It's said that time heals all wounds, and apparently that even applies to wounds on the Earth itself. Woodleigh Crater in Western Australia could be one of the largest impact craters on the planet, but getting an exact measure is hard when there's hundreds of millions of years of dirt and rock swept over the top of it. But now, researchers from Curtin University have discovered new evidence that the crater could be bigger than previously thought – thanks to the presence of one of the rarest minerals ever found.
The Woodleigh Crater is believed to have formed during the Late Devonian period about 360 million years ago, but nailing down its size is difficult because it isn't exposed at the surface. Estimates have placed its diameter anywhere from 60 to 160 km (37.3 to 99.4 mi), and if it's found to be towards the upper end of that scale, it would be the largest crater in Australia and one of the largest in the world.
But rather than breaking out the tape measure, the Curtin researchers found new evidence while studying the geology of the impact site. In core samples drilled from the center of the crater, the team found reidite, a mineral that's so incredibly rare it's only been found in five other places around the world.
The common factor for all six of these locations? They're all impact craters. Reidite is only formed when the zircon in the Earth's crust is subjected to extreme pressure of over 30 gigapascals (GPa), which can be reached in the event of an asteroid or comet impact. In this case, the team discovered the reidite in a region of the crater called the central uplift, where deeper rock is pushed towards the surface by the impact.
"Central uplifts are desirable targets for learning about impact conditions," says Aaron Cavosie, an author of a study describing the discovery. "They bring profoundly damaged rocks closer to the surface, and in some instances, are associated with exploration targets. Finding reidite at Woodleigh was quite a surprise as it is much rarer than diamonds or gold, though unfortunately not as valuable."
Along with the reidite, the team found formations called deformation twins. These features are only created when zircon grains are shocked in an impact, and their presence at Woodleigh backs up the idea that it's larger than thought.
"Previous research estimated the size of the impact crater between 60 km (37 mi) and more than 120 km (75 mi) in diameter," says Morgan Cox, an author of the study. "However, our discovery of reidite near the base of the core suggests a larger crater. The research team is now using numerical modelling to refine the size of Woodleigh and if we establish its diameter is greater than 100 km (62 mi), it would be the largest-known impact crater in Australia."
The research was published in the journal Geology.
Source: Curtin University