From CSIRO via SCI NEWS: “Meet Zealandia, Earth’s New Continent”

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Commonwealth Scientific and Industrial Research Organisation

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Feb 14, 2017
Natali Anderson

Zealandia — a 4.9 million km2 region of the southwest Pacific Ocean — was once part of the ancient supercontinent Gondwana and today it is 94% submerged, according to a research team led by New Zealand’s geoscience agency GNS Science.

Based on various lines of geological and geophysical evidence, particularly those accumulated in the last two decades, Nick Mortimer et al argue that Zealandia is not a collection of partly submerged continental fragments but is a coherent 4.9 million km2 continent. 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. Image credit: Nick Mortimer et al, doi: 10.1130/GSATG321A.1.

Most people view the continents and oceans as discrete entities of land and water across Earth’s surface. However, even a cursory look at our world establishes the problem.

Are North America and South America truly separate continents with their connection through the Isthmus of Panama? Where and why does one distinguish Europe, Africa, and Asia considering the Bosphorus and Sinai Peninsula?

One might suggest a geological reason: continents are large, identifiable areas underlain by continental crust.

A new paper by GNS Science geologist Dr. Nick Mortimer and co-authors follows this idea, but then throws a fascinating twist on the subject: Zealandia.

“Several islands, notably New Zealand and New Caledonia, are connected by submerged continental crust across a large area of Earth’s surface,” the authors explained.

“This region has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure.”

“Its isolation from Australia and large area support its definition as a continent — Zealandia,” they said.

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. Image credit: Nick Mortimer et al, doi: 10.1130/GSATG321A.1.

Zealandia is approximately the area of greater India and, like India, Australia, Antarctica, Africa, and South America, was a former part of Gondwana.

As well as being the seventh largest continent, Zealandia is the youngest, thinnest, and most submerged.

“The identification of Zealandia as a geological continent, rather than a collection of continental islands, fragments, and slices, more correctly represents the geology of this part of Earth,” the scientists said.

“Currently used conventions and definitions of continental crust, continents, and microcontinents require no modification to accommodate Zealandia.”

Roughly 94% of the area of Zealandia currently is submerged.

“It is not unique in this regard: an ice-free, isostatically corrected West Antarctica would also largely be submerged,” Dr. Mortimer and his colleagues said.

“Zealandia and West Antarctica were formerly adjacent to each other along the southeast Gondwana margin 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.”

Zealandia once made up approximately 5% of the area of the supercontinent Gondwana, according to the team.

“It contains the principal geological record of the Mesozoic convergent margin of southeast Gondwana and, until the Late Cretaceous, lay Pacificward of half of West Antarctica and all of eastern Australia,” the researchers said.

“Thus, depictions of the Paleozoic-Mesozoic geology of Gondwana, eastern Australia, and West Antarctica are both incomplete and misleading if they omit Zealandia.”

“The importance of Zealandia is not so much that there is now a case for a formerly 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,” they added.

“Zealandia illustrates that the large and the obvious in natural science can be overlooked.”

The paper was published online first in the journal GSA Today on February 8, 2017.

See the full article here .

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