| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | June 26, 2013 |
| Latest Amendment Date: | June 26, 2013 |
| Award Number: | 1246700 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Robin Reichlin
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2013 |
| End Date: | August 31, 2017 (Estimated) |
| Total Intended Award Amount: | $249,923.00 |
| Total Awarded Amount to Date: | $249,923.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1109 GEDDES AVE STE 3300 ANN ARBOR MI US 48109-1015 (734)763-6438 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1100 North University Avenue Ann Arbor MI US 48109-1005 |
| 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): | Geophysics |
| 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
Continents slowly drift across the Earth's surface due to the forces of plate tectonics. Oceanic crust is generated at mid-oceanic ridges and is returned after some one hundred million years back into the Earth's interior at subduction zones. Seismological investigations give us a blurry few of the subducting slabs that appear to sink towards the base of the mantle. Geochemical sampling at mid-oceanic ridge volcanoes and at hotspots such as Hawaii tell us the long term story about how the ancient slabs are absorbed by the mantle and brought back up by the slow churning of mantle convection. The formation and recycling of oceanic crust has a clear strong influence on the chemical and the thermal evolution of the Earth, but we remain in the dark as how changes in physical properties, that occur deeper in the Earth, affect the behavior of the crust and its mixing back into the mantle. This research project will add a third way of looking at the dynamic Earth by use mathematical models that predict how plate tectonics affects the composition and thermal state of the Earth. The mathematical models are suited to predict the dynamical evolution of the Earth over its entire age. The predictions can then be compared to the observations of the present day Earth (as provided by seismology) and the longer term perspective that geochemistry provides.
The new aspects of the modeling approach include the consistent treatment of compressibility and the associated phase changes that occur primarily between 440 and 670 km depth in the Earth's mantle. The compressible effects will allow the PI to consider thermodynamically consistent modeling where the results can be compared directly to seismological observations of the present day state of the Earth's mantle. The investigators will use high resolution finite element models of mantle convection that include a energetically consistent approach to simulated plates.
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.
Plate tectonics is the surface manifestation of slow convection in the mantle. At mid-oceanic ridges oceanic crust is formed by melting and this crust is recycled at subduction zones. Once it is subducted the oceanic crust is denser than the surrounding mantle and descends to the core-mantle boundary where it slowly warms up and is mixed back in. It can rise in thermal plumes that underlie Earth's major hotspots such as Iceland and Hawaii.
Much as marshmallows can be squeezed to a more compact and higher density form, Earth's silicates compress as they are buried under increasing weight. This also leads to solid-solid phase changes in the silicates that make up the mantle and crust leading to higher densities and potential locations for slabs to founder or plumes to be slowed down or accelerated, leading to geometrical changes in the plume conduit.
We have explored various aspects of the plate tectonic - mantle convective system focusing in particular on the recycling of oceanic crust and mantle plumes. Seismic waves can scatter of heterogeneity leading to distinct wave forms in seismic records. By combining mantle convection models of crustal reycling we showed that these scattered waves can be satisfactorily explained by the presence of large pools of recycled oceanic crust, which is also in line with evidence from geochemical observations. We also tested how plumes that rise in a compressible mantle and interact with the main phase changes between 400 and 670 km depth can be imaged by traditional seismological methods. We showed that the general lack of clear imaging of the deep mantle plumes by seismology is due to the lack of sufficiently broad and dense seismic networks.
Last Modified: 01/25/2018
Modified by: Peter E Van Keken
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