Researchers searching for why cold environmentalists mysteriously disappeared from geological records during the early stages of Earth’s evolution may have found the answer, and with it clues that could help locate important minerals today.
“Cold bloggers mysteriously disappeared from the Earth’s rock record between 1.8 and 1.2 billion years ago before reappearing after this time,” said Dr Derek Hasrock, Lecturer in the Department of Earth Sciences at the University of Adelaide.
“Cold eclogites are important because they are sensitive to temperatures in the upper mantle and provide evidence of rapid transport of rocks deep beneath the Earth’s surface along geological fault lines that occur when tectonic plates collide.
“The prevailing belief is that cold eclogites are only preserved when supercontinents merge. But there is ample evidence of a nearly continuous geological record of cold eclogites over the past 700 million years during which two supercontinents formed and separated.”
Eclogites are high-pressure metamorphic rocks composed primarily of chalcedony and omphasite (a sodium-rich type of pyroxene).
Associated with this change in eclogites is a change in the concentration of several trace elements in igneous rocks found elsewhere in the crust, which provides further evidence of subcontinental heating. These trace elements are found in important minerals. Vital minerals are vital to the economic well-being of the world’s major and emerging economies.
Lead author Dr. Renee Tamblyn worked with Dr. Hasrock and fellow researchers Professor Martin Hand and Ph.D. Student Matthew Gard from the University of Adelaide on the study published in the journal geology.
“We have found evidence from the chemistry of the trace elements of the granite that indicates a large-scale heating of the continents about 2 billion years ago that corresponds to the pool of Nuna, a supercontinent that completed its formation 1.6 billion years ago,” said Dr. Tamblyn. .
“Earth has generally been cold since its formation but Nuna has had an insulating effect on the mantle, like a thick blanket, causing subcontinents to warm temperatures and preventing the preservation of eclogites and changing the chemistry of the granites.
“Changes in chemistry resulting from this unusual warming during Earth’s geological past can help locate specific critical minerals by searching for rocks that formed before or after this heating event – depending on the element being searched for.”
Much of Western Australia is over 2 billion years old while southern Australia and the eastern states are generally younger.
Dr Hasrock said: “The rocks in the Northern Territory and North Queensland are a little older than 1.8 billion years, so it may be a place where we can continue our investigations into this mysterious geological state.”
New model suggests early Earth’s lost continents
R. Tamblyn et al, Mantle heating in California. 2 Ga by continental segregation: guides from granites and eclogites, geology (2021). doi: 10.1130/G49288.1
the quote: Geological Cold Case May Reveal Critical Minerals (2021, Sep 24) Retrieved on Sep 24, 2021 from https://phys.org/news/2021-09-geological-cold-case-reveal-critical.html
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