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Influence of crystal size on apatite (U-Th)/He thermochronology: an example from the Bighorn Mountains, Wyoming

Reiners, Peter W. and Farley, Kenneth A. (2001) Influence of crystal size on apatite (U-Th)/He thermochronology: an example from the Bighorn Mountains, Wyoming. Earth and Planetary Science Letters, 188 (3-4). pp. 413-420. ISSN 0012-821X. doi:10.1016/S0012-821X(01)00341-7.

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Near-surface tectonic and geomorphic processes involve cooling of rocks through low temperatures (50–200°C). Because rates of helium diffusion in apatite, titanite, and zircon are sensitive to temperature variations in this range, uranium–thorium/helium thermochronometry ((U–Th)/He dating) is well-suited to establishing the timing and rates of these processes in the geologic record. However, because fractional loss of He is controlled by crystal size such that larger crystals retain a larger fraction of radiogenic He, (U–Th)/He ages must vary not only with thermal history but also with crystal size. Here we present crystal size-correlated He ages from co-existing apatites from the Bighorn Mountains, Wyoming that range from 100 to 350 Ma. These correlations are a sensitive indicator of the rock’s thermal history in a temperature range below the system’s nominal closure temperature (T_c∼70°C for apatite), and are consistent with a thermal history involving residence in the upper 2–3 km of crust since the Precambrian, with maximum temperatures of 65–80°C just prior to Laramide orogenic exhumation. The influence of crystal size on He ages will be most apparent in rocks where temperatures have been in the range of partial He retention for long periods of time (∼30–70°C for >10^7 years). In such cases, accurate interpretation of (U–Th)/He ages must incorporate the effect of crystal size, and this method may provide insights to thermal histories of rocks in previously inaccessible low-temperature ranges.

Item Type:Article
Related URLs:
URLURL TypeDescription
Reiners, Peter W.0000-0001-7240-2373
Farley, Kenneth A.0000-0002-7846-7546
Additional Information:© 2001 Elsevier Science B.V. Received 28 November 2000; received in revised form 23 March 2001; accepted 3 April 2001. We gratefully acknowledge the collaboration of the 1999 Keck-Bighorn participants (especially Peter Crowley, Joanna Reuter, and Grant Kaye), and Cathy Manduca. Thanks also to Charles Knaack for valuable technical assistance at WSU. We appreciate helpful reviews by Terry Spell and Peter Zeitler. This work was supported in part by NSF Grant EAR 0073576 to P.W.R.[RV]
Funding AgencyGrant Number
NSFEAR 0073576
Subject Keywords:thermochronology; exhumation; helium; Laramide Orogeny; Th/U; U/He
Issue or Number:3-4
Record Number:CaltechAUTHORS:20121113-131731135
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Official Citation:Peter W. Reiners, Kenneth A. Farley, Influence of crystal size on apatite (U–Th)/He thermochronology: an example from the Bighorn Mountains, Wyoming, Earth and Planetary Science Letters, Volume 188, Issues 3–4, 15 June 2001, Pages 413-420, ISSN 0012-821X, 10.1016/S0012-821X(01)00341-7. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35438
Deposited By: Ruth Sustaita
Deposited On:13 Nov 2012 21:33
Last Modified:09 Nov 2021 23:15

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