| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 10, 2018 |
| Latest Amendment Date: | July 10, 2018 |
| Award Number: | 1841806 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Jennifer Wade
jwade@nsf.gov (703)292-4739 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | June 1, 2018 |
| End Date: | January 31, 2019 (Estimated) |
| Total Intended Award Amount: | $7,388.00 |
| Total Awarded Amount to Date: | $7,388.00 |
| Funds Obligated to Date: |
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| Recipient Sponsored Research Office: |
140 COMMONWEALTH AVE CHESTNUT HILL MA US 02467-3800 (617)552-8000 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
140 Commonwealth Ave Chestnut Hill MA US 02467-3800 |
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Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| NSF Program(s): | Petrology and Geochemistry |
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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
Recycling of Earth's crust back down into the deep Earth has been invoked to explain a wide variety of Earth processes, including changes in the forces that move tectonic plates, and how the thickness and composition of Earth's crust evolved. All of these processes take place at depths inaccessible to humans. A volcanic eruption in the Pamir Mountains of Tajikistan has brought to light pieces of rock from 90 km deep in Earth that can be used to test recycling-related hypotheses. This project will provide training and research opportunities for graduate student Madeline Shaffer and several undergraduate students. Visits to local elementary schools will expose potential future scientists to Earth science. Continued development of the laser-ablation split-stream technique will benefit the broad range of visitors to their laboratory.
This collaborative US-Tajik-Romanian project has a two-pronged approach: 1) Laboratory geochronology and petrology that will constrain the timescale of recycling, and the compositions, densities and wavespeeds of the recycling materials. With some assumptions about protolith composition, the evolution in these physical properties can be calculated. 2) Geodynamic modeling of recycling crustal sections with different compositions and layers in different thermal gradients. The models will yield the calculated evolution of the physical properties of recycling crust and determine the types of crustal sections that may recycle. Because the Pamir-Tibetan Plateau is an archetypal continent-continent collision, ideas developed there can be applied globally.
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.
Recycling of continental crust into the mantle is among the most important processes driving the chemical and physical evolution of Earth’s crust. Understanding the compositional variability of the continental crust is important for human society, as the crust represents our source for natural resources and its structure controls the processes that lead to natural hazards. Continental crust is recycled through two dominant mechanisms: (1) subduction, where tectonic plates sink back into the mantle carrying continental material with them; and (2) foundering, or the removal of dense material from base of existing continental crust. These processes dictate the rates and types of crustal chemical and physical evolution—such as the secular evolution of continental volume—but are only loosely understood. This limitation has led to a wide range of viewpoints on the efficiency of the recycling process. For example, some studies predict nearly 95% of the continental crustal material entering subduction zones is returned to the deep mantle. By contrast, others argue that subducted material undergoes buoyancy-driven segregation, in which the dense (mafic) material returns to the mantle, but the light (felsic) material is relaminated to the base of the crust.
This award supported numerical modeling of the processes by which continental crust is recycled into the mantle and provided new constraints on the geologic conditions that governed recycling in the Earth’s past. This modeling effort was led by Behn (now at Boston College, formerly at Woods Hole Oceanographic Institution) in collaboration with co-PIs Brad Hacker and John Cottle at UC Santa Barbara. In particular, the award facilitated the research of UC Santa Barbara graduate student Ryan Stoner, former WHOI postdoc (now assistant professor at Peking University) Nan Zhang, and MIT/WHOI Joint Program Student William Shinevar. All three presented research supported by this award at international conferences; and Zhang and Stoner have submitted or are currently preparing manuscripts on their results. The source code for the models developed through this award has been made openly available to the community via the GitHub software repository.
Last Modified: 04/29/2019
Modified by: Mark D Behn
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