Geologist Rose Turnbull was searching for microscopic zircon crystals in a lab at California State University in 2018 to solve the puzzle of Te Riu-a-Māui, the eighth continent of Zealandia. The crystals were mined from rocks found on the islands of New Zealand, one of the few areas in the almost two million square miles of Zealandia that rises above the ocean. The youngest, thinnest, and most submerged continent discovered to date is Zealandia. Turnbull and her colleagues found under the eastern edge of the South and Stewart Islands of New Zealand, a billion-year-old supercontinent.
Photo credit-www.forbes.com
The argument for Zealandia's continental status may be strengthened by this discovery, which raises the possibility that the continent is older than previously believed.
An old mystery regarding the geologic origins of the continent may be resolved by a recently discovered piece of ancient rock in Zealandia, Antarctica. A craton is a core of rock that is found on most continents. It is a geologic nucleus that is at least one billion years old. Geologically speaking, the earliest continental crust discovered on Zealandia dates to around 500 million years ago, which is rather young. We may be living on a continent if this recently discovered piece of old rock is indeed Zealandia's missing piece. The discovery adds to the greater mystery of how any continental crust, including Zealandia, came to be.
Finding the continent-
Scientists have been working on defining Zealandia as a continent for decades, but defining it has proven challenging due to the lack of a clear definition. The seafloor around New Zealand is composed of rocks rich in silica, such as granite, found in continental crust. The rocks span a large, thicker, and elevated area compared to the oceanic crust surrounding it. A team led by Nick Mortimer of New Zealand's GNS Science made a convincing case for calling Zealandia a continent in 2017. However, they noted the absence of any obvious craton.
Continental crust is more buoyant than oceanic counterparts, so it resists processes that recycle surface rocks back into the mantle. The stable cratonic nucleus of these rocks provides a foundation for continents to grow over time. Zealandia's oldest crust took shape around 500 million years ago, when the continent made up the edge of the supercontinent Gondwana. A new study focuses on 169 samples from New Zealand's South and Stewart Islands, revealing hints of older rocks, including bits of the mantle as old as 2.7 billion years.
The story in the Crystals-
Researchers have shown that some of the zircons found in the southern islands of New Zealand date back 1.3 billion years, and that they were most likely formed by magma pockets during a worldwide collision. The zircons also provide evidence of Zealandia's breakup from its parent supercontinent because of the low amounts of the oxygen isotope O-18. Under Rodinia, a heated mantle plume caused the development of these crystals.
An infant continent-
Zealandia's crust is older than previously thought, but younger than its continental cousins. All major continents host rocks over 3 billion years old. The study's conclusions come from traces below, not pieces of Rodinia in hand, so there's uncertainty in the precise steps leading to the chemistries found. More work is needed to bring the picture of Zealandia's origins into focus.
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