MOSCOW, Oct 7, Tatyana Pichugina . Scientists say that New Zealand is only a small part of a huge fragment of Gondwana, almost completely hidden in the ocean. In recent years, thanks to sea expeditions and satellite data, they have not only built a detailed map of the seventh continent — Zealand, but also explained its sharp dive under water.
The Gondwana Split
Hundreds of millions of years ago on Earth there was a giant supercontinent called Gondwana, which united Africa and South America, Antarctica and Australia. Gradually, under the influence of processes within the planet, Gondwana disintegrated. About 80 million years ago, in the Cretaceous period, when dinosaurs still roamed the land, the eastern edge of the supercontinent experienced a powerful stretch, it was literally torn into blocks: Antarctica, Australia and the easternmost part — Zealand.
About the seventh continent, geologists have been talking since the 19th century. This was indicated by ancient rocks on the islands of New Zealand and neighboring archipelagos, characteristic of continents — shales, granites, greywackes (very hard sandstones).
In articleIn 2003, New Zealand scientist Nick Mortimer, who devoted his life to exploring this region and proving the existence of the seventh continent, wrote that expeditions lifted continental rocks from the Campbell and Challenger sea plateaus, located on both sides of New Zealand. This made it possible to roughly outline the boundaries of the block and estimate its area.
Discovery of Zealand
Up to 95 percent of Zealand is hidden under water. Scientists have been accumulating data from sea expeditions and satellites for many years and have finally reconstructed a picture of this section of the earth’s crust.
In 2014, Mortimer and his colleague Hamish Campbell published the book “Zealand: We Discovered the Continent,” and later several years ago, an article by a large team of authors in GSA Today with detailed evidence created a worldwide sensation.
«Zealand is an example of how something big and obvious can be overlooked. Based on a large amount of data obtained mainly in the last two decades, we have established that Zealand is not sea islands, but an entire continent with an area of five million square kilometers «, the scientists write. Zealandia is comparable to India, which was also part of Gondwana. It is the youngest and thinnest continent.
Zealand has plains, mountains, plateaus, depressions and shelves. Only this is all under water. The mainland is separated from Australia by the Tasman Sea, which filled a large rift in the earth's crust that stopped about 50 million years ago. Thus, Zealand is the youngest continent on the planet.
The oldest rocks discovered here were formed half a billion years ago. Researchers hope to find older ones, like on other continents. This is indicated by dating based on the ratio of radioactive isotopes in detrital zircons and inclusions of mantle melts — older than 2.5 billion years.
Continents are very ancient blocks of the earth's crust, composed of repeatedly processed granites and gneisses, covered on top with thick layers of sedimentary rocks. Thickness — 30-45 kilometers. They seem to float in the middle of young, heavy and thin basalt slabs.
Zealandia is about three times thinner. Although, according to geophysical data, in some places the thickness reaches 30 and even 40 (on the South Island of New Zealand) kilometers, on average — 18 kilometers. This oddity was explained by Russian scientists. In an article published in the Proceedings of the Academy of Sciences, they analyzed data from offshore drilling and concluded that after separation from Australia, Zealand, for example, in the area of the Lord Howe Rise, was much less drowned and even drained.
The authors draw attention to the similarity with the Lomonosov Ridge in the Arctic Ocean, which is considered a continuation of Eurasia. There is the same thin foundation and three to four kilometers under water. “Both areas were located near sea level for a long time, and then experienced rapid subsidence to great depths,” the scientists note. If we were talking about the ocean floor, then a sharp subsidence and thinning would follow a strong stretching of the earth's crust — by about 30 percent. But in the case of Zealand and the Lomonosov Ridge, another mechanism was at work — compaction of crustal rocks in the lithospheric layer due to the penetration of mantle fluids there. This can explain the deep depressions in the Gulf of Mexico, the Caspian Sea, and the northern Barents Sea.
Map of the seventh continent
For geologists, the existence of the seventh continent is a practically resolved question; whether geographers recognize it and put it in textbooks is not so important. The main thing is to study the region and its history in detail. Marine expeditions help with this, where they take rock samples from great depths and carefully analyze them. Thus, scientists from New Zealand and Canada discovered traces of deep melt, which was introduced into the strata during the collapse of this part of Gondwana. And the melt is similar in composition to that found at the roots of ancient continents. This is another argument in favor of the reality of Zealandia.
In a new paper, Mortimer and his colleagues completed a detailed geological map of the continent and were able to more accurately describe the breakup of Gondwana. According to them, about 100 million years ago the united Australia and Antarctica separated, while Zealandia was still connected to western Antarctica. They separated for about two tens of millions of years, which led to severe thinning of the continent’s base and flooding.