| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | March 6, 2020 |
| Latest Amendment Date: | March 6, 2020 |
| Award Number: | 1945763 |
| Award Instrument: | Standard Grant |
| Program Manager: |
David Lambert
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | March 15, 2020 |
| End Date: | August 31, 2022 (Estimated) |
| Total Intended Award Amount: | $152,520.00 |
| Total Awarded Amount to Date: | $152,520.00 |
| Funds Obligated to Date: |
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| 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: |
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): | Instrumentation & Facilities |
| Primary Program Source: |
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| 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
This project will support the acquisition of a new apparatus to study the properties of viscously deforming rocks at high pressure and temperature. The viscous flow of rocks is an essential aspect of the growth of mountains, the convection of the mantle, and the motion of tectonic plates. Moreover, the deformation of rocks is elemental to numerous geologic hazards, such as earthquakes, tsunami, and volcanic eruptions. By studying rock rheology in controlled laboratory setting we can develop new insight into the materials science of rocks, and provide tools for numerous geological or geophysical investigations. Unlike many other disciplines, the primary instrumentation used in rock deformation laboratories cannot be purchased commercially, but must be built to specification. Nearly every apparatus used in a rock deformation lab has special capabilities that enable specific types of investigations. The apparatus that will be built for this project is particularly useful for the study of rocks that experience extremely large magnitudes of deformation, such as those that might be sheared along the boundaries between tectonic plates.
The objective of this project is to construct a second Large Volume Torsion (LVT) apparatus, building upon an existing successful design. The LVT has several key characteristics that render it unique among rock deformation apparatuses. It is able to generate high pressures and temperatures, as well as large shear strains, on samples that are large enough to provide statistically meaningful information about deformation microstructures. Pressure, up to several GPA, is generated using tapered Drickamer-style anvils and a solid ceramic confining medium. Resistance heaters generate temperatures up to 1600 K. Large shear strains (> 10) can be generated by rotating one anvil with respect to the other. There are a number of projects underway that use data from the LVT apparatus, as well as several targets for future efforts. Experiments on the deformation and mixing of two-phase composites are used to understand the origins of mylonites and the rheology of plate boundary shear zones. Experiments on grain-size evolution over a large range of shear strains help clarify strain-weakening processes. Experiments to investigate the development of crystallographic preferred orientation are used to better interpret seismic anisotropy in the mantle. Experiments at low strain-rates will be used to elucidate the rate dependence of microstructural evolution. The acquisition of a second apparatus will effectively double the capacity of the rock deformation lab at Washington University in St. Louis, allowing the PIs to train more students, host visitors, develop new techniques, and explore new parameter space.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
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.
This award supported the construction of a new device for shearing rocks at tremendous pressures and temperatures. The purpose of this device is to recreate the conditions in Earth's interior, particularly along the boundaries between tectonic plates where deforming rocks create mountain belts and generate numerous geologic hazards. The device is known as a Large Volume Torsion (LVT) apparatus; this is the second LVT apparatus that has been built in the Experimental Studies of Planetary Materials (ESPM) lab at Washington University in St. Louis.
The new apparatus - LVT2 - is capable of deforming relatively large specimens (4.2 mm diameter cylinders) at pressures up to 3 GPa and temperatures up to 1300°C, to shear strains in excess of γ = 50. To do so, a torsional actuator capable of turning freely under large normal loads is placed inside a 150 ton electronically-controlled hydraulic press. Gear reduction of ~1,000,000:1 is applied so that the torsional actuator can be rotated slowly by a small stepper motor (as slowly as 1 full rotation in approximately 30 years). Typical shear strain-rates range from 10-5 - 10-7 s-1. Tapered tungsten carbide anvils concentrate the force of the hydraulic press so that large pressures and stresses are generated. Temperature is generated by running a large current through a graphite resistance heater. All parts of the sample assembly are contained in a water-cooled pressure vessel with an inner diameter of 40 mm. A high precision load / torque transducer is used to monitor the forces applied to the deforming specimens.
By building a second LVT apparatus the ESPM lab is able to accommodate more scientists, including undergraduate and graduate students, and postdoctoral trainees. In effect, the construction of the LVT2 apparatus has doubled the research capacity of the ESPM lab. Future experiments will include studies of deformation at conditions relevant to the deep crust and uppermost mantle.
Last Modified: 01/03/2023
Modified by: Philip Skemer
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