| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | September 24, 2012 |
| Latest Amendment Date: | July 21, 2014 |
| Award Number: | 1148027 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Margaret Benoit
mbenoit@nsf.gov (703)292-7233 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | October 1, 2012 |
| End Date: | September 30, 2016 (Estimated) |
| Total Intended Award Amount: | $115,000.00 |
| Total Awarded Amount to Date: | $115,000.00 |
| Funds Obligated to Date: |
FY 2014 = $36,682.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
2550 NORTHWESTERN AVE # 1100 WEST LAFAYETTE IN US 47906-1332 (765)494-1055 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
550 Stadium Mall Drive West Lafayette IN US 47907-2051 |
| 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): | EARTHSCOPE-SCIENCE UTILIZATION |
| Primary Program Source: |
01001415DB 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
Geophysical Investigation of the Mid-Continent Rift System
Surprisingly, the Central U.S. is an ideal place to study one of the more important processes shaping our planet - the breaking apart of continents to form new oceans. Throughout earth's history, continents have split along rifts, long zones of volcanism and stretching, which become spreading centers along which new ocean basins form and can grow to the size of the Atlantic and Pacific. It even looks like similar rifting may have happened on other planets.
Understanding how rifting works is important for both science and society, because rifting provides conditions for the deposition of hydrocarbons and other mineral resources. The problem is that when rifting succeeds in forming a new ocean, not much remains from its early stages so it's hard to see what happened.
To get around this, researchers are studying a spectacular rift that failed, the Mid-Continent Rift System. This system evolved around 1.1 billion years ago, when North America nearly split. However, the rift failed, leaving a 2000 km long belt of volcanic and sedimentary rocks left from the early rifting stage. This fossil rift, which is similar in length to the present East African and Baikal rifts, has two major arms meeting in the Lake Superior region. One extends southwestward at least as far as Kansas, and the other extends southeastward through Michigan. These arms are identified using the large gravity and magnetic anomalies resulting from dense and highly magnetic igneous rocks. They are largely covered by younger sediments but outcrop near Lake Superior and can be followed further south in drill cores.
The study combines seismic and magnetotelluric data being acquired by NSF's EarthScope program with gravity and magnetic data to develop an integrated three-dimensional image of the rift system and constrain its evolution. One of its goals is to learn whether the rift formed as a response to melting in the underlying mantle, as commonly proposed for the East African Rift, or because of stresses transmitted within the lithosphere, as appears to be the case for Asia's Baikal Rift.
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.
The major goal of Purdue component of this project was to assess dynamic hypothesis relating to the cessation of the opening in the Mid-Continental Rift System (MCRS) 1.1 billion years ago. The main hypothesis relating to the failure of the MCRS relates to a change in the far-field boundary stress related to progression of the Grenville orogeny generating compression that slowed and stopped the extension. In this study we tested a new hypothesis that the success of one branch of the rift can change the overall distribution of the Gravitational Potential Energy (GPE) variations and thus reverse the deviatoric stress field on other branches, thus shutting down a rift without changes in far-field boundary stresses.
We solved the force balance equations for variations in two and three branch rifts to isolate which regions were in extension and compression in order to evaluate the likelihood that changes in density distribution relating to slow and fast spreading ridges changed the deviatoric stress field causing the slow spreading ridge to fail. We found that as long as the ridges were held at the same elevation even for different spreading rates they both produced the same gravitational potential energy estimates (although for the faster spreading rifts it was over a larger area) and remained in extension. In order to produce reverse directions in regions that were previously in extension and achieve compression across the slow spreading ridge, thus generating a failed rift required the slow spreading ridge subside faster than the faster spreading ridge. We found that when the slow spreading ridge subsided to a depth 500m below the fast spreading ridge force balance put the ridge into compression. This was true for both the two and three pronged rift system.
Last Modified: 03/03/2017
Modified by: Lucy Flesch
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