| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 31, 2013 |
| Latest Amendment Date: | July 31, 2013 |
| Award Number: | 1251877 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Gregory Anderson
greander@nsf.gov (703)292-4693 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 1, 2013 |
| End Date: | December 31, 2015 (Estimated) |
| Total Intended Award Amount: | $91,414.00 |
| Total Awarded Amount to Date: | $91,414.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
21 N PARK ST STE 6301 MADISON WI US 53715-1218 (608)262-3822 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1215 W Dayton St Madison WI US 53706-1215 |
| 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: |
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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
The aim of this project is to determine the link between topographic uplift, erosion and exhumation, pre-existing geologic boundaries, and the underlying mantle dynamics that drive deformation. The field area is the Salmon River suture zone of western Idaho, which is the boundary between Precambrian North America underlying most of Idaho and younger (Phanerozoic) accreted terranes of the Blue Mountains in Oregon. The Idaho batholith formed exclusively on the North American side of this boundary. Post-collision and ongoing deformation affect different parts of the region differently, representing differences in pre-existing geologic structure and/or in deep driving forces. The timing, rates, and amounts of uplift of the various mountain ranges will be related to the current subsurface geometry -- determined using seismic data -- to identify motions in the Earth?s crust and mantle that elevated topography on regional scales. The work entails a combination of seismic data analyses, to provide a detailed sub-surface architecture, and thermochronology, to determing the timing of uplift and exhumation of rocks from depth and the development of the current topography.
The work spans three main study areas and includes a final project synthesis: 1) Documentation of the exhumation path of the Atlanta lobe of the Idaho batholith to determine if it was uplifted by younger magmatism; 2) Evaluation of potential differential exhumation along the trans-Challis fault zone that cross-cuts the Idaho batholith; and 3) Documentation of exhumation in the Blue Mountains, in order to compare its history to that of adjacent North America. A particular focus is whether the Salmon River suture zone was reactivated by post-Columbia River Basalt extension. The combination of the thermochronology and seismic results with recent geology, geochronology, and geochemistry studies will allow synthesis of a regional tectonic evolution and can illuminate the relationship between inherited lithospheric structures and active tectonic processes.
Two graduate and two undergraduate students at the University of Florida and Virginia Tech are directly supported by this work. Tectonic synthesis will involve graduate students at all three institutions, several of whom are funded by other sources.
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.
Western Idaho marks the boundary between the ancient North America continent and “accreted” or “suspect” terranes to the west. Accreted terranes consist of rocks that originated in an ocean basin that were added to the western edge of North America approximately 150 million year ago. There is no evidence left of the original collision between the accreted terranes and North America in western Idaho. Rather, the current boundary is the result of a major geological structure, called the western Idaho shear zone, which has altered the effects of the original collision. The western Idaho shear zone – a type of fault - had a major component of horizontal, northward transport (strike-slip motion), similar to the modern San Andreas fault system in California. Following this northward movement, a large body of magma - known as the Idaho batholith - intruded into central Idaho to the east of the boundary. Our study indicates that the Idaho batholith cooled through 200° C about 30 million years after intrusion of the magma. The consistency of the results indicates that the Idaho batholith formed a coherent tectonic block, and the Idaho batholith remains a tectonic block to present with major earthquakes occurring along the boundaries. The data from the Idaho batholith also suggest that the magma intruded into a region of elevated topography (~3-4 km high), similar to the Tibetan plateau of Asia.
To the west of the western Idaho shear zone, the accreted terrane rocks cooled significantly earlier than rocks to the east. Rocks on the opposite side of the western Idaho shear zone do not share a common tectonic history until 17 million years ago, when the Columbia River basalt flows covered both areas. Using available data, rocks currently in eastern Oregon were located significantly further South, restoring to northern Nevada (at a minimum). The ancient boundary (western Idaho shear zone) is preferentially reactivated by faults, but unexpectedly it is not affected by younger magmas. Neither the magmas of the Idaho batholith nor the vertical conduits of the Columbia River basalt flows affect the western Idaho shear zone.
The project supported multiple undergraduate research projects and three graduate student theses. Further, it allowed us to integrate the geological, geophysical, and geochemical datasets to provide a coherent view of the tectonic development of this area.
Last Modified: 07/11/2016
Modified by: Basil Tikoff
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