Reiners, Peter W. and Farley, Kenneth A. (1999) Helium diffusion and (U–Th)/He thermochronometry of titanite. Geochimica et Cosmochimica Acta, 63 (22). pp. 3845-3859. ISSN 0016-7037 http://resolver.caltech.edu/CaltechAUTHORS:20121120-151948085
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We have explored the diffusivity characteristics of radiogenic He in titanite (sphene) and have developed analytical techniques for (U–Th)/He dating of this mineral. Results of incremental He outgassing experiments performed on titanites from a variety of geological environments suggest a thermally activated volume diffusion mechanism with an activation energy of 44.6 ± 3.4 (2σ) kcal/mol and a frequency factor of ∼60 cm^2/s. Diffusivity is highly linearly correlated with the inverse square of the grain size, indicating that the He diffusion domain in titanite is the crystal itself. For typical titanite grains of 200- to 800-μm minimum dimension, the He closure temperature is in the range 191 to 218°C (for a cooling rate of 10°C/Myr). There is no indication in the titanites we studied that radiation damage plays a major role in He diffusion. (U–Th)/He ages of titanites from quickly cooled rocks yield ages (with ∼5–8% 1σ reproducibility) that are concordant with known ages, and (U-Th)/He ages of titanites from slowly cooled rocks are consistent with independently established cooling paths, supporting the closure temperature estimates. These experiments suggest that titanite (U–Th)/He ages may be useful for constraining cooling histories at temperatures near the lower limit of those accessed by feldspar ^(40)Ar/^(39)Ar dating but higher than apatite fission track or (U-Th)/He dating.
|Additional Information:||© 1999 Elsevier Science Ltd. Received December 14, 1998; accepted in revised form April 21, 1999. We thank Martha House for providing us with MH96–6 titanite, Barry Kohn for the Arkaroola, FCT, and MD samples, and Matt Heizler for the MH-10 and 42 samples. Thanks also to Lindsey Hedges, Sujoy Mukhopadyay, and Martha House for valuable help and advice in the lab, Mark Garcia for preparing the Gold Butte samples, Paul Carpenter for electron microprobe assistance, and Anna Johansen, Tatiana Piatina, Penny Kneebone, and Yaniv Dubowski for ICP-MS advice. We appreciate constructive reviews from Frank Richter and an anonymous reviewer. This work was funded by a Caltech Texaco Postdoctoral Fellowship to Peter Reiners and by a Packard Fellowship and an NSF grant to Ken Farley.|
|Official Citation:||Peter W Reiners, Kenneth A Farley, Helium diffusion and (U–Th)/He thermochronometry of titanite, Geochimica et Cosmochimica Acta, Volume 63, Issue 22, November 1999, Pages 3845-3859, ISSN 0016-7037, 10.1016/S0016-7037(99)00170-2. (http://www.sciencedirect.com/science/article/pii/S0016703799001702)|
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|Deposited By:||Ruth Sustaita|
|Deposited On:||20 Nov 2012 23:30|
|Last Modified:||20 Nov 2012 23:30|
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