Magnetic And Gravity Anomalies Found In China Hint At Site Of Mysteriously Missing Impact Crater Wafact

Tektites are natural glass formed from terrestrial debris falling back to Earth after a meteorite impact. Based on their distribution and chemical composition, researchers mapped out four large strewn fields of terrestrial tektites.

The North American tektites have been associated with the 35-milion-year-old Chesapeake Bay impact crater, the European tektites with the 15-million-year-old Nördlinger Ries, and the Ivory Coast tektites with the one-million-year-old Lake Bosumtwi crater.

But the source crater for the Australasian tektites, forming the most extensive strewn field, has so far eluded scientists. Australasian tektites have been found all over the Indian Ocean, Australia, Indonesia, Southeast Asia and even Antarctica. This is somewhat of a geological mystery, as the impact’s relatively young age — estimated around 800,000 years ago — and size — the impact must have left behind a 20-kilometer-wide crater — should make this event easily detectable.

Based on the distribution of the tektites, most researchers agree that this impact must have happened somewhere in Asia or Indonesia. A study published in 2019 suggested that a large basalt plateau stretching from Cambodia to Laos was all that remained of an impact melting the uppermost layers of Earth and injecting molten droplets high into the atmosphere. Falling back and cooling quickly, the molten droplets solidified to form the glassy tektites. Other researchers disagreed, arguing for a volcanic origin of the plateau.

Employing gravity and magnetic data derived from satellites, a new study suggest that a large impact structure exist in the underground of the Badain Jaran desert in Northwest China. As sand dunes in deserts are highly mobile, this could explain how the crater was buried so quickly and eluded earlier detection.

According to the authors, the recovered gravity data can be explained by a meteorite impact. Slamming into Earth, the meteorite pushed down the ground, but then the Earth rebounded, forming a central mountain-sized uplift with a lower density (and gravitational pull) than the undisturbed bedrock. The shock waves following the impact shattered the rocks in a typical annular pattern as seen in other impact craters.

Magnetic data seems to support this interpretation. According to the study, underground magnetic anomalies are not distributed randomly, but form a pattern likely following the rim of the crater.

To confirm the meteoritic origin and age of the structure, the scientists will need to recover rock samples from within the crater. Geological evidence, like minerals formed only under the extreme conditions of a meteorite impact or characteristic rock fracture patterns (like shatter cones) could definitively prove the impact hypothesis.

About 200 terrestrial impact craters are currently known. Over half are located in Europe, North America and Australia. The ages of the great majority of preserved impact structures are less than 200 million years, and structures smaller than 5 kilometers are greatly underrepresented. The observed distributions of crater sizes and ages have been biased by post-impact processes. Erosion tends to quickly destroy or bury craters (especially the smaller ones) in tectonically active areas, like near fault zones or on the seafloor.

The study “Formation of Australasian tektites from gravity and magnetic indicators” was published in the journal scientific reports (2023).

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