2.         Radiation Damage in Zircon and the uranium component

a.†† We are developing a technique of using the Raman signals of individual fission track (FT) dated grains to determine remnant radiation damage so that we can isolate the low-retentive zircon (LRZ) and reduce grain-age dispersion [1,2]. This approach, if successful, will radically change FT dating in zircon, which is notoriously difficult due to over-dispersion in grain ages.

Our central hypothesis is that LRZ grains have high levels of remnant radiation damage, and these grains have the lowest effective closure temperature. As such, in a rock exhumed in an orogenic belt, these LRZ have the youngest fission track ages because they were the last ones to pass through closure. More retentive grains, with lower radiation damage, have higher annealing temperatures and in some cases are more resistant to annealing. These other grains cause the grain-age distribution to become overdispersed. We have used Raman spectroscopy to measure disorder in these zircon grains [3].†††††††††††††††††††

 

[Need to process micro-Raman measurements for zircon? Here is a useful excel spreadsheet Raman Zircon v1.0 for which I would appreciate any suggestion or feedback to improve it]

 

b.There is a question of how the natural high-uranium zircon result in a higher density of radiation damage compared to a low-uranium zircon and this difference may have important implications. We seek to better define and constrain Radiation Damage in zircon using Raman Spectroscopy and investigate the potential effects on fission track retention systematics using annealing experiments. Further implications of this research associate the possible determination of uranium content of low-moderate amount, in zircons and a new geochronometer [1,5] using Raman Spectroscopy (Marsellos, A.E., Garver, J.I., Kidd, W.S.F., 2008). More references (see my CV)

 

 

 

 

 

 

 

 

 

 

References

[1] Marsellos, A.E. & Garver, J.I., 2010 (In press). Radiation damage and uranium concentration in zircon as assessed by Raman spectroscopy and neutron irradiation. American Mineralogist.

 

[2] Marsellos, A.E. & Garver, J.I., 2009. Discriminating Fission-Track age of Low-Retentive Zircons using micro-Raman Spectroscopy. Am.Geoph.Union Joint Assembly, Toronto, Canada; EOS, Trans. Amer. Geophys. Union, 90 (22), Abstract V33E-03, (pdf).

[3] *Marsellos, A.E., Garver, J.I., Thomas, J.B., Kidd, W.S.F.,  2008. A Raman Spectroscopic Study of zircons with low to medium uranium content. In: Proceedings from the 11th International Conference on Thermochronometry, Anchorage Alaska, Sept. 2008, p.165-167 (pdf).

[4] *Montario, M.J., Garver, J.I. & Marsellos, A., 2008. Annealing of radiation damage in a Grenville zircon from the eastern Adirondacks, NY State. In: Garver, J.I., and Montario, M.J., Proceedings from the 11th International Conference on Thermochronometry, Anchorage Alaska, Sept. 2008, p.174-176 (pdf).

[5] Doctoralís Dissertation: Extension and Exhumation of the Hellenic forearc & Radiation Damage in Zircon. 2008. (Abstract link)