You might think you know all the continents, but what about Zealandia? In 2017, a previously unknown contingent of the shores of New Zealand was discovered - making headlines globally. Zealandia, known as Te Riu-a-Maui in the Maori language, covers more than 5 million square kilometres, making it twice the size of the subcontinent of India.
You may be wondering why, then, was it not discovered sooner? The reason is that 95 per cent of its area is submerged beneath the southwest Pacific Ocean, disappearing long before humans existed on Earth. Only a large mountain chain (the two islands of New Zealand) and some small oceanic islands are visible on the surface.
Little is known about the recently discovered continent, mainly due to it being almost completely inaccessible. However, a team of geologists from all over the world have compiled a new geological map containing Zealandia. The map was formed using a combination of rock samples recovered from the sea and geophysical mapping methods.
Geologists discovered large sandstone formations and deposits of basaltic rock pebbles, following the outer margins of Zealandia as they searched for samples. The sandstones are believed to be around 95 million years old and contain older granite and volcanic pebbles, suggesting that when Zealandia was dry land the rivers flowing from volcanic highlands filled up tectonic basins. The highlands were an active volcanic range at least 30 to 50 million years earlier but were likely eroded when the sandstone was deposited.
Geologists believe that Zealandia was gradually flooded around 40 million years ago, thanks to the discovery of the basalt pebbles, which are associated with underwater volcanism.
The study 'Reconnaissance basement geology and tectonics of North Zealandia' was published in the journal Tectonics (2023).
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