Mars tremors and recent volcanism suggest Mars still has a mantle plume

The Mars InSight lander included the first seismograph placed on the Red Planet, and it captured everything from earthquakes to impacts and provided plenty of new information about Mars’ interior. But perhaps his most striking discovery was that nearly all of Mars’ seismic activity appears to originate from a single location, a site called Elysium Planitia.

This area is also the site of the most recent volcanic activity we have detected on Mars. In a paper published this week, scientists say the two derive from a single source: a plume of hot material rising through the mantle. It’s the kind of geologic activity that creates hotspots like Iceland and Yellowstone on Earth, but Mars was thought to have cooled too much to support such activity.

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Elysium Planitia is a generally flat region covering approximately one million square kilometers. It’s right on the edge of the northern lowlands of Mars, but it’s nearly a mile above them. Many of its features are ancient, including a series of ridges thought to be caused by compression of Mars’ interior as it cooled. But it also shows signs of recent volcanic activity, though not as much as the nearby Tharsis region, which contains the largest volcanoes on Mars.

Instead, there are signs of large floods of volcanic material released from large fissures in Elysium Planitia. There are also signs of pyroclastic flows that appear to be the product of the most recent volcanic activity on the Red Planet, dating to less than 200,000 years ago.

These signs made it interesting for scientists and one of the reasons the InSight lander was sent to the region. And, as far as we could tell, all major earthquakes originate from this region.

Obviously, volcanic activity and earthquakes are likely to be linked. The question is how.

There are potential explanations for these and other features of Elysium Planitia, but researchers say a hot mantle plume is the only one that makes sense. “Although alternative explanations may exist for some of these sightings,” they write, “only an active mantle plume can explain them all.”

It’s a plume

As mentioned above, Elysium Planitia exhibits a series of fractures usually associated with compression, and these are thought to be the product of ancient terrain subsiding as the interior of Mars cools. But Elysium Planitia is also nearly a kilometer higher than the surrounding lowland terrain, suggesting it may have been uplifted by tectonic forces. There is also the Cerberus Fossae, a series of what appear to be volcanic vents, and the deposits derived from them.

These deposits are extensive, suggesting that a major source of magma fueled activity in the area, ruling out some potential sources of the rock. Although widespread, the deposits are generally no thicker than about 100 meters, which means they cannot account for the elevation of the area. And measurements of local variations in gravitational pull suggest that Elysium Planitia’s uplift is supported from deep within the crust. Finally, the region’s volcanic material has much higher levels of iron than other regions on Mars, a feature found in mantle plume-driven volcanism on Earth.

The researchers therefore suggest that the region had undergone the normal contraction fault that appears to be widespread across the surface of Mars. But more recently, a mantle plume has reached the crust below, uplifting the region and adding the kinds of faulting associated with Cerberus Fossae volcanic vents.

So they built a mantle plume model and adjusted it until it matched the various surface features and seismic data in the area. Based on the model, they estimate the plume to be about 4,000 kilometers in diameter and about 200 to 500 kilometers thick in the area immediately beneath the crust. They also estimate that it is 100 to 300 Kelvin hotter than the surrounding material.

How did it happen?

The activity levels found at Elysium Planitia are much lower than hotspot-driven sites elsewhere on Mars, and they’re on the low end of what you’d see at similar sites on Earth. But the surprise is that it happens at all. Earlier activity driven by mantle plumes should have removed some of the water from Mars’ interior, making it harder for rocks to melt. The prior compression of the region should also make it harder for molten rock to work its way to the surface.

But, more importantly, the interior of Mars should have cooled considerably since the period when Mars built the massive volcanoes of Tharsis. In fact, some models of the interior of Mars have suggested that this type of activity should have ended at this point in the planet’s history. Understanding what is happening here can therefore be essential to improving these models.

Unfortunately, this is where the big problem with InSight makes it difficult. It was supposed to deploy a tool that measures the heat flux from Mars’ interior to its surface, which should have illuminated any hot material nearby (InSight’s landing site is just above the plume of the Mars). proposed coat). But the lander team was unable to insert the instrument into Mars and ultimately abandoned attempts to make it work.

But the new paper definitely suggests that Elysium Planitia deserves an extra look.

natural astronomy2022. DOI: 10.1038/s41550-022-01836-3 (About DOIs).