| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | January 21, 2010 |
| Latest Amendment Date: | January 30, 2012 |
| Award Number: | 0841063 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Candace Major
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | February 1, 2010 |
| End Date: | January 31, 2015 (Estimated) |
| Total Intended Award Amount: | $445,769.00 |
| Total Awarded Amount to Date: | $445,769.00 |
| Funds Obligated to Date: |
FY 2011 = $151,208.00 FY 2012 = $159,730.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 (508)289-3542 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 |
| 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): |
Marine Geology and Geophysics, GeoPRISMS |
| Primary Program Source: |
01001112DB NSF RESEARCH & RELATED ACTIVIT 01001213DB 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
This project will utilize active- and passive source seismic techniques, using short period and broad band OBSs, respectively, in the Mariana forearc, trench, and outer rise, in order to image the distribution of upper mantle serpentinization. This study will address a central question regarding the importance of serpentinite for understanding subduction zones. The research will quantify the flux of water subducted by upper-mantle serpentinite, and explore the relationships between serpentinization and seismicity in the outer forearc and outer rise.
Broader Impacts: This study has much relevance to arc magnatism and will help quantify the hydration state of the earth's mantle, thus addressing a primary goal of the Subduction Factory initiative of the MARGINS program. The project provides educational support for several graduate and undergraduate students.
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.
Water released from the earth through volcanoes needs to be replenished so that plate tectonics can continue to operate; and plate tectonics needs to operate to maintain a living planet. Our best current hypothesis for how the earth is rehydrated is through the hydration of subducting mantle, which is enabled by faults created as the subducting plate bends. The primary goal of this project is to test this hypothesis.
To test the hypothesis, we are measuring the seismic velocity (a physical property related to strength) of the upper mantle beneath the bent plate where faults form and comparing this to measurements of unbent regions. If water has infiltrated the mantle, the mantle’s velocity will decrease. Seismic velocity will also decrease due to the presence of faults, and so a focus of our work has been to separate these two effects. We do this by measuring the azimuthal variation of seismic velocity. Making such a measurement near a trench is new, and much of our efforts have been spent developing methodology. In addition, we are making these measurements in two locations, the Marianas and offshore Central America. The plates in these two regions have different temperatures, due to their different ages, and consequently should retain different amounts of water. We have completed the measurement in Central America, and it seems that there is water in the mantle, but less water than has been estimated using techniques that do not account for azimuthal variation. It may be that the plate there is hotter than we think.
In Mariana, we collected a large dataset that we are still analyzing. These data are more complex than Central America because of the great depths here and because of the more involved history of this much older plate. A key event in this history was a dramatic re-intrusion of magma into the plate millions of years after it formed. Our results show that this re-intrusion has modified both the crust and the mantle, and we now understand these modifications sufficiently to compare the modified, unbent plate to the modified, bent and faulted plate. That work is progressing. When the results from Mariana are complete, we will have a better understanding of how Earth rehydrates itself.
Last Modified: 05/31/2015
Modified by: Daniel Lizarralde
