Zealandia: Earth may have brand new continent

Zealandia provides a fresh context in which to investigate processes of continental rifting, thinning, and breakup. Photo: AFP (Representational)

MELBOURNE: A hidden realm as big as the Indian subcontinent that is submerged under the Pacific Ocean deserves to be recognised as a new continent 'Zealandia', according to a new study released on Friday. The 4.9 million kilometre region of the southwest Pacific Ocean is made up of continental crust, researchers said. The region is elevated relative to surrounding oceanic crust, has diverse and silica-rich rocks and a relatively thick and low-velocity crustal structure. Its isolation from Australia and large area support its definition as a continent - Zealandia. Today it is 94 per cent submerged, mainly as a result of widespread Late Cretaceous crustal thinning preceding supercontinent breakup and consequent isostatic balance. According to researchers including those from Victoria University of Wellington in New Zealand and University of Sydney in Australia, 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. Zealandia provides a fresh context in which to investigate processes of continental rifting, thinning, and breakup. Earth's surface is divided into two types of crust, continental and oceanic, and into 14 major tectonic plates. 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 modelling aspects of plate tectonics at various scales. There have also been advances in 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 However, continents are Earth's largest surficial solid objects and it seems unlikely that a new one could ever be proposed, until now, researchers said. "The 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 continent - Zealandia," the researchers wrote in the study published in GSA Today. "This is not a sudden discovery but a gradual realisation; as recently as 10 years ago we would not have had the accumulated data or confidence in interpretation to write this paper," they said. Zealandia once made up nearly five per cent of the area of Gondwana. It contains the principal geological record of the Mesozoic convergent margin of southeast Gondwana and until the Late Cretaceous. 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.