Morokweng

Morokweng Impact Structure

The Morokweng impact structure is a vast, buried geological feature located in South Africa's North West province, near the town of Morokweng and close to the border with Botswana. Its immense size and the rare discovery of asteroid fragments make it a significant site for scientific study.

Description and Discovery

First identified in 1994, the Morokweng structure was detected through magnetic and gravimetric surveys, as it is not exposed at the surface but lies buried beneath the Kalahari Desert. Estimates of its diameter vary, with some studies suggesting figures ranging from 75 to over 240 kilometers. More recent analyses, combining borehole petrographic data with national gravity and airborne magnetic field imagery, point to a likely diameter of approximately 190 kilometers. The impact event is dated to 146.06 ± 0.16 million years ago, placing it firmly within the Tithonian stage of the Late Jurassic period, just before the transition to the Cretaceous.

The Impacting Asteroid and Its Remains

Core samples indicate that the impact was caused by an L chondrite asteroid, estimated to have been between 5 and 10 kilometers in diameter. A remarkable discovery occurred in May 2006 when a group of scientists drilling into the site unearthed a 25-centimeter-diameter fragment of the original asteroid at a depth of 770 meters. The presence of such substantial fragments was unexpected, as it was generally assumed that asteroids of this size would be almost entirely vaporized upon impact. The composition of these fragments is also notable, containing iron-rich silicates and sulfides but lacking metallic iron. Some of these recovered asteroid pieces are now on display at the Science Museum in London and the "Museo del cielo e della Terra" in Italy.

Geological Significance

Further research, including a 2007 paper, has utilized microgravity, aeromagnetic, satellite, and borehole data to suggest that the Morokweng structure may extend up to 240 kilometers in diameter and exhibit a complex, multi-ringed morphology. The potential significance of this impact extends beyond South Africa, as an iridium layer found in the Tithonian strata of the Araripe basin in northeastern Brazil has been tentatively linked to this event, suggesting a possible role in the extinction events of that era.