| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 24, 2024 |
| Latest Amendment Date: | July 24, 2024 |
| Award Number: | 2420591 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Rachel Teasdale
rteasdal@nsf.gov (703)292-7977 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 1, 2024 |
| End Date: | July 31, 2027 (Estimated) |
| Total Intended Award Amount: | $174,786.00 |
| Total Awarded Amount to Date: | $174,786.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1 GRAND AVE BLDG 15 SAN LUIS OBISPO CA US 93407-9000 (805)756-2982 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1 GRAND AVE BLDG 15 SAN LUIS OBISPO CA US 93407-9000 |
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Performance Congressional District: |
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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
The rocks that form the towering cliffs of Half Dome and spires of Tuolumne Meadows in Yosemite National Park are part of a giant body of granitic rocks called the Tuolumne Intrusive Suite (TIS). Previous research has found that the TIS magmas crystallized slowly beneath the surface over ~10 million years. These magmas increased in silica and decreased in age toward the center of the body. This project will test two competing models that describe the emplacement of the TIS in the upper crust. The first model suggests that the TIS formed by sequential emplacement of 3?5 large batches of magma that were physically mixed and chemically modified in the upper crust. A second model suggests that the TIS formed via emplacement of numerous smaller batches of magma that were chemically modified in the lower crust and did not mix in the upper crust. Resolution between these models has implications for how granitic bodies form in mountains like the Sierra Nevada. This project will also support undergraduate student research projects. Results of this work will also be shared in field trip guides to help Interpretive Rangers at Yosemite National Park communicate the geologic history of the TIS with park visitors.
To test models for the emplacement of Tuolumne Intrusive Suite (TIS) magmas, this project builds upon preliminary geochronologic and geochemical results from zircon crystals extracted from modern stream sands. These analyses characterize the zircon geochemistry from each of the TIS units, yield evidence for the presence of older TIS zircon in younger TIS units and identify a change in zircon geochemistry between early and late TIS units. This work highlights the ability of zircons to track the magmatic evolution of granitic bodies, and provides a framework for this project which will investigate three first-order questions. 1) What is the volume of inherited zircon in the younger, interior portions of the TIS, and how does the volume of inherited zircon vary spatially? 2) What is the volume of inherited material in layered granitic rocks, and how do they form? 3) How does zircon geochemistry vary at the scale of individual crystals? To address these questions, this project will make new geochronologic and geochemical analyses of zircon extracted from granitic rocks collected across the TIS. Cumulatively, this line of questioning will place new constraints on the models for TIS magma emplacement. The first two questions will define the degree of physical and chemical mixing of TIS magmas in the upper crust, and thus constrain the relative size of individual TIS magma batches. The third question will help characterize the processes that created chemical differences in early and late TIS units, and thus place new constraints on the lower crust versus upper crustal location of TIS magma differentiation. Beyond these immediate scientific impacts, this project will prepare students for careers in the geosciences by supporting multiple undergraduate research projects. Results of this work will also be shared with Yosemite National Park staff on field trips developed to help Interpretive Rangers communicate the significance of the scientific debate around the TIS with park visitors.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
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