petrographic evidence. Evidence of UHP metamorphism: garnet inclusions and exsolution mineralogy. (A) Numerous orthogonal inclusions comprising carbonates (calcite, aragonite, dolomite, and calcite Mg), graphite, and microdiamonds. (B) Radial decompression fractures around the quartz that are interpreted to have formed after coesite. Fractures filled by posterior chlorite. (C) Crystallographically controlled oriented inclusion trails and rutile exsolution. (D) Numerous exsolution needles of rutile and apatite. (E) Apatite and rutile exsolution flakes. (F) Amphibole exsolution slides. (G and H) Slats of quartz exsolution. qtz, quartz; Coes, coesita; Mdia, microdiamond. Credit: Progress of science (2022). DOI: 10.1126/sciadv.abo2811
Science Advances (2022). DOI: 10.1126/sciadv.abo2811″ width=”800″ height=”530″/>
A trio of researchers from James Cook University, in collaboration with a colleague from the University of Adelaide, have found metamorphic diamonds in rocks near the northeast coast of Australia. In his article published in the journal Progress of scienceAlexander Edgar, Ioan Sanislav, Paul Dirks and Carl Spandler describe how they found the tiny diamonds and why they believe the find will help reveal more about Australia’s early history and formation.
Metamorphic diamonds are very rare, they only form in very specific places. They are also very small, from microscopic to nanometric. Single diamonds are formed in subduction zones鈥擳he pressure of opposing plates grinding against each other over millions of years results in the creation of diamonds so small they cannot be seen with the naked eye, which is why they are so rarely found. They have only been found in six other places on Earth. In this new effort, the researchers found a bunch of them inside rocks along the Clarke River Fault, which occurred when crustal blocks coalesced about 500 million years ago.
The researchers began to investigate the rocks throughout the fault line after one of their students told them some stone formations they had observed that seemed to have been revealed when one of the tectonic plates he pushed them above the surface of the ground around him.
The researchers ventured to the site and collected some of the rocks and brought them back to their lab for study. There they cut them into very thin slabs and used Raman spectroscopy to help identify the minerals they contained. In doing so, they found evidence of silica, amphibole, apatite, rutile sheets, coesite, quartz, and most importantly, metamorphic diamonds.
The researchers note that the diamonds they observed were the first to be found in the Gondwana-Pacific part of the Terra Australis Orogen. They also suggest that because metamorphic diamonds can only be created under very specific conditions, studying them and the places where they are found could provide more clues about how Australia formed.
Alexander Edgar et al, Gondwana Northeast Margin Metamorphic Diamond: Paradigm-Shifting Implications for One of Earth’s Largest Orogens, Progress of science (2022). DOI: 10.1126/sciadv.abo2811
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Citation: Discovery of metamorphic diamonds in northeast Queensland could provide clues to how Australia formed (July 29, 2022) Retrieved July 30, 2022 from https://phys.org/news/2022-07-discovery- metamorphic-diamonds-northeast-queensland .html
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