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February 3, 2020

Numerical Models Predict the Presence of Abundant Solid Argon
in the Earths Deep Interior and Provide Insights
into the Mechanism of Argon Cycling

1. Key Points

The results of numerical experiments conducted on a supercomputer showed that solid argon descends in to the Earth’s deep mantle, where it can be found in great abundance.
High-temperature and high-pressure experiments revealed that solid argon is lighter in density than the surrounding minerals that comprise the mantle, which raises the possibility that solid argon accelerates mantle upwelling.
The results of this study provide insights into the process of argon circulation within Earth’s deep interior and can be used to understand the mechanisms underlying the cycling of compounds with similar properties, such as water and carbon dioxide.


Shigeaki Ono, of the Research Institute for Marine Geodynamics at the Japan Agency for Marine–Earth Science and Technology (JAMSTEC), has found that an abundance of solid argon may exist in the Earth’s deep interior. This conclusion is based on the results of numerical models, as well as high-temperature and high-pressure experiments, conducted on a supercomputer to reproduce the conditions of argon in extreme environments. Argon, which is the third most abundant element in the atmosphere after nitrogen and oxygen, is also found dissolved in seawater, from which it may be incorporated into oceanic plates and descend into the Earth’s interior via subduction along ocean trenches. The transitions this argon undergoes before it erupts onto the Earth’s surface through volcanoes and other channels have not been well understood.

The results of Dr. Ono’s experiments revealed that the melting temperature of argon increases sharply as its pressure increases, indicating that argon descends into the Earth’s interior in a stable, solid condition. As solid argon is lighter in density than the minerals that comprise the mantle, it is possible that solid argon accelerates mantle upwelling flow. Furthermore, solid argon (Fig. 1) may stably exist in extreme environments, with temperatures of 2000ºC or higher and pressures of 1 million atmospheres (atm) or more, and it is thus believed to occur throughout the entire lower mantle*1 (~55% of the Earth’s total volume). These findings provide insight into the mechanism of global argon cycling (Fig. 2), which has previously remained enigmatic. In the future, Dr. Ono and his team at JAMSTEC plan to study other noble gases, such as helium, neon, and xenon, as well as volatiles, such as water and carbon dioxide, with the aim of understanding the evolution and roles of volatile compounds throughout Earth’s history. The study summarized here is scheduled for publication in Scientific Reports, an academic journal published by the Nature Publishing Group, on February 3, 2020 (JST).

Title: Fate of subducted argon in the deep mantle
Authors: Shigeaki Ono1,
1. Volcanoes and Earth’s Interior Research Center, Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology

*1. The Earth’s mantle is divided into the upper mantle, the transition zone, and the lower mantle, which extend to depths of 410 km, 660 km, and 2,900 km, respectively.


Fig. 1. Crystal structure of solid argon, which can remain stable under extreme conditions comparable to those in Earth’s core.


Fig. 2. Schematic of the mechanism of argon cycling within the Earth. At depths ≥660 km, abundant solid-state argon is present. Abbreviations: MOR, mid-ocean ridge.


(For this study)
Shigeaki Ono, Scientist, Volcanoes and Earth’s Interior Research Center , JAMSTEC
(For press release)
Public Relations Section, Marine Science and Technology Strategy Department , JAMSTEC
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