Massive meteorite impact created the hottest mantle rock ever
The hottest rock ever discovered in Earth’s crust, a fist-sized piece of black glass, was discovered in 2011 and was formed in temperatures reaching 2,370 degrees Celsius – hotter than much of the Earth’s mantle. A new analysis of minerals from the same site revealed that this record-scorching heat was real. The rocks melted and reformed in a meteorite impact about 36 million years ago in what is today Labrador, Canada. The impact formed a 17-mile-wide crater, where Michael Zanetti, then a doctoral student at Washington University in St Louis, picked up the glassy rock during a Canadian Space Agency-funded study of how to coordinate astronauts and rovers working together to explore another planet or moon.
The chance find turned out to be an important one. An analysis of the rock revealed that it contained zircons, extremely durable minerals that crystallise under high heat. The structure of zircons can show how hot it was when they formed. But to confirm the findings, researchers needed to date more than one zircon. In a new study, Gavin Tolometti, a postdoctoral researcher at Western University in Canada, and colleagues analysed four more zircons in samples from the crater. These came from varying types of rocks in different locations, giving a comprehensive view of how the impact
heated the ground. One was from a glassy rock formed in the impact, two others from rocks that melted and resolidified and one from a sedimentary rock that held fragments of glass formed in the impact.
Results showed that the impact-glass zircons were formed in at least 2,370-degree-celsius heat, as previously believed. In addition, the glass-bearing sedimentary rock had been heated to 1,673 degrees Celsius. This broad range will help researchers narrow down places to look for the most super-heated rocks in other craters.
The researchers also found a mineral called reidite within zircon grains from the crater.
Reidite forms when zircons undergo high temperatures and pressures. Their presence allowed the researchers to calculate the pressures experienced by the rocks in the impact. They found that the impact introduced pressures of between 30 and 40 gigapascals – just one gigapascal is over 101 million kilograms per square metre of pressure. This would have been the pressure at the edges of the impact. Where the meteorite hit the crust directly, rocks wouldn’t have just melted, but vaporised. The findings can be used for other craters on Earth, and elsewhere. The researchers hope to use similar methods to study rocks brought back from impact craters on the Moon during the Apollo missions.