On Earth, shifting tectonic plates reshape the planet’s surface and create a dynamic interior, so the lack of such processes on Mars has led many to consider it a dead planet, where nothing happened. much in the last 3 billion years.
In the current issue of natural astronomy, University of Arizona scientists are challenging current views of Martian geodynamic evolution with a report of the discovery of an active mantle plume pushing the surface upward and causing earthquakes and volcanic eruptions. The discovery suggests that the planet’s deceptively calm surface may be hiding a more tumultuous interior than previously thought.
“Our study presents several lines of evidence that point to the presence of a giant active mantle plume on present-day Mars,” said Adrien Broquet, postdoctoral researcher at the UArizona Lunar and Planetary Laboratory and co-author of the study. with Jeff Andrews. -Hanna, associate professor of planetary sciences at LPL.
Mantle plumes are large masses of hot, floating rock that rise from deep within a planet and push through its middle layer – the mantle – to reach the base of its crust, causing earthquakes, faults and volcanic eruptions. The Hawaiian island chain, for example, formed as the Pacific plate slowly drifted over a mantle plume.
“We have strong evidence of mantle plume activity on Earth and Venus, but that’s not expected on a small, supposedly cold world like Mars,” Andrews-Hanna said. “Mars was most active 3-4 billion years ago, and the prevailing view is that the planet is essentially dead today.”
“An enormous amount of volcanic activity early in the planet’s history built the tallest volcanoes in the solar system and covered most of the northern hemisphere with volcanic deposits,” Broquet said. “What little activity has occurred in recent history is generally attributed to passive processes on a cooling planet.”
The researchers were drawn to a surprising amount of activity in an otherwise indescribable region of Mars called Elysium Planitia, a plain in the northern lowlands of Mars near the equator. Unlike other volcanic regions on Mars, which have not seen major activity for billions of years, Elysium Planitia has seen major eruptions in the past 200 million years.
“Previous work by our group found evidence at Elysium Planitia of the youngest known volcanic eruption on Mars,” Andrews-Hanna said. “It created a small volcanic ash explosion about 53,000 years ago, which in geologic time is basically yesterday.”
The volcanism at Elysium Planitia stems from the Cerberus Fossae, a collection of young fissures that stretch more than 800 miles across the Martian surface. Recently, NASA’s InSight team discovered that nearly all Martian quakes, or quakes, emanate from this region alone. Although this young volcanic and tectonic activity was documented, the underlying cause remained unknown.
On Earth, volcanism and earthquakes tend to be associated with either mantle plumes or plate tectonics, the global cycle of continental drift that continually recycles the crust.
“We know that Mars does not have plate tectonics, so we investigated whether the activity we see in the Cerberus Fossae region could be the result of a mantle plume,” Broquet said.
The mantle plumes, which can be seen as analogous to hot wax drops rising in lava lamps. reveal their presence on Earth through a classic sequence of events. The hot plume material pushes against the surface, lifting and stretching the crust. The molten rock from the plume then erupts as flooded basalts that create vast volcanic plains.
When the team studied the features of Elysium Planitia, they found evidence of the same sequence of events on Mars. The surface has been uplifted more than a mile, making it one of the highest regions of the vast northern lowlands of Mars. Analyzes of subtle variations in the gravity field indicated that this uplift is supported from deep within the planet, which is consistent with the presence of a mantle plume.
Further measurements showed that the bottoms of impact craters are tilted in the direction of the plume, further supporting the idea that something pushed the surface up after the craters formed. Finally, when the researchers applied a tectonic model to the region, they found that the presence of a giant plume, 2,500 miles wide, was the only way to explain the extension responsible for the formation of Cerberus Fossae.
“As far as what you would expect to see with an active mantle plume, Elysium Planitia ticks all the right boxes,” Broquet said, adding that the discovery poses a challenge to models used by planetary scientists to study evolution. thermics of the planets. “This mantle plume affected an area of Mars roughly equivalent to that of the continental United States. Future studies will need to find a way to account for a very large mantle plume that was not supposed to be there.
“We used to think that InSight had landed in one of the most geologically dull regions of Mars – a nice flat surface that should be roughly representative of the planet’s lowlands,” Broquet added. “Instead, our study demonstrates that InSight landed just above an active plume head.”
The presence of an active plume will affect interpretations of seismic data recorded by InSight, which must now take into account that this region is far from normal for Mars.
“Having an active mantle plume on Mars today is a paradigm shift for our understanding of the geological evolution of the planet,” Broquet said, “similar to when analyzes of seismic measurements recorded during the Apollo era demonstrated that the moon’s core was molten”.
Their findings could also have implications for life on Mars, the authors say. The region studied has experienced liquid water flooding in its recent geological past, although the cause has remained a mystery. The same heat from the plume that fuels ongoing volcanic and seismic activity could also melt ice to cause flooding and cause chemical reactions that could sustain life at depth.
“Microbes on Earth thrive in environments like this, and that could also be true on Mars,” Andrews-Hanna said, adding that the discovery goes beyond explaining the enigmatic seismic activity and resurgence of volcanic activity. “Knowing that there is an active giant mantle plume beneath the Martian surface raises important questions about how the planet will evolve over time. We are confident that the future holds more surprises.”
Adrien Broquet & JC Andrews-Hanna, Geophysical evidence for an active mantle plume beneath Elysium Planitia on Mars, natural astronomy (2022). DOI: 10.1038/s41550-022-01836-3. www.nature.com/articles/s41550-022-01836-3
Provided by the University of Arizona
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