Press Releases
JAMSTEC
Using Fluorine to Understand the Behavior of Water Inside the Earth
and Estimating the Water Content of the Juvenile Mantle
1. Key Points
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- It was discovered through the analysis of deep sea volcanic glass that fluorine content can be used to calculate the initial water content of Earth’s mantle.
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- The initial water content of Earth’s mantle was estimated to be approximately 0.075%, roughly 7 times higher than the upper mantle’s current water content.
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- The results of this study are expected to not only provide clues as to the origin of water on Earth, but also to contribute to our understanding of the environmental changes on Earth’s and the evolution of life.
2．Overview
Kenji Shimizu and colleagues at the Japan Agency for Marine-Earth Science and Technology’s (JAMSTEC) Super-cutting-edge Grand and Advanced Research (SUGAR) Program Kochi Core Laboratory conducted high-precision analyses of seafloor basaltic glass. These samples, which were collected worldwide, were formed when magma from the melted mantle erupted onto the seafloor and quenched, turning to glass. From their analyses, the team discovered that the fluorine content of these samples was a reliable indicator of the water content of the mantle. Additionally, they successfully estimated the amount of water initially contained within the Earth’s mantle using this indicator.
Water in the mantle has circulated through the interior and surface of the Earth throughout the planet’s 4.6-billion-year history, and it is thought to have had a major impact on changes in Earth’s surface and interior environments (Figure 1). Therefore, accurately estimating both the initial and current water content of the mantle is extremely important. However, this water is escaped from magma whenever there are volcanic eruptions (i.e., via degassing), and since the formation of volcanic rocks in the ocean occurs secondarily, extracting precise information about mantle-derived water from volcanic glass has been difficult until now.
In response to the aforementioned conditions, the research team carefully selected volcanic glass samples from ocean surveys in various locations around the world (Figures 2 and 3) and conducted high-precision analyses of their components, including water and fluorine. The results showed that among samples without water dispersal or additional effects, there was an extremely high correlation between water and fluorine content, with the water and fluorine content changing over time in the same way as the mantle (Figure 4). It was estimated that the initial water content of the Earth’s mantle was approximately 0.075%, roughly 7 times higher than the upper mantle’s current water content.
In the future, fluorine is likely to become an essential element for understanding water in the Earth’s interior. The results of this study have wide-ranging applications. Additionally, these findings are expected to play a role in clarifying the origin of water on Earth and the mechanism(s) of global geochemical cycle within the Earth’s interior.
This study was supported by JPSP KAKENI Grant Number JP18H04372, JP16H01123, JP15H02148, JP26287142, JP25610160, JP18H01320, and JP15H03751. The above results were published in Chemical Geology on July 17th, 2019 (JST).
Title: Identifying volatile mantle trend with the water-fluorine-cerium systematics of basaltic glass
Authors: Kenji Shimizu1, Motoo Ito1, Qing Chang2, Takashi Miyazaki2, Kenta Ueki2, Chiaki Toyama2,3, Ryoko Senda2, Bogdan S. Vaglarov2, Tsuyoshi Ishikawa1, Jun-Ichi Kimura2
Affiliations: 1. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology 2. Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology 3. Institute of Geology and Geoinformation, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST) 4. Graduate School of Social and Cultural Studies, Kyushu University
Figure 1. Areas of oceanic basalt with the same isotopic chemical compositions. Several mantle components have been proposed as explanations for the observed compositional range. Over the course of 4.6 billion years, depletions of water and magma (thick red arrow) from the initial mantle (a.k.a., the deep mantle), and accretions of pelagic sediments and oceanic crust to the initial mantle (thick blue arrows) occurred. This is considered to be the way the modern mantle diversified and became heterogeneous. Black arrows denote zones mantle components enriched in recycled materials.
Figure 2. Sampling sites for the seafloor basaltic glass used in this study. The symbols of samples used in this figure are indentical to those plotted in Figure 4. Circle, diamond and triangle symbols indicate massive glass, small glass analyzed in this study and small glass in previous study, respectively.
Figure 3. Massive basaltic glass from the seafloor (width: 5 cm) collected from the East Pacific Rise at a depth of 2600 m. Since the eruption occurred on the deep seafloor, the glass has no observable vesicles, indicating that original signatures of volatiles, such as water, were preserved.
Figure 4. Strong linear correlation between water and fluorine in the deep seafloor volcanic glass discovered in this study. The proposed mantle trend shown here is attributed to the mixture of upper mantle water and deep mantle water. Samples from seawater that had high concentrations of chlorine contamination or were rich in recycled materials were excluded, and only the samples marked with a circle (high-precision analysis values for large massive glass) were used to calculate the trend.
Contacts:
- (For this study)
- Kenji Shimizu, Research Scientist, Isotope Geochemistry Research Group,
Institute for Extra-cutting-edge Science and Technology Avant-garde Research, Kochi Institute for Core Sample Research - (For press release)
- Public Relations Section, Marine Science and Technology Strategy Department