In 2017, groundbreaking research by GNS scientists confirmed that Te Riu-a-Māui / Zealandia is indeed Earth’s hidden eighth continent, defined by its thick, varied crust, vast size, and geographic isolation from Australia. However, only 5% of Zealandia rises above the ocean’s surface, making exploration a significant challenge. A major step came when an international team embarked on a pre-2017 expedition to gather seabed rock samples near New Caledonia.
Now, in 2023, these samples have unveiled transformative findings: the mapping of North Zealandia’s full geology, the discovery of a massive volcanic region linked to the breakup of the Gondwana supercontinent, and confirmation of Zealandia’s 4,000 km-long granite backbone. These insights illuminate Zealandia’s dramatic geological past and lay the groundwork for ongoing research into its unique evolution.
Size and mapping of Zealandia
Te Riu-a-Māui / Zealandia spans approximately 4.9 million square kilometres and stretches 4,300 km in length. Mapping Zealandia‘s extensive submarine shelves was challenging, as 95% of its area lies underwater. This made it the last continent to be fully charted to its submerged boundaries, encompassing its geology, volcanic zones, and sedimentary basins.
North Zealandia’s geological mapping
Building on a 2019 GNS study that detailed the 1.5 million square kilometres of South Zealandia, the 2023 publication in Tectonics shifted focus to North Zealandia, mapping the region between New Zealand, New Caledonia, and Australia. This achievement marks a global first, as Zealandia is now the only continent fully mapped to its underwater limits.
Volcanic region led to Gondwana’s breakup with Zealandia
The 2023 findings uncovered a massive volcanic zone that developed during Zealandia’s separation from Gondwana between 100 and 60 million years ago. Lead author Nick Mortimer noted the scale of magma eruptions across Zealandia, while co-author Wanda Stratford emphasised that previous research underestimated magma’s role in the supercontinent’s breakup. This volcanic area spans 250,000 square kilometres, roughly the size of New Zealand itself, and was identified using magnetic field data.
Rock samples from Fairway Ridge near New Caledonia revealed granite formations belonging to a 4,000 km-long geological feature called the Median Batholith. This granite belt, aged between 250 and 100 million years, forms Zealandia’s backbone and connects its underwater and terrestrial components. The study’s dating and chemical analysis solidified these links.
Zealandia: Ongoing research and future implications
While Zealandia has been fully mapped, there is still much to explore, including the timing, causes, and mechanisms behind its significant geological changes. This comprehensive framework supports further research on New Zealand’s natural hazards, resources, and environment.
The 2016 ECOSAT II expedition, which collected vital seabed samples, was funded by the Australian government and led by University of Sydney geoscientists. The latest paper was supported by the New Zealand Government and the Royal Society of New Zealand’s James Cook Fellowship awarded to Nick Mortimer.
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