Single Grain (U-Th)/He Ages from EET14074, an Acapulcoite Meteorite

Authors

  • Christian James Anderkin University of Florida

DOI:

https://doi.org/10.32473/ufjur.v20i1.106303

Keywords:

undergraduate research, meteorites, geological sciences,

Abstract

EET14074 is a member of the acapulcoite-lodranite family of meteorites and was discovered in Antarctica in 2014 by the Korean Polar Research Institute (KOPRI).  Herein, we obtained (U-Th)/He ages from 20 phosphate aggregates in EET14074 to constrain the sample’s thermal history. The ages range between 116.8 Ma ± 145.7 Ma (1σ) and 4211.5 Ma ± 1089.1 Ma, with an average of 2530 ± 260 Ma (n=20). Excluding outlier ages with large uncertainties, the 13 most concentrated ages yielded a theoretical minimum age of 3000 ± 150 Ma. This age corresponds to a fraction helium loss (f) of ~31% assuming crystallization age of ~4.55 Ga. The uranium abundances in single aliquots are in the range of 1.52 - 289.93 fmol, with an average of 58.00 fmol (n = 20), whereas the thorium abundance ranges between 2.51 and 2337.06 fmol with an average of 1149.29 fmol (n = 20). To explain the observed He loss, thermal diffusion modeling was performed with an assumption that the He loss occurred during a recent passage of the meteorite in Earth’s atmosphere. For the most likely t-T condition of compressional heating in Earth’s atmosphere of this meteorite (T = ~430 ˚C, t = ~10 sec), a fractional loss of 29.3% was calculated when the diffusion domain radius (r) of 92.8 µm was assumed. This estimation is nearly indistinguishable from the observed fractional loss of 31.3%. Additionally, diffusion modeling for another set of data with a different size (r = 40.4 µm) yielded a very similar fractional loss. Therefore, the observed (U-Th)/He age distribution is likely derived from compressional heating during the passage of EET14074 in Earth’s atmosphere.                    

 

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Author Biography

Christian James Anderkin, University of Florida

Undergraduate Research Assistant - Department of Geological Sciences

References

. Chang, J., & Qiu, N. (2012). Closure temperature of (U-Th)/He system in apatite obtained from natural drillhole samples in the Tarim basin and its geological significance. Chinese Science Bulletin, 57(26), 3482-3490.

. Ehlers K. and Powell R., 1994. An empirical modification of Dodson's equation for closure temperature in binary systems. Geochimica et Cosmochimica Acta 58, 241-248.

. P.W. Reiners. (U-Th)/He Chronometry Experiences a renaissance, EOS (2002)

. E. Anders, Meteorites and the early solar system, Annu. Rev. Astron. Astrophys. 9 (1971) 1-34.

. D.S. McKay, E.K. Gibson Jr., K.L. Thomas-Keprta, H. Vali, C.S. Romanek, S.J. Clemett, X.D.F. Chillier, C.R. Maechling, R.N. Zare, Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001, Science 273 (1996) 924-930.

. T.J. McCoy, K. Keil, R.N. Clayton, T.K. Mayeda, D.D. Bogard, D.H. Garrison, G.R. Huss, I.D. Hutcheon, R. Wieler, A petrologic, chemical, and isotopic study of Monument Draw and comparison with other acapulcoites: Evidence for formation by incipient partial melting, Geochimica Cosmochimica Acta 60 (1996) 2681-2708.

. Min, Kyoungwon, et al. “Single grain (U–Th)/He ages from phosphates in Acapulco meteorite and implications for thermal history.” Earth and Planetary Science Letters, vol. 209, no. 3-4, (2003) 323–336.

. Reiners, P.W. and Nicolescu, S. (2006), Measurement of parent nuclides for (U-Th)/He chronometry by solution sector ICP-MS, ARHDL Report 1, http://www.geo.arizona.edu/~reiners/arhdl/arhdl.htm

Daniel Sheikh (Research assistant) in discussion, April 2018

Farley, K., Wolf, R., & Silver, L. (1996). The effects of long alpha-stopping distances on (U-Th)/He ages. Geochimica Et Cosmochimica Acta, 60(21), 4223-4229. doi:10.1016/s0016-7037(96)00193-7

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Published

2018-12-12