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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 and Müller, 2010). Other proposed controls
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 (Fig. 1), Zealandia is the youngest, thinnest,
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
www.geosociety.org/gsatoday
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
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.
REFERENCES CITED
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indicate a possible Precambrian basement under
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