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thickness, as well as plate tectonics (e.g., Figure 3. Present day map of CRUST1.0 crustal thickness (Laske et al., 2013) showing the dispersed
Kearey et al., 2009). The existence of Gondwana continents of Australia, Zealandia, East and West Antarctica, and South America. Note
positive bathymetric features north and thin continental crust in vicinity of Mesozoic arc. M—Marion Plateau; R—Ross Sea; W—Weddell Sea;
south of New Zealand has been known for F—Falkland-Malvinas Plateau. LIP abbreviations: KP—Kerguelen Plateau; OJP—Ontong Java Pla-
more than a century (Farquhar, 1906). The teau; MP—Manihiki Plateau; HP—Hikurangi Plateau. Thick coastlines in Antarctica are isostatically
accuracy and precision of seafloor map- corrected ice-free coastlines (Jamieson et al., 2014). Orthographic projection.
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 Batholith and Haast Schist are parts, can be orogenic belts on which a broad exten-
tracked through onland New Zealand and sional province and several narrow rift
By itself, relatively high elevation is not across Zealandia (Fig. 2). Thus, there is a zones have been superimposed (Mortimer
enough to establish that a piece of crust is predictable regional coherency and conti- and Campbell, 2014).
continental. Oceanic large igneous prov- nuity to the offshore basement geology.
inces such as the Ontong Java Plateau Atop its geological basement rocks,
(Fig. 1; Coffin and Eldholm, 1994) are Traditionally, continents have been sub- Zealandia has a drape of at least two dozen
elevated but not continental. Rocks of the divided into cratons, platforms, Phanerozoic spatially separate Late Cretaceous to
modern oceanic crust typically comprise orogenic belts, narrow rifts, and broad Holocene sedimentary basins. These typi-
basalt and gabbro of Jurassic to Holocene extensional provinces (Levander et al., cally contain 2–10-km-thick sequences of
age. In contrast, continents have diverse 2005). Eurasia, Africa, North America, terrigenous and calcareous strata (Zealandia
assemblages of Archean to Holocene igne- South America, Antarctica, and Australia Megasequence of Mortimer et al., 2014) and
ous, metamorphic, and sedimentary rocks, all contain Precambrian cratons. The old- include a widespread continental breakup
such as granite, rhyolite, limestone, quartz- est known rocks in Zealandia are Middle unconformity of ca. 84 Ma age (Bache et
ite, greywacke, schist, and gneiss, arranged Cambrian limestones of the Takaka al., 2014). The Zealandia Megasequence
in orogenic belts and sedimentary basins. Terrane and 490–505 Ma granites of the provides a Zealandia-wide stratigraphic
Jacquiery Suite (Mortimer et al., 2014). record of continental rifting, and marine
Essential geological ground truth for Precambrian cratonic rocks have not yet transgression events, similar to that seen in
Zealandia is provided by the many island been discovered within Zealandia, but formerly conjugate east Australian basins
outcrop, drill core, xenolith, and seabed their existence has been postulated on the (Blewett, 2012).
dredge samples of Paleozoic and Mesozoic basis of Rodinian to Gondwanan age
greywacke, schist, granite, and other sili- detrital zircon ratios (Adams and Griffin, Crustal Structure
ceous continental rocks that have been 2012). Furthermore, some Zealandia man-
found within its limits (Fig. 2). Many of tle xenoliths give Re-Os ages as old as Continental crust varies considerably
these have been obtained from expeditions 2.7 Ga (Liu et al., 2015). Geologically, in thickness and physical properties.
in the past 20 years (see Fig. 2, caption). Zealandia comprises multiple Phanerozoic Christensen and Mooney (1995) give an
Orogenic belts, of which the Median average P wave velocity of 6.5 km-1 and

30 GSA Today | March–April 2017