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Chlorine Heterogeneity in Volcanic Glass as a Faithful Record of Silicic Magma Degassing
| Title: | Chlorine Heterogeneity in Volcanic Glass as a Faithful Record of Silicic Magma Degassing |
| Authors: | Yoshimura, Shumpei Browse this author →KAKEN DB | | Nakagawa, Mitsuhiro Browse this author |
| Keywords: | bubble growth | | bubble resorption | | chlorine | | corrosion | | degassing | | open-system gas loss | | welding |
| Issue Date: | May-2021 |
| Publisher: | American Geophysical Union |
| Journal Title: | Journal of geophysical research. Solid earth |
| Volume: | 126 |
| Issue: | 5 |
| Start Page: | e2020JB021195 |
| Publisher DOI: | 10.1029/2020JB021195 |
| Abstract: | Degassing processes occurring within silicic magma, such as bubble growth, bubble resorption, the welding of magma fragments, and open-system gas loss are crucial in the control of volcanic eruption and lava emplacement, yet their details are still debated. To examine the possibility that these degassing processes are recorded in volcanic glass as heterogeneous Cl distribution patterns, we experimentally simulated these processes by heating rhyolitic obsidian and analyzed the distribution of Cl content in the recovered sample. The results showed that, for bubble growth, Cl diffused toward the bubble interface, leading to Cl depletion around the bubble. For bubble resorption, Cl was discharged from the bubble to the melt, leading to Cl enrichment in the ambient melt. For welding of magma fragments, Cl was depleted near the welded interface because each fragment had degassed Cl at the surface before the welding took place. For open-system gas loss, Cl exsolved at the bubble interface while the bubble itself was being collapsed into a chain of small bubbles and a Cl-depleted tail. These results indicate that Cl distribution is a reliable record of the experienced degassing processes. We then analyzed the Cl distribution in silicic lava from Naruko volcano, Japan, to study the gas flow mechanism. We observed that the glassy matrix was progressively corroded into porous crystalline material. The interface of the glass was highly enriched in Cl. We conclude that a Cl-rich gas fluxed through hot lava and corroded the glass, developing a porous, gas-permeable region. |
| Rights: | Copyright 2021 American Geophysical Union. |
| Type: | article |
| URI: | http://hdl.handle.net/2115/83128 |
| Appears in Collections: | 理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)
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Submitter: 吉村 俊平
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