From The Woods Hole Oceanographic Institution: “Arc volcanoes are wetter than previously thought with scientific and economic implications”

From The Woods Hole Oceanographic Institution

May 26, 2022

Benjamin Urann, who graduated from the MIT-WHOI Joint Program in 2021 and is now a NSF postdoctoral fellow at University of Wyoming, analyzes water in minerals with a secondary ion mass spectrometer at the Woods Hole Oceanographic Institution. Photo by Ben Urann, © Woods Hole Oceanographic Institution.

The percentage of water in arc volcanoes, which form above subduction zones, may be far more than many previous studies have calculated.

This increased amount of water has broad implications for understanding how Earth’s lower crust forms, how magma erupts through the crust, and how economically important mineral ore deposits form, according to a new paper led by authors from the Woods Hole Oceanographic Institution (WHOI) published in Nature Geoscience.

Credit: Pixabay/CC0 Public Domain.

The estimated water concentrations in primitive arc magmas from this study are more variable and significantly higher than the average of about four weight percent of water found in other studies, according to the paper. The results show that primitive arc magmas may contain ~0.6–10wt% H2O and may reach H2O saturation of ~20wt% H2O after extensive crystal fractionation in the lower arc crust, the paper adds.

“The big picture here is that water is essentially the lubricant of plate tectonics. The water content is going to affect all sorts of different parameters involved in how tectonic plates move,” says lead author Benjamin Urann, who was a doctoral student in the Massachusetts Institute of Technology (MIT) – WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering at the time of the study.

“Being able to get some idea of what the actual water content of the arc magmas is, which is what we did in this study, can help refine estimates of how much water is being subducted deep into the mantle globally; quantify different water reservoirs on Earth, including surface and deep water reservoirs; and better understand the transport between these different reservoirs,” says Urann, who is currently a National Science Foundation Ocean Sciences Postdoctoral Research Fellow at the University of Wyoming. Urann added that the paper also discusses the implications of water content for forming economically important ore deposits, such as porphyry copper deposits. These deposits make up about 60% of the world’s source of copper, according to the U.S. Geological .

Many earlier studies have relied on techniques such as measuring melt inclusions—which are tiny droplets of magma that have been trapped by a crystals that grows around them—and measuring lava and other volcanic deposits that have erupted to the Earth’s surface. “However, these methods have inherent limitations that obfuscate the full range of H20 in arc magmas,” the paper states.

Urann and his Ph.D. supervisor, Véronique Le Roux, who is a co-author of the paper, developed methods with the Secondary Ion Mass Spectrometry instrument located at WHOI to measure water content in minerals, with their work building on other efforts that suggested that arc magmas should contain significantly more H20 than inferred from melt-inclusion measurements.

The researchers determined that instead of examining lava samples that have erupted to the Earth’s surface, it would be fruitful to examine deep crustal magmas that have not lost too much of their water content.

“Although you can’t retrieve the liquid magma at these depths, what you may be able to sample is a cumulate: it is magma that has solidified at depth in the crust. We’re lucky enough that sometimes with plate tectonics, some of those really deep crusts are exhumed at the surface,” says says Le Roux, associate scientist in the Geology and Geophysics department at WHOI, and Faculty member of the MIT-WHOI Joint Program. The researchers used cumulates that the paper’s co-authors had collected from the Kohistan paleo-arc terrane in the Himalaya Mountain range in northwestern Pakistan.

Instead of examining surface rocks that travel far up through the crust as magma, and lose much of their water content in the process, the researchers examined magma – lower crustal cumulates – that had crystallized deep down in the crust at a high enough pressure to retain their original water content signature.

Le Roux says that “analyzing water in cumulate minerals is a new promising approach to access the deep levels of the crust in subduction zones”.

The researchers calculated that the magma they analyzed contained between 10-20 weight percent of water depending on the magma’s composition. “While this weight percent of water had been predicted experimentally as being possible, it had never been shown on natural samples,” Le Roux said.

“The bottom line is that arc magmas can be wetter than we thought,” said Urann.

This study was supported by NSF awards to Le Roux, Behn, and Chin, funding from the Woods Hole Oceanographic Institution Ocean Venture Fund and from the National Science Foundation’s (NSF, USA) Division of Ocean Sciences Post-doctoral Research Fellow grant to Urann;; and support from the Visiting Scholar at SCIENCE programme at the University of Copenhagen, Denmark, to Le Roux.

See the full article here .


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The Woods Hole Oceanographic Institution is dedicated to advancing knowledge of the ocean and its connection with the Earth system through a sustained commitment to excellence in science, engineering, and education, and to the application of this knowledge to problems facing society.

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The ocean is a defining feature of our planet and crucial to life on Earth, yet it remains one of the planet’s last unexplored frontiers. For this reason, WHOI scientists and engineers are committed to understanding all facets of the ocean as well as its complex connections with Earth’s atmosphere, land, ice, seafloor, and life—including humanity. This is essential not only to advance knowledge about our planet, but also to ensure society’s long-term welfare and to help guide human stewardship of the environment. WHOI researchers are also dedicated to training future generations of ocean science leaders, to providing unbiased information that informs public policy and decision-making, and to expanding public awareness about the importance of the global ocean and its resources.

The Institution is organized into six departments, the Cooperative Institute for Climate and Ocean Research, and a marine policy center. Its shore-based facilities are located in the village of Woods Hole, Massachusetts and a mile and a half away on the Quissett Campus. The bulk of the Institution’s funding comes from grants and contracts from the National Science Foundation and other government agencies, augmented by foundations and private donations.

WHOI scientists, engineers, and students collaborate to develop theories, test ideas, build seagoing instruments, and collect data in diverse marine environments. Ships operated by WHOI carry research scientists throughout the world’s oceans. The WHOI fleet includes two large research vessels (R/V Atlantis and R/V Neil Armstrong); the coastal craft Tioga; small research craft such as the dive-operation work boat Echo; the deep-diving human-occupied submersible Alvin; the tethered, remotely operated vehicle Jason/Medea; and autonomous underwater vehicles such as the REMUS and SeaBED.
WHOI offers graduate and post-doctoral studies in marine science. There are several fellowship and training programs, and graduate degrees are awarded through a joint program with the Massachusetts Institute of Technology. WHOI is accredited by the New England Association of Schools and Colleges . WHOI also offers public outreach programs and informal education through its Exhibit Center and summer tours. The Institution has a volunteer program and a membership program, WHOI Associate.

On October 1, 2020, Peter B. de Menocal became the institution’s eleventh president and director.


In 1927, a National Academy of Sciences committee concluded that it was time to “consider the share of the United States of America in a worldwide program of oceanographic research.” The committee’s recommendation for establishing a permanent independent research laboratory on the East Coast to “prosecute oceanography in all its branches” led to the founding in 1930 of the Woods Hole Oceanographic Institution.

A $2.5 million grant from the Rockefeller Foundation supported the summer work of a dozen scientists, construction of a laboratory building and commissioning of a research vessel, the 142-foot (43 m) ketch R/V Atlantis, whose profile still forms the Institution’s logo.

WHOI grew substantially to support significant defense-related research during World War II, and later began a steady growth in staff, research fleet, and scientific stature. From 1950 to 1956, the director was Dr. Edward “Iceberg” Smith, an Arctic explorer, oceanographer and retired Coast Guard rear admiral.

In 1977 the institution appointed the influential oceanographer John Steele as director, and he served until his retirement in 1989.

On 1 September 1985, a joint French-American expedition led by Jean-Louis Michel of IFREMER and Robert Ballard of the Woods Hole Oceanographic Institution identified the location of the wreck of the RMS Titanic which sank off the coast of Newfoundland 15 April 1912.

On 3 April 2011, within a week of resuming of the search operation for Air France Flight 447, a team led by WHOI, operating full ocean depth autonomous underwater vehicles (AUVs) owned by the Waitt Institute discovered, by means of sidescan sonar, a large portion of debris field from flight AF447.

In March 2017 the institution effected an open-access policy to make its research publicly accessible online.

The Institution has maintained a long and controversial business collaboration with the treasure hunter company Odyssey Marine. Likewise, WHOI has participated in the location of the San José galleon in Colombia for the commercial exploitation of the shipwreck by the Government of President Santos and a private company.

In 2019, iDefense reported that China’s hackers had launched cyberattacks on dozens of academic institutions in an attempt to gain information on technology being developed for the United States Navy. Some of the targets included the Woods Hole Oceanographic Institution. The attacks have been underway since at least April 2017.