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Throughout the planet, there are only a handful of known tektite strewn fields, which are large swaths of land where natural glass (tektite) was strewn about after forming from terrestrial material and being ejected from a meteorite impact. The tektite glass can be ejected extremely long distances, placing strewn fields far from their origins.

One of the youngest known tektite strewn fields is the Australasian field, which stretches from China to Australia and is thought to have been formed less than a million years ago. The tektites associated with this field are generally referred to as "australites."

But, among the australites, there were some oddball tektites that didn't have quite the same properties as the others. found that this group showed anomalous compositions, like higher Na/K ratios, and dating methods placed this group much further back on the timeline—albeit with large uncertainties.

To further investigate these anomalous australites, a team of researchers in France conducted a follow-up study, which was recently in the journal Earth and Planetary Science Letters. The team surveyed thousands of specimens from the South Australian Museum (SAM) using specific gravity and magnetic susceptibility to identify additional outliers.

Only six new specimens were identified on which the team conducted a wide range of analyses, such as 3D X-ray tomography, electron microscopy, XRF, microprobe, HR-ICP-MS, and 40Ar/39Ar dating. These were compared with the data from the eight anomalous samples from the first study, although the original samples were unavailable.

The 40Ar/39Ar dating determined the samples to be almost 11 million years old (10.76 ± 0.05 million years), making them far older than other australites. The results also showed that the tektites had a unique composition, a high Na/K ratio, and arc-related trace element signatures—similar to the other eight samples. All of these were unique compared to other australites.

To distinguish this new group, the team named the group "ananguites"—a reference to an Aboriginal group from the region where the tektites were found. The ananguite strewn field covers an oblong area of around 900 km long, with systematic differences between the samples found in the eastern and western parts of the strewn field.

"They stand out due to their significant extraterrestrial contamination compared to other tektite fields. Based on these combined features, we propose that they deserve to be ranked among bona fide tektites, making them the sixth tektite strewn field confirmed in a peer-reviewed publication," the study authors write.

The team was also interested in determining the initial source of the ananguites. However, this proved somewhat difficult. "No well-dated crater of compatible age is currently known. If we consider a strewn field-to-crater distance similar to that of belizites, ivorites, or moldavites (< 2000 km), the source crater should be located within Australia."

Although it is still somewhat unclear, none of the Australian regions fit the bill for the place of origin. The small sample size also makes identifying the origin a difficult task. Although more research is needed, the team does have some ideas.

They say, "The geological context suggests a magmatic intrusion of adamellite composition. Therefore, it is much more likely that the source crater should be sought in the subduction-related island arcs surrounding Australia. Within a 3500 km radius of Lake Wilson, potential areas include subduction zones extending from Java to New Zealand."

Their data suggests the source was a volcanic arc, likely in the Philippines (Luzon), Indonesia (Sulawesi), or Papua New Guinea (Bismarck region). Still, they say other areas cannot be completely ruled out. The study also highlights the possibility that there may be even more undiscovered tektite fields with distinct origins, implying there is more to Earth's impact history than previously thought.