Back in 2011, a glass rock containing small zircon grains was discovered by University of Western Ontario researcher Michael Zanetti, but it was in 2017 when the rock was first reported in the journal Earth and Planetary Science Letters. The rock, discovered in Mistastin Lake crater in Canada, was found to reach 4,298 degrees Fahrenheit (2,370 degrees Celsius) resulting from an asteroid impact.
And now, a new study used the samples that were gathered between 2009 and 2011 and confirmed the record-breaking heat of the stone. The rocks are known to be formed during a meteorite impact that also formed the Mistastin Lake crater approximately 36 million years ago. The results of the study that confirms the indications of the 2017 study have been published in the journal Earth and Planetary Science Letters on April 15th.
The 17-mile-wide (28 kilometers) Mistastin Lake crater shows similarity to Moon craters, therefore, it is often used as a stand-in for space research. The rocks were also discovered during such an occasion when researchers from Washington University St. Louis were conducting a study on the coordination and astronauts and rovers working together.
As a result of this coincidental discovery, it has been found that the rock contains zircons, an incredibly durable mineral that condenses under high heat. Additionally, the researchers have found a mineral called reidite that forms in the condition of zircons undergoing high temperatures and pressures.
Minimum peak shocks from 30 to 40 gigapascals
Reidite allows researchers to estimate the level of pressure - estimated between 30 and 40 gigapascals - caused by the impact. “Considering how big the reidite was in our samples, we knew the minimum pressure it probably recorded was about 30 gigapascals. But since there are a lot of reidites still present within some of these grains, we know that it could even be above 40 gigapascals,” said Gavin Tolometti, a postdoctoral student at the University of Western Ontario, in a statement.
“The biggest implication is that we are getting a much better idea of how hot these impact melt rocks are, which initially formed when the meteorite struck the surface, and it gives us a much better idea of the history of the melt and how it cooled in this particular crater,” Tolometti added.
The results of this research may be used to study different craters brought from other planets, especially the Moon.
The production of superheated melt during hypervelocity impact events has been proposed to be a common occurrence on terrestrial planetary bodies. Recent direct evidence of superheated impact melt temperatures exceeding >2370°C from the Kamestastin (Mistastin Lake) impact structure, Canada, was based on a single impact glass sample. Such high superheated melt temperatures have strong implications for the evolution of crustal material, the thermal history of impact cratering events, and the rheology of impact melt. However, although widely predicted in previous studies, with the exception of the Mistastin Lake impact glass, there is little direct evidence for superheated temperatures in multiple settings across an impact structure. Therefore, an outstanding question is how heterogeneous are superheated conditions across a single impact structure. In this work, we analyze the crystallographic orientations and microstructures of zircon grains and the precursor parent phases of baddeleyite crystals, from four different samples representing the entire melt-bearing stratigraphy at Mistastin: an impact glass, a vesicular clast-poor impact melt rock, a clast-rich impact melt rock, and a glass-bearing impact breccia. Using electron microprobe analysis followed by electron backscatter diffraction, we discovered that four zircon grains with vermicular coronae of baddeleyite crystals from the impact glass contain evidence for a cubic zirconia precursor, indicative of temperature conditions >2370°C. We also report evidence of superheating up to 1673°C in the glass-bearing impact breccia. In addition, we also report the first occurrence at Mistastin of the high-pressure zircon polymorph reidite and former reidite in granular neoblastic (FRIGN) zircon in grains from the glass-bearing impact breccia, implying minimum peak shocks from 30–40 GPa. The identification of superheating from two localities at Mistastin demonstrates (1) that superheating is not restricted solely to rapidly cooled impact melt rock samples and is, therefore, more distributed across impact structures, and (2) we can investigate the P-T evolution pathways of impact melt from different impact settings, providing a clearer picture of the thermal conditions and history of the impact structure.