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Scientists have surveyed the lost continent of Zealandia in the South Pacific:
A team of 32 scientists from 12 countries returned last week from a nine-week voyage to study the once-lost continent of Zealandia in the South Pacific. This mostly submerged or hidden continent is an elevated part of the ocean floor, about two-thirds the size of Australia, located between New Zealand and New Caledonia. Scientists said earlier this year they thought Zealandia should be recognized as a full-fledged Earth continent. This was one of the first extensive surveys of the region, and the scientists who carried it out – affiliated with the International Ocean Discovery Program (IODP) at Texas A&M University – have just arrived back in Hobart, Tasmania, aboard the research vessel JOIDES Resolution. They said their work has already revealed that Zealandia might once have been much closer to land level than previously thought, providing pathways for animals and plants to cross between continents.
Little is known about Zealandia because it's submerged about two-thirds of a miles (more than a kilometer) under the sea. Until now, the region has been sparsely surveyed and sampled.
Scientists taking part in the 2017 expedition drilled deep into Zealandia's seabed at six sites in water depths of more than 4,000 feet (1,250 meters). They collected 8,000 feet (2,500 meters) of sediment cores from layers that record how the geography, volcanism and climate of the region have changed over millions of years.
Also at Smithsonian Magazine, The Guardian, and the JOIDES Resolution blog (drilling ship).
Zealandia: Earth's Hidden Continent (open, DOI: 10.1130/GSATG321A.1) (DX)
Previously: Geologists Spy an Eighth Continent: Zealandia
(Score: 2) by eravnrekaree on Wednesday October 04 2017, @02:00AM (1 child)
The earths crust is made of oceanic crust, which is mainly basalt, which contains a lot of metals and is heavier, as dense as the Magma. It is bouyant and easily subducted. The continental crust contains lighter rocks, with fewer metals, like granite. It is bouyant enough to not be subducted. Continental crust began as oceanic crust. My understanding is how things work is that oceanic crust is subducted. The crust sort of partially melts as it dives down into the mantle. The lighter elements float up as magma and intrude into overthrusting plate. This creates emplacements of granite and other light rocks in the overthrusting crust, increasing its bouyancy. It creates a chain of volcanic islands at the surface. Eventually subduction will pull this chain onto a continent, When the islands hit the continent, instead of subducting they end up getting docked onto the edge of the continent. The continent therefore grows. The continents are therefore made of aggregation of crust decreasing in age toward the edge of the continent. Since the continental crust is lighter, it floats higher and therefore can break the surface of the seas. Continental crust can be much older, is a variety ages, because it is not subducted. Oceanic crust is regularly recycled, there is no oceanic crust older than 200 million years (some of the oldest is in the Gulf of Mexico). Research has shown that the oldest continental crust is probably in Australia where a 4.4 billion zircon was found, the rock it came from could not be found but it was lodged in a 3.8 billion year old sandstone.
(Score: 2) by eravnrekaree on Wednesday October 04 2017, @02:25AM
Whoops, i meant to say the oceanic crust is not very bouyant, the continental crust is. Because the melting of subducting crust, happens in a way that only the lighter elements manage to float upward and into the overthrusting plate, the magma ends up poor in metals and is light, rocks such as granite. the continental crust contains a lot of light rock like granite. Continents do not generally grow by erosion. They grow by the accretion of the island arcs formed by plate subduction and island arc magmatism processes I mentioned that creates the chains of volcanos. An example of this is Japan which is brand new continental crust being created and will become a part of asia when it is pulled towards and collides with asia. the buoyancy of contintental crust and isostatic balancing is what keeps the higher profile of continental crust. It just floats higher than oceanic crust. Because its lighter.
Plants have only been around, by the way, since about 400 million years ago or whatever, on land anyway. So for most of earths history, there were no plants, going back to 4.5 billion years. Australia is 4.4 billion years old, the average age of continental crust is something like 1.5 billion years. So the continents survived without plants around.
There are sedimentary contributions from the collision of island arcs to the edge of the continents which forms coastal mountains, the erosion of such mointains that can supply sediment to the interior of the continents. Marine transgressions like zuni sequence have also built up sedimentary layers on continents. carbonate rocks like limestone are not from erosion materials. There is some effect of this in reversing the effects of erosion.