| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 9, 2014 |
| Latest Amendment Date: | April 30, 2018 |
| Award Number: | 1424932 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Jennifer Wade
jwade@nsf.gov (703)292-4739 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | July 15, 2014 |
| End Date: | June 30, 2019 (Estimated) |
| Total Intended Award Amount: | $7,053.00 |
| Total Awarded Amount to Date: | $7,053.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1000 JEFFERSON DR SW WASHINGTON DC US 20560-0008 (202)633-7110 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1000 Constitution Avenue, NW Washington DC US 20560-0001 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Petrology and Geochemistry |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
One of the most influential chemical components found in magmatic systems on Earth is H2O (water). It affects both the physical and chemical behavior of magmas by changing their density, viscosity, and the minerals that crystallize from them during cooling. Due to its large change in volume as magmas erupt, H2O also strongly influences how explosive and hazardous a volcano may be. It also plays a large role in the formation of magma-related ore deposits by interacting with other important ore-forming elements such as S, Cl, and F. Despite its critical role, the chemical behavior of H2O in magmas at concentrations below saturation (i.e. where H2O is dissolved in the silicate melt portion of the magma, but no fluid/vapor phase is present), or where a fluid/vapor phase is present but not composed of pure H2O (i.e. is mixed with another volatile component such as CO2), is relatively unconstrained by laboratory experiments. This knowledge deficit creates a significant gap in the current understanding of magmatic behavior, and hampers the modeling of important physical characteristics such as magma density and viscosity, as well as an understanding of the overall chemical evolution of a magma body. The experimental work of this project will address this need by directly measuring the chemical activity of H2O in magmas at these conditions. This study includes support for one undergraduate student. The researchers also plan to share splits of the calibration
glasses developed as part of this project with the National Rock and Ore Collection at the Smithsonian. From there, they will be made available for loan to the international research community.
The experimental measurement of the chemical activity of H2O in magmas at undersaturated conditions will be accomplished by synthesizing hydrous melts from natural rock compositions at high pressure and temperature. These melts will equilibrate at P-T-XH2O conditions above their liquidus using a double capsule method with a known oxygen fugacity buffer in the outer capsule. After coming to equilibrium, the melts will be rapidly quenched to a glass. By measuring the oxidation state of iron in the resulting glass using both X-ray Absorption Near Edge Structure spectroscopy (XANES) and wet chemistry, the oxygen fugacity of the melt will be known, and the activity of H2O in the melt can be calculated from the oxygen fugacity difference between melt and the experimental oxygen buffer. By varying the initial concentration of H2O added to the melt (and pressure and temperature), the activity-concentration relations for a given magma composition will be determined. This data will then be used to develop descriptive thermodynamic equations, which in turn will be used to improve existing comprehensive phase equilibria models (i.e. MELTS) at H2O-undersaturated conditions.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
You may find it surprising that red hot lava contains dissolved water, but in fact, the magmas (molten rock plus or minus minerals and gas bubbles) that reside beneath volcanoes have many weight percent of dissolved water. The water dissolved in magma strongly influences the style of volcanic eruptions we see and the ability of magmas to change chemically and physically deep in the Earth.
Our goal with this project was to make the first direct experimental measurements of water’s influence (its chemical activity) in water-undersaturated magmas (magmas that don’t have steam bubbles). The ultimate goal is to apply these laboratory data in thermodynamic models to improve their predictive capability about real magmas on Earth and other planets.
In the course of this work we had to develop new spectroscopic methods for analyzing the oxidation state of iron atoms dissolved in the hydrous experimental melts we created in the lab. The X-ray dose we routinely apply during analysis of anhydrous glasses was too high for these more fragile, hydrous, glasses. We resolved this issue by developing new methodology. The resultant publication (Cottrell et al., 2018 in American Mineralogist) that describes the new methodology should assist both academic and industrial glass chemists around the world to improve their analytical protocols.
In the end, we found that the activity of water in our experiments was in good agreement with existing, calculated, solubility models. This confirmation represents an important step in our understanding of the chemical behavior of hydrous melts of rock, and has significant implications for modeling that behavior in real water-undersaturated magmas.
This project also provided the opportunity for Jack Touran to work as an undergraduate research assistant. In the course of his time as a research assistant (approximately 2 years), he gained significant experience using high pressure and temperature laboratory equipment and analytical equipment including electron microprobe and Fourier transform infrared spectrometry, as well as X-ray absorption near edge structure spectroscopy. Jack is now a graduate student at Washington University pursuing a PhD in the geosciences.
Last Modified: 06/24/2020
Modified by: Elizabeth Cottrell
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