| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | April 27, 2016 |
| Latest Amendment Date: | July 9, 2018 |
| Award Number: | 1606793 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Robin Reichlin
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | June 1, 2016 |
| End Date: | May 31, 2019 (Estimated) |
| Total Intended Award Amount: | $360,000.00 |
| Total Awarded Amount to Date: | $360,000.00 |
| Funds Obligated to Date: |
FY 2018 = $119,132.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
W5510 FRANKS MELVILLE MEMORIAL LIBRARY STONY BROOK NY US 11794-0001 (631)632-9949 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
167 ESS Building Stony Brook NY US 11794-2100 |
| 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): | STUDIES OF THE EARTHS DEEP INT |
| Primary Program Source: |
01001819DB 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
Heat convection in the Earth is controlled by flow of the hot, but solid mantle. This convection drives plate tectonics, generating major societal hazards (e.g., earthquakes, volcanic eruptions, tsunamis, etc.) and controls the compositional and thermal evolution of the planet. Since the early 1960s, quantifying the deformation properties of mantle rocks has been a major goal in experimental Earth Sciences. Advancement has been limited by technology, owing to serious difficulties in conducting experiments involving deformation of minerals at the extreme pressures and temperatures prevailing in Earth's deep interior. The upper-mantle (top 410 km) consists of peridotites, rocks comprised dominantly of olivine, i.e., the semi-precious gem known as peridot. In the transition zone (410-670 km depth) at pressure in excess of 140,000 atm, olivine is no longer stable and transforms into high-pressure minerals, wadsleyite and ringwoodite, which have comparable compositions but denser structures. Decades of experimental work have provided strong constraints on olivine plasticity, yet little is known about the viscosity of minerals in the transition-zone. The aim of the present project is to provide accurate computational models for the viscosity of Earth's transition zone, which will integrate new experimental data on wadsleyite and ringwoodite obtained in state-of-the art high-pressure deformation devices set at synchrotron facilities. These experiments, involving newly developed devices and analytical techniques, are at the forefront of research on the mechanical behavior of materials at high pressure. Besides advancing our understanding of mantle convection, this program will provide support and training in modern experimental science to one graduate student as well as undergraduate students. All the new experimental and analytical tools will become available to other scientists, advancing our general knowledge in high-pressure research. The team's results will find direct applications in Geophysics and Seismology, and broader applications in Materials Science.
Flow laws for Earth materials provide vital constraints on mantle dynamics, while knowledge of deformation mechanisms at the atomic scale provides insights into crucial observables such as seismic anisotropy. The complexity of the stress field within deforming rocks, which varies from grain to grain as plastic properties are anisotropic, can now be observed in situ using new high-pressure devices coupled with X-ray synchrotron radiation, and addressed by self-consistent mean-field modeling. In this project, the investigators will take advantage of these recent developments to address the plasticity of the transition zone. Specifically, they will study the flow properties of wadsleyite and ringwoodite as a function of iron and water contents, and constrain strength contrasts with olivine, using the Deformation-DIA apparatus and the newly developed D-TCup and DT-25. In situ X-ray radiography and diffraction will be used to measure strain, stress and texture (i.e., lattice preferred orientation). The new flow laws will be integrated into models for the effective viscosity and seismic anisotropy of the transition-zone. Modeling efforts will benefit from the second-order (SO) method, a recent improvement in mean-field schemes which describes accurately highly non-Newtonian materials, such as silicates. The models will account for stress-field heterogeneities due to crystal orientations, complex deformations mechanisms (dislocation glide and diffusion), incorporate several minerals, and improve confidence for extrapolation of results to geologic strain rates. The model construction will be flexible, allowing integration of additional phases and flow law parameters as they become available in the future. The outcome will give crucial insights on transition-zone viscosity, and the crystal preferred orientations that produce seismic anisotropy.
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.
The slow motions of tectonic plates generates numerous hazards such as earthquakes and tsunamis. Plate motions are driven by convective flows in the Earth’s rocky interior, the mantle. Down to 410-km depth, the main constituent of the mantle is olivine. This magnesium-iron silicate is also known as peridot, a semi-precious stone. Deeper in the mantle, in the transition zone, increasing pressures and temperatures transform olivine into denser minerals called ringwoodite and wadsleyite. It is critical to understand how these minerals behaves to model mantle thermal convection. Yet, studying their deformation at the extreme conditions of Earth’s interior is challenging. Here, the researchers used state-of-the art deformation devices to achieve this goal. They deformed mantle minerals at pressures and temperatures in excess of 150,000 atmospheres and 1400 degree Celsius. The devices are coupled with powerful X-rays at national synchrotron facilities which allow recording the stress and strain experienced by the minerals during deformation. Results are combined into mathematical expressions called rheological laws which account for mineral compositions and deformation conditions. These laws are ultimately used to model the dynamic behavior of the mantle in the aim to constrain the motions of tectonic plates.
In a first part of the project, the team measured the strength contrast between olivine and its high-pressure polymorph ringwoodite. The two minerals of same composition do not coexist at given pressure and temperature. The researchers, thus, used polymorphs of different compositions. They deformed iron-rich ringwoodite together with olivine containing less iron. By varying the iron content in each mineral, they quantified their relative strengths along the olivine/ringwoodite phase boundary. Using iron-rich compounds also allowed carrying out this study in a relatively lower range of pressures. These pressures are accessible in the Deformation-DIA, an apparatus used routinely at the Advance Photon Source at Argonne National Laboratory (IL). In a second part of the project, the team investigated the deformation of iron-poor olivine and wadsleyite, as those present in the Earth’s mantle. These more challenging experiments were carried out at higher pressure in a newly-developed deformation device called the DT-25. The team carried out among the very first experiments using this apparatus. The researchers had to overcome numerous technical challenges to successfully deform wadsleyite specimens and record its properties. This effort, besides providing new data, also participated to the development of the apparatus. The DT-25 is now up and running at the National Synchrotron Light Source II at Brookhaven National Laboratory (NY).
This project pushed the boundary of our understanding of how minerals, and more generally materials, deform at extremely high pressures and temperatures. These conditions prevail in planetary interiors as well as during impacts, whether natural or artificial. The project outcomes help better constraining the deformation properties of the Earth’s mantle, thus, better understand plate tectonics and associated hazards. Results were presented at international conferences and will be published in peer-reviewed journal articles (in preparation). They have broad impacts across scientific fields, notably mineral physics, geodynamic and materials science. This project also promoted training in high-pressure mineral physics for two graduate students at Stony Brook University (NY) and Brown University (RI).
Last Modified: 11/01/2019
Modified by: Donald J Weidner
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