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Marsquakes, recent volcanism suggest Mars still has a mantle plume
Enlarge / One of the rifts in the Cerebrus Fossae area, potentially created by the stretching of the crust driven by a mantle plume.
The Mars InSight lander included the first seismograph placed on the red planet, and it has picked up everything from marsquakes to impacts and provided lots of new information on Mars’ interior. But perhaps its most striking finding has been that almost all of Mars’ seismic activity appears to originate from a single location, a site called Elysium Planitia.
That area is also the site of the most recent volcanic activity we’ve detected on Mars. In a paper released this week, scientists argue that both derive from a single source: a plume of hot material rising through the mantle. It’s the sort of geological activity that creates hotspots like Iceland and Yellowstone on Earth, but it had been thought that Mars had cooled too much to support those activities.
Building a case
Elysium Planitia is a generally flat region covering roughly a million square kilometers. It’s just at the edge of Mars’ northern lowlands, but it sits nearly a kilometer above them. Many of its features are old, including a series of ridges thought to be caused by the compression of Mars’ interior as it cooled. But it also has signs of recent volcanic activity, though not nearly as much as the nearby Tharsis region, 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 from less than 200,000 years ago.
Those signs made it interesting to scientists and one of the reasons that the InSight lander was sent to the area. And, as far as we’ve been able to tell, all of the significant marsquakes come from this area.
Obviously, the volcanic activity and marsquakes are likely to be connected. The question is how.
There are some potential explanations for these and other features of Elysium Planitia, but the researchers argue that a hot mantle plume is the only one that makes sense. “While alternative explanations may exist for some of these observations,” they write, “only an active mantle plume can account for all of them.”
It’s a plume
As mentioned above, Elysium Planitia has a series of fractures that are typically associated with compression, and these are thought to be a product of old terrain that’s subsiding as the interior of Mars cools. But Elysium Planitia is also nearly a kilometer higher than the surrounding lowland terrain, suggesting that it might have been elevated by tectonic forces. There’s also the Cerberus Fossae, a series of what appear to be volcanic vents, and the deposits that derive from them.
Those deposits are extensive, suggesting a major source of magma fed the activity in the region, which rules out some potential sources of the rock. While they’re widespread, the deposits typically aren’t thicker than about 100 meters, meaning they can’t account for the area’s elevation. And measures of the local variations in gravitational pull suggest the Elysium Planitia’s elevation is supported from deep within the crust. Finally, the volcanic material in the area has much higher levels of iron than other areas of Mars, a feature found in volcanism driven by mantle plumes on Earth.
So the researchers suggest that the region had been undergoing the normal contraction faulting that appears widespread across the surface of Mars. But more recently, a mantle plume reached the crust below it, elevating the region and adding the sorts of faults associated with the volcanic vents of Cerberus Fossae.
So they built a model of a mantle plume and adjusted it until it fit the region’s various surface features and seismic data. Based on the model, they estimate the plume is about 4,000 kilometers in diameter, and it’s about 200 to 500 kilometers thick in the area immediately beneath the crust. They also estimate that it’s from 100 to 300 Kelvin hotter than the surrounding material.
How did this happen?
The activity levels found in Elysium Planitia are much lower than hotspot-driven sites elsewhere on Mars, and they’re at the low end of what you’d see at similar sites on Earth. But the surprise is that it’s happening at all. Earlier activity driven by mantle plumes should have removed some of the water from Mars’ interior, making it more difficult for rocks to melt. The prior compression of the region should also make it more difficult for molten rock to force its way to the surface.
But, more critically, Mars’ interior should have cooled significantly from the period when Mars built the massive volcanoes of Tharsis. In fact, some models of Mars’ interior have suggested that this sort of activity should have ended by this point in the planet’s history. So understanding what’s going on here may be critical to improving those models.
Unfortunately, this is where the big glitch with InSight makes things difficult. It was supposed to deploy an implement that measures the heat flow from Mars’ interior to its surface, which should have shed light on any hot material nearby (the InSight landing site is right on top of the proposed mantle plume). But the lander team couldn’t get the instrument inserted into Mars and eventually abandoned attempts to get it to work.
But the new paper definitely suggests that Elysium Planitia is worth an additional look.
Nature Astronomy, 2022. DOI: 10.1038/s41550-022-01836-3 (About DOIs).
Massive Mantle Plume Pushing the Surface of Mars Upward
Artist’s impression of an active mantle plume – a large blob of warm and buoyant rock – rising from deep inside Mars and pushing up Elysium Planitia, a plain within the planet’s northern lowlands. Volcanism at Elysium Planitia originates from the Cerberus Fossae, highlighted in red, a set of young fissures that stretches for more than 800 miles across the Martian surface. Recently, NASA’s InSight lander found that nearly all Martian quakes, or marsquakes, emanate from this one region. Credit: Adrien Broquet & Audrey Lasbordes
Giant Mantle Plume Reveals Mars Is More Active Than Previously Thought
Orbital observations unveil the presence of an enormous mantle plume pushing the surface of
Scientists from the University of Arizona challenge current views of Martian geodynamic evolution with a report on the discovery of an active mantle plume pushing the surface upward and causing earthquakes and volcanic eruptions. The finding, which was published in the current issue of the journal Nature Astronomy, suggests that the planet’s deceptively quiet surface may hide a more tumultuous interior than previously thought.
“Our study presents multiple lines of evidence that reveal the presence of a giant active mantle plume on present-day Mars,” said Adrien Broquet, a postdoctoral research associate in the UArizona Lunar and Planetary Laboratory (LPL) and co-author of the study with Jeff Andrews-Hanna, an associate professor of planetary science at the LPL.
Artist’s impression of an active mantle plume – a large blob of warm and buoyant rock – rising from deep inside Mars and pushing up Elysium Planitia, a plain within the planet’s northern lowlands. Credit: Adrien Broquet & Audrey Lasbordes
Mantle plumes are large blobs of warm and buoyant rock that rise from deep inside a planet and push through its intermediate layer – the mantle – to reach the base of its crust, causing earthquakes, faulting and volcanic eruptions. The island chain of Hawaii, for example, formed as the Pacific plate slowly drifted over a mantle plume.
“We have strong evidence for mantle plumes being active on Earth and
“Previous work by our group found evidence in Elysium Planitia for the youngest volcanic eruption known on Mars,” Andrews-Hanna said. “It created a small explosion of volcanic ash around 53,000 years ago, which in geologic time is essentially yesterday.”
This image taken by the European Space Agency’s Mars Express orbiter shows an oblique view focusing on one of the fractures making up the Cerberus Fossae system. The fractures cut through hills and craters, indicating their relative youth. Credit: SA/DLR/FU Berlin, CC BY-SA 3.0 IGO
Volcanism at Elysium Planitia originates from the Cerberus Fossae, a set of young fissures that stretch for more than 800 miles across the Martian surface. Recently,
“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.
Mantle plumes, which can be viewed as analogous to hot blobs of wax rising in lava lamps. give away their presence on Earth through a classical sequence of events. Warm plume material pushes against the surface, uplifting and stretching the crust. Molten rock from the plume then erupts as flood 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 by more than a mile, making it one of the highest regions in Mars’ vast northern lowlands. Analyses of subtle variations in the gravity field indicated that this uplift is supported from deep within the planet, consistent with the presence of a mantle plume.
Other measurements showed that the floor of impact craters is tilted in the direction of the plume, further supporting the idea that something pushed the surface up after the craters formed. Finally, when researchers applied a tectonic model to the area, they found that the presence of a giant plume, 2,500 miles wide, was the only way to explain the extension responsible for forming the Cerberus Fossae.
“In terms of what you expect to see with an active mantle plume, Elysium Planitia is checking all the right boxes,” Broquet said, adding that the finding poses a challenge for models used by planetary scientists to study the thermal evolution of planets. “This mantle plume has affected an area of Mars roughly equivalent to that of the continental United States. Future studies will have to find a way to account for a very large mantle plume that wasn’t expected to be there.
“We used to think that InSight landed in one of the most geologically boring regions on Mars – a nice flat surface that should be roughly representative of the planet’s lowlands,” Broquet added. “Instead, our study demonstrates that InSight landed right on top of an active plume head.”
The presence of an active plume will affect interpretations of the seismic data recorded by InSight, which must now take into account the fact 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 planet’s geologic evolution,” Broquet said, “similar to when analyses of seismic measurements recorded during the Apollo era demonstrated the moon’s core to be molten.”
Their findings could also have implications for life on Mars, the authors say. The studied region experienced floods of liquid water in its recent geologic past, though the cause has remained a mystery. The same heat from the plume that is fueling ongoing volcanic and seismic activity could also melt ice to make the floods – and drive chemical reactions that could sustain life deep underground.
“Microbes on Earth flourish in environments like this, and that could be true on Mars, as well,” Andrews-Hanna said, adding that the discovery goes beyond explaining the enigmatic seismic activity and resurgence in volcanic activity. “Knowing that there is an active giant mantle plume underneath the Martian surface raises important questions regarding how the planet has evolved over time. “We’re convinced that the future has more surprises in store.”
Reference: “Geophysical evidence for an active mantle plume underneath Elysium Planitia on Mars” by A. Broquet and J. C. Andrews-Hanna, 5 December 2022, Nature Astronomy.
DOI: 10.1038/s41550-022-01836-3
Researchers discovered a rare mineral that comes directly from Earth’s lower mantle
“For jewelers and buyers, the size, color, and clarity of a diamond all matter, and inclusions — those black specks that annoy the jeweler — for us, they’re a gift,” said Oliver Tschauner in a press release from the University of Nevada, Las Vegas, and co-leader of the study.
Regarding davemaoite’s unlikely ascent, he commented to Nature, “It’s the strength of the diamond that keeps the inclusions at high pressure.”
A specialized X-ray technique, known as a synchrotron, revealed the new mineral
Tschauner and collaborators, including geochemist Shichun Huang from the University of Nevada, Las Vegas (UNLV), acquired the diamond before employing a specialized X-ray known as a synchrotron. This enabled them to analyze its internal structure more thoroughly.
They discovered a novel crystalline substance that they termed “davemaoite”– a name chosen to honor experimental geophysicist Ho-Kwang “Dave” Mao, who created many of the methods Tschauner and his associates employ today.
Davemaoite has since been approved as a brand-new natural mineral by the Commission of New Minerals, Nomenclature, and Classification of the International Mineralogical Association.
Davemaoite can be blasted onto Earth’s surface by meteorites
The discovery of davemaoite by Tschauner demonstrates just one of the two ways that highly pressured minerals are discovered in nature: from the interior of meteorites or between 410 and 560 miles beneath the Earth’s surface.
Better yet, Tschauder has already made strides in the former path (interior of meteorites) when he discovered the mineral “bridgmanite” back in 2014.
Mickey Mantle card: The most expensive baseball card in history just sold for $12.6 million
A Mickey Mantle baseball card from 1952 sold for a jaw-dropping $12,600,000 early Sunday morning, according to a news release from Heritage Auctions shared with CNN. The sale makes the card the most valuable sports collectible in the world, according to the auction house.
The price almost doubled the previous record for a baseball card set when a rare Honus Wagner sold for $6.6 million last year. And it also beat out the record for any item of sports memorabilia, bypassing the $9.3 million sale of Diego Maradona’s famous ‘Hand of God’ jersey.
The Mickey Mantle card is especially valuable because it’s so well-preserved. The card was graded “Mint+ 9.5” by the Sportscard Guaranty Corporation, according to Heritage Auctions.
Mantle spent 17 years playing for the New York Yankees and was inducted into the Baseball Hall of Fame in 1974. The record-breaking card is from his rookie season and was produced by trading card giant Topps.
For the auction house, the sale represents the growing draw of sports collectibles.
“An eight-figure auction result in the sports market was the stuff of fantasy just a decade ago,” said Chris Ivy, Heritage’s director of sports auctions, said in the release.
“We always knew this card would shatter records and expectations. But that doesn’t make it any less of a thrill to be part of an auction during which a single item breaks the eight-figure threshold for the first time. It’s an extraordinary accomplishment for our wonderful team of sports experts at Heritage Auctions. And, of course, we could not have done it without our consignor, Anthony Giordano, who put his trust in Heritage to bring this amazing card to market.”
Anthony Giordano bought the Mantle card for what was a record-breaking price in 1991: $50,000. He kept it hidden away for three decades before bringing it to Heritage Auctions, according to the release.
“It bears the finest qualities any 1952 Topps can possess: perfect centering, registration and four sharp corners,” said Ivy in the release. “That this Mantle rookie card remained in this condition for 70 years is a true miracle.”
Two Giant Blobs Lurk Deep Inside Earth, And It Looks Like They’re Shape-Shifters
Deep in the Earth beneath us lie two blobs the size of continents. One is under Africa, the other under the Pacific Ocean.
The blobs have their roots 2,900 km (1,800 miles) below the surface, almost halfway to the centre of the Earth. They are thought to be the birthplace of rising columns of hot rock called “deep mantle plumes” that reach Earth’s surface.
When these plumes first reach the surface, giant volcanic eruptions occur – the kind that contributed to the extinction of the dinosaurs 65.5 million years ago. The blobs may also control the eruption of a kind of rock called kimberlite, which brings diamonds from depths 120-150 km (and in some cases up to around 800 km) to Earth’s surface.
Scientists have known the blobs existed for a long time, but how they have behaved over Earth’s history has been an open question. In new research, we modeled a billion years of geological history and discovered the blobs gather together and break apart much like continents and supercontinents.
(Ömer Bodur)
Above: Earth’s blobs as imaged from seismic data. The African blob is at the top and the Pacific blob at the bottom.
A model for Earth blob evolution
The blobs are in the mantle, the thick layer of hot rock between Earth’s crust and its core. The mantle is solid but slowly flows over long timescales. We know the blobs are there because they slow down waves caused by earthquakes, which suggests the blobs are hotter than their surroundings.
Scientists generally agree the blobs are linked to the movement of tectonic plates at Earth’s surface. However, how the blobs have changed over the course of Earth’s history has puzzled them.
One school of thought has been that the present blobs have acted as anchors, locked in place for hundreds of millions of years while other rock moves around them. However, we know tectonic plates and mantle plumes move over time, and research suggests the shape of the blobs is changing.
Our new research shows Earth’s blobs have changed shape and location far more than previously thought. In fact, over history they have assembled and broken up in the same way that continents and supercontinents have at Earth’s surface.
We used Australia’s National Computational Infrastructure to run advanced computer simulations of how Earth’s mantle has flowed over a billion years.
These models are based on reconstructing the movements of tectonic plates. When plates push into one another, the ocean floor is pushed down between them in a process known as subduction.
The cold rock from the ocean floor sinks deeper and deeper into the mantle, and once it reaches a depth of about 2,000 km it pushes the hot blobs aside.
Above: The past 200 million years of Earth’s interior. Hot structures are in yellow to red (darker is shallower) and cold structures in blue (darker is deeper).
We found that just like continents, the blobs can assemble – forming “superblobs” as in the current configuration – and break up over time.
A key aspect of our models is that although the blobs change position and shape over time, they still fit the pattern of volcanic and kimberlite eruptions recorded at Earth’s surface. This pattern was previously a key argument for the blobs as unmoving “anchors”.
Strikingly, our models reveal the African blob assembled as recently as 60 million years ago – in stark contrast to previous suggestions the blob could have existed in roughly its present form for nearly ten times as long.
Remaining questions about the blobs
How did the blobs originate? What exactly are they made of? We still don’t know.
The blobs may be denser than the surrounding mantle, and as such they could consist of material separated out from the rest of the mantle early in Earth’s history. This could explain why the mineral composition of the Earth is different from that expected from models based on the composition of meteorites.
Alternatively, the density of the blobs could be explained by the accumulation of dense oceanic material from slabs of rock pushed down by tectonic plate movement.
Regardless of this debate, our work shows sinking slabs are more likely to transport fragments of continents to the African blob than to the Pacific blob.
Interestingly, this result is consistent with recent work suggesting the source of mantle plumes rising from the African blob contains continental material, whereas plumes rising from the Pacific blob do not.
Tracking the blobs to find minerals and diamonds
While our work addresses fundamental questions about the evolution of our planet, it also has practical applications.
Our models provide a framework to more accurately target the location of minerals associated with mantle upwelling. This includes diamonds brought up to the surface by kimberlites that seem to be associated with the blobs.
Magmatic sulfide deposits, which are the world’s primary reserve of nickel, are also associated with mantle plumes. By helping target minerals such as nickel (an essential ingredient of lithium-ion batteries and other renewable energy technologies) our models can contribute to the transition to a low-emission economy.
Nicolas Flament, Senior Lecturer, University of Wollongong; Andrew Merdith, Research fellow, University of Leeds; Ömer F. Bodur, Postdoctoral research fellow, University of Wollongong, and Simon Williams, Research Fellow, Northwest University, Xi’an.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Primordial Helium From Billions of Years Ago Seems to Be Leaking Out of Earth’s Core
Ancient, primordial helium that was forged in the wake of the Big Bang is leaking from Earth’s core, scientists report in a new study.
There’s no cause for alarm. Earth isn’t deflating like a sad balloon. What it does mean is that Earth formed inside a solar nebula – the molecular cloud that gave birth to the Sun, a detail about our planet’s birth that has long been unresolved.
It also suggests that other primordial gases may be leaking from Earth’s core into the mantle, which in turn could yield information about the composition of the solar nebula.
Helium on Earth comes in two stable isotopes. By far the most common is helium-4, with a nucleus containing two protons and two neutrons. Helium-4 accounts for arund 99.99986 percent of all the helium on our planet.
The other stable isotope, accounting for just about 0.000137 percent of Earth’s helium, is helium-3, with two protons and one neutron.
Helium-4 is primarily the product of the radioactive decay of uranium and thorium, made right here on Earth. By contrast, Helium-3 is mostly primordial, formed in the moments after the Big Bang, but it can also be produced by the radioactive decay of tritium.
It’s the Helium-3 isotope that has been detected leaking out of Earth’s interior, mostly along the mid-ocean volcanic ridge system, giving us a pretty good indication of the rate at which it escapes the crust.
That rate is about 2,000 grams (4.4 pounds) a year: “about enough to fill a balloon the size of your desk,” explains geophysicist Peter Olson from the University of New Mexico.
“It’s a wonder of nature, and a clue for the history of the Earth, that there’s still a significant amount of this isotope in the interior of the Earth.”
What is less clear is the provenance; how much of the helium-3 might be emerging from the core, versus how much is in the mantle.
This would tell us the source of the isotope. When Earth formed, it did so by accumulating material from the dust and gas floating around the newborn Sun.
The only way significant amounts of helium-3 could be inside the planetary core is if it were formed in a thriving nebula. That means, not at its outskirts, and not as it dissipated and blew away.
Olson and his colleague, geochemist Zachary Sharp of the University of New Mexico, investigated by modeling Earth’s inventory of helium as it evolved. First, as it formed, a process during which the protoplanet accumulated and incorporated helium; and then after the Great Impact.
This, astronomers think, is when an object the size of Mars smacked into a very young Earth, sending debris flying into Earth’s orbit, eventually recombining to form the Moon.
During this event, which would have re-melted the mantle, much of the helium locked inside the mantle would have been lost. The core, however, is more resistant to impact, suggesting that it could be quite an effective reservoir for holding onto helium-3.
In fact, this is what the researchers found. Using the current rate at which helium-3 is leaking from the interior, as well as models of helium isotope behavior, Olson and Sharp found that there are likely 10 teragrams (1013 grams) to a petagram (1015 grams) of helium-3 in our planet’s core.
This suggests that the planet had to have formed inside a thriving solar nebula. However, several uncertainties remain. The likelihood of all the conditions being met for the sequestering of helium-3 in Earth’s core are moderately low – which means that there may be less of the isotope than the team’s work suggests.
However, it’s possible that there is also abundant primordial hydrogen in our planet’s core, caught up in the same process that may have accumulated helium-3. Looking for evidence of hydrogen leakage could help validate the findings, the researchers say.
The research has been published in Geochemistry, Geophysics, Geosystems.
Two Massive Blobs in Earth’s Mantle Baffle Scientists With Their Surprising Properties
A 3D view of the blob in Earth’s mantle beneath Africa, shown by the red-yellow-orange colors. The cyan color represents the core-mantle boundary, blue signifies the surface, and the transparent gray signifies continents. Credit: Mingming Li/ASU
Earth is layered like an onion, with a thin outer crust, a thick viscous mantle, a fluid outer core, and a solid inner core. Within the mantle, there are two massive blob-like structures, roughly on opposite sides of the planet. The blobs, more formally referred to as Large Low-Shear-Velocity Provinces (LLSVPs), are each the size of a continent and 100 times taller than Mt. Everest. One is under the African continent, while the other is under the Pacific Ocean.
Using instruments that measure seismic waves, scientists know that these two blobs have complicated shapes and structures, but despite their prominent features, little is known about why the blobs exist or what led to their odd shapes.
Arizona State University scientists Qian Yuan and Mingming Li of the School of Earth and Space Exploration set out to learn more about these two blobs using geodynamic modeling and analyses of published seismic studies. Through their research, they were able to determine the maximum heights that the blobs reach and how the volume and density of the blobs, as well as the surrounding viscosity in the mantle, might control their height. Their research was recently published in
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2 giant blobs in Earth’s mantle may explain Africa’s weird geology
Deep within Earth’s mantle, there are two giant blobs. One sits under Africa, while the other is almost precisely opposite the first, under the Pacific Ocean. But these two blobs are not evenly matched.
New research finds that the blob under Africa extends far closer to the surface — and is more unstable — than the blob under the Pacific. This difference could ultimately help to explain why the crust under Africa has been lifted upward and why the continent has seen so many large supervolcano eruptions over hundreds of millions of years.
“This instability can have a lot of implications for the surface tectonics, and also earthquakes and supervolcanic eruptions,” said Qian Yuan, a graduate associate in geology at Arizona State University (ASU) who led the research.
A pair of blobs
The mantle blobs are properly known as “large low-shear-wave-velocity provinces,” or LLSVPs. This means that when seismic waves generated by earthquakes travel through these deep-mantle zones, the waves slow down. This deceleration indicates that there’s something different about the mantle at this spot, such as density or temperature — or both.
Scientists aren’t sure why the mantle blobs exist. There are two popular hypotheses, Yuan told Live Science. One is that they’re made up of accumulations of crust that have subducted from Earth‘s surface to deep inside the mantle. Another is that they’re the remnants of an ocean of magma that may have existed in the lower mantle during Earth’s early history. As this magma ocean cooled and crystallized, it may have left behind areas that were denser than the rest of the mantle.
Prior studies had hinted that these two blobs may not have been created equal, Yuan said, but none of this research had used global data sets that could easily compare the two. He and his adviser, ASU geodynamics assistant professor Mingming Li, examined 17 global seismic-wave data sets to determine the height of each blob.
They found that the African blob extends about 620 miles (1,000 kilometers) higher than the Pacific blob. That’s a difference of roughly 113 Mount Everests. In total, the Pacific blob extends 435 to 500 miles (700 to 800 km) upward from the boundary between the core and the mantle. The African blob extends upward about 990 to 1,100 miles (1,600 to 1,800 km).
Blobular instability
The researchers then used computer modeling to figure out which features of the blobs could explain these differences. The most important ones, they found, were the density of the blobs themselves and the viscosity of the surrounding mantle. Viscosity refers to the ease with which the mantle rocks can be deformed.
For the African blob to be so much taller than the Pacific blob, it must be far less dense, according to Yuan. “Because it’s less dense, it’s unstable,” he said.
The African blob is still far from Earth’s crust — the mantle is 1,800 miles (2,900 km) thick in total — but this deep structure’s instability may have implications for the planet’s surface. LLSVPs may be a source of hot plumes of mantle material that rise upward. These plumes, in turn, might cause supervolcano eruptions, tectonic upheaval and possibly even continental breakup, Yuan said.
The African blob “is very close to the surface, so there is a possibility that a large mantle plume may rise from the African blob and may lead to more surface rising and earthquakes and supervolcano eruptions,” Yuan said.
These processes occur over many millions of years and have been ongoing in Africa. There does seem to be a connection between the African blob and major eruptions, Yuan said. A 2010 paper published in the journal Nature found that in the past 320 million years, 80% of kimberlites, or huge eruptions of mantle rock that bring diamonds to the surface, have occurred right over the boundary of the African blob.
Yuan and Li published their findings March 10 in the journal Nature Geoscience. They are now working on research into the origins of the blobs. Though those findings have not yet been published in a peer-reviewed journal, the researchers presented the results at the 52nd Lunar and Planetary Science Conference in March 2021; that research suggested that the blobs might be remnants of the planet-size object that slammed into Earth some 4.5 billion years ago, forming the moon.
Originally published on Live Science.
Geologists Have Closely Analyzed Two Bizarre ‘Blobs’ Detected Deep Inside Earth
Earth’s interior is not a uniform stack of layers. Deep in its thick middle layer lie two colossal blobs of thermo-chemical material.
To this day, scientists still don’t know where both of these colossal structures came from or why they have such different heights, but a new set of geodynamic models has landed on a possible answer to the latter mystery.
These hidden reservoirs are located on opposite sides of the world, and judging from the deep propagation of seismic waves, the blob under the African continent is more than twice as high as the one under the Pacific ocean.
After running hundreds of simulations, the authors of the new study think the blob under the African continent is less dense and less stable than its Pacific counterpart, and that’s why it’s so much taller.
“Our calculations found that the initial volume of the blobs does not affect their height,” explains geologist Qian Yuan from Arizona State University.
“The height of the blobs is mostly controlled by how dense they are and the viscosity of the surrounding mantle.”
3D view of the blob in Earth’s mantle beneath Africa. (Mingming Li/ASU)
One of the principal layers inside Earth is the hot and slightly goopy mess known as the mantle, a layer of silicate rock that sits between our planet’s core and its crust. While the mantle is mostly solid, it behaves sort of like tar on longer timescales.
Over time, columns of hot magma rock gradually rise through the mantle and are thought to contribute to volcanic activity on the planet’s surface.
Understanding what’s going on in the mantle is thus an important endeavor in geology.
The Pacific and African blobs were first discovered in the 1980s. In scientific terms, these ‘superplumes’ are known as large low-shear-velocity provinces (LLSVPs).
Compared to the Pacific LLSVP, the current study found the African LLSVP stretches about 1,000 kilometers higher (621 miles), which supports previous estimates.
This vast height difference suggests both of these blobs have different compositions. How this impacts the surrounding mantle, however, is unclear.
Perhaps the less stable nature of the African pile, for instance, can explain why there is such intense volcanism in some regions of the continent. It could also impact the movement of tectonic plates, which float on the mantle.
Other seismic models have found the African LLSVP stretches up to 1,500 kilometers above the outer core, whereas the Pacific LLSVP reaches 800 kilometers high at max.
In lab experiments that seek to replicate Earth’s interior, both the African and Pacific piles appear to oscillate up and down through the mantle.
The authors of the current study say this supports their interpretation that the African LLSVP is probably unstable, and the same could go for the Pacific LLSVP, although their models didn’t show this.
The different compositions of the Pacific and African LLSVPs could also be explained by their origins. Scientists still don’t know where these blobs came from, but there are two main theories.
One is that the piles are made from subducted tectonic plates, which slip into the mantle, are super-heated and gradually fall downwards, contributing to the blob.
Another theory is that the blobs are remnants of the ancient collision between Earth and the protoplanet Thea, which gave us our Moon.
The theories are not mutually exclusive, either. For instance, perhaps Thea contributed more to one blob; this could be part of the reason why they look so different today.
“Our combination of the analysis of seismic results and the geodynamic modeling provides new insights on the nature of the Earth’s largest structures in the deep interior and their interaction with the surrounding mantle,” says Yuan.
“This work has far-reaching implications for scientists trying to understand the present-day status and the evolution of the deep mantle structure, and the nature of mantle convection.”
The study was published in Nature Geoscience.