House, Martha A. and Farley, Kenneth A. and Kohn, Barry P. (1999) An empirical test of helium diffusion in apatite: borehole data from the Otway basin, Australia. Earth and Planetary Science Letters, 170 (4). pp. 463-474. ISSN 0012-821X. http://resolver.caltech.edu/CaltechAUTHORS:20121119-112755758
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We have analyzed helium ages of apatites from several boreholes in the Otway basin, Australia, to evaluate whether laboratory helium diffusivity can be accurately extrapolated to conditions relevant in nature. Downhole apatite helium ages define a broad swath of values from 78–71 Ma at the surface (15°C) to nearly zero at depths corresponding to ambient temperatures of ∼80°C. The width of the swath results from uncertainties in corrected borehole temperatures, differences in the thermal history experienced by the various boreholes, and possibly from slightly different helium diffusivities among the detrital apatite grains studied. In the eastern Otway basin, the shape and position of the helium age profile is in good agreement with predictions based on the extrapolation of laboratory diffusivity data for Durango apatite coupled with published thermal histories for this part of the basin. In contrast, helium ages are much younger than predicted in the western Otway basin. Based on measured ages from Otway sediments, which have been essentially isothermal over the last few million years, an empirical diffusivity (D/α^2) of 2×10^(−15) s^(−1) can be assigned to apatites residing at downhole temperatures of 67–97°C. This empirical diffusivity is consistent with laboratory diffusion measurements, demonstrating that such measurements are reasonably accurate and can be applied with confidence to natural geologic settings. Given this confirmation of the laboratory diffusivity data, the discrepancy between the observed and modeled helium age profiles in the western Otway basin suggests that these sediments recently experienced higher temperatures than presently supposed.
|Additional Information:||© 1999 Elsevier Science B.V. Received 26 June 1998; accepted 5 May 1999. Acknowledgement is made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research (M.A.H.) and grants from the National Science Foundation (K.A.F.). Lindsey Hedges of the Noble Gas Laboratory at Caltech provided analytical assistance. Ken Wilson, Bob Harms and Kathy Hill of Petroleum Division of the Victorian Department of Natural Resources and Environment greatly facilitated the examination of the Otway basin well reports studied and the collection of core samples. Comments by C.W. Naeser and two anonymous reviewers and editorial assistance from M. Kastner greatly improved the manuscript. Part of this study was conducted as part of the Australian Geodynamic Cooperative Research Centre and this paper is published with the permission of the Director, AGCRC. [MK]|
|Subject Keywords:||helium; age; apatite; diffusivity; Otway Basin|
|Official Citation:||Martha A House, Kenneth A Farley, Barry P Kohn, An empirical test of helium diffusion in apatite: borehole data from the Otway basin, Australia, Earth and Planetary Science Letters, Volume 170, Issue 4, 30 July 1999, Pages 463-474, ISSN 0012-821X, 10.1016/S0012-821X(99)00120-X. (http://www.sciencedirect.com/science/article/pii/S0012821X9900120X)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||19 Nov 2012 19:42|
|Last Modified:||19 Nov 2012 19:42|
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