Researcher confirms the hottest rock ever recorded

Zircon with baddeleyite rim maintain cubic zirconia directions. Credit: University of Western Ontario

If there was any doubt that a 2011 discovery by a postdoctoral student was indeed the hottest rock on Earth, new findings from a Western-led research team demolish that uncertainty.

Eleven years after researchers from the West discovered what at the time was considered the hottest rock on Earth, a recent study found four additional grains of zircon – a hard mineral generally known as a substitute for diamond – that confirmed the rock’s previous 2,370°C warming. . .

The study published in the journal Earth and Planetary Science Letters, led by geosciences postdoctoral student Gavin Tolomiti and co-authors: Timmons Erickson of NASA’s Johnson Space Center, Gordon Osinsky and Catherine Nesch of the Earth Sciences Division; and Kiron Cyril of the Thermomechanical Metallurgy Laboratory.

In 2011, then Ph.D. Student Michael Zanetti was working with Usinski in the crater of Lake Mistastin in Labrador when he found a glass boulder with tiny zircon grains frozen inside. Those rocks were later analyzed and found to have formed at a temperature of 2370°C as a result of an asteroid impact. These results were shared in a study published in 2017.

In their own study using samples collected between 2009 and 2011, Tolomiti and colleagues were able to find four additional zircon grains that validated the 2011 discovery. They also located and found evidence at a different location within the same shock structure that molten rocks – rocks that Formed after rock and soil melted into liquid after a meteorite impact – they were heated differently in more than one location, to a greater degree than my previous theory.

“The biggest impact is that we get a much better idea of ​​how hot these melt rocks, which were initially formed when the meteorite hit the surface, give us a better idea of ​​the history of the melt and how they cooled in this particular crater.”

“It could also give us insight into studying temperature and melting in other impact craters.”

Tolomiti also noted that most of the preserved evidence, such as glass samples and impact melt samples, were found near the crater floor. By applying this knowledge to other archaeological pits, researchers may be able to find more evidence for the temperature conditions found in other craters but in less comprehensive studies.

“We’re starting to realize that if we want to find evidence of warming, we need to look at specific areas rather than randomly choosing across the entire crater,” he said.

Other discoveries

The paper also noted that this is the first time redite – a mineral formed when zircon is exposed to high pressures and temperatures – has been discovered at this site. The team found three rosettes still preserved in the zircon grains, evidence of two more before but crystallizing when temperatures exceeded 1,200 degrees Celsius, at which point the redite is no longer stable.

This mineral allows the researchers to better constrain pressure conditions indicating that there may have been a peak pressure condition around 30 to more than 40 GPa. These are the pressure conditions that arose when the meteorite hit the surface at that time. The closer something is to the impact event, the greater the pressure. Some minerals that have been greatly compressed by this event – referred to as shock – leave behind structures that can be studied.

“Looking at the size of reddits in our samples, we knew the minimum pressure they recorded was probably around 30 GPa. But because there’s a lot of reddit inside some of these grains, we know it could be above 40 GPa,” Tolomiti explained.

This provides a better idea of ​​how much pressure was created outside the melting region when the meteorite hit the surface. The melting zone will, hypothetically, have pressures above 100 gigapascals, at which point the rocks will either completely melt or evaporate outside of these conditions.

Expand your search

The research group plans to extend this work to other impact craters on Earth. some Ph.D. Students will work with Osinski to look at other craters such as Lac Wiyâshâkimî (Clearwater West crater) in Quebec. Tolometti is also looking to expand this work and take a look at the Apollo lunar samples brought back to Earth, which have plenty of evidence for formation from impact craters.

“If we find evidence of microstructures in zircon or other grains under pressure conditions, we can get a much better idea of ​​the impact of craters on the Moon,” he said.

“It could be a step forward in trying to understand how the rocks were modified by impact impact across the entire solar system. This data can then be applied in impact models to improve the results we get.”

Transformations to granular zircon revealed: Meteor Crater, Arizona

more information:
GD Tolometti et al, Hot rocks: thermal conditions of Lake Mistastin constrain the effect of sediment melt using zircon grain microstructures, Earth and Planetary Science Letters (2022). DOI: 10.1016 / j.epsl.2022.117523

Thames et al. Nicholas E. Thames et al., Cubic zirconia records in impact melt >2370 °C the Earth’s hottest crust, Earth and Planetary Science Letters (2017). DOI: 10.1016 / j.epsl.2017.08.012

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