Three years in the past, the identification of Zealandia as a continent made world headlines.
Now, newly revealed outcomes from our scientific drilling expedition reveal the largely submerged Zealandia continent, which stretches throughout 5 million sq. kilometres beneath the southwest Pacific Ocean, was formed by two tectonic occasions.
First it was ripped away from Australia and Antarctica, after which it was carved by forces that began the Pacific Ring of Hearth.
Why Zealandia is so totally different to different continents
Zealandia has an uncommon geography for a continent. Greater than half the floor space of Earth’s different six continents are composed of low-lying land and shallow seas, they usually have comparatively slim mountain ranges and steep continental slopes within the deep ocean.
In distinction, Zealandia is generally hidden beneath a couple of kilometre (zero.6 miles) of water and could possibly be labeled as greater than 90 % continental slope. This makes it a problem to discover.
The primary scientific drilling expedition to pattern within the space the place we now know Zealandia is befell in 1972 between Australia, New Zealand and New Caledonia.
The outcomes recommended tectonic forces stretched and thinned Zealandia’s crust till it was ripped from the traditional supercontinent Gondwana about 85 million years in the past, in the course of the time of dinosaurs. This created a deep ocean: the Tasman Sea.
The proof stays compelling that that is not less than a part of the reply to how the geography of Zealandia shaped. However detailed surveys in the course of the 1990s and 2000s, carried out to determine sovereignty over the Zealandia continental mass by New Zealand, Australia and France, recommended different contributing elements.
How the Pacific Ring of Hearth formed Zealandia
In 2017, we led a nine-week expedition into the southwest Pacific as a part of the Worldwide Ocean Discovery Program (IODP), with 32 scientists on board the analysis vessel JOIDES Decision.
Our intention was to unravel why Zealandia is so totally different from the opposite continents.
Our newly revealed outcomes have been drawn from that expedition 371, the place we collected new samples and sought to check our speculation that formation of the Pacific Ring of Hearth performed a key function in shaping Zealandia.
We collected sediment cores from as much as 864 metres (2,834 toes) beneath the seabed at six websites far-off from land or shallow water.
On the deepest web site, the water was 5 km (three.1 miles) deep and our drill weighed 300 tonnes. We used fossils from three of the websites to indicate northern Zealandia grew to become a lot shallower and sure even had land areas between 50 and 35 million years in the past.
At about that point, two different websites grew to become submerged into deeper water, after which the entire area subsided a further kilometre to its current depth.
These dramatic modifications in northern Zealandia, an space in regards to the measurement of India, coincided with buckling of rock layers (often called strata) and the formation of underwater volcanoes all through the western Pacific.
The Pacific Ring of Hearth is a zone of volcanoes and earthquakes working alongside the west coasts of north and south America, previous Alaska and Japan, after which by means of the western Pacific to New Zealand.
The violent geological exercise on this zone displays deeper unrest on the boundaries of tectonic plates, attributable to “subduction processes” – the place one tectonic plate converges on one other and sinks again deep into the earth.
We all know the Pacific Ring of Hearth shaped about 50 million years in the past, however the course of stays a thriller. We suggest a “subduction rupture occasion” – a course of related to an enormous slow-moving earthquake – unfold round the entire of the western Pacific at the moment.
We recommend this course of resurrected historical subduction faults, which had lain dormant for a lot of thousands and thousands of years however have been primed to start out shifting once more.
This idea of “subduction resurrection” is a brand new thought and should assist clarify a variety of various geological observations. The subduction rupture occasion included distinctive geological phenomena that that don’t have any present-day comparability, and there could have been fewer than 100 such large occasions since Earth shaped.
Our new proof from Zealandia reveals these occasions can dramatically alter the geography of continents.
What have been the implications of those geographic modifications for vegetation, animals and regional local weather? Can we make a pc mannequin of the geological processes that occurred at depth? We’re nonetheless figuring a few of this out, however we do know the occasion modified the course and pace of motion of most tectonic plates on Earth.
It was an occasion of actually world significance – and we now have actually good observations and concepts to assist us resolve what occurred and why.
Rupert Sutherland, Professor of tectonics and geophysics, Te Herenga Waka-Victoria College of Wellington and Gerald Dickens, Professor, Rice College.
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