Left: 3D visualization of the magnetoteluric exploration of the interior of Erebus (red is the most conductive and magma); Right: schematic representation of magmatic processes. The upward flow from a deep area of the crustal valve experiences an episodic advance of CO2 and entrained magma. The spatially continuous upward flow of CO2-dominated magma contrasts with the shallow-depth magma zones of H2O arc volcanoes. Credit: Phil Wannamaker
Antarctica has long been a land of mystery and heroic feats made famous by the explorations of James Ross, Roald Amundsen, Robert Scott and Ernest Shackleton. A key piece of the puzzle for understanding global continental evolution, Antarctica contains examples that define the spectrum of Earth’s volcanic processes. Now, a joint study by the University of Utah and the University of Canterbury, New Zealand, shows how underground CO2 helps keep magma trapped in the depths of the Earth and allows it to reach and cluster on the surface. .
The study, published in Communications of nature “Expands our understanding of the sources and transport of various types of magma and volatile gases to the surface,” said Phil Wannamaker, second study author and geophysicist at the University of Energy’s Institute of Energy and Geoscience. Utah.
“Mount Erebus is an example of a CO2-dominated rift volcano, a complement to the most well-known arctic volcanoes on the Pacific coast and elsewhere, dominated by H2O,” adds New Zealand co-researcher Graham Hill. lead author of the study.
“Understanding both H2O and CO2 volcanoes is important in calculating the budget for these volatile gases in the depths of the earth that involves injecting material into the Earth’s mantle and returning it to the surface to start over,” says Wannamaker. .
Wannamaker and Hill conducted the study with Utah Alumni John Stodt and Michal Kordy and Associate Scientist Virginie Maris; geophysicists Paul Bedrosian of the U.S. Geological Survey, Martyn Unsworth of the University of Alberta and Yasuo Ogawa of the Tokyo Institute of Technology and senior volcanologist Phil Kyle of the New Mexico Institute of Mining and Technology. Co-authors also included Erin Wallin of the University of Hawaii and mountaineer Danny Uhlmann, who is now studying geology at the University of Lausanne.
Those Other Volcanoes
Mount Erebus is the only active volcano in Antarctica. He and his sleeping volcano, Mount Terror, were named after Sir James Ross’ explorer ships, which he discovered and the trans-Antarctic mountains in 1841. Mount Erebus was first ascended by Sir Ernest Shackleton and party in 1908.
Erebus exemplifies a family of volcanoes with an alkaline chemical composition, with lavas relatively rich in sodium, potassium, and other elements including rare earth elements, although they are relatively poor in silica.
Alkaline volcanoes are very different from volcanoes such as the Cascade Range, which stretches from northern California through British Columbia to Alaska. The waterfalls are in a place where the Earth’s tectonic plates are pushing each other, with the oceanic crust forced under the crust of the continent. As the oceanic crust sinks to the Earth and partially melts, the water in the rocks becomes part of the melt and is the dominant “volatile”, or molecule that is easily extinguished, or bubbles come out. of a solution like the gas of a carbonated beverage.
This evolving magma rises in and through the crust, but usually does not reach the surface because, as the pressure of the superimposed crust decreases with ascent, water explodes, sometimes explosively, as in the case of Mount St Helens in 1980 or Mount Lassen in 1912. The remaining magma stops and freezes in place, usually at a depth of about three miles (five kilometers).
But Erebus Volcano on Ross Island in Antarctica is in a continental rift zone. Continental rifting occurs when the Earth’s crust and mantle separate. Western Utah is an example of a rift zone. It is located on the eastern edge of the Great Basin Geological Province, which is actively spreading and slowly spreading from east to west. Erebus is on the fringes of the West Antarctic Rift System, which originated tens of millions of years ago and continues today.
Wannamaker and Hill complete an MT site near the edge of Erebus Crater, with the flags of the US Antarctic Program and the Marsden Fund of the Royal Society of New Zealand. Credit: Mark Deaker.
Rift zone magmas also contain volatile substances from the recycling of crust and ocean sediments, but these are much older and are released to the surface through the rift process. Instead of water, the volatiles in these magmas are dominated by CO2.
Erebus also has a persistent lava lake, a classic feature of an evolved CO2-rich rift volcano. But lava lakes, also exemplified by the Nyiragongo volcano in East Africa and others, are not found in arc volcanoes like the Cascades and show that there must be something in the rift volcanoes that allows magma reach the surface relatively peacefully.
Representing the magma inside the Earth
It is not practical to collect rock samples from depths of more than a few kilometers below the surface, so researchers rely on geophysical methods to infer structures and processes at greater depths. This is similar to computed tomography of the human body. The most applied and familiar geophysical techniques are seismic, where sound waves are used for internal imaging. This is widely applied, for example, in oil and gas exploration. However, the natural seismic sources that can reach the depths of the Earth are scarce around the Erebus volcano, and the images that use these have only been obtained at shallow depths.
Hill, Wannamaker, and colleagues used a method called magnetoteluric probing. Magnetoteluric sounding uses natural electromagnetic waves generated by the sun and lightning. Most of these waves travel through the air, but “some of them penetrate the Earth, scatter the rock structures of interest and return to the surface, where we can measure them” with sophisticated “voltmeters,” says Wannamaker.
As electromagnetic waves travel through the Earth’s interior, they travel faster or slower depending on the extent to which rock and other materials conduct or resist electricity. Magma is conductive, so it can be detected with this technique.
This is not the Wannamaker’s first geophysical foray into Antarctica. They, with U’s alum and co-author Dr. John Stodt, were pioneers in the technique of high-fidelity magnetoteluric measurements in polar ice sheets. In addition to studying in central West Antarctica and the South Pole, Wannamaker led a multi-season campaign in the Central Transantarctic Mountains showing how these mountains rose. His technique is now being used by other researchers in both the Arctic and Antarctic polar regions.
From 2014 to 2017, Wannamaker and his colleagues measured 129 magnetoteluric sites covering Ross Island in Erebus. A computer program then assembled the patterns of backscattered electromagnetic radiation from all stations to create an image of the Earth’s crust and upper mantle across the island and volcano at a depth of about 60 miles (100 km). ).
Its magnetoteluric data show a steep conduit of low electrical resistivity that originates in the upper mantle: the source of magma. But the conduit makes a sharp side turn into the deep crust before reaching a shallower magmatic storage and lava lake from the summit. “We interpret the lateral rotation to represent a structural‘ fault valve ’that controls the episodic flow of magma and CO2 gases, which fill and heat the evolutionary chamber of high-level phonolite magma,” says Wannamaker. Phonolite is the type of rock formed by Erebus magma.
This magmatic valve is probably formed by the intersection of north-south and east-west faults, as it is known that there are faults with the same east-west orientation in the area around Erebus and provides the path of the magma to the surface.
Unlike the H2O-rich arc volcanoes of the Cascades and Pacific Rim, the CO2-dominated Erebus shows the structures that allow magma to rise directly into the volcanic lava lake, as the magma does not ‘stops in the crust like water-dominated magmas. .
“Understanding the transport controls and pathways of this type of CO2-dominated volcano reveals to us the scales and volumes of volatile transport on Earth,” says Wannamaker. “These volcanoes elsewhere are important hosts for essential mineral deposits such as rare earths, increasingly important for society’s future resource needs.”
Below: Volcanic Secrets Revealed More Information: Transcorporal Structural Control of CO2-Rich Extensional Magmatic Systems Revealed on Mount Erebus Antarctica, Communications of nature (2022). DOI: 10.1038 / s41467-022-30627-7 Provided by the University of …