Scientists discover giant, fan-shaped structure deep beneath the East Antarctic Ice Sheet

Scientists have discovered a giant, fan-shaped structure that connects several well-known basins deep beneath the East Antarctic Ice Sheet — and it may have formed in the breakup of the ancient supercontinent Gondwana.

The feature is the product of a tectonic process known as distributed rotational extension, in which Earth's crust deforms outward from a fixed, central point, like fingers spreading out on a human hand. The gaps between the "fingers" in East Antarctica are triangular basins that were previously described but not recorded as belonging to a single system, researchers reported in a new study.

"Rotational extension is known from other tectonic settings, but recognizing a feature of this scale, hidden beneath the East Antarctic Ice Sheet, is quite remarkable," first author Egidio Armadillo, an associate professor and researcher in the Applied Geophysics Laboratory at the University of Genoa in Italy, told Live Science in an email. "If our interpretation is correct, this may be one of the largest and clearest examples of distributed rotational extension yet recognized in continental crust."

The discovery began with the simple observation that many buried basins in East Antarctica seem to radiate from the same place. From there, Armadillo and his colleagues examined the region's subglacial landscape and geology, as well as gravitational, magnetic and seismic data. They also used models to simulate the formation of the structure, which they named the East Antarctic Fan-Shaped Basin Province.

The results, published June 3 in the journal Nature Geoscience, support the idea that some of East Antarctica's best-known features — including the Wilkes and Aurora basins and the basin that hosts Lake Vostok, the largest known subglacial lake on Earth — were formed by distributed rotational extension. But it's unclear exactly when this happened, Armadillo said.

"The structure may have developed in more than one phase," he said. "However, we think it is likely connected to the long tectonic evolution that preceded and accompanied the breakup of Gondwana, especially the separation between Antarctica and Australia."

Gondwana splintered around 180 million years ago, creating the landmasses and continents we know today. The split between Antarctica and Australia occurred roughly 70 million years ago, toward the end of the Cretaceous period (145 million to 66 million years ago). The East Antarctic Fan-Shaped Basin Province may have facilitated this late separation by weakening a zone to the north of the province that eventually tore apart, but the province may have continued to fan out after Antarctica and Australia broke apart, Armadillo said.

The precise mechanism that drove East Antarctica's distributed rotational extension remains unknown. "In my view, this is one of the most exciting aspects of the study: it does not close the problem, but opens a new research direction," Armadillo said.

Overall, the results suggest East Antarctica has a much more dynamic tectonic history than scientists previously thought. "East Antarctica is often regarded as an old, cold and relatively stable cratonic [ancient and deeply rooted] region," Armadillo said. "In our model, the formation of the fan-shaped basin province strongly influences the surrounding landscape."

The structure opened several enormous basins that are now concealed under more than 1.8 miles (3 kilometers) of ice. To the west, the structure's formation may have contributed to the uplift of the Gamburtsev Mountains, which are similar to the European Alps in scale and shape but completely buried in ice. And to the east, the spreading of the "fingers" likely helped rotate and break up the Transantarctic Mountains, which divide East and West Antarctica, Armadillo said.

"The main message is that a large part of East Antarctica may not simply be a collection of separate subglacial basins, but a coherent tectonic province produced by a continent-scale deformation process," he said. "At the same time, our model is a hypothesis that can and should be tested further. In particular, better constraints on the timing of deformation will be essential."

The discovery could shed light on how the East Antarctic Ice Sheet will respond to climate change, because tectonic processes influence the paths followed by glaciers and ice streams when they melt. However, the broader significance of the findings is that Antarctica still conceals many geological secrets, Armadillo said.

"More than 99% of the bedrock is hidden beneath the ice, so integrating subglacial topography, gravity, magnetics, crustal structure and ice-sheet observations is essential," he noted.

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