| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | August 1, 2013 |
| Latest Amendment Date: | June 19, 2015 |
| Award Number: | 1321976 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Sonia Esperanca
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 1, 2013 |
| End Date: | July 31, 2017 (Estimated) |
| Total Intended Award Amount: | $312,841.00 |
| Total Awarded Amount to Date: | $312,841.00 |
| Funds Obligated to Date: |
FY 2015 = $99,914.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
660 S MILL AVENUE STE 204 TEMPE AZ US 85281-3670 (480)965-5479 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Arizona State University Tempe AZ US 85287-1604 |
| 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: |
01001314DB NSF RESEARCH & RELATED ACTIVIT |
| 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
Silica, or SiO2, is one of the primary chemical components of the Earth's crust and mantle, and forms the common minerals quartz, tridymite and coesite on the Earth's surface. At higher pressures characteristic of the mantle, these minerals transform into denser minerals, ultimately transforming into the mineral stishovite (also found in impact sites such as Meteor Crater). Stishovite is of great interest because if its high density and high (6-fold) coordination of the silicon atom, as well as its expected presence in rocks initially formed at the surface, but brought deep into the Earth by subduction. Recent findings by the team, using a multi-anvil high pressure apparatus, demonstrate that under high pressure and modest temperature, ordinary water, H2O, is absorbed by stishovite in relatively significant amounts (up to several weight percent), and the hydrogen becomes part of the crystal structure of the mineral in the form of an OH- ionic molecule. The structural volume of the mineral expands as a result of the addition of H2O. No additional components are needed to achieve this behavior ? only pure H2O and SiO2. This surprising discovery raises new questions about the structural chemistry of stishovite, and the behavior of stishovite and other minerals in the Earth.
In the proposed research, the investigators will pursue a more detailed study of the rates and quantities of water absorbed in stishovite at different pressures and temperatures, including those relevant to the Earth's interior. Furthermore, they will study the effect of water contents on the physical properties of the stishovite such as compressibility and sound velocity. This research is expected to contribute to fundamental understanding of the behavior of H2O in contact with silicates at high pressures, which is important for delineating processes involved in the Earth's overall hydrologic cycle. Results will clarify the crystal chemical implications of stishovite hydration. Also this research is of significant mineralogical interest in the understanding of hydrogen in minerals, and may be important in understanding the mineralogical make-up of gas giant planets.
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.
Silica, or SiO2, is one of the primary chemical components of the Earth’s crust and mantle, and forms the common minerals quartz, tridymite and coesite on the Earth’s surface. At higher pressures of the mantle, these minerals transform into denser minerals, ultimately transforming into the mineral stishovite (also found in impact sites such as Meteor Crater). Stishovite is of great interest because of its high density and high (6-fold) coordination of the silicon atom, as well as its expected presence in rocks initially formed at the surface, but brought deep into the Earth by subduction.
In this project, through experimental investigations, we have examined the hypothesis if the dense forms of silica can contain significant amount of H2O in their crystal structures in the deep mantle. We have created the extreme pressure and temperature conditions expected for the deep mantle in the laser heated diamond anvil cell and studied how silica changes under the conditions using bright X-ray sources at the Advanced Photon Source and Advanced Light Source. We discovered that dense silica can store significant amounts (up to several weight percent) of H2O, and the hydrogen becomes part of the crystal structure of the mineral in the form of an OH- ionic molecule. No additional components are needed to achieve this behavior – only pure H2O and SiO2.
The deep mantle has been believed to contain very little OH. However, our discovery opens up possibilities that significant amount of water can be transported into the deep mantle and stored there. Because OH can make rocks melting at lower temperatures, the possible presence of OH in silica will impact our understanding on the chemistry of the deep mantle. Because OH decreases strength of rocks, our results have important implications for the vigor of convection in the deep mantle. Given that the mantle convection vigor and melting are ultimately related to some important volcanoes and tectonic motions on the surface, our results provide important data for building our knowledge on how deep processes affect the surface environment. Our study also shed lights on the depth extent and geological time scale of the cycle of water, which is a critical ingredient for the habitability of our planet, through incorporation of the role of the deep interior of the Earth.
Last Modified: 10/30/2017
Modified by: Sang-Heon Shim
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