South African Vredefort Crater May Have Once Been Filled By A Sea Of Magma
Amid the boundless plains of South Africa's Free State Province, lays the nigh other worldly Vredefort crater. At 187 miles across and roughly two billion years old, it is the oldest and largest impact crater, or crater caused by the impact of a meteorite, on Earth. And though the Vredefort crater has been relentlessly studied, new research published in a recent issue of the journal Geology suggests that a series of green-black rocks that have long been mistaken as residual geological material from the area before impact, may actually be the remains of a magma sea that once filled the crater.
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"It's like discovering a new rock type in the Grand Canyon," said study co-author Desmond Moser, a geochronologist at Western University in Ontario, Canada. "Vredefort has been walked over for 100 years."
When a meteorite hits a planet or moon, the temperature and pressure surrounding the point where the asteroid or comet hits are so high that large amounts of rock can be instantly melted. In the case of incredibly large meteorites like the one that caused the Vredefort crater, so much melt is produced that it forms a roiling pool of magma or melted rock in the central parts of the impact crater. Over time the pool of melt cools producing a variety of unusual crystalline and glassy igneous rocks. These early-formed rocks, like those made billions of years ago, are thought to erode relatively quickly.
This recent study is saying that these rocks haven't eroded — they've stuck around for longer than previously thought, right through to the present day. This is important because properly identifying these rocks as impact as opposed to local rocks means that should they show up in other locations we'll be able to better connect the dots between the two. Case in point: in the same issue of Geology, impact spherules, the molten droplets that are formed after an asteroid hits the earth, found in Karelia, Russia, are thought to have come from the Vredefort impact event. When combined with other evidence, this suggests that the distance from the impact site to where the rocks were ejected was roughly 1,500 miles. Today the distance from Karealia to Vredefort spans some 6,200 miles, potentially giving us improved insight into how the continents were arranged some two billion years ago, and when and how they drifted.
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