| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | June 15, 2015 |
| Latest Amendment Date: | June 15, 2015 |
| Award Number: | 1513714 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Dennis Geist
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | July 1, 2015 |
| End Date: | June 30, 2018 (Estimated) |
| Total Intended Award Amount: | $184,543.00 |
| Total Awarded Amount to Date: | $184,543.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1 PROSPECT ST PROVIDENCE RI US 02912-9100 (401)863-2777 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
164 Angell Street Providence RI US 02912-1929 |
| 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): | INTEGRATED EARTH SYSTEMS |
| 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 involves an interdisciplinary study of hydration, carbonation and oxidation of mantle peridotite interacting with aqueous fluids at temperatures below ~ 300C. The PIs will combine observations of outcrops and boreholes, geochemical analyses, structural measurements, geomechanical experiments and numerical modeling to investigate feedback between alteration and fluid transport, and to quantify the resulting geochemical fluxes. Field observations and sampling will take place mainly in the Samail ophiolite of Oman, where peridotite has undergone spreading-ridge-related hydrothermal alteration, hydration and carbonation in the hanging-wall of the subduction zone that emplaced the ophiolite over metasediments, and subaerial weathering. The PIs project will provide matching funds and results that dovetail with the 2015-2018 International Continental Scientific Drilling Program (ICDP) Oman Drilling Project, and the many other related efforts just getting underway. The PIs will continue their independently supported research on subduction zone alteration of mantle wedge peridotites at a range of pressures and temperatures, and work closely with other groups investigating seafloor and subduction-related peridotite alteration, in order to quantify the similarities and differences in alteration processes in these different tectonic environments. They will generalize their results to global alteration processes and geochemical cycles.
Alteration of peridotite is an essential process in Earth dynamics. Hydration of oceanic crust and mantle, followed by subduction, supplies water to drive arc volcanism, and modulates the hydrogen content of the mantle over time. Carbonate formation during alteration of peridotite, near the surface and in the hanging wall in subduction zones, is an important but poorly characterized link in the carbon cycle. Oxidation of minerals and concomitant reduction of fluids produces H2 and hydrocarbons, and a niche for chemosynthetic microbes. Chemical weathering is as important as magmatism and plate tectonics in shaping the Earths surface. The interplay of chemical and physical mechanisms of peridotite alteration is not well understood, but will be transformed as a result of emerging understanding of equilibria and kinetics in peridotite alteration, and reaction-driven cracking that has left us poised on the brink of a breakthrough at this little-studied frontier. The PIs will take advantage of low temperature, near surface, active peridotite alteration in Oman to study inputs, outputs, and the reaction zone in situ. Such a study is more difficult in smaller peridotite exposures with limited outcrop and more rainfall, nearly impossible in submarine hydrothermal systems, and completely impossible in studies of ancient systems. Such a comprehensive approach via 250 to 600 meter boreholes is very rare, if not unprecedented.
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 Brown University, our contributions to the project "Collaborative Research: Alteration of mantle peridotite: Geochemical fluxes and dynamics of far from equilibrium transport" involved running state-of-the-art deformation experiments designed to investigate links between crack growth, strain localization, and reactions at high temperatures. The machines we use are capable of deforming rock samples at pressures and temperatures consistent with conditions deep in the Earth, where both brittle deformation and high temperature creep processes are active. Much of our progress here involved understanding how higher temperatures stabilize crack growth. The application of higher temperatures allows cracks to grow more slowly, which results in a mode of strain that tends to be less localized. For this project, the tendency for strain to be either localized or distributed is important, as fluid fluxes and fluid pathways will be very different for these different styles of deformation. Another important contribution involved studying how the presence of hydrothermal fluids influenced the styles of deformation. At high pressures, we found evidence that the influence of fluids on the strength of altered peridotite increases after the onset of microcracking. We interpreted these data to indicate that crack opening results in an increase in the surface area over which the fluids act, making the role of fluid “more effective”. Conventional wisdom holds the opposite, namely that when crack growth initiates, the pressure in the fluid drops (owing to the increase in volume resulting from the crack opening), which in turn is expected to mitigate the role of fluids on strength. Understanding how the presence of fluids influences the brittle strength of rocks at high temperature and pressure conditions has a lot of potential applications for academic research in Earth Sciences, understanding of geohazards, and the energy industry.
Last Modified: 02/16/2019
Modified by: J. Gregory Hirth
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