| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
|
| Initial Amendment Date: | March 24, 2017 |
| Latest Amendment Date: | June 24, 2019 |
| Award Number: | 1654637 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Jennifer Wade
jwade@nsf.gov (703)292-4739 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | July 1, 2017 |
| End Date: | June 30, 2022 (Estimated) |
| Total Intended Award Amount: | $143,550.00 |
| Total Awarded Amount to Date: | $143,550.00 |
| Funds Obligated to Date: |
FY 2019 = $47,271.00 |
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
2385 IRVING HILL RD LAWRENCE KS US 66045-7563 (785)864-3441 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
2385 Irving Hill Road Lawrence KS US 66045-7568 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | Petrology and Geochemistry |
| Primary Program Source: |
01001920DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
|
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
One of the most accurate and useful ways of determining the age of rocks that formed more than about 500,000 years ago is uranium-lead (U-Pb) geochronology. Earth scientists use U-Pb geochronology to put together the geologic history of entire regions and of specific events, like the mass extinction of all non-avian dinosaurs about 66 million years ago or the catastrophic eruptions of supervolcanoes like the one currently centered at Yellowstone. The mineral zircon is often utilized because it is abundant, durable, and readily incorporates uranium into its crystal structure. But it excludes thorium, whose isotope 230Th is part of the naturally occurring isotopic decay chain from 238U to 206Pb. Calculating a date from the relative abundances of 206Pb and 238U therefore requires a correction for the missing 230Th. Existing experimental and observational constraints on the way U and Th behave when zircon crystallizes from a melt are imprecise, so we propose to quantify this behavior in a series of controlled laboratory experiments. The results of this study will reduce the largest source of uncertainty in dating young zircons and improve the accuracy of U-Pb dates, improving our ability to tell time during geologic processes. The attainment of more accurate timing of the geologic timescale is important to geologists of all disciplines, from paleontology to planetary cosmochemistry to geobiology. The data from this study will be broadly disseminated to the geoscience community. The data will be packaged and presented in an interactive visualization, hosted on the web, to illustrate why a correction must be made to geochronology data, how to calculate the magnitude of the correction, and how the correction will vary with compositional parameters. The results of this grant will also support the admission and mentoring of students in underrepresented groups and support the professional and laboratory development of two early career investigators.
Synthetic zircon will be grown at high temperature from melts doped with U and Th that mimic natural magmas at a range of temperatures, pressures, and compositions. The liquids will be quenched so that the melt turns into glass. Zircons will be separated from their coexisting glass and using high precision and high-spatial-resolution techniques, the abundance and distribution of U and Th in each phase will be measured. The experiments proposed will result in precise determination of the zircon/melt uranium and thorium partition coefficients under a wide variety of naturally occurring conditions. This data will be fit to a multidimensional surface using maximum likelihood regression techniques, so that the ratio of partition coefficients can be calculated for any set of known parameters. Measurement uncertainties from the isotope dilution analyses, as well as any observed experimental scatter will be incorporated into these uncertainties, and we expect that they will conservatively be on the order of 1-5%. This is compared to the existing experimental data, which has yielded uncertainties on the order of 50-100%.
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.
Executive Summary:
This report presents the outcomes and findings from a research project funded by the National Science Foundation (NSF) aimed at experimentally calibrating actinide partitioning behavior between the mineral zircon and silicate melt. The research objectives were to explore the fundamental processes governing actinide behavior in zircon in igneous systems and provide specific guidelines for how this information should be incorporated into uranium-lead geochronology methods that require correction for non-secular equilibrium uptake of actinides into crystallizing zircon.
Research Methodology:
Throughout the project, extensive experimental investigations were conducted to examine the partitioning behavior of actinides, specifically uranium (U) and thorium (Th) between zircon and silicate melt. The experiments were designed to simulate the conditions encountered in high-temperature geological environments, such as magmatic systems. Multiple experimental techniques were employed including one-atmosphere pressure-controlled fugacity furnaces and piston cylinder devices for higher pressure. Analytical techniques, including electron microprobe analysis, secondary ion mass spectrometry, and inductively coupled plasma mass spectrometry, were employed to determine the distribution coefficients and partitioning behaviors of the actinides.
Key Findings:
1. Partitioning Behavior: The experimental results revealed significant insights into the partitioning behavior of actinides between zircon and silicate melt. It was observed that the partition coefficients of U and Th varied strongest with temperature, and less so from melt composition. These findings contribute to our understanding of the mechanisms controlling actinide behavior in igneous systems.
2. Understanding complex U/Th partitioning: The research highlighted the role of zircon in influencing the fractionation of U and Th during igneous crystallization. Zircon was found to preferentially incorporate U over Th, thus reducing the ratio of U/Th in the melt. However, complexities such as temperature dependence, sector zoning of the crystals, and fractional crystallization leading to core-rim zoning, all had to be studied in detail, and accounted for, to create our final recommendations for the geochronology applications.
3. Geochronological Applications: The experimental data obtained were used to develop recommended models for predicting actinide partitioning behavior in zircon-silicate systems. These models will provide the necessary framework for precise correction of U-Pb dates because of the non-secular equilibrium incorporation of actinides into zircon. In particular this funded project is the first experimental study to link the fields of geochronology and experimental petrology, and successfully come up with accurate uncertainties on the Th-correction to geochronological dates.
Training and Professional Development:
This project has provided funding and training for graduate student Ashley Cocciadiferro, and later employment as an isotope geochemist at KU. Cocciadiferro is now an actinide geochemist at Lawrence Livermore National Lab. In addition, a collaborating student, Yuanyuan Liang, has visited KU several times to get training in clean lab work and isotopic analysis, as well as MATLAB coding, regression, and uncertainty propagation.
Publications and Dissemination:
Throughout the project, the research team presented their findings at national and international conferences, AGU annual fall meetings, and Goldschmidt annual geochemical society meetings.
Temperature Dependence of Uranium and Thorium Partitioning in Igneous Zircons
Y Liang, MJ Krawczynski, N McLean
AGU Fall Meeting Abstracts 2022, V23A-08
Measuring actinide partitioning in zircon to improve the 230Th correction for 206Pb/238U dates
A Cocciadiferro, N McLean, M Krawczynski
AGU Fall Meeting Abstracts 2019, V51F-0109
Experimental Determination of Zircon-Melt DTh and DU
JP Touran, AN Cocciadiferro, MJ Krawczynski, NM McLean
Goldschmidt 2018 Boston
Measuring Actinide Partitioning to Improve the 230-Th Correction
A Cocciadiferro, N McLean, MJ Krawczynski, J Touran
Goldschmidt 2018 Boston
The 230Th correction is the 1st priority for accurate dates of young zircons: U/Th partitioning experiments and measurements
M Krawczynski, N McLean
AGU Fall Meeting Abstracts 2017, V11B-0347
Two theses, including the in-progress Ph.D. dissertation of Yuanyuan Liang, contain chapters stemming from this funded project. We anticipate Liang’s thesis to become publicly available in 2024.
Measuring actinide partitioning in zircon to improve the 230Th correction for 206Pb/238U dates
A Cocciadiferro
MS Thesis, University of Kansas, 2020
Summary manuscripts are being prepared for peer-reviewed journals, including one on the temperature effect on actinide partitioning and another on high-precision measurements of U and Th concentrations in zircon and glass with isotope dilution ICPMS. The team also actively engaged with the scientific community through workshops and collaborations, fostering knowledge exchange and the dissemination of project outcomes.
Conclusion:
The NSF-funded project: investigating actinide partitioning experiments between zircon and silicate melt has made significant progress in understanding the behavior of U and Th in igneous systems. The findings contribute to our fundamental knowledge of actinide partitioning, with implications for increasing the accuracy of geochronology dates based on the zircon U-Pb system. The project has successfully achieved its objectives, and the outcomes will serve as a foundation for future research in the field.
Last Modified: 05/22/2023
Modified by: Noah M Mclean
Please report errors in award information by writing to: awardsearch@nsf.gov.
