Vredefort Crater - Formation and Structure

Formation and Structure

The asteroid that hit Vredefort is estimated to have been one of the largest ever to strike Earth (at least since the Hadean eon some four billion years ago). The asteroid is thought to have been approximately 5–10 km (3.1–6.2 mi) in diameter. The bolide that created the Sudbury Basin could have been even larger.

The crater has a diameter of roughly 250–300 km (160–190 mi), larger than the 200 km (120 mi) Sudbury Basin and the 170 km (110 mi) Chicxulub Crater. This makes Vredefort the largest known impact structure on Earth. If the Wilkes Land Crater in Antarctica is an impact crater, then it is the largest known at 500 km (310 mi) in diameter.

The Vredefort Crater's age is estimated to be 2.023 billion years (± 4 million years), which places it in the Paleoproterozoic era. It is the second-oldest known crater on Earth, a little less than 300 million years younger than the Suavjärvi Crater in Russia. In comparison, it is about 10% older than the Sudbury Basin impact (at 1.849 billion years).

The dome in the center of the crater was originally thought to have been formed by a volcanic explosion, but in the mid-1990s, evidence revealed it was the site of a huge bolide impact, as telltale shatter cones were discovered in the bed of the nearby Vaal River.

The crater site is one of the few multiple-ringed impact craters on Earth, although they are more common elsewhere in the Solar System. Perhaps the best-known example is Valhalla Crater on Jupiter's moon Callisto, although Earth's Moon has a number, as well. Geological processes, such as erosion and plate tectonics, have destroyed most multiple-ring craters on Earth.

The nearby Bushveld Igneous Complex (BIC) and Witwatersrand Basin were created during this same period, leading to speculation that the Vredefort bolide's mass and kinetics were of sufficient magnitude to induce regional volcanism. The BIC is the location of most of the world's known reserves of platinum group metals, while the Witwatersrand basin holds most of the known reserves of gold.