| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | January 8, 2014 |
| Latest Amendment Date: | February 22, 2018 |
| Award Number: | 1352306 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Robin Reichlin
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | February 1, 2014 |
| End Date: | January 31, 2020 (Estimated) |
| Total Intended Award Amount: | $600,000.00 |
| Total Awarded Amount to Date: | $600,000.00 |
| Funds Obligated to Date: |
FY 2015 = $137,861.00 FY 2016 = $137,115.00 FY 2017 = $152,612.00 FY 2018 = $112,551.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1 BROOKINGS DR SAINT LOUIS MO US 63130-4862 (314)747-4134 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1 Brookings Drive St. Louis MO US 63130-4899 |
| 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): |
Tectonics, Geophysics |
| Primary Program Source: |
01001516DB NSF RESEARCH & RELATED ACTIVIT 01001617DB NSF RESEARCH & RELATED ACTIVIT 01001718DB NSF RESEARCH & RELATED ACTIVIT 01001819DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The theory of plate tectonics is the basis for most Earth science, providing context for interpreting such diverse phenomena as earthquakes and volcanoes, mountain building, and global climate. In spite of its broad scientific and societal importance, there are still fundamental unanswered questions about the underlying physical mechanisms of plate tectonics. The basic differences between the manifestation of tectonics on Earth and other terrestrial bodies are a major outstanding question in geophysics and planetary science. This research applies novel experimental approaches to study how rocks deform at the pressures and temperatures of planetary interiors to help understand the origins of plate tectonics on Earth.
To fulfill these research objectives, large strain torsional deformation experiments will be conducted on rocks of crustal and mantle composition. These experiments will be performed in the PI's newly built Large Volume Torsion apparatus (LVT), which has been optimized for experimental investigations at pressures of up to 6 GPa and temperatures of up to 1300 C. The focus of these investigations will be on the microphysical interaction between various mineral phases, in polymineralic rocks. The goal is to better understand how large shear strains modify the rheological properties of realistic rocks, and identify the conditions where these data deviate from experiments conducted to small strains on monomineralic material. Microstructural data will be incorporated into numerical models to simulate how variations in rheology influence the dynamical evolution of tectonic plates. This project also includes an integrated plan for teaching and research in rock mechanics at the undergraduate level. Few undergraduate curricula incorporate rock mechanics, and more exposure is needed to broaden research capabilities in this critical area. The PI will be developing a research-grade bench-top rock deformation apparatus that will be incorporated into the curricula of several undergraduate colleges with strong programs in Earth Science. Through curriculum and infrastructure development, this effort seeks to expand the number of undergraduate students who consider further research in experimental rock deformation.
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.
At high temperatures and pressures in Earth's interior rocks behave like a viscous fluid. Viscous deformation is necessary for the mantle to undergo convection, and is therefore essential to plate tectonics. The purpose of this project is to understand how rocks deform at mantle conditions, specifically at the highly sheared boundaries between tectonic plates. To achieve this goal we deformed composites of two different minerals, with varying proportions, at high pressure and temperature. Deformation experiments were conducted in the Large Volume Torsion (LVT) apparatus at Washington University in St. Louis. The LVT apparatus twists rock specimens and is capable of generating larger degrees of distortion or "strain" than other rock deformation apparatuses. After each experiment the specimens were examined using electron microscopy, which provides insight into the physics of how the minerals react to deformation.
Our results show that deformation of realistic polymineralic aggregates is different from monomineralic materials in several important ways. While both monomineralic and polymineralic materials undergo grain-size reduction via dynamic recrystallization, polymineralic rocks exhibit an additional process where the two mineral phases become intermixed. This phase mixing process reduces grain-size even further, which leads to additional weakening in rocks that deform by grain-size sensitive mechanisms. Phase mixing also inhibits coarsening of grains following deformation, which effectively keeps the rocks weaker for longer periods of time. Both grain-size reduction and the inhabitation of grain growth play a key role in the formation of mylonites, which are highly sheared rocks commonly found along plate boundaries. Our studies have also shown that the strains required to generate mylonitic microstructures are significantly larger than previously understood. This suggests that the dynamic weakening that occurs during the deformation of polymineralic rocks is a long, transient process, rather than one that rapidly achieves steady state during changing conditions. The evolution of rock rheology as a function of strain is an important factor that affects the origin and development of Earth-like plate tectonics.
Last Modified: 03/03/2020
Modified by: Philip Skemer
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