surveys in support of New Zealand’s
Law of the Sea submission (Wood et al.,
2003; UNCLOS, 2008).
Zealandia is everywhere substantially
elevated above the surrounding oceanic
crust. The main difference with other con-
tinents is that it has much wider and deeper
continental shelves than is usually the case
(Fig. 1). Zealandia has a modal elevation of
~-1100 m (Cogley, 1984) and is ~94% sub-
merged below current sea level. The high-
est point of Zealandia is Aoraki–Mount
Cook at 3724 m.
Geology
By itself, relatively high elevation is not
enough to establish that a piece of crust is
continental. Oceanic large igneous prov-
inces such as the Ontong Java Plateau
(Fig. 1; Coffin and Eldholm, 1994) are
elevated but not continental. Rocks of the
modern oceanic crust typically comprise
basalt and gabbro of Jurassic to Holocene
age. In contrast, continents have diverse
assemblages of Archean to Holocene igne-
ous, metamorphic, and sedimentary rocks,
such as granite, rhyolite, limestone, quartz-
ite, greywacke, schist, and gneiss, arranged
in orogenic belts and sedimentary basins.
Essential geological ground truth for
Zealandia is provided by the many island
outcrop, drill core, xenolith, and seabed
dredge samples of Paleozoic and Mesozoic
greywacke, schist, granite, and other sili-
ceous continental rocks that have been
found within its limits (Fig. 2). Many of
these have been obtained from expeditions
in the past 20 years (see Fig. 2, caption).
Orogenic belts, of which the Median
Batholith and Haast Schist are parts, can be
tracked through onland New Zealand and
across Zealandia (Fig. 2). Thus, there is a
predictable regional coherency and conti-
nuity to the offshore basement geology.
Traditionally, continents have been sub-
divided into cratons, platforms, Phanerozoic
orogenic belts, narrow rifts, and broad
extensional provinces (Levander et al.,
2005). Eurasia, Africa, North America,
South America, Antarctica, and Australia
all contain Precambrian cratons. The old-
est known rocks in Zealandia are Middle
Cambrian limestones of the Takaka
Terrane and 490–505 Ma granites of the
Jacquiery Suite (Mortimer et al., 2014).
Precambrian cratonic rocks have not yet
been discovered within Zealandia, but
their existence has been postulated on the
basis of Rodinian to Gondwanan age
detrital zircon ratios (Adams and Griffin,
2012). Furthermore, some Zealandia man-
tle xenoliths give Re-Os ages as old as
2.7 Ga (Liu et al., 2015). Geologically,
Zealandia comprises multiple Phanerozoic
orogenic belts on which a broad exten-
sional province and several narrow rift
zones have been superimposed (Mortimer
and Campbell, 2014).
Atop its geological basement rocks,
Zealandia has a drape of at least two dozen
spatially separate Late Cretaceous to
Holocene sedimentary basins. These typi-
cally contain 2–10-km-thick sequences of
terrigenous and calcareous strata (Zealandia
Megasequence of Mortimer et al., 2014) and
include a widespread continental breakup
unconformity of ca. 84 Ma age (Bache et
al., 2014). The Zealandia Megasequence
provides a Zealandia-wide stratigraphic
record of continental rifting, and marine
transgression events, similar to that seen in
formerly conjugate east Australian basins
(Blewett, 2012).
Crustal Structure
Continental crust varies considerably
in thickness and physical properties.
Christensen and Mooney (1995) give an
average P wave velocity of 6.5 km-1
and
Figure 3. Present day map of CRUST1.0 crustal thickness (Laske et al., 2013) showing the dispersed
Gondwana continents of Australia, Zealandia, East and West Antarctica, and South America. Note
thin continental crust in vicinity of Mesozoic arc. M—Marion Plateau; R—Ross Sea; W—Weddell Sea;
F—Falkland-Malvinas Plateau. LIP abbreviations: KP—Kerguelen Plateau; OJP—Ontong Java Pla-
teau; MP—Manihiki Plateau; HP—Hikurangi Plateau. Thick coastlines in Antarctica are isostatically
corrected ice-free coastlines (Jamieson et al., 2014). Orthographic projection.

mean density of 2830 kgm-3
with an aver-
age thickness of 46 km for orogens and 30
km for extended crust. In contrast, oceanic
crust is typically 7 km thick, and, in its
lower part typically has a P wave velocity
of 7.5 km-1
(White et al., 1992).
From geophysical work, we know that
Zealandia has a continental crust velocity
structure, Vp, generally <7.0 km-1
, and a
thickness typically ranging from 10 to
30 km throughout its entire extent to
>40 km under parts of South Island (Shor
et al., 1971; Klingelhoefer et al., 2007;
Grobys et al., 2008; Eberhart-Phillips et
al., 2010; Segev et al., 2012). Whereas most
of Zealandia’s crust is thinner than the
30–46 km that is typical of most conti-
nents, the above studies show that it is
everywhere thicker than the ~7-km-thick
crust of the ocean basins. This result is
visible in the global CRUST1.0 model of
Laske et al. (2013) shown in Figure 3.
Collectively, the crustal structure results
show that the rock samples of Figure 2 are
not from separate continental fragments or
blocks now separated by oceanic crust, but
are from a single continental mass.
The thinnest crust within Zealandia is in
the 2200-km-long and 200–300-km-wide
New Caledonia Trough, where the water
depth varies from 1500 to 3500 m (Fig. 2).
This raises the question as to whether the
trough is floored by oceanic crust or is a
failed continental rift. Two wide-angle
seismic profiles across the trough near
New Caledonia (Klingelhoefer et al., 2007)
both show ~2–5 km of sedimentary cover
over 8.5 km of crustal basement that has a
velocity of ~7 km-1
throughout much of its
thickness. Klingelhoefer et al. (2007) noted
these profiles as atypical of normal oce-
anic crust. Sutherland et al. (2010) and
Hackney et al. (2012) interpreted the New
Caledonia Trough as continental crust that
was thinned in the Late Cretaceous and
re-deepened in the Eocene due to litho-
sphere delamination.
Limits and Area
Where oceanic crust abuts continental
crust, various kinds of continent-ocean
boundaries (COBs) define natural edges to
continents (Fig. 1; Eagles et al., 2015).
Despite its large area, Greenland is uncon-
troversially and correctly regarded as part
of North America (Figs. 1 and 4). This is
because, despite oceanic crust intervening
between southern Greenland and Labrador
and Baffin Island, North American
continental geology is continuous across
Nares Strait between northernmost
Greenland and Ellesmere Island
(Pulvertaft and Dawes, 2011). Tectonic
plate boundaries, with or without interven-
ing oceanic crust, provide the basis for
continent-continent boundaries between
Africa and Eurasia, and North and South
America (Fig. 1). Large area is an inherent
part of the definition of a continent sensu
stricto (Neuendorf et al., 2005). Cogley
(1984) defined Central America (1.3 Mkm2
),
Arabia (4.6 Mkm2
), and greater India
(4.6 Mkm2
) as modern-day continents.
This schema has not been generally
adopted, probably because Central
America (the Chortis block) is a piece of
displaced North America, and Arabia and
India are transferring to, and are now
contiguous with, Eurasia and have clearly
defined COBs in the Red Sea and Indian
Ocean (Fig. 1). The six commonly recog-
nized geological continents (Africa,
Eurasia, North America, South America,
Antarctica, and Australia) are thus not only
large but they are also spatially isolated by
geologic and/or bathymetric features.
At the other end of the size spectrum, a
number of continental crust fragments in
the world’s oceans are referred to as
microcontinents. Examples include the
Madagascar, East Tasman, Jan Mayen,
Mauritia, and Gulden Draak microconti-
nents (Gaina et al., 2003; Torsvik et al.,
2013; Whittaker et al., 2016). Discriminating
between what is a continent and what is a
microcontinent may be considered an arbi-
trary exercise. Nonetheless, maps like
Figure 1 need labels. Therefore, following
Cogley (1984) and the vagaries of general
conventional usage, we propose that the
name continent be applied to regions of
continental crust that are >1 Mkm2
in area
and are bounded by well-defined geologic
limits. By this definition India, prior to its
collision with Eurasia, would be termed a
continent.
The edges of Australia and Zealandia
continental crust approach to within 25 km
across the Cato Trough (Fig. 2). The Cato
Trough is 3600 m deep and floored by oce-
anic crust (Gaina et al., 1998; Exon et al.,
2006). The Australian and Zealandian
COBs here coincide with, and have been
created by, the Cato Fracture Zone along
which there has been ~150 km of dextral
strike slip movement, linking Paleogene
spreading centers in the Tasman and Coral
seas (Fig. 2; Gaina et al., 1998). This spatial
and tectonic separation, along with inter-
vening oceanic crust, means that the
Zealandia continental crust is physically
separate from that of Australia. If the Cato
Trough did not exist, then the content of this
Figure 4. Areas and submergence of all of Earth’s geological con-
tinents (red symbols) along with microcontinents (brown symbols)
and intraoceanic large igneous provinces (LIPs, blue symbols)
shown in Figures 1 and 2. Note x-axis is log scale. Data mainly
after Cogley (1984) except Zealandia data from Mortimer and
Campbell (2014); microcontinents after Gaina et al. (2003) and
Torsvik et al. (2013). Emergent land area for Antarctica is the iso-
statically-corrected ice-free bedrock surface from Jamieson et al.
(2014). New Guinea and Greenland are arbitrarily given the same
submergence value as their parent continents. AP—Agulhas
Plateau; KP—Kerguelen Plateau; OJP—Ontong Java Plateau;
MP—Manihiki Plateau; HP—Hikurangi Plateau; N Am—North
America; S Am—South America.

paper would be describing the scientific
advance that the Australian continent was
4.9 Mkm2
larger than previously thought.
Being >1 Mkm2
in area, and bounded by
well-defined geologic and geographic lim-
its, Zealandia is, by our definition, large
enough to be termed a continent. At 4.9
Mkm2
, Zealandia is substantially bigger
than any features termed microcontinents
and continental fragments, ~12× the area
of Mauritia and ~6× the area of Madagascar
(Fig. 4). It is also substantially larger than
the area of the largest intraoceanic large
igneous province, the Ontong Java Plateau
(1.9 Mkm2
). Zealandia is about the same
area as greater India (Figs. 1 and 4). Figure
4 makes a case for a natural twofold group-
ing of continents and microcontinents.
DISCUSSION AND IMPLICATIONS
Recognition
Satellite gravity-derived bathymetry
maps (e.g., Fig. 2) have been of immense
use in visualizing Zealandia, clarifying
its limits, focusing attention on intra-
Zealandia structures, and planning
research voyages. If the elevation of
Earth’s solid surface had first been mapped
in the same way as those of Mars and
Venus (which lack the arbitrary datums of
opaque liquid oceans), we contend that
Zealandia would, much earlier, have been
investigated and identified as one of
Earth’s continents. Even relatively recently,
some papers refer to the offshore ridges
and plateaus of Zealandia as an amalgam
of continental fragments and slivers (e.g.,
Gaina et al., 2003; Blewett, 2012; Higgins
et al., 2015) with the explicit or implicit
notion that oceanic crust intervenes
between the continental fragments. The
way in which Zealandia has been divided
into blocks to make it amenable to rigid
plate reconstructions and the way in which
coastlines and outlines have been drafted
as “floating” in the Pacific Ocean (e.g.,
Gaina et al., 1998, 2003; Lisker and Läufer,
2013; Higgins et al., 2015) has probably
sustained this false impression of remote
and discombobulated tectonic allochthony
and poorly defined COBs. In contrast, we
view Zealandia as a coherent, albeit
thinned and stretched, continent with
interconnected and throughgoing geologi-
cal provinces (Figs. 2 and 5; Mortimer et
al., 2006; Grobys et al., 2008; Tulloch et
al., 2009; Adams and Griffin, 2012; Bache
et al., 2014; Graham, 2015). Like parts of
North America and Eurasia, Zealandia has
undergone active deformation in a zone
between two essentially rigid plates—in
Zealandia’s case, the Pacific and
Australian (Fig. 2).
Several elevated bathymetric features
north of Zealandia are possible candidates
for Zealandia prolongations or separate
microcontinents (Fig. 2). These include the
Three Kings, Lau-Colville, and Tonga-
Kermadec ridges and Fiji, which are
known Cenozoic volcanic arcs (Graham,
2015), and the Mellish Rise and Louisiade
and West Torres plateaus. However, no
continental basement rocks have yet been
sampled from any of these features, so
their continental nature remains unproven.
Development and Submergence
As shown in Figure 4, ~94% of the area
of Zealandia currently is submerged. It is
not unique in this regard: an ice-free, iso-
statically corrected West Antarctica would
also largely be submerged (Figs. 3 and 4;
Jamieson et al., 2014). Zealandia and West
Antarctica were formerly adjacent to each
other along the southeast Gondwana mar-
gin and, prior to thinning and breakup, the
orogenic belts, Cordilleran batholiths, and
normal continental crustal thickness of
eastern Australia would have projected
along strike into these areas (Figs. 3 and 5).
Figure 5. Zealandia as part of the former Gondwana supercontinent. Upper panel shows Mesozoic
orogen convergent margin that was active until ca. 105 Ma. Lower panel shows pre-breakup intra
continental extension of Zealandia and West Antarctica from 105 to 85 Ma; seafloor spreading sub-
sequently split Gondwana into its present-day constituent continents (Fig. 3). Orthographic projec-
tions with East Antarctica fixed. From Mortimer and Campbell (2014).

Several continental metamorphic core
complexes (Lister and Davis, 1989) of Late
Cretaceous age have been identified in
Zealandia and West Antarctica, but not in
Australia or East Antarctica (Figs. 3 and 5;
Kula et al., 2007). These have been
explained by Lister et al. (1991) and Kula
et al. (2007) in terms of an asymmetric
continent-scale detachment fault model in
which Zealandia and West Antarctica are
highly extended, lower-plate passive conti-
nental margins, and Australia and East
Antarctica are relatively unstretched upper
plate margins. There is also abundant sup-
porting sedimentary basin evidence that
Zealandia experienced widespread Late
Cretaceous (ca. 105–85 Ma) extension
prior to Gondwana supercontinent breakup
(e.g., Luyendyk, 1995; Klingelhoefer et al.,
2007; Bache et al., 2014; Mortimer et al.,
2014; Higgins et al., 2015). The situation of
Zealandia’s Phanerozoic orogen overlying
Precambrian mantle (Liu et al., 2015) pos-
sibly suggests major tectonic detachments
along the Moho.
Thermal relaxation and isostatic balance
of the thinned continental crust of Zealandia
and West Antarctica ultimately led to their
submergence. Despite the pervasive thin-
ning, the only part of Zealandia that might
qualify as a hyper-extended zone (i.e.,
stretched by a factor of 3–4 with crustal
thinning to 8 km or less; Doré and Lundin,
2015) is the New Caledonia Trough.
Zealandia and West Antarctica seemingly
record a mode of continental crust defor-
mation in which extension, although sub-
stantial, is more distributed and less focused
than in most examples of continental
breakup. Zealandia has a widespread syn-
rift Late Cretaceous volcanic record (Tulloch
et al., 2009; Mortimer et al., 2014); thus,
processes that operate at volcanic rifted
margins (Menzies et al., 2002) may be
applicable to the broad area of Zealandia.
Significance
Zealandia once made up ~5% of the area
of Gondwana. It contains the principal
geological record of the Mesozoic conver-
gent margin of southeast Gondwana
(Mortimer et al., 2014) and, until the Late
Cretaceous, lay Pacificward of half of
West Antarctica and all of eastern
Australia (Figs. 3 and 5). Thus, depictions
of the Paleozoic-Mesozoic geology of
Gondwana, eastern Australia, and West
Antarctica are both incomplete and mis-
leading if they omit Zealandia.
The importance of Zealandia is not so
much that there is now a case for a for-
merly little-known continent, but that, by
virtue of its being thinned and submerged,
but not shredded into microcontinents, it is
a new and useful continental end member.
Zealandia started to separate from
Gondwana in the Late Cretaceous as an
~4000-km-long ribbon continent (Fig. 5)
but has since undergone substantial intra
continental deformation, to end up in its
present shape and position (Figs. 1–3). To
date, Zealandia is little-mentioned and/or
entirely overlooked in comparative studies
of continental rifting and of COBs (e.g.,
Buck, 1991; Menzies et al., 2002; Franke,
2013). By including Zealandia in investiga-
tions, we can discover more about the rhe-
ology, cohesion, and extensional deforma-
tion of continental crust and lithosphere.
Gondwana breakup along the paleo-
Pacific margin resulted in continents with
wide, thinned shelves, such as Zealandia
and West Antarctica (Figs. 1 and 3). In
contrast, breakup of Gondwana’s core
resulted in continents with narrow shelves,
such as Africa and its neighbors (Fig. 1).
Various lithospheric versus mantle controls
on styles of continental rifting and breakup
are still debated (Ebinger and van Wijk,
2014; Whittaker et al., 2016). The broad
spatial association of stretched continental
crust with a pre-softened, Mesozoic, paleo-
Pacific convergent margin from the
Falkland Plateau, through West Antarctica
and Zealandia to the Marion Plateau
(Fig. 3), is possibly no coincidence (cf. Rey
and Müller, 2010). Other proposed controls
on the localization of Zealandia-Gondwana
breakup include a mantle plume (Weaver
et al., 1994), plate capture (Luyendyk,
1995), and/or impingement of an oceanic
spreading ridge (Mortimer et al., 2006).
Gaina et al. (2003) proposed that micro-
continents are created by plume-controlled
ridge jumps during the early stages of
supercontinent breakup. The general cohe-
sion of continental crust in extension is
attested to by the contrast in size between
Zealandia and its neighboring continental
fragments of East Tasman, Gilbert, and
Bollons seamounts (Figs. 2 and 4). Condie
(2015) postulated that ancient and modern
continent-continent collisions were a lead-
ing cause of continental elevation. The
geological history of Zealandia would sup-
port this hypothesis: The Paleozoic and
Mesozoic orogens of Zealandia are non-
collisional (Mortimer et al., 2014), and
there is only incipient collision between
northern and southern Zealandia across the
present-day Pacific-Australian plate
boundary. Ironically, for a continent so
thoroughly shaped by extensional pro-
cesses and subsidence, it is the more
widely recognized and better-studied con-
vergence across the Cenozoic Pacific-
Australian plate boundary that has resulted
in any of Zealandia being above the sea.
CONCLUSIONS
Zealandia illustrates that the large and
the obvious in natural science can be over-
looked. Based on various lines of geologi-
cal and geophysical evidence, particularly
those accumulated in the last two decades,
we argue that Zealandia is not a collection
of partly submerged continental fragments
but is a coherent 4.9 Mkm2
continent
(Fig. 1). Currently used conventions and
definitions of continental crust, continents,
and microcontinents require no modifica-
tion to accommodate Zealandia.
Satellite gravity data sets, New Zealand’s
UNCLOS program, and marine geological
expeditions have been major influences in
promoting the big picture view necessary
to define and recognize Zealandia (Fig. 2).
Zealandia is approximately the area of
greater India and, like India, Australia,
Antarctica, Africa, and South America,
was a former part of the Gondwana super-
continent (Figs. 3 and 5). As well as being
the seventh largest geological continent
(Fig. 1), Zealandia is the youngest, thinnest,
and most submerged (Fig. 4). The scientific
value of classifying Zealandia as a conti-
nent is much more than just an extra name
on a list. That a continent can be so sub-
merged yet unfragmented makes it a useful
and thought-provoking geodynamic end
member in exploring the cohesion and
breakup of continental crust.
ACKNOWLEDGMENTS
We thank Belinda Smith Lyttle for GIS work
and Patti Durance, Ron Hackney, and Brendan
Murphy for comments. Formal reviews by Peter
Cawood, Jerry Dickens, and an anonymous ref-
eree greatly improved the focus and content. This
paper is based on work supported by New Zealand
Government core funding grants to GNS Science.
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