Mars earthquakes, recent volcanism indicate that Mars still has a mantle plume

Zoom in / One of the faults in the Cerebrus Fossae region, likely caused by crustal expansion driven by a plume from the mantle.

The Mars InSight lander included the first seismograph placed on the Red Planet, and it picked up everything from marshes to impacts and provided plenty of new information about Mars’ interior. But perhaps the most surprising finding is that most of Mars’ seismic activity appears to originate from a single site, a site called Elysium Planitia.

This region is also the site of the last volcanic activity we discovered on Mars. In a paper released this week, scientists argue that both derive from a single source: a plume of hot material billowing through the mantle. It’s the kind of geological activity that creates hotspots like Iceland and Yellowstone on Earth, but Mars was thought to have cooled too much to support these activities.

build case

Elysium Planitia is a generally flat area covering nearly a million square kilometres. It’s just on the edge of the northern lowlands of Mars, but it’s about a kilometer above it. Many of its features are ancient, including a ridge thought to be caused by the pressure of Mars’ interior as it cooled. But it also has signs of recent volcanic activity, though not nearly as well as nearby Tharsis, which contains Mars’ largest volcanoes.

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 back less than 200,000 years.

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

Obviously, volcanic activity and earthquakes are likely connected. The question is how.

There are a few possible explanations for these and other features of Elysium Planitia, but the researchers argue that only the hot mantle plume makes sense. “While alternative explanations may exist for some of these observations,” they write, “only an active mantle plume can explain all of these observations.”

It’s a column

As mentioned earlier, Elysium Planitia has a series of fractures that are usually associated with pressure, and are thought to be the product of ancient terrain that receded as the interior of Mars cooled. But Elysium Planitia is also about a kilometer higher than the surrounding lowland terrain, suggesting that it may have been uplifted by tectonic forces. There’s also the Cerberus Fossae, a series of what appear to be volcanic vents, and the sediments that spring from them.

These deposits are extensive, indicating that there is a major source of magma fueling activity in the area, which rules out some potential sources of rocks. While they are widespread, the deposits are usually only about 100 meters thick, which means they cannot account for the height of the area. Measurements of local variations in gravitational force indicate that Elysium Planitia’s elevation is supported by the depths of the crust. Finally, volcanic material in the region contains much higher levels of iron than other regions of Mars, a feature found in mantle plume-driven volcanoes on Earth.

So the researchers suggest that the region was subject to natural deflation faults that appear to be spreading across the surface of Mars. Recently, however, a plume from the mantle has reached into the crust below it, raising the area and adding the types of faults associated with the volcanic vents of Cerberus Fossae.

So they built a mantle plume model and fine-tuned it to fit different area surface features and seismic data. Depending on the model, they estimate the plume to be about 4,000 kilometers in diameter, and about 200 to 500 kilometers thick in the region just below the crust. They also estimate that it is 100 to 300 K hotter than the surrounding material.

How did this happen?

The activity levels found at Elysium Planitia are much lower than hotspot-driven sites elsewhere on Mars, and are on the lower end of what you’d see at similar locations on Earth. Surprisingly, it doesn’t happen at all. Previous activity driven by mantle plumes should have removed some water from Mars’ interior, making it more difficult for rocks to melt. Also, the pre-compression of the region would make it more difficult for molten rock to force 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 at Tharsis. In fact, some internal models of Mars have suggested that this type of activity should have ended at this point in the planet’s history. So understanding what’s going on here could be critical to improving those models.

Unfortunately, this is where InSight’s big flaw makes things difficult. It was to deploy an instrument measuring heat flux from Mars’ interior to its surface, which should have shed light on any hot material nearby (InSight’s landing site is located directly above the proposed mantle plume). But the rover team was unable to get the instrument into Mars and eventually gave up on trying to get it to work.

But the new paper certainly indicates that Elysium Planitia is worth an extra look.

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

#Mars #earthquakes #volcanism #Mars #mantle #plume

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